Class SSio--^ 
 Book. ?■ ■ •• 
 
 US2 
 
 Copyright N° 
 
 \\\S 
 
 COPYRIGHT DEPOSJT. 
 
■ / 
 
 i 
 
Ube IRural Science Series 
 
 Edited by L. H. BAILEY 
 
 PLANT-BREEDING 
 
El)e Eural Science Series 
 
 The Soil. King. 
 
 The Spraying of Plants. Lodeman. 
 
 Milk AND ITS Products, Wing. Enlarged and Revised. 
 
 The Fertility of the Land. Boberts. 
 
 The Principles of Fruit-growing. Bailey. '20th 
 
 Edition., Bevised. 
 Bush-fruits. Card. 
 Fertilizers. Voorhees. 
 The Principles of Agriculture. Bailey. 15th Edition,, 
 
 Bevised. 
 Irrigation and Drainage. King. 
 The Farmstead. Boberts. 
 Rural Wealth and Welfare. Fairchild. 
 The Principles of Vegetable-gardening. Bailey. 
 Farm Poultry. Watson. Enlarged and Bevised. 
 The Feeding of Animals. Jordan. 
 The Farmer's Business Handbook. Boberts. 
 The Diseases of Animals. Mayo. 
 The Horse. Boberts. 
 How to Choose a Farm. Hunt. 
 Forage Crops. Voorhees. 
 
 Bacteria in Relation to Country Life. Lipman. 
 The Nursery-book. Bailey. 
 Plant-breeding. Bailey and Gilbert. Bevised. 
 The Forcing-book. Bailey. 
 The Pruning-book. Bailey. 
 
 Fruit-growing in Arid Regions. Paddock and Whipple. 
 Rural Hygiene. Ogden. 
 Dry-farming. Widtsoe. 
 Law for the American Farmer. Green. 
 Farm Boys and Girls. McKeever. 
 The Training and Breaking of Horses. Harper. 
 Sheep-farming in North America. Craig. 
 Cooperation in Agriculture. Powell. 
 The Farm Woodlot. Cheyney and Wentling. 
 Household Insects. Herrick. 
 
PLANT-BREEDING 
 
 ^PAILEY 
 
 NEW EDITION REVISED BY 
 
 ARTHUR W. GILBERT, Ph.D. 
 
 • 
 
 PROFESSOR OF PLANT-BREEDING IN THE NEW YORK 
 
 STATE COLLEGE OF AGRICULTURE AT 
 
 CORNELL UNIVERSITY 
 
 THE MACMILLAN COMPANY 
 1915 
 
 All rights reserved 
 
^\ 
 
 Copyright, 1S95, 1906, 
 By L. H. bailey. 
 
 Set up and electrotyped. Published December, 1895. Reprinted 
 April, 1896; August, October, 1897; March, 1902; March, 1904. 
 
 Fourth edition, with additions, April, 1906: April, 1907; July, 
 1908; August, 1910; February, 1912; October, 1913. 
 
 New Revised Edition, Entirely Reset. 
 
 Copyright, 1915, 
 By the MACMILLAN COMPANY. 
 
 Set up and electrotyped. Published February, 1915. 
 
 J. 8. Cushing Co. — Berwick & Smith Co., 
 Norwood, Mass., U.S.A. 
 
 FEB II 1915 
 
 ©CI,A'J9360il 
 
HISTORY 
 
 This book had its beginning in a lecture that I gave 
 twenty-three years ago (December 1, 1891) before the Mas- 
 sachusetts State Board of Agriculture, in Boston, on " Cross- 
 Breeding and Hybridizing"; and this lecture, in turn, was 
 the outgrowth of one given in 1885 and soon afterwards 
 published. Under the same title, but with a bibliography 
 added, the Boston lecture was published as a pamphlet in 
 1892, and placed on sale, by the Rural Publishing Company 
 of New York, as one of the Rural Library Series. It com- 
 prised forty-four pages, and sold for 40 cents. In the sum- 
 mer of 1895, I gave two addresses on variation and the 
 origination of domestic varieties of plants under the auspices 
 of the American Society for the Extension of University 
 Teaching at the University of Pennsylvania. In the mean- 
 time, I had been teaching the subject to my classes in 
 horticulture in Cornell University. In the latter part of 
 1895, I put together these materials in book form, and hav- 
 ing no short descriptive title I used the word or compound 
 ''Plant-Breeding." Of this work, the Massachusetts lec- 
 ture comprised Chapter II, and the Philadelphia lectures 
 Chapters I and III. The bibliography was not included. 
 Chapter IV comprised ''Borrowed opinions" from the 
 writings of Verlot, Carriere, and Focke. .Carriere's work 
 on "Production et Fixation des Varietes dans les Vege- 
 taux" had been translated, with a view to publication, as 
 early as 1886. The book, " Plant-Breeding," was translated 
 
vi History 
 
 into the French by J. M. and E. Harraca, and published in 
 Paris in 1901 as " La Production des Plantes." 
 
 Having been thrice reprinted, the second edition was 
 issued in 1902, although, through an inadvertence, it was 
 not so marked on the title-page. Few text-changes were 
 made, but the bibliography was included. 
 
 Early in 1904 the third edition was issued. The bibli- 
 ography was extended, and some changes were made in the 
 text; but the principal departure was a new Chapter IV, 
 from which the old '- Borrowed opinions " were omitted, 
 and " Recent opinions " were substituted, comprising a dis- 
 cussion of the work of de Vries, Mendel, and others, and 
 a statement of the current tendencies of American plant- 
 breeding practice. " In the eight years since this book was 
 sent to the printer," it was stated in the preface to the third 
 edition, ''there have been great changes in our attitude 
 toward most of the fundamental questions that are dis- 
 cussed in its pages. In fact, these years may be said to 
 have marked a transition between two habits of thought in 
 respect to the means of the evolution of plants, — from the 
 points of view held by Darwin and the older writers to 
 those arising from definite experimental studies in species 
 and varieties. We have not given up the old nor wholly 
 accepted the new, but it is certain that our outlook is shift- 
 ing. So far as practical plant-breeding is involved, the 
 changing attitude is concerned chiefly with discussions of 
 the nature of varieties and the nature of hybridization." 
 It was declared that " the time cannot be far distant when 
 the subject of plant-breeding will be rewritten from a new 
 point of view." 
 
 In 1906, the fourth edition appeared, with a new chapter 
 on " Current plant-breeding practice " ; and the book had 
 
History vii 
 
 grown from the 293 pages of the original edition to 483 
 pages. This edition was translated into the Japanese by 
 D. Karashima, and published in 1907. 
 
 We now come to the present edition. The book has been 
 made over by Dr. Gilbert, who has rewritten some of it 
 and who has added all the new material, and in whose 
 hands I have been glad to place it. My work in this 
 edition has been only editorial. A considerable part of the 
 old work has been preserved, whether wisely or not will 
 be the occasion for different opinions. It has seemed to be 
 desirable to retain something of a former point of view 
 while at the same time expressing the applications of the 
 work in the method and the language of the day. Con- 
 siderable use has been made of the work of others, as is 
 apparent in the pages. The Open Court Publishing Com- 
 pany has loaned illustrations from the important work of 
 de Vries, and pictures have been taken from the Yearbooks 
 of the United States Department of Agriculture. All these 
 aids we are glad to acknowledge. 
 
 These new investigations have taken us far from the 
 point of view of Darwin, in which the original editions of 
 the book were founded. I doubt whether the students 
 receiving their instruction to-day, Avith all their abounding 
 facilities and opportunities, have any such feeling for a 
 master-spirit as we had in those days when the studies of 
 Darwin had given a new meaning to nature, when there 
 were still a few naturalists left, and when the glow of his 
 writings was warm in every person's work. To one coming 
 out of a plant-growing relationship, the masterful works of 
 Darwin had introduced order, and the forms of cultivated 
 plants had been made worthy of serious study. This inter- 
 est was further stimulated by the writings of Wallace and 
 
viii History 
 
 others. All these writings were fascinating to read. How 
 to produce new forms of vegetation seized some of us with 
 irresistible power. The literature has now become complex 
 and difficult, with considerable gain, no doubt, in a closer 
 acquaintance with the subject, and a nearer approach to the 
 ultimate truth ; but the charm of the simple literature is 
 largely buried, and I fear that much of our interest is now 
 expressed in the discussion of methods and in disputing 
 about the reasons. Yet we are accumulating knowledge, 
 and after a time we shall come back to clarity and to a 
 simplicity that the layman can use. 
 
 L. H. BAILEY. 
 
 Ithaca, N. Y., 
 
 December 1, 1914. 
 
TABLE OF CONTENTS 
 
 CHAPTER I 
 
 PAGES 
 
 The Fact and Philosophy of Variation . . . 1-13 
 
 The fact of individuality, 2 — variation and adapta- 
 tion, 7 — species-formation, 8— conception of unit char- 
 acters, 9 — differences between plants and animals with 
 regard to general association of parts and their methods 
 of reproduction, 10 — bud-variation and bud-varieties, 11. 
 
 chaptp:r II 
 
 The Causes of Individual Differences .... 13-33 
 Fortuitous variation, 14 — action of natural selection 
 on variation, 14 — sex as a factor in the variation of 
 plants, 15 — physical environment and variation, 16 — 
 do external influences produce permanent effects in 
 plants, 17 — natal and post-natal variations, 18 — con- 
 ception of biotypes, 19 — variation in food supply, 20 
 — variation in climate, 22 — food supply in different 
 branches, 23 — what cultivation is, 24 — variation in cli- 
 mate, 25 — man's control over climate as a means of 
 making plants vary, 27 — change of seed, 28 — bud- 
 variation, 29 — struggle for life a cause of variation, 30. 
 
 CHAPTER III 
 
 The Choice and Fixation of Variations . . . 34-40 
 What is a variety, 35 — adaptation in nature, 37 — 
 artificial selection, 37— bud selection, 39 — variation 
 and selection not entirely within man's control, 39. 
 
 ix 
 
X Table of Contents 
 
 CHAPTER IV 
 
 PAGES 
 
 The Measurement of Variation 41-51 
 
 The science of biometry, 41 — type, 43 — biometrical 
 expression of variability, 43 — mode, 44 — modal coeffi- 
 cient, 45 — mean, 45 — use of mean, 46 — mathematical 
 expression of variability, 47 — average deviation, 47 — 
 standard deviation, 48 — coefficient of variability, 49 — 
 probable error, 50 — use of statistical methods, 51. 
 
 CHAPTER V 
 
 Mutations 52-91 
 
 Evolutionary theories of Darwin and de Vries, 52 — 
 differences between fluctuating variations and mutations, 
 54 — history of mutation, 55 — history of the appear- 
 ance of double flowers, 56 — de Vries' experiment with 
 Oenotheras, 59 — analytical table of seedlings (after de 
 Vries), 68 — how the mutants were produced in the gar- 
 den, 71 — mutating strains of O. Lamarkiana^ 72 — de 
 Vries' laws of mutability of the evening-primroses, 72 — 
 frequency of occurrence of mutations, 79 — spontaneous 
 occurrence of new elementary species in the wild state, 
 80 — spontaneous occurrence of new elementary species 
 and varieties under cultivation, 80 — experimental study 
 of the origin of nuitations, 84 — experiments in the pro- 
 duction of double flowers, 86 — what do new characters 
 come from, 90 — can mutations be produced artificially, 
 90 — economic significance of mutations, 90. 
 
 CHAPTER VI 
 
 The Philosophy of the Crossing of Plants, considered 
 IN Reference to their Improvement under 
 Cultivation 92-148 
 
 The struggle for life, 92 — survival of the most fit, 93 
 — flexibility as an aid to survival, 93 — causes of varia- 
 bility, 94 — origin and function of sex, 95 — effects of 
 
Table of Contents xi 
 
 crossing on the species, 97 — the limits of crossing, 97 
 
 — swamping effects of inter-crossing, 98 — what deter- 
 mines tlie limits of crossing, 98 — the limits of crossing 
 tend to preserve the identity of spocies, 99 — the refusal 
 to cross, the result of natural selection, 100 — for the 
 production of useful hybrids, do not have the parents 
 too diverse, 101 — function of the cross, 101 — rarity of 
 natural hybrids, 102 — change of seed and crossing, 103 
 
 — results from change of stock, 105 — crossing from 
 standpoint of plant improvement, 108 — understanding 
 of terms, 108 — history of plant hybrids, 110 — what 
 plants can be hybridized, 111 — vigor as a result of 
 crossing, 112 — Darwin's experiments with morning- 
 glories, 114 — Darwin's results with other plants, 115 — 
 increased vigor in other crosses, 115 — three factors, 117 
 
 — the outright production of new varieties, 118 — how 
 to overcome antipathy to crossing, 121 — variability of 
 hybrids, 122 — characteristics of crosses, 123 — difficul- 
 ties in making successful crosses, 125 — hybridization 
 and asexual propagation, 125 — in-breeding, 127 — expe- 
 rience with egg-plants and squashes, 128 — influence of 
 sex on hybrids, 138 — uncertainties of pollination, 140 
 
 — graft hybrids, 142 — the case of Cytisus Adami, 142 
 
 — Winkler's SoJanum graft-hybrids, 146 — are these 
 real graft-hybrids, 147. 
 
 CHAPTER VII 
 
 Heredity 149-208 
 
 Heredity studied collectively, 149 — the coefficient of 
 heredity, 152 — notation, 153 — conception of unit char- 
 acters, 154 — knowledge of heredity has come through 
 experimental breeding, 154 — rediscovery of Mendel's 
 work by de Vries and others, 155 — Mendel's experi- 
 ments, 157 — explanation of mendelian results, 166 — 
 explanation of diagram, 171 — Mendel's results with the 
 offspring of hybrids in which several differentiating char- 
 
xu 
 
 Table of Contents 
 
 actei-s are associated. 171 — Mendel's law of inheritance 
 of unit characters (table), 175 — results in F-2 with com- 
 plete dominance in every character-pair (table 1), 176 — 
 results involving three pairs of characters (trihybrid), 
 177 — incomplete dominance, 179 — presence and ab- 
 sence hypothesis. 181 — examples of mendelian inherit- 
 ance due to the presence and absence of a single unit, 
 181 — mendelian inheritance of color, 185 — white flowers 
 in F-2 from red x cream, 187 — the ratio 9:3:4, 188 — 
 colored forms from white x white and the 9 : 7 ratio, 
 188 — Emerson's experiments with beans, 189 — absence 
 factors. 192 — mutations resulting from mendelian segre- 
 gation and recombination, 193 — mutations which men- 
 delize are constant, 193 — mendelism in wheat, 194 — 
 mendelism sunmiarized, 200 — application to plant- 
 breeding, 202 — the probable limits of mendelism in the 
 production of new varieties, 204 — conclusion, 208. 
 
 CHAPTER VIII 
 
 How Domestic Varieties Originate .... 
 
 Indeterminate varieties, 209 — plant-breeding, 212 — 
 plant-breeding by selection, 218 — rules for breeding 
 plants, 222 — specific examples. 253 — the dewbeiTy and 
 blackberry. 253 — the apple, 255 — beans, 260 — cannas, 
 265 — thecabbage family, 267 — the chrysanthemum, 267. 
 
 209-269 
 
 CHAPTER IX 
 
 PoLLixATiox : OR How TO Cross Plants .... 270-293 
 The structure of the flower, 270 — manipulating the 
 flowers, 281. 
 
 CHAPTER X 
 
 The Forward Movement in Plant-Breeding . . . 294-323 
 
 Systematic improvement of plants, 295 — the plant- 
 breeder should aim toward definite ideals, 297 — plant 
 
Table of Contents xiii 
 
 PAGES 
 
 improvement a serious business, 298 — the results of 
 plant-breeding effort, 299 — state plant-breeding associ- 
 ations, 300 — other plant-breeding associations. 304 — 
 commercial breeding agencies, 308 — work of the council 
 of grain exchanges. 310 — United States Department of • 
 
 Agriculture and state experiment stations, 310 — work 
 of the state agricultural experiment stations, 314 — in- 
 struction in plant-breeding in the United States, 321 — 
 Luther Burbank, 321. 
 
 APPEXDIX A 
 Glossary of Technical Plant-breedixg Terms , . 325-327 
 
 APPEXDIX B 
 Plant- BREEDING Books ....... 328-331 
 
 APPEXDIX C 
 
 List of Periodicals containing Breeding Literature 332-334 
 
 APPEXDIX D 
 Bibliography 335-393 
 
 APPEXDIX E 
 
 Laboratory Exercises 394-467 
 
 Exercise 1 — Field study of variations by making an 
 herbarium of variations 394-399 
 
 Exercise 2 — The statistical study of type and 
 variability 399-412 
 
 Exercise 3 — Correlation ...... 412—420 
 
 Exercise 4 — Statistical study of apples from different 
 trees 420 
 
 Exercise 5 — Statistical study of branches of different 
 trees 420-423 
 
xiv Table of Contents 
 
 Exercise 6 — Statistical study of the quantity of grapes 
 
 from different grape vines 423 
 
 Exercise 7 — Study of variation in pressed specimens 
 of ragweed or some plant showing many different types 423 
 
 Exercise 8 — Study of bud variation and reversions in 
 
 ferns 423-424 
 
 Exercise 9 — Study of the morphology of different 
 
 kinds of flowers 424-426 
 
 Exercise 10 — Technique of the cross-pollination of 
 
 plants 426-428 
 
 Exercise 11 — Embryological studies from slides show- 
 ing cell division at different stages, chromosomes, pollen 
 mother cells, development of the embryo sac, etc. . 428 
 
 Exercise 12 — Study of pollen germination and 
 
 fecundation . 428 
 
 Exercise 13 — Practice in the cross-pollination of ap- 
 ples, pears, peaches, plums, etc 429 
 
 Exercise 14 — Studies of mendelian inheritance . 429-435 
 
 Exercise 15 — A study of mendelian characters in 
 
 timothy and oats 435-438 
 
 Exercise 16 — Mendelian problems .... 438-445 
 Exercise 17 — Ear-to-row test with corn . . . 445-447 
 
 Exercise 18 — Corn judging 447-448 
 
 Exercise 19 — Statistical study of ears of corn . . 448-449 
 Exercise 20 — Study of correlations of characters in 
 
 corn 449-450 
 
 Exercise 21 — Corn selection — laboratory study . 450-452 
 Exercise 22 — A study in potato selection . . . 452-457 
 Exercise 23 — Study of citrus hybrids . . . 457-458 
 
 Exercise 24 — Study of the results of the plant-to-row 
 tests of wheat, oats, cabbage, onions, or any crop where 
 data are available ........ 458 
 
 Exercise 25 — Studies of origin of varieties — corn, 
 wheat, apples, plums, grapes, etc. .... 458 
 
 Exercise 26 — Field trip to experimental grounds . 458-459 
 Exercise 27 — Working plans for practical breeding 
 experiments 459 
 
LIST OF ILLUSTRATIONS 
 
 PIGTTRE PAGE 
 
 1. Variation in heads of timothy ...... 3 
 
 2. Two seedling timothy plants, growing side by side, showing 
 
 a common kind and degree of difference ... 4 
 
 3. A productive timothy plant 5 
 
 4. A timothy plant that runs much to seed .... 6 
 
 5. A timothy plant that runs almost wholly to leaf ... 7 
 
 6. Couch or quack grass, showing means of asexual propaga- 
 
 tion by underground root stalks 13 
 
 7. Orange hawk weed . 32 
 
 8. A frequency curve illustrating the distribution of the height 
 
 of the pea plants ........ 42 
 
 9. Variations in statures of (Enothera nanella^ a mutant, and 
 
 CEnothera Lamarkiana, its parent . . . . .53 
 
 10. Variations in the amount of sugar in 40,000 beets . . 54 
 
 11. Ghelidonium majus 55 
 
 12. Chelidonium Jaciniatum . 56 
 
 13. Anemone coronaria, single-flowered form . . . . 57 
 
 14. Anemone coronaria, semi-double-flowered form ... 57 
 
 15. Anemone coronaria var. Jlorepleno ..... 58 
 
 16. Hugo de Vries .59 
 
 17. CEnothera Lamarkiana and (Enothera nanelJa in bloom . 60 
 
 18. CEnothera Lamarkiana. Curve exhibiting variations in the 
 
 length of fruits of 568 plants 61 
 
 ] 9. CEnothera lata — CEnothera Lamarkiana — CEnothera nanella 63 
 
 20. J., spike with almost ripe fruits of CEnothera gigas, a mutant 
 
 species; B, the same of CEnothera I^amarkiana, its 
 
 parent form 66 
 
 21. The cage in Professor de Vries' experiment garden, showing 
 
 corn and various species of CEnothera .... 70 
 
 XV 
 
XVI 
 
 List of Illustrations 
 
 22. 
 23. 
 24. 
 25. 
 
 26. 
 
 27. 
 28. 
 29. 
 
 30. 
 
 31. 
 
 32 
 33. 
 
 34. 
 35. 
 36. 
 
 37. 
 38. 
 39. 
 40. 
 41. 
 42. 
 43. 
 44. 
 45. 
 
 46. 
 47. 
 
 48. 
 49. 
 50. 
 51. 
 
 Cupid sweet pea (photo by Beal) . 
 
 Linaria vulgaris — peloric flowers 
 
 Linaria vulgaris peloria 
 
 Antirrhinum majus .... 
 
 Chrysanthemum segetum plenum . 
 
 Chrysanthemum inodorum plenissim um 
 
 Ancestral generations of Chrysanthemum segetum plenum 
 
 A^ Chrysanthemum segetum; B, Chrysanthemum segetum 
 grandiflorium (after purification) . . . . . 
 
 Extreme variability in the shape of the leaves of hybrid pop- 
 pies. Second generation from a cross between the Bride 
 variety of the Opium poppy and the Oriental poppy 
 
 Inbred corn plants, showing lessened vigor of growth 
 (adapted from Yearbook) 
 
 Hybrid walnut and parents . 
 
 A hybrid walnut {Juglans calif ornica nigra).) reaching 
 double the height of ordinary trees 
 
 Variation in hybrid pineapples 
 
 Variation in hybrid squashes 
 
 Hybrid citrange and its parents, Poncirus (citrus) trifoliata 
 and common sweet orange .... 
 
 Hybrid tangelo and its parents, pomelo and tangerine 
 
 Samson tangelo (adapted from Yearbook) . 
 
 Citranges (hybrid of orange and Poncirus (citr^is) trifoliata) 
 
 Teosinte and its hybrids with Indian corn 
 
 Cytisus Adami ...... 
 
 Cytisus Adami . . . . . 
 
 Mendelism in maize 
 
 Diagrammatic representation of Mendel's law 
 
 Hybrid carnation between a single and a burster, showing 
 intermediacy 
 
 Fowls' combs 
 
 Three generations of hybrid wheat 
 
 Mendelism in tomatoes .... 
 
 Pride of Georgia, a good short-staple cotton 
 
 Select Jones improved cotton with uniform long staple 
 
 Improving the tomato ...... 
 
 PAGE 
 
 78 
 81 
 
 82 
 83 
 
 86 
 87 
 
 88 
 
 89 
 
 96 
 
 113 
 117 
 
 119 
 123 
 129 
 
 132 
 133 
 134 
 135 
 137 
 143 
 144 
 162 
 170 
 
 180 
 184 
 195 
 203 
 213 
 214 
 215 
 
List of Illustrations 
 
 xvii 
 
 FIGURE PAGE 
 
 52. Crop averages in corn breeding for high and for low protein. 
 
 Results of twelve generations. (111. Exp. Sta.) . . 216 
 
 .53. Fruit of wild elderberry 217 
 
 54. Fruit of a cultivated variety of the elderberry which ap- 
 
 peared as a variation from the wild form . . .218 
 
 55. Field of wilt-resistant watermelons, growing free from disease 
 
 on infected land (from Yearbook) .... 219 
 
 56. Disease resistance in cowpeas . . . . . . 220 
 
 57. Improved types of lettuce and the varieties from which they 
 
 were developed ........ 221 
 
 58. Wild cabbage 240 
 
 59. Curled kale 241 
 
 60. Collard 242 
 
 61. Brussels sprouts . 243 
 
 62. Savoy cabbage , 244 
 
 63. Cabbage shapes 245 
 
 64. Swede turnip, kohl-rabi, and cauliflower .... 248 
 
 65. Wild form of Chrysanthemum morifolium .... 249 
 
 66. Wild form of Chrysanthemum indicum .... 250 
 
 67. Pompon anemone type 251 
 
 68. Single type 252 
 
 69. Type of pompon chrysanthemum ...... 253 
 
 70. Japanese anemone type ....... 256 
 
 71. The small and regular anemone type ..... 257 
 
 72. A pompon chrysanthemum ....... 258 
 
 73. Type of Japanese incurved chrysanthemum . . . 259 
 
 74. Japanese anemone chrysanthemum when fully expanded . 262 
 
 75. New type with short stem ....... 263 
 
 76. Incurved type 264 
 
 77. Hairy type 267 
 
 78. Japanese type 268 * 
 
 79. Reflexed type 269 
 
 80. Beimower 270 
 
 81. Flower of white lily 271 
 
 82. Flower of greenhouse cypripedium . . . . . 272 
 
 83. Flower of night-blooming cereus ...... 273 
 
 84. Flower of the shrubby hibiscus {Hibiscus syriacus) . . 274 
 
xviii List of Illustrations 
 
 FIGCRK PAGE 
 
 85. Bugbane {Cimicifuga racemosa) 275 
 
 86. Blossom of flowering raspberry {Rulms ocloratus) . . 276 
 
 87. Se^uash flowers of each sex ....... 277 
 
 88. Flowers of clematis ( CZewia^is vzrgfjwmna) .... 278 
 
 89. Tobacco flowers, showing the parts of the flower, a bud 
 
 ready to be emasculated, and an emasculated subject . 282 
 
 90. Zinnia flowers • 283 
 
 91. Instruments used in pollinating flowers .... 284 
 
 92. Ladle for pollinating house tomatoes ..... 285 
 
 93. Bag for covering the flowers ...... 286 
 
 94. Fuchsias, showing the stamens and pistils, and a bud ready 
 
 to be emasculated .... 
 
 95. Fuchsia flower emasculated 
 
 96. Fuchsia flower tied up after emasculation 
 
 97. Tomato and quince 
 
 98. Pollinating kit 
 
 99. Pollinating kit 
 
 100. Main building of Seed Association, offices o 
 
 pany (photo by Xewman) 
 
 101. Gardens at Luther Burbank's 
 
 102. Some of Burbank's frames and garden beds . . . 320 
 
 103. Spineless and spine-bearing cacti at Burbank's . . . 322 
 
 104. A specimen herbarium sheet, showing variations in the 
 
 leaves of the mulberry ....... 395 
 
 105. A specimen herbarium sheet, showing differences between 
 
 two leaves of the horse radish ..... 396 
 
 106. A specimen herbarium sheet, showing variations in leaves 
 
 of the Persian lilac ....... 398 
 
 107. A specimen herbarium sheet, showing variations in leaves 
 
 of the blackberry 400 
 
 108. A common form of ragweed 421 
 
 109. Another form of ragweed ....... 422 
 
 1 10. Demonstration of allelomorphism and of complete dominance 431 
 
 111. Demonstration of presence and absence hypothesis and of 
 
 intermediacy . 432 
 
 112. Demonstration of the presence of an inhibitor factor . . 434 
 
 113. Explanation of so-called " dominance and absence " . . 436 
 
 . 287 
 
 . 288 
 
 . 289 
 
 . 290 
 
 . 291 
 
 . 292 
 f Swedish Com- 
 
 . 307 
 
 . 319 
 
XLbc IRural Science Series 
 
 Edited by L. H. BAILEY 
 
 PLANT-BREEDING 
 
PLANT-BREEDING 
 
 CHAPTER I 
 
 THE FACT AND PHILOSOPHY OF VARIATION 
 
 There is no one fact connected with agriculture that 
 more greatly interests all persons than the existence of 
 numerous varieties of plants that seem to satisfy every need 
 of the gardener. Whence came all this multitude of 
 forms? What are the methods employed in securing 
 them? Are they merely isolated facts or phenomena 
 of gardening, or have they some relation to the broader 
 phases of the evolution of the forms of life ? These are 
 some of the questions that occur to every reflective 
 mind when it contemplates an attractive garden, but 
 they are questions that seem never to be answered. 
 Whatever attempt the garden/sr may make at answer- 
 ing them is either obscured by an effort to define what 
 a variety is, or else it consists in simply reciting how a 
 few given varieties came to be known. But there must 
 be some method of arriving at a conception of the ways 
 whereby the varieties of fruits and flowers and other culti- 
 vated plants have originated. If there is no such method, 
 then the origination of these varieties must follow no 
 law, and the discussion of the whole subject is fruitless. 
 But we have every confidence in the consecutive uniform- 
 
2 Plant-Breeding 
 
 ity of the operations of nature, and it were strange if 
 some underlying principle of the unfolding or progression 
 of plant-life does not dominate the origin of the varied 
 and innumerable varieties which, from time unknown, 
 have responded to the touch of the cultivator. Let us 
 first, therefore, make a broad survey of the subject in 
 a philosophical spirit, and later, discuss the more specific 
 instances of the origination of varieties. 
 
 The fact of individuality. — There is universal difference 
 in nature. No two Hving things are counterparts, for no 
 two are born alike or into exactly the same conditions and 
 experiences. Every living object has individuality; that 
 is, there is something about it that enables the acute 
 observer to distinguish it from all other objects, even of 
 the same class or species. Every plant in a row of lettuce 
 is different from every other plant, and the gardener, 
 when transplanting them, selects out, almost uncon- 
 sciously, some plants that please him and others that do 
 not. Every apple tree in an orchard of a thousand 
 Baldwins is unlike every other one, perhaps in size or 
 shape, or possibly in the vigor of growth or the kind of 
 fruit it bears. Persons who buy apples for export know 
 that fruit from certain regions stands the shipments better 
 than the same variety from other regions ; and if one were 
 to go into the orchards where these apples are grown, he 
 would find the owner still further refining the problem by 
 talking about the merits of individual trees in his orchard. 
 If one were to make the effort, he would find that it is 
 possible to distinguish differences between every two 
 spears of grass in a meadow, or every two heads of wheat 
 in a grain-field. 
 
The Fact and Philosophy of Variation 3 
 
 In timothy, one of the commonest of our grasses, a 
 casual observer may find differences in the length, shape, 
 and color of heads ; tendency of some plants to produce 
 asexual leaves in the head; form of base of the head; 
 
 m % 
 
 i) '^. 
 
 1 / Z -ij 4 6 6i 7 1 « 3; /Oj //,, /Z 
 
 Fig. 1. — Variation in heads of timothy. 
 
 length, mdth, and color of leaves ; erect or drooping 
 character of the leaves ; susceptibility of the leaves and 
 stems to rust ; period of blooming ; habit of growth of 
 plant, — erect or decumbent ; few or many culms to the 
 plant ; ability to recover after cutting ; quantity of seed 
 
Plant-Breeding 
 
The Fact and Philosophy of Variation 5 
 
 Fig. 3. — A productive timothy plant. 
 
 produced, and others (Figs. 1-5). Similar differences 
 may be found in any group of plants if the group is suffi- 
 ciently studied. 
 
Plant-Breeding 
 
 Fig. 4. — A timothy plant that runs much to seed. 
 
 Variation and adaptation. — All this is equivalent to 
 saying that plants are infinitely variable. The ultimate 
 
The Fact aiid Philosophy of Variation 7 
 
 causes of all this variation are beyond the purposes of the 
 present discussion, but it must be evident, to the reflective 
 mind, that these differences are a means of adapting 
 the innumerable individuals to every little difference or 
 
 Fig. 5. — A timothy plant that runs almost wholly to leaf. 
 
 advantage in the environment in which they live. And 
 if the result of variation is better adaption to the physical 
 conditions of life, then the same forces must have been 
 present in the circumstances which determined the birth 
 of the individual. This change in environment may be 
 
8 Plant-Breeding 
 
 the cause of much of the variation in plants, since differ- 
 ences in plants were positively injurious if it were possible 
 for the conditions of environment to be the same. 
 
 Species-formation. — If no two plants are anywhere 
 alike, then it is not strange if now and then some de- 
 parture, more marked than common, is named and becomes 
 a garden variety. We have been taught to feel that 
 plants are essentially stable and inelastic, and that any 
 departure from the type is an exception and calls for im- 
 mediate explanation. The fact is, however, that plants 
 are essentially unstable and plastic, and that variation 
 between the individuals must everywhere be expected. 
 This erroneous notion of the stability of organisms comes 
 of our habit of studying what we call species. We set 
 for ourselves a type of plant or animal, and group about it 
 all those individuals that are more like this type than 
 they are like any other, and this group we name a species. 
 
 Nowadays, the species is regarded as nothing more than a 
 convenient and arbitrary expression for classifying our 
 knowledge of the forms of life, but the older naturahsts 
 conceived that the species is the real entity or unit in 
 nature, and we have not yet wholly outgrown the habit of 
 mind which was born of that fallacy. Nature knows 
 little about species ; she is concerned with the individual, 
 the ultimate complete and working unit. This individual 
 she molds and fits into the opportunities of environment, 
 and each individual tends to become the more unlike its 
 birthmates the more the environments of the various in- 
 dividuals are unlike. 
 
 We must consider, therefore, as a fundamental concep- 
 tion to the discussion of the general subject before us, the 
 
The Fact and Philosophy of Variation 9 
 
 importance of the individual plant, rather than the im- 
 portance of the species ; for thereby we put ourselves as 
 nearly as possible in sympathetic attitude with nature, and, 
 resting upon the ultimate object of her concern, we are 
 able to understand what may be conceived to be her motive 
 in working out the problem of life. Recall the fact that 
 the whole tendency of contemporary civihzation, in soci- 
 ology and religion, is to deal with the individual person 
 and not with the mass. The present-day method of study- 
 ing the evolution of plants and animals is essentially an- 
 alytical. As the chemist attempts to discover the smallest 
 units from which the substances of nature have been built 
 up, so the student of biology and evolution is seeking for 
 the smallest heritable units of which plants and animals 
 are composed. This is only an unconscious feehng after 
 natural methods of solving the most complex of problems, 
 for it is exactly the means to which every organic thing 
 has been subjected from the beginning. 
 
 Conception of unit-characters. — The student of evolution 
 now conceives animals and plants to be composed of what 
 he terms ''unit-characters," analogous, roughly, to the 
 atoms of the chemist. These are the smallest heritable 
 units that a plant or animal may possess. Any distinct 
 entity that can be traced from one generation to another, 
 such as the presence or absence of pubescence on the leaves 
 or stems, the height of the plant, whether dwarf or tall, 
 the color of the flower or fruits, and very many others are 
 now known as unit-characters. The more any group of 
 plants is studied, the more definite and distinct these 
 unit-characters become. The time may come when the 
 gardener, from long experience, shall become acquainted 
 
10 Plant-Breeding 
 
 with these quahties, so that he may synthetically put 
 many units together by crossing and produce new varieties 
 almost at will. 
 
 Differences between plants and animals with regard to 
 general association of "parts and their methods of reproduction. 
 — Unit-characters are nature's blocks, which she uses to 
 build up plants and animals into various shapes for dif- 
 ferent purposes. These combinations of units when 
 added together in proper extent and proportion consti- 
 tute the plant and animal as we know it, the ultimate 
 living and working organism, with power of growth and 
 reproduction. 
 
 In looking for the ultimate working unit, individuality or 
 personality in nature, we must make a broad distinction 
 between the animal and the plant. Every higher animal 
 is itself a working unit ; it is one. It has a more or less 
 definite span of life, and every part and organ contributes 
 a certain indispensable part to the life and personality 
 of the organism. No part is capable of propagating itself 
 independently of the sex-organs of the animal, nor is it 
 capable of developing sex-organs of its own. If any part 
 is removed, the animal is maimed and perhaps it dies. 
 The plant, on the contrary, has no definite or distinct 
 autonomy. Most plants live an indefinite existence, 
 dependent very closely upon the immediate conditions in 
 which they grow. Every part or branch of the plant lives 
 largely for itself, it is capable of propagating and multi- 
 plying itself when removed from the parent or the colony 
 of branches of which it is a member, and it develops sex- 
 organs and other individual features of its own. If any 
 branch is removed, the tree or plant does not necessarily 
 
The Fact and Philosophy of Variation 11 
 
 suffer; in fact, the remaining branches usually profit 
 by the removal, a fact which shows that there is a competi- 
 tion, or struggle for existence, between the different 
 branches or elernents of the plant. The whole theory and 
 practice of pruning rests upon the fact of the individual 
 unlikenesses of the branches ; and the unlikenesses are of 
 the same kind and often of the same degree as those that 
 exist between different plants grown from seeds. 
 
 Bud-variation and hud-varieties. — The branches of a 
 Crawford peach tree, for example, differ amongst them- 
 selves in size, shape, vigor, productiveness, and season 
 of maturity, much the same as any two or more separate 
 Crawford trees, or any number of trees of other varieties, 
 differ the one from the others. If any one of these 
 branches or buds is removed and is grown into an inde- 
 pendent tree, a person could not tell — if he were ignorant 
 of its history — whether this tree were derived from a 
 branch or a seed. This proves that there is no essential 
 unlikeness between branches and independent plants, ex- 
 cept the mere accident that one grows upon another branch 
 or plant whilst the other grows in the ground. " But the 
 branch may be severed and grown in the ground, and the 
 seedling may be pulled up and grafted on the tree, and no 
 one can distinguish the different origins of the two. And 
 then, as a matter of fact, a very large proportion of our culti- 
 vated plants are not distinct plants at all, in the sense of 
 being different creations from seeds, but are simply the 
 result of the division of branches of one original plant or 
 branch. All the fruit trees of any one variety are obtained 
 from the dividing up and multiplication of the branches of 
 the first or original tree. 
 
12 Plant-Breeding 
 
 The reader is curious to know how this original tree came 
 to be, and this we may find out before we are done ; but 
 for the present, let it be said that it is equally possible for 
 it to have come from a seed, or to have sprung from a 
 branch which some person had noticed to be very dif- 
 ferent from the associated branches in the tree-top. In 
 other words, the ultimate unit or individual of variation 
 is the bud and the bit of wood or tissue to which it is 
 attached ; for every bud, like every seed, produces an 
 offspring that can be distinguished from every other 
 offspring whatsoever. 
 
CHAPTER II 
 THE CAUSES OF INDIVIDUAL DIFFERENCES 
 
 We have now gone back to the starting-point, to that 
 unit with which nature begins to make her initial differ- 
 ences or individuahties ; that is, to the point where varia- 
 tions arise. This point is the bud and the seed, — one 
 sexless, or the offspring of one parent ; the other sexual, 
 or the offspring of two parents. Now, inasmuch as the 
 horticultural variety is only a well-marked variation which 
 the gardener has chanced to notice and to propagate, it 
 follows that the only logical method of determining how 
 garden varieties originate is to discover the means by 
 which plants in general vary or differ one from another. 
 
 There is probably no one fact of organic nature concern- 
 ing the origin of which modern philosophers are so much 
 divided as the causes or reasons for the beginnings of 
 variations or differences. It seems to be an inscrutable 
 problem, and it would be useless, therefore, for us to 
 attempt to discover these ultimate forces in the present 
 book. Still, we must give them sufficient thought to 
 enable us to satisfy our minds as to how far these variations 
 may be produced by man ; and, in doing this, we must 
 discover at least the underlying philosophy of plant 
 variation. It is the nature of organisms to be unlike 
 their parents and their birthmates. Why? 
 
 13 
 
14 Plant-Breeding 
 
 Fortuitous variation. — It will probably never be pos- 
 sible to refer every variation to a distinct cause, for it is 
 probable that some of them have no antecedent. If we 
 conceive of the forms of life as having been created with 
 characters exactly uniform from generation to generation, 
 then we should be led to look for a distinct occasion or 
 cause for every departure from the type ; but we know, as 
 has already been pointed out, that heredity by its very 
 nature is not so exact as to carry over every attribute, and 
 no other, of the parent to the offspring. Plasticity is a 
 part of the essential constitution of all organic beings. 
 There is perhaps no inherent tendency in organisms 
 towards any ultimate or predetermined completion of 
 forms, as the older naturalists supposed, but simply a 
 laxity or indefiniteness of constitution which is expressed in 
 numberless minor differences in individuals. 
 
 That is, some variation may be simply fortuitous, an 
 inevitable result of the inherent plasticity of organisms, 
 and it may have no immediate inciting cause. 
 
 Action of natural selection on variation. — If we were to 
 assume that every minor difference is the result of some 
 immediate cause, then we should expect every individual 
 plant or animal to fill some niche, to satisfy some need, to 
 produce the definite effect for which the cause stands. 
 But it is apparent to one who contemplates the operations 
 of nature that very many — certainly more than half — of 
 the organisms which are born are not useful to the per- 
 petuity of the species and very soon perish. From these 
 fortuitous variations nature selects, to be sure, many 
 individuals to be the parents of other generations because 
 they chance to be fitted to live, but this does not affect 
 
The Causes of Individual Differences 15 
 
 the methods or reasons of their origin. It is possible that, 
 whilst many of these mere individual differences have no 
 direct and immediate cause, they may still be the result of 
 a devious line of antecedent causes long since so much 
 diffused and modified that they will remain forever un- 
 recognizable ; but even so, the fact still remains that 
 these present differences or variations may be purposeless, 
 and it is quite as well to say that the}^ exist because it is a 
 part of the organic constitution of living things that un- 
 like produces unlike. 
 
 Sex as a factor in the variation of plants. — All plants 
 have the faculty, either potential or expressed, of propagat- 
 ing themselves by means of buds, or asexual parts. This is 
 obviously the cheapest and most direct possible method 
 of propagation for many-membered plants, since it re- 
 quires no special reproductive organization and energy, 
 and, as only one parent is concerned in it, there is none of 
 the risk of failure that obtains in any mode of propaga- 
 tion in which two parents must find each other and form 
 a union. There must be some reason, therefore, for the 
 existence of such a costly mechanism as sex aside from 
 its use as a mere means of propagation. 
 
 It may be said that sex exists because it is a means of 
 more rapid multiplication than bud-propagation, but such 
 is not necessarily the fact. Many plants produce buds as 
 freely as they produce seeds ; and then, if mere multipli- 
 cation were the only destiny of the plant, bud-production 
 would no doubt have greatly increased to have met the 
 demand for new generations. The chief reason for 
 the existence of sex in the vegetable world seems to be the 
 need for a constant rejuvenation and modification of the 
 
16 Plant-Breeding 
 
 offspring by uniting the features of two individuals into 
 one. There thus arises from every sexual union a number 
 of new or different forms from which nature may select 
 the best, — that is, those best fitted to live in the condi- 
 tions in which they chance to be placed. But whilst 
 sex is undoubtedly one of the most potent sources of pres- 
 ent unlikenesses, it is not necessarily an original cause of 
 individual differences, since the two parties to any sexual con- 
 tract must be unlike before they can produce unlike. When 
 once the initial unlikenesses were established, every new 
 sexual union must produce new combinations, so that 
 now, when every new form, from whatever source it 
 appears, comes into existence, there are other intimately 
 related forms with which it may cross. This state of 
 things has existed to a greater or less degree from the 
 moment sex first appeared, so that the organic world is 
 now endlessly varied as the result of a most complex 
 ancestry. 
 
 Physical environment and variation. — Every phase and 
 condition of physical circumstances, which are not ab- 
 solutely prohibitive of plant life, have plants which thrive in 
 them. Every soil and climate, every degree of humidity, 
 hills, swamps, and ponds, — every place is filled with 
 plants. Even the trunks and branches of trees support 
 other plants, as epiphytes and parasites. That is, plants 
 have adapted themselves to every physical environment ; 
 or, to turn the proposition around, every physical en- 
 vironment produces adaptive changes in plants. There 
 are those, like Weismann and his adherents, who contend, 
 from purely speculative reasons, that these changes do 
 not become hereditary or permanent until they have in- 
 
The Causes of Individual Differences 17 
 
 fluenced a certain physiological substance which is assumed 
 to reside in the reproductive regions of the organisms, 
 and that all those changes which have not yet reached 
 this germ-plasm are, therefore, lost, or die with the or- 
 ganisms. 
 
 Do external influences produce permanent effects in 
 plants f — It is not necessary to discuss here the intri- 
 cate arguments in the time-honored controversy of the 
 permanent inheritance of external modifications. Such 
 violent modifications as traumatic injury do not affect its 
 germ cells and are not inherited. But it is the common 
 experience of gardeners that the modifications of the envi- 
 ronment of plants, such as changing food supply or changing 
 seed from one environment to another, produce changes 
 which eventually become hereditary. Whether these 
 changes of environment act directly upon the germ-plasm 
 to produce the change or whether they stimulate a ger- 
 minal change which was otherwise latent, is a question 
 which long and patient experimentation must decide. 
 Certain it is, that plants have gone through a profound 
 modification and it is easy to believe that environment has 
 played no little part in these changes. 
 
 Weismann teaches that ''acquired characters," or those 
 variations which first appear in the life-time of the indi- 
 vidual because of the influences of environment, are lost, 
 because they have not yet affected the reproductive sub- 
 starices ; but if these characters are induced by the effect 
 of impinging environment during two or more generations, 
 they may come to be so persistent that the plant cannot 
 throw them off, and they become, thereby, a part of the 
 hereditary and non-negotiable property of the species. 
 
18 Plant-Breeding 
 
 Now, it is apparent that in one or another of the genera- 
 tions which are thus acted upon by the environment, there 
 must be a beginning towards the fixing or hereditable 
 permanency of the new forms, and we might as well 
 assume that this beginning takes place in the first genera- 
 tion as in the last, since there can be no proof that it does 
 not take place in either one. The tendency towards 
 fixity, if it exists at all, imdoubtedly originates at the very 
 time that the variation itself originates, and it is only 
 sophistry to assume that the form appears at one time 
 and the tendency towards permanency at another time. 
 Since plants fit themselves into their circumstances by 
 means of adaptive variations, we must conclude that all 
 adaptive variations have the power of persisting, upon 
 occasion. 
 
 All these remarks, whilst somewhat abstruse, have a 
 most important bearing on the philosophy of the origin 
 of garden varieties, because they show, first that changes 
 in the conditions in which plants grow introduce modifi- 
 cations in the plants themselves, and second, that wher- 
 ever any modification occurs it is probable that it may 
 be fixed and perpetuated. 
 
 Natal and post-natal variations. — It is necessary at this 
 point that we distinguish between natal and post-natal 
 variations, — that is, between those variations which are 
 born with plants, and those which appear, as a result of 
 environment, after the plant has begun to grow. It is 
 commonly assumed that the form and general characters 
 of the plant are already determined in the seed, but a 
 moment's reflection will show that this is far from the 
 truth. One may sow a hundred selected peas, for example, 
 
The Causes of Individual Differences 19 
 
 all of which may be ahke in every discernible character. 
 If these are planted in a space of a foot apart, it will be 
 found, after two or three weeks, that some individuals 
 are outstripping the others, although all of them came up 
 equally well and were at first practically indistinguishable. 
 This means that, because of a little advantage in food or 
 moisture, or other circumstances, some plants have ob- 
 tained the mastery and are crowding out the less fortunate 
 ones. The theory and practice of agriculture rests on 
 the fact that plants can be modified greatly by the condi- 
 tions in which they grow, after they have become thor- 
 oughly established in the soil. Plants may start equal, 
 but differ widely at the harvest ; and this difference may 
 be controlled to a nicety by the cultivator. Every farmer 
 is confident, also, that the best results for the succeeding 
 year are to be got only when he selects seeds from the best 
 that he has been able to produce this year. So, given 
 uniformity or equality at the start, the operator molds 
 the individual plants largely at his will. 
 
 Conception of biotypes. — Most varieties are not as 
 uniform as would at first appear. A careful study of 
 plants, when growing, indicates that they are not only 
 modified in different degrees by environment but the plants 
 themselves are not the same. They have different po- 
 tentialities to begin with. Environment causes direct 
 modifications to appear ; it also allows expression in differ- 
 ^ ent degrees of the inherent variability present. Most 
 varieties of plants are polytypic, being composed of many 
 distinct types, or '' biotypes" as they have been called by 
 Johannsen. All this is a matter of the commonest ob- 
 servation with the gardener, who is so accustomed to 
 
20 Plant-Breeding 
 
 seeing great differences arise in batches of plants, all of 
 which start apparently equal and with an equal chance, 
 that he never thinks to comment upon the occurrence. 
 
 Having noticed that physical environments may modify 
 plants, we are now ready to consider just what changes 
 in these circumstances of plant life are most fruitful in 
 the production of new forms. 
 
 Variation in food supply. — The greater part of the 
 changes in the physical conditions of life hinge upon the 
 relative supply of food. Climbing plants assume their 
 form because, by virtue of the divergence of character, 
 they are enabled to fit themselves into places that other 
 plants cannot occupy. They rear their foliage into the 
 air, where food and sunlight are unappropriated. The 
 lower branches of tree-tops die, and the others thereby 
 appropriate the more food and grow the faster. The 
 entire practice of agriculture is built upon the augmenta- 
 tion of the food supply. For this purpose, we set the 
 plants in isolated positions, we till the ground, keep down 
 other plants or weeds, add plant-food to the soil, and prune 
 the tree and thin the fruit. 
 
 Thomas Andrew Knight, the chief of horticultural 
 philosophers, appears to have been the first clearly to 
 enunciate the law that excess of food supply is the most 
 prolific cause of the variations of plants. Darwin sub- 
 scribes to it without reserve: "Of all the causes which 
 induce variability, excess of food, whether or not changed 
 in nature, is probably the most powerful." Alexander 
 Braun, an earlier philosophical writer on natural history, 
 said that "it appears rather, on the whole, as if the unusual 
 conditions favorable to a luxuriant state of development, 
 
The Causes of Individual Differences 21 
 
 afforded by cultivation, awakened in the plant the inward 
 impulse to the display of all those variations possible 
 within the more or less narrowly circumscribed limits of 
 the species." It is generally agreed by those who have 
 given the matter much thought, that an excess of food 
 above the amount normally or habitually received is one 
 of the very chief, if not the most dominant, causes of in- 
 dividual differences in plants. Certainly every farmer 
 or gardener knows that the richer the soil in available 
 plant-food, the stronger and the more abnormal and 
 unusual his product will be. 
 
 If, then, excess of food supply is a strong factor in the 
 modification of plants, and the one fundamental aim of 
 agriculture is to supply food in excess of natural conditions, 
 it must naturally follow that cultivated plants should be, 
 of all others, the most variable. This is notably true. 
 Now, the first variation that usually comes of this liberal 
 food supply is increase in mere bulk. Probably every 
 plant which has ever been cultivated has increased its 
 stature or the size of some or all of its parts. Moreover, 
 this is generally the direct object of cultivation, — to 
 secure larger herbage, fruits, seeds, or flowers. Inci- 
 dentally, we find here an indubitable proof of the truth 
 of the hypothesis of evolution, for if it were impossible for 
 plants to vary or to assume new characters, there would be 
 no cultivation and no agriculture ; for there would be 
 little object in cultivating a product if it grew equally well 
 in the wild. 
 
 This variation into mere bigness is more important than 
 it may seem at first. All thoughtful horticulturists agree 
 in thinking that the first thing to be done in ameliorating 
 
22 Plant-Breeding 
 
 any plant is to ''break the type," that is, to cause it to vary. 
 The particular direction of variation is not so important, 
 at first ; for all experience has shown that if once the 
 seedlings of a plant begin to depart from the parental 
 type, other and various modifications will soon follow. If 
 a plant is once strongly modified in size, variations in 
 shape, color, flavor, or other attributes are forthcoming. 
 This apparent accumulation of variation seems at first to 
 be incapable of scientific explanation, but the reasons for 
 it are not difficult to understand when once they are 
 presented. 
 
 We now ask ourselves why these many variations appear 
 when once the type begins to modify itself. Consider 
 the fact that the world is now full of plants. In untamed 
 nature, but one more plant can grow unless another plant 
 dies. All plants, therefore, are held down to narrow limits 
 of numbers, and since there are so few individuals, — in 
 comparison with the seeds and buds which each plant 
 produces for the chance of multiplying itself, ■ — there 
 must be, also, few kinds and degrees of individual dif- 
 ferences. The farther and more freely a plant distributes 
 itself, the greater must be the differences between various 
 individuals, because they must adapt themselves to a 
 wider range of conditions. All plants are held in equilib- 
 rium, so to speak ; but the plant organism is plastic by 
 nature and quickly responds to every touch of environ- 
 ment ; so, as soon as the pressure is removed in any direc- 
 tion, the plant at once springs into the breach. Recall 
 the monotonous vegetation of the deep forest, where the 
 battle of centuries has subdued all but the strongest. 
 Clear away the forest, and then observe the fierce scramble 
 
The Causes of Individual Differences 23 
 
 for place and life amongst a multitude of forms which 
 spring in for an opportunity to better their conditions. 
 In a few years more, the tender low herbs have gone. 
 The briers and underbrush have usurped the land. As 
 time goes on, one species after another perishes, and when 
 the place is again reforested, two or three species hold un- 
 disputed sway over the land. The poplars that followed 
 the pines have long since perished and pines again dominate 
 the forest. Or, if the area were turned to pasture a few 
 years after the woods were removed, the herbs and bushes 
 die with the browsing, and in time the June-grass covers 
 the whole landscape with the mantle of conquest. So 
 plants may be said to be always ready to fill new places 
 in the polity of nature by adapting themselves to the new 
 circumstances as they grow into them. The appearance 
 of any one marked variation, therefore, is indication that 
 the plant may have found a new condition, that pressure is 
 somewhat lifted, and that the whole plastic organization 
 may soon respond to the new environment. It is ap- 
 parent, then, how the simplest and rudest cultivation has 
 been able, through the centuries, so profoundly to modify 
 our domestic plants that we are often unable to recognize 
 the forms from which they have sprung. 
 
 Food supply of different branches. — We must not forget 
 to notice, at this point, that the food supply differs amongst 
 the various branches of the same plant. Some branches, 
 by reason of position with reference to the main trunk or 
 with reference to air and sunlight, or, because of a better 
 start in the beginning as a result of some incidental 
 advantage, gain the mastery over others and crowd 
 them out. We have already seen that no two branches 
 
24 Plant-Breeding 
 
 on a plant are alike ; and we are now able to understand 
 that sports or bud-varieties are no more inexplicable 
 than seed-varieties. 
 
 What cultivation is. — Cultivation is really but an ex- 
 tension or intensification of nature's methods of dealing 
 with the plant world. The ultimate result of both nature 
 and man is to supply more food. The variations which 
 arise from the effects of mere cultivation, therefore, are in 
 kind very like those which nature produces, the chief 
 differences being that of degree. The accustomed opera- 
 tions of the farmer, therefore, have been powerful agents 
 in the evolution of vegetable forms. The ways in which 
 cultivation affords a more liberal food supply are as 
 follows : — 
 
 1. By isolating the individual plant. The husbandman 
 sets each plant by itself, and then protects it by destroying 
 the weeds or plants which endeavor to crowd it out. 
 There is a partial exception to this in the ''sowed crops," 
 like the grains, and it is noticeable that variation in these 
 plants is usually less marked than in the ''hoed crops." 
 
 2. By giving the plant the advantage of position, 
 whereby it is allowed the most congenial exposure to sun 
 and contour of land. 
 
 3. By increasing the fertility of the land, either by tillage 
 or the direct apphcation of plant-food, or both. Rich 
 and moist soils tend to "break" the type, — or to cause 
 initial variations, — to produce verdant colors and loss 
 of saccharine and pungent qualities, to induce redundant 
 growth, and to delay maturity and thereby to render 
 plants tender to cold winter climates. 
 
 4. By thinning the tops of plants and the fruits, whereby 
 
The Causes of Individual Differences 25 
 
 the remaining parts receive an amount of food in excess 
 of the habitual allowance. 
 
 5. By divergence of character in associated plants. 
 It is well known that a field planted so thickly to corn 
 that it cannot grow more with profit, may still grow 
 pumpkins between. The pumpkins and the corn are so 
 unlike in form that they complement each other, the one 
 filling the place which the other is not fitted to occupy. 
 We have already seen that a copse ever so full of bushes 
 may still grow vines. A meadow full of timothy may still 
 grow clover in the bottom, and land covered with apple 
 trees still grows weeds beneath. " The more di versed the 
 descendants from one species become in structure, con- 
 stitution, and habits," writes Darwin, ''by so much will 
 they be better enabled to seize on many and widely diver- 
 sified places in the polity of nature, and so be enabled to 
 increase in numbers." 
 
 Variation in climate. — The fact that any distinct 
 climatic region usually has plants that are very closely 
 related to those of other climatic regions in the same 
 zone, points strongly to the probable profound modifica- 
 tion of plants by climate. And, furthermore, we should 
 expect that if the food environment modifies plants, the 
 climatic environment must have the same power. More- 
 over, there is abundant historical and experimental proof 
 that climate is capable of greatly modifying the vegetable 
 kingdom. There are those who contradict any great effect 
 of climate in the variation of plants, and acclimatization 
 has been even stoutly denied. These persons make the 
 mistake of asking that a visible modification take place 
 at once upon the transfer of a plant from one climate to 
 
26 Plant-Breeding 
 
 another, and they also err in supposing that a plant can 
 adapt itself to a cold climate only by developing a capa- 
 bility to w-ithstand more cold. Indian corn is sometimes 
 cited as proof that plants do not become acclimatized, 
 for it is as tender to frost now as ever, for ajl that we know. 
 Yet this very plant affords a most unequivocal example of 
 complete acclimatization, because it has shortened its 
 period of gro^i:h fully one-half whereby it escapes the 
 cold of the Xorth. 
 
 The influence on plants of a change of climate, or, 
 what may amount to the same thing, the result of a trans- 
 fer of plants to new climates, is so complex and so general 
 that no discussion of the subject can be made at this 
 time. It will answer present purposes briefl}- to designate 
 the ways in which climate modifies plants: — - 
 
 1. Climate generally modifies the stature of plants. 
 They become dwarfer in high latitudes and altitudes. 
 
 2. It modifies form. Plants tend to be broader-headed, 
 and also more prostrate, in high latitudes and altitudes. 
 
 3. Proportionate leafiness generally increases, at the 
 same time. 
 
 4. There is also often a gain in comparative fruitful- 
 ness following transfer towards the poles. 
 
 5. The colors of leaves, flowers, fruits, and seeds are 
 greatly influenced by climate, there being a general 
 tendency, in plants of temperate regions, to augmentation 
 in intensity of colors as they are carried towards the poles. 
 
 6. There is modification in the flavor and essential 
 ingredients of various parts, following a change of climate. 
 
 7. There is a variation in variability itself. The more 
 difficult the climate in which a plant finds itself, the more 
 
The Causes of Individual Differences 27 
 
 it tends to vary to meet the uncongenial en\4ronnients. 
 In the high Xorth, man}' plants are so variable that the 
 marks used to identify the species in other latitudes are 
 often lost. 
 
 8. There may be a profound variation or modification 
 in constitution and habit by which plants become ac- 
 climatized, or enabled to endure a climate at first injurious 
 to them. This may occur by a variation in the constitu- 
 tion of the descendants, which enables them directlj' to 
 endure more untoward conditions. It generally comes 
 about, however, through a change in habit, by which 
 plants, when transferred towards the poles, shorten their 
 season of groTsi;h or even become annuals. Plants become 
 more sensitive to spring temperatures in cold climates, 
 so that the}' start relativeh' much earher in the season — 
 that is, at a lower sum-temperature — than in warm 
 climates. Any one who has passed the springtime in both 
 the Xorth and South must have noticed how much more 
 suddenly the vegetation comes forward in the Xorth ; 
 and it is surprising how the spring-sown crops accelerate 
 their gro'^'th in the Xorth over those in the South. 
 
 Mans control over clifnate as a means of making plants 
 to vary. — The characters that result from a change of 
 climatic en\aronment are peculiarh' within the control 
 of the agriculturist, for a leading factor in his business 
 is the transfer of plants far and wide over the earth. So 
 it has come that the staple varieties of the important 
 grains and fruits are unlike in Europe and America and 
 in all great geographical areas, although all the various 
 forms may have sprung from one ancestor within historic 
 times. A new countrv is stocked with varieties from 
 
28 Plant-Breeding 
 
 the mother country ; but in the course of a few genera- 
 tions it is found that the varieties in cultivation are unUke 
 the ones originally introduced, and from which they came. 
 As wild plants have become separated from each other as 
 species in the different geographical regions, so the cul- 
 tivated plants soon begin to follow similar lines of diver- 
 gence. In the beginning of the colonization of this 
 country, for example, all the varieties of apples were of 
 European origin. But in 1817, over sixty per cent of the 
 apples recommended for cultivation here were of American 
 origin, that is American-grown seedlings from the original 
 stock. At present, probably fully ninety per cent of the 
 popular apples of the Atlantic States are American pro- 
 ductions. The northern states of the Mississippi Valley 
 to which most of our eastern apples are not adapted, are 
 now witnessing a similar transformation in the adaptation 
 and modification of the varieties introduced from the East 
 and from Russia. The recently introduced Japanese 
 plums are conceded to be great acquisitions to our fruit- 
 growing, but no doubt the best results are yet to come 
 with the origination of domestic varieties of them. So 
 there is an irresistible tendency towards a divergence of 
 forms in different continental or geographical regions, 
 and much of the inevitable result is no doubt chargeable 
 to climatic environment. 
 
 Change of seed. — We may now pause for a moment to 
 consider two agencies or phenomena often associated with 
 the genesis of varieties. One of these is the fact that 
 the simple change of seed from one locality to another 
 usually gives a larger or better product or even more 
 marked variation. Mere transfer of seed is not of itself, 
 
The Causes of Individual Differences 29 
 
 however, a cause of variation. The change is beneficial 
 because it fits together characters and environments that 
 are not in equilibrium with each other. A plant grown 
 for several years in one set of conditions becomes fitted 
 to them, so to speak, and it is in a state of comparative 
 rest. When the plant or its progeny is taken to other 
 conditions, all the adjustments are broken up, and in 
 the refitting to the new circumstances new or strange 
 characters are likely to appear. We shall leave this sub- 
 ject for the present, expecting to give it a fuller treatment 
 in a later chapter. 
 
 Bud-variation. — Bud-variation, or sport, is a name 
 given to those branches which are so much unlike the 
 normal plant in any particular that they attract atten- 
 tion. Many garden varieties are simply multiplications 
 of such abnormal branches. This bud-variation is com- 
 monly held to be such an unusual and inexplicable phenom- 
 enon that it is considered apart from all the general 
 discussions of variation. It is not, of course, a cause of 
 variability, but only an effect of some antecedent, the 
 same as seed-variation is. We have already seen that all 
 the different branches, or even nodes of any plant are, 
 in a very important sense, distinct individuals, since 
 every one develops its own organs, each is capable of 
 reproducing itself independently, and each is unlike every 
 other because it is acted upon differently by environment 
 and food supply. It is not strange, therefore, that some 
 of these individuals should now and then depart very 
 widely from the ordinary type, and thereby attract the 
 attention of the gardener, who would forthwith make 
 cuttings or set grafts from the part. Every branch is a 
 
30 Plant-Breeding 
 
 bud-variety, just as truly as every seedling is a seed- 
 variety, — since no seedling is ever like its parent, — and 
 there should be no greater mystery connected with the 
 sports of buds than there is with the varieties from seeds, 
 for the causes that produce the one may be and probably 
 are equally competent to produce the other (Figs. 6, 7). 
 
 Struggle for life a cause of variation. — We have seen 
 that the world is full of plants. There is room for more 
 only as the present individuals die. Yet nearly every 
 species produces a great number of seeds, and makes a 
 most strenuous effort to multiply its kind. Any one 
 plant, if left to itself, is capable of covering the earth in 
 a comparatively short time. A fierce struggle for a chance 
 to live is therefore inevitable. This conflict is most 
 apparent to the general observer in the springtime, when 
 every ''herb yielding seed after his kind, and the tree 
 yielding fruit, whose seed was in itself, after his kind," are 
 sending forth a host of sturdy offspring. The very land 
 seems to be pregnant with weeds and aspiring young 
 growths. But by midsummer the numbers may be 
 less. The weaker and less fortunate ones have perished, 
 and the victors have waxed stronger thereby. The 
 annual and half of the biennial species complete their 
 course upon the approach of winter, and the older peren- 
 nial herbs are becoming weak ; so in the succeeding 
 springtime there is again a fierce combat for the vacant 
 places. 
 
 One of the results of this conflict is the adjustment of 
 plants to each other. We have seen how the climbing 
 plant insinuates itself amongst the shrubberies and ties 
 them together in an impenetrable tangle in order that 
 
The Causes of Individual Differences 31 
 
 Fig. 6. — Couch-grass or quack-grass. Showing means of sexual propa- 
 gation by seed and a sexual propagation by underground rootstocks. 
 (After Clark and Fletcher.) 
 
 it, itself, may have a chance to live. So the low plants 
 of the deep forest are such as have been plastic enough to 
 
32 
 
 Plant- Breeding 
 
 Fig. 7. — Orange hawkweed. This plant can withstand the struggle for 
 existence. It produces immense quantities of seed and also repro- 
 duces itself by underground rootstocks. (After Clark and Fletcher.) 
 
 adapt themselves to the damp shades. Thus plants have 
 developed companionships or divergences in character, 
 
The Causes of Individual Differences 33 
 
 by means of which, under the stress of circumstances, 
 they are able to live together. Plants have adapted 
 themselves to other plants as truly as to soil or climate ; 
 and if these latter environments are ever the' sources or 
 causes of variation, then the first must be also. We must 
 look upon the struggle for existence, therefore, as itself 
 a cause of individual differences, since we know that any 
 continued pressure from without awakens an adaptive 
 response in the form of the vegetable organisms. 
 
CHAPTER III 
 THE CHOICE AND FIXATION OF VARIATIONS 
 
 We have now seen that every living object is unlike 
 every other. In plants, even every branch is unlike any 
 other branch. We have endeavored to discover some of 
 these universal differences. We have found that they 
 are intimately associated with the welfare of the type or 
 species, inasmuch as they appear, for the most part, 
 to be the means of fitting the plant to live in the conditions 
 in which it is placed. But we have also seen that there 
 are more individuals than can find a place to live. How, 
 then, does nature choose the best from the poorest (or, 
 rather, the fit from the unfit), and, having chosen them, 
 how does she endeavor to fix them or to make them more 
 or less stable ? 
 
 ''This preservation of favorable individual differences 
 and variations, and the destruction of those which are 
 injurious, I have called Natural Selection or the Survival 
 of the Fittest." This is the philosophy which was pro- 
 pounded by Darwin, and which will carry his name to the 
 last generation of men. It looks simple enough. Those 
 forms which are best fitted to live, do live, because they 
 crowd out the others. Yet, this simple principle of 
 natural selection was the first explanation of the process 
 of evolution that seemed to be capable of interpreting 
 
 34 
 
The Choice and Fixation of Variations 35 
 
 the complex phenomena of the forms of organic hfe. For 
 a time, this philosophy was thought to be the one funda- 
 mental motive of the evolution or progression of life, but 
 we are now convinced that there are other motives or forces 
 at work; but it seems to be indisputable that natural 
 selection is a major force underlying the evolution of 
 plants, and it is the only one with which the person who 
 desires to breed plants need intimately concern himself. 
 
 We must now determine what a variety is. This is a 
 vexed question, and one which seems never to be capable 
 of an answer that is satisfactory to the gardener. Time 
 and again, some person has introduced what he considered 
 to be a distinct new variety, only to find that other horticul- 
 turists dispute him and declare that it is only some old 
 variety renamed. And yet the introducer knows that 
 he has not renamed an old variety, but that he has propa- 
 gated a form which appeared or originated on his own 
 grounds. 
 
 What is a variety ? — Now, let us see. Nature starts 
 out with the individual to make a new form. Every in- 
 dividual is unlike every other one. When the individual 
 differences are so well marked that we can readily de- 
 scribe and distinguish them, and so permanent that they 
 pass down nearly intact to a few generations, we say that 
 we have a variety. If the differences are still more 
 marked, we say that we have a species. Where the 
 variety ends and the species begins it may be utterly 
 impossible to determine ; and so we mark off at a certain 
 point and say, arbitrarily, that this much is variety and 
 that much is species. Asa Gray once said that ''species 
 are judgments." Now, if there is no hard and fast line 
 
36 Plant-Breeding 
 
 between the variety and the species, so there is none 
 between the individual and the variety; for a variety is 
 only the family of descendants from some one individual. 
 That is, the idea of variety or species rests on difference, 
 but just how much difference shall constitute one grade 
 or another is a matter of individual opinion. There is 
 no standardized practice. So, when two gardeners cannot 
 agree as to whether a given introduction is a new variety 
 or not, they are having the same kind of difficulty that two 
 botanists have when they cannot decide whether two plants 
 are two species or one. 
 
 It is apparent, then, that every individual plant is 
 a distinct variety, only that the differences between it and 
 other individuals may be so slight that they have no 
 practical utility and cannot be described and recorded. 
 Just as soon as an individual plant has characters so un- 
 like its kin that it has some commercial value, then the 
 plant will be increased by cuttings or grafts or seeds, 
 the brood of offspring will be given a name, and a new 
 variety is born. 
 
 Individuals with the same general features may appear 
 simultaneously in two or more places, and two or more 
 men may propagate, name, and introduce them. When 
 they are all brought together and compared, it will be said 
 that they are all the same variety, that, according to the 
 rules of nomenclature, the brood which chanced to be 
 named first must ''stand" or be held to be the type of the 
 variety and the other names must become synonyms. 
 Yet some persons may discover minor differences in them 
 and demand that the variety be kept distinct. So the 
 see-saw goes on — a variety is a variety so long as it an- 
 
The Choice and Fixation of Variations 37 
 
 swers some purpose in use or trade, and it is not a variety 
 when it is so much like some other variety that it has no 
 merit that the other does not possess. 
 
 As soon as a plant appears with some features which 
 are more desirable than anything that has preceded it, 
 therefore, it may be the beginning of a new variety. Man 
 chooses it, and then propagates it. This is human selec- 
 tion. If nature did the same thing, it would be natural 
 selection. 
 
 It must not be understood that there are no definite 
 species in nature. Some plants are so distinct, and so 
 constant in their characters, as to leave no doubt. But 
 wide variability is very common, and it may obscure the 
 relationship. 
 
 Adaptation in nature. — Now, how does nature preserve 
 or fix this type? She does not preserve it. She simply 
 chooses it as a beginning and gradually modifies it and 
 shapes it into the form which she needs. She has no 
 permanent forms. There is a general onward progression 
 of one type either towards other types or towards ex- 
 tinction. We have seen that nature is constantly choosing 
 and selecting. If she selects an individual for the be- 
 ginning of a race, then she selects just as keenly from every 
 offspring of that individual, and so on to the end of time. 
 The process never stops. So nature fixes her forms by 
 keeping them moving, growing, constantly developing 
 farther away from their beginnings. 
 
 The vexed question as to whether there is an accumula- 
 tive effect in variation, need not be considered here, as it 
 is foreign to the particular point of view at this place. 
 
 Artificial selection. — Now, man does the same thing. 
 
38 Plant-Breeding 
 
 A plant in a cabbage row pleases him. It has a solid 
 small head and stout stem. He stores it away for seed. 
 Amongst the offspring, perhaps fifty per cent are as good 
 as the parent. These are saved. So the process goes 
 on, from season to season. In four or five generations 
 of plants, he finds that ninety per cent of the seeds '^come 
 true." Then he names it and introduces it. It is well 
 advertised in the seed catalogues. Many persons buy the 
 seeds. Some of these persons will grow their own seeds, 
 and every one of them has a different ideal in mind when 
 selecting the seed parents. So, in the course of a few 
 years it is found that there are really several more or less 
 different forms under the same name. Some persons may 
 observe this difference and legitimately introduce one or 
 more of the forms as distinct varieties. Some other 
 person, however, who has known the history of the stock 
 and who is not aware that varieties pass into other forms, 
 objects to the new names and declares that the introducer 
 is imposing on the public. 
 
 This is the history of ninety out of every hundred 
 varieties which are habitually propagated by seeds, like 
 the kitchen-garden vegetables and the annual flowers. 
 Some peculiar individual, appearing we know not why, is 
 discovered, and seeds are saved and selection — perhaps 
 unconscious selection — begins. After a time the variety 
 is broken up into several, or else, if it varies only slightly, 
 into divergent forms, the whole body or generations of 
 the variety move onward, gradually departing from the 
 initial type until it is no longer the same, although it 
 may bear the same name. The life of seed varieties, in 
 their pure and original forms, is very short. Even the 
 
The Choice and Fixation of Variations 39 
 
 best of them are usually measured by a score of years or 
 less. They run out or pass out by variation, into other 
 forms. The Trophy tomato is not the Trophy tomato 
 which was introduced over forty years ago, although it bears 
 the old name and is a direct descendant of the first stock. 
 
 Bud selection. — In plants multiplied by buds — that is, 
 by budding, grafting, cuttings, tubers, and the like — 
 there is less variation in the offspring than in those prop- 
 agated by seeds. Yet we have seen that no two Baldwin 
 apple trees — all of which are but divisions, more or less 
 remote, of the same original tree — are alike, and now 
 and then one branch of a fruit tree may '^ sport " or develop 
 a strange bud-variety. We know, also, that the same 
 variety of fruit tree takes on different characters in 
 different geographical regions, so that the Greening apple 
 is no longer the Greening of Rhode Island in the West 
 and South. So, it is apparent that even when we divide 
 a plant into many parts and distribute the members far 
 and wide, and when there is no occasion for concerning 
 ourselves with fixing the type, — even here there is 
 variation. In some cases, particularly in those in which 
 we multiply the plant by dividing abnormally developed 
 parts, there is a tendency to scatter or to vary in many 
 directions, and also a tendency to run out by degeneration. 
 This is admirably true of the potato, varieties of which, 
 in ten years or less, become so mixed in their characters, 
 through rapid variation and deterioration, that we must 
 return to seedling productions for a new start. 
 
 Variation and selection not entirely within man's con- 
 trol. — Man is only rarely the direct means of originating 
 variations. He finds them among the normal plants of 
 
40 Plant-Breeding 
 
 the fields and gardens. His skill and science are exercised 
 in the selection and so-called breeding of the offspring, 
 more than in the original genesis of the new form. It is 
 usually only in those plants which he multiplies by simple 
 division that he gains much immediate profit by crossing 
 or hybridizing. It is the slow and patient care and selec- 
 tion, day by day, which permanently ameliorates and 
 improves the vegetable world. Nature starts the work; 
 man may complete it. 
 
 It is now generally held that species in nature some- 
 times originate suddenly, by means of ''leaps." In fact, 
 the de Vriesian view is that real species so originate, 
 and the steps whereby a few species come into existence 
 are called mutations. (See Chapter V.) However this 
 may be, it is nevertheless true that these mutations are 
 yet beyond the power of man directly to produce. Selec- 
 tion is still a powerful agent with which to ameliorate 
 domestic plants. 
 
CHAPTER IV 
 THE MEASUREMENT OF VARIATION 
 
 It is often desirable to describe a plant or a group of 
 plants in exact mathematical terms. Most of the plant 
 characters with which a breeder deals are measurable, 
 and an individual plant may be described as having so 
 many leaves, so many grains, and so on throughout a 
 long list of measurements ; or a group of plants may be 
 expressed in the form of averages ; likewise, the degree 
 of resemblance or difference between plants and their 
 offspring, or among plants of a certain group or ''popula- 
 tion. " The degree or extent of correlation or association 
 of plant characters may also be expressed mathematically. 
 
 The science of biometry. — The expression of variation 
 and heredity by means of statistical methods is known as 
 the science of Biometry. This method of description is 
 now being widely employed by experimental plant-breeders. 
 It is another tool which the breeder uses to record his 
 progress and describe his plants. The biometrician 
 should be cautioned to keep his use of mathematical 
 treatment subservient to the biological facts, not forgetting 
 that biometry is simply a means toward an end and not 
 an end in itself. It is better first of all to become ac- 
 quainted with the real plants before any mathematical 
 treatment of their variability is attempted. It is often 
 
 41 
 

 
 to 
 
 •0 
 
 •0 
 
 o 
 
 CVJ 
 42 
 
 
The Measurement of Variation 43 
 
 desirable, however, to treat plants in groups by means of 
 statistical generalizations. 
 
 ■ Type. — In the study of any group of plants, called a 
 "population," whether it be corn, wheat, the ray-florets 
 of daisies, or what not, the breeder has in mind a certain 
 type around which the individuals tend to center. 
 
 The corn breeder has in mind a certain length of an ear 
 of corn which is his ideal type. He chooses ears of this 
 length and plants them in his plat, and at harvest time 
 what does he get ? Not all ears of this length, but ears 
 ranging above and below this length. The offspring will 
 be distributed, in all probability, above and below this 
 parental type and may possibly reach the upper and lower 
 limits of the race. There will be a group near the average 
 which will contain a larger number of individuals than 
 any other and thus we have another conception of type. 
 There is the ideal parental type which the breeder has in 
 mind, and another type, probably different, shown by the 
 offspring. To find the latter, the ears of corn are care- 
 fully measured and their average length determined. 
 This average constitutes a concrete mathematical expres- 
 sion for the type of the offspring. 
 
 BiometricaL expression of variability. — The amount and 
 range of variability may also be well expressed statistically. 
 
 As an illustration, a number of pea plants were measured 
 and their height was found to range from 5 to 30J inches. 
 A few were short and a few were tall, but most of the plants 
 were of average height. For the sake of convenience, the 
 plants having similar measurements were placed together 
 in one class. When all the results had been brought 
 together they appeared as in the following table : — 
 
44 Plant-Breeding 
 
 _T T Number of Individ- 
 
 Height IN Inches ^^ls in Each Class (/) 
 
 5.1- 6.5 1 
 
 6.6- 8 4 
 
 8.1- 9.5 6 
 
 9.6-11 29 
 
 11.1-12.5 30 
 
 12.6-14 37 
 
 14.1-15.5 39 
 
 15.6-17 43 
 
 17.1-18.5 34 
 
 18.6-20 26 
 
 20.1-21.5 18 
 
 21.6-23 8 
 
 23.1-24.5 5 
 
 24.6-26 2 
 
 26.1-27.5 2 
 
 27.6-29 1 
 
 29.1-30.5 1 
 
 286 
 
 Here we have what is called a ''frequency distribution," 
 representing the crop as it falls into the different groups. 
 
 The curve in Fig. 8, known as the ''Quetelet curve," 
 represents the results graphically. 
 
 The frequencies, that is, the number of times each 
 measurement appears (see column / in the table), are 
 plotted on the axis of ordinates, line A-C, and the classes 
 on the axis of abscissas, line C-B. For the purpose of 
 plotting and working the data the mid-class is used, that 
 is, 5.8 inches instead of 5.1-6.6 inches, and so forth. 
 
 Mode. — We see by inspection of the foregoing data 
 that there is one group of the most common height, that is, 
 there are more plants having a height of 15.6 to 17 inches 
 (16.3) than any other class. 
 
 The group containing the greatest number of plants, 
 
The Measurement of Variation 45 
 
 that is, of the greatest frequency, is called the mode. 
 It is an excellent expression of type. When the group of 
 plants or population which is being studied is measured 
 and arranged with some suitable grouping, as illustrated 
 here, we see what the variety tends to do on the whole. 
 
 Modal coefficient. — It is desirable to know what per- 
 centage of the individuals falls into this group of highest 
 frequency, called the mode. This can be readily found by 
 dividing the number of individuals in this class (43) by 
 the total number (286) and multiplying by 100. This is 
 called the modal coefficient, and denotes the percentage of 
 individuals conforming to type. This modal coefficient is 
 .15 or 15%; that is, fifteen per cent of all of the plants 
 in this variety are found in one class. 
 
 However, as this is dependent on the system of measure- 
 ment, one modal coefficient is not directly comparable 
 with another unless the same practice of measurement has 
 been used. Moreover, one could not compare the modal 
 coefficient of height directly with that of weight or any 
 other character of a different nature. 
 
 It may readily be seen that a knowledge of the distribu- 
 tion of plants as represented by the mode or modal coeffi- 
 cient is of scientific and practical importance. It enables 
 the breeder at any time to spread out before himself a 
 fair representation of his variety. He can see at a glance 
 what is the prevaifing type and in what direction and to 
 what degree his breeding is extending. 
 
 Mean. — There is another conception of type known 
 as the mean or average. One can understand that the 
 average height will differ in most cases from the 
 commonest height. The mean is most easily obtained by 
 
46 
 
 Plant-Breeding 
 
 multiplying the mid-value of each class, say 5.8, by the 
 number in that class, adding their products, and dividing 
 by the total number of individuals. This is expressed 
 
 by the formula M (mean) 
 
 _S/F 
 
 n 
 
 where V represents the 
 
 variables, / the frequency of each variable, n the total 
 number of individuals, and 2 the summation of fV. 
 
 Mean. — 
 
 V 
 
 / 
 
 fV 
 
 
 5.8 
 
 1 
 
 5.8 
 
 
 7.3 
 
 4 
 
 29.2 
 
 
 8.8 
 
 6 
 
 52.8 
 
 
 10.3 
 
 29 
 
 298.7 
 
 
 11.8 
 
 30 
 
 354.0 
 
 
 13.3 
 
 37 
 
 492.1 
 
 
 14.8 
 
 39 
 
 577.2 
 
 
 16.3 
 
 43 
 
 700.9 
 
 
 17.8 
 
 ■ 34 
 
 605.2 
 
 
 19.3 
 
 26 
 
 501.8 
 
 
 20.8 
 
 18 
 
 374.4 
 
 
 22.3 
 
 8 
 
 178.4 
 
 
 23.8 
 
 5 
 
 119.0 
 
 
 25.3 
 
 2 
 
 50.6 
 
 
 26.8 
 
 2 
 
 53.6 
 
 
 28.3 
 
 1 
 
 28.3 
 
 
 29.8 
 
 1 
 
 29.8 
 
 
 n = 286 
 
 2 = 4451.8 
 
 Mnnn.(S/F) 
 
 4451.8 . 
 
 .^ .^ inohps. 
 
 
 n 
 
 286 
 
 Use of mean. — The mean gives a good average value 
 of the character and is often more useful than the mode 
 in expressing type. The breeder must use his judgment 
 
The Measurement of Variation 47 
 
 as to which should be used in each case, the mean or the 
 mode. 
 
 Mathematical expression of variability. — After the 
 average or mean of any group of plants has been deter- 
 mined, it is desirable to know the amount of deviation of 
 the different individuals from the mean. This determina- 
 tion gives a concrete expression which is an index of the 
 amount of variabiHty exhibited. This variabiUty is ex- 
 pressed as the average deviation or the standard deviation. 
 The latter is ordinarily employed by mathematicians. 
 
 Average deviation. — The average deviation is deter- 
 mined by obtaining, first of all, the amount which each 
 class varies from the mean and multiplying each deviation 
 by the number of individuals concerned. For example, 
 the column D is obtained by finding the difference between 
 the mean, 15.5, and the variations in column T^ : thus 
 in the first case the difference between 5.8 and 15.5 is - 9.7 
 while farther down column V we find 16.3, which is greater 
 than the mean, giving us a value of 0.8 in column D. 
 
 Now, if there were the same number of individuals in 
 each class, the average deviation could be found by adding 
 up the deviations in column D, and dividing by the total 
 number of individuals in column /, but there is one indi- 
 vidual deviating - 9.7 while there are 43 deviating 0.8 
 and 18 deviating 5.3, and so forth. In order to overcome 
 this the deviations are multiplied by the number of in- 
 dividuals giving the column fD. The sum of this column 
 divided by the total number of individuals gives the 
 average deviation. This is an index of variabiHty. 
 The average deviation is expressed by the following 
 formula : — 
 
48 
 
 Plant-Breeding 
 
 Average deviation = 
 
 2D/ 
 
 n 
 
 Standard deviation. — The operations for finding the 
 standard deviation are the same as for the average devia- 
 tion except that the deviations in column D are squared 
 before multipl3dng by the frequency numbers (/), thus 
 giving the columns D^ and D^f respectively. The sum 
 of the latter divided by the total number of individuals 
 and the square root of the result extracted gives the 
 standard deviation. This can be expressed by the follow- 
 ing formula : — ^ T^2f 
 
 ar= =^* 
 
 n 
 
 The details of determining the average and standard 
 deviation are as follows : — 
 
 V 
 
 / 
 
 D 
 
 fD 
 
 Z)2 
 
 D^f 
 
 5.8 
 
 1 
 
 - 9.7 
 
 9.70 
 
 94.09 
 
 94.09 
 
 7.3 
 
 4 
 
 - 8.2 
 
 32.80 
 
 67.24 
 
 268.96 
 
 8.8 
 
 6 
 
 - 6.7 
 
 40.20 
 
 44.89 
 
 269.34 
 
 10.3 
 
 29 
 
 - 5.2 
 
 150.80 
 
 27.04 
 
 784.16 
 
 11.8 
 
 30 
 
 - 3.7 
 
 111.00 
 
 13.69 
 
 410.70 
 
 13.3 
 
 37 
 
 - 2.2 
 
 81.40 
 
 4.84 
 
 179.08 
 
 14.8 
 
 39 
 
 - 0.7 
 
 27.30 
 
 0.49 
 
 19.11 
 
 16.3 
 
 43 
 
 0.8 
 
 34.40 
 
 0.64 
 
 28.12 
 
 17.8 
 
 34 
 
 2.3 
 
 78.20 
 
 5.29 
 
 179.86 
 
 19.3 
 
 26 
 
 3.8 
 
 98.80 
 
 14.44 
 
 375.44 
 
 20.8 
 
 18 
 
 5.3 
 
 95.40 
 
 28.09 
 
 505.62 
 
 22.3 
 
 8 
 
 6.8 
 
 54.40 
 
 46.24 
 
 369.92 
 
 23.8 
 
 5 
 
 8.3 
 
 41.50 
 
 68.89 
 
 551.12 
 
 25.3 
 
 2 
 
 9.8 
 
 19.60 
 
 96.04 
 
 192.08 
 
 26.8 
 
 2 
 
 11.3 
 
 22.60 
 
 127.69 
 
 255.38 
 
 28.3 
 
 1 
 
 12.8 
 
 12.80 
 
 163.84 
 
 163.84 
 
 29.8 
 
 1 
 
 14.3 
 
 14.30 
 925.20 
 
 204.49 
 
 204.49 
 
 
 n=286 
 
 2 = 4851.31 
 
The Measurement of Variation 49 
 
 925 20 
 Average deviation = ^ = 3.24 inches. 
 
 Standard deviation, (o-) = -y/ — !^ = 4.1+ in. 
 
 Coefficient of variability. — The average deviation or 
 standard deviation as outlined above is always determined 
 in the denomination of the unit in which the plant is 
 measured ; if it is height of plant in inches, the deviation 
 will be in inches and so forth. This prohibits the careful 
 comparison of the deviations of different plants or parts 
 of a plant because some deviations may be in pounds 
 or others in inches, and hence they will not be directly 
 comparable. 
 
 It is desirable, therefore, to have an abstract expression 
 so that the relative amount of variabiUty of one class of 
 organs may be directly compared with the variabihty of 
 another. This is called the coefficient of variability. It is 
 found by dividing the standard deviation by the mean. 
 Thus an abstract number is found which expresses the 
 variability. In our case the standard deviation = 4.1 
 inches and the mean = 15.5 inches, so that 
 
 ^^ = .264 = 26.4 % = the coefficient of variabihty. 
 15.5 
 
 If the coefficient of variabihty of the weight of the plants 
 had to be determined and was found to be, say, .384, it 
 would follow at once that the height of the plant was 
 considerably more variable than the weight. 
 
 The coefficient of variabihty may be expressed as 
 follows : — 
 
50 Plant-Breeding 
 
 C = -^x 100. 
 M 
 
 Probable error. ^ — It is obvious that these mathematical 
 expressions of type and variability will be modified some- 
 what by the number of individuals measured. The 
 greater the number of individuals employed, the less the 
 error. These differences which arise from the fewness 
 of individuals employed is known as the probable error. 
 It is expressed by a pair of divergences {=^ E), the one 
 above and the other below the actual value found, and 
 indicates that the chances are even that the true value 
 lies somewhere between the value found plus the error 
 and the value minus the error. For example, the probable 
 error of the mean in the problem here cited is =•= .016 and 
 is found by the formula given below. This means that 
 
 1 Formulae for probable errors : — 
 
 ET _i_ ^T^c standard deviation . ^^^-f 
 
 E mean = =•= .6745^ ^ — 7-^ -, or ± .674o- 
 
 number of individuals n 
 
 E standard deviation = ± .6745 standard de _viation ^ ^^ 
 
 .6745 
 
 V 2 X number of individuals 
 
 E coefficient of variability = =fc .6745 
 
 V2n 
 
 coefficient of variabilitv 
 
 = ± .6745 
 
 V2n 
 
 V 2 X number of individuals 
 C 
 
 But when C is greater than 10% use the formula 
 
 EC = ^ .6745— ^ri+2f— VT 
 
The Measurement of Variation 51 
 
 the true mean is probably somewhere between 15.5 + .016 
 and 15.5 — .016 or between 15.516 and 15.484. The size 
 of the error is generally indicative of thje number of the 
 individuals employed and the general dependability of the 
 work. 
 
 Use of statistical methods. — The use of statistical 
 methods enables the breeder to express quite accurately 
 the amount of variability which would otherwise be 
 expressed with considerable difficulty. It enables him 
 also to keep an accurate record of his work from year to 
 year and affords him a convenient method of comparing 
 one year's crop with another. 
 
 It will be seen later that statistical methods may also be 
 employed to express correlation and extent of inherit- 
 ance. 
 
CHAPTER V 
 MUTATIONS 
 
 There is endless dissimilarity in nature. No two 
 plants and no two animals are exactly alike. There are 
 more plants and animals than can find a place in which 
 to live and thrive. There results a struggle for existence. 
 Those animals or plants which, by virtue of the individual 
 differences or pecuUarities, are best fitted to the condi- 
 tions in which they are placed, survive in this struggle 
 for existence. They are " selected to live." Those that 
 survive, propagate their pecuharities. By virtue of 
 continued variation, and of continued selection along a 
 certain line, the peculiarities may become augmented; 
 finally the gulf of separation from the parental stem 
 becomes great, and what we call a new species has origi- 
 nated. 
 
 Evolutionary theories of Darwin and de Vries. — This, 
 in epitome, is the philosophy of Darwin in respect to evolu- 
 tion of organic forms. It contains the well-known postu- 
 late of natural selection, the principle that we know as 
 Darwinism. This principle has had more adherents 
 than any other hypothesis of the process of evolution. 
 All recent hypotheses in some way relate to it. A number 
 of them modify it, and some dispute it. The most pro- 
 nounced counter-hypothesis is also the newest. It is that 
 
 52 
 
Mutations 
 
 53 
 
 of Professor de Vries, botanist, of Amsterdam, Holland, 
 who denies that natural selection is competent to produce 
 species, or that organic ascent is the product of small 
 differences gradually enlarging into great ones. According 
 to de Vries' view, species-characters arise suddenly, or 
 all at once, and they are ordinarily stable from the moment 
 they arise. 
 
 -i 6-10 10-16 l&-iO 20-2J 26-SO S0-3i i^-*0 4(M6 
 
 70-7S 7i-«0 eu-bi Sj-OO 1I0-SI5 O'ylOO iOO 
 
 Fig. 9. — Variations in statures of (Enothera nanella (left), a mutant, 
 and (Enothera Lamarkiana (right), its parent. Oenothera nanella : 
 Range, 7-35 cm. ; M., 22.81 ± 1.02 cm. ; <t, 7.26 ± 0.72 cm. ; C. V., 
 31.84=^3.16 per cent. (Enothera Lamarkiana: Range, 77—96 cm.; 
 M., 88.68 ± 0.55 cm. ; <t, 4.76 ± 0.39 cm. ; C. V. 5.37 ± 0.44 per 
 cent. 
 
 De Vries conceives that variations, or differences, are of 
 two general categories : (1) Variations proper, or small, 
 fluctuating, unstable differences pecuUar to the individual 
 (only partially transmitted to offspring) ; and (2) muta- 
 tions, or differences that are usually of marked character, 
 appear suddenly and without transition to other forms 
 and are at once the starting-points of new species or races. 
 Variations proper may be due to the immediate environ- 
 
54 
 
 Plant- Breeding 
 
 ment in which tlie plant Uves. The mutations arise from 
 causes yet unkno^vn, although these causes are considered 
 to be physiological. Probably many so-called mutations 
 are hybrids and hence not mutations in the strictest 
 sense. 
 
 Differences between fluctuating variations and mutations: — ■ 
 
 1. Fluctuating variations are very common and are 
 to be found in all plants and animals. Mutations occur 
 intermediately and are rare. 
 
 2. Fluctuating variations are thought not to be trans- 
 
 mitted. ]\Iuta- 
 tions are trans- 
 mitted. 
 
 3. Fluctuating 
 variations pre- 
 sent a series of 
 differences which 
 may be plotted 
 on a frequency 
 curve and obey 
 the laws of 
 chance. ]\Iuta- 
 tions or saltatory 
 variations do not 
 obe}" the laws of 
 chance, and can- 
 not be plotted in 
 the form of a 
 frequency curve. 
 4. Fluctuating variations do not lead to a new perma- 
 nent mean of the race. Mutations cause a new mean to be 
 
 lis 12 IIS IJ OLJ /fr 7W IS liJ 16 16.5 n ns IS 18J 19 
 
 Fig. 10. — Variations in the amount of sugar 
 in 4t),000 beets. 
 
Mutations 
 
 55 
 
 formed, around which is grouped a new series of fluctuating 
 variations, forming a frequency curve. (See Fig. 9.) 
 
 5. In a fluctuating variation no new unit characters are 
 added. The same char- 
 acters are merely found 
 in greater or less quan- 
 tity or number (Fig. 10) . 
 Where a mutation oc- 
 curs, new unit charac- 
 ters are added or old 
 ones lost. 
 
 6. Fluctuating vari- 
 ations represent indi- 
 viduals or parts of them. 
 Mutations represent 
 groups of individuals. 
 
 In fluctuating vari- 
 ations, the small differ- 
 ences are grouped 
 around what may be 
 called a '^center of fluc- 
 tuation," which is the 
 mean of the frequency 
 curve. When a mutation is formed, a new center of 
 fluctuation is established around a new mean. 
 
 History of mutation. — The first mutation was recorded 
 in 1590. In the garden of Sprenger, an apothecary of 
 Heidelberg, was found a peculiar form of Chelidoniwn 
 majus. The new form appeared suddenly and without 
 intermediates from a lot of plants which had been culti- 
 vated for many years. This mutant had ''leaves cut into 
 
 Fig. 11. — Chelidonium majus. 
 
56 
 
 Plant-Breeding 
 
 narrow lobes with almost linear tips, and the petals were 
 also cut up." The new species has been constant since 
 the first, and follows Mendel's law when crossed with 
 
 C. majus, its par- 
 ent. (See Figs. 
 11 and 12.) 
 
 The word 
 '' mutation" was 
 first used in 1650 
 by Dr. Thomas 
 Browne, in his 
 book ^'Pseudo- 
 doxia Epidem- 
 ic a .' ' Lock 
 quotes from 
 Book VI, Chap- 
 ter X, ^'Of the 
 Blackness of Ne- 
 groes," as fol- 
 lows : — 
 
 ''We may say 
 that men become 
 black in the same 
 manner that 
 some foxes, squir- 
 rels, lions, first turned of this complexion, whereof there 
 are a constant sort in diverse countries ; that crows 
 became pyed, all which mutations, however, they began, 
 depend upon durable foundations and such as may con- 
 tinue forever." 
 
 History of the appearance of double flowers. — Double 
 
 Fig. 12. — Chelidonium laciniatum. A flower of 
 it to the left. Below a flower of C. tnajus. 
 
Mutations 
 
 57 
 
 flowers which have persisted for a long time are thought to 
 be mutations from single types. Some of the first re- 
 corded appearances of double flowers were described in 
 
 1671 by Abraham Hunting in a 
 book called, ''Waare Oeffeninge 
 der Planten" or "True Exercises 
 with Plants." This large book 
 on garden plants contained a 
 long Hst of double flowers which 
 
 Fig. 13. — Anemone coro- 
 naria, single-flowered 
 form. 
 
 Fig. 14. — Anemone coronaria, semi- 
 double-flowered form. 
 
 were found growing in gardens at that time. Double 
 flowers of such plants as poppies, hver-leaf (hepatica), 
 wallflowers (cheiranthus) , violets, caltha, althea, colchium, 
 and periwinkle {vinca), were described. 
 
58 
 
 Plant-Breeding 
 
 Other double forms have since been added. The double 
 marigold {Chrysanthemum indicum) came from Japan; 
 double zinnias from Mexico ; and double dahlias which 
 were first produced in Belgium in 1814, are examples. 
 
 The garden anemone {Anemone coronaria) is said to 
 have been first found double in an EngUsh nursery in 
 the first half of the last century. One flower with a single 
 
 broadened stamen was 
 observed by WilKam- 
 son, owner of the nurs- 
 ery. The seed from this 
 was saved separately 
 and planted the next 
 year. After a few gen- 
 erations of selection of 
 this kind, the double 
 flowers appeared as mu- 
 tations and bred true to 
 type (Figs. 13-15). 
 
 The origin of the 
 double petunia dates 
 back to the year 1855, 
 when it suddenly arose from ordinary seed in a garden 
 at Lyons. Carriere reported that from this one plant 
 all double races and varieties of petunias have been 
 derived by natural and partly by artificial crosses, and 
 he added that hkewise other species were known at that 
 time to produce new double varieties rapidly. 
 
 Geoffroy St. Hilaire, about 1825, expressed his belief 
 in saltatory variations as a means of evolution. He 
 thought that evolution does not take place entirely by 
 
 Fig. 15. 
 
 — Anemone coronaria, var. flore- 
 pleno. (Full double.) 
 
Mutations 
 
 59 
 
 the slow changes advocated by Lamark. His ideas were 
 theoretical, however, and at that time were not borne out 
 by experimental evidence. 
 
 Darwin recognized the appearance of sudden variations 
 of a marked character, such as is seen in the origin of 
 large-crested PoHsh fowls and short-legged Ancon sheep. 
 He thought that these new and strange forms would be 
 lost soon by intercrossing and, being rare, that they pos- 
 sessed no value. He held that the slow accumulation 
 of minute fluctuating variations was the important factor 
 in evolution. 
 
 De Vries' experiment with Oenotheras. — De Vries became 
 convinced long ago that Darwin's theory of the origin 
 of species through ac- 
 cumulation of minute 
 changes was not the only 
 means of creating new 
 types. He determined 
 to produce mutations ex- 
 perimentally, if possible. 
 His results in the forma- 
 tion of a new variety of 
 the corn marigold will be 
 described later. After 
 making preliminary ex- 
 periments with some 
 hundred species, de Vries 
 
 finally decided upon (Enothera Lajnarkiana as the most 
 suitable form to use (Figs. 17 and 18). ''Only one of my 
 tests met with expectations. This species proved to be 
 in a state of mutation, producing new elementary forms 
 
 Fig. 16. — Hugo de Vries. 
 
60 
 
 Plant-Breeding 
 
 continually, and it soon became the chief member of my 
 experimental garden. It was one of the evening prim- 
 roses/' This (E. Lamarkiana was found to produce a 
 large number of mutants, both when growing wild and 
 under cultivation. 
 
 The (E. Lamarkiana plants which became the basis of 
 
 Fig. 17. — (Enothera Lamarkiana and (Enothera nanella in bloom. 
 
 future experiments were found growing wild in a field at 
 Hilversum, near Amsterdam, Holland. Little is known 
 of its history except that it is a native of America. It has 
 not been found growing wild in America in recent years, 
 although there seems to be evidence that it was seen and 
 collected in the Southern States in the last century. The 
 near relatives of (E. muricata, which were very common in 
 the sandy regions of Holland, are very stable ; de Vries 
 
Mutations 
 
 61 
 
 found no appreciable change in them, although he watched 
 them for more than forty years. 
 
 Lamark's evening-primrose is grown in Europe as a cul- 
 tivated plant, used principally for ornamental planting. 
 It seeds abundantly and some of the plants have escaped 
 cultivation. Groups of plants are found growing wild 
 in many places. These wild plants remain in groups 
 rather than being widely scattered, suggesting a definite 
 
 V K n tS tl> XO Xr ZZ Z3 »r ZS 2e 27 ZS 29 JO si'jX 33 Jt.Hhu, 
 
 Fig. 18. — (Enothera Lamarkiana. Curve exhibiting variations in the 
 length of fruits of 568 plants. The dotted line is that given by 
 Quetelet-Galton Law. 
 
 origin for each group. (E. Lamarkiana is described as a 
 ''stately plant with a stout stem, attaining often a height 
 of 1.6 meters and more. When not crowded, the main 
 stem is surrounded by a large circle of smaller branches, 
 growing upwards from its base so as often to form a dense 
 bush. These branches in their turn have numerous 
 lateral branches. Most of them are crowded with flowers 
 in summer, which regularly succeed each other, leaving 
 behind them long spikes of young fruits. The flowers are 
 
62 Plant- Breeding 
 
 large and of a bright yellow color, attracting immediate 
 attention, even at a distance. They open towards 
 evening, as the name indicates, and are pollinated by 
 bumble-bees and moths. On bright days their duration 
 is confined to one evening, but during cloudy weather they 
 may still be found open on the following morning. Con- 
 trary to their congeners, they are dependent on visiting 
 insects for pollination. 
 
 ''In (E. Lamarkiana no self-fertilization takes place. 
 The stigmas are above the anthers in the bud, and as the 
 style increases in length at the time of the opening of 
 the corolla, they are elevated above the anthers and do 
 not receive the pollen. Ordinarily the flowers remained 
 sterile if not visited by insects or pollinated by myself, 
 although rare instances of self-fertilization were seen." 
 
 (E. Lamarkiana is a biennial, producing rosettes in 
 the first year and stems in the second year. This species 
 was found to be variable in all periods of its life cycle, — 
 in the seedlings, the rosettes, and the stems. 
 
 De Vries pursued three methods in obtaining his muta- 
 tions : — 
 
 1. Observations and studies of the plants while growing 
 in the wild state in the fields. 
 
 2. Some of the plants were removed from the wild state 
 and placed under cultivation. Many of the plants were 
 self-fertilized and their seed sown under controlled con- 
 ditions. By this method several mutants were found 
 which were too weak to withstand the competition of field 
 conditions. 
 
 3. Repetition of the sowing process for several genera- 
 tions, leading to the production of new forms. 
 
Mutations 
 
 63 
 
 De Vries divided the new types of plants into five groups, 
 classified as follows : — 
 
 1. Retrograde varieties witli 'negative attributes, 
 (E. Icevifolia, (E. brevistylis, and (E. nanella (Figs. 17 
 and 19). 
 
 Fig. 19. — (Enothera lata (left), (Enothera Lamarkiana (middle), 
 CEnothera nanella (right). 
 
 2. Progressive elementary species possessing new 
 characters, and appearing as vigorous as the parent plant, 
 CE. gigas and (E. ruhrijiervis. 
 
64 Plant-Breeding 
 
 3. Progressive elementary species, which are weaker 
 than the parent species, CE. albida and (E. ohlonga. 
 
 4. Organically incomplete forms, (E. lata (Fig. 19). 
 
 5. Fertile but inconstant species forms, CE. scintillans 
 and (E. elliptica. 
 
 The new species and varieties may be described as 
 follows : — 
 
 Group I, retrograde varieties, which have lost some 
 of the characters possessed by the parent, (E. Lamarkiana : — 
 
 (E. Icevifolia is easily distinguished from its parent, 
 (E. Lamarkiana, by having smooth, bright leaves, without 
 undulations. These leaves are narrower and more slender 
 than in Lamarkiana and the flowers of the brighter yellow. 
 This variety was constant from seed, showing no reversion. 
 It is a strong-growing plant and perfectly fertile. 
 
 CE. brevistylis is a short-styled form. The ovarj^ of 
 this plant is abnormally situated and is not conducive to 
 proper fertilization. The ovary is reached by only a few 
 pollen tubes and fertilization must be incomplete. The 
 few seeds that are obtained reproduce this type without 
 reversion to Lamarkiana. CE. brevistylis may be dis- 
 tinguished from the other forms before blossoming as 
 the buds are much shorter and thicker than in the other 
 species. The presence of leaves more rounded at the 
 tip also distinguishes this form from others before 
 flowering. 
 
 CE. nanella is a dwarf form, attaining often only one- 
 fourth the height of the other types. The flowers on this 
 dwarf form are as large as upon Lamarkiana, which is a 
 striking feature. The size of the leaves is proportionate 
 to the height of the plant, but retain the same form as the 
 
Mutations 65 
 
 parent species. The stems are unbranched and very 
 brittle. (E. nanella is frequently produced as a mutation 
 and is absolutely constant (Figs. 17 and 19). 
 
 Group II, progressive elementary species, possessing new 
 characters : — 
 
 (E. gigas is a giant form which is much larger in every 
 respect than its parent, except in height. The stems are 
 much larger ; internodes are shorter and the leaves more 
 numerous than the parent species (CE. Lamarkiana). 
 The flower-buds are large and closely crowded on the 
 spike, and when the flowers open, they make a beautiful 
 appearance (Fig. 20) . 
 
 (E. ruhrinervis is characterized by the red veins and red 
 streaks on the fruits. This plant is as tall as (E. gigas, 
 but a little more slender. A feature of this type is the 
 brittleness of the leaves and stems, especially in the annual 
 individuals, of which many are found. 
 
 Many of these mutants may be recognized before the 
 adult stage has been reached, for example, at about the 
 age of two months. The leaves of (E. gigas are broad, of a 
 deep green, the blade sharply cut off from the stalk, all 
 of the rosettes becoming stout and crowded with leaves. 
 In (E. ruhrinervis, on the contrary, the leaves are thin, 
 of a paler green, and with a silvery white surface ; the 
 blades are in the form of an ellipse, acute at the apex, 
 and gradually narrowing into the petiole. 
 
 Both of these species are quite constant and do not 
 revert to (E. Lamarkiana. However, other mutants have 
 sprung from these two species, especially from ruhrinervis, 
 which is produced in greater numbers from Lamarkiana 
 than is gigas. 
 
jTiG. 20. — A, spike with almost ripe fruits of (Enothera gigas, a mutant 
 species ; B, the same of (Enothera Lamarkiana, its parent form. 
 
 66 
 
Mutations 67 
 
 Group III, progressive elementary species which make a 
 very weak growth : — 
 
 CE. alhida has whitish, narrow leaves, apparently in- 
 capable of producing sufficient quantities of organic food, 
 and hence are very weak. These plants are not suffi- 
 ciently robust to withstand competition in the field and 
 require transplanting into rich soil in pots in order to 
 allow them to live through the first year so that they 
 can produce seed the second year. When these seeds 
 are planted they produce individuals true to type. 
 
 (E. oblonga is a small plant about half the size of Lamark- 
 iana and may be grown either as an annual or as a bien- 
 nial. It is characterized by its narrow leaves, which are 
 fleshy and of a bright green color. Another striking 
 feature of this type is the presence of numerous little 
 capsules covering the axis of the spike after the fading 
 away of the petals. (E. oblonga is very constant if grown 
 from pure seed. 
 
 The forms already described are relatively very con- 
 stant and never revert to the parent form. Contrasted 
 with these constant forms, de Vries found several incon- 
 stant types as follows : — • 
 
 Group IV, organically incomplete types : — 
 
 CE. lata is characterized by the fact that only pistillate 
 flowers are formed. The anthers seem to be robust, 
 but they are dry, wrinlded, and nearly devoid of contents. 
 It is a low plant with very dense and luxuriant, but brittle, 
 foliage. It has bright yellow flowers which open only 
 partially and remain wrinkled throughout the flowering 
 time. CE. lata may be recognized by its seedlings, which 
 have leaves of a nearly orbicular shape and are very 
 
68 * Plant-Breeding 
 
 sharply set off against the stalk. The mature plant 
 has broad sinuate leaves with rounded tips, which are 
 often crowded together on the summits of the stems and 
 branches to form rosettes. (E. lata may be considered 
 a true mutation, and when crossed with CE. Lamarkiana, 
 the progeny of the second generation segregates into 
 mendelian proportions, lata being recessive (Fig. 19). 
 Group V, perfectly fertile but inconstant species : — 
 CE. scintillans is characterized by the production of 
 deep green leaves with smooth, shiny surfaces, ''glisten- 
 ing in the sunshine." The plants are smaller and less 
 branched than the parental type. CE. scintillans is a 
 very inconstant form ; from the seeds which are produced 
 in great numbers, there results not only scintillans, but 
 Lamarkiana, oblonga, lata, and nanella, with a predomi- 
 nance of the parental Lamarkiana. In regard to its in- 
 stability, de Vries says, ''The instability seems to be a 
 constant quality, although the words themselves are at 
 first sight contradictory. I mean to convey the con- 
 ception that the degree of instability remains unchanged 
 during the successive generations." 
 
 CE. elliptica is a very rare form both in the wild state 
 and in cultivation. It is characterized by having narrow 
 elliptical leaves and elliptical petals. 
 
 ANALYTICAL TABLE OF SEEDLINGS (After de Vries) 
 
 I. Leaves stalked. 
 
 A. Leaves of the same breadth or 
 broader. 1 
 L Of the same breadth and shape, 
 not to be distinguished as 
 seedhngs. 
 
 ^ *' (than in Lamarkiana) " as also in the other analytical tables. 
 
Mutations 
 
 69 
 
 a. 
 h. 
 
 c. 
 
 2. Broader, pointed, with many 
 
 crumples. 
 
 3. Broader, rounded at the tip 
 
 with very deep crumples, 
 
 edge incurved. 
 a. 
 b. 
 
 1. (E. Lamarkiana. 
 
 2. CE. brevistylis. 
 
 3. (E. leptocarpa. 
 
 4. (E. gigas. 
 
 5. (E. lata. 
 
 6. CE. semilata. 
 
 B. Leaves narrower. 
 
 1. Broadest in the middle. 
 
 a. Very long with long stalks, 
 
 with narrow veins, almost 
 smooth. 
 
 b. Small with broad leaf- stalk 
 
 and broad, principal veins, 
 very smooth, shiny dark 
 green. 
 
 2. Of equal breadth over the 
 
 greater part of their length. 
 
 a. Green. 
 
 a. 1. Only slightly nar- 
 rower, smooth with- 
 out, or almost with- 
 out crumples. 
 
 a. 2. Very narrow with 
 
 broad leaf-stalks 
 and broad veins 
 which often are red- 
 dish ; wrinkled. 
 
 b. Whitish. 
 
 b. 1. Crumples many, 
 
 pointed, narrowing 
 off into the stalk. 
 b. 2. Crumples few, nar- 
 rowing off into the 
 stalk, wavy, brittle, 
 veins reddish. 
 
 7. (E. elliptica. 
 
 8. (E. scintillans. 
 
 9. (E. Icevijolia. 
 
 10. (E. oblonga. 
 
 11. (E. albida. 
 
 12. CE. rubrinervis. 
 
70 
 
 Plant-Breeding 
 
Alutations 71 
 
 6. 3, Crumples few, 
 scarcely narrowing 
 into the stalk, 
 almost grasslike. 13. CE. sublinearis. 
 
 ]I. Leaves sessile, short and broad, 
 
 almost heart-shaped, crumpled. 14. (E. nanella. 
 
 How the mutants were produced in the garden. — Most 
 of the types previously described were found growing 
 wild near their parent species, (E. Lamarkiana. 
 
 De Vries wished to determine whether these mutations 
 could be produced from seed of (E. Lamarkiana planted in 
 the garden (Fig. 21). Four series of experiments were 
 performed, lasting through five to nine generations in 
 which thousands of individuals were grown and studied. 
 A description is here given of one of these experiments.^ 
 The others were very similar. The pedigree culture began 
 in 1886, when seed was planted in the garden from 
 nine plants found growing wild. These nine plants 
 constituted the first generation. The second generation 
 flowered in 1889. This generation consisted of fifteen 
 thousand seedlings of which ten were distinct mutations 
 — five lata and five nanella. There were no intermediates. 
 
 The third generation of ten thousand plants produced for 
 the first time in pedigree cultures a plant of (E". ruhrinervis, 
 along with three plants of CE. lata and three of (E. nanella. 
 
 The fourth generation of fourteen thousand plants 
 yielded a higher percentage of mutants. These were 
 as follows : oblonga 176 ; lata 73 ; nanella 60 ; alhida 15 ; 
 ruhrinervis 8 ; scintillans 1 ; and gigas 1 . 
 
 1 De Vries, "Species and Variation, their Origin by Mutation," pp. 
 549-575. 
 
72 
 
 Plant-Breeding 
 
 At this stage of the experiment, de Vries became expert 
 in detecting variations at an early period. This accounts 
 in part for the large number of mutants found in the 
 fourth generation. By being able to pick out the mutat- 
 ing forms at an early age, a much larger number of the 
 diverging types could be obtained in proportion to the 
 total number of individuals. 
 
 De Vries gives the following table which represents 
 graphically the results from eight generations of a mutating 
 strain of (E. Lamarkiana : — 
 
 Mutating Strains of CE. Lamarkiana 
 
 Genera- 
 tions 
 
 GiGAS 
 
 Albida 
 
 Ob- 
 
 LONGA 
 
 RUBRI- 
 
 NERVI8 
 
 Lamark- 
 iana 
 
 Na- 
 nella 
 
 Lata 
 
 SCINTIL- 
 LAN8 
 
 I 
 II 
 
 
 
 
 
 15000 
 
 5 
 
 5 
 
 
 III 
 
 
 
 
 1 
 
 10000 
 
 3 
 
 3 
 
 
 IV 
 
 1 
 
 15 
 
 176 
 
 8 
 
 14000 
 
 60 
 
 73 
 
 1 
 
 V 
 
 
 25 
 
 136 
 
 20 
 
 8000 
 
 49 
 
 112 
 
 6 
 
 VI 
 
 
 11 
 
 29 
 
 3 
 
 1800 
 
 9 
 
 5 
 
 1 
 
 VII 
 
 
 
 9 
 
 
 3000 
 
 11 
 
 
 
 VIII 
 
 
 5 
 
 1 
 
 
 1700 
 
 21 
 
 1 
 
 
 De Vries^ laws of mutability of the evening-primroses. — 
 de Vries deduced certain laws from the mutations in these 
 (Enotheras. ''Obviously," he says, "they apply not only 
 to our evening-primroses, but may be expected to be of 
 general validity." 
 
 These laws are as follows : — 
 
 1. New elementary species appear suddenly, without 
 intermediate steps. 
 
Mutations 73 
 
 The ordinary conception had been that new types of 
 plants had been produced by the slow and gradual piling 
 up of small fluctuating variations. The experience with 
 the primroses shows that new types are formed in much 
 less time than it would take by the accumulation of small 
 variations. It is remarkable that so many different new 
 types of forms should have "been produced from the same 
 parent and with no intermediates appearing. When 
 (E. lata, which is a pistillate form, was crossed with 
 (E. Lamarkiana, the progeny of the second generation 
 segregated in mendelian proportion to the pure types of 
 the parents, with no intermediates. This same absence 
 of intermediacy is found when the progeny of the in- 
 constant forms return each year to the parent species, 
 Lamarkiana. 
 
 2. New forms spring laterally from the main stem. 
 
 This conception of the origin of new forms differs 
 markedly from the Darwinian idea which assumes that 
 species are slowly converted into others in the same 
 direction and in the same degree. 
 
 In such plants as draba or helianthemum, from which 
 mutations have been known to arise, no center or "main 
 stem" of mutation would have been known if it had not 
 been seen to occur in pedigree-cultures. For instance, 
 if gigas, ruhrinervis, and Lamarkiana had been found 
 growing side by side in equal numbers in the wild state, 
 it would have been impossible to tell which type had 
 been the center of fluctuation. Many years of crossing, 
 together with some vicinism which would probably have 
 followed, would have been necessary to determine this. 
 De Vries says, ''According to the current belief the con- 
 
74 Plant-Breeding 
 
 version of a group of plants growing in any locality and 
 flowering simultaneously would be restricted to one type. 
 In my own experiments several new species arose from 
 the parental form at once, giving a wide range of new forms 
 at the same time and under same conditions." 
 
 3. New elementary species attain their full constancy 
 at once. 
 
 '^Constancy is not the result of selection or of improve- 
 ment. It is a quality of its own. It can neither be 
 constrained by selection, if it is absent from the beginning, 
 nor does it need any natural or artificial aid if it is present." 
 
 No atavism was exhibited by the primrose mutations 
 with the exceptions of CE. scintillans and (E. elUptica. 
 These latter types reproduce themselves only in part in 
 the offspring. De Vries says that the instability in these 
 types seems to be as permanent a quality as the stability 
 of the other forms. 
 
 4. Some of the new strains are evidently elementary 
 species, while others are to be considered as retrograde 
 varieties. 
 
 Such new forms as CE. gigas, ruhrinervis, ohlonga, and 
 alhida may be called new elementary species. They are 
 not differentiated from Lamarkiana by one or two main 
 features, but they differ from it in nearly all organs, and 
 hence may be considered new elementary species. The 
 differences exist, not only in the foliage where they are 
 most manifest, but in the stems, flowers, seeds, and in- 
 deed, in many instances, to the minutest cell structure. 
 
 CE. Icevifolia, CE. brevistylis, and CE. nanella, on the 
 other hand, may be considered as retrograde varieties. 
 They seem to differ from the parental form in but one 
 
Mutatidns 75 
 
 character ; loevifolia is characterized by the loss of the 
 crinkhng of the leaves ; hrevistylis, by the partial loss of 
 the pistil ; and nanella, by the loss of stature. 
 
 5. The new species are produced in a large number of 
 individuals. 
 
 It will be remembered that there were produced a 
 large number of similar mutants in the same year, and 
 also that the same mutations were produced in successive 
 generations. 
 
 There is obviously some cause for the production of 
 these mutations. Whatever the exciting cause may be, 
 the different mutants are not affected in the same way. 
 Ohlonga, nanella, and lata are frequently produced, while 
 gigas, rubrinervis, and scintillans are more rare. It has 
 been found through later studies by Gates, Davis, Shull, 
 and others that some of the types formerly thought by 
 de Vries and others to be mutations are hybrids. 
 
 It was found also that when the mutants were crossed 
 together, types were found in the progeny which were 
 the same as produced by (E". Lamarkiana itself. For 
 example, (E. rubrinervis was observed by de Vries 
 to arise in the hybrid progeny of (E. lata x nanella; 
 (E. lata X brevistylis; CE. nanella x brevistylis ; and (E. 
 scintillans X nanella. 
 
 In nature, repeated mutations are probably of far more 
 importance than isolated ones. The competition of 
 plants is so great that the chances of the survival of one 
 divergent individual are much less than as if these mutants 
 were repeatedly produced in considerable quantity. 
 
 6. Mutabihty is distinct from fluctuating variability. 
 The foregoing evidence points to the fact that new 
 
76 Plant-Breeding 
 
 forms are produced from quick sudden leaps. The new 
 type is formed regardless of fluctuating variability, but 
 the new form becomes a center of fluctuating variability 
 similar to that around the parental form. 
 
 7. The mutations take place in nearly all directions. 
 
 De Vries says, ''Some of my new types are stouter and 
 others weaker than their parents, as shown by gigas and 
 albida. Some have broader leaves and some narrower 
 (lata and ohlonga). Some have larger flowers (gigas) or 
 deeper yellow ones (rubrinervis) or smaller blossoms 
 (scintillans) or of a paler hue (albida). In some the 
 capsules are longer (rubrinervis) or thicker (gigas) or 
 more rounded (lata) or small (oblonga) or nearly destitute 
 of seeds (brevistylis) . The unevenness of the surface of 
 the leaves may increase as in lata or decrease as in Icevi- 
 folia. The tendency to become annual prevails in ru- 
 brinervis, but gigas tends to become biennial. Some are 
 rich in pollen, while scintillans is poor. Some have large 
 seeds, others small. Lata has become pistillate, while 
 brevistylis has nearly lost the faculty to produce seeds. 
 Some undescribed forms were quite sterile, and some I 
 observed which produced no flowers at all." 
 
 Examples of mutations. Shirley poppy. — Lock cites ^ 
 the Shirley poppy as a mutation from the wild field poppy 
 (Papaver Rhoeas) so common in England. It was first 
 noticed in 1880 by the Rev. W. Wilks, Vicar of Shirley, 
 near Croydon, England, in a patch of the wild forms 
 growing in a waste corner of his garden. There suddenly 
 appeared a solitary flower showing a very narrow border 
 
 ^ " Recent Progress in the Study of Variation, Heredity, and Evolu- 
 tion," p. 133. 
 
Mutations 77 
 
 of white. The seeds from this plant were saved and 
 sown the next year. From this progeny of two hundred 
 plants, four or five individuals appeared which showed 
 the same diverging characteristics. 
 
 ''From these, by further horticultural processes, the 
 strain of Shirley poppies originated." Lock remarks, 
 in passing, that if the original plant had been self-pol- 
 linated, a much larger proportion of the new type might 
 have been expected to appear in the next generation. 
 
 Cupid sweet pea. — Another example of a mutation is 
 found in the case of the Cupid sweet pea (Fig. 22) . Until 
 about fifteen years ago the only sweet peas known were 
 the tall, climbing sorts, which grew to a height of 
 three to six feet, depending on the richness of the soil. 
 At this time, there was found in the seed trial grounds of 
 Morse & Company of California, a small dwarf sweet 
 pea plant only about six/ or eight inches high. This was 
 growing in a row of the Emily Henderson variety, one of 
 the ordinary tall sorts from which it evidently sprang. 
 Seed of this dwarf plant was saved and grown and it was 
 found to reproduce plants of the same dwarf character. 
 The variety was designated ''The Cupid," under which 
 name it was introduced to the seed trade and distributed 
 over the world. The Cupid differed from other sweet 
 peas not only in height, but in its closely set leaves and 
 general habit of growth. Indeed, it is as distinct from 
 other sweet peas as are distinct species of plants in 
 nature. 
 
 It has been found that this dwarf Cupid sweet pea 
 mendelized with the tall ordinary sorts and appears as 
 recessive. 
 
78 
 
 Plant-Breeding 
 
 Fig, 
 
 22. _ Cupid sweet peas. (Photo by Beal.) 
 
Mutations 79 
 
 Frequency of occurrence of mutations. — In general, it 
 may be said that the occurrence of mutations is rare.^ 
 
 In order to obtain a clear understanding of this subject, 
 it may be divided into four sections : — 
 
 1. Spontaneous occurrence of new varieties in the wild 
 state. 
 
 2. Spontaneous occurrence of new species in the wild 
 state. 
 
 3. Spontaneous occurrence of new varieties under 
 cultivation. 
 
 4. Spontaneous occurrence of new species under 
 cultivation. 
 
 The term "variety" as here used carries the meaning 
 given by de Vries, — that of a group of plants differing 
 from others in one systematic character. 
 
 Spontaneous occurrence of new varieties in the wild 
 state? — New varieties of plants are seen to occur rather 
 rarely in the wild state. This may be due to two causes : 
 (1) A lack of critical examination of wild plants for such 
 spontaneous mutation ; and (2) if these mutations do 
 occur, they are likely to meet premature death because 
 of the severe competition to which all wild forms are 
 subjected. 
 
 As our wild plants are being studied more critically, 
 it is being found that they do produce a much larger 
 number of new varieties than was formerly supposed. 
 
 In the case of the peloric toad-flax, which has been 
 studied carefully by de Vries, the mutations are so numer- 
 
 1 De Vries, p. 191. 
 
 2 De Vries, "Species and Varieties, their Origin by Mutation," 
 chapter on the Origin of Wild Species and Varieties, p. 576. 
 
80 Plant-Breeding 
 
 ous that they seem to be quite regular. The peloric 
 type is known to have originated from the ordinary type 
 at different times and in different countries, under more 
 or less divergent conditions. 
 
 White varieties of many species of bluebells, gentians, 
 and nearly all of the berry-bearing species in the large 
 heather family are quite common. The same is true of 
 the white flowers of Brunella vulgaris, Ononis repens, and 
 Thymus vulgaris. 
 
 Sponta7ieous occurrence of new elementary species in the 
 wild state. — It will be remembered that new elementary 
 species of the (Enothera were found to occur in the wild 
 state before any attempt was made to study them under 
 cultivation. It is difficult to say how frequently these 
 mutations occurred in the wild because unquestionably 
 most of them were destroyed prematurely, from the com- 
 petition of other plants. 
 
 The occurrence of new elementary species in the wild 
 state seems to be much more rare than the occurrence of 
 new varieties. This is natural, for, of course, elementary 
 species present greater differences from the parental 
 forms than do varieties. 
 
 The spontaneous origin of the new elementary species, 
 Capsella Heegeri, in 1897, has never been observed to have 
 been repeated since that time.^ This new form of shep- 
 herd's purse originated in the market-place near Landau, 
 in Germany. 
 
 Spontaneous occurrence of new elementary species and 
 varieties under cultivation. — Whenever new forms occur 
 spontaneously under cultivation, it should first be deter- 
 
 1 De Vries, " Species and Varieties, their Origin by Mutation," p. 582. 
 
Mutations 
 
 81 
 
 mined whether they are the product of pure lines or not. 
 If they come from pure lines, in all probability they are 
 mutations ; if not, the new forms maybe a result of hybridi- 
 zation, which may have taken place immediately preced- 
 ing the appearance of the anomaly or at a considerable 
 time previous to its appearance. 
 
 New varieties and elementary species are seen to occur 
 more often under cultivation for three reasons : — 
 
 1. When new forms do occur, they are more Hkely to be 
 seen. 
 
 2. Because of the relative lack of competition and hence 
 a better opportunity for preservation. 
 
 3. The transfer of plants from the wild to the cultivated 
 state has a tendency to break the type and cause spon- 
 taneous new forms to ap- 
 pear. For this reason, 
 we may expect a more 
 frequent occurrence of 
 mutations under culti- 
 vation. 
 
 It is commonly ob- 
 served among gardeners 
 that so-called "sports" 
 are of very common oc- 
 currence. Some of these 
 are monstrosities which 
 are not inherited, but 
 many of them are mu- 
 tations and are inherited 
 true to type. The occurrence of double-flowered types 
 as mutations is common. 
 
 G 
 
 Fig. 23. — A, B, Linaria vulgaris; C, 
 D, peloric flowers. 
 
82 
 
 Plant-Breeding 
 
 Fig. 24. — Linaria vulgaris peloria. A riclily branched stem of a plant 
 of the second generation. Raised in 1898 from seed of the first 
 generation of 1897, and photographed in August, 1900. All flowers 
 are peloric. 
 
Mutations 
 
 83 
 
 Many mutations among cultivated plants are the result 
 of continued selection for a period of years. This selection 
 assists in breaking the type and thus permits the mutation 
 to occur, and after the mutation has appeared, constant 
 selection is not necessary to keep the new variety pure. 
 
 It has been stated that the peloric type of toad-flax 
 is of frequent occurrence in the wild state (Figs. 23 and 
 24). De Vries found its appearance even more common 
 under cultivation than when growing wild. He planted 
 the seed of two toad-flax plants, one of which contained 
 a single peloric flower. Eighteen hundred plants were 
 obtained, of which seventeen, or nearly one per cent, 
 were wholly peloric. 
 
 The snapdragon {Antirrhinum majus) is also known to 
 produce peloric flowers from time to time as mutations 
 (Fig. 25). Pelorics occur sometimes in Linaria dalmatica 
 and other species of Linaria; in fox-glove {Digitalis pur- 
 
 FiG. 25. — Antirrhinum majus: A, peloric flower from the middle of an 
 otherwise normal raceme ; B, normal flower of the same spike. 
 
84 Plant-Breeding 
 
 purea), and in gloxinia. Many other instances of peloric 
 flowers are on record, which indicates that pelorism as a 
 mutation is frequent. 
 
 Experimental study of the origin of mutations. — De Vries 
 has conducted a series of experiments for the purpose of 
 observing the origin of mutations, if any should occur. 
 One of the plants chosen for these studies was the peloric 
 toad-flax (Linaria vulgaris peloria). The most accurate 
 laboratory methods were applied. The plants were 
 carefully isolated in his garden. 
 
 The reason for this choice of the peloric toad-flax lay 
 in the fact that this form is known to have originated 
 from the ordinary type at different times and in different 
 countries under more or less divergent conditions. The 
 ordinary toad-flax bears exceedingly unsymmetrical 
 flowers. (See Fig. 23, A.) But symmetrical flowers are 
 not uncommon in such plants as the toad-flax and snap- 
 dragon, which have similar types of flowers. In these 
 experiments, de Vries sought to observe the birth of this 
 anomaly in his pedigree cultures. 
 
 The experiments were begun in 1886 with normal 
 plants ; a few peloric flowers were produced, however, 
 which is not an uncommon occurrence among plants of 
 this genus. Throughout the next few generations, 
 nothing more than the normal number of peloric flowers 
 were produced. 
 
 In the third generation, among the many thousands of 
 flowers there occurred one having five spurs. This was 
 inbred by hand and produced a considerable quantity of 
 seed. All other seed was discarded and this plant now 
 became the parent of all future plants. 
 
Mutations 85 
 
 The next (fourth) generation contained about twenty 
 plants having only one peloric flower among them. The 
 plant bearing this flower, and one other plant, were saved 
 and all others discarded. These two were bred together 
 and produced a considerable quantity of seed. 
 
 In the next year (1894) fifty plants were in flower. 
 Eleven of these were found to bear the normal number 
 of peloric flowers. In addition to these eleven, there was 
 found one plant which bore peloric flowers only. This 
 was a mutation. Its appearance had been observed. It 
 was found to breed true in future generations. 
 
 In regard to the production of this mutation, de Vries 
 says, '^Here we have the first experimental mutation of 
 a normal into a peloric race. The facts were clear and 
 simple : First, the ancestry was known for over a period 
 of four generations. This ancestry was quite constant 
 as to the peloric peculiarity remaining true to the wild 
 type as it occurs everywhere in any country and showing 
 in no respect any tendency to the production of a new 
 variety. 
 
 ''Second, the mutation took place at once. It was a 
 sudden leap from the normal plants with very rare peloric 
 flowers to a type exclusively peloric. The parents them- 
 selves had borne thousands of flowers during two sum- 
 mers, and these were inspected nearly every day in the 
 hope of finding some peloric and of saving their seed 
 separately. Only one such flower was seen. There was 
 no visible preparation for this sudden leap. 
 
 ''This leap, on the other hand, was full and complete. 
 No reminiscence of the former condition remained. Not 
 a single flower on the mutated plant reverted to the 
 
86 
 
 Plant-Breeding 
 
 previous type. The whole plant departed absolutely 
 from the old type of its progenitors." 
 
 What is true of the toad-flax is also true of the snap- 
 dragon and other unsymmetrical flowers — the production 
 of peloric flowers by mutation. 
 
 Fig. 26. — Chrysanthemum segetum plenum. One of the six inflorescences 
 which in 1899 first exhibited true "doubling." The figure represents 
 the parent plant of the " double " variety. 
 
 Experiments in the production of double flowers (Figs. 26- 
 29) . — De Vries performed a series of experiments with the 
 corn marigold {Chrysantheinam segetum) with the object 
 of the production of double flowers. This plant has never 
 been known to produce double flowers. The cultivated 
 variety {grandiflorum) was found to be more stable and 
 was used as a basis of the experiments. This cultivated 
 
Mutations 
 
 87 
 
 form has on the average twenty-one petals on each flower. 
 In the population of the next generation there appeared 
 one plant having twenty-one petals, but on one of its 
 secondary heads twenty-two petals were found. This 
 had never been observed before. This plant was the 
 
 Fig. 27. — Chrysanthemum inodorum plenissimum : A, inflorescence with 
 central disk of tube florets (fertile) ; B, with scattered tongue florets 
 in the disk {ha,\i fertile) ; C, highest degree of " doubling " (sterile). 
 
 beginning of what developed later into the desired muta- 
 tion. 
 
 This plant produced the next year (1897) plants having 
 thirty-four rays to the head. Next year (1898) this was 
 increased to forty-eight; next year (1899) to sixty-six. 
 
88 
 
 Plant-Breeding 
 
 During this time the means of the different generations 
 were gradually increasing. So far there was observed a 
 
 12 15 18 ?l 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99l02 
 
 J^JL 
 
 1897. 
 
 1898. 
 
 /-\ 
 
 A A ^ 
 
 1899. 
 
 1900. 
 
 M 
 
 12 15 18 21 24 27 30 33 36 39 42 45 18 51 54 5' 60 63 66 69 72 75 78 61 84 87 90 93 96 99 102 
 
 Fig, 28. — Ancestral generations of Chrysanthemum segetum plenum. 
 Curves of the number of rays in the terminal inflorescence in the 
 several individuals of the generations of 1897—1900. 
 
 rapid increase in number of petals, but no indication of 
 doubling. 
 
 But this character soon appeared ; three secondary 
 heads on one plant in the fall of 1899 showed a few ray- 
 
Mutations 
 
 89 
 
 florets scattered over the disk. An indication of the 
 mutation was now seen. 
 
 The next year, 1900, the highest number of rays arose 
 to one hundred, and reached two hundred in 1901. These 
 
 12 13 
 
 A 
 
 15 16 17 18 19 20 21 22 23 24 25 26 27 28 
 
 B 
 
 Fig. 29. — A, Chrysanthemum segetum; B, Chrysanthemum segetum 
 grandiflorum (after purification). Curves of the races after isolation : 
 A, curve of the 13-rayed race in 1894 ; B, curve of the 21 -rayed race 
 in 1897. The ordinates give the number of individuals with like num- 
 ber of ray-florets in the primary inflorescences of the individual plants. 
 The number of ray-florets themselves is given below the abscissa. 
 
 heads were completely double and the mutation had ap- 
 peared, not quite as suddenly, perhaps, as with toad- 
 flax, but nevertheless as surely. The new race was per- 
 manent and constant. 
 
 Complete doubleness caused sterility, so that the race 
 had to be perpetuated from slightly inferior stock. 
 
 Here, again, was the origin of a new mutation produced 
 in control cultures by careful laboratory methods. 
 
90 Plant-Breeding 
 
 What do new characters come from f — If mutations are 
 the result of the appearance of new characters or the loss 
 of old ones, where do these new characters come from 
 and what causes the loss of existing ones ? The answer 
 to this question would give us the keynote to the whole 
 situation. If breeders possessed definite knowledge of 
 the cause of mutations, they would then have within 
 their control a kind of variation which could be made 
 of tremendous economic importance. The causes are 
 evidently from an internal origin. In all probability, 
 many so-called mutations are due to hybrid origin and 
 in the strictest sense are not mutations at all, even though 
 they may be bred true. Much experimental evidence 
 is necessary to determine with certainty their cause and 
 control. 
 
 Can mutations be produced artificially f — Must breeders 
 passively wait for mutations to arise, or may they be 
 produced artificially ? Many experiments are now being 
 conducted to test this. So far, experiments do not seem 
 to have led to any definite conclusion. 
 
 Economic significance of mutations. — Agricultural and 
 horticultural literature is full of accounts of the sudden 
 origin, or at least the sudden finding, of exceptionally good 
 plants which, when propagated, became the progenitors 
 of new and valued races. So great is their number that 
 not even an attempt to catalogue them can be made here. 
 
 The pages of ^'Evolution of our Native Fruits" (Bailey) 
 are filled with examples of mutation. The experience of 
 plant-breeders and nurserymen show the origin of many 
 varieties in this way. 
 
 Many observing growers of cereals and other plants 
 
Mutations 91 
 
 have originated varieties by finding occasionally unusually 
 good plants and propagating from them. These excep- 
 tional plants seem to bear no relationship to the others 
 among which they are growing. Hybrid origin may 
 account for certain of them and mutations for the others. 
 Many of our well-known races of wheat have originated 
 in this way. The Fultz wheat, which is a very popular 
 and excellent race grown extensively in the Eastern States, 
 was found in 1862 in a field of Lancaster Red by Mr. 
 Abraham Fultz of Pennsylvania. Some beautiful heads 
 of smoother wheat attracted his attention and they were 
 saved and the seeds planted by themselves. These pro- 
 duced the wheat later named the Fultz. The Tappa- 
 hannock wheat, which, in 1872, was considered to be a 
 valuable race, was found in 1854 by a Mr. Boughton, of 
 Essex County, Virginia. The account of its discovery 
 as given in the Report of the Department of Agriculture 
 for 1872 is as follows: ''He noticed in his field a bunch 
 of wheat of such growth as to attract his attention. . . . 
 At harvest he found it to be a white wheat, at least two 
 weeks earlier than the surrounding red wheat." Gold 
 Coin Wheat, a seedling sport, differing from the hybrid 
 Mediterranean in being bald and white, was found by 
 Ira W. Green, of New York, in a field of that race and 
 improved by selection. In the next five years the type 
 was fixed and increased in yield about ten per cent. The 
 American races, Wheatland Red, Pride Butte, and the 
 well-known English races, Hopetown and Cavalier, were 
 other accidental seedling races. 
 
CHAPTER VI 
 
 THE PHILOSOPHY OF THE CROSSING OF 
 PLANTS, CONSIDERED IN REFERENCE TO 
 THEIR IMPROVEMENT UNDER CULTIVA- 
 TION 
 
 It is now understood that the specific forms or groups 
 of plants have been determined largely by the survival 
 of the fittest in a long and severe struggle for existence. 
 The proof that this struggle everywhere exists becomes 
 evident on a moment's reflection. We know that all 
 organisms are eminently variable. In fact, no two plants 
 or animals in the world are exactly alike. We also know 
 that a very few of the whole number of seeds which are 
 produced in any area ever grow into plants. If all the 
 seeds produced by the elms upon Boston Common in 
 any fruitful year were to grow into trees, the city would 
 become a forest as a result. If all the seeds of the rarest 
 orchids in our woods were to grow, in a few generations 
 of plants even our farms would be overrun. If all the 
 rabbits which are born were to reach old age, and all 
 their offspring were to do the same, in less than ten years 
 every vestige of herbage would be swept from the country, 
 and our farms would become barren. 
 
 The struggle for life. — There is, then, a wonderful 
 
 92 
 
Hybridization 93 
 
 latent potency in these species ; but the same may be said 
 of every species of plant and animal, even of man himself. 
 If one species of plant would overrun and usurp the land, 
 if it increased to the fullest extent of its possibilities, 
 what would be the result if each of the two thousand and 
 sixty-one plants known to inhabit Middlesex County 
 were to do the same ? And then fancy the result if each 
 of the animals from rabbits and mice to frogs and leeches 
 were to increase without check! The plagues of Egypt 
 would be insignificant in the comparison ! 
 
 Survival of the most fit. — The fact is, the world is not 
 big enough to hold the possible first offspring of the 
 plants and animals at this moment living upon it. 
 Struggle for existence, then, is inevitable, and it must 
 be severe. It follows as a necessity that those seeds 
 grow or those plants live which are the best fitted to 
 grow and live, or which are fortunate enough to find a 
 congenial foothold. It would never appear, at first 
 thought, that much depends on the accident of falling 
 into a congenial place, or one unoccupied by other plants 
 or animals; but, inasmuch as scores of plants are con- 
 tending for every unoccupied place, it follows that every- 
 where only the fittest can germinate or grow. In the 
 greater number of cases, plants grow in a certain place 
 because they are better fitted to grow there, to hold 
 their own, than any other plants are; and the instances 
 are rare in which a plant is so fortunate as to find an un- 
 occupied place. We are likely to think that plants chance 
 to grow where we find them, but the chance is determined 
 by law, and, therefore, is not chance. 
 
 Flexibility as an aid to survival. — Much of the capa- 
 
94 Plant-Breeding 
 
 bility of a plant to persist under all this struggle depends, 
 therefore, upon how much it varies ; for the more it varies, 
 the more likely it is to find places of least struggle. It 
 grows under various conditions, in the sun and shade, 
 in sand and clay, by the sea-shore or upon the hills, in 
 the humidity of the forest, or the aridity of the plain. 
 In some directions it very likely finds less struggle than 
 in others, and in these directions it may expand itself, 
 multiply, and gradually die out in other directions ; so it 
 happens that it tends to take on new forms or to undergo 
 an evolution. In the meantime, all the intermediate 
 forms, which are at best only indifferently adapted to 
 their conditions, tend to disappear. In other words, 
 gaps appear that we call '' missing links." The weak 
 links break and fall away, and what was once a chain 
 becomes a series of rings. So the '^missing links" are 
 amongst the best proofs of evolution. 
 
 Causes of variability. — The question now arises as to 
 the cause of these numerous variations in animals and 
 plants. Why are no two individuals in nature exactly 
 alike? The question is exceedingly difficult to answer. 
 It was once said that plants vary because it is their nature 
 to vary ; that variation is a necessary function, as much 
 as growth or fructification. This really removes the ques- 
 tion beyond the reach of philosophy ; and direct observa- 
 tion leads us to think that some variation, at least, is 
 due to external circumstances. We are now looking for 
 the cause of variation as a part of the scheme of evolu- 
 tion ; and we are wondering whether the varied surround- 
 ings, or, as Darwin puts it, '^ changed conditions of life," may 
 not actually induce variability. This conclusion would 
 
Hybridization 95 
 
 seem to follow from the fact of the severe and universal 
 struggle in nature whereby plants are constantly forced 
 into new and strange conditions. But there is un- 
 doubtedly much variation which has sprung from more 
 remote causes, one of which it is our purpose to discuss 
 here. 
 
 In the lowest plants and animals — which are merely 
 single cells — the species multiplies by means of simple 
 division or budding. One individual, of itself, becomes 
 two, and the two are therefore recasts of the one. But, 
 as organisms multiplied and conditions became more 
 complex, that is, as struggle increased, there came a 
 differentiation in the parts of the individual, so that one 
 cell or one cluster of cells performed one labor and other 
 cells performed other labor ; and this tendency resulted 
 in the development of organs. Simple division, there- 
 fore, might no longer reproduce the whole complex in- 
 dividual ; and, as all organs are necessary to the existence 
 of life, the organism may die if it is divided. 
 
 Origin and function of sex. — Along with this specializa- 
 tion came the differentiation into sex ; and sex clearly 
 has two offices : to hand over the complex organization 
 of the parent to the offspring and also to unite the essen- 
 tial characters or tendencies of two beings into one. The 
 second office is manifestly the greater, for, as it unites 
 two organisms into one, it insures that the offspring is 
 somewhat unlike either parent, and is therefore better 
 fitted to seize upon any place or condition new to its 
 kind. And as the generations increase, the tendency to 
 variation in the offspring may be constantly greater be- 
 cause of the impressions of the greater number of ancestors 
 
96 
 
 Plant-Breeding 
 
 transmitted to it. We have said that this office of sex to 
 induce variation is more important than the mere fact of 
 reproduction of a complex organization ; for it must be 
 borne in mind that the complexity of organization is 
 itself a variation and adaptation made necessary by the 
 increasing struggle for existence. 
 
 Fig. 30. — Extreme variability in the shape of the leaves of hybrid 
 poppies. Second generation from a cross between the Bride variety 
 of the Opium poppy and the Oriental poppy. 
 
 If, therefore, the philosophy of sex is to promote variation 
 by the union of different individuals, it must follow that 
 the greatest variation must come from parents consider- 
 ably unlike each other in their minor characters (Fig. 30) . 
 Thus it comes that in-breeding tends to weaken a type 
 and cross-breeding tends to strengthen it. At this point 
 we meet that particular subject that we wish to discuss. 
 
Hybridization 97 
 
 This preliminary discussion has been introduced because 
 we can understand crossing only as we make it a part of 
 the general philosophy of nature. There are the vaguest 
 notions concerning the possibilities of crossing, some of 
 which may be corrected by presenting the subject in its 
 relations to the general aspects of the vegetable world. 
 ^^ Effects of crossing on the species. — We are now pre- 
 pared to understand that crossing is good for the species, 
 because it constantly revitalizes offspring with the strong- 
 est traits of the parents, and ever presents new com- 
 binations that enable the individuals to stand a better 
 chance of securing a place in the polity of nature. The 
 further discussions of the subject are such as have to do 
 with the extent to which crossing is possible and advisable, 
 and the general results of the operation. 
 
 The limits of crossing. — If crossing is good for the 
 species, which philosophy and direct experiment abun- 
 dantly show, it is necessary at once to find out to what 
 extent it can be carried. Does the good increase in pro- 
 portion as the cross becomes more violent or as the parents 
 are more and more unlike ? Or do we soon find a limit 
 beyond which it is not profitable or even possible to go ? 
 If great variability is good for the species in the struggle 
 for existence, and if crossing induces variability because 
 of the union of unlike individuals, it would seem to follow 
 that the more unlike the parents, the greater will be 
 the variation in offspring and the more the type will 
 prosper; and, carrying this thought to its logical con- 
 clusion, we shall expect to find that the most closely 
 related plants would constantly tend to refuse to cross, 
 because the offspring of them would be little variable 
 
98 Plant-Breeding 
 
 and, therefore, little adapted to struggle for existence; 
 while the most widely separated plants would constantly 
 tend to cross more and more, because their offspring 
 would present the greatest possible degree of differences. 
 
 Swamping effects of inter-crossing. — Now, essentially 
 this reason has been advanced to combat the evolution 
 of plants and animals by means of natural selection ; and 
 this proposition that inter-mixing must constantly tend 
 to obliterate all differences between plants and to prevent 
 the establishment of well-marked types, has been called 
 the '^ swamping effects of inter-crossing." It is exceed- 
 ingly important that we consider this question, for it 
 really lies at the foundation of the improvement of cul- 
 tivated plants by means of crossing, as well as the persist- 
 ence and evolution of varieties and species under wholly 
 natural conditions. 
 
 What determines the limits of crossing f — We find, 
 however, that distinct species, as a rule, refuse to cross ; 
 and the first question which naturally arises is, what is 
 the immediate cause of the refusal of plants to cross ? 
 How does this refusal express itself ? It comes about 
 in many ways. The commonest cause is the positive 
 refusal of a plant to allow its ovule to be impregnated 
 by the pollen of another plant. The pollen will not 
 ''take." For instance, if we apply the pollen of a Hub- 
 bard squash to the flower of a common field pumpkin, 
 there will be no result, — the fruit will not form. The 
 same is true of the pear and the apple, the oat and the 
 wheat, and most very unlike species. Or the refusal may 
 come in the sterility of the cross or hybrid : the pollen 
 may ''take" and seeds may be formed and the seeds 
 
 •/ i 
 
Hybridization 99 
 
 may grow, but the plants they produce may be wholly 
 barren, sometimes even refusing to produce flowers 
 as well as seeds, as in the instance of some hybrids be- 
 tween the Wild Goose plum and the peach. Sometimes 
 the refusal to cross is due to some difference in the time 
 of blooming or some incompatibility in the structure of 
 the flowers. But it is enough for our purpose to know 
 that there are certain characters in widely dissimilar 
 plants which prevent inter-crossing, and that these 
 characters are just as closely and just as much influenced 
 by change of environment and natural selection as are 
 size, color, reproductiveness, and other characters. 
 
 The limits of crossing tend to preserve the identity of 
 species. — Here, then, is the sufficient answer to the prop- 
 osition that inter-crossing must swamp all natural 
 selection, and also the explanation of the varying and 
 often restricted limits within which crossing is possible. 
 That is, the checks to crossing have been deyeloped 
 through the principle of universal variability and natural 
 selection, as has been shown by Darwin and Wallace. 
 Plants vary in their reproductive organs and powers, 
 as they do in other directions ; and when such a varia- 
 tion is useful it is perpetuated, and when hurtful it is 
 lost. Suppose that a certain weU-marked individual of 
 a species should find an unusually good place in nature, 
 and it should multiply rapidly. Crosses would be made 
 between its own offspring and perhaps between those 
 offspring and itself in succeeding years; and it is fair 
 to suppose that some of the crosses would be particularly 
 well adapted to the conditions in which the parents 
 grew, and these would constantly tend to perpetuate 
 
100 Plant-Breeding 
 
 themselves, while less adaptive forms would tend similarly 
 to disappear. Now the same thing would take place 
 if this individual or its adaptive offspring were to cross 
 with the main stock of the parent species ; for all the 
 offspring of such a cross which is intermediate in character 
 and therefore less adapted to the new conditions would 
 tend to disappear, and the two types would, as a result, 
 become more and more fixed and the tendency to cross 
 would constantly decrease. 
 
 The refusal to cross, the result of natural selection. — 
 The refusal to cross, therefore, becomes a positive character 
 of separation, and the '^missing links" that result from 
 crossing are no more or no less inexplicable than the 
 ''missing links" due to simple selection; or, to state the 
 case more accurately, natural selection weeds out the tend- 
 ency to promiscuous crossing, when it is hurtful, in the 
 same way that it weeds out any other injurious tendency. 
 It makes no difference in what way this tendency ex- 
 presses itself, whether in some constitutional refusal to 
 cross, — if such exists, — or infertility of offspring, or 
 in different times of blooming: all equally come under 
 the power of natural selection. We are likely to look upon 
 infertility as the absence of a character, a sort of negative 
 feature which is somehow not the legitimate field of 
 natural selection ; but such is not the case. We are 
 perhaps led the more to this feeling because the word 
 infertiUty is itself negative, and because we associate 
 full productiveness with the positive attributes of plants. 
 But loss of productiveness is surely no more a subject 
 of wonder than loss of color or size, if there is some corre- 
 sponding gain to be accomplished. In fact, we see, in 
 
Hybridization 101 
 
 numerous plants which propagate usually by means of 
 runners and suckers, a very low degree of productiveness, 
 that is, infertility. 
 
 For the production of useful hybrids, do not have the 
 parents too diverse. — Now, if this reasoning is sound, 
 it leads us to conclusions quite the reverse of those held 
 by the advocates of the swamping effects of inter-crossing, 
 and these conclusions are of the most vital importance 
 to every man who tills the soil. The logical result is 
 simply this : the best results of crossing are obtained, 
 as a rule, when the cross is made between different in- 
 dividuals of the same variety, or at farthest, between 
 different individuals of the same species. In other words, 
 crosses between species are very rarely useful in nature, 
 and it follows that the more unlike the species, the less 
 useful will be the hybrids. This is counter to the notions 
 of most horticulturists, and, if true, must entirely over- 
 throw our common thinking upon this subject. But we 
 shall be able to show that observation and experiment 
 lead to the same conclusion to which our philosophy 
 has brought us. 
 
 Function of the cross. — At this point, we must ask 
 ourselves what we mean by ''best results." This phrase 
 may be taken to refer to those plants that are best fitted to 
 survive in the struggle for existence, those that are most 
 vigorous or most productive or most hardy, or that 
 possess any well-marked character or characters which 
 distinguish them in virility from their fellows. We 
 commonly associate the term more particularly with 
 marked vigor and productiveness ; these are the char- 
 acters most useful in nature and also in cultivation, the 
 
102 Plant-Breeding 
 
 ones which we oftenest desire to obtain. Another type 
 of variation that we constantly covet is something 
 that we call a new character, which will lead to the 
 production of a new cultural variety, and we are always 
 looking to this as the legitimate result of crossing. We 
 have forgotten — if, indeed, we ever knew — that the 
 commoner, all-pervading, more important function of the 
 cross is to introduce some new feature or power into the 
 offspring, to improve or to perpetuate an existing variet}^, 
 rather than to create a new one. Or, if a new one is 
 created, it comes from the gradual passing of one into 
 another, an inferior variety into a good one, a good one 
 into a superlative one. So nature usually employs crossing 
 in a process of slow or gradual improvement, one step 
 leading to another, and not in any bold or sudden creation 
 of new forms. And there is evidence to show that some- 
 thing akin to this must be done to secure the best and 
 most permanent results under cultivation. 
 
 Rarity of natural hybrids. — Think of the great rarity 
 of hybrids or pronounced crosses in nature. No doubt 
 all the authentic cases on record could be entered into 
 one or two volumes, but a list of all the individual plants 
 of the world could not be compressed into ten thousand 
 volumes. There are a few genera, in which the species 
 are not well defined, or in which some character of in- 
 florescence favors promiscuous crossing, in which hybrids 
 are conspicuous ; but even here the number of individual 
 hybrids is very small in comparison to the whole number 
 of individuals. That is, the hybrids are rare, while the 
 parents may be common. This is well illustrated even 
 in the willows and the oaks, in which, perhaps, hybrids 
 
Hybridization 103 
 
 are better known than in any other American plants. 
 The great genus Carex, or sedge, which occurs in great 
 numbers and many species in almost every locality in 
 the United States, and in which the species are particularly 
 adapted to inter-crossing by the character of their in- 
 florescence, furnishes but few undoubted hybrids. Among 
 one hundred and eighty-five species and prominent 
 varieties inhabiting the Northeastern States, there are 
 only about a score of hybrids recorded, and all of them are 
 rare or local, some of them having been collected but 
 once. Species of Carex of remarkable similarity may 
 grow side by side for years, even inter-tangled in the 
 same clump, and yet produce no hybrid. These examples 
 show that nature avoids J iybr-idization, a conclusion at 
 which we have already arrived from philosophical con- 
 siderations. And we have reason to infer the same 
 conclusion from the fact that flowers of different species 
 are so constructed as not to invite inter-crossing. But, 
 on the other hand, the fact that all higher plants habitually 
 propagate by means of seeds, which is far the most ex- 
 pensive to the plant of all methods of propagation, while 
 at the same time most flowers are so constructed as to 
 prevent self-fertilization, shows that some corresponding 
 good must come from crossing within the limits of the 
 species or variety ; and there are also philosophical reasons, 
 as we have seen, that warrant this conclusion. 
 
 Change of seed and crossing. — Bearing in mind these 
 good influences of crossing, let us recall another series 
 of facts following the simple change of seed. Almost 
 every farmer and gardener at the present day feels that 
 an occasional change of seed results in better crops, and 
 
104 Plant-Breeding 
 
 there are definite records to show that such is often the 
 case. In fact, much of the rapid improvement in fruits 
 and vegetables in recent years is probably due to the 
 practice of buying plants and seeds so largely of dealers, 
 by means of which the stock is often changed. Even 
 a slight change, as between farms or neighboring villages, 
 sometimes produces marked results, such as more vigorous 
 plants and often more fruitful ones. We must not sup- 
 pose, however, that because a small change gives a good 
 result, a violent or very pronounced change gives a better 
 one. There are many facts on record to show that 
 great changes often profoundly influence plants, and when 
 such influence results in lessened vigor or lessened pro- 
 ductiveness, we call it an injurious one. Now, this in- 
 jurious influence may result even when all the condi- 
 tions in the new place are favorable to the health and 
 development of the plant ; it is an influence wholly in- 
 dependent, as far as we can see, of any condition which 
 interferes injuriously with the simple processes of growth. 
 Seeds of a native physalis, or husk-tomato, were sent from 
 Paraguay in 1889 by Dr. Thomas Morong, then traveling 
 in that country. It was grown from cuttings in the house 
 and out of doors, and for two generations it failed to set 
 fruit, even though the flowers were hand pollinated ; yet the 
 plants were healthy and grew vigorously. The third cut- 
 ting-generation grown out of doors set freely. This is an 
 instance of the fact that very great changes of conditions 
 may injuriously affect the plant, and an equally good 
 illustration of the power to overcome these conditions. 
 Now there is great similarity between the effects of slight 
 and violent changes of conditions and small and violent 
 
Hybridization 105 
 
 degrees of crossing, as both Darwin and Wallace have 
 pointed out, and it is pertinent to this discussion to 
 endeavor to discover why this similarity exists. It is 
 well proved that crossing is good for the resulting off- 
 spring, because the difference between the parents carries 
 over new combinations of characters, or at least new 
 powers into the crosses. It is a process of revitaliza- 
 tion, and the more different the stocks in desirable 
 characters within the limits of the variety, the greater 
 may be the revitalization ; and frequently the good is of a 
 more positive kind, resulting in pronounced characters 
 which may serve as the basis for new varieties. In the 
 cross, therefore, a new combination of characters or a 
 new power fit it to live better than its parents in the 
 conditions under which they lived. 
 
 Results from change of stock. — In the case of change of 
 stock we find the reverse, which, however, amounts to the 
 same thing, that the same characters or powers fit the plant 
 to live better in conditions new to it than plants which 
 have long lived in those conditions. In either case, the 
 good comes from the fitting together of new characters or 
 powers and new environments. Plants which live during 
 many generations in one place become accustomed to the 
 place, thoroughly fitted into its conditions, and are in 
 what Spencer calls a state of equilibrium. When either 
 plant or conditions change, new adjustments must take 
 place; and the plant may find an opportunity to take 
 advantage, to expand in some direction in which it has 
 before been held back ; for plants always possess greater 
 power than they are able to express. ^' These rhythmical 
 actions or functions (of the organism)," writes Spencer, 
 
106 Plant-Breeding 
 
 "and the various compound rhythms resulting from their 
 combinations, are in such adjustment as to balance the 
 actions to which the organism is subject. There is a 
 constant or periodic genesis of forces which, in their kind, 
 amounts, and directions, suffice to antagonize the forces 
 which the organism has constantly or periodical!}^ to bear. 
 If, then, there exists this state of moving equilibrium 
 among a definite set of internal actions, exposed to a 
 definite set of external actions, what must result if any of 
 the external actions are changed ? Of course there is no 
 longer an equilibrium. Some force which the organism 
 habitualh^ generates is too great or too small to balance 
 some incident force ; and there arises a residuary force 
 exerted by the environment on the organism, or by the 
 organism on the environment. This residuary' force, this 
 unbalanced force, of necessity expends itself in producing 
 some change of state in the organism." 
 
 The good results, therefore, are processes of adaptation, 
 and when adaptation is perfect or complete, the plant may 
 have gained no permanent advantage over its former 
 conditions, and new crossing or another change may be 
 necessary ; yet there is often a permanent gain, as when a 
 plant becomes visiblj^ modified by change to another cli- 
 mate. Xow this adaptive change may express itself in 
 two ways : either by some direct influence on the stature, 
 vigor, or other general characters ; or directly on the 
 reproductive powers, tiy which some new influence is 
 carried to the offspring. If the direct influences become 
 hereditary, as observations seem to show may sometimes 
 occur, the two directions of modification may amount, 
 ultimately, to the same thing. 
 
Hybridization 107 
 
 For the purpose of this discussion it is enough to know 
 that crossing within the variety and change of stock within 
 ordinary bounds are beneficial, that the results in the two 
 cases seem to flow from essentially the same causes, and 
 that crossing and change of stock combined may give 
 better results than either one alone ; and this benefit is 
 expressed more in increased vigor and yield than in novel 
 and striking variations. These processes are much more 
 important than any mere groping after new variations, 
 as we have already said, not only because they are surer, 
 but because they are universal and necessary means of 
 maintaining and improving both wild and cultivated 
 plants. Even after one succeeds in securing and fixing 
 the new variety, one must employ these means to a greater 
 or less extent to maintain fertility and vigor, and to keep 
 the variety true to its type. In the case of some garden 
 crops, in which many seeds are produced in each fruit and 
 in which the operation of pollination is easy, actual hand- 
 crossing from new stock now and then may be found to be 
 profitable. But in most cases the operation can be left 
 to nature, if the new stock is planted among the old. 
 Upon this point Darwin expressed himself as follows : 
 ''It is a common practice with horticulturists to obtain 
 seeds from another place having a very different soil, so as 
 to avoid raising plants for a long succession of generations 
 under the same conditions ; but with all the species which 
 freely inter-crossed by the aid of the insects or the ^vind, it 
 would be an incomparably better plan to obtain seeds of 
 the required variety, which had been raised for some 
 generations under as different conditions as possible, and 
 sow them in alternate rows with seeds matured in the old 
 
108 Plant-Breeding 
 
 garden. The two stocks would then intercross, with a 
 thorough blending of their whole organizations, and with 
 no loss of purity to the variety, and this would yield far 
 more favorable results than a mere change of seed." 
 
 CROSSING FROM STANDPOINT OF PLANT IMPROVEMENT 
 
 The making of crosses for man's use may have a very dif- 
 ferent meaning from the effect of crossing upon the plant 
 itself. Man removes from a plant by cultivation most of 
 the factors which make for struggle and determines whether 
 the plant shall survive or not. In making crosses or 
 hybrids with a practical object in view, the welfare of the 
 species is taken into account only sufficiently to insure 
 vigorous plants particularly adapted to man's purposes. 
 
 Understanding of terms. — At this point it is worth 
 while to consider a few definitions. 
 
 The Latin word hybrida, or ibrida, has been assumed to be 
 derived from the Greek vfipL<;, an insult or outrage, and a 
 hybrid has been supposed to be an outrage on nature, an un- 
 natural product. The term hybrid is by many applied only 
 to the offspring obtained by crossing two plants or animals 
 sufficiently different to be considered by naturalists as 
 distinct species, while the term cross is used to designate 
 the offspring of two races or varieties of one species. A 
 closer scrutiny of the facts, however, makes the term 
 hybridism less isolated and more vague. The words 
 species and genera, and still more sub-species and varieties, 
 do not correspond with clearly marked botanical categories, 
 and no exact line can be drawn between the various kinds 
 of crossings from those between individuals apparently 
 identical to those belonging to genera universally recog- 
 
Hybridization 109 
 
 nized as distinct. It was formerly supposed that all 
 hybrids were more or less sterile, in contradistinction to 
 crosses, which were thought to be very fertile. It has 
 been found, however, that many hybrids, in the narrow 
 sense, are very fertile, and that some crosses are nearly 
 sterile. Since it is impossible to indicate by any two words, 
 such as hybrid or cross, the various degrees of difference 
 of the forms crossed, the word hybrid is now generally 
 used as a generic term to include all organisms arising 
 from a cross of two forms noticeably different, whether the 
 difference be great or slight. Adjectives are sometimes 
 used to indicate the grade of the forms crossed, such as 
 racial hybrids, bigeneric hybrids, and so forth. 
 
 The offspring produced by the union of two plants 
 identical in kind, but separated in descent by at least 
 several seed generations, is often called a cross, cross- 
 fertilized, or cross-bred plant, but it is not a hybrid, as 
 the essential character of a hybrid is that it results from 
 the union of plants differing more or less in kind, or, in 
 other words, is the result of a union between different races, 
 varieties, species, or genera. On the other hand, flowers 
 impregnated with their own pollen, with the pollen of 
 another flower on the same plant, or even pollen from 
 another plant derived from the same original stock by 
 cuttings or grafts, are said to be self-fertilized, and the 
 offspring resulting from such unions are often termed self- 
 fertilized plants. Strictly speaking, however, self- or close- 
 fertilization is impregnation with pollen of the same flower. 
 With such plants as tobacco and wheat, self-fertilization 
 is the rule. In many cases, however, the flowers are so 
 constructed that cross-fertilization is favored, as in corn 
 
110 Plant-Breeding 
 
 and rye, and in some cases cross-fertilization is necessary, 
 all possibility of self-pollinization being precluded, as in 
 the case of hemp and other plants having the male and 
 female flowers on separate individuals. 
 
 History of plant hybrids. — Inasmuch as the sexuality of 
 plants was unknown, or at least very imperfectly under- 
 stood, prior to the last two centuries, while a knowledge 
 of the sex distinction of animals dates from the dawn of 
 human history, it is not surprising that while the hybridiz- 
 ing of animals was well understood by the ancients, they 
 did not know that crossing was possible with plants. 
 Experimental proof of the sexuality of plants was pub- 
 lished for the first time by Camerarius, December 28, 
 1691, and only after this discovery was the function 
 of pollen and its necessity for seed formation under- 
 stood. 
 
 The earliest recorded observation of a plant hybrid is by 
 J. G. Gmelin toward the end of the seventeenth century ; 
 the next is that of Thomas Fairchild, who in the second 
 decade of the eighteenth century produced the cross 
 which is still grown in literature under the name of 
 ''Fairchild's Sweet William." It was a cross between the 
 carnation and sweet William. 
 
 Linnaeus made many experiments in the cross-fertiliza- 
 tion of plants and produced several hybrids, but Joseph 
 Gottheb Kolreuter (1733-1806) laid the real foundation 
 of our scientific knowledge of the subject. Later on, 
 Thomas Andrew Knight, a celebrated English horticul- 
 turist, devoted much successful labor to the improvement 
 of fruit trees and vegetables by crossing. In the second 
 quarter of the nineteenth century, C. F. Gartner made 
 
Hybridization 111 
 
 and published the results of a number of experiments that 
 have not been equaled by any other worker. 
 
 What plants can be hybridized ? — It is a fact of prime 
 importance that plants so different as to be classed by 
 botanists in widely different families never yield offspring 
 when crossed ; for example, it is impossible successfully 
 to cross Indian corn and lilies or the apple and the wal- 
 nut. Usually plants diverse enough to be considered as 
 belonging to clearly distinct genera, even though of the 
 same natural family, are perfectly sterile when crossed ; 
 for example, Indian corn yields no offspring when cross- 
 pollinated with wheat, nor does wheat when crossed with 
 oats, although all belong to the great family of grasses.' 
 Plants belonging to the different cultivated races or to 
 natural varieties of the same species are almost invariably 
 fertile when crossed. Indeed, as will be shown later, they 
 are sometimes more fertile when crossed with a related 
 species than when fertilized with their own pollen. Dif- 
 ferent species of plants closely enough related to be placed 
 in the same genus by naturalists are very often, though by 
 no means always, capable of being hybridized. 
 
 Gartner found that '^one of the tobaccoes, Nicotiana 
 acuminata, which is not a particularly distinct species, 
 obstinately failed to fertilize or to be fertilized by no less 
 than eight species of Nicotiana." Darwin states that ''in 
 the same family there may be a genus, as Dianthus, in 
 which very many species can most readily be crossed ; 
 and another genus, as Silene, in which the m.ost persever- 
 ing efforts have failed to produce, between extremely close 
 species, a single hybrid." Again, there is considerable 
 diversity in results in certain reciprocal crosses between 
 
 i^ 
 
112 Plant-Breeding 
 
 the same two species. "Mirabilis jalapa can easily be 
 fertilized by the pollen of M. longiflora, and the hybrids 
 thus produced are sufficiently fertile ; but Kolreuter tried 
 more than two hundred times during eight following years 
 to fertilize reciprocally M. longiflora with the pollen of 
 M. jalapa and utterly failed/' as have also many other 
 hybridizers. Frequently very closely related species 
 absolutely refuse to cross. This is true of the pumpkin 
 {Cucurhita Pepo) and squash (C. maxima). It is, never- 
 theless, true that hosts of very distinct species hybridize 
 readily, and a number of cases are known of species be- 
 longing to different and quite distinct genera having 
 hybridized, producing the so-called bigeneric hybrids. 
 For example, wheat and rye, and wheat and barley, be- 
 longing to closely related genera, cross with difficulty, and 
 Luther Burbank is said to have succeeded in obtaining a 
 hybrid of strawberry and raspberry. Bigeneric hybrids 
 are many among the orchids, even though they are highly 
 specialized plants ; and some trigeneric hybrids are known. 
 
 Hybrids between plants belonging to different families 
 are very rare. The results obtained by hosts of experi- 
 menters and practical gardeners show conclusively that 
 the greater part of closely related species can be readily 
 crossed, while very distinct species, and species belonging 
 to distinct genera, can be crossed in only comparatively 
 few cases. It is impossible to predict what plants may or 
 may not be hybridized. 
 
 Vigor as a result of crossing. — Darwin was the first to 
 show that crossing within the limits of the species or 
 variety results in a constant revitalizing of the offspring, 
 and that this is the particular ultimate function of crossing 
 
Hybridization 
 
 113 
 
 or cross-fertilization. Kolreuter, Sprengel, Knight, and 
 others had observed many, if, indeed, not all, the facts 
 obtained by Darwin ; but they had not generalized upon 
 them broadly, and did not conceive the relation to the 
 complex life of the vegetable world. Darwin's results 
 are, concisely, these : self-fertilization tends to weaken the 
 offspring (Fig. 31) ; crossing between different plants of the 
 
 Fig. 31. — Inbred corn plants, showing lessened vigor of growth. 
 (Adapted from Yearbook.) 
 
 same variety gives a stronger and more productive offspring 
 than arises from self-fertilization ; crossing between stocks 
 of the same variety grown in different places or under 
 different conditions gives better offspring than crossing 
 between different plants grown in the same place or under 
 similar conditions ; and his researches have also shown that, 
 as a rule, flowers are so constructed as to favor cross- 
 
114 Plant-Breeding 
 
 fertilization. In short, he found, as he expressed it, that 
 '' nature abhors perpetual self-fertilization." Some of his 
 particular results, although often quoted, will be useful in 
 fixing these facts in our minds. 
 
 Darwin's experiments with morning-glories. — Plants 
 from crossed seeds of morning-glory exceeded in height 
 those from self-fertilized seeds as 100 exceeds 76, in the 
 first generation. Some flowers from these plants were 
 self-pollinated and some were crossed, and in this second 
 generation the crossed plants were to the uncrossed as 
 100 is to 79 ; the operation was again repeated, and in the 
 third generation, the plant having been grown in mid- 
 winter, when none of them did well, 100 to 86 ; fifth 
 generation, 100 to 75 ; sixth generation, 100 to 72 ; seventh 
 generation, 100 to 81 ; eighth generation, 100 to 85 ; ninth 
 generation, 100 to 79 ; tenth generation, 100 to 54. The 
 average total gain in height of the crossed over the un- 
 crossed was as 100 to 77, or about 30 per cent. There 
 was a corresponding gain in fertihty, or the number of 
 seeds and seed-pods produced. Yet, striking as the results 
 are, they were produced by simple crossing between plants 
 grown near together, and under what would ordinarily 
 be called uniform conditions. In order to determine the 
 influence of crossing with fresh stock, plants of the same 
 variety were obtained from another garden and these 
 were crossed with the ninth generation mentioned above. 
 The offspring of this cross exceeded those of the other 
 crossed plants as 100 exceeds 78, in height ; as 100 exceeds 
 57, in the number of seed-pods ; and as 100 exceeds 51, 
 in the weight of the seed-pods. In other words, crosses 
 between fresh stock of the same variety were nearly 30 
 
Hybridization 115 
 
 per cent more vigorous than crosses between plants grown 
 side by side for some time and over 44 per cent more 
 vigorous than plants from self-fertilized seeds. On the 
 other hand, experiments showed that crosses between 
 different flowers on the same plant gave actually poorer 
 results than offspring of self-fertilized flowers. It is 
 evident, from all of these figures, that nature desires 
 crosses between plants, and, if possible, between plants 
 grown under somewhat different conditions. All these 
 results are exceedingly interesting and important ; and 
 there is every reason to beUeve that, as a rule, similar 
 results can be obtained with all plants. 
 
 Darwin'' s results with other plants. — Darwin extended 
 his investigation to many plants, only a few of which need 
 be discussed here. Cabbage gave pronounced results. 
 Crossed plants were to self-fertilized plants in weight as 
 100 is to 37. A cross was now made between these crossed 
 plants and a plant of the same variety from another 
 garden, and the difference in weight of the resulting off- 
 spring was the difference between 100 and 22, showing a 
 gain of over 350 per cent, due to a cross with fresh stock. 
 Crossed lettuce plants exceeded uncrossed in height as 
 100 exceeds 82. Buckwheat gave an increase in weight 
 of seeds as 100 to 82, and in height of plants as 100 to 69. 
 Beets gave an increase in height represented by 100 to 87. 
 Maize, when full grown, from crossed and uncrossed seeds, 
 gave the difference in height between 100 and 91. Canary 
 grass gave similar results. 
 
 Increased vigor in other crosses. — Results as well 
 marked as these have been secured on a large and what 
 might be called a commercial scale. The first gen- 
 
116 Plant-Breeding 
 
 eration was raised from seeds of known parentage, 
 the flowers from which they came having been carefully 
 poUinated by hand. In some instances the second genera- 
 tions were grown from hand-crossed seeds, but in other 
 cases the second generations were grown from seeds simply 
 selected from the first-year patches. As the experiments 
 have been made in the field and upon a somewhat exten- 
 sive scale, it was not possible accurately to measure the 
 plants and the fruits from individuals in all cases ; but the 
 results have been so marked as to admit of no doubt as 
 to their character. In 1889, several hand-crosses were 
 made among egg-plants. The fruits matured, and the 
 seeds from them were grown in 1890. Some two hundred 
 plants were grown, and they were characterized through- 
 out the season by great sturdiness and vigor of gro^vth. 
 They grew more erect and taller than other plants near by 
 gro^vn from commercial seeds. It was impossible to deter- 
 mine productiveness, from the fact that the seasons were 
 too short for egg-plants, and only the earliest flowers, in 
 the large varieties, perfect their fruit, and the plant blooms 
 continuously through the season. In order to determine 
 how much a plant will bear, it must be gro^vn until it 
 ceases to bloom. When frost came, httle difference could 
 be seen in productiveness between these crossed plants 
 and commercial plants. A dozen fruits were selected from 
 various parts of the patch, and in 1891 about twenty-five 
 hundred plants were grown from them. Again the plants 
 were remarkably robust and healthy, with fine foliage, 
 and they grew erect and tall, — an indication of vigor. 
 They were also very productive ; but, as the cross had 
 been made between unhke varieties, and the offspring 
 
Hybridization 
 
 117 
 
 was therefore unlike either parent, an accurate comparison 
 could not be made. But they compared well with com- 
 mercial egg-plants, and un- 
 doubtedly they would have 
 shown themselves to be 
 more productive than com- 
 mon stock could they have 
 grown a month or six weeks 
 longer. Professor Munson, 
 of the Maine Experiment 
 Station, grew some of this 
 crossed stock in 1891, and 
 found that it was better 
 than any commercial stock 
 in his gardens. 
 
 In extended experiments 
 in the crossing of pumpkins, 
 squashes, and gourds, con- 
 ducted several years, in- 
 crease in productiveness 
 due to crossing has been 
 marked in many instances. 
 Marked increase in produc- 
 tiveness has been obtained 
 from tomato crosses even 
 when no other results of 
 crossing could be seen. 
 
 Three factors. — Attention 
 has been called by WiUis to 
 
 three factors in the gain resulting from cross-fertihzation, 
 viz. (a) fertility of mother plant ; (b) vigor of offspring ; 
 
 Fig. 32. — Hybrid walnut and 
 parent.s : m, California black 
 walnut {Juglans calif arnica), 
 male parent; /, Eastern black 
 walnut (./. nigra), female par- 
 ent ; h, hybrid. Natural size. 
 (After Bur bank.) 
 
118 Plant-Breeding 
 
 and (c) fertility of offspring. The relative values of these 
 factors varies with different plants. In the carnation, for 
 instance, factor (a) of cross-fertilized plants was 9 per cent 
 greater than in self -fertilized plants, (6) was 16 per cent 
 greater, and (c) was 54 per cent greater ; in tobacco, 
 factor (a) was 33 per cent less than in self-fertiHzed plants, 
 but factor (h) was 28 per cent greater and factor (c) 3 per 
 cent greater. Even when the fertility of the mother 
 plant is greatly reduced by hybridizing with a distinct 
 species and the hybrids themselves are sterile or very 
 infertile, they nevertheless often show extraordinary vigor, 
 that is, (b) is often greater in hybrids than in pure-bred 
 plants, but factors (a) and (c) are usually less. In plant- 
 breeding the importance of this increased vigor is very 
 great (Figs. 32 and 33). 
 
 The outright production of new varieties. — ^The reader is 
 waiting for a discussion of the second of the great features 
 of crossing, — the summary production of new varieties. 
 This is the subject that is almost universally associated 
 with crossing in the popular mind, and even among hor- 
 ticulturists themselves. It is the commonest notion that 
 the desirable characters of given parents can be definitely 
 combined in a pronounced cross of hybrids. There are 
 two or three philosophical reasons which somewhat oppose 
 this doctrine, and which we will do well to consider at the 
 outset. In the first place, nature is opposed to hybrids, 
 for species have been bred away from each other in the 
 ability to cross. If, therefore, there is no advantage for 
 nature to hybridize, we may suppose that there would be 
 little advantage for man to do so ; and there would be no 
 advantage for man did he not place the plant under condi- 
 
Fig. 33. — A hybrid walnut {Jiiglans californica nigra), reaching double 
 the height of ordinary trees. 
 
120 Plant-Breeding 
 
 tions different from nature, or desires a different set of 
 char^^cters. We have seen that nature's chief barriers to 
 hybridization are total refusal of many species to unite, 
 and entire or comparative seedlessness of offspring. 
 
 The notion is somewhat firmly rooted in the popular 
 mind that new varieties can be produced with the greatest 
 ease by crossing parents of given attributes. There is 
 something captivating about the notion. It smacks of a 
 somewhat magic power that man evokes as he passes his 
 wand over the untamed forces of nature. But the wand 
 is often a gilded stick, and is likely to serve no better 
 purpose than the drum major's pretentious baton ! 
 
 Let it be said further that crossing alone can accompHsh 
 comparatively Httle. The chief power in the evolution or 
 progression of plants appears to be selection, or, as Darwin 
 puts it, the law of ^^preservation of favorable individual 
 differences and variations, and the destruction of those 
 which are injurious." Selection is the force which aug- 
 ments, develops, and fixes types. Man must not only 
 practice a judicious selection of parents from which the 
 cross is to come, which is in reality but the exercise of a 
 choice, but he must constantly select the best from among 
 the crosses, in order to maintain a high degree of usefulness 
 and to make anj^ advancement ; and it sometimes happens 
 that the selection is much more important to the cultivator 
 than the crossing. 
 
 Further discussion of this subject naturally falls under 
 two heads : the improvement of existing types or varieties 
 by means of crossing, and the summary production of new 
 varieties. As already stated, the former office is the more 
 important, and the proposition is easy of proof. It is 
 
Hybridization 121 
 
 the chief use which nature makes of crossing, to strengthen 
 the type. 
 
 How to overcome antipathy to crossing. — We can over- 
 come the refusal to cross in many cases by bringing the 
 plant under cultivation; for the character of the species 
 becomes so changed by the wholly new conditions that its 
 former antipathies may be overpowered. Yet, it is doubt- 
 ful whether such a plant will ever acquire a complete willing- 
 ness to cross. In like manner we can overcome in a meas- 
 ure the comparative seedlessness of hybrids, but it is very 
 doubtful whether we can ever make such hybrids com- 
 pletely fruitful. 
 
 It is evident that species which have been differentiated 
 or bred away from each other in a given locality will have 
 more opposed quaUties or powers than similar species 
 which have arisen quite independently in places remote 
 from each other. In the one case the species have Ukely 
 struggled with each other until each one has attained to a 
 degree of divergence which allows it to persist ; while in 
 the other case, there has been no struggle between species, 
 but similar conditions have brought about similar results. 
 These similar species which appear independentl}^ of each 
 other in different places are called representative species. 
 Islands remote from each other but similarly situated with 
 reference to climate very often contain representative 
 species ; and the same may be said of other regions much 
 like each other, as eastern North America and Japan. 
 Now, it follows that, if representative species are less 
 opposed than others, they are more Hkely to hybridize with 
 good results ; and this fact is remarkably well illustrated in 
 the Kieffer and allied pears, which are hybrids between 
 
122 Plant-Breeding 
 
 representative species of Europe and Japan ; and the 
 same may be found to be true of the common European 
 applp and the wild crab of the Mississippi Valley. 
 Various crabs of the Soulard type, which were once 
 thought to constitute a distinct species, appear upon 
 further study to be hybrids. We will also recall that 
 the hybrid grapes which have so far proved most 
 valuable are those obtained by Rogers between the 
 American Vitis Labrusca and the European wine grape, 
 Vitis vinifera; and that the attempts of Haskell and 
 others to hybridize associated species of native grapes have 
 given, at best, only indifferent results. To these good 
 results from hybrids and fruit trees and vines, we shall 
 revert presently. 
 
 Variability of hybrids. — Another theoretical point 
 which is borne out by practice is the conclusion that, 
 because of the great differences and lack of affinity between 
 parents, pronounced hybrid offsprings are unstable. This 
 is one of the greatest difficulties in the way of the summary 
 production of new varieties by means of hybridization. 
 It would appear, also, that, because of the unlikeness of 
 parents, hybrid offspring must be exceedingly variable ; 
 but, as a matter of fact, in many instances the parents are 
 so pronouncedly different that the hybrids represent a 
 distinct type by themselves, or else they approach very 
 nearly to the characters of one of the parents. There are, 
 to be sure, many examples of exceedingly variable hybrid 
 offspring, but they are usually the offspring of variable 
 parents (Fig. 34) . In other words, variability in offspring 
 appears to follow rather as a result of variability in parents 
 than as a result of mere unhkeness of characters. But 
 
Hybridization 
 
 123 
 
 the instability of hybrid offspring when propagated by 
 seed is notorious. We shall see the reasons for this later 
 when discussing mendelism. Wallace writes that ''the 
 effect of occasional crosses often results in a great amount 
 of variability, but it also leads to instability of character, 
 and is therefore very little employed in the production of 
 fixed and well-marked races." We may remark again that, 
 because of the unequal and unknown powers of the parents, 
 we can never predict what characters will appear in the 
 
 Fig. 34. — Variation in hybrid pineapples. 
 
 hybrids, although we are now beginning to understand 
 the reasons and to have rather definite expectations as 
 to probabilities. This fact is well expressed by Lindley a 
 half century ago, in the phrase, ''Hybridizing is a game 
 of chance played between man and plants." 
 
 Characteristics of crosses. — Bearing these fundamental 
 propositions in mind, let us pursue the subject somewhat 
 in detail. We shall find that the characters of hybrids, 
 as compared with the characters of simple crosses between 
 stocks of the same variety, are ambiguous, negative, and 
 
124 Plant- Breeding 
 
 often prejudicial. Focke lays down the five following 
 propositions concerning the character of hybrid offspring : 
 
 1. ''All individuals which have come from the crossing 
 of two pure species or races, when produced and grown 
 under like conditions, are usually exactly like each other, 
 or at least scarcely more different from each other than 
 plants of the same species are." This proposition, al- 
 though perhaps true in the main, appears to be too broadly 
 and positively stated. 
 
 2. ''The characters of hybrids may be different from 
 the characters of the parents. The hybrids differ most in 
 size and vigor and in their sexual powers. 
 
 3. "Hybrids are distinguished from their parents by 
 their powers of vegetation or growth. Hybrids between 
 very different species are often weak, especially when 
 young, so that it is difficult to raise them. On the other 
 hand, crossbreds are, as a rule, uncommonly vigorous ; 
 they are distinguished mostly in size, rapidity of growth, 
 early flowering, productiveness, longer life, stronger repro- 
 ductive power, unusual size of some special organs, and 
 similar characteristics. 
 
 4. "Hybrids produce a less amount of pollen and fewer 
 seeds than their parents, and they often produce none. 
 In cross-breeds this weakening of the reproductive powers 
 does not occur. The flowers of sterile or nearly sterile 
 hybrids usually remain fresh a long time. 
 
 5. "Malformations and odd forms are likely to appear 
 in hybrids, especially in the flowers." 
 
 Some of the relations between hybridization and cross- 
 ing within narrow limits are stated as follows by Darwin : 
 " It is an extraordinary fact that with many species flowers 
 
Hybridization 125 
 
 fertilized with their own pollen are either absolutely or in 
 some degree sterile ; if fertilized with pollen from another 
 flower on the same plant, they are sometimes, though 
 rarely, a little more fertile ; if fertilized with pollen from 
 another individual or variety of the same species, they 
 are fully fertile ; but if with pollen from a distinct species, 
 the}^ are sterile in all possible degrees, until utter sterility 
 is reached. We thus have a long series with absolute 
 sterility at the two ends; at one end due to the sexual 
 elements not having been sufficiently differentiated, and 
 at the other end to their having been differentiated in too 
 great a degree, or in some peculiar manner," 
 
 Difficulties in making successful crosses. — The diffi- 
 culties in the way of successful results through hybridiza- 
 tion are, therefore, these : the difficulty of effecting the 
 cross, infertility, instability, variability, and often weak- 
 ness and m.onstrosity of the hybrids ; and the general 
 impossibility in most cases of predicting results. The 
 advantage to be derived from a successful hybridization 
 is the securing of a new variety which shall combine in 
 some measure the most desirable features of both parents ; 
 and this advantage is often of so great moment that it is 
 worth while to make repeated efforts and to overlook 
 numerous failures. 
 
 Hybridization and asexual propagation. — Among the 
 various characters of hybrid offspring, probably the most 
 prejudicial one is their instability, their tendency to vary 
 into new forms or to return to one or the other parent 
 in succeeding generations. At the outset, we notice that 
 this discouraging feature is manifested chiefly through 
 the fact of seed-reproduction, and we thereby come 
 
126 Plant-Breeding 
 
 upon what is perhaps the most important practical con- 
 sideration in hybridization, — the fact that the greater 
 number of the best hybrids in cultivation are increased 
 by bud-propagation, as cuttings, layers, suckers, buds, or 
 grafts. In fact, there are very few examples in this country 
 of good undoubted hybrids which are propagated with 
 practical certainty by means of seeds. The genera in 
 which the hybrids are most common are those in which 
 bud-propagation is the rule ; as begonia, pelargonium, 
 orchids, gladiolus, rhododendron, roses, cannas, and the 
 fruits. This simply means that it is difficult to fix hybrids 
 so that they will come ^'true to seed," and makes apparent 
 the fact that if we desire named hybrids, we must expect 
 to propagate them by means of buds. 
 
 This point appears to have been overlooked by those 
 who contend that hybridization must necessarily swamp 
 all results of natural selection ; for, as comparatively 
 few plants propagate habitually by means of buds, 
 whatever hybrids might have appeared would have been 
 speedily lost, and all the more because, by the terms of 
 their reasoning, the hybrids would cross with other and 
 dissimilar forms, and therefore lose their identity as 
 intermediates. Or, starting ^vith the assumption that 
 hybrids are intermediates, and would therefore obliterate 
 specific types, we must conclude that they should have 
 some marked degree of stability if they are to swamp or 
 obliterate the characters of species ; but, as all hybrids 
 tend to break up when propagated by seeds, it must follow 
 that bud-propagation would become more and more 
 common, and this is associated in nature with decreased 
 seed-production. Now, seed-production is the legitimate 
 
Hybridization 127 
 
 function of flowers; and we must concede that, as seed- 
 production decreased, floriferousness must have decreased ; 
 and that, therefore, pronounced inter-crossing would have 
 obliterated the very organs upon which it depends, or have 
 destroyed itself! 
 
 In-breeding. — But we may be met with objection that 
 there is no inherent reason why hybrids should not become 
 stable through seed-production by in-breeding, and we 
 might be cited to the opinion of Darwin and others that 
 in-breeding tends to fix any variety, whether it originates 
 by crossing or other means. And it is a fact that in- 
 breeding tends to fix varieties within certain limits, but 
 those limits are often overpassed in the case of very pro- 
 nounced crosses, whether cross-breeds or true hybrids. 
 And if it is true, as all observation and experiments show, 
 that sexual or reproductive powers of crosses are weakened 
 as the cross becomes more violent, we shall expect less and 
 less possibilit}^ of successful in-breeding ; for in-breeding 
 without disastrous results is possible only with compara- 
 tively strong reproductive powers. As a matter of fact, 
 it is found in practice that it is exceedingly difficult to fix 
 pronounced hybrids by means of in-breeding. It some- 
 times happens, also, that the hybrid individual that we 
 wish to perpetuate ma}' be infertile with itself, as has been 
 often found in the case of squashes. It is often advised 
 that we cross the hybrid individual which we wish to fix 
 with another like individual, or \\dth one of its parents. 
 These results are often successful, but oftener they are not. 
 In the first place, it often happens that the hybrid individ- 
 uals maj' be so diverse that no two of them are alike ; 
 this has been the experience in many cases. And, again 
 
128 Plant-Breeding 
 
 crossing with a parent may draw the hybrid back again to 
 the parent form. So long ago as last century Kolreuter 
 proved this fact with Nicotiana and Dianthus. A hybrid 
 between Nicotiana rustica and N. paniculata was crossed 
 with N. paniculata until it was indistinguishable from it ; 
 and it was then crossed with N. rustica until it became 
 indistinguishable from that parent. Yet there is no other 
 way of fixing a hybrid to be propagated by seeds than 
 by in-breeding, and by constant attention to selection. 
 Fortunately, it occasionally happens that a hybrid is 
 stable, and therefore needs no fixing. 
 
 Experience with egg-plants and squashes. — Offspring of 
 egg-plant crosses were grown in 1890, and upon some of 
 the most promising plants some flowers were self -pollinated. 
 But these self-pollinated seeds gave just as variable offspring 
 in 1891 as those selected almost at random from the patch ; 
 and what was worse, none of them reproduced the parents, 
 or ''came true to seed," and all further motive for in- 
 breeding was gone. ''My labor, therefore, amounted to 
 nothing more than my own edification. M}^ experience 
 in crossing pumpkins and squashes has now extended 
 through many years ; and, although I have obtained about 
 one thousand types not named or described, I have not 
 yet succeeded in fixing one. The difficulty here is an 
 aggravated one, however. The species are so exceedingly 
 variable that all the hybrid individuals may be unlike, so 
 that there can be no crossing between identical stocks ; 
 and, if in-breeding is attempted, it may be found that the 
 flowers will not in-breed. And the refusal to in-breed is 
 all the more strange because the sexes are separated in 
 different flowers on the plant. In other words, in my 
 
Hybridization 
 
 129 
 
 experience, it is very difficult to get good seeds from 
 squashes fertilized by a flower upon the same vine. 
 The squashes may grow normally to full maturity but be 
 entirely hollow, or contain only empty seeds. In some 
 instances the seeds may appear to be good, but may 
 refuse to grow under the best conditions. Finally, a 
 
 Fig. 35. — Variation in hybrid squashes. 
 
 small number of flowers may give good seeds. I have 
 many times observed this refusal of squashes (Cucurhita 
 Pepo) to in-breed. It was first brought to my attention 
 through efforts to fix certain types into varieties. The 
 figures of the season's tests will sufficiently indicate the 
 character of the problem. In 1890, one hundred and 
 
130 Plant-Breeding 
 
 eighty-five squash flowers were carefully pollinated with 
 staminate flowers taken from the same vine that bore the 
 pistillate flowers. Only twenty-two of these produced 
 fruit, and of those only seven, or less than one-third, bore 
 good seeds, and in some of these the seeds were few. Now, 
 these twenty-two fruits represented as many different 
 varieties, so that the inability to set fruit with pollen, 
 from the same vine is not a peculiarity of a particular 
 variety. The records of the seeds of the seven fruits in 
 1891 are as follows : — ■ 
 
 ''Fruit No. 1. Four vines were obtained, with four 
 different types, two of them being white, one yellow, and 
 one black. 
 
 ''Fruit No. 2. Twenty-three vines. Fifteen types very 
 unlike, twelve being white and three yellow. 
 
 *' Fruit No. 3. Two vines. One type of fruit, which is 
 almost like one of the original parents. 
 
 "Fruit No. 4. Thirty-two vines. Six types, differing 
 chiefly in size and shape. 
 
 "Fruit No. 5. Twenty vines. Nineteen types, of which 
 ten were white, eight orange, one striped, and all very unlike. 
 
 "Fruit No. 6. Thirteen vines. Eleven types, — eight 
 yellow, two black, one white. 
 
 "Fruit No. 7. One vine. 
 
 "These offspring were just as variable as those from 
 flowers not in-bred and no more likely, apparently, to 
 reproduce the parent. These tests leave me without any 
 method of fixing a pronounced cross of squashes, and lead 
 me to think that the legitimate process of origination of 
 new kinds here, as, indeed, if not in general, is a more 
 gradual process of selection, coupled, perhaps, with minor 
 crossing. 
 
Hybridization 131 
 
 ''I will relate a definite attempt towards the fixation of 
 a squash that I had obtained from crossing. The his- 
 tory of it runs back to 1887, when a cross was effected 
 between a summer yellow crook-neck and a white bush 
 scallop squash. In 1889 there appeared a squash of 
 great excellence, combining the merits of summer and 
 winter squashes with very attractive form, size, and color, 
 and a good habit of plant. I showed the fruit to one of 
 the most expert seedsmen of the country, and he pro- 
 nounced it one of the most promising types he had 
 ever seen; and, as he informed me that he had fixed 
 squashes by breeding in and in, I was all the more anxious 
 to carry out my own convictions in the same direction. 
 It is needless to say that I was very happy over what I 
 regarded as a great triumph. Of course, I must have a 
 large number of plants of my new variety, that I might 
 select the best, both for in-breeding and for crossing similar 
 types. So I selected the very finest squash, having placed 
 it where I could admire it for some days, and saved every 
 seed of it. These seeds were planted on the most con- 
 spicuous knoll in my garden in 1890. It was soon 
 evident that something was wrong. I seemed to have 
 everything except my squash. One plant, however, bore 
 fruits almost like the parent, and upon this I began my 
 attempts towards in-breeding. But flower after flower 
 failed, and I soon saw that the plant was infertile with itself. 
 Careful search revealed two or three other plants very 
 like this one, and I then proceeded to make crosses with 
 them. I was equally confident that this method would suc- 
 ceed. When I harvested my squashes in tlie fall and took 
 account of stock, I found that the seeds of my one squash 
 
132 
 
 Plant-Breeding 
 
 had given just as many different types as there were 
 plants, and I actually counted one hundred and ten kinds 
 distinct enough to be named and recognized. Still con- 
 fident, in 1891 I planted the seeds of my few crosses, and 
 as the summer days grew long and the crickets chirped 
 in the meadows, I watched the expanding squash blossoms 
 and wondered what they would bring forth. But they 
 
 Fig. 36. 
 
 Hybrid citrange and its parents, Citrus (or Poncirus) trifoliata 
 and common sweet orange. 
 
 brought only disappointment. Not one seed produced a 
 squash like the parent. My squash had taken an unscien- 
 tific leave of absence, and I do not know its whereabouts. 
 And when the frost came and killed every ambitious blos- 
 som, my hope went out and has not yet returned ! " ^ 
 
 Important hybrids of fruits and vegetables. — Let us 
 now recall how many undoubted hybrids there are, named 
 
 1 Bailey, "Plant-Breeding," earlier editions. See also, "A Medley of 
 Pumpkins," Proc. Intern. PI. Breeding Conf., New York City. 
 
Hybridization 
 
 133 
 
 and known, among our fruits and vegetables. In grapes 
 there are the most. There are Rogers' hybrids, as the 
 Agawam, Lindley, Wilder, Salem, and Barry ; and there 
 is some reason for supposing that the Delaware, Catawba, 
 and other varieties are of hybrid origin. And many 
 hybrids have come to notice lately through the work of 
 
 POMELO ? 
 
 .HYBRID TANGELO 
 
 TAN&ELO 
 
 rANDELO 
 
 Fig. 37. — Hybrid tangelo and its parents, pomelo and tangerine. 
 
 Munson and others. But it must be remembered that 
 grapes are naturally exceedingly variable, and the specific 
 limits are not well known, and that hybridization among 
 them lacks much of that definiteness which ordinarily 
 attaches to the subject. In oranges, hybrid citranges and 
 tangelos made by Webber and Swingle are now reaching 
 considerable commercial importance (Figs. 36-39). In 
 
134 
 
 Plant- Breeding 
 
 Fig. 38. — Samson tangelo. § natural size. (Adapted from Yearbook.) 
 
Hybridization 
 
 135 
 
 Fig. 39. — Citranges (hybrids of orange and Citrus trifoliata). Top 
 fruit Citrus (or Poncirus) trifoliata. Top pair, rusk citrange. 
 Bottom pair, Willits citrange. f natural size. (Reduced from 
 colored figures in Vearbook of the Department of Agriculture.) 
 
136 Plant-Breeding 
 
 pears there is the Kieffer class. In apples, peaches, plums, 
 cherries, and currants, there are no important recognized 
 commercial hybrids. In blackberries there is the black- 
 berry-dewberry class, represented by the Wilson Early and 
 others. Some of the raspberries, as the Philadelphia and 
 Shaffer, are hybrids between the red and black species. 
 Hybrids have been produced between the raspberry and 
 blackberry by two or three persons, but they possess 
 no /promise of economic results. It is probable that 
 some of the gooseberries are hybrids. Among all the 
 list of garden vegetables (plants which are propagated 
 by seeds) there is apparently not a single important 
 recorded hybrid ; and the same is true of wheat, — unless 
 the Carman wheat-rye varieties become prominent, — 
 oats, the grasses, and other farm crops (Fig. 40). But 
 among ornamental plants there are many ; and it is signifi- 
 cant that the most numerous, most marked, and most 
 successful hybrids occur in the plants most carefully 
 cultivated and protected, those, in other words, that are 
 farthest removed from all untoward circumstances and an 
 independent position. This is nowhere so well illustrated 
 as in the case of cultivated orchids, in which hybridization 
 has played no end of freaks, and in which, also, every 
 individual plant is* nursed and coddled.^ With such 
 plants the struggle for existence is reduced to its lowest 
 terms ; for it must be borne in mind that, even in the 
 garden, plants must fight severely for a chance to live, 
 and even then only the very best can persist, or are even 
 allowed to try. 
 
 1 Consult E. Bohnhof, " Dictionnaire des Orchidees Hybrides," Paris, 
 1905 ; also the recent Sanders lists. 
 
Hybridization 
 
 137 
 
 This list of hybrids is much more meager than most 
 catalogues and trade-Ksts would have us believe. It is, 
 of course, equivalent to saying that most of the so-called 
 hybrid fruits and vegetables are doubtful. There is every- 
 
 FiG. 40. — Teosinte and its hybrids with Indian corn: a and h, ears of 
 teosinte, showing an entire absence of cob, kernels being attached to 
 each other ; c and d, ears of first-generation cross of teosinte and 
 Indian corn; e and /, Zea canina, a fourth-generation hybrid of 
 teosinte and corn. All are natural size and were grown by the 
 Department of Agriculture in 1900 on the Potomac Flats near 
 Washington, D.C. 
 
 where a misconception of what a hybrid is, and how it 
 comes to exist ; and yet, perhaps because of this indefinite 
 knowledge, there is a wide-spread feeHng that a hybrid 
 is necessarily good, while the presumption is directly 
 the opposite. The identity of a hybrid in the popular 
 
138 Plant-Breeding 
 
 mind rests entirely on some superficial character, and 
 proceeds upon the assumption that it is necessarily inter- 
 mediate between the parents. Hence, we find one of our 
 popular authors asserting that, because the kohl-rabi bears 
 its thickened part midway of its stem, it is evidently 
 a hybrid between the cabbage and turnip, which bear 
 respectively the thickened parts at the opposite extrem- 
 ities of the stem! And then there are those who con- 
 found the word hybrid with high-bred, and who build 
 attractive castles upon the unconscious error. And thus 
 is confusion confounded! 
 
 Influence of sex on hybrids. — But, before leaving this 
 subject of hybridization, we must speak of the old yet 
 common notion that there is some peculiar influence 
 exerted by each sex in the parentage of hybrids. It 
 was held by certain early observers, of whom the great 
 Linnaeus was one, that the female parent determines the 
 constitution of the hybrid, while the male parent gives 
 the external attributes, as form, size, and color. The 
 accumulated experience of nearly a century and a half 
 appears to contradict this proposition, and Focke, who has 
 gone over the whole ground, positively declares that it is un- 
 true. There are instances, to be sure, in which this old idea 
 is affirmed, but there are others in which it is contradicted. 
 It is usually impossible to determine beforehand which 
 parent is the stronger. It is certain that strength does not 
 lie in size, neither in the high development of any character. 
 It appears to be more particularly associated with what 
 we call fixity or stability of character, or the tendency 
 towards invariability. 
 
 *' This has been well illustrated in my own experiments 
 
Hybridization 139 
 
 with squashes, gourds, and pumpkins. The common 
 httle pear-shaped gourd will impress itself more strongly 
 upon crosses than any of the edible squashes and pumpkins 
 with which it will effect a cross, whether it is used as male 
 or female parent. It contains many dominant unit- 
 characters. Even the imposing and ubiquitous great 
 field pumpkin which every New Englander associates 
 with pies, is overpowered by the Uttle gourd. Seeds from 
 a large and sleek pumpkin which had been fertilized by 
 gourd pollen produced gourds and small hard-shelled 
 globular fruits which were entirely inedible. A more inter- 
 esting experiment was made between the handsome 
 green-striped Bergen fall squash and the little pear gourd. 
 Several flowers of the gourd were pollinated by the Ber- 
 gen in 1889. The fruits raised from these seeds in 1890 
 were remarkably gourd-hke. Some of these crosses were 
 pollinated again in 1890 by the Bergen, and the seeds were 
 grown in 1891. Here, then, were crosses into which the 
 gourd had gone once and the Bergen twice, and both 
 parents are to all appearances equally fixed, the difference 
 in strength, if any, attaching rather to the Bergen. Now, 
 the crop of 1891 still carried pronounced characters of the 
 gourd. Even in the fruits that most resembled the Ber- 
 gen, the shells were almost flinty hard, and the flesh, even 
 when thick and tender, was bitter. Some of the fruits 
 looked so much like the Bergen that I was led to think 
 that the gourd had largely disappeared. The very hard 
 but thin paper-Hke shell which the gourd had laid over 
 the thick yellow flesh of the Bergen, I thought might 
 serve a useful purpose, and make the squash a better 
 keeper. And I found that it was a great protection, for 
 
140 Plant-Breeding 
 
 the squash could stand any amount of rough-handUng, 
 and was not even injured b}^ ten degrees of frost. All 
 this was an acquisition, and, as the squash was handsome 
 and exceedingly productive, nothing more seemed to be 
 desired. But it still remained to have a squash for dinner. 
 The cook complained of the hard shell, but, once inside, 
 the flesh was thick and attractive, and it cooked nicely. 
 But the flavor ! Dregs of quinine, gall, and boneset ! 
 The gourd was still there ! " ^ 
 
 Uncertainties of pollination. — We have now seen that 
 uncertainty follows hybridization, as well as the mere act 
 of poUination. Between some species which are closely 
 allied and which have large and strong flowers, four- 
 fifths of the attempts towards cross-poUination may be 
 successful ; but such a large proportion of successes is 
 not common, and it may be infrequent even in pollination 
 between plants of the same species or variety. Some of 
 the failure is due in many cases to unskillful operation, but 
 even the most expert operators fail as often as they suc- 
 ceed in promiscuous poUinating. There is good reason to 
 believe, as Darwin has shown, that the failure may be due 
 to some selective power of individual plants, by which 
 they refuse pollen which is, in many instances, acceptable 
 to other plants even of the same variety or stock. The 
 lesson to be drawn from these facts is that operations 
 should be as many as possible, and that discouragement 
 should not come from failure. 
 
 "Two hundred and thirty-four pollinations of gourds, 
 pumpkins, and squashes, mostly between varieties of one 
 species {Cucurhita Pepo), and including some individual 
 
 1 Bailey, earlier editions of " Plant-Breeding." 
 
Hybridization 141 
 
 pollinations, gave one hundred and seventeen failures and 
 one hundred and seventeen successes. These crosses 
 were made in varying weather, from July 28 to August 30. 
 In some periods nearly all the operations would succeed 
 and at other times most of them would fail. I have 
 always regarded these experiments as among my most 
 successful ones, and yet but half of the polKnations 'took.' 
 But one must not understand that I actually secured seeds 
 from even all these one hundred and seventeen fruits, 
 for some of them turned out to be seedless, and some were 
 destroyed by insects before they were ripe, or they were 
 lost by accidental means. A few more than half of the 
 successful poUinations — if by success we mean the for- 
 mation and growth of fruit — really secured us seeds, 
 or about one-fourth of the whole number of efforts. 
 
 '' Twenty pollinations were made between potato flowers, 
 and they all failed ; also, seven poUinations of red peppers, 
 four of husk tomato, two of Nicotiana affinis upon petunia 
 and two of the reciprocal cross, twelve of radish, one of 
 Mirahilis jalapa upon M. longiflora and two of the recip- 
 rocal cross, three Convolvulus major upon C. minor and 
 one of the reciprocal, one muskmelon by squash, two 
 muskmelons by watermelon, and one muskmelon by cu- 
 cumber. 
 
 ''This is but one record. Let me give another : — 
 "Cucumber, ninety-five efforts: fifty-two successes; 
 forty-three failures. Tomato, forty-three efforts : nine- 
 teen successes ; twenty-four failures. Egg-plant, seven 
 efforts : one success ; six failures. Pepper, fifteen efforts : 
 one success ; fourteen failures. Husk-tomato, forty-five 
 efforts : forty-five failures. Pepino, twelve efforts : twelve 
 
142 Plant-Breeding 
 
 failures. Petunia by Nicotiana affinis, eleven efforts : 
 eleven failures. Nicotiana affinis by petunia, six efforts : 
 six failures. General Grant tobacco by Nicotiana affinis, 
 eleven efforts : eight successes ; three failures. Nicotiana 
 affinis by General Grant tobacco, fifteen efforts : fifteen 
 failures. General Grant tobacco by General Grant 
 tobacco, one effort : one success. Nicotiana affinis by 
 Nicotiana affinis, three efforts : two successes ; one failure. 
 Tuberous begonia, five efforts : five successes. 
 
 "Total, three hundred and twelve efforts: eighty-nine 
 successes, two hundred and twenty-three failures." ^ 
 
 Graft-hybrids. — It is well known that, when two varie- 
 ties or aUied species are grafted together, each retains its 
 distinctive characters. But to this general, if not uni- 
 versal, rule there are on record several alleged exceptions, 
 in which either the cion is said to have partaken of the 
 qualities of the stock, the stock of the cion, or each to 
 have affected the other. Supposing any of these in- 
 fluences to have been exerted, the resulting product would 
 deserve to be called a graft-hybrid. 
 
 It is clearly a matter of great interest to ascertain 
 whether such formation of hybrids by grafting is really 
 possible ; for, even if one example of such formation could 
 be unequivocably proved, it would show that sexual 
 and asexual reproduction are essentially identical. 
 
 The case of Cytisus Adami (Figs. 41, 42). — The cases of 
 alleged graft-hybridization are exceedingly few, considering 
 the enormous number of grafts that are made every year 
 by horticulturists and have been made for centuries. 
 
 Of these cases, one of the most celebrated is that of 
 
 ^ Bailey, earlier editions. 
 
Hybridization 
 
 143 
 
 Fig. 41. — Cytisus Adami, A, A', A"; B, a branch of C. lahurum, L, 
 U, L", with numerous racemes bearing ripe pods. 
 
 Adam's laburnum {Cytisus Adami). This plant is now 
 flourishing in many places throughout Europe, all of the 
 trees having been raised as cuttings from the original 
 graft, which was made by inserting a bud of the purple 
 
144 
 
 Plant-Breeding 
 
 Fig. ^2. — Cytisus Adami, A, A', bearing at 7 a bunch of twigs of 
 C. purjmreus, P, H, and /. 
 
Hybridization 145 
 
 laburnum {Cytisus purpureus) into a stock of the yellow 
 {Cytisus laburnum). M. Adami, who made the graft at 
 Vitry, near Paris, about 1826, has left on record that from 
 it there sprang the existing hybrid. There can be no 
 question as to the truly hybrid nature of the latter. It 
 is, however, absolutely sterile, and is multiphed by grafts. 
 It bears three kinds of flowers — some pink, others large 
 and yellow, others small and purple. That is to say, it 
 bore its own hybrid flowers, also those of its two parents, 
 and the leaves and ramifications of the parts of the tree 
 which bore these three kinds of flowers were hkewise of 
 the same three kinds and could be distinguished even in 
 winter. 
 
 Strasburger made a careful cytological study of Cytisus 
 Adami, which has been retained in cultivation ever since 
 its origin some eighty years ago. He came to the con- 
 clusion that Cytisus Adami was a real sexual hybrid and 
 not a graft-hybrid. He thinks that if the latter were 
 true, the nuclei of the hybrid would show a double number 
 of chromosomes. This, of course, implies that in hybrids 
 arising otherwise than sexually, assuming that a nuclear 
 fusion would precede the formation of such a hybrid, 
 there would be no reduction division of the nuclei com- 
 parable to that which normally occurs before the fusion 
 of the sexual cells in normal fertiUzation. 
 
 Nemec, however, thinks that a reduction division 
 does occur and there is, therefore, no reason to expect 
 an increase in the number of chromosomes in the cells 
 of the hybrid. If such a reduction does occur, Cytisus 
 Adami would show the same number of chromosomes as 
 C. laburnum, which has the same number as C. purpureus. 
 
 L 
 
146 Plant-Breeding 
 
 Winkler's Solanum graft-hybrids. — Professor H. Winkler 
 of Tubingen has carefully performed experiments in 
 making graft-hybrids with the black nightshade, Solanum 
 nigrum, and two varieties of the tomato, Solanum lyco- 
 persicum. These two species are very distinct, and indeed 
 many botanists regard the tomato as belonging to a dis- 
 tinct genus lycopersicum, so that Winkler's graft-hybrids 
 may be regarded as bigeneric hybrids. SeedUngs of each 
 were grown and reciprocal grafts made. The graft and 
 stock united readily whether the nightshade or the tomato 
 was used as the stock. 
 
 Naturally the majority of the shoots arising from the 
 cut surface of the stem were either pure nightshade or 
 pure tomato. But finally shoots were observed which 
 were evidently of mixed origin. The first of these graft- 
 hybrids were obviously composed of pure elements 
 derived from the two parents. Some of these shoots were 
 almost equally divided by a median Hne, on one side of 
 which the organs — stem, leaf — were those of the night- 
 shade, while on the other the organs were evidently derived 
 from the tomato. It is obvious that such unusual forms, 
 which Winkler called '^Chimsera,'' are not hybrids in any 
 true sense of the word, but have arisen from buds which 
 contain the tissue of the two parent formed at the junction 
 of the stock and graft. 
 
 Later on there developed, however, shoots which were 
 evidently of hybrid origin. Cell fusion had unquestion- 
 ably taken place. Several hybrids with different attributes 
 were produced. These have been given different names 
 by Professor Winkler, and may be described as follows : — 
 
 1. Solanum tubingense is intermediate in the size and 
 
Hybridization 147 
 
 shape of the leaves and the color and type of the flowers 
 between the nightshade and the tomato. The fruit is 
 very much Uke that of the nightshade, but is rather larger, 
 and although it is black there are some traces of the red 
 or yellow color of the tomato. 
 
 2. Solarium proteus has very variable leaves, which, 
 on the whole, are more divided than those of S. tuhingense, 
 while in the characters of the flowers and the fruit it is 
 more like the tomato than like the nightshade. 
 
 3. Solanum Kolreuterianum, and 
 
 4. Solanum Gdrtnerianum. These forms have been 
 produced several times. The first is more like the tomato, 
 the second more like the nightshade, but each differs in 
 important particulars from either of the parents. 
 
 5. Solanum Darwinianum. The point of especial inter- 
 est in connection with this form is that of all the so-called 
 ^^graft-hybrids" secured by Winkler this seems to be the 
 only one which is hkely to prove a hybrid in the strict 
 sense of the word. The fruit of this plant, unhke the 
 others, was sterile, no perfect seeds being formed. The 
 fruit itself is a round small berry Uke the fruit of the night- 
 shade in form, but having the color and structure of the 
 tomato. 
 
 Are these real graft-hybrids f — In all of these forms when 
 seed was produced at all, it produced seedlings of one parent 
 or the other, never producing the apparent hybrid. 
 
 It has been suggested by Bauer that these apparent 
 true hybrids might be chimseras of a type which he has 
 called ''periclinal," i.e. the outer tissues are derived 
 from one parent, and the inner tissues from the other, 
 but none of the tissues themselves are of hybrid origin. 
 
148 Plant-Breeding 
 
 This explanation has also been applied to Cytisus hybrids 
 in which it has been shown that the epidermal tissues were 
 strikingly Uke those of C. purpureus, while the inner tissues 
 were like those of C. laburnum. 
 
 In a later paper, Winkler arrives at the following 
 conclusions : — 
 
 Hybrids may be arranged in two groups, sexual and 
 graft-hybrids. The latter may be divided into three 
 classes according to the theoretical possibiUty of their 
 method of origin, viz. : (1) Fusion graft-hybrids arising 
 from a fusion of two somatic cells derived from distinct 
 species. (2) ''Influenced" graft-hybrids which arise from 
 specific influences of one graft component upon the other 
 without cell fusion (as through chemical substances, trans- 
 location of cytoplasm, etc.). (3) Chimaeras, in which 
 specifically pure cells from both graft components are 
 combined to form a new individual. These chimseras may 
 be : (a) Sectorial chimseras in which the two sorts of cells 
 in the growing point are divided by a longitudinal plane. 
 (b) PericUnal chimseras in which the perichnal cell layers 
 of the growing point are furnished respectively from one or 
 the other parent form, (c) Hyper-chimseras in which the 
 growing point is made up of a mosaic of cells derived from 
 the two parent forms. 
 
CHAPTER VII 
 HEREDITY 
 
 All plants arise from parents more or less like them- 
 selves. This reproduction has a visible material basis in 
 the egg-cells and pollen-grains liberated from the parental 
 bodies. By inheritance is meant all the qualities which 
 have their physical basis in the fertilized egg-cell, the ex- 
 pression of which results in the organism. ''Thus/' says 
 Thomson, ''heredity is no force, no principle, but a con- 
 venient term for the genetic relation between successive 
 organisms." 
 
 The inheritance of plants may be studied by considering 
 parents and their offspring collectively or by studying 
 the separate characters and their modes of transmission. 
 The former is statistical, the latter, analytical. Studies 
 of heredity from both points of view are being extensively 
 conducted by the biometricians on the one hand and the 
 mendehans on the other. 
 
 Heredity studied collectively. — "To define heredity," 
 says Davenport, "as the direct and personal relation 
 between the individual parent and the individual offspring 
 is not only to restrict its meaning within too narrow Umits, 
 but to destroy its significance to the breeder and deceive 
 him as to the actual facts of transmission during descent. 
 * Heredity' properly refers to the group that constitutes 
 
 149 
 
150 
 
 Plant-Breeding 
 
 Number of Tubers — 3909 
 
 V 
 
 1.5 
 
 3.5 
 
 5.5 
 
 7.5 
 
 9.5 
 
 11.5 
 
 13.5 
 
 15.5 
 
 17.5 
 
 19.5 
 
 21.5 
 
 23.5 
 
 1.5 
 
 
 1 
 
 2 
 
 
 
 
 1 
 
 
 
 
 
 
 3.5 
 
 1 
 
 6 
 
 6 
 
 3 
 
 2 
 
 2 
 
 
 
 
 
 
 
 5.5 
 
 
 4 
 
 6 
 
 8 
 
 8 
 
 5 
 
 G 
 
 1 
 
 2 
 
 
 
 
 7.5 
 
 
 4 
 
 7 
 
 11 
 
 8 
 
 8 
 
 3 
 
 2 
 
 
 
 
 
 9.5 
 
 
 2 
 
 7 
 
 17 
 
 13 
 
 15 
 
 4 
 
 1 
 
 3 
 
 1 
 
 
 1 
 
 11.5 
 
 
 2 
 
 2 
 
 14 
 
 11 
 
 14 
 
 6 
 
 3 
 
 4 
 
 2 
 
 
 
 13.5 
 
 
 
 1 
 
 5 
 
 4 
 
 10 
 
 7 
 
 3 
 
 5 
 
 
 1 
 
 1 
 
 15.5 
 
 1 
 
 1 
 
 1 
 
 1 
 
 5 
 
 9 
 
 6 
 
 5 
 
 2 
 
 3 
 
 3 
 
 1 
 
 17.5 
 
 
 
 
 2 
 
 4 
 
 2 
 
 3 
 
 2 
 
 2 
 
 3 
 
 
 1 
 
 19.5 
 
 
 
 1 
 
 
 1 
 
 2 
 
 2 
 
 
 
 2 
 
 2 
 
 
 21.5 
 
 
 
 
 
 2 
 
 1 
 
 
 1 
 
 1 
 
 1 
 
 
 2 . 
 
 23.5 
 
 
 
 
 
 2 
 
 1 
 
 
 1 
 
 1 
 
 1 
 
 
 
 25.5 
 
 
 
 
 
 
 1 
 
 
 
 1 
 
 
 
 
 27.5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 29.5 
 
 
 
 
 1 
 
 
 
 
 
 
 ( 
 
 
 
 31.5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 33.5 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 4 
 
 2 
 
 20 
 
 33 
 
 62 
 
 60 
 
 70 
 
 38 
 
 il9 
 
 22 
 
 13 
 
 6 
 
 6 
 
 ^ 
 
 3 
 
 ^ 
 
 Lt 
 
 ^ 
 
 ^ 
 
 ^ 
 
 ^ 
 
 ( LC 
 
 c 
 
 LO 
 
 o 
 
 o 
 
 1 "v 
 
 re 
 
 t^ 
 
 1—1 
 
 
 
 it 
 
 X 
 
 Lt 
 
 C: 
 
 X 
 CO 
 
 CO 
 lO 
 01 
 
 o 
 M 
 
 1—1 
 
 O 
 
 i> 
 
 i> 
 
 t^ 
 
 r^ 
 
 t^ 
 
 ?c 
 
 ^ 
 
 o 
 
 ^ 
 
 CO 
 
 CO 
 
 o 
 
 CO 
 
 Q 
 
 C5 
 1 
 
 1 
 
 1 
 
 
 1 
 
 + 
 
 •M 
 
 rt^ 
 
 ^"^ 
 
 X 
 
 ^ 
 
 01 
 
 
 S 
 
 ?i 
 
 CI 
 
 s 
 
 X 
 
 -. 
 
 ?l 
 
 i; 
 
 c: 
 
 X 
 
 2- 
 
 01 
 
 Q 
 
 C5 
 
 Lt 
 
 
 rc 
 
 (M 
 
 
 Lt 
 
 X 
 
 CO 
 
 X 
 
 - 
 
 lO 
 
 © 
 
 00 
 
 1—1 
 
 ,i 
 
 1—1 
 
 X 
 
 ^ 
 
 ^ 
 
 23 
 
 1—1 
 
 ro 
 
 X 
 1— ( 
 
 lO 
 
 LO 
 
 
 c 
 
 1—1 
 
 00 
 
 1— i 
 
 C5 
 
 C 
 
 1—1 
 
 00 
 
 1— 1 
 
 
 ?5 
 
 i-H 
 
 !^5 
 
 CO 
 X 
 
 lO 
 X 
 
 3 
 
 o 
 
Heredity 
 
 151 
 
 25.5 
 
 27.5 
 
 41.5 
 
 43.5 
 
 /lO 
 
 /ool^og 
 
 Do9 -D^o9 
 
 -D^09/o9 
 
 2P 
 
 
 
 . . . . i 
 
 1 
 
 4 
 
 6 
 
 -9.83 96.62 
 
 386.48 
 
 165.14 
 
 
 
 
 
 
 20 
 
 70 
 
 -7.83 61.30 
 
 1226.00 
 
 814.32 
 
 
 
 
 
 
 40 
 
 220 
 
 -5.83 33.98 
 
 1359.20 
 
 443.08 
 
 
 1 
 
 
 
 
 44 
 
 330 
 
 -3.83 14.66 
 
 645.04 
 
 347.76 
 
 
 
 
 
 1 
 
 65 
 
 617.5 
 
 -1.83 3.34 
 
 217.10 
 
 92.41 
 
 
 
 
 
 
 58 
 
 667 
 
 0.17; .02 
 
 1.16 
 
 - 4.18 
 
 
 
 
 
 
 37 
 
 499.5 
 
 2.17 4.70 
 
 173.90 
 
 119.56 
 
 2 
 
 1 
 
 
 
 
 41 
 
 635.5 
 
 4.17 17.38 
 
 712.58 
 
 535.01 
 
 
 
 
 
 
 19 
 
 332.5 
 
 6.17 38.06 
 
 723.14 
 
 318.98 
 
 
 
 
 
 
 10 
 
 195 
 
 8.17 66.74 
 
 667.40 
 
 285.95 
 
 
 
 
 
 
 8 
 
 172 
 
 10.17 103.42 
 
 827.36 
 
 410.86 
 
 
 1 
 
 
 
 
 7 
 
 164.5 
 
 12.17 148.10 
 
 1036.70 
 
 390.65 
 
 
 
 
 
 
 2 
 
 51.0 
 
 14.17 200.78 
 
 401.56 
 
 93.52 
 
 
 
 
 
 
 
 
 
 16.17 261.46 
 
 
 
 
 
 
 
 
 1 
 
 29.5 
 
 18.17 330.14 
 
 330.14 
 
 -67.22 
 
 
 
 
 
 
 
 
 
 20.17 406.82 
 
 
 
 1 
 
 
 
 
 1 2 
 
 67 
 
 22.17 491.50 
 
 983.0 
 
 456.70 
 
 3 
 
 3 
 
 
 1 358 
 
 4057 
 
 
 9690.76 4402.54 
 
 1 
 
 u^ 
 
 L': XT. c 
 
 
 1 
 
 
 
 3/o9 = 11.33 ± .182 
 
 
 
 
 
 J/io = 11.20 ± .182 
 
 i 
 
 o 
 
 1—1 
 
 
 1 
 
 O"09 
 
 r 
 
 = 5.20 ± .130 
 = 5.23 ± .131 
 
 4402.54 ... 
 
 2 
 
 
 c: 
 
 r: Oi 
 
 358(5.2) (5.23) 
 
 ?5 
 
 
 X 
 
 ^^. .6745(1 -r^) 
 
 .6745 (.80) _^ 03 
 18.9 
 
 
 
 
 CO 
 1—1 
 
 1> C: 
 
 
 
 
152 Plant-Breeding 
 
 the parentage and the related group that constitutes 
 the offspring." 
 
 The coefficient of heredity. — The degree of inheritance 
 between a parental group of plants and their corresponding 
 group of offspring is determined by the use of a correlation 
 table. The degree of correlation or the resemblance is 
 determined between the parents and offspring. This may 
 be expressed mathematically and the result is known as 
 the ''coefficient of heredity." The latter is, therefore, 
 nothing more nor less than the correlation coefficient (r) 
 obtained from a table in which two sets of individuals 
 related by descent are tabulated with respect to the same 
 character. The coefficient of heredity is expressed as a 
 decimal, somewhere between and 1. The nearer 1, 
 the greater the closeness of resemblance between parents 
 and offspring, and conversely the nearer 0, the smaller 
 the degree of resemblance. 
 
 In the table (pp. 150-151) will be found the number of 
 tubers in hills of potatoes in 1909 as compared with the off- 
 spring from these hills in 1910. For example, there were 3 
 hills of seedUng potatoes having either 7 or 8 tubers in 1909 
 represented in the table by the midpoint 7.5 which gave 
 offspring in 1910 having either 3 or 4 tubers (3.5) ; 8 
 parental hills numbering either 7 or 8 tubers in 1909 which 
 produced offspring in 1910 having either 5 or 6 tubers ; 
 11 parental hills having the same number of tubers as 
 above which produced offspring having either 7 or 8 hills, 
 and so forth for each number in the table : — 
 
 Notation. — 
 
 n = Total number of individuals in the population, 
 equals summation of all frequencies. 
 
Heredity 153 
 
 /o9 = Class frequencies of total population in 1909. 
 
 Fo9 = Value or measurement corresponding to a given 
 frequency in 1909. 
 
 Mo9 = Mean number of potatoes per hill in 1909. 
 
 Do9 = Deviation of number of tubers per hill from mean, 
 1909. 
 
 O-09 = Standard deviations of number of tubers per hill, 
 1909. 
 
 /lo = Class frequencies of total population in 1910. 
 
 7^0 = Value or measurement corresponding to a given 
 frequency in 1910. 
 
 Mio = Mean number of potatoes per hill in 1910. 
 
 Dio = Deviation of numbers of tubers per hill from 
 mean, 1910. 
 
 o-io = Standard deviation of number of tubers per hill, 
 1910. 
 
 r = Coefficient of correlation. 
 
 The process of finding the mean and standard devia- 
 tion is the same as is given in Chapter IV, so that the 
 only column that needs explanation is the one headed 
 
 As an example, we will take the column on the 1910 
 tubers, beginning with 15.5. The figures 1, 1, 1, 1, 5, 
 9, 6, 5, 2, 3, 3, 1, 2, 1 are known as a horizontal array ; 
 similarly the vertical columns are known as a vertical 
 array. We will now show how 535.01 in 5P column is 
 obtained. 
 
 The first number after 15.5 is 1. Going down the verti- 
 cal column to column Dio, we find - 9.7, which is multi- 
 pUed by 1 ; the same process is gone through for each 
 number following 15.5 and the algebraic sum is taken, 
 
154 Plant-Breeding 
 
 which is multiplied by 4.17, found in column D09 opposite 
 15.5. So the result is as follows : — 
 
 4.17+ l(-9.7) +l(-7.7)+ 1 (-5.7)+ l(-3.7) + 5(-1.7) + 
 9(0.30) +6(2.3) +5(4.3) +2(6.3)+3(8.3) +3(10.3) + 1(12.3) 
 + 2(14.3)+ 1(16.3) = 535.01. 
 
 Having obtained all the numbers in the 2P column, the 
 sum is taken and the coefficient of correlation is found ac- 
 cording to the following formula : — 
 
 r= 4402.54 ^^^^^ 
 
 358(5.20) (5.23) 
 
 Conception of unit-characters. — Most recent studies are 
 analytical in their nature. We now conceive of plants 
 and animals to be composed of separately heritable units 
 known as unit-characters. It is not possible at present to 
 say exactly what a unit-character is, but we may call it 
 the smallest heritable part or attribute a plant may 
 possess. For example, the color of the flower, size and 
 shape of leaf, height of the plant, susceptibiUty or im- 
 munity to disease, and so forth, may be unit-characters. 
 
 Knowledge of heredity has come through experimental 
 breeding. — Much has been written and many conjectures 
 made by earher horticulturists in their attempt to classify 
 hybrids so that inheritance could be found to proceed in 
 an orderly and regular manner. All of these attempts 
 had been more or less failures until Gregor Mendel, an 
 Austrian monk, began a series of classic experiments in 
 
Heredity 155 
 
 crossing garden peas. Mendel's work, however, was little 
 known at the time and did not receive public recognition 
 until many years afterwards. 
 
 Rediscovery of MendeVs work by de Vries and others. — 
 de Vries made a thorough search of the literature of plant 
 evolution. In an American publication ^ he saw a ref- 
 erence to an article on plant hybrids by G. Mendel, 
 pubHshed in 1865 in the proceedings of a natural history 
 of Briinn in Austria. 
 
 On looking up this paper he was astonished to find that 
 it discussed fundamental questions of hybridization and 
 heredity, and that it had remained practically unknown 
 for a generation. In 1900 he pubUshed an account of it, 
 and this was soon followed by independent discussions 
 by Correns, Tschermak, and Bateson. In May, 1900, 
 Bateson gave an abstract of Mendel's work before the 
 Royal Horticultural Society of England; and later the 
 society published a translation of Mendel's original paper. 
 It is only within the last 10 or 12 years that a knowledge 
 of Mendel's work has become widespread in this country. 
 Perhaps the agencies that are most responsible for dis- 
 
 1 The following extract from a letter from Professor de Vries (printed 
 here by permission) will explain the reference in the text : " Many years 
 ago you had the kindness to send me your article on ' Cross-breeding and 
 Hybridizing ' of 1892 ; and I hope it will interest you to know that it was 
 by means of your bibliography therein that I learnt some years after- 
 wards of the existence of Mendel's papers, which now are coming to so 
 high credit. Without your aid I fear I should not have found them at 
 all." My reference to Mendel in the bibliography referred to was taken 
 from Focke's writing. I had not seen Mendel's paper. The essay, 
 "Cross-breeding and Hybridizing," formed Chapter II of the old 
 "Plant-Breeding"; but the bibliography that accompanied it was not 
 reprinted until the second edition of the book. — L. H. B. 
 
156 Plant-Breeding 
 
 semination of the mendelian ideas in America are the in- 
 struction given by Webber and others in the Graduate 
 School of Agriculture at Columbus, Ohio, in the summer 
 of 1904 and the prolonged discussion before the Interna- 
 tional Conference on Plant Breeding at New York in the 
 fall of 1902. Since that time many articles on the subject 
 have appeared from our scientific press. 
 
 Mendel's work is important because it cuts across many 
 of the current notions respecting hybridization. As 
 de Vries' discussions call a halt in the current beUef re- 
 garding the gradualness and slowness of evolution, so 
 Mendel's call a halt in respect to the common opinion 
 that the results of hybridizing are largely chance, and that 
 hybridization is necessarily only an empirical subject. 
 Mendel found uniformity and constancy of action in 
 hybridization, and to explain this uniformity he proposed 
 a theory of heredity. 
 
 One of the most significant points connected with 
 Mendel's work is the great care he took to select plants 
 for his experiments. He thought that hybridism is a 
 complex and intricate subject, and that, if we are ever to 
 discover laws, we must begin with the simplest and least 
 compHcated problems. He was aware of the general 
 opinion that the most diverse and contradictory results are 
 Ukely to follow any hybridization. He conceived that 
 some of this diversity may be due to instability of parents 
 rather than to the proper results of hybridizing. He also 
 saw that he must exclude all inter-crossing in the progeny. 
 Furthermore, the progeny must be numerous, for, since 
 incidental and aberrant variation may arise in the plants, 
 it is only by a study of averages of large numbers that the 
 
Heredity 157 
 
 true results of the hybridization are to be discovered. 
 Moreover, the study must be more exact than a mere con- 
 trasting and comparing of plants : character must be com- 
 pared with character. 
 
 MendeVs experiments. — The garden pea seemed to fulfill 
 all of the requirements. Mendel chose well-marked hor- 
 ticultural races or varieties. He grew these two years 
 before the experiment proper was begun in order to de- 
 termine their stability or trueness to type. When the 
 experiments were finally begun, he used only normal 
 plants as parents, throwing out such as were weak or 
 aberrant. Peas are self-fertile. It was to be expected 
 that under such conditions the hybrid offspring would 
 show uniformity of action ; and it did. 
 
 In order to study the behavior of the hybrids, it was 
 necessary to choose certain prominent marks or characters 
 for comparison. Seven of these characters were chosen 
 for observation. These marks pertain to seed, fruit, 
 position of flowers, and length of stem, and they may be 
 assumed to be representative of all other characters in 
 the plant. These characters were paired (practically 
 opposites) as long-stem vs. short-stem, round-seed vs. 
 angular-seed, inflated pods vs. constricted pods. They 
 were '^ constant" and '^differentiating." Of course every 
 parent plant possessed one or the other of every pair of 
 contrasting characters ; but in order to facihtate his 
 studies, Mendel chose a special set of parents to illustrate 
 each character. 
 
 The seed-shape characters were roundness and angu- 
 larity — the former being the ''smooth" pea of gardeners 
 and the latter the "wrinkled" pea. Let us suppose that 
 
158 Plant-Breeding 
 
 twenty-five flowers on round-seeded plants were cross- 
 pollinated in the summer of 1900 with pollen from angular - 
 seeded plants, or vice versa, and that an average of four 
 seeds formed in each pod. With the death of the parent 
 plants the old generation ended, and the 100 seeds that 
 matured in 1900 — the year in which the cross was made — 
 began the next generation ; and these 100 seeds were 
 hybrids. Now, all of these 100 seeds were round. Round- 
 ness in this case was '^dominant." (Dominance per- 
 taining to the vegetative stage of the plant of course would 
 not appear until 1901, when the seeds ^^grow.") These 
 seeds are sown in the spring of 1901. If each seed be 
 supposed to give rise to four seeds, — or 400 in all, — this 
 next generation of seeds (produced in 1901) will show 
 300 round and 100 angular seeds. That is, the other seed- 
 shape now appears in one-fourth of all the progeny; this 
 character is said to have been ''recessive" in the first 
 hybrid generation. If the 100 angular seeds, or reces- 
 sives, are sown in 1902, it will be found that all the progeny 
 will be angular-seeded or will "come true"; and this 
 occurs in all succeeding generations, providing no crossing 
 takes place. If the 300 round seeds, or dominants, are 
 sown in the spring of 1902, it will be found that 100 of them 
 produce dominants only, and that 200 of them behave as 
 before — one-fourth giving rise to recessives and three- 
 fourths to dominants ; and this occurs in all succeeding 
 generations, providing no crossing takes place. In other 
 words, the three-fourths of dominants in any generation 
 are of two kinds, — one-third that produce only dominants, 
 and two-thirds that are hybrids. That is, there is con- 
 stantly appearing from the hybrids one-fourth that are 
 
Heredity 
 
 159 
 
 recessives, one-fourth that are constant dominants, and 
 one-half that are dominants to all appearances, but which 
 in the next generation break up again into dominants 
 and recessives. This one-half part that breaks up into 
 the two characters are the true hybrids ; but they are 
 hybrids only in the sense that they hold each of the two 
 parental characteristics — roundness and angularity — in 
 their purity and not as blends or intermediates ; and these 
 two characteristics reappear in all succeeding generations 
 in a definite mathematical ratio. Proportionally, these 
 facts may be expressed as follows : — 
 
 1900. 
 
 1901. 
 
 1 seed 
 
 16 R 
 
 It will be seen that two-thirds of the dominants break 
 up the following year into one-fourth constant dominants, 
 one-fourth recessives, and one-half that again break up, 
 the half that break up being the hybrids. This formula 
 for the hybrids is Mendel's law. In words, it may be 
 expressed as follows : Differentiating characters in plants 
 reappear in their purity and in mathematical regularity 
 
160 Plant-Breeding 
 
 in the second and succeeding hybrid offspring of these 
 plants; the mathematical law is that each character 
 separates in each of these generations in one-fourth of the 
 progeny and thereafter remains true. In concise figures, 
 it is expressed as follows : — 
 
 ID: 2DR:1R. 
 
 1 D and 1 R come true, but 2 DR breaks up again into 
 dominant and recessives in the ratio of 3 to 1. 
 
 Mendel found that this law holds more or less for the 
 other characters that he studied in the pea, as well as for 
 the seed-shape. He did not conclude, however, that it 
 holds good for all plants, but left the subject for further 
 investigation. It will be seen at once that it will be a 
 very difficult matter to follow this law when many char- 
 acters are to be constrasted, particularly when the char- 
 acters are quantitative, or qualitative which grade into 
 each other. 
 
 The dominant characters pertain to either parent. Some 
 of them may come from the seed parent and some from 
 the pollen parent. When this roundness is dominant from 
 the male parent, there can be seen the immediate effect of 
 pollen, the same as if the dominant roundness came from 
 the female parent. In the case of the pea, the seed-content 
 is embryo and we are not surprised to find this immediate 
 effect of pollen. In those plants in which the embryo 
 is embedded in endosperm, however, the effect of the cross- 
 fertilization is not seen until the seed has been planted 
 and produced a new generation. The endosperm is a part 
 of the female parent and is not ordinarily changed by the 
 process of cross-fertilization. In the case of a few plants, 
 
Heredity 161 
 
 of which the Indian corn is the most conspicuous example 
 (Fig. 43), there is double fecundation, both the embryo and 
 endosperm being fertilized, and hence if the male parent 
 contains dominant characters, they will be seen immediately 
 because of the cross-fertilized endosperm. This is called 
 Xenia and has been carefully worked out by de Vries, 
 Webber,^ and others. 
 
 MendeVs numerical residts.^ — 
 
 In the experiments conducted by Mendel with peas the 
 relative numbers obtained for each pair of differentiating 
 characters are as follows : — 
 
 Experiment 1. — Form of seed. From 253 hybrids, 
 7324 seeds were obtained in the second trial year. Among 
 them were 5474 round and roundish and 1850 angular, 
 wrinkled ones. Therefore, the ratio 2.96 is to 1 is de- 
 duced. 
 
 Experiment 2. — Color of albumen. 258 plants yielded 
 8023 seeds, 6022 yellow and 2001 green ; their ratio, there- 
 fore, is 3.01 to 1. 
 
 Experiment 3. — Color of seed-coats. Among 929 
 plants, 705 bore violet-red flowers and gray-bro^\Ti seed- 
 coats ; 224 had white flowers and white seed-coats, giving 
 the proportion of 3.15 to 1. 
 
 Experiment 4. — Form of pods. Of 1181 plants, 882 
 had them simply inflated and in 299 they were constricted. 
 Resulting ratio 2.95 to 1. 
 
 Experiment 5. — Color of unripe pods. The number 
 
 1 Bull. 22, Div. of Veg. Phys. and Path., U. S. Dept. of Agric, 1900. 
 
 2 The following is taken from a translation of Mendel's article as given 
 by Bateson, and slightly revised. See Bateson-Mendel's "Principles of 
 Heredity," Appendix. 
 
 M 
 
Fig 43.-Mendelisminmaize.-StowellEvergreen (^-^^/J1^>J^^^^^ 
 inated with Indian flour corn, giving a hybrid similar to the latter the 
 first veaT This was self-pollinated, giving the ear o^^th^J^^^^*' ^^^ 
 pollinated with the evergreen, giving the ear on the left (Webber). 
 
 162 
 
Heredity 163 
 
 of trial plants was 500, of which 428 had green pods and 
 152 yellow pods. Consequently these stand in the ratio 
 2.82 to 1. 
 
 Experiment 6. — Position of flowers. Among 858 cases, 
 651 had inflorescence axial and 207 terminal. Ratio 3.14 
 to 1. 
 
 Experiment 7. — Length of stem. Out of 1064 plants 
 in 787 cases the stem was long and in 277 short. Hence 
 a mutual ratio of 2.84 to 1. 
 
 If the results of the whole experiment be brought to- 
 gether, there is found, as between the numbers of forms 
 with the dominant and recessive characters, an average 
 ratio of 2.98 to 1 or 3 to 1. 
 
 The following is an account of Mendel's results with 
 peas in their third hybrid generation {F^) : — 
 
 These forms which in the F2 generation exhibit the 
 recessive character do not further vary in the F^ generation 
 as regards this character : they remain constant in their 
 offspring. 
 
 It is otherwise with those that possess the dominant 
 character in the second generation. Of these, two-thirds 
 yield offspring that display the dominant and recessive 
 characters in the proportion of 3 to 1, and thereby show 
 exactly the same ratio as the hybrid forms, while only 
 one-third remain with the dominant character constant. 
 
 The separate experiments yield the following results : — 
 
 Experiment 1. — Among 665 plants which were raised 
 from round seeds of the second generation, 193 yielded 
 round seeds only, and remained, therefore, constant in 
 this character; 372, however, gave both round and 
 wrinkled seeds, in the proportion of 3 to 1. The number 
 
164 Plant-Breeding 
 
 of the hybrids, therefore, as compared with the constants, 
 is 1.93 to 1. 
 
 Experiment 2. — Of 509 plants which were raised from 
 seeds whose albumen was of yellow color in the second 
 generation, 166 jdelded exclusively yellow,while 353 yielded 
 yellow and green seeds, in the proportion of 3 to 1. There 
 resulted, therefore, a division into hybrid and constant 
 forms in the proportion of 2.13 to 1. 
 
 For each separate trial in the following experiments, 
 100 plants were selected which displayed the dominant 
 character in the second generation, and in order to as- 
 certain the significance of this, ten seeds of each were 
 cultivated. 
 
 Experiment 3. — The offspring of 36 plants yielded 
 exclusively gray-brown seed-coats, while of the off- 
 spring of 64 plants some had gray-brown and some 
 had white. 
 
 Experiment 4. — The offspring of 29 plants had only 
 inflated pods; of the offspring of 71, on the other hand, 
 some had inflated and some had constricted. 
 
 Experiment 5. — The offspring of 40 plants had only 
 green pods ; of the offspring of 60 plants, some had green 
 and some yellow ones. 
 
 Experiment 6. — The offspring of 33 plants had only 
 axial flowers ; of the offspring of 67, on the other hand, 
 some had axial and some terminal flowers. 
 
 Experiment 7. — The offspring of 28 plants inherited 
 the long axis, and those of the 72 plants some of the long 
 and some of the short axis. 
 
 In each of these experiments a certain number of plants 
 came constant with the dominant character. For the 
 
Heredity 165 
 
 determination of the proportion in which the separation 
 of the forms with the constantly persistent character 
 results, the first two experiments are of especial importance 
 since in these a greater number of plants can be compared. 
 The ratios 1.93 to 1 and 2.3 to 1 gave together almost 
 exactly the average ratio of 2 to 1. The sixth experiment 
 gave a quite concordant result; in the others the ratio 
 varies more or less, as was only to be expected in view of 
 the small number of 100 trial plants. Experiment 5, 
 which shows the greatest departure, was repeated, and 
 then in place of the ratio of 60 and 40 that of 65 and 35 
 resulted. The average ratio of 2 to 1 appears, therefore, 
 as fixed with certainty. It is, therefore, demonstrated 
 that, of those forms which possess the dominant character 
 in the second generation, two-thirds have the hybrid- 
 characters, while one-third remain constant with the 
 dominant characters. 
 
 The ratio of 3 to 1, in accordance with which the dis- 
 tribution of the dominant and recessive characters re- 
 sults in the second generation, resolves itself, therefore, in 
 all experiments into the ratio of 2 : 1 : 1 if the dominant 
 character be differentiated according to its significance 
 as a hybrid-character or as a parental one. Since the 
 second generation (F2) springs directly from the seed of 
 the first generation (Fi), it is now clear that the hybrids 
 from seeds have one or the other of the two differen- 
 tiating characters, and of those one-half develop again 
 the hybrid form, while the other yields plants which re- 
 main constant and receive the dominant or the recessive 
 characters, respectively, in equal numbers. 
 
 Dominance and recessiveness. — Which characters will 
 
166 Plant-Breeding 
 
 be dominant in any species we cannot determine until we 
 perform the experiment ; that is, there is no mark or 
 attribute which distinguishes to us a priori a dominant or 
 a recessive character. However, the mere fact as to 
 whether the one or the other character is dominant is 
 relatively unimportant, for constant dominance is no 
 more a regular behavior than recessiveness is. In various 
 subsequent experiments it has been found that even 
 when marked dominance is not shown in the first product, 
 the hybridization may follow the law in essential numeri- 
 cal results. The really important points are : (1) That 
 the characters typically remain pure or do not blend, 
 and (2) that their reappearance follows a numerical 
 order. 
 
 Explanation of mendelian results. — After finding such 
 surprising results as these, Mendel naturally endeavored 
 to discover the reasons why. The product of his specu- 
 lations is the theory of gametic purity (to use our present- 
 day terminology), which is a partial theory of heredity. 
 Every plant is the product of the egg, or female, cell 
 fertilized by the sperm, or male, cell. When constant 
 progeny is produced, it must be because the two cells, or 
 gametes, are of like character. When inconstant progeny 
 is produced, it must be because the sperm-cell is of one 
 character and the egg-cell of another. When these un- 
 like gametes come together, they will unite according to 
 the law of mathematical probabilities, one-fourth of those 
 of each kind coming together and one-half of those of 
 both kinds coming together. If A and B represent the 
 contrasting parental characteristics, they would combine 
 as : — 
 
Heredity 167 
 
 A -\-A = A'. 
 A +B = AB. 
 B -i-A = BA. 
 B +B = BK 
 
 A 2 and B^ are equivalent only to A and B. Since both 
 of the opposed or contrasted characters cannot be visible 
 at the same time, we have the following : — 
 
 A 
 
 B 
 
 in which small h represents the character that for the 
 time being is not able to express itself, or is recessive, and 
 large B represents the same character fully expressed. 
 
 In these gametes, the unit-characters of the plants that 
 bear them are pure. Even in hybrid plants the pollen- 
 grains and the egg-cells are not hybrids. According to 
 the hypothesis of gametic purity, therefore, hybrids 
 follow natural and numerical laws; but these laws are 
 always obscured by new crossing. True intermediate 
 characters do not occur. If new characters appear, it is 
 because they have been recessive or latent for a genera- 
 tion, or because the plant has varied from other causes ; 
 they are not the proper results of hybridization, unless 
 they are due to a reconstruction of characters. We may 
 suppose that a new character that appears because of 
 some internal change may be impressed on the gametes 
 and thereby be perpetuated. The results of hybridiza- 
 tion, according to the mendelian view, are not funda- 
 
168 Plant-Breeding 
 
 mentally a mere game of chance, but follow a law of 
 regularity of averages ; but the results are so often masked 
 that it is sometimes impossible to recognize the law. 
 
 It is a question, of course, whether the proportional 
 results secured by Mendel and others express a biological 
 principle, or whether they are only the numerical propor- 
 tions that may be adduced from the averages of large 
 numbers of combinations — whether these combinations 
 are of gametes or letters, or words, or figures. It is a 
 fundamental necessity that certain proportions follow 
 from '^ chance " combinations often repeated. But whether 
 the ''theorem of probabilities" can express a real bio- 
 logical fact may well be doubted. Perhaps the basis of 
 heredity is something more than the mechanico-physical 
 conceptions that we habitually apply to it. 
 
 Mendel's law of heredity is stated as follows by Bateson 
 and Saunders : "The essential part of the discovery is the 
 evidence that the germ-cells or gametes produced by 
 cross-bred organisms may in respect of given characters 
 be of the pure parental types and consequently incapable 
 of transmitting the opposite character; that when such 
 pure similar gametes of opposite sexes are united together 
 in fertilization, the individuals so formed and their pos- 
 terity are free from all taint of the cross, that there may 
 be, in short, perfect or almost perfect discontinuity 
 between these germs in respect of one of each pair of op- 
 posite characters." 
 
 The genetic constitutions of plants, if they are known, 
 may be conveniently represented by formulae containing 
 the gametic make-up of the parents entering into their 
 union. At least such unit-characters as are known may 
 
Heredity 
 
 1G9 
 
 be represented in this manner. For example, RR may 
 represent a plant which has been formed by the union 
 of a red pollen-grain (pollen-grain from a pure red parent) 
 R and a red egg-cell R. This plant if self-fertilized will 
 always remain red. Similarly rr represents a plant 
 which has the absence (or the opposite) of red, say, yellow. 
 If a red plant R were crossed with a yellow plant r, the 
 result would be a hybrid Rr. Red being dominant, the 
 first generation hybrid, F\, would appear as red. 
 
 The following method of squares will be found very 
 convenient to illustrate the action of chance which governs 
 the union of gametes to form the Fi hybrid plants : — 
 
 •/? 
 
 
 Pollen-grains 
 
 I I 
 
 R. r 
 
 (1) 
 
 RR 
 
 (2) 
 Rr 
 
 (3) 
 Rr 
 
 (4) 
 rr 
 
 Square (1) represents a plant {RR) formed from the 
 union of a red pollen-grain R with a red egg-cell R, 
 and is pure red. Square (2) represents a hybrid plant 
 {Rr) formed by r pollen-grain and R egg-cell. Square (3) 
 
170 
 
 Plant-Breeding 
 
 ^ 
 % 
 ^ 
 
 
 u: 
 
Heredity 171 
 
 is, the same as (2) except formed by pollen-grain R and 
 egg-cell r, and square (4) is a pure recessive rr in which 
 pollen-grain r united with egg-cell r. 
 
 This may be illustrated diagrammatically in another 
 manner, as in the colored plate (Fig. 44) . 
 
 Explanation of diagram. — It is assumed that a variety 
 having red flowers {R) is crossed with another variety 
 having yellow flowers (r). The arrow indicates the 
 direction of the cross and also the transfer of pollen from 
 the anthers of the yellow variety to the stigma of the red. 
 The plants produced from these fertilized ovules will 
 have red flowers because redness is dominant. This Fi 
 hybrid, however, contains both red and yellow qualities 
 and at the time of the formation of its gametes will give 
 rise to red and yellow pollen-grains and egg-cells. During 
 the process of self-fertilization the law of chance will 
 govern the union of the red and yellow egg-cells. These 
 Fi ovules will give rise to the plants indicated by F2. 
 The subsequent operations are assumed to follow regular 
 mendelian ratios. 
 
 MendeVs results with the offspring of hybrids in which 
 several differentiating characters are associated. — Two ex- 
 periments were made with a considerable number of plants. 
 In the first experiment the parental plants differed in the 
 form of the seed and in the color of the albumen. Experi- 
 ments with seed characters give the results in the simplest 
 and most certain way. 
 
 Experiment 1 . — Seed parent = round seeds (R) and 
 yellow cotyledons (F). Both dominant and hence their 
 symbols are expressed as capital letters. Pollen parent 
 = angular seeds (r) and green cotyledons (y). Round 
 
172 Plant-Breeding 
 
 yellow (RY) X angular green (ry) = RrYy appearing as 
 round and yellow in Fi. 
 
 Gametes of Fi = RR, Ry, rY, and ry. 
 
 Visible types oi F^ = 9 (apparently) RY, 3 Ry, 3 vY, 
 and 1 ry. 
 
 The following were actually found by Mendel in F2: — ■ 
 
 RY, round and yellow, 315. 
 
 rY, angular and yellow, 101. 
 
 Ry, round and green, 108. 
 
 ry, angular and green, 32. 
 These figures stand approximately in the ratio of 9 RY : 
 3 rF : 3 Ry : 1 ry, but these forms, which appeared to be 
 only four classes, were found in the next generation to be 
 made up of nine really different classes. 
 
 From the round yellow seeds (apparently RY) there 
 were obtained in the next year : — 
 
 1. RY, round and yellow seeds, 38 
 
 2. RYy, round, yellow and green seeds, 65 
 
 3. RrY, round, yellow and angular seeds, 60 
 
 4. RrYy, round, yellow and green angular, yellow 
 and green, 138 
 
 From the round and green seeds (apparently Ry) were 
 obtained : — 
 
 5. Ry, round and green seeds, 35 
 
 6. Rry, round angular and green seeds, 67 
 From the angular and yellow seeds (apparently rY) 
 
 were obtained : — 
 
 7. rY, angular and yellow seeds, 28 
 
 8. rYy, angular and yellow-green seeds, 67 
 From the angular and green ry seeds were obtained : — 
 
 9. ry, angular and green seeds, 30 
 
Heredity ' 173 
 
 Compare this carefully with problem 4 with special 
 reference to the actual counts as compared with theo- 
 retical ones. 
 
 The offspring of the hybrids appeared, therefore, under 
 nine different forms, some of them in very unequal num- 
 bers. When these are collected and coordinated, we 
 find : — 
 
 38 plants with the sign RY. 
 
 35 plants with the sign Ry. 
 
 28 plants with the sign rY. 
 
 30 plants with the sign ry. 
 
 65 plants with the sign RYy. 
 
 68 plants with the sign rYY. 
 
 60 plants with the sign RrY. 
 
 76 plants with the sign Rry. 
 138 plants with the sign RrYy. 
 
 The whole of the forms may be classed into three essen- 
 tially different groups. The first includes those with 
 the signs RY (or RRYY, as previously designated — it is 
 not necessary, however, to repeat the letters), Ry, rY, and 
 ry ; they possess only constant characters and do not vary 
 again in the next generation. Each of these forms is 
 represented, on the average, thirty-three times. 
 
 The second group includes the signs RYy, RrY, Rry; 
 these are constant in one character and hybrid in another, 
 and vary in the next generation only as regards the 
 hybrid character. Each of these appears, on the average, 
 sixty-five times. The form RrYy occurs 138 times; it 
 is hybrid in both characters and behaves as do the hybrids 
 from which it is derived. 
 
174 Plant-Breeding 
 
 If the numbers in which the forms belonging to these 
 classes appear, be compared, the ratios of 1,2, and 4 are 
 evidently unmistakable. The numbers 32, 65, 138 present 
 very fair approximations to the ratio numbers of 33, 66, 132. 
 
 The developmental series consists, therefore, of nine 
 classes of which four appear therein always once and are 
 constant in both characters; the forms RY, ry resemble 
 the parental forms, the two others present combinations 
 between the conjoined characters R, r, F, y, which com- 
 binations are likewise possibly constant. Four classes 
 appear always twice, and are constant in one character 
 and hybrid in the other. One class appears four times, 
 and is hybrid in both characters. Consequently the off- 
 spring of the hybrids, if two kinds of differentiating char- 
 acters are combined therein, are represented by the ex- 
 pression RY — Ry — rY — ry — 2 RYy — 2 rYy — 2 RrY 
 
 — 2Rry — 4:RrYy. 
 
 This expression is indisputably a combination series 
 in which the two expressions for the characters R and r, 
 y and Y are combined. We arrive at the full number of 
 the classes of the series by the combinations of the ex- 
 pressions. 
 
 The following, quoted from East, has reduced the 
 above to a mathematical expression : ''The numerical rela- 
 tions found are approximately the following series : AB, 
 Ab, aB, ah, 2 ABb, 2 aBb, 2 Aab, 2 AaB, and 4 AaBb. This 
 is really a combination by multiplication of the two series 
 (A — 2Aa — a) x {B — 2 Bb — b) = AB — Ab — aB 
 
 — ab — 2 ABb — 2 aBb — 2 Aab — 2 AaB — 4 AaBb. 
 The two pairs of characters behave independently of each 
 other and as if chance only governed their combinations. 
 
Heredity 
 
 175 
 
 Moreover, three pairs of contrasted characters were found 
 to behave in exactly the same manner, the number of 
 forms found being what would theoretically be expected 
 if the above product were multiplied by another series 
 represented by C — 2 Cc — c. 
 
 ''These results can be reduced to still simpler terms, as 
 is shown in the following table. Let N represent the 
 number of pairs of contrasted characters in the parents. 
 When they are crossed the second generation, when self- 
 fertilized, shows visible differences of 2 to the nth power. 
 These visibly different classes actually contain 3 to the 
 nth power different classes, the phenomena of dominance 
 obscuring part of them. Finally, when crossing to secure 
 combinations of n characters, we must have 4 to the nth 
 power number of individuals, to be theoretically certain 
 of at least one individual in each class. 
 
 Mendel's Law of Inheritance of Unit-characters 
 
 No. OF Pairs 
 OF DiF. BE- 
 TWEEN Parents 
 
 No. OF VISIBLY 
 
 DiF. Classes 
 Each cont. One 
 Pure Individual 
 
 2n 
 
 2 
 
 4 
 
 8 
 
 16 
 
 32 
 
 64 
 
 No. OF Actual 
 
 Classes Both 
 
 Pure and Hybrid 
 
 3n 
 
 3 
 
 9 
 
 27 
 
 81 
 
 243 
 
 729 
 
 Smallest No. Offspring, 
 
 allowing at least One to 
 
 A Class 
 
 An 
 Experimentally 
 tested by Men- 
 del for peas 
 
 Calculated 
 
 A is substituted for R, a for r, B for T, and b for t, and 
 instead of writing AA and aa in the series, one of the 
 letters is dropped." 
 
176 
 
 Plant-Breeding 
 
 a, 
 
 U 
 
 W 
 O 
 
 w 
 
 o 
 Q 
 
 w 
 
 H 
 
 •J 
 111 
 
 o 
 O 
 
 W 
 % 
 
 
 m 
 Eh 
 
 o 
 
 " I 
 
 r '^ 
 
 W « 
 
 & fe. 
 
 « o 
 
 a <> 
 
 o J 
 
 ^^ 
 
 w 3 
 
 H ^ 
 
 ^ 2 
 
 ^ a 
 
 93 hA 
 
 H 
 
 <: 2: 
 
 Oi 
 
 o 
 
 — I o 
 
 o 
 
 o 
 
 1—1 CO 
 
 00 00 
 
 ^ CO Q =2 
 
 o 2 "^ 
 o o 
 
 00 
 CO TfH lo 
 
 o o '^^ o 
 o o o 
 
 c5 (5 CD 
 
 o X CO t^ 
 
 .— I lO ■* lO 
 
 O iX) -^ O CO O (N 
 
 O O CO O CN O 
 
 o o o ^ o 
 
 Tfi CO 1^ CO 
 
 rHTjIt^OOOOCO^OO 
 
 o 
 d 
 
 r^ c^^ -r" Xi T* '-' o 
 
 o 
 d 
 
 O (M 
 
 d 
 
 o o 
 
 o 
 
 (M CO 
 
 ^•^s^s^g 
 
 o c5 
 
 O 05 
 
 CO o)^(M=^r-it^^^o;^§ 
 d d d d d 
 
 C5 C5 Tjl 1— I 00 05 
 
 0-<^!>Ot^OiOt005COt^rt<I>00 
 »0 ^ --H XI (M CO CO '^ >0 CO 00 OJ O) fT-l 
 
 LO v^ C5 
 (M '^ O 
 
 «o 
 
 ^ 
 
 CO (M --• 
 
 c^ ^; c^i '": ^o "^ '^ ^ 
 
 I— I I— ( o o 
 
 0»OcOiO'-'COtO'!*<OX 
 lO X Tti O t^ lO rt^ CO (M.-I1-H 
 
 Cq ,— I r-( .—I 
 
 o 
 o 
 
 o 
 o 
 
 lo 
 (M 
 
 Ci 
 
 
 CO 
 
 o 
 x 
 
 CO 
 
 rH fO 
 
 lO 1:0 
 
 Oi-HO'— lO"— '(M'-H'-Hi— (COl-Ht-l— ICO'— lOi— It^rHlO 
 Ot^lO^COCS|r-li-li-l 
 
 <^ o 
 
 H • 
 
 o o 
 
 
 
 iM 
 
 '^^ 
 
 X 
 
 
 
 (M 
 
 ■* 
 
 1—1 
 
 CO 
 
 
 
 Ol 
 
 
 
 I— 1 
 
 (>< 
 
 
 
 
 T— 1 
 
 04 
 
 
 
 
 
 b <J 
 
 U 
 
 
 ao 
 
 
 
 
 
 
 
 
 
 
 
 
 K 
 
 Bh 
 
 
 
 »— 1 
 
 fl 
 
 CO 
 
 ■* 
 
 10 
 
 CO 
 
 i> 
 
 X 
 
 Oi 
 
 
 
 « 
 
 <! 
 
 
 
 
 
 
 
 
 
 
 
 "— ' 
 
 H 
 
 CM 
 
 
 
 
 
 
 
 
 
 
 
 
Heredity 177 
 
 Results involving three pairs of characters (trihyhrid) . — 
 When three allelomorphic pairs are concerned, the num- 
 ber of forms in the second and subsequent generations is 
 greatly increased. For illustration, let us take a hypo- 
 thetical case. Suppose we cross together a tomato having 
 red fruit, dwarf vine, and hairy stems and leaves (the 
 latter is hypothetical) with a variety having yellow fruit, 
 tall vine, and smooth stems. Their formulae would be as 
 follows, using capitals again to represent dominant units 
 and small letters to . represent recessive units : red, 
 dwarf, hairy (RtH) x yellow, tall, smooth (rTh) = red, 
 tall and hairy (in appearance) RrTtHh. F^ generation 
 will be as shown in table on page 178. 
 
 In order to get a better understanding of the probable 
 union of gametes of various kinds of crosses, the student 
 should carefully master the method of squares, always 
 having in mind that the use of formulae is only a con- 
 venient method of representing plants. Each square 
 represents a plant. (See methods as already outlined on 
 page 169.) Capital letters will be used for dominant 
 units and small letters for recessives as formerly. Plants 
 having as their formulae large and small of any letter, i.e. 
 Rr, are hybrids (heterozygous) for that character, and those 
 in which the letters are the same, i.e. RR, are pure (homo- 
 zygous) for that character. 
 
 It will be seen that when three pairs of characters are 
 involved, at least 64 squares are necessary to allow for 
 the theoretically possible number of combinations to be 
 formed. A very careful study of the table will show that 
 there are produced 8 visible types (2") with proportions 
 as follows : 27 Red Tall Hairy, RTH ; 9 Red Tall smooth, 
 
 N 
 
178 
 
 Plant-Breeding 
 
 Pollen-grains 
 
 CO 
 
 W 
 o 
 
 I 
 
 o 
 o 
 
 
 RTH 
 
 RTh 
 
 RtH 
 
 Rth 
 
 rTH 
 
 rTh 
 
 rtH 
 
 rth 
 
 
 RR 
 
 RR 
 
 RR 
 
 RR 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 RTH 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 RR 
 
 RR 
 
 RR 
 
 RR 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 RTh 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 RR 
 
 RR 
 
 RR 
 
 RR 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 RtH 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 RR 
 
 RR 
 
 RR 
 
 RR 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rth 
 
 Tt 
 
 Tt 
 
 ft 
 
 tt 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 rr 
 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 rr 
 
 rr 
 
 rr 
 
 rTH 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 rr 
 
 rr 
 
 rr 
 
 rr 
 
 rTh 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 TT 
 
 TT 
 
 Tt 
 
 Tt 
 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 rr 
 
 rr 
 
 rr 
 
 rr 
 
 HH 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 
 HH 
 
 Hh 
 
 HH 
 
 Hh 
 
 HH 
 
 rr 
 
 Hh 
 
 HH 
 
 Hh 
 
 Rr 
 
 Rr 
 
 Rr 
 
 Rr 
 
 rr 
 
 rr 
 
 rr 
 
 rth 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Hh 
 
 hh 
 
 Note. It must be remembered that these are different visible types 
 and not actual types. For example, the 27 which appear as RTh are 
 not all alike, their identity is obscured of dominance. 
 
Heredity 179 
 
 RTh ; 9 Red dwarf Hairy, RtH ; 9 yellow Tall Hairy, rTH ; 
 3 Red dwarf smooth, Rth ; 3 yellow Tall smooth, rTh ; 
 3 yellow dwarf Hairy, rtH ; and 1 yellow dwarf smooth, 
 rth. Of course most of the visible types are multiple, 
 containing both pure and hybrid forms. The number of 
 actually different types is 27 (3") . 
 
 Incomplete dominance. — It was stated previously that 
 dominance is due to an unequal potency between the 
 unit-characters associated in a cross, the dominant unit 
 being '' stronger" and covering up the weaker unit in the 
 Fi generation. 
 
 This is not always the rule, by any means. There are 
 various degrees of equiUbrium between the opposed 
 units : if one is much stronger than the other, complete 
 dominance occurs ; if they are of equal potency, we 
 have a form in the first generation which is intermediate 
 between the two parents. This intermediacy may 
 lean to one parent or the other in proportion to their 
 strength. 
 
 When intermediacy exists, the mendehan ratios are 
 somewhat modified. Instead of having 3 : 1 ratio, we 
 have a 1 : 2 : 1, in which the 2 represents the heterozygous 
 or intermediate forms and the Ts represent the homo- 
 zygous forms. 
 
 If we are concerned with more than one allelomorphic 
 pair, complete dominance may occur in certain units and 
 intermediacy or incomplete dominance in others. 
 
 The commercial carnation is a heterozygous form which 
 is an intermediate between a single type and a type 
 which in commerce is called a ''bull-head" or a ''buster." 
 This latter is exceedingly double. When the hybrid 
 
180 Plant-Breeding 
 
 commercial types are self-fertilized, they produce progeny 
 in the approximate ratio of 1 single : 2 commercial doubles : 
 1 double-double or bull-head (Fig. 45). 
 
 Fig. 45. — Hybrid carnation (center) between a single and a burster, 
 
 showing intermediacy. 
 
 The hybrids between a large, apple-shaped tomato 
 and a small, pear-shaped one are intermediate between 
 the parents in the first generation, as has already been 
 noted. In all probabiUt}^ there are represented in the 
 above characters more than one unit. Emerson has 
 made similar observations in beans, gourds, and maize, 
 Locke in maize, and Castle in rabbits. 
 
 ''While it is not uncommon," says Spillman, ''for a 
 character to be dominant or recessive in a cross, it is 
 seldom that dominance is absolute. The presence of the 
 recessive characters can easily be detected, and in some 
 cases very easily. Thus in the cross between bearded 
 
Heredity 181 
 
 and smooth wheat the hybrids usually show a slight tend- 
 ency to be bearded. Likewise, the cross between horned 
 and polled cattle may have scars (hornlessnessis dominant). 
 It frequently happens that instead of either of two opposite 
 characters being dominant, we get a form intermediate 
 between the two parent forms. Thus, in the cross be- 
 tween long-headed wheat and the short-headed club 
 wheats of the Pacific Coast, the hybrids have heads of 
 intermediate length, though they are much more Hke 
 club wheat than they are like the ordinary kinds, so that 
 the club character is at least partially dominant. In cer- 
 tain crosses between red-flowered and white-flowered 
 ornamental plants the hybrids are pink." 
 
 Presence-and-absence hypothesis. — The phenomena of 
 mendelian inheritance may be explained in one of two 
 ways : first, the presence of a definite substance in the 
 germ cells of both parents representing each unit-character 
 in the allelomorphic pair, and, second, the ''presence-and- 
 absence" hypothesis. The latter assumes that what 
 appears to be a pair of characters is really the presence 
 and absence of a single character. 
 
 Examples of mendelian inheritance due to the presence- 
 and-absence of a single unit. — ^ Red flowers may be 
 due to the presence of red, and white flowers to its 
 absence. 
 
 The wrinkled pea owes its character to the absence of 
 something which the round pea possesses. Darbishire 
 has found in the round pea that all of the sugar has been 
 converted into starch, while only a part of it has been 
 thus converted in the wrinkled pea and the wrinkUng is 
 primarily due to the escape of the water from the solu- 
 
182 Plant-Breeding 
 
 tion of sugar left over after ripening, and, consequently, 
 in the last resort due to the absence of that which completes 
 the conversion of the sugar into starch or, at any rate, 
 to an insufficiency in the quantity of that substance, 
 whatever it is. The round pea has the full share of this 
 substance, the wrinkled pea an insufficient one. Some- 
 thing is absent from the wrinkled which is fully present 
 in the round. 
 
 The same author applies the presence-and-absence 
 hypothesis to another pair of characters in peas, the 
 color of the cotyledons. The two characters which meet 
 the eye are yellow and green. But the matter is not 
 so simple as this. Bunyard has shown that there is a 
 yellow and a green pigment both in the yellow and in 
 the green cotyledon. When both are present at 
 the same time, as in the ripe but still moist pea, 
 the green masks the yellow. All peas, both yellow 
 and green varieties, are green when they are eaten. 
 Just as cooks think that all peas are round, so they 
 think that all peas are green. It is only gardeners who 
 sow and harvest them who know the distinction between 
 yellow and green. 
 
 The ripe but still moist cotyledons of both yellow- and 
 green-seeded varieties are, therefore, green. The yellow 
 kinds become yellow as they ripen ; the green do not 
 change color during this process. The yellowing of the 
 former is brought about by the gradual fading and dis- 
 appearance of the green pigment, which thus leaves the 
 yellow pigment (which is present in both kinds) exposed. 
 The successive stages in the fading of the green can be 
 easily observed. The simultaneous presence of both 
 
Heredity 183 
 
 green and yellow pigment in yellow and in green peas 
 has also been demonstrated. 
 
 Green-seeded varieties therefore contain two pigm,ents 
 in their cotyledons, a yellow and a green ; neither of them 
 fades during the process of ripening, and inasmuch as 
 the green masks the yellow, the ripe seed is green. Yellow- 
 seeded varieties also contain the same two pigments, but 
 the green fades in the process of ripening, so that the 
 ripe seed is yellow. This fading of the green pigment in 
 the yellow pea is supposed to be brought about by the 
 presence of some substance which is absent from the green 
 pea. Similarly, when the apparent absence of a character 
 is dominant, as in the case of dominance of hornlessness in 
 cattle and of white color in swine, there is believed to be 
 present an inhibiting factor or ''inhibitor" which pre- 
 vents the formation of the black pigment. In other 
 words, it is the presence of the inhibitor (causing white) 
 over its absence (black) which explains the phenomena of 
 the dominance of white over black. 
 
 It is not the dominance of an absent factor, but the 
 presence of an unseen inhibitor, which reacts upon the 
 otherwise visible character, causing it to disappear. 
 
 Let us now consider another type of cause which may 
 be explained on the basis of the presence-and-absence 
 hypothesis. The heredity of the combs of fowls has been 
 carefully studied by Bateson, Davenport, Punnett, and 
 others. The latter gives an excellent description ^ of this 
 on the presence-and-absence hypothesis. 
 
 Four types of combs are recognized ; namely, rose, pea, 
 walnut, and single. (See Fig. 46.) 
 
 1 Punnett, " Mendelism," pp. 35, 36. 
 
184 
 
 Plant-Breeding 
 
 Rose and pea combs behave as simple dominants to 
 single comb, segregating in the F2 generation in the nor- 
 mal 3 : 1 ratio. What happens when the two dominants 
 are bred together? It was found that a third type ap- 
 peared as an Fi hybrid, the so-called walnut comb. 
 When these Fi hybrids were bred inter se, four types of 
 
 combs were found 
 among the F2 prog- 
 eny ; namely, walnut, 
 pea, rose, and single 
 in the approximate 
 ratios of 9:3:3:1 
 respectively. What 
 is the explanation 
 of this unusual phe- 
 nomenon ? 
 
 We are evidently 
 concerned with two 
 allelomorphic pairs 
 of characters, which 
 are the presence-and- 
 absence of rose comb 
 (R) and the presence-and-absence of pea comb (P). 
 As suggested by Punnett, let us denote the rose comb 
 by RRpp (containing the presence of rose and the 
 absence of pea) and the pea comb by rrPP. When these 
 are crossed together, the zygote RrPp results. This 
 differs from either and has a walnut comb. When these 
 Fi hybrids are crossed together (RrPp x RrPp), the fol- 
 lowing results may be graphically expressed in the series 
 of squares : — ■ 
 
 Fowls' combs : A, pea ; B, rose ; 
 C, single ; D, walnut. 
 
Hereditij 
 
 185 
 
 RP 
 
 Spermatozoa 
 RV rP 
 
 rp 
 
 RP 
 
 Rp 
 
 < 
 > 
 O 
 
 rP 
 
 rp 
 
 RP 
 RP 
 
 Walnut 
 
 RP 
 
 Rp 
 
 Walnut 
 
 RP 
 
 rP 
 
 Walnut 
 
 RP 
 
 rp 
 Walnut 
 
 RP 
 
 Rp 
 
 Walnut 
 
 Rp 
 Rp 
 
 Walnut 
 
 Rp 
 
 rP 
 
 Walnut 
 
 Rp 
 rp 
 Rose 
 
 RP 
 
 rP 
 
 Walnut 
 
 Rp 
 
 rP 
 
 Walnut 
 
 rP 
 rP 
 Pea 
 
 rP 
 rp 
 Pea 
 
 RP 
 
 rp 
 Walnut 
 
 Rp 
 rp 
 Rose 
 
 rp 
 rP 
 Pea 
 
 rp 
 
 rp 
 
 Single 
 
 Diagram to illustrate the nature of the F2 generation from the cross of 
 rose comb X pea comb. (After Punnett.) 
 
 All the resulting zygotes containing both rose and pea 
 (RP) will be walnut ; those containing rose only {R) and 
 not pea (p) will be rose and those containing pea only (P) 
 and not rose (r) ^vill be pea-combed. But all individuals 
 containing neither rose nor pea will have single combs. 
 This was found to be a pure recessive and to breed true. 
 The character of singleness seems to underUe all the types 
 of comb and appears whenever allowed to do so by the 
 absence of something representing the other kinds. 
 
 Mendelian inheritance of color. — Colors of plants or 
 animals are generally very complex and often consist of 
 many units of different kinds. Very rarely a certain color 
 may be said to be due to a single unit acting alone. A 
 knowledge of the kinds of color and the constitution of 
 each is necessary to understand their inheritance. 
 
186 Plant-Breeding 
 
 1. White is due to the absence of pigment, and to the 
 reflection of light from the cells. 
 
 2. Green color is caused by the presence of a green 
 pigment in the chlorophyll. 
 
 3. Yellow, cream, and related colors are due to a 
 yellow pigment either associated with green in the chloro- 
 plasts or found alone in the chromoplasts, generally the 
 latter. Yellow may sometimes come from the cell-sap. 
 
 4. Red color may, under certain circumstances, be due 
 to the presence of that pigment in the chromoplasts, but 
 it is ordinarily a cell-sap color. 
 
 5. Most of the remaining colors, purple, blue, generally 
 red, pink, etc., are due to pigments in the cell-sap. 
 
 6. Many of the colors and shades found in flowers 
 are the result of both plastid colors and cell-sap colors 
 acting together in various amounts. 
 
 7. Certain of the denser plastids or cell-sap colors may 
 cover up the more delicate colors so that they cannot be 
 seen. 
 
 8. Finally, the color in the cell-sap may be due to 
 the relative presence of a non-nitrogenous and chemical 
 substance anthocyanin. This is blue in an alkahne and red 
 in acid reacting cell-sap, and, under certain conditions, 
 also dark red, violet, dark blue, and even blackish blue. 
 Anthocyanin can be obtained from the supersaturated 
 cell-sap of a number of deeply colored parts of plants in 
 a crystalline or amorphous form. Blood-colored leaves, 
 such as those of the Copper Beach, owe their characteris- 
 tic appearance to the united presence of green chlorophyll 
 and anthocyanin. The different colors of flowers are due 
 to the varying color of the cell-sap, to the different dis- 
 
Heredity 187 
 
 tribution of the cells containing the colored cell-sap, 
 and also to the combinations of dissolved coloring 
 matter with the yellow, orange, and red chromoplasts 
 and the green chloroplasts. There is occasionally found 
 in the cell-sap a yellow coloring matter known as xan- 
 thein ;• it is nearly related to xanthophyll, but soluble in 
 water. 
 
 Thus we see the plant colors are not always unit-charac- 
 ters, such as hairiness, glabrousness, and the like. Certain 
 colors found in plants, purple flowers, for example, are 
 the result of the union of certain other pigments. These 
 pigments are produced by definite units in the gametes. 
 Color inheritance thus becomes very complicated as the 
 results of certain crossings indicate. 
 
 White flowers in F2 from red X cream. — Bateson points 
 out a typical case of the paradoxical appearance of white- 
 flowered individuals in the Fi from the cross of a sap- 
 colored variety with a variety having cream-colored 
 flowers. For example, in sweet peas or stocks, when a 
 red-flowered type is crossed with a cream, i^i is red with- 
 out any cream color. F^ consists of 9 without cream, 3 
 reds with cream, 3 whites, 1 cream. 
 
 The red-flowered variety consists of red sap color only 
 and the cream variety of yellow plastids only. These 
 are inherited separately in the hybrids. The 9 reds of 
 the F2 hybrids have a much brighter red color than the 
 red-creams. In the latter the red is diluted by the yellow 
 plastids. 
 
 When the allelomorphs are correctly distinguished, the 
 significance of this series is obvious. The operations may 
 be shown in tabular form, thus : — 
 
188 
 
 Plant-Breeding 
 
 Parents . 
 Allelomorphs 
 
 F2 
 
 Red variety X 
 
 Red sap (D) 
 Colorless corpuscles (D) 
 
 Cream variety 
 Colorless sap (r) 
 Yellow corpuscles (r) 
 
 Red sap 
 
 Colorless corpuscles 
 
 III I 
 
 Red sap Red sap Colorless sap Colorless sap 
 
 Colorless Yellow Colorless Yellow 
 
 corpuscles corpuscles corpuscles corpuscles 
 
 Appearance 9 red 3 red-cream 3 white 1 cream 
 
 The ratio 9:3:4- — The F2 ratio, 9 : 3 : 4, is one which 
 very frequently occurs in mendelian analysis. For ex- 
 ample, as Tschermak found, when a pink-and-white 
 flowered eating pea {Pisum, sativum) is crossed with a 
 white-flowered type, Fi is often the original purple-flowered. 
 Then F2 wAX be 
 
 9 purple : 3 pink and white : 4 white. 
 
 In this case the factor for purple is evidently brought in 
 by the albino. The latter contains the presence of 
 purple, which needs a factor from the other parent to 
 bring it out, and the absence of pink and white. The 
 other parent contains the presence of pink and white 
 and the absence of a factor for purple. All that is essen- 
 tial for the production of the ratio in Fi is that Fi should 
 be heterozygous for two factors, of which one is percep- 
 tible whenever present, while the other needs the presence 
 of the first in order that its own effects may be mani- 
 fested. 
 
 Emerson^ s experiments with heans. — By crossing self- 
 colored varieties of beans with white varieties, Emerson 
 
Heredity 189 
 
 obtained in the Fi generation, 65 mottled. In F2 genera- 
 tion there were 113 mottled, 52 self-colored, and 70 
 white, that is, in the ratio of 6.45 : 2.97 : 4 instead of 
 9:3:4. 
 
 In the F3 generation he secured the following results : — 
 
 1. All white seeds produced white seeds. 
 
 2. 7 mottled gave 22 mottled, 19 self-colored, 11 white. 
 
 3. 2 mottled yielded 13 mottled, 13 self-colored. 
 
 4. 4 mottled bore 5 mottled, 5 white. 
 
 5. 2 mottled produced 6 mottled. 
 
 6. 5 self-colored gave 63 self-colored. 
 
 7. 9 self-colored yielded 80 self-colored, 29 whites. 
 For the purpose of explaining the above, Emerson adopted 
 the formula of ShuU. 
 
 1. P and p for the factor presence and absence of pig- 
 ment. 
 
 2. M and m for the factor presence and absence of 
 mottUng. 
 
 3. Pm = self-colored. 
 
 4. pM = white. 
 
 5. PM = mottled. 
 
 Thus he considers a self-colored variety containing the 
 factor for pigment and having no factor for mottUng. 
 The white variety lacks the factor for pigment, but has 
 the factor for mottling. The mottled form is originated 
 by the presence of two factors, for the pigment and 
 mottling. 
 
 If we follow these formulae, we must confer to the F\ 
 generation the following gametic composition, PpMm, 
 since Fi hybrids will produce 9 mottled, 3 self-colored, 
 and 4 white for the F2 generation as seen on page 190 : — 
 
190 
 
 Plant-Breeding 
 
 PM 
 
 Pollen-grains 
 Pm pM 
 
 pm 
 
 PM 
 
 Pm 
 
 
 pm 
 
 PM 
 
 PM 
 
 Mottled 
 
 Pm, 
 PM 
 
 Mottled 
 
 pM 
 
 PM 
 
 Mottled 
 
 pm 
 
 PM 
 
 Mottled 
 
 PM 
 
 Pm 
 Mottled 
 
 Pm 
 Pm, 
 Self 
 
 pM 
 
 Pm 
 
 Mottled 
 
 pm, 
 Pm 
 Self 
 
 PM 
 
 pM 
 
 Mottled 
 
 Pm 
 
 pm 
 
 Mottled 
 
 pM 
 
 pM 
 
 White 
 
 pm 
 
 pM 
 
 White 
 
 PM 
 
 pm 
 Mottled 
 
 Pm 
 
 pm 
 Self 
 
 pM 
 
 pm 
 White 
 
 pm 
 
 pm 
 
 White 
 
 The ratio of 6.45 : 2.97, instead of 9:3:4, seems to be 
 chiefly due to the paucity of number treated for hybridi- 
 zation. Doubtless it is no small importance to study 
 the ratio of offspring in F^ in the Ught of the theoretical 
 deduction. But here again the insufficient number of 
 seeds informs us of its inadvisibility. 
 
 In conclusion Emerson says: "The result of most of 
 my own experiments might be explained as due to the 
 mendehan behavior of an allelomorphic pair, Mm presence 
 and absence of motthng, M being visible only in the pres- 
 ence of P." 
 
 Colored forms from white X white and the 9 : 7 ratio. — ■ 
 In the case of the sweet peas, Bateson has shown that the 
 formation of color in the flowers can be proved to depend 
 on the coexistence of two complementary factors in the 
 individual. 
 
 He says that the first indication of this phenomenon 
 
Heredity 191 
 
 was found in the fact that two plants, each totally devoid 
 of color in the flowers and stems and each breeding true 
 to albinism may, when crossed together, give purple 
 flowers in Fi. The two white parents each contain a 
 factor which, alone, is incapable of forming color. Each 
 of these factors is independently transmitted in gameto- 
 genesis, and thus in F2 the ratio of colored individuals to 
 whites is 9 : 7. This proportion depends on the fact that 
 a series of 16 individuals is necessary to exhibit all the 
 possible combinations of germ cells, for, as in any example 
 of hybridization involving two pairs of allelomorphs, 
 there will be four types of female cells and four types of 
 male cells produced by Fi. Of these sixteen individuals, 
 9 will contain both the dominant or present factors, while 
 of the remaining seven individuals, 3 will contain one 
 dominant, 3 will contain the other, and 1 will contain 
 neither. There will, therefore, be 9 which are colored 
 and 7 which are albino. In the diagram (p. 192) C 
 and R are the symbols representing the two comple- 
 mentary factors, c and r being their respective allelomor- 
 phic absences. 
 
 Absence factors. — It may be well for us in this connection 
 to touch upon the different conceptions of several investiga- 
 tors on such characters as cannot be seen without resorting 
 to breeding tests. Tschermak considers the appearance of 
 motthng in Fi between a white and self-colored varieties 
 due to the presence of mottling in a latent condition in 
 the self-colored variety. Latency in his view is inactivity. 
 Shull often speaks of latent characters, but latency, 
 according to him, means invisibility and not dormancy or 
 inactivity. 
 
192 
 
 Plant-Breeding 
 Pollen-grains 
 
 
 CR 
 
 Cr 
 
 cR 
 
 cr 
 
 
 CR 
 
 Cr 
 
 cR 
 
 cr 
 
 CR 
 
 CR 
 
 CR 
 
 CR 
 
 CR 
 
 • 
 
 Colored 
 
 Colored 
 
 Colored 
 
 Colored 
 
 
 CR 
 
 Cr 
 
 cR 
 
 cr • 
 
 2 Cr 
 
 Cr 
 
 Cr 
 
 Cr 
 
 Cr 
 
 
 Colored 
 
 White 
 
 Colored 
 
 White 
 
 1 
 
 o 
 
 CR 
 
 Cr 
 
 cR 
 
 cr 
 
 cR 
 
 cR 
 
 cR 
 
 cR 
 
 
 Colored 
 
 Colored 
 
 White 
 
 White 
 
 
 CR 
 
 Cr 
 
 cR 
 
 cr 
 
 cr 
 
 cr 
 
 cr 
 
 cr 
 
 cr 
 
 
 Colored 
 
 White 
 
 White 
 
 White 
 
 Composition of the 9 colored and 7 albino offspring in F2 from the 
 cross between the albino Cr with albino cR, showing the ratio 9 colored : 
 7 albino. 
 
 On the other hand, Bateson advocates the undesir- 
 ability of using such a terminology. He scorns the idea 
 that there is latency of mottling or red in the white forms. 
 Certain factors may be present which are absolutely 
 necessary for the production of such pigments, but this 
 fact does not lead us to contend that there are those colors 
 latent. He emphasizes stating that ^'sulphate of copper 
 is blue and chloride of copper is green, but it would be 
 incorrect to speak of blue as latent in sulphuric acid, or 
 of green as latent in hydrochloric acid." 
 
 Hurst seems to have difficulty to perceive a factor for 
 absence. He brings forth three distinct views : — 
 
 1. The absence factor may be a concrete one, literally 
 representing absence. 
 
Heredity 193 
 
 2. It may be nothing but presence in a latent state. 
 
 3. There may not be such a factor as the absence 
 factor. 
 
 Of the three proposed, the first seems to be, Hurst 
 remarks, the simplest, but it is difficult to realize and 
 understand how such an absence factor is originated. 
 Furthermore, he says: ''There are many cases where 
 the factor for presence is in a latent condition." The 
 third explanation meets an objection in the fact that there 
 is no pairing of factors in cross-breeding. Consequently, 
 it follows that, according to this view, it is impossible to 
 explain the phenomenon of segregation. 
 
 Mutations resulting from mendelian segregation and re- 
 combination. — It is very probable that many mutations 
 which appear suddenly and remain constant are the result 
 of mendelian segregation and recombination. If many 
 unit-characters are involved, it is easily perceived how 
 certain combinations of these would produce plants 
 of unusual appearance which will be homozygous and 
 breed true. Reference to Table I, p. 176, will show the 
 great possibilities of obtaining apparently new characters 
 by new combinations of old ones. It will be noted that 
 when as many as 10 allelomorphs are involved, and this 
 does not seem to be an impossible number, there is the 
 possibihty of producing 1024 different visible types. 
 
 Mutations which mendelize are co7istant. — The effect 
 of swamping of mutations by crossing is prevented be- 
 cause of their continued identity due to the purity of the 
 germ-cells which represent them. 
 
 Mutations may be due to three things : (a) the ac- 
 quisition of one or more new characters, (6) the loss of 
 o 
 
194 Plant-Breeding 
 
 one or more characters, and (c) recombination of existing 
 characters. 
 
 If the mutation is due to the addition of a new char- 
 acter and it remains constant, there must be present in 
 its germ-cells some unit to represent that new character as 
 there was in the gametes of the parent which produced it. 
 Likewise, if a character is lost, its germinal potentiality 
 must have become lost or entered into a latent condition. 
 
 If mutations of these types are crossed, the new gametic 
 representatives or absences in the case of a lost character 
 become pure in the germ-cells and reappear in the next 
 generation. Hence they are not lost. 
 
 If the mutation has a hybrid beginning and is due to 
 an unusual combination of characters, this condition can- 
 not be lost, as this certain combination which has once 
 occurred will reproduce true if it is homozA^gous, or if not, 
 it having occurred once may appear again through a like 
 combination of unit-characters even though crossing and 
 amphimixis may have taken place. 
 
 Mendelism in wheat. — As a specific example of evident 
 mendelian results, W. J. Spillman, agriculturist of the 
 Department of Agriculture, here explains some of his ex- 
 periments with, wheat. ^ Mr. Spillman independently dis- 
 covered numerical results, before the knowledge of the 
 mendelian experiments had become generally kno\\Ti. 
 
 ''The photograph (Fig. 47) shows three generations of 
 one of my hybrid wheats. Of the three heads in the 
 upper row, the left-hand one is the male parent (variety 
 Valley) ; the right-hand one is the female parent (variety 
 
 1 Published in fourth edition of this work, 1906; and here reproduced 
 nearly entire for its historical as well as for its plant-breeding value. 
 
Heredity 
 
 195 
 
 Fig. 47. — Three generations of hybrid wheat: A 1 = male parent, 
 A 2 = the hybrid, A 3 = female parent : B 1-6 = the progeny of A 2 ; 
 C 1 = progeny of B 1 , C 2-4 = progeny of B 2, C 5 = progeny of B 3, 
 C 6 and 7 = progeny of B 4, C S-13 = progeny of B 5, C 14 and 15 
 = progeny of B 6. The results in the fourth generation, available 
 too late to include in the photograph, indicate that B 2 and B 3, 
 while not always separable on external appearances, are absolutely 
 different, the one being hybrid, the other pure. 
 
 Little Club); and the middle one is the hybrid. The 
 second row shows the second generation, and the third 
 row the third generation. Of the six types in the second 
 generation, the following points are important : Each 
 
196 
 
 Plant-Breeding 
 
 type was present in a certain proportion, which was ap- 
 proximately the same as in thirteen other similar cases, 
 and the average of these fourteen cases approximated the 
 theoretical numbers called for by Mendel's hypothesis 
 of the disjunction of parental characters. The three 
 at the left, being bearded, possess a character which 
 was latent in the first generation. The fact that the 
 beards show in these three indicates that the opposite 
 character is absent, and they should therefore remain 
 bearded in succeeding generations. That is, they are no 
 longer hybrid with reference to this character. It will 
 be observed that this was actually the case, for no beard- 
 less heads appeared in the progeny of either of these three 
 (see lower row, first five heads). The following diagram 
 will show the character of each of the six types in row 2. 
 In this diagram the letters have the following meanings : — 
 
 B = bearded (written b when latent) . 
 S = smooth (not bearded). 
 L = long heads. 
 C = Club heads (short). 
 
 / = Intermediate in length of head. (The hybrid was 
 intermediate in this respect.) 
 
 Parents First Generation 
 
 BL 
 
 Sbl 
 
 sc 
 
 Second Generation 
 
 1 
 
 BL 
 
 2 
 
 BI 
 
 1 
 
 BC 
 
 2 
 
 SbL 
 
 4 
 
 Sbl 
 
 2 
 
 SbC 
 
 1 
 
 SL 
 
 2 
 
 SI 
 
 1 
 
 SC 
 
 16 
 
 
Heredity 197 
 
 ''This diagram shows the nine types called for by 
 Mendel's theory. Of these, BL, BC, SL, and SC are 
 no longer hybrids — at least they have no latent char- 
 acters, and vnW therefore reproduce true to seed. Of the 
 remaining five types, BI and SI are hybrid only ^^dth 
 reference to length of head, and SbL and ShC only with 
 reference to beards; while Sbl is hybrid with reference 
 to both characters, as in the preceding generation. 
 
 ''It will readily be seen that the types BL and BC can 
 be separated from the others even by external appearances, 
 and obtained in a pure state. BL is the type showTi at 
 the left in the second row in the picture, and all its prog- 
 eny was like it, showing that it conformed to theory. BC 
 is the type sho^vn at No. 3 in the second row of heads ; 
 being pure, it should reproduce itself true to tjq^e, which 
 it did, with an easily explained exception to be noted be- 
 low. The type BI (sho\^^l at No. 2, row 2), being hybrid 
 with reference to length of head, should produce again 
 all types based on this character, and it did this, as is seen 
 in heads 2-4, row 3. Referring again to the above 
 diagram, it will be seen that the types SL and SbL cannot 
 be distinguished by external characters. SL ^^^ll of course 
 reproduce true to type, while SbL will reproduce SL, 
 SbL, and BL. Now .SL and SbL being mixed together in 
 the selection made in the second generation, we shall find 
 a large percentage of SL mixed with some SbL from which 
 it cannot be distinguished, and a small percentage of BL 
 in the third generation. Heads 6 and 7, row 3, show that 
 the types called for actually occurred. Types SI and Sbl 
 of the diagram appear alike externally, and were there- 
 fore selected together in the' second generation (see head 
 
198 Plant-Breeding 
 
 5, row 2). Now SI should produce the types SL, SI, 
 SC, while Shi should produce all nine types again 
 (these nine types can be separated only into six by exter- 
 nal appearance). It is therefore seen that the group 
 represented by head 5, row 2, should produce all six types 
 again. Heads 8-13, row 3, show these types. Types 
 SbC and SC of the diagram are alike externally, and were 
 hence selected together last year. Of these SC should 
 produce only SC, while SbC should produce SC, SbC, and 
 BC. But since SC and SbC look alike, the progeny of 
 these two types should show only SC and BC. The last 
 two heads in row 3 show that this actually occurred. 
 ''In the single set of heads shown, there were two easily 
 explained exceptions to theory. It will be seen that 
 heads 2 and 3, row 2, differ only in length ; now the group 
 represented by head 2 varied in length from that of 1 to 
 that of 3. In separating 2 and 3, it might easily happen 
 that some of 3 should be placed with 2. In this case 
 the progeny of 3 would show a few heads like 1, and this 
 was the case. I have shown in the photograph only the 
 heads called for by theory, for it would only lead to con- 
 fusion to include the exceptions which would probably 
 not have occurred if 2 and 3 of row 2 had been accurately 
 separated last year. Again, in the progeny of the group 
 represented by head 5, row 2, only five of the six types 
 shown (row 3, heads 8-13) were found in this particular 
 case, though all six were found in most of the others. 
 As the missing type should constitute only 4^ per cent 
 of the group, and as it differed from one of the others 
 only slightly, it is possible that it was included with the 
 related type when the selections were made. 
 
Heredity 199 
 
 ''I have not yet seen the data for the third generation 
 of all these wheats, but those which are at hand are 
 decidedly interesting. The following are the data for 
 the third generation of the cross between Jones Winter 
 Fife (male) and Little Club (female). The fife is long- 
 headed and has velvet chaff (F) ; the Club short-headed, 
 and has glabrous chaff (G). Velvet proved to be domi- 
 nant over glabrous and the hybrids were intermediate in 
 length. Type I of the second generation included the 
 two t}Tpes VL and VgL, since these could not be distin- 
 guished by external appearances. Seed of Type I pro- 
 duced in the third generation : — 
 
 Percentage of Types 
 Plot I = FL ll = GL 
 
 1 87 13 
 
 2 8]_ 29_ 
 
 Theory 83^ IGf 
 
 The figures for the remaining five second-generation types 
 are as follows : — 
 
 
 
 
 Type II = 
 
 GL 
 
 
 
 
 
 
 
 Percentage op 
 
 Types 
 
 
 Plot 
 
 
 
 
 II 
 
 
 
 1 
 
 
 
 
 100 
 
 
 
 2 
 
 
 
 
 100 
 
 
 
 Theory 
 
 
 • 
 
 100 
 
 
 
 
 Type III = VI 
 
 AND Vgl 
 
 
 
 Plot 
 
 I 
 
 II 
 
 III 
 
 IV 
 
 V 
 
 VI 
 
 1 
 
 21 
 
 7 
 
 38 
 
 9 
 
 20 
 
 5 
 
 2 
 
 19 
 
 ii 
 
 38 
 
 12 
 
 15 
 
 41 
 
 Theory 
 
 201 
 
 41 
 
 41f 
 
 8i 
 
 201 
 
 4i 
 
200 
 
 Plant-Breeding 
 
 Plot 
 
 Type IV = GI 
 
 II IV VI 
 
 28 52 20 
 
 31 47 22 
 
 Theory 
 
 
 25 
 
 50 
 
 2^ 
 
 
 Type V = VC 
 
 AND VgC 
 
 
 Plot 
 
 I 
 
 II 
 
 V 
 
 VI 
 
 1 
 2 
 
 2.4 
 4.7 
 
 2.6 
 
 80.0 
 
 79.8 
 
 17.6 
 12.9 
 
 Theory 
 
 
 Type VI 
 
 83f 
 
 161 
 
 Plot 
 
 
 II 
 
 
 VI 
 
 1 
 2 
 
 
 7.7 
 
 
 92.3 
 100.0 
 
 Theory 
 
 100.0 
 
 "The only departures from theory of any consequence 
 in these data are the occurrence of small amounts of 
 Types I and II in the progeny of V, and of II in the prog- 
 eny of \T. Now, Type V of the second generation 
 {VC and VgC) differed from Type III (VI) only in being 
 slightly shorter. If a few individuals of III had been 
 included in V in separating the types of the second gen- 
 eration, we should have the actual result obtained in the 
 third generation. Likewise, Type VI of the second gen- 
 eration (GC) differed from II (GI) in the same manner. 
 Evidently a few plants of II got into the Type VI last 
 year, and thus gave the results shown." 
 
 Mendelism smmnarized. — This, in barest epitome, is the 
 teaching of Mendel. This teaching strikes at the root 
 of two or three difficult and vital problems. It represents 
 
Heredity 201 
 
 a new conception of the proximate mechanism of heredity, 
 although it does not represent a complete hypothesis of 
 heredity, since it begins with the gametes after they are 
 formed and does not account for the constitution of the 
 gametes, nor the way in which the parental characters 
 are impressed upon them. This hypothesis focuses our 
 attention along new lines, and will arouse more discussion 
 than Weismann's h\T)othesis did ; and it will have a much 
 wider influence. Whether it expresses the actual means 
 of heredity or not it is yet much too earlj^ to say ; but 
 this h^-pothesis is a greater contribution to science than 
 the so-called ''Mendel Law" as to the numerical results 
 of h\'bridization : the hypothesis attempts to explain the 
 "law." 
 
 One great merit of the hj^^othesis is the fact that its 
 basis is a morphological unit, or at least an appreciable 
 unit, not a mere imaginary concept. This unit should be 
 capable of direct study, at least in some of its phases. 
 It would seem that the mendelian hj^jothesis would give 
 a new direction to cytological research. ^ 
 
 It is yet too early to say how far ^lendel's law appUes. 
 We shall need to restudy the work that has been done 
 and to do new work along more definite lines. There 
 are relatively few former results or experiments that can 
 be conformed to Mendel's law, because the data are not 
 complete enough or not made from the proper point of 
 view. We should expect the fundamental results to 
 be masked when the plants -^-ith which we work are 
 
 ^ See, for example, "A Cytological Basis for the Mendelian Laws," 
 Bull. Torr. Bot. Club, 29, 657 (1902), by W. A. Cannon; and other 
 papers of this kind. 
 
202 Plant-Breeding 
 
 themselves unstable, when cross-fertilization is allowed 
 to take place, or when the pairs of contrasting characters 
 are very numerous and very complex. 
 
 Application to plant-breeding. — The wildest prophecies 
 have been made in respect to the appUcation of Mendel's 
 law to the practice of plant-breeding, for the mathe- 
 matical formulae express only definiteness and precision. 
 Unfortunately, the formulae cannot express the indefinite- 
 ness and the unprecision which even Mendel found in his 
 work. The greatest benefit of Mendel's work to the 
 plant-breeder will be in improving the methods of ex- 
 perimenting. We can no longer be satisfied with mere 
 ''trials" in hybridizing: we must plan the work with 
 great care, have definite ideals, ''work to a Une," and 
 make accurate and statistical studies of the separate 
 marks or characters of plants. His work suggests what 
 we are to look for. 
 
 The time may come when the hybridizer will be able 
 with many plants to make out beforehand plans and speci- 
 fications for their breeding and for carrying these through 
 with a large degree of exactness. 
 
 The best breeders now breed to unit-characters, for this 
 is the significance of such expressions as "avoid breeding 
 for antagonistic characters," "breed for one thing at a 
 time," "know what you want," "have a definite ideal," 
 "keep the variety up to a standard." In certain classes 
 of plants the mendelian laws will be found to apply with 
 great regularity, and in these we shall be able to know be- 
 forehand about what to expect (Fig. 48). The number of 
 cases in which the law or some modification of it applies 
 is being extended daily, both for animals and plants ; but 
 
FEMALE PARENT 
 Variety — Yellow Plum 
 
 F. HYBRID 
 
 MALE PARENT . 
 Variety — Quarter Century 
 
 Height— hiH 
 
 Color — yellow 
 Size — small jilitni. 
 
 4^ 
 
 Height— <o/t 
 
 Color — red 
 
 Size — small plum 
 
 Height— dwarf 
 Color — red 
 Size— small plum 
 
 M^ 
 
 Helzht— tall 
 
 Color — red 
 
 Size — large round 
 
 
 Height — dwarf 
 
 Color— rcrf 
 
 Size — large round 
 
 Height— ;a« 
 
 Color — red 
 
 Size — intermediate 
 
 F2 HYBRIDS 
 
 Height— <a« 
 
 Color— red 
 
 Size — intermediate 
 
 Height — dwarf 
 Color — red 
 Size— intermediate 
 
 Height— /aZi 
 Color — yellow 
 Size — intermediate 
 
 Height— rfifor/ 
 Color — yellow 
 Size — intermediate 
 
 Height— d war/ 
 Color — red 
 Size— {arye rOund 
 
 Height— toH 
 Color — yellow 
 Size — amall plum 
 
 Height— dwarf 
 Color — yellow 
 Size — small plum 
 
 Height— tall 
 Color — yellow 
 Size— large round 
 
 "Height— dwarf 
 CQlor-yellow 
 Size — large round 
 
 Fig. 48. — Mendelism in tomatoes. There were found in a field of F2 
 hybrids, the 12 distinct types, ilhistrated above. This redistribution 
 of characters illustrates an important economic bearing of Mendel s 
 law. 
 
 203 
 
204 Plant-Breeding 
 
 in practice we shall probably find as many exceptions to 
 the formulae as confirmations of them, even though the 
 exceptions can be explained, after we fiiid them, by Men- 
 del's principles of heredity. 
 
 The probable limits of mendelism in the production of 
 new varieties. — It has been said that we shall soon be 
 able, as a result of Mendel's discoveries, to predict varie- 
 ties in plant-breeding. Before considering this question, 
 we must recall the fact that a cultural variety is a succes- 
 sion of plants with characters sufficiently marked and 
 uniform to make it worth while cultivating in place of 
 some older variety. Now and then it may be worth 
 while to introduce some new energy or new trend into a 
 general lot of offspring by making wholesale crosses, not 
 expecting ever to segregate any particular variety or 
 strain from the progeny ; but these cases are rare, and the 
 gain is indefinite and temporary. So far as our knowledge 
 at present goes, we see no warrant for the hope that we can 
 predict varieties with any degree of exactness, at least 
 not beyond a very narrow effort. Following are some of 
 the reasons that seem to argue against the probability 
 of useful prophecy of varieties so far as the mende- 
 lian results are concerned : (1) We do not know what 
 plants will mendelize until we try. (2) Even in plants 
 that do not mendelize, one-half of the offspring have 
 stable characters. But we cannot predict for even this 
 half, for it is impossible to determine beforehand which 
 seeds showing dominant characters (and these are three- 
 fourths of the offspring) will ''come true." Dominance, 
 as we have seen, is of two kinds in respect to its behavior 
 in the next generation, — constant and hybrid; and the 
 
Heredity 205 
 
 hybrid dominance, which is twice as frequent as the 
 other, breaks up into constant dominance, hybrid domi- 
 nance, and recessiveness. (3) Mendel's law deals pri- 
 marily with mere characters, not with a variety or with 
 a plant as a whole. Every plant is a composite of a mul- 
 titude of characters, and from the plant-breeder's point 
 of view there may be as many undesirable characters as 
 desirable ones. No plant is perfect ; if it were, there 
 would be no need of plant-breeding. The breeders want 
 to preserve the desirable characters or traits and elimi- 
 nate the undesirable ones ; but under the strict interpre- 
 tation of mendelism this may be difficult and perhaps 
 impossible. The one egg gamete and the one sperm 
 gamete that unite to make the new plant, each contains 
 all the alternative parental characters; these various 
 characters appear in the offspring, and all that the breeder 
 gains is a new combination or arrangement of characters, 
 and the undesirable attributes may be as troublesome 
 as before. (4) The breeder usually wants wholly new 
 characters as well as recombinations of old ones, or he 
 wants augmented characters, and these lie outside the 
 true mendelian categories. For example, a carnation 
 grower wants a four-inch flower, but he has only three- 
 inch flowers to work with, and the augmentation of char- 
 acters is no part of the original mendelian law. Perhaps 
 these augmented and new characters are to be got by 
 means of ordinary variation and selection, or other extra- 
 crossing means ; but we know, as a matter of fact, that 
 augmented characters do sometimes appear in hybrids. 
 (5) New and unpredictable characters are likely to arise 
 from the influence of environment or other causes, and 
 
206 Plant-Breeding 
 
 very likely may be recorded in the gametes and vitiate 
 the final results. (6) Variability itself may be a unit- 
 character and therefore pass over. There is probably 
 such a thing as a ''tendency to vary," wholly aside from 
 the fact of variation. (7) Many of the plants with which 
 we need most to work in plant-breeding are themselves 
 eminently variable, and the results, even if there is true 
 mendelism, may be so uncertain as to be wholly unpre- 
 dictable. (8) Many plants with which we must work 
 will not close-fertilize. Some of them are monoecious or 
 dioecious. Even if there is gametic purity in such plants, 
 the probability is that the fact can be discovered only by 
 a long line of scientific experimenting for that particular 
 purpose and not by the work of the man who desires only 
 to breed new plants. (9) A cultural variety, in any true 
 acceptation of the term, is a series of closely related 
 plants having a pedigree. It runs back to one individ- 
 ual plant, from which propagation has been made 
 by seeds or asexual parts. Now, one can never predict 
 just what combination of characters any plant will have, 
 even though it be strictly mendelian. A person might 
 have a thousand hybrids of which no one plant shows any 
 two characters in the proportion of 3 to 1 (both seed-char- 
 acters may appear in the same pod or in different pods) on 
 the same plant, let alone all the characters as 3 to 1 or in 
 other definite relation ; and yet the total average numeri- 
 cal results might conform exactly to the mendelian law. 
 Mendel's law is a law of averages. For example, in ten 
 plants of peas, Mendel found the following ratios in respect 
 to seed-shape and seed-color. (Similar ratios were found 
 for other characters.) 
 
Heredity 
 
 207 
 
 Shape 
 
 Color 
 
 Shape 
 
 Color 
 
 3.75 
 
 
 2.27 
 
 
 4.33 : 1 
 
 3.33 : 1 
 
 3.37 
 
 
 4.57 
 
 
 3.66 
 
 1 
 
 2.43 
 
 1 
 
 3.43 
 
 
 2.80 
 
 
 2.20 
 
 1 
 
 4.88 
 
 1 
 
 1.90 
 
 
 2.59 
 
 
 4.66 
 
 1 
 
 3.57 
 
 1 
 
 2.91 
 
 
 1.85: 
 
 
 3.57 
 
 1 
 
 2.44 
 
 1 
 
 Mendel reports one instance in which the ratio in seed- 
 shape was 21 to 1, and another of 1 to 1. He also reports 
 instances of seed-color of 32 to 1, and 1 to 1. It has been 
 said that, because of Mendel's work, we shall be able to 
 produce hybrid varieties with the same certainty that we 
 produce chemical compounds. Now, a plant is made 
 up of many combinations of many units, and these com- 
 binations are the results of mathematical chance or prob- 
 ability. Of course, when the offspring are numerous, 
 all possible combinations are likely to occur; but these 
 occurrences are essentially fortuitous. Chemical com- 
 pounds are specific entities in which the parts combine by 
 necessity with definiteness. The comparison is fallacious 
 and the conclusion unsound. 
 
 We must remember that there are whole classes of cases 
 of plant-breeding that do not fall under hybridization at 
 all. Granting the de Vriesan view that selection is incom- 
 petent to produce species from individual fluctuations, it 
 is nevertheless well established (and admitted by de Vries) 
 that very many of our best cultural varieties have been 
 brought to their present state of perfection by means of 
 selection ; and by selection they are maintained in their 
 usefulness. Selection will always be a most important 
 agency in the hands of the gardener and the plant-breeder 
 
208 Plant-Breeding 
 
 — none the less so now that we have challenged its role 
 in the evolution of the plant kingdom. For the time 
 being, the new discussions of hybridizations are likely 
 to overshadow all other agencies in plant-breeding; but 
 selection under cultivation is as important now as it was 
 in the days of van Mons and Darwin. 
 
 Conclusion. — Now, in conclusion, what are the great 
 things that we have learned 'from these newer studies? 
 (1) In the first place, we have been brought to a full stop 
 in respect to our ways of thinking on these evolution 
 subjects. (2) We are compelled to give up forever the 
 taxonomic idea of rigid species as a basis for studying the 
 process of evolution. (3) The experimental method has 
 finally been completely launched and set under way. 
 Laboratory methods, comparative morphology, embry- 
 ological recapitulation, life-history studies, ecological in- 
 vestigations — all these means are likely to be overshad- 
 owed for a time by experiments in actually growing the 
 things under conditions of control. (4) We must study 
 great numbers of individuals and employ statistical 
 methods of comparison. (5) The doctrine of discontin- 
 uous evolution is now clearly before us. (6) We are 
 beginning to find a pathway through the bewildering maze 
 of hybridization. 
 
CHAPTER VIII 
 HOW DOMESTIC VARIETIES ORIGINATE 
 
 ''The key is man's power of accumulative selection: 
 nature gives successive variations ; man adds them up 
 in certain directions useful to him." This, in Darwin's 
 phrase, is the essence of the cultivator's skill in ameliorat- 
 ing the vegetable kingdom. So far as man is concerned, 
 the origin of the initial variation is largely chance, but 
 this start or variation once given, he has the power, in 
 most cases, to perpetuate it and to modify its characters. 
 There, then, are two very different factors or problems 
 in the origination of garden varieties, — the production 
 of the first departure or variation, and the subsequent 
 breeding of it. Persons who give little thought to the 
 subject look upon variation as the end of their endeavors, 
 thinking that a form comes into being with all its char- 
 acters well marked and fixed. In reality, however, 
 variation may be but the beginning in the process ; selec- 
 tion is the end so far as the plant-breeder is concerned. 
 
 Indeterminate varieties. — There are two general classes 
 of garden varieties in respect to the method of their 
 origin, — those that come into existence somewhat 
 suddenly and which require little else of the husband- 
 man than the multiplication of them, and those that 
 p 209 
 
210 Plant-Breeding 
 
 are the result of a slow evolution or direct breeding. The 
 former are indeterminate or uncertain, and the latter are 
 determinate or definite. The greater part of those in the 
 first class are plants that are multiplied or divided by 
 bud-propagation. They comprise nearly all our fruits, 
 the woody ornamental plants, and such herbaceous gen- 
 era as begonia, canna, gladiolus, lily, dahlia, carnation, 
 chrysanthemum, and the like, — in fact, all those multi- 
 plied by grafting, cuttings, bulbs, or other asexual parts. 
 The original plant may be either a seedling or a bud-sport. 
 The gardener, who is always on the look-out for novelties, 
 discovers its good qualities and propagates it. 
 
 Varieties which are habitually multiplied by buds, as 
 in those plants that have been mentioned in the last para- 
 graph, vary widely when grown from seeds, so that every 
 seedling may be markedly distinct. As soon, however, as 
 varieties are widely and exclusively propagated by seeds, 
 they develop a capability of carrying the greater part of 
 the individual differences down to the offspring. That 
 is, seedlings from bud-multiplied plants do not ''come 
 true," as a rule, whilst those from seed-propagated plants 
 do ''come true." The reason of this difference will be- 
 come apparent on a moment's reflection. In the seed- 
 propagated plants, like the kitchen-garden vegetables 
 and the annual flowers, we select the seeds and thereby 
 eliminate all those variations which would have arisen had 
 the discarded seeds been sown. In other words, we are 
 constantly fixing the tendency to ''come true," for this 
 feature of plants is as much a variation as is form or 
 color or any other attribute. Suppose, for example, that a 
 certain variation were to receive two opposite treatments, 
 
How Domestic Varieties Originate 211 
 
 the seeds from one-half of the progeny being carefully 
 selected year by year, and all those from untypical plants 
 discarded, whilst in the other half all the seeds from all 
 the plants, whether good or bad, are saved and sown. In 
 the one case, it will be seen, we are fixing the tendency 
 to '^come true," for this is all that constitutes a horticul- 
 tural variety, — a brood very much like all its parents. 
 In the other case, we are constantly eliminating the 
 tendency to ''come true" by allowing every modifying 
 agency full chance. So the very act of taking seeds only 
 from plants that have ''come true," tends still more 
 strongly to fix the hereditary force within narrow limits. 
 Working against this restrictive force, however, are all 
 the agencies of environment and atavism, so that, fortu- 
 nately, now and then a seed gives a "rogue," or a plant 
 widely unlike its parents, and this may be the start for a 
 new variety. 
 
 With bud-multiplied varieties, however, the case is 
 very different. Here every seed may be sown, as in the 
 illustrative case above, because the seedlings are not 
 wanted for themselves, but only as stocks on which 
 to bud or graft the desired varieties. So there is no seed 
 selection in the ordinary propagation of apples, pears, 
 peaches, and the usual orchard fruits. The seeds are 
 taken indiscriminately from pomace or the refuse of can- 
 ning or evaporating factories. Moreover, many such 
 varieties are hybrid, and when propagated by seed, split 
 up into many forms. But every annual garden vegetable 
 is always grown from seeds more or less carefully saved 
 from plants that possess some desired attribute. There is 
 no reason why the tree fruits should not reproduce them- 
 
212 Plant-Breeding 
 
 selves from seeds just as closely as do the annual herbs, 
 if they were to be as carefully propagated by selected seeds 
 through a long course of generations. There is excellent 
 proof of this in the well-marked races or families of Rus- 
 sian apples. In that country, grafting had been little 
 employed, and consequently it has been necessary to select 
 seeds only from acceptable trees in order that the off- 
 spring might be more acceptable. So the Russian apples 
 have come to run in groups or families, each family bear- 
 ing the mark of some strong ancestor. Most of the 
 seedlings of the Oldenburg are recognizable because of 
 their likeness to the parent. We may thus trace an 
 incipient tendency in our own fruits towards racial 
 characters. The Fameuse type of apples, for example, 
 tends to perpetuate itself ; and a similar tendency is very 
 well marked in the Damson and Green Gage plums, the 
 Orange quince. Concord grapes, and Hill's Chili and 
 Crawford peaches. But inasmuch as bud-multiplication 
 is so essential in nursery practice, we can hardly hope 
 for the time when our trees and shrubs, or even our per- 
 ennial herbs, will ''come true" with much certainty. In 
 them, therefore, we get new varieties by simply sowing 
 seeds ; but in seed-propagated varieties we must depend 
 either on chance variations or else we must resort to 
 definite plant-breeding. 
 
 Plant-breeding. — The breeding of domestic animals is 
 attended, for the most part, with such definite and often 
 precise results that there has come to be a general desire 
 to extend the same principles to plants. It is not unusual 
 to hear well-informed people say that it is possible to breed 
 plants with as much certainty and exactness as it is to 
 
Holo Domestic Varieties Originate 
 
 213 
 
 73 
 O 
 O 
 
 2 
 
 'So 
 
 o 
 
 o 
 
 o 
 
 05 
 
 
214 
 
 Plant-Breeding 
 
 -a 
 
 
 c3 
 
 s 
 
 o 
 
 f/3 
 
 > 
 o 
 
 
 CC 
 
 o 
 6 
 
How Domestic Varieties Originate 215 
 
 breed animals. The fact is, however, that such exactness 
 will never be possible, because plants are very unlike 
 animals in organization, and because, also, the objects 
 sought in the two 
 cases are character- 
 istically unlike. 
 Plants, as we have 
 seen, are made up 
 of a colony of poten- 
 tial individuals, and 
 to breed between 
 two plants by cross- 
 ing means that we 
 must choose the 
 sex-parents from 
 amongst as many 
 individuals as there 
 are flowers or 
 branches on the two 
 plants, whilst in 
 animals we choose 
 two definite personal 
 parents. And these 
 
 personal parents are Fig. 51. — improving the tomato : A, fruit of 
 
 either male or fe- approximately ideal form secured by cross- 
 
 , 1 , . ing and selection; B, fruit showing im- 
 
 male, and the union perfections and undesirable characters, 
 
 is essential to the (Yearbook, U. S. Dept. Agric.) 
 
 production of offspring, whilst in plants each parent — 
 that is, each flower — is usually both male and female 
 and the union of two is not essential to the produc- 
 tion of offspring, for the plant is capable of multiplying 
 
216 
 
 Plant-Breeding 
 
 itself by buds. The element of chance, therefore, is one 
 hundred, or more, to one in crossing plants as compared 
 with crossing animals. Then, again, the plant-parents 
 may be modified profoundly by every environmental condi- 
 tion of soil and temperature and sunshine, or other ex- 
 ternal conditions, since they possess no bodily tempera- 
 
 /s 
 
 /4 
 /J 
 
 
 
 
 
 
 
 
 
 
 ///^ 
 
 ^ P/ 
 
 :>/: P. 
 
 &■/ 
 
 
 
 
 
 
 
 
 / 
 
 
 
 ^^ 
 
 
 
 
 
 
 / 
 
 
 
 / 
 
 
 
 ^^'^> 
 
 
 
 
 
 / 
 
 / 
 
 
 y 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 ^ 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 N 
 
 "\ 
 
 y 
 
 \ 
 
 
 y 
 
 ^l-c 
 
 ^yfy 
 
 ^t.P 
 
 '9f. 
 
 
 
 
 
 
 \ 
 
 
 y 
 
 ^ 
 
 
 \ 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 / 
 
 ^ ^ ^ ^s ^ ^ 
 
 ^ 
 
 /L 
 
 *Jf ^O ^Jt ^yy '/■» 
 
 Fig. 52. — Crop averages in corn breeding for high and for low protein. 
 Results of twelve generations. (Illinois Experiment Station.) 
 
 ture, no choice of conditions, and no volition to enable 
 them to overcome the circumstances in which they are 
 placed. Animals, on the contrary, have all these ele- 
 ments of personality, and the breeder is also able to con- 
 trol the conditions of their lives to a nicety. In view of 
 all these facts, it is not strange that animals can be bred 
 by crossing with more confidence than can plants. But 
 there is another and even more important difference 
 
HoiD Domestic Varieties Originate 
 
 217 
 
 between the breeding of animals and the breeding of 
 plants. In animals, our sole object is to secure simply 
 one animal or one brood of offspring. In plants, our 
 object is, in general, to secure a race or generation of 
 
 Fig. 53. — Fruit of wild elderberry. 
 
 offspring, which may be disseminated freely over the 
 earth. In the bovine race, for example, our object in 
 breeding is to produce one cow with given characters; 
 in turnips, our object is to produce a new variety, the 
 seed of which will reproduce the variety, whether sown in 
 Pennsylvania or Ceylon. It is apparent, therefore, that 
 
218 
 
 Plant-Breeding 
 
 any comparisons drawn between the breeding of animals 
 and plants are likely to be fallacious. 
 
 Is there, then, any such thing as plant-breeding, any 
 possibility that the operator can proceed with some con- 
 
 FiG. 54. — Fruit of a cultivated variety of the elderberry which appeared 
 as a variation from the wild form. 
 
 fidence that he may obtain the ideal he has in mind? 
 Yes, to a certain extent. 
 
 Plant-breeding by selection. — It is apparent that the 
 very first effort on the part of the plant-breeder must be 
 to secure individual differences ; for so long as the plants 
 
How Domestic Varieties Originate 
 
 219 
 
 that he handles are very closely alike, so long there will 
 be little hope of obtaining new varieties. He must, 
 therefore, cause his plants to vary. In plants that 
 are comparatively unvariable, it is frequently impossible 
 to produce variations in the desired direction at once, but 
 it is more important to ''break" the type, — that is, to 
 
 Fig. 55. — Field of wilt-resistant watermelons, growing free from disease 
 on infected land. (From Yeaibook.) 
 
 make it depart markedly from its normal behavior in 
 any or many directions. If the type once begins to vary, 
 to break up into different forms, the operator may expect 
 that it will soon become plastic enough to allow of modi- 
 fication in the ways he desires. But whilst it is impor- 
 tant or even necessary to break a well-marked type into 
 many forms, it would no doubt be unwise to encourage this 
 
220 
 
 Plant-Breeding 
 
 tendency after it once appears, lest the plant acquire a too 
 strong habit of scattering. This initial variation is induced 
 by changing the conditions in which the plant has habit- 
 ually grown, as a change of seed, change of soil, tillage, 
 varying the food supply, crossing, and the like. 
 
 As a matter of fact, however, nearly all plants that 
 
 Fig. 56. — Disease resistance in cowpeas. Showing a variety which 
 is immune (on the left) and a susceptible variety (on the right) 
 to cowpea wilt. 
 
 have been long cultivated are already sufficiently variable 
 to afford a starting-point for breeding. The operator 
 should have a vivid mental picture of the variety which 
 he designs to obtain ; then he should select that plant in 
 his plantation which is nearest his ideal, and sow the 
 seeds of it. From the seedlings he should again select 
 his type, and so on, generation after generation, until 
 
Hotv Domestic Varieties Originate 
 
 221 
 
 the desired object is attained. It is important, if he is 
 to make rapid progress, that he keep the same ideal in 
 
 (1) Grand Rapids, one parent 
 used in developing improved 
 types. 
 
 (2) Golden Queen, the other 
 parent used in developing 
 improved types. 
 
 (3) New loose type for the 
 western market, secured by 
 crossing the varieties shown 
 in (1) and (2). 
 
 (4) New head type for eastern 
 conditions, secured by cross- 
 ing the varieties shown in 
 (1) and (2). 
 
 Fig. 57. — Improved types of lettuce and the varieties from which 
 
 they were developed. 
 
 mind year after year, otherwise there will be vacillation, 
 and the progress of one year may be undone by a counter- 
 direction the following year. In this way it will be 
 
222 Plant' Breeding 
 
 found that almost any character of a plant may be either 
 intensified or lessened within certain limits. This is man's 
 nearest approach to the Creator in his control over the 
 physical forms of fife, and it is great and potent in pro- 
 portion as it sets for itself correct ideals in the beginning 
 and adheres to them until the end. 
 
 For examples of improvement by selection see Figs. 49- 
 56, that represent familiar results. 
 
 RULES FOR BREEDING PLANTS 
 
 When beginning this selection or breeding for an ideal, 
 it is important that impossible or contradictory results be 
 avoided. Some of the cautions and sugges-tions that 
 need to be considered are these : — 
 
 1. Avoid striving after features that are antagonistic 
 or foreign to the species or genus with which you are 
 working. Every group of plants has become endowed 
 with certain characters or lines of development, and the 
 cultivator will secure quicker and surer results if he works 
 along the same lines, rather than attempt to thwart them. 
 Nature gives the hint : let man follow it out, rather than 
 to endeavor to create new types of characters. Consider 
 some of the solanaceous plants for examples. There 
 are certain types of the genus Solanum which have a 
 natural habit of tuber-bearing, as the potato. Such 
 species should be bred for tubers and not for fruits. There 
 are other Solanums, however, as the egg-plants and the 
 pepinoes, which naturally vary or develop in the direc- 
 tion of fruit-bearing, and these should be bred for fruits 
 and not for tubers ; and the same should be true in the 
 related genera of tomatoes, red peppers, and physalis. 
 
How Domestic Varieties Originate 223 
 
 Those ambitious persons who are always looking for a 
 tuber-bearing tomato, therefore, might better concen- 
 trate their energies on the potato, for the tomato is not 
 developing in that direction ; and even if the tomato 
 could be made to produce tubers, it would thereby lessen 
 its fruit production, for plants cannot maintain two diverse 
 and profitable crops at the same time. It is more rea- 
 sonable, and certainly more practicable, to grow potatoes 
 on potato plants and tomatoes on tomato plants. 
 
 2. The quickest and most marked results are to be ex- 
 pected in those groups or species which are normally the 
 most variable. There are a greater number of variations 
 or starting-points in such species ; but it also follows that 
 the forms are less stable, the more the species is variable. 
 Yet the variations, being very plastic, yield themselves 
 readily to the wishes of the operator. Carri^re puts the 
 thought in this form: ''The stabihty of forms, in any 
 group of plants, is, in general, in inverse ratio to the num- 
 ber of the species which it contains, and also to the degree 
 of its domestication." 
 
 The most variable types are the most dominant ones 
 over the earth ; that is, they occur in greater numbers 
 and under more diverse conditions than the compara- 
 tively invariable types do. The Compositse, or sunflower- 
 hke plants, comprise a ninth or tenth of the total species 
 of flowering plants, and the larger part of the subordinate 
 types or genera contain many forms or species. Aster, 
 goldenrod, the hawkweeds, thistles, and other groups, are 
 representative of the cosmopolitan or variable types of 
 composites. Whenever, for any reason, any type begins to 
 decline in variabiHty, it usually begins to perish ; it is then 
 
224 Plant-Breeding 
 
 tending towards extinction. Monotypic genera — those 
 which contain but a single species — are usually of local 
 or disconnected distribution, and are probably, for the 
 most part, vanishing remnants of a once important type. 
 As a rule, most of our widely variable and staple culti- 
 vated species are members of large, or at least polytypic, 
 genera. Such, for example, are the apples and pears, 
 peaches and plums, oranges and lemons, roses, bananas, 
 chrysanthemums, pinks, cucurbits, beans, potatoes, 
 grapes, barley, rice, cotton. A marked exception to this 
 statement is maize, which is immensely variable and is 
 generally held to have come from a single species ; but 
 the genesis of maize is unknown, and it is possible that 
 more than one species is concerned in it. Wheat is also 
 a partial exception, although the original specific type is 
 not understood ; and the latest monographers admit three 
 or four other species to the genus, aside from wheat. 
 There are other exceptions, but they are mostly unim- 
 portant, and, in the main, it may be said that the domi- 
 nant domestic types of plants represent markedly poly- 
 typic genera. 
 
 3. Breed for one thing at a time. The person who 
 strives at the same time for increase or modification in 
 proUficacy and flavor will be likely to fail in both. He 
 should work for one object alone, simply giving sufficient 
 attention to subsidiary objects to keep them up to normal 
 standard. This is really equivalent to saying that there 
 can be no such thing as the perfect all-around variety that 
 so many people covet. Varieties must be adapted to 
 specific uses, — one for shipping, one for canning, one for 
 dessert, one for keeping qualities, and the like. The 
 
How Domestic Varieties Originate 225 
 
 more good varieties there are of any species, the more 
 widely and successfully that species can be cultivated. 
 A knowledge of Mendel's laws of heredity assists the 
 breeder to secure more rapidly the proper combination 
 of qualities and to fix them. 
 
 4. Do not desire contradictory attributes in any variety. 
 A variety, for example, that bears the maximum number 
 of fruits or flowers cannot be expected greatly to increase 
 the size of those organs without loss in numbers. This is 
 well shown in the tomato. The original tomato produced 
 from six to ten fruits in a cluster, but as the fruits in- 
 creased in size the numbers in each cluster fell to two or 
 three. That is, increase in size proceeded somewhat at 
 the expense of numerical productivity ; yet the total 
 weight of fruit to the plant has greatly increased. The 
 same is true of apples and pears ; for whilst these trees bear 
 flowers in clusters, they generally bear their fruits singly. 
 Originally, every flower normally set fruit. The reason 
 why blackberries, currants, and grapes do not increase 
 more markedly in size, is probably because the size of 
 cluster has been given greater attention than the size of 
 berry. Plants which now bear a full crop of tubers can- 
 not be expected to increase greatly in fruit bearing, as 
 already explained under Rule 1. This fact is illustrated 
 in the potato, in which, as tuber-production has increased, 
 seed-production has decreased, so that growers now com- 
 plain that potatoes do not produce bolls as freely as they 
 did years ago. 
 
 5. When selecting seeds, remember that the character 
 of the whole plant is more important than the character 
 of any one branch or part of the plant ; and the more 
 
 Q 
 
226 Plant-Breeding 
 
 uniform the plant in all its parts, the greater is the likeli- 
 hood that it will transmit its characters. If one is striv- 
 ing for larger flowers, for example, he \Adll secure better 
 results if he choose seeds from plants that bear large 
 flowers throughout, than he will if he choose them from 
 some one of the large flowering branches on a plant that 
 bears indifferent flowers on the remaining branches, even 
 though this given branch produces much larger flowers 
 than those borne on the large-flowered plant. Small 
 potatoes from productive hills give a better product than 
 large potatoes from unproductive hills. The habit of 
 selecting large ears from a bin of corn, or large melons 
 from the grocer's wagon, is much less efficient in producing 
 large products the following season than the practice of 
 going into the fields and selecting the most uniformly 
 large-fruited parents. A very poor plant may occasion- 
 ally produce one or two very superior fruits, but the seeds 
 are more Hkely to perpetuate the characters of the plant 
 than of the fruits. 
 
 The following experiences detailed by Henri L. de 
 Vilmorin illustrate the proposition admirably: ''I tried 
 an experiment with seeds of Chrysanthemum carinatum 
 gathered on double, single, and semi-double heads, all 
 growing on one plant, and found no difference whatever 
 in the proportion of single and double-flowered plants. 
 In striped verbenas, an unequal distribution of the color 
 is often noticed ; some heads are pure white, some of a 
 self-color, and most are marked with colored stripes on 
 white ground. I had seeds taken severally from all and 
 tested alongside one another. The result was the same. 
 All the seeds from one plant, whatever the color of the 
 
How Domestic Varieties Originate 227 
 
 flower that bore them, gave the same proportion of plain 
 and variegated flowers." 
 
 The second part of the proposition is equally as impor- 
 tant as the first, — the fact that a plant which is uniform 
 in all its branches or parts is more Ukely to transmit its 
 general features than one which varies within itself. 
 It is well known that bean plants often produce beans 
 with various styles of markings on the same plant or even 
 in the same pod, yet these variations rarely, if ever, perpet- 
 uate themselves. The same remark may be apphed to 
 variations in peas. These illustrations only add emphasis 
 to the fact that intending plant-breeders should give 
 greater heed than they usually do to the entire plant, 
 rather than confine their attention to the particular 
 part or organ which they desire to improve. 
 
 At first thought, it may look as if these facts are 
 directly opposed to the proposition emphasized in the first 
 chapter that every branch of a plant is a potential auton- 
 omy, but it is really a confirmation of it. The variation 
 itself shows that the branch is measurably independent, 
 but it is not until the conditions or causes of the variation 
 are powerful enough to affect the entire plant that they 
 are sufficiently impressed upon the organization of the 
 plant to make their effects hereditary through seeds. 
 
 There is an apparent exception to the law that the 
 character of the entire plant is more important than any 
 one organ or part of it, in the case of the seeds themselves. 
 That is, better results usually follow the sowing of large 
 and heavy seeds than of small or unselected seeds from the 
 same plant. This, however, does not affect the main 
 proposition, for the seed is in a measure independent of 
 
228 Plant-Breeding 
 
 the plant body, and is not so directly influenced by envi- 
 ronment as are the other organs. And, again, the seed 
 receives a part of its elements from a second or male 
 parent. The good results which follow the use of large 
 seeds are, chiefly, greater uniformity of crop, increased 
 vigor, often a gain in earliness and sometimes in bulk, 
 and usually a greater capacity for the production of 
 seeds. These results are probably associated less with 
 any innate hereditable tendencies than with the mere 
 vegetative strength and uniformness of the large seeds. 
 The large seeds usually germinate more quickly than the 
 small ones, provided both are equally mature, and they 
 push the plantlet on more vigorously. This initial 
 gain, coming at the most critical time in the life of the new 
 individual, is no doubt responsible for very much of the 
 result that follows. The uniformity of crop is the most 
 important advantage which comes of the use of large 
 seeds, and this is obviously the result of the elimination of 
 all seeds of varying degrees of maturity, of incomplete 
 growth and formation, and of low vitaUty. 
 
 Another important consideration touching the selection 
 of seeds, is the fact that very immature seeds give a feeble 
 but precocious progeny. This has long been observed 
 by gardeners, but Sturtevant, Arthur, and Goff have made 
 a critical examination of the subject. ''It is not the 
 sHghtly unripe seeds that give a noticeable increase in 
 earUness," according to Arthur, ''but very unripe seeds, 
 gathered from fruit (tomatoes) scarcely of full size and 
 still very green. Such seeds do not weigh more than 
 two-thirds as much as those fully ripe. They germinate 
 readily and are more easily affected by retarding or harm- 
 
How Domestic Varieties Originate 229 
 
 ful influences. If they can be brought through the early 
 period of growth and become well estabhshed, and the 
 fohage or fruit is not attacked by rots or blights, the 
 grower will usually be rewarded by an earlier and more 
 abundant crop of sHghtly smaller and less firm fruit. 
 These characters will be more shghtly emphasized in sub- 
 sequent years by continuous seed propagation." Goff 
 remarks that the increase in earliness in tomatoes, fol- 
 lowing the use of markedly immature seeds, ''is accom- 
 panied by a marked decrease in the vigor of the plant, and 
 in the size, firmness, and keeping quality of the fruit." 
 These results are probably closely associated with the 
 chemical constitution and content of the immature seeds. 
 The organic compounds have probably not yet reached 
 a state of stabiUty, and therefore they respond quickly 
 to external stimuli when placed in conditions suitable to 
 germination ; and there is httle food for nourishment of 
 the plantlet. The consequent weakness of the plantlet 
 results in a loss of vegetative vigor, which is earliness. 
 (See Rule 2.) 
 
 Still another feature connected with the choice of seeds 
 is the fact that in some plants, as in various Ipomoeas, for 
 example, the color of the seed is more or less intimately 
 associated with the color of the flower which produced 
 them and also with the color of the flower which they 
 will produce. 
 
 6. Plants that have any desired characteristics in 
 common may differ widely in their abiUty to transmit 
 these characters. It is usually impossible for the cul- 
 tivator to determine, from the appearance of any given 
 progeny, which is the most unvariable and the most Uke 
 
230 Plant- Breeding 
 
 its parent ; but it may be said that those individuals that 
 grow in the most usual or normal environments are most 
 likely to perpetuate themselves. A very unusual condi- 
 tion, as of soil, moisture, or exposure, is not easily im- 
 itated when providing for the succeeding generation, and 
 a return to normal conditions of environment may be ex- 
 pected to be followed by a more or less complete return 
 to normal attributes on the part of the plant. If the same 
 variation, therefore, were to occur in plants growing under 
 widely different conditions, the operator who wishes to 
 preserve the new form should take particular care to 
 select his seeds from those individuals that seem to have 
 been least influenced by the immediate conditions in 
 which they have grown. 
 
 Again, if the same variation appears both in uncrossed 
 and crossed plants, the best results should be expected 
 in selecting seeds from the former. We have already 
 seen, in the seventh chapter, how it is that crosses are 
 unstable, and how the unstability is likely to be the 
 greater the more violent the cross. ''Cross-breeding 
 greatly increases the chance of wide variation," writes 
 Henri L. de Vilmorin, ''but it makes the task of fixation 
 more difficult." 
 
 It is very important, therefore, when selecting seeds 
 from plants which seem to give promise of a new variety, 
 to sow seeds of each plant separately, and then make the 
 subsequent selections from the most stable generation ; 
 and it is equally important that the operator should not 
 trust to a single plant as a starting-point, whenever he 
 has several promising plants from which to choose. 
 
 7. The less marked the departure from the genus of 
 
How Domestic Varieties Originate 231 
 
 the normal type, the greater, in general, is the likeli- 
 hood that it will be perpetuated, although this may 
 not be true of sports. This is admirably illustrated in 
 crosses. The seed-progeny of crosses between closely 
 related varieties, or between different plants of the same 
 variety, is more uniform and usually more easy of improve- 
 ment by selection than the progeny of hybrids. In un- 
 crossed plants, the general tendency is to resemble their 
 parents, and the greater the number of like ancestors, 
 the greater is the tendency to ^'come true." There is 
 thought to be a tendency, though necessarily a weak 
 one, to return to some particular ancestor, or to ''date 
 back." This is known as atavism. The so-called ata- 
 vistic forms are likely to be unstable, to break up into 
 numerous forms, or to return more or less completely to 
 the type of the main line of the ancestry. The following 
 statements touching some of the relations of atavism to 
 the amelioration of plants are the results of an excellent 
 study of heredity in lupines by Louis Leveque-de Vil- 
 morin : — 
 
 ''1. The tendency to resemble its parents is generally 
 the strongest tendency in any plant ; 
 
 ''2. But it is notably impaired as it comes into conflict 
 with the tendency to resemble the general line of its 
 ancestry. 
 
 ''3. This latter tendency, or atavism, is constant, 
 though not strong, and scarcely becomes impaired by the 
 intervention of a series of generations in which no rever- 
 sion has taken place. 
 
 ''4. The tendency to resemble a near progenitor (only 
 two or three generations removed), on the other hand, is 
 
232 Plant-Breeding 
 
 very soon obliterated if the given progenitor is different 
 from the bulk of its ancestors." 
 
 8. The crossing of plants should be looked upon as a 
 means or starting-point, not as an end. We cross two 
 flowers and sow the seeds. The resulting seedlings may 
 be unlike either parent (see Fig. 57). Here, then, is varia- 
 tion. The operator should choose that plant which most 
 nearly satisfies his ideal, and then, by selection from its 
 progeny and the progeny of succeeding generations, gradu- 
 ally obtain the plant which he desires. It is only in plants 
 which are propagated by asexual parts — as grafts, cut- 
 tings, layers, bulbs, and the like — that hybrids or crosses 
 are commonly immediately valuable ; for in these plants 
 we really cut up and multiply the one individual plant 
 which pleases us in the first batch of seedlings, rather than 
 to take the offspring or seedlings of it. Thus, if any par- 
 ticular plant in a lot of seedlings of crosses of cannas, or 
 plums, or hops, or strawberries, or potatoes, is valuable, 
 we multiply that one individual. There is no reason for 
 fixing the variety. But any satisfactory plant in a lot of 
 seedlings of crosses of pumpkins, or wheat, .or beans, must 
 be made the parent of a new variety by sowing the seeds 
 of it and then by selecting for seed-parents, year by year, 
 those plants which are the best. ^'The unsettled forms 
 arising from crosses," Focke writes, ''are the plastic 
 material out of which gardeners form their varieties." 
 
 But even in the fruits, and other bud-propagated 
 plants, crossing may often be used to as good advantage 
 for the purpose of originating variation as it may in peas 
 or buckwheat. It only requires a longer time to fix and 
 select variations because the plants mature so slowly. 
 
How Domestic Varieties Originate 233 
 
 Ordinarily, if the operator does not find satisfactory plants 
 among the seedlings of any cross of fruit trees, he roots 
 up the whole batch as profitless. But if he were to allow 
 the best plants to stand and were to sow seeds from them, 
 the second generation might produce something more to 
 his liking. But it is generally quicker to make another 
 cross and to try the experiment over again, than to wait 
 for unpromising seedlings to bear. This repeated repeti- 
 tion of the experiment, however, — continual crossing 
 and sowing and uprooting, — is gambling. Throwing dice 
 to see what will turn up is a comparable proceeding. 
 The sowing of uncrossed seed is little better. Peter M. 
 Gideon sowed over a bushel of apple seed, and one seed 
 produced the Wealthy apple.^ D. B. Wier raised a mil- 
 lion seedlings of soft maple, and one plant of the lot had 
 finely divided leaves, and is now Wier's Cut-leaved maple. 
 Teas' Weeping mulberry, which is now so deservedly 
 popular, was, as Mr. Teas tells me, ''merely an accidental 
 seedhng." So this explains why the production of new 
 varieties of fruits is always chance, while a skilled man 
 can sit in his study in the winter time and picture to 
 himself a new bean or muskmelon, and then go out in the 
 next three or four summers and produce it. 
 
 9. If it is desired to employ crossing as a direct means 
 
 1 The facts in the origination of the Wealthy apple, as related to me 
 by Mr. Gideon, are these : he first planted a bushel of apple seeds and 
 then each year, for nine years, he planted enough to give a thousand trees. 
 At the end of ten years, all the seedlings had perished (this was in Min- 
 nesota) except one hard seedling crab. Then a small lot of seeds of 
 apples and crab apples was obtained in Maine, and from these the 
 Wealthy came. There were only about fifty seeds in the batch of crab 
 seed which gave the Wealthy; but before this variety was obtained, 
 much over a bushel of seed had been sown. 
 
234 Plant-Breeding 
 
 of producing new varieties, each parent to the proposed 
 cross should be chosen in agreement with the rules already 
 specified, and also because it possesses in an emphatic 
 degree one or more of the qualities which it is desired to 
 combine ; and the more uniformly and persistently the 
 parent presents a given character, the greater is the chance 
 that it will transmit that character. It has already been 
 said that crossing for the instant production of new va- 
 rieties is most certain to give valuable results in those 
 species which are propagated by buds, because the initial 
 individual differences are not dissipated by seed reproduc- 
 tion. This is especially true of crossing between distinct 
 species ; for in such violent crossing as this the offspring 
 is particularly likely to be unstable when propagated by 
 seeds. The results of hybridization appear to be most 
 certain in those plants grown under glass, and in which, 
 therefore, the selection of the seed-parents is most care- 
 fully made, and where the conditions of existence are 
 most uniform. The most remarkable results in hybridiza- 
 tion yet attained are with the choicer glass-house plants, 
 such as orchids, begonias, anthuriums, and the like. 
 
 The more violent the cross, the less is the likelihood 
 that desirable offspring will follow. Species which refuse 
 to give satisfactory results when hybridized directly or 
 between the pure stocks, may give good varieties when 
 the "blood" has become somewhat attenuated through 
 previous crossings. The best results in hybrichzing our 
 native grape with the European grape, for example, have 
 come from the use of one parent which is already a hy- 
 brid. Two notable examples are the Brighton and Diamond 
 Grapes, raised by Jacob Moore. The Brighton is a cross 
 
How Domestic Varieties Originate 235 
 
 of Concord (pure native) by Diana-Hamburg (hybrid of 
 impure native and European). Diamond is a cross of 
 Concord by lona, the latter parent undoubtedly of impure 
 origin, containing a trace of the European vine. T. V. 
 Munson's Brilliant is a secondary hybrid, its parents, 
 Lindley and Delaware, both containing hybrid blood. 
 Others of his varieties have similar histories. Even when 
 the cross is much attenuated — or three or four or even 
 more times removed from a pure hybrid origin by means 
 of subsequent crossings — it may still produce marked 
 effects in a cross without introducing such contradictory 
 characters as to jeopardize the value of the offspring. 
 
 Among American fruit plants there are comparatively 
 few valuable species-hybrids. The most conspicuous are 
 grapes, particularly the various Rogers varieties, such 
 as Agawam, Lindley, Wilder, Barry, and others, which 
 are hybrids of the European and native species. Other 
 hybrids are the Keiffer and allied pears (between the 
 common pear and the Oriental pear), probably the 
 Transcendent and a few other crabs (between the com- 
 mon apple and the Siberian crab), the Soulard and kin- 
 dred crabs (between the common apple and the native 
 Western crab), a few blackberries of the Wilson Early 
 type (between the blackberry and the dewberry), the 
 purple-cane raspberries (between the native red and 
 black raspberries, and possibly sometimes combined with 
 the European raspberry), the Utah Hybrid cherry (be- 
 tween the Western sand cherry and the sand plum), prob- 
 ably some plums, and a few others. There is undoubtedly 
 a fertile field for further work in hybridizing our fruits, 
 particularly those of native origin, and also many of the 
 
236 '■ Plant-Breeding 
 
 ornamental plants ; the danger is that persons are likely 
 to expect too much from hybridization, and too little 
 from the betterment of all the other conditions which so 
 profoundly modif}^ plants. Violent hybridizations gen- 
 erally give unsatisfactory and unreliable results; but 
 subsequent crossings, when the ''blood" of the original 
 species to the contract is considerably attenuated, may be 
 expected to correct or overcome the first incompatibility, 
 as explained above. 
 
 10. Establish the ideal of the desired variety firml}^ in 
 mind before any attempt is made at plant-breeding. If 
 one is to make any progress in securing new varieties, he 
 must first be an expert judge of the capabilities and merits 
 of the plants with which he is dealing, otherwise he may 
 attempt the impossible or he may obtain a variety that 
 has no merit. Make frequent use of a score-card to famil- 
 iarize yourself with all details. It is important, also, 
 that the person bear in mind the fact that a variety which 
 is simply as good as any other in cultivation is not worth 
 introducing. It should be better in some particular than 
 any other in existence. The operator must know the 
 points of his plant, as an expert stock-breeder knows the 
 points of an animal, and he must possess the rare judgment 
 to determine which characters are most likely to reappear 
 in the offspring. Inasmuch as a person can be an expert 
 in only a few plants, it follows that he cannot expect satis- 
 factory results in breeding any species that may chance 
 to come before him. Persistent and uniform effort, con- 
 tinued over a series of years, is usually demanded for 
 the production of really valuable varieties. Thus it often 
 happens that one man excels all competitors in breeding a 
 
How Domestic Varieties Originate 237 
 
 particular class of plants. The horticulturists will recall, 
 for example, Lemoine in the breeding of gladiolus, Eckford 
 in peas, Crozy in cannas, Bruant in pelargoniums, and 
 others. There are now and then varieties which arise 
 from no effort, but because of that very fact they reflect 
 no credit upon the so-called originator, who is really only 
 the lucky finder. So far as the originator is concerned, 
 such varieties are merely chance. If, however, the 
 operator — himself an expert judge of the plant with 
 which he deals — chooses his seeds with care and dis- 
 crimination, and then proposes, if need be, to follow up 
 his work generation after generation of plants by means 
 of selection, the work becomes plant-breeding of the 
 highest type. 
 
 First of all, therefore, the operator must know what 
 he can likely get, and what will likely be worth getting. 
 Many persons, however, begin at the other end of the 
 problem, — they get what they can, and then let 
 the public judge whether the effort has been worth 
 the while. 
 
 11. Having derived a specific and correct ideal, the 
 operator must next seek to make his plant vary in the 
 desired direction. This may be done by crossing, or by 
 modifjdng the conditions under which the plant grows. 
 If there are any two plants that possess indications of 
 the desired attributes, cross them ; among the seedhngs 
 there may be some that may serve as starting-points for 
 further effort. 
 
 A change in the circumstances or environment of the 
 plant may start the desired attribute. If the plant must 
 be dwarfer, plant it on poorer or drier soil, transfer it 
 
238 Plant-Breeding 
 
 towards the poles, plant it late in the season, or transplant 
 it repeatedly. Dwarf peas become climbing peas on rich, 
 moist lands. If the plant must have large fruits, allow it 
 more food and room, and give attention to pruning and 
 thinning. Certain geographical regions develop certain 
 characters in plants, as we have seen; if, therefore, the 
 desired feature does not appear spontaneously or as a 
 result of any other treatment, transfer the plant for a 
 time to that region which is characterized by such attri- 
 butes, if there is any such. It is not intended to convey 
 the impression that the placing of plants on poor soil will 
 directly cause a dwarfing which will be inherited, or large 
 size on good soils, but if the plant already holds the 
 characteristic of dwarfness or some other quahty in a 
 latent form, it will probably appear if the conditions are 
 made right. 
 
 The importance of growing the plant under conditions 
 or environments in which the desired type of characters 
 is most frequently found, is admirably emphasized in the 
 evolution of varieties which are adapted to forcing under 
 glass. Within a century — and in many instances within 
 a score of years — species that are practically unknown 
 to glass-houses have produced varieties perfectly adapted 
 to them. This has been accomplished by growing the 
 most tractable existing varieties, selecting those which 
 most completely adapt themselves to their environment 
 and to the ideals of the operator. One of the most re- 
 markable examples of this kind is afforded by the carna- 
 tion. In Europe it was chiefly a border or outdoor plant, 
 but within a generation it had produced hosts of excellent 
 forcing varieties in America, where it is grown almost ex- 
 
Hoiv Domestic Varieties Originate 239 
 
 clusively as a glass-house flower. So the carnation types 
 of Europe and America have been widely unlike. 
 
 Sowing the seeds of hardy annual plants in autumn 
 often stimulates a tendency to produce thickened roots. 
 The plant, finding itself unable to perfect seeds, stores its 
 reserve in the root, and it therefore tends to become 
 biennial. In this manner, with the aid of selection and 
 the variation of the soil, Carriere was able to produce 
 good radishes from the wild slender-rooted charlock 
 (Raphanus Raphanistrum) . 
 
 Lessened vigor, so long as the plant continues to be 
 healthy, nearly always results in a comparative increase of 
 fruits or reproductive organs. It is an old horticultural 
 maxim that checking growth induces fruitfulness. It is 
 largely in consequence of this fact that plants bear heaviest 
 when they attain approximate maturity. Trees are 
 often thrown into bearing by girdling, heavy pruning, 
 the attacks of borers, and various accidental injuries. 
 The gardener knows that if he keeps his plants in vigorous 
 growth by constantly putting them into larger pots, he 
 will get Httle, or at least very late, bloom. The plant- 
 breeder, therefore, may be able to induce the desired 
 initial variation by attention to this principle. (See dis- 
 cussion of variation in relation to food supply.) Arthur 
 has recently put the principle into this formula: '^A 
 decrease in nutrition during the period of growth of an 
 organism favors the development of the reproductive 
 parts at the expense of the vegetative parts." 
 
 A most important means of inducing variation is the 
 simple change of seed, the philosophical reasons for 
 which are explained on earher pages. A plant becomes 
 
240 
 
 Plant-Breeding 
 
 closely fitted or accustomed to one set of conditions, and 
 when it is placed in new conditions, it at once makes an 
 effort to adapt itself to them. This adaptation is varia- 
 tion. No doubt the free interchange of seeds between 
 seed-merchants and customers is one of the causes of 
 the enormous increase in varieties in recent times. 
 
 When once a novel variety appears, others of a similar 
 kind are likely soon to follow in other places, and some 
 
 persons have supposed 
 that there is a synchro- 
 nistic variation in 
 plants, or a tendency 
 for like variations to 
 appear simultaneously 
 in widely separated lo- 
 calities. There is per- 
 haps some remote reason 
 for this opinion, because 
 there is, as Darwin ex- 
 presses it, an accumula- 
 tive effect of domestica- 
 tion or cultivation, by virtue of which plants that long 
 remain comparatively invariable may, within a short 
 time, when cultivation has been continued long enough, 
 vary widely and in many directions ; and it is to be ex- 
 pected that even when plants have long since responded 
 to the wishes of the cultivator, an equal amount or accumu- 
 lation of the force of domestication would tend to produce 
 like effects in different places. But it is probable that by 
 far the greater part of this synchronistic variation is 
 simply apparent, for whenever any marked novelty appears 
 
 Fig. 58. — Wild cabbage. 
 
Hoic Domestic Varieties Originate 
 
 241 
 
 the attention of all interested persons is directed to looking 
 for similar variations amongst their own plants. 
 
 12. The person who is wishing for new varieties should 
 look critically to all perennial plants, and particularly to 
 trees and shrubs, for bud-varieties or sports. It has 
 already been said that the branches of a tree may vary 
 among themselves in the same way in which seedhngs 
 
 Fig. 59. — Curled kale. Brassica oleracea var. acephala. 
 
 vary, and for the same reason. As a rule, any marked 
 sport is capable of being perpetuated by bud-propagation. 
 The number of bud-varieties now in cultivation is really 
 very large. Many of the cut-leaved and colored or 
 variegated varieties of ornamental plants were originally 
 found on other trees as sports. The ''mixing in the 
 hill" of potatoes is bud-variation. Nectarines are de- 
 rived from the peach, some of them as sports and some as 
 seedhngs. The moss-rose was probably originally a sport 
 
 R 
 
242 
 
 Plant- Breeding 
 
 from the Provence rose. Greening apple trees often bear 
 Russet apples, and Russets sometimes bear Greenings. 
 
 Bud-varieties may not only come from buds, — as 
 grafts, cuttings, and layers, — but they sometimes 
 perpetuate themselves by seeds. Now, these seedlings 
 
 are amenable to selec- 
 tion, just the same as 
 any other seedlings are ; 
 the bud-variety, there- 
 fore, may give the in- 
 itial starting-point for 
 plant-breeding. But, 
 more than this, it is 
 sometimes possible to 
 improve and fix the 
 type by bud-selection 
 as well as by seed-se- 
 lection. Darwin cites 
 this interesting testi- 
 mony : ''Mr. Salter 
 brings the principle of 
 selection to bear on 
 variegated plants prop- 
 agated by buds, and has thus greatly improved and 
 fixed several varieties. He informs me that at first a 
 branch often produces variegated leaves on one side alone, 
 and that the leaves are marked only with an irregular 
 edging, or with a few lines of white and yellow. To im- 
 prove and fix such varieties, he finds it necessary to en- 
 courage the buds at the bases of the most distinctly marked 
 leaves and to p""opagate from them alone. By following, 
 
 Fig. 60. — Collard. 
 
How Domestic Varieties Originate 
 
 243 
 
 with perseverance, this plan during three or four successive 
 seasons a distinct and fixed variety can generally be 
 secured." Ernest Walker, then a gardener at New Al- 
 bany, Indiana, is of the opinion that the abnormal charac- 
 ter of sports often intensifies itself if the sport is allowed 
 to remain on the parent plant for a considerable time. 
 He has observed this particularly in coleus, where color 
 sports are frequent. ''In these," he says, ''the sport 
 begins with a branch which may 
 be taken off and propagated as 
 a new variety. If left on the 
 parent, other parts of the plant 
 are apt to show similar varia- 
 tions. Indeed, I think it is not 
 best to be in too great hurry to 
 remove a sporting branch, for its 
 character seems to tend to be- 
 come more fixed if it remains on 
 the plant." 
 
 13. The starting-point once 
 given, all permanent progress lies 
 in continued selection. This, as 
 we have already pointed out, is really the key to the whole 
 matter. In the great number of cases, the operator cannot 
 produce the initial variation which he desires, but, by look- 
 ing carefully among many plants, he may find one which 
 shows an indication of his ideal. This plant must be 
 carefully saved, and all of the seeds sown in a place where 
 crossing with other types cannot take place. Of a hundrtHl 
 seedUngs from this plant, perhaps one or two will still 
 further emphasize the character which is sought. These, 
 
 Fig. 61. — Brussels sprouts. 
 
244 
 
 Plant- Breeding 
 
 again, are saved, and all the seeds are sown. So the 
 operation goes on, patiently and persistently, and there is 
 a reward at the end. This is the one fundamental practice 
 that underlies the amelioration of plants under the touch 
 of man ; and because we know, from experience, that it 
 is so important, we are sure, as Darwin was, that selec- 
 tion in nature must be a factor in the progress of the 
 vegetable world. 
 
 But suppose this suggestion of the new variety does 
 
 not appear among the 
 batch of plants that 
 we raise ? Then sow 
 again ; vary the con- 
 ditions; choose the 
 most widely variable 
 types ; cross ; at length 
 
 — if the ideal is true 
 
 — the suggestion will 
 come. ''Cultivation, 
 diversification of the 
 conditions of existence^ 
 
 and repeated sowings" are the means which Verlot 
 would employ to induce variations. But the skill and 
 the character of the final result he not so much in the 
 securing of the initial start, as in the subsequent se- 
 lection. Nature affords starting-points in endless num- 
 bers, but there are few men alert and skillful enough 
 to take the hint and improve it. If we want a new 
 tomato, we first endeavor to discover what we want. We 
 decide that we must have one hke the Acme in color, but 
 more spherical, with a firmer flesh, and a httle earlier. 
 
 Fig. 62. — Savoy cabbage. 
 
How Domestic Varieties Originate 
 
 245 
 
 Then we shall raise an acre of Acme tomatoes, and closel}^ 
 allied varieties ; if we cannot do that, we make arrange- 
 ments to inspect the neighbor's fields. We scrutinize 
 every plant as the first fruits are ripening. Finally, one 
 plant is found — not one fruit — which is something like 
 the variety desired. Very well. Wait two to five j^ears 
 and you shall see the new variety. 
 
 
 Fig. 63. — Cabbage shapes: flat; round or ball; egg-shaped; oval; 
 
 conical. 
 
 Some of these initial variations possess no tendency to 
 reproduce themselves. The seedUngs of them may break 
 up into a great diversity of forms, no form representing 
 the parent closely. In such cases, it is generally useless 
 to proceed further with this brood. Another start 
 should be made with another plant. So it is alwaj^s im- 
 portant, as we have already seen (Rule 6), to have as 
 
246 Plant-Breeding 
 
 many starting-points as possible, to lessen the risk of 
 failure. Whilst it requires nice judgment to choose 
 those plants which possess the most important and the 
 most transmissible combination of characters, the great- 
 est skill is nevertheless required to carry forward a correct 
 system of selection. 
 
 14. Even when the desired variety is obtained, it must 
 be kept up to the standard by constant attention to 
 selection. That is, there is no real stability in the forms 
 of Ufe. So long as the conditions of existence vary, 
 so long will the plants make the effort to adapt themselves 
 to the changes. No two seasons are alike ; and no two 
 fields, or even parts of fields, are alike ; and there are no 
 two cultivators who give exactly the same and equal at- 
 tention to tillage, fertilizing, and the other treatment of 
 plants. All forms or varieties, therefore, tend to ''run 
 out" by variation or gradual evolution into other forms; 
 but because we keep the same name for all the succeeding 
 generations, we fancy that we still have the same variety. 
 
 " In 1887 I found a single tomato plant in my garden 
 in Michigan, that had several points of superiority over 
 any other of the one hundred and seventy varieties I 
 was then growing. It came from a packet of German 
 seed of an inferior variety. The tomato was very solid, 
 an unusually long keeper, productive, and attractive in 
 size and appearance. The variation was so promising 
 that I named it in a sketch of tomatoes that I pubHshed 
 that year, calhng it the Ignotum (that is, unknown), 
 to indicate that the origin of it was no merit of my own. I 
 sent seeds to a few friends for testing. I sowed the seeds 
 for about five hundred plants in 1888 in an isolated patch 
 
How Domestic Varieties Originate 247 
 
 on uniform soil. The larger part of the plants were more 
 or less like the parent. A few reverted. A few of the 
 best plants were selected and the seed saved. I then 
 moved to New York and took the seed with me. This 
 was sown in uniform soil in an isolated position in 1889. 
 This crop, probably as a result of the careful selection of 
 the year before and of the change of locality, was re- 
 markably uniform and handsome. Of the 442 plants 
 I grew that year, none reverted to the little Eiformige 
 Dauer, the German variety from which it had come, but 
 there was some variation in them due to different methods 
 of treatment. I again saved the seeds, and I was now 
 ready to introduce the variety. I therefore sold my seeds, 
 six pounds, to V. H. Hallock & Son, Queens, New York, 
 who introduced it in 1890. The very next year, 1891, I 
 obtained the Ignotum from fifteen dealers and grew the 
 plants side by side. Of the fifteen lots, eight bore small 
 and poor fruits which were not worth growing and which 
 could not be recognized as Ignotum ! Grown from our 
 own seeds, it still held its character well. Here, then, 
 only a year after its introduction, half the seedsmen were 
 selling a spurious stock. It is possible that some of this 
 variation arose from substitution of other varieties by 
 seedsmen, although I have yet secured no evidence of any 
 unfair deahng. It is possible, also, that the product of 
 some of the samples which I early sent out for testing had 
 found their way into seedsmen's hands. But I am 
 convinced that very much of this variation was a legiti- 
 mate result of the various conditions in which the crops of 
 1890 had been grown, and the varying ideals of those who 
 saved seeds. I am the more positive of this from the 
 
248 
 
 Plant-Breeding 
 
 fact that the Ignotum tomato, as I first knew it and bred 
 it, appears now to be lost to cultivation, although the name 
 
 is still used for the legitimate 
 family of descendants from my 
 original stock. All this experi- 
 ence illustrates how quickly varie- 
 ties pass out by variation and by 
 the unconscious and unlike selec- 
 tion practiced by different per- 
 sons." — ^ Bailey, earher editions. 
 
 The longevity of any variety 
 is inversely proportional to the 
 frequency of its generations. An- 
 nual plants, other conditions 
 being the same, run out sooner 
 than perennials, because seed-re- 
 production — or the generations 
 — intervenes more frequently. 
 Trees, on the other hand, carry 
 their variations longer, because 
 the seed generations — in which 
 departures chiefly take place — 
 are farther apart. Of all the so- 
 called fruit plants, the strawberry 
 runs out soonest and the varie- 
 ties change the oftenest, because 
 a new generation can be brought 
 into fruit-bearing in two years, 
 whilst it may require ten years or 
 more to bring a new generation of apples or chestnuts into 
 bearing. '^ Yet, my reader will remind me that the Wilson 
 
 Fig. 64. — Swede turnip 
 (top) ; kohl-rabi (middle) ; 
 cauliflower (bottom). 
 
How Domestic Varieties Originate 249 
 
 strawberry has been and is the leading variety in many 
 places for nearly forty years, to which I reply that the Wilson 
 of to-day is not necessarily the same as that introduced 
 
 
 Fig. 65. — Wild form of Chrysanthemum morifolium,, as grown in 
 
 England. 
 
 by James Wilson, simply because the name is the same. 
 Every different soil or treatment tends to produce a different 
 strain or variation in the Wilson strawberr}^, as it does in 
 any other plant ; anti every grower, when setting a new 
 
250 
 
 Plant-Breeding 
 
 plantation, chooses his plants from that part of his field 
 which pleases him best, rather than from those plants 
 that most nearly correspond to the original type of the 
 Wilson. That is, the unconscious selection on the part 
 of the grower takes no account of what the variety was, 
 but only of what it ought to be, and this ideal differs with 
 
 Fig. 66. — Wild form of Chrysanthemum indicum, as grown in England. 
 
 every person. It is not surprising, therefore, to find strains 
 of Wilson strawberry as unlike as are many named vari- 
 eties ; and it is to be expected that all the strains now in 
 existence have departed considerably from the original 
 type." — Bailey, earlier editions. 
 
 This example borrowed from the strawberry is a most 
 important one, because it illustrates how a variety may 
 
How Domestic Varieties Originate 251 
 
 . ^' ff /'. 
 
 vary and pass out of existence even though it is propa- 
 gated wholly asexually or by buds. There are to-day 
 several different types of Rhode Island Greening apple in 
 cultivation which have probably originated from varia- 
 tions induced by environment and by the different ideals 
 of propagators ; and the same is true in other fruits. 
 
 All the foregoing remarks illustrate the importance 
 of constant attention to selection if 
 one desires to maintain the exact 
 type of any variet}^ which he has 
 produced. They explain the value 
 of the "roguing" — or systematic 
 destruction of all ''rogues" or non- 
 typical plants — which is invariably 
 practiced by all good seed growers. 
 But they still more emphatically 
 show that every variety is essen- 
 tially unstable, and that the only 
 abiding result is constant evolution, 
 the old forms being left behind as 
 the type expands into new and 
 better forms. Varieties to be valu- 
 able, therefore, ought not to be rigidly fixed, and, for- 
 tunately, nature has prescribed that they cannot be. 
 Probably every ten years sees a marked change in every 
 variety of any annual species which is propagated ex- 
 clusively from seeds, and every century must see a like 
 change in the tree fruits. These changes are so gradual 
 and the original basis of comparison fades away so com- 
 pletely that we generally fail to recognize the evolution. 
 
 15. It is evident, therefore, that the most abiding 
 
 Fig. 67. — Pompon anem- 
 one chrysanthemum. 
 
252 
 
 Plant-Breeding 
 
 progress in the amelioration of plants must come as a re- 
 sult of the very best cultivation and the most intelligent 
 selection and change of seed. Every reflective person 
 must admit that the cultivation of plants — which is the 
 fundamental conception of agriculture — has been and is 
 
 crude and imperfect, and that 
 there has been no conscious effort 
 on the part of the human race to 
 produce any given final result 
 upon the cultivated flora. Yet, 
 this imperfect cultivation has al- 
 ready modified plants so pro- 
 foundly that we cannot deter- 
 mine the originals of many of 
 them, and we can trace the evo- 
 lution of but few. The science of 
 rural industry is now fairly well 
 understood in its essential funda- 
 mental principles, and the in- 
 telligence of those classes of per- 
 sons who deal with plants is 
 rapidly enlarging. The first part 
 of the twentieth century will vir- 
 tually mark a new era for agri- 
 culture, and from that time on the onward evolution 
 of plants should proceed confidently and unchecked. 
 Our eyes are too often dazzled by the novelties which 
 suddenly thrust themselves upon us, and we look for 
 some mystic power which shall enable us to produce 
 varieties forthwith at our will. We need not so much 
 varieties with new names as we do a general increase 
 
 Fig. 68. — Single type. 
 
How Domestic Varieties Originate 
 
 253 
 
 . *vy|; & 
 
 in productiveness and efficiency of the types we 
 already possess ; and this augmentation must come 
 chiefly in the form of a gradual evolution under the 
 stimulus of good care. The man who will accomplish 
 most for the amelioration and unfolding of the forms of 
 plants is he who fixes his eyes steadily upon the future, 
 and, with the inspiration of a long forecast, urges the 
 betterment of all conditions in which plants grow. 
 
 SPECIFIC EXAMPLES 
 
 The foregoing principles and discussions will become 
 more concrete if a few actual examples of the origination 
 of varieties are given. To 
 begin with a very simple 
 case, we relate the intro- 
 duction of the varieties of 
 the dewberries, for this 
 fruit is yet little cultivated, 
 the varieties are few, and 
 the domestication of it is 
 not yet fifty years old. 
 
 The dewberry and black- 
 berry. — The dewberries 
 are native fruits, and it is 
 only within twenty-five 
 years that they have 
 become prominent among 
 fruit-growers. The most 
 important is the Lucretia. 
 This was found growing 
 wild on a plantation in 
 
 
 Fig. 69. — Type of pompon chrys- 
 anthemum. Grown outdoors, 
 with no special care. 
 
254 Plant-Breeding 
 
 West Virginia in war time. In 1876, a few of the plants 
 were sent to Ohio, and from this start the present stock 
 has come. It is probable that similar wild varieties are 
 growing to-day in many parts of the country, but they 
 have not chanced to have been seen by persons who are 
 interested in cultivating them. It is a forrji of the com- 
 mon wild dewberry that grows all over the Northeastern 
 states. Just why this particular patch in West Virginia 
 should have been so much better than the general run of 
 the species nobody knows, but it was undoubtedly the 
 product of some local environment or special ancestry. 
 
 Early in the seventies, T. C. Bartel, of Huey, Clinton 
 County, Illinois, observed very excellent dewberries grow- 
 ing in rows between the lines of stubble in an old cornfield, 
 where the plant had evidently been quick to avail itself 
 of unoccupied land. This was introduced as the Bartel 
 dewberry, and is now the second in point of prominence 
 amongst the cultivated varieties. Other varieties have 
 appeared in much the same way. A fruit-grower in 
 Michigan found an extra good dewberry in a neighboring 
 wood-lot, and introduced it under the name of Geer, in 
 compliment to the owner of the place. In Florida an 
 unusually good plant of the common wild dewberry of 
 that region was discovered, and introduced by Reasoner 
 Brothers under the name of Manatee. There are now 
 about twenty named varieties of dewberries in cultivation 
 as described in our horticultural writings, all of which, 
 apparently, are chance plants from the wild. 
 
 As the dewberries become more widely grown, good seed- 
 lings will now and then appear in cultivated ground, and 
 these will be named and sold. After a time persons will 
 
How Domestic Varieties Originate 255 
 
 begin to sow seed for the purpose of producing new 
 varieties; and those seedhngs which chance to possess 
 unusual merit will be propagated, and in due time intro- 
 duced. This is the history of the cultivated blackberries 
 and raspberries which have come from the wild plants in 
 little more than half a century. These fruits are now so 
 far developed that we no longer think of looking to the 
 woods and copses for new varieties of promise, yet the 
 novelties are mostly chance seedlings from cultivated 
 varieties. A few years ago a friend purchased plants of 
 the Snyder blackberry. When they came into bearing, 
 he noticed that one plant was better than the others. It 
 bore larger fruits, and the bearing season was longer. He 
 took suckers from this plant, and from these others were 
 taken, until he had a large plantation of the novelty, 
 mostly selected from plants which pleased him best. 
 The variety had such distinct merit that it was named 
 the Mersereau, in honor of the man who recognized and 
 propagated it. 
 
 The apple. — The original apple is not definitely known, 
 but it was certainly a very small and inferior crabbed 
 fruit, borne mostly in clusters. When we first find it 
 described by historians, it was still of small value. Pliny 
 said that some kinds were so sour as to take the edge off 
 a knife. But better and better seedlings continued to 
 come up about habitations, until, when printed descrip- 
 tions of fruits began to be made, three or four hundred 
 years ago, there were many named kinds in existence. 
 The size had vastly improved, and with this increase 
 came the reduction of the number of fruits in the cluster ; 
 so that, at the present time, whilst apple flowers are borne 
 
256 
 
 Plant-Breeding 
 
 in clusters, the fruits are usually borne singly. That 
 is, most of the flowers fail to set fruit, and they complete 
 their mission when they have shed their pollen for the 
 benefit of the one which persists. 
 
 The American colonists brought with them the staple 
 varieties of the mother countries. But the needs of the 
 
 new countrj^ were unlike those 
 of the old, and the tastes and 
 fashions of the people were chang- 
 ing. So, as seedlings came up 
 about the buildings and along 
 the fences, where the seeds had 
 been scattered, the ones that 
 promised to satisfy the new needs 
 were saved, and many of the old 
 varieties were allowed to pass 
 away. In 1817, the date of the 
 first American fruit-book, over 
 sixty per cent of the varieties 
 particularly recommended for 
 cultivation in this country were 
 of American origin. In 1845, 
 nearly two hundred varieties of 
 apples were described as having been fruited in this 
 country, of which over half were of American origin. 
 Between these two dates introduction of foreign varie- 
 ties had been freely made, so that the percentage of 
 domestic varieties had fallen. But the next thirty years 
 saw a great change. Of 1823 varieties described in 
 1872, nearly or quite seventy per cent were American, 
 and a still greater proportion of the most prized 
 
 Fig. 70. 
 
 Japanese anemone 
 type. 
 
How Domestic Varieties Originate 257 
 
 kinds were of domestic origin. In the older states, the 
 apple had now become so completely accustomed to its 
 environment, and the tastes of the people were so well 
 supplied, that there was no longer much need for the in- 
 
 FiG, 71. — The small and regular anemone type. 
 
 troduction of foreign kinds. It was not so in the North- 
 west. There the apples of the Eastern states did not 
 thrive. The chmate was too cold and too dry. Atten- 
 tion was turned to other countries with similar or rigorous 
 
 s 
 
258 
 
 Plant-Breeding 
 
 climate. In 1870, the Department of Agriculture at 
 Washington imported cions of many varieties of apples 
 from Russia, but these did not satisfy all fruit-growers 
 
 of the Northern states. 
 It was then conceived 
 that the great interior 
 plain of Russia should 
 yield apples adapted to 
 the upper Mississippi 
 Valley, whilst those al- 
 ready imported had come 
 from the seaboard terri- 
 tory. Accordingly, early 
 in the eighties, Charles 
 Gibb, of the province of 
 Quebec, and Professor 
 Budd, of Iowa, went to 
 Russia to introduce the 
 promising fruits of the 
 central plain. The re- 
 sults have been most in- 
 teresting to the pacific 
 looker-on. There are ar- 
 dent advocates of the 
 Russian varieties, and 
 there are others who see 
 nothing good in them. 
 There are those who 
 think that all progress must come by securing seedhngs 
 from the hardiest varieties of the Eastern states ; there 
 are others who would derive everything from the Siberian 
 
 Fig. 72. 
 
 ■A pompon chrysanthemum. 
 (Xi) 
 
How Domestic Varieties Originate 
 
 259 
 
 crabs; and still others who hold that the final result lies 
 in improving the native crabs. There has been no end 
 of discussion and cross-purposes. In the meantime, nature 
 is quietly doing the work. Here is a good seedUng of some 
 old variety, there a good one from some Russian, and 
 now and then one from the crab stocks. The new varie- 
 
 FiG. 73. — Type of Japanese incurved chrysanthemum. 
 
 ties are gradually supplanting the old, so quietly that few 
 people are aware of it ; and by the time the contestants are 
 done disputing, it will be found that there are no Russians 
 and no Eastern apples, but a brood of Northwestern apples 
 that have grown out of the old confusion. 
 
 All these new apples are simply seedlings, almost all 
 of them chance trees which come up here and there 
 
260 Plant-Breeding 
 
 wherever man has allowed nature a bit of ground upon 
 which to make garden as she likes. In 1892, there were 
 878 varieties of apples offered for sale by American nursery- 
 men, and it is doubtful if one of the whole lot was the 
 result of any attempt on the part of the originator to pro- 
 duce a variety with definite qualities. And what is true 
 of the apple is about equally true of the other fruit trees. 
 In the small fruits and the grapes, where the generations 
 are shorter and the results quicker, more has been done 
 in the way of direct selection of seeds and the crossings 
 of chosen parents ; but even here, the methods are mostly 
 haphazard. Latterly, however, the professional experi- 
 menters have begun the breeding of the apple and new 
 varieties on a new basis have been secured ; and there is 
 now considerable literature on the subject. 
 
 Beans. — Perhaps there are no plants more tractable 
 in the hands of the plant-breeder than the garden beans. 
 A few years ago, a leading Eastern seedsman conceived 
 of a new form of bean pod that would at once com- 
 mend itself to his customers. He was so well con- 
 vinced of the merits of this prospective variety, that he 
 made a descriptive and ''taking" name for it. He 
 then wrote to a noted bean-raiser, describing the proposed 
 variety and giving the name. ''Can you make it for 
 me?" he asked. "Yes, I will make you the bean," re- 
 plied the grower. The seedsman then announced in his 
 catalogue that he would soon introduce a new bean, and, 
 in order to hold the name, he published it, along with the 
 announcement. Two years later, I visited the bean- 
 grower. "Did you get the bean?" I asked. "Yes, here 
 it is." Sure enough, he had it, and it answered the re- 
 
How Domestic Varieties Originate 261 
 
 quirements very well. Another seedsman would like a 
 round-podded, stringless, green-podded bean. This same 
 man produced it, and I went into a field of fifteen acres 
 of it, where it was growing for seed, and the most fas- 
 tidious person could not have asked for a closer approach 
 to the ideal which the dealer had set before him some 
 four or five years before. 
 
 How is all this done? It looks simple enough. The 
 ideal is established first of all. The breeder revolves it 
 in his mind, and eliminates all the impracticable and con- 
 tradictory elements of it. Then he goes carefully and 
 critically through his bean fields, particularly through 
 those varieties most like the desired kind, and marks 
 those plants which most nearly approach his ideal. The 
 seeds of these are carefully saved, and they are planted 
 in an isolated position. If he finds no promising variations 
 among his plantations, then he must start off the varia- 
 tion in some other way. This is usually done by crossing 
 those varieties which are most like the proposed kind. 
 He has got a start ; but now the care and skill begin. 
 Year by year he selects just those plants which please 
 him best and which he judges, from experience, will most 
 surely carry their features over to the offspring. He 
 starts with one plant ; the next year he may have only 
 two. If he has ten or twenty good ones, then the task 
 is easy, for the variety has elements of permanence 
 — that is, of hereditability — in it. But he may have 
 no plants the second year. In that case, he begins again ; 
 for if the ideal is true, it can be attained. This par- 
 ticular bean-breeder upon whom many of our best seeds- 
 men rely for new varieties, says that he has discarded 
 
262 
 
 Plant-Breeding 
 
 fully three thousand varieties and forms as profitless. 
 
 This only means that he is a most astute judge of beans, 
 
 and that he knows when any type is likely to prove to be 
 
 a poor breeder. 
 
 The bean also affords an excellent example of the care 
 
 which it is generally 
 necessary to exercise to 
 keep any variety true to 
 the type. The person of 
 whom we have spoken, 
 in common with all care- 
 ful seed-growers, searches 
 his field with great pains 
 to discover the '^ rogues," 
 or those plants which 
 vary perceptibly from 
 the type of the given 
 variety. The rogue may 
 be a variation in size or 
 habit of plant, season of 
 maturity, color or form 
 of pods, productiveness, 
 ■^ susceptibility to rust, or 
 
 Fig. 74. — Japanese anemone chrys- +V. K T +1 
 
 anthemum when fully expanded. otner aberrance. Ill tne 
 
 dwarf or bush beans, 
 which are now most exclusively grown, the most fre- 
 quent rogue is a climbing or half-climbing plant. This 
 is a reversion to the ancestral type of the bean, which 
 was no doubt a twining plant. This rogue is always 
 destroyed even though it may be, itself, a good bean. 
 In some cases, the men who perform the roguing are 
 
 
 
How Domestic Varieties Originate 263 
 
 sent along every row of a whole field on their hands 
 and knees, critically examining every plant. The effect 
 of this continual selection is always to push the variety 
 to greater excellence. The various 'improved" strains 
 of plants are obtained in essen- 
 tially this way. If the grower 
 has been painstaking with his 
 roguing, he soon finds that 
 his seed gives better and 
 more uniform crops than the 
 common stock of the variety. 
 If the improvement is marked, 
 he may dignify his strain 
 with a distinct name, and 
 it thereby becomes a new 
 variety The improvement 
 may be a very important one 
 to a careful bean-grower and 
 at the same time be so slight 
 as to escape the attention of 
 the general farmer, or even 
 of experimenters who are not 
 particularly skilled in judging 
 the merits of beans. 
 
 All these examples drawn from the bean are excellent 
 illustrations of the best and most scientific plant-breeding, 
 and the same methods — varied to suit the different needs 
 — apply to the amelioration of all other plants. The 
 recent dwarf lima beans may be cited as examples of 
 accidental or fortuitous varieties, in which the precon- 
 ceived ideal of the plant-breeder had no place. Four 
 
 Fig. 75. — New type wdth short 
 stem, which is becoming very 
 popular with commercial 
 growers. 
 
264 
 
 Plant-Breeding 
 
 or five of these beans have attained some prominence. 
 Henderson and Kumerle Dwarf hmas were introduced in 
 1889, Burpee in 1890, and Barteldes in 1892 or 1893. 
 The variety now called the Henderson was piclced up 
 thirty or more years before by a negro, who found it 
 
 growing along a roadside in Vir- 
 ginia. It was afterwards grown 
 in various gardens, and about 
 1885 it fell into the hands of a 
 seedsman in Richmond. Hen- 
 derson purchased the stock of it 
 in 1887, grew it in 1888, and offered 
 it to the general public in 1889. 
 The introduction of Henderson's 
 bean attracted the attention of 
 Asa Palmer, of Kennett Square, 
 Pennsylvania, who had also been 
 growing a dwarf lima. He called 
 on Burpee, the well-laiown seeds- 
 man of Philadelphia, described 
 his variety, and left four beans 
 for trial. These were planted in' 
 the test grounds and were found 
 Fig. 76. -Incurved type. ^^ ^^ valuable. Mr. Palmer's 
 
 entire stock was then purchased, — comprising over an 
 acre, which had been carefully inspected during the 
 season, — and Burpee Bush lima was presented to the 
 public in the spring of 1890. Mr. Palmer's dwarf lima 
 originated in 1883, when his entire crop of Large White 
 (Pole) limas was destroyed by cut-worms. He went 
 over his field to remove the poles before fitting the land 
 
How Domestic Varieties Originate 265 
 
 for other uses, but he found one Uttle plant, about ten 
 inches high, which had been cut off about an inch above 
 the ground, but which had re-rooted. It bore three pods, 
 each containing one seed. These three seeds were planted 
 in 1884, and two of the plants were dwarf, like the parent. 
 By discarding all plants which had a tendency to climb, 
 in succeeding crops, the Burpee Bush lima, as we now 
 have it, was developed. 
 
 The Kumerle, Thorburn, or Dreer, Dwarf lima origi- 
 nated from occasional dwarf forms of the Challenger Pole 
 lima, which J. W. Kumerle, of Newark, New Jersey, 
 found growing in his field. The stock which came from 
 these selected dwarf plants was introduced by Thorburn 
 and Dreer, under their respective names. The singular 
 Barteldes Bush lima came from Colorado, and is a 
 similar dwarf sport of the old White Spanish or Dutch 
 Runner bean. Barteldes received about a peck of the 
 seed and introduced it sparingly. It attracted very little 
 attention, and as the following season was dry, Barteldes 
 himself failed to get a crop, and the variety was lost to 
 the trade. 
 
 Carinas. — Few plants have shown more remarkable 
 evolution in very recent years than the cannas. At the 
 present time, the Crozy cannas — so named from Crozy, 
 of Lyons, PYance, who has introduced the greater number 
 of them — are most popular. This type is often called 
 the French Dwarf, or the Flowering Canna, and it is 
 marked by comparatively low stature, and very large 
 and showy spreading flowers in many colors, whereas 
 the cannas of former years were very tall plants, with 
 small and late dull red narrow flowers, and they were 
 
266 Plant-Breeding 
 
 grown for their foliage effects. How has this transforma- 
 tion come about? 
 
 In the first place, it should be said that there are many 
 species of canna, and about a half-dozen of these were 
 well known to gardeners at the opening of last century. 
 About 1830, the cannas began to attract much attention 
 from cultivators, and the original species were soon 
 variously hybridized. Crossed seeds, and seeds from 
 the successive generations of hybrids, introduced a host 
 of new and variable forms. The first distinct fashion in 
 cannas seems to have been tall late-flo wiring forms. 
 In 1848, Annee, a cultivator in France, sowed seeds of 
 Canna nepalensis, a tall oriental species, and there sprung 
 up a race of plants which has since been known as Canna 
 Anncei. It is probable that this Canna nepalensis had 
 become fertilized with other species growing in Annee's 
 collection, very likely with Canna glauco.. At all events, 
 this race of cannas became popular, and was to its time 
 what the French dwarfs are to the present day. The 
 plants were freely introduced into parks, beginning about 
 1856, but their use began to decline by 1870 or before. 
 Descendants of this type, variously crossed and modified, 
 are now frequently seen in parks and gardens. 
 
 The beginning of the modern race of dwarf large- 
 flowered cannas was in 1863, when one of the smaller- 
 flowered Costa Rican species (Carina Warscewiczii) was 
 crossed upon a larger-flowered Peruvian species {Canna 
 iridiflora). The offspring of this union came to be called 
 Canna Ehemannii. This hybrid has been again variously 
 crossed with other species, and modified by cultivation 
 and selection, until the present composite type is the re- 
 
How Domestic Varieties Originate 267 
 
 
 suit. Seeds give new varieties; and any seedling which 
 is worth saving is thereafter multiplied by divisions of the 
 root, and the resulting plants are introduced to commerce. 
 The cabbage family (see Figs. 58-64).— A good illustra- 
 tion of unconscious improvement is to be found in cabbage, 
 kale, collard, borecale, Brussels sprouts, kohl-rabi, and cau- 
 liflower. These probably came 
 from a single, somewhat woody, 
 branching perennial {Brassica 
 oleracea) which is to be found 
 growing wild on limestone bluffs 
 in southwestern Europe. Some 
 are a modification of the leaf, as 
 in the cabbage and kale, others 
 of the stem, as kohl-rabi, while 
 in the cauliflower it is the selec- 
 tion of the inflorescence that 
 has caused the peculiar modifi- 
 cation. Some of these types 
 have twenty and more varieties, 
 so that there are probably over 
 one hundred distinct forms from 
 this one wild type. All of these forms are the result of long 
 and patient selection of variations that were considered 
 desirable by the gardener without any conscious attempt 
 to produce these specific forms. 
 
 The chrysanthemum. —An excellent illustration of the 
 appearing of a wide range of forms within the epoch of 
 the systematic botanists is afforded by the florist's chrys- 
 anthemum (Figs. 65-79). These chrysanthemums are now 
 so widely variable and so little referable to wild species 
 
 Fig. 77. — Hairy type. 
 
268 
 
 Plant- Breeding 
 
 
 
 that they have recently been named as a garden group- 
 species, Chrysanthemum hortorum (Stand. Cyc. Hort. ii. 
 755) . These plants now comprise forms sirfgle and double ; 
 pompon and giant ; discoid, flat-rayed, and quilled ; ball- 
 head and reflexed ; hairy-rayed ; a wide range of colors ; 
 bizarre forms ; and marked differences in stature and habit 
 of plant. If one were to bring together the little pompons, 
 ... . the hardy border types, the 
 
 anemone-flowered, the Japanese 
 incurved, and the slender singles, 
 he would have difficulty in refer- 
 ring them to any single origin. 
 
 And yet the records show that 
 these multitudes of forms have 
 come from one oriental feral 
 group, or what some botanists re- 
 gard as two very similar species. 
 The original was introduced to 
 England about 150 years ago. 
 In 1796 the Botanical Magazine figured an important large- 
 flowered departure, marking the beginning, or practicaUy 
 the beginning, of the modern record and development. 
 The plants may have been long cultivated and consider- 
 ably modified in China and Japan. What are considered 
 to be the feral forms have been introduced within very 
 recent years. They are most unpromising looking herbs, 
 one (C. morifolium) with white rays, and the other (C. 
 indicum) with yellow rays. They look no more promising 
 than many weedy composites of the fields ; and yet some 
 process has evolved a multitude of astonishing forms 
 without our knowing how or why even though the evolu- 
 
 FiG. 78. — Japanese type. 
 
How Domestic Varieties Originate 269 
 
 tion has proceeded under our eyes and within the period 
 when plants have been under close scrutiny. 
 
 These various examples are but types of what has 
 been and can be accomplished in a given group of plants. 
 There is nothing mysterious 
 about the subject, so far as 
 the cultivator is concerned. 
 He simply sets his ideal, makes 
 sure that it does not contra- 
 dict any of the fundamental 
 laws of development of the 
 plant with which he is to work, 
 then patiently and persistently 
 keeps at his task. He must 
 have good judgment, skill, and 
 inspiration, but he does not 
 need genius. 
 
 ''In the improvement of 
 plants," writes Henri L. de 
 Vilmorin, ''the action of man, 
 much like influences which act in the wild state, only 
 brings about slow and gradual changes, often scarcely 
 noticeable at first. But if the efforts towards the de- 
 sired end be kept on steadily, the changes will soon be- 
 come greater and greater, and the last stages of the 
 improvement will become much more rapid than the 
 first ones." 
 
 Fig. 79. — Reflexed type. 
 
CHAPTER IX 
 
 POLLINATION: OR HOW TO CROSS PLANTS 
 
 Pollination is the act of conveying pollen from the 
 anther to the stigma. It is the manual part of the cross- 
 ing of plants. The word fertilization is often used in a 
 like sense, although erroneously; for it is the office of 
 the pollen, not of the operator, to fertilize or fecundate 
 
 that part of the flower 
 which is to develop 
 into a seed. 
 
 The structure of the 
 flower. — The chief re- 
 quirement in pollinat- 
 ing flowers is to know 
 the parts of the flower 
 itself. The conspicu- 
 ous or showy part of 
 the flower is the envelope, which is endlessly modified in size, 
 form, and color. This envelope covers the inner or essential 
 organs, and it also attracts insects, which often perform 
 the labor of pollination. This floral envelope is usually 
 of two series or parts, — an outer and commonly green 
 series known as the^calyx, and an inner and usually more 
 showy series known as the corolla. These two series are 
 well shown in the bellflower, Fig. 80. The calyx, with 
 
 270 
 
 Fig. 80. — Bellflower. 
 
Pollination: or How to Cross Plants 271 
 
 its reflexed lobes, is at C, and the large bell-form part 
 is the corolla. When the calyx is composed of separate 
 parts or leaves, each part is called a sepal ; in like manner 
 each separate part of the corolla is a petal. In the lily. 
 Fig. 81, there is no distinction between calyx and corolla; 
 or, it may be said, the calyx 
 is wanting. These envelopes 
 of the flower are often much 
 disguised. This is particu- 
 larly true in the orchids, one 
 of which, a lady-slipper, is 
 illustrated in Fig. 82. The 
 sepals are seen at DD. They 
 are apparently only two, but 
 there is reason to believe that 
 the lower sepal is really made 
 up of a union of two. The 
 three inner leaves are the 
 petals, the lower one, H, 
 being enlarged into the sac 
 or slipper. 
 
 The most important organs 
 of the flower, however, to 
 one who wishes to make crosses, are the so-called sexual 
 organs, the stamens and pistils. They can be readily 
 distinguished in the lily. Fig. 81. The six bodies shown 
 at S are the ends of the stamens, or so-called male organs. 
 These stamens generally have a stalk or stem, known as 
 a filament, and the enlarged tip as the anther. It is in 
 this anther that the pollen is borne. The pollen is usu- 
 ally made up of very minute yellow or brownish grains, 
 
 Fig. 81 . — Flower of white lily. 
 
272 
 
 Plant-Breeding 
 
 although it is sometimes in the form of a more or less 
 glutinous or adhesive mass, as in the milk-weeds and 
 orchids. The irritating dust which falls from the corn 
 tassels at the later cultivatings is the pollen. 
 
 The pistil, or so-called female organ, is shown at OP, 
 
 Fig. 81. The enlarged 
 portion at is the ovary, 
 which develops into the 
 seed-pod. The stigma, or 
 the enlarged and rough- 
 ened part which receives 
 the pollen, is at P. Be- 
 tween these two parts is 
 the slender style, a part 
 that is absent in many 
 flowers. 
 
 The stamens and pistils 
 are known as the essen- 
 tial organs of the flower, 
 for, whilst the calyx and 
 corolla may be entirely 
 absent, either one or both 
 of these organs is present ; 
 and these are the parts 
 that are directly concerned in the reproduction of the species. 
 Like the floral envelopes, these essential organs are often 
 modified, so much so that botanists are sometimes perplexed 
 to distinguish them from each other or from modified forms 
 of the petals or sepals. The particular features of these 
 organs which the plant-breeder must be able to distin- 
 guish are the anther and the stigma ; for the anther bears 
 
 Fig. 82. 
 
 — Flower of greenhouse 
 cypripedium. 
 
Pollination: or How to Cross Plants 273 
 
 the pollen and the stigma must receive it. In Fig. 80, the 
 stamens are shown at E. In the flower A, which has just 
 
 Fig. 83. — Flower of night-blooming cereus. 
 
 expanded, these stamens are rigid and in condition to 
 shed the pollen, but in the flower B, they have shed the 
 pollen and have collapsed. The stigma in this case is 
 
 T 
 
274 
 
 Plant-Breeding 
 
 divided into three parts, but when the flower first opens, 
 these parts are closed together, H in flower A, so that it 
 is impossible that they receive any pollen from the same 
 flower; when the stamens have withered, however, as in 
 B, the stigma, H, spreads open and is ready to receive 
 any pollen which may be brought to it by insects or 
 
 Fig. 84. — Flower of the shrubby hibiscus {Hibiscus syriacus). 
 
 other agencies. In this case, the ovary or young seed-pod, 
 which is in the bottom of the flower, is not shown in the 
 engraving. 
 
 Some of the particular forms of essential organs are 
 well illustrated in the accompanying photographs. In 
 the night-blooming cereus, Fig. 83, the many-rayed stigma 
 is shown just below the center of the mouth of the flower, 
 
Pollination: or How to Cross Plants 275 
 
 and the numerous stamens are 
 arranged in a circular form out- 
 side of it. The many petals and 
 numerous spreading sepals are 
 also well shown. The hibiscus, 
 Fig. 84, has a central column 
 with the anthers hanging upon 
 it, and a large stigma raised 
 beyond them. The wild bug- 
 bane, or cimicifuga, is seen in 
 Fig. 85, natural size. Here fs a 
 long spike or cluster of flowers. 
 At the top are the unopened 
 buds, in the center the expanded 
 flowers with the floral envelopes 
 fallen away, — the fringe-like 
 stamens very prominent, — and 
 below are seen the pistils, the 
 stamens having fallen. These 
 pistils will now ripen into pods, 
 but the tip-like stigma may still 
 be seen on them. The stamens 
 and the long protruding style 
 are also shown in the fuchsia. 
 Fig. 94. The essential organs 
 of orchids are curiously dis- 
 guised. They are combined into 
 a single body. In the lady-slip- 
 per, Fig. 82, the lip-like stigma 
 is shown at P. On either side, 
 at its base; is an anther, S. Pro- 
 
 FiG. 85. — Bugbane {Cimici- 
 fuga racemosa). 
 
276 
 
 Plant-Breeding 
 
 jecting over the stigma is a greenish ladle-Hke body, T, 
 which is a transformed and sterile anther. In all lady- 
 slippers, these organs are essentially the same as in the 
 drawing, although they vary much in size and shape ; 
 but in most other orchids, the two side anthers, S, are 
 
 wholly wanting, 
 and the terminal 
 organ, T, is a 
 pollen-bearing 
 anther. In nu- 
 merous plants, 
 there are many 
 distinct pistils 
 in each flower. 
 Such is the case 
 in the straw- 
 berry, where 
 each little yellow 
 ''seed" on the 
 ripened berry 
 represents a pis- 
 til ; and the 
 blackberry and 
 the raspberry, 
 where each little grain or drupelet of the fruit stands 
 for the same organ. A flowering raspberry is illustrated 
 natural size in Fig. 86, for the purpose of showing the 
 ring of many anthers near the center of the flower, inside 
 of which, in the very center, is a little head of pistils. 
 
 It frequently occurs that the stamens and pistils are 
 borne in different flowers, rather than together in the 
 
 Fig. 
 
 86. — Blossom of flowering raspberry 
 (Rubus odoratus) . 
 
Pollination: or How to Cross Plants 277 
 
 same flower, as they are in the examples we have studied. 
 In these cases the flower is said to be staminate, or 
 male or sterile, in one case, and pistillate, female or fer- 
 
 FiG. 87. — Squash flowers of each sex. 
 
 tile, in the other case. If these two kinds of flowers are 
 borne together on the same plant, as in pumpkins, 
 melons, cucumbers, chestnuts, oaks, and begonias, the 
 plant is said to be monoecious; but if the staminate and 
 
278 • Plant-Breeding 
 
 pistillate flowers are on entirely different plants, as in 
 willows and poplars, the plant is dioecious. The two kinds 
 of squash flowers are shown in Fig. 87. The pistillate 
 flower is on the left, and it is at once distinguished by the 
 ovary or little squash below the colored part, or corolla 
 of the flower. The lobed stigma is seen in the center. 
 The staminate flower is on the right. It has a longer 
 
 HIH 
 
 ■■ 
 
 imHP^^'^^sn 
 
 H^^^H 
 
 ■ ^ 
 
 ^^^^^^^N^^^^^jHjSSH 
 
 igPf 
 
 
 ^ ^gj^^^^ ^-J^^^'. ^•'^'^^v^''^-' ■'3 
 
 H 
 
 ^£^^ 
 
 
 &X^ 
 
 h' -"Jl^Km 
 
 
 B^"^ 
 
 HJ^l 
 
 B ^^' ■ ^'"^^^MH 
 
 !sS. 
 
 mk 
 
 I^H^n^^HK. "^'^ J^^^^^^^^^H 
 
 Fig. 88. — Flowers of clematis {Clematis virginiana) . 
 
 stem, no ovary, and the anthers are united into a con- 
 spicuous cone in the center. The flowers expand early 
 in the morning. Insects carry pollen to the pistillate 
 flower, which then begins to set its fruit, whilst the 
 staminate flower dies. The flower of the common wild 
 clematis is shown in Fig. 88. On the right are the 
 sterile flowers, which are wholly staminate. On the left, 
 the flowers with larger sepals — the petals are absent — 
 have a cone of pistils in the center, and a few short and 
 
Pollination: or How to Cross Plants 279 
 
 sterile stamens spreading from the base of the cone. 
 These different flowers are borne on different plants in 
 this species of clematis, and the plants are therefore 
 practically dioecious, because the stamens of the pistillate 
 flowers generally bear no pollen. A similar mixed ar- 
 rangement occurs in some strawberries, except that there 
 are no purely staminate flowers. There are purely pistil- 
 late varieties, others, as the Crescent, with a few nearly 
 or quite abortive stamens at the base of the cone of pistils, 
 and others in which the flowers are perfect or hermaph- 
 rodites, that is, containing the two sexes. 
 
 The compositous flowers — as the asters, daisies, golden- 
 rods, sunflowers, dahlias, zinnias, chrysanthemums, and 
 their kin — need to be considered in still a different 
 category. In these plants, the head, or so-called flower, 
 is an aggregation of several or many small flowers or 
 florets. Each seed in a sunflower head, for example, 
 represents a distinct flower. Sometimes all of these flowers 
 are perfect, — contain the two sexes, — and sometimes 
 they are pistillate or staminate in different parts of the 
 head; and in some cases the plants are dioecious. In 
 many plants of the composite family, the flowers near the 
 border of the head are unlike those of the center or disk, 
 in having a long ray-like corolla; and these ray-flowers 
 are frequently of different form from the others in the 
 character of the essential organs. Very frequently the 
 ray-flowers are pistillate, whilst the disk flowers are 
 generally hermaphrodite. The anthers in these plants 
 are united in a ring closely about the style and below the 
 stigma. 
 
 The ovary, as we have seen, ripens into the pod, berry. 
 
280 Plant-Breeding 
 
 or other fruit ; but it is not able to bear seeds until it is 
 assisted by the pollen. The pollen falls upon the roughish 
 or sticky surface of the stigma, and there germinates or 
 sends a minute tube downwards through the style and 
 finally reaches the ovule, which, when fertihzed, rapidly 
 ripens into the seed. The nature of this fecundation is 
 not germane to the present subject ; but it may be said 
 that only one pollen-grain is necessary to the fertilization 
 of a single ovule, but the addition of a superabundance 
 of pollen greatly stimulates the growth of the fleshy or 
 enveloping parts of the fruit. It is important that the 
 person who desires to cross plants should become familiar 
 with the stigma when it is ''ripe," receptive, or ready to 
 receive the pollen. This condition is usually indicated 
 by the glutinous or sticky or moist condition of the stigma, 
 or in those stigmas which are not glutinous it is told by 
 the appearing of a distinctly roughened or papillose 
 condition. This receptive condition generally occurs 
 about as soon as the flower opens. If pollen is withheld, 
 the stigma will remain receptive much longer than when 
 fertilization has taken place, — in some flowers for two 
 or three days. 
 
 The pollen is discharged from the anther in various 
 ways, but it most commonly escapes through a chink or 
 crack in the side of the anther. Sometimes it escapes 
 through pores at one end of the anther ; and in other 
 cases there are more elaborate mechanisms to admit of 
 its discharge. In most plants, the anthers and stigma 
 in the same flower mature at different times, so that 
 close-fertilization or in-breeding is avoided. This is 
 well illustrated in the bellflower. Fig. 80. Here the anthers 
 
Pollination: or How to Cross Plants 281 
 
 wither and die before the stigmatic lobes open. In other 
 cases, the stigma matures first, although this is not the 
 usual condition. 
 
 Manipulating the flowers. — We are now familiar with 
 the essential principles in the pollination of flowers. 
 Before a person proceeds to operate on a flower with which 
 he is unfamiliar, he should carefully study its structure, 
 so as to be able to locate the different organs, and to dis- 
 cover when the pollen and the stigma are ready for work. 
 
 The first and last rule in the pollinating of plants is this : 
 Exercise every precaution to prevent any other pollina- 
 tion than that which you design to give. The anthers, 
 therefore, must be removed from the flower before it 
 opens. This removal of the anthers is known as emascula- 
 tion. Just as soon as this is done, tie up the flower securely 
 in a bag to protect it from foreign pollen, which may be 
 brought by winds or insects. As soon as the stigma is 
 ripe, remove the bag and apply the desired pollen, placing 
 the bag on the flower again, where it must remain until 
 the seeds begin to form. The stigma may be receptive 
 the day following emasculation, or, perhaps, not until a 
 week afterwards. Much depends on the age of the bud 
 when emasculation takes place. It is commonly best 
 to delay emasculation as long as possible and not have 
 the flower open ; but the operator must be sure that 
 the anthers do not discharge or that insects do not get 
 into the flower before he has emasculated it. The bud at 
 B, in Fig. 82, is nearly ready to emasculate. The older 
 buds on the top of the spike of bugbane. Fig. 85, are 
 ready to operate ; and so is the bud seen at the left in 
 Fig. 86. 
 
282 
 
 Plant-Breeding 
 
 The manner of emasculating the flower varies with the 
 operator. It is a common practice to cUp off the anthers 
 with a pair of small scissors, or to hook them out with a 
 bent pin or a crochet hook. There are disadvantages 
 in any of these methods, because the anthers are hkely 
 
 Fig. 89. — Tobacco flowers, showing the parts of the flower, a bud ready 
 to be emasculated, and an emasculated subject. 
 
 to drop into the bottom of the corolla, where it is some- 
 times difficult to rescue them ; and if one uses tweezers, 
 there is always danger that the anthers may be crushed 
 and that some of the pollen may adhere to the instrument 
 and contaminate future crosses. We may therefore cut 
 the corolla completely off just above the ovary, with a 
 
Pollination: or How to Cross Plants 283 
 
 pair of small, long-handled surgeon's scissors (see Fig. 
 91), removing everything but the pistil. The operation 
 is explained in Fig. 89, which shows the tobacco flower. 
 
 Fig. 90. — Zinnia flowers ; the upper head ready for emasculation, the 
 lower one showing the operation performed. 
 
 The flower at the left shows the pin-head stigma in the 
 center of the throat, and the five anthers surrounding 
 it. The second flower is spread open for the purpose 
 of showing these organs. The third figure is a bud in 
 
284 
 
 Plant-Breeding 
 
 Fig. 91. — liisULuueiiis UMti 111 pollinating flowei.-«, iiatural size. Pin 
 
 scalpel, scissors, lens. 
 
 the right condition for operation. The right-hand figure 
 shows this bud cut around with the points of the scissors, 
 
Pollination: or Hov) to Cross Plants 285 
 
 leaving only the pistil. The line at W, in Fig. 81, shows 
 where the flower of the lily might be cut off. 
 
 The method for a compositous flower is shown in the 
 picture of the zinnia, Fig. 90. In this plant the outer 
 flowers of the head are pistillate, whilst those of the 
 disk are perfect. It is only necessary, therefore, to remove 
 the central stamen-bearing flowers before any of them 
 open, and to cover the flower up before any of the pistils 
 near the border have protruded themselves. The upper 
 head in Fig. 90 shows the untreated sample, while the 
 lower one shows the same with the cone of central flowers 
 puUed out. This treated head should now be covered, 
 
 Fig. 92. — Ladle for pollinating house tomatoes. 
 
 to await the maturing of the stigmas. In many composi- 
 tous plants, however, the case is not so simple as this, 
 because all the flowers are perfect. In such cases, nearly 
 all the florets should be removed from the head, and a 
 few remaining ones emasculated in essentially the same 
 method as described for the tobacco, Fig. 89. 
 
 Whenever flowers are borne in clusters, nearly all of 
 them should be removed and the attention confined to 
 Only two or three of them. One is then more certain of 
 getting seeds to set. In some cases, like the apple cluster, 
 only one or two flowers of any cluster ever set fruit, 
 and the operator should then choose the two or three 
 strongest and most promising buds, and cut all the others 
 off. 
 
286 
 
 Plant-Breeding 
 
 Flowers that bear no stamens, as the pistillate flowers 
 of squashes, strawberries, and many other plants, of 
 course do not require emasculating. They should ]:>e 
 tied up while in bud, however, to prevent the access of any 
 foreign pollen. Indian corn is a case in point. The 
 
 pistillate flowers are on the ear, each 
 kernel of corn representing a single 
 flower. The silks are the stigmas. 
 If it is desired to cross corn, there- 
 fore, the ear should be covered before 
 any silks are protruded, and the 
 pollen should be applied some days 
 later, when the silks are fully grown. 
 The staminate or male flowers are 
 in the tassel. 
 
 The pollen should be derived from 
 a flower which has also been pro- 
 tected from wind and insects, be- 
 cause foreign pollen may have been 
 dropped upon an anther by an insect 
 visitor, and it may be unknowingly 
 transferred by the operator. The 
 pollen-bearing parent needs no oper- 
 ation, of course, but the flower should have been tied up in 
 a bag when it was in bud. The pollen is best obtained by 
 picking off a ripe anther and crushing it upon the thumb- 
 nail. Then it is transferred to the stigma by a tiny scalpel 
 made by hammering out the small end of a pin, as shown, 
 full size, at the left in Fig. 91. The stigma should be 
 entirely covered with the pollen, if possible. It is often 
 advised to use a camel' s-hair brush to transfer pollen, 
 
 >3 — ^^"■^f^ 
 
 Fig. 93. — Bag for cov 
 ering the flowers. 
 
Pollination: or How to Cross Plants 287 
 
 but much of the poUen sticks amongst the hairs of the 
 brush and is ready to contarninate a future cross ; and 
 when the pollen is scarce it cannot be conserved to ad- 
 
 FiG. 94. — Fuchsias, showing the stainens and pistils, and a bud ready 
 
 to be emasculated. 
 
 vantage by a brush. In some cases the pollen is discharged 
 so freely that the anther may be rubbed upon the stigma, 
 or even shaken over it, but in most instances it will be 
 
288 
 
 Plant-Breeding 
 
 necessary actually to place the pollen upon the stigma 
 with some hand instrument. When pollinating house- 
 grown melons and cucumbers, the staminate flower is 
 broken off, the corolla stripped back, and the anther- 
 cone inserted into the pistillate flower, where it is allowed 
 to remain until it dries and falls away. In pollinating 
 house tomatoes, an implement shown in Fig. 92, one-third 
 size, is used. This is simply a watch-glass, T, secured to a 
 
 Fig. 95. — Fuchsia flower emasculated. 
 
 handle. When the house is dry, at midday, the watch- 
 glass is held under the flowers, which are tapped, and the 
 pollen falls into the glass. The glass is then held up 
 under another flower until the stigma rests in the pollen. 
 It should be said, however, that this pollination of toma- 
 toes is for the purpose of making the fruit set in the ab- 
 sence of insects, not to effect a cross. If the latter pur- 
 pose were the object sought, the flowers which are to 
 bear the seeds would need to be emasculated. 
 
Pollination: or How to Cross Plants 289 
 
 Sometimes it is im- 
 possible to secure the 
 pollen at the time the 
 stigma is ready. In 
 some cases of this kind, 
 the intended parents can 
 be grown under glass so 
 as to bring them into 
 bloom at the same time. 
 In other cases, it is nec- 
 essary to keep the pollen 
 for some time. The 
 length of time that pol- 
 len will keep varies with 
 the species and probably 
 also with the strength 
 and vigor of the plants 
 that bear it. As a rule, 
 it will not keep more 
 than a week or two, 
 and, in general, it may 
 be said that the fresher 
 it is, the better it may 
 be expected to act. It 
 is best kept in dry and 
 tight paper bags, such 
 as are used for covering 
 the flowers. 
 
 Something more should be said about the bags which are 
 used for covering the flowers. It has been found that 
 light transparent oiled paper bags are the best. For 
 
 Fig. 96. 
 
 Fuchsia flower tied up after 
 emasculation. 
 
 U 
 
290 
 
 Plant-Breeding 
 
 small flowers use the two-ounce bags and for larger flowers 
 use the four-ounce size. If oiled bags are not available, 
 the ordinary manilla bags may be used. When they are 
 still flat, as they come from the packages, a hole is made 
 near the opening, and a string is passed through it and 
 then tied at one of the folds, as shown in Fig. 93. The 
 bag is then ready for use. Before it is put on the flower, 
 the lower end of it is dipped in water to soften it so that 
 
 Fig. 97. — Tomato and quince, showing how the sepals were cut off 
 
 in emasculating. 
 
 it can be puckered tightly about the stem and thereby 
 prevent the entrance of any insect. A bag is put upon 
 the seed-bearing flower when emasculation is performed, 
 and upon the intended pollen parent when the flower is 
 still in bud. The bag may be removed from the emas- 
 culated flower from time to time to examine the stigma, 
 and again when the pollen is applied ; but it should 
 not be taken off permanently until the pod or fruit 
 begins to grow. 
 
 By way of recapitulation, let us consider the crossing 
 
Pollination: or How to Cross Plants 291 
 
 of a fuchsia flower. In Fig. 94 two flowers are shown in 
 full bloom, with the long style and the eight shorter sta- 
 mens. The single bud is just the right age to emasculate. 
 We therefore cut off the two flowers and emasculate the 
 bud, as in Fig. 95. The pollen of another flower is apphed 
 and the bag is tied on, as seen in Fig. 96. The best label 
 is a small merchandise tag, and this records the staminate 
 parent and the date. 
 
 It will be seen that in 
 the operation of emas- 
 culating the fuchsia 
 flower- we cut off the 
 sepals as well as the 
 petals. In some plants 
 the calyx adheres- to 
 the full-grown fruit, 
 as on the apple, pear, 
 quince, gooseberry, or 
 persists at the base 
 of the fruit, as in the 
 tomato, pea, raspberry. 
 In these fruits, there- 
 fore, the cutting away 
 of the calyx leaves an 
 indelible mark which 
 
 Fig. 98. — Pollinating kit. 
 
 , at once distinguishes the fruits which have been crossed, 
 even if the labels are lost. In Fig. 97 a tomato and quince 
 are shown thus marked. 
 
 All the foregoing remarks do not apply to the crossing 
 of ferns, lycopodes, and the like, because these plants 
 have no flowers; yet cross-fertilization may take place 
 
292 
 
 Plant-Breeding 
 
 in them. When the spores of these flowerless plants are 
 sown, a thin green tissue, or prothallus, appears and 
 spreads over the ground. In this tissue the separate 
 sex-organs appear, and after fecundation takes place, 
 the fern, as we commonly understand it, springs forth. 
 Thereafter, this fern lives an asexual life and produces 
 spores year after year ; but it is only in this primitive 
 prothallic stage that fertilization takes place, once in the 
 
 life time of the plant. 
 If these plants are to 
 be crossed, the only 
 procedure open to the 
 gardener is to sow the 
 spores of the intended 
 parents together in 
 Fig. 99. — Pollinating kit. the hope that a nat- 
 
 ural mixing may take 
 place. There are various well-authenticated fern hy- 
 brids. 
 
 The pollination of flowers is such a siniple work that 
 few implements are required for its easy performance. 
 Great care is more important than any number of tools. 
 Every one who expects to cross plants should provide him- 
 self with the three instruments shown in Fig. 91, — a pin 
 scalpel, sharp-pointed scissors, and a large hand-lens. If 
 one contemplates much experimenting in this direction, 
 however, it is economy of time to have some sort of box 
 in which there are compartments for the various necessi- 
 ties. These various compartments suggest at once whatever 
 accessories are wanting, and they hold a sufficient supply 
 for several hundred operations. There should be a com- 
 
Pollination: or How to Cross Plants 293 
 
 partment for bags, string, lens, scissors, and pencils, tags, 
 note-book, and the like. Figs. 98 and 99 show a con- 
 venient case for an experimenter, and one that has been 
 used with satisfaction for several years. This kit is 
 twelve inches long, nine inches wide, and three inches 
 deep. 
 
CHAPTER X 
 
 THE FORWARD MOVEMENT IN PLANT- 
 BREEDING 
 
 The first specific interest in cultivated plants was in 
 the gross kinds or species. As the contact with plants be- 
 came more intimate, various indefinite form-groups were 
 recognized within the limits of the species. Gradually, 
 with the intensifying of domestication and cultivation, 
 very particular groups appeared and were recognized. 
 These smaller groups came finally to be designated by 
 names, and the idea of the definite and homogeneous 
 cultural variety came into existence. The variety-con- 
 ception is really a late one in the development of the human 
 race. It is practically only within the past two centuries 
 that cultivated varieties of plants have been recognized 
 as being worthy of receiving designative names. It is 
 within this period, also, that most of the great breeds of 
 animals have been defined and separately named. 
 
 All this measures the increasing intimacy of our contact 
 with domesticated plants and animals. It is a record 
 of our progress. The peoples that are most advanced in 
 the cultivation of any plant are the ones that have the 
 most named varieties of that plant. In Japan, to this 
 day, the plums are said to pass under ill-defined class 
 
 294 
 
The Forward Movement in Plant-Breeding 295 
 
 names. We have introduced these classes, have sorted 
 out the particular forms that promise to be of value to us, 
 and have given them specific American names. Some time 
 ago a native professor in Japan wrote me asking for cions 
 of these plums, in order that he might introduce Japanese 
 plums into Japan. The Russian apples are designated to 
 some extent by class names ; in fact, it was not until the 
 appearance of Kegel's work, about a generation ago, that 
 Russian pomology may be said to have begun. What 
 constitutes a variety is increasingly more difficult to define, 
 because we are constantly differentiating on smaller 
 points. The growth of the variety-conception is really 
 the growth of the power of analysis. 
 
 The earlier recognized varieties seem to have come into 
 existence unchallenged. There is very little record of 
 inquiry as to how or why or even where they originated. 
 That is, the quest of the origin arose long after the 
 recognition of the variety as a variety. Even after 
 inquisitive search into origins had begun, there was Httle 
 effort to produce these varieties. The describing of varie- 
 ties and the search into their histories was a special work 
 of the nineteenth century. One has only to consult such 
 American works as Downing's ''Fruits and Fruit Trees 
 of America," and Burr's ''Field and Garden Vegetables of 
 America," to see how carefully and methodically the 
 descriptions and synonymy of the varieties were worked 
 out. These are types of excellent pieces of editorial and 
 formal systematic work. 
 
 Systematic improvement of plants. — There have been 
 isolated efforts at producing varieties for many years. 
 These efforts began before the time of the general discus- 
 
296 Plant-Breeding 
 
 sion of organic evolution. In fact, it was on such experi- 
 ments that Darwin drew heavily in some of his most 
 important writing. Roughly speaking, however, the 
 conception that the kinds of plants can be definitely modi- 
 fied and varied by man is a product of the last half century. 
 We now think that there is such a possibility as plant- 
 breeding. It is really a more modern conception, so far 
 as its general acceptance is concerned, than animal- 
 breeding. But both animal-breeding and plant-breeding 
 are the results of a new attitude toward the forms of 
 life — a conviction that the very structure, habits, and 
 attributes are amenable to change and control by man. 
 This is really one of the great new attitudes of the modern 
 world. 
 
 The term plant-breeding itself is new. It occurs only 
 in the most recent supplements of dictionaries. Before this 
 term came into use, such words as ''improvement" and 
 ''amelioration" of plants were employed, although cross- 
 breeding had long been current. The early writings of 
 Verlot and Carriere were under the title of " production 
 and fixation of varieties of plants." The term plant- 
 breeding carries the conception of a definite purpose in the 
 producing of new forms and attributes of plants, by cross- 
 ing, selection, and whatever other means may be useful. 
 
 One of the "signs of the times" in North America is the 
 attention that is being given to the practical breeding of 
 plants. A host of persons is actually at work. There 
 are professorships devoted to the subject. Many societies 
 are giving special attention to the practical improvement 
 of plants. Results are accumulating rapidly with very 
 many kinds of plants, and the literature is growing rapidly. 
 
The Forward Movement in Plant-Breeding 297 
 
 Eventually, of course, we shall be able to formulate 
 somewhat definite statements as to how to proceed to 
 secure desired results, and then the literature of plant- 
 breeding can be intelligently rewritten. However, there 
 is no hope that plant-breeding can ever proceed with such 
 exactness as to enable us to produce forthwith the things 
 that we desire, in the way in which the mechanician devises 
 new machines, notwithstanding all the suggestions of 
 persons who write with much self-assurance. For all 
 that we can now see, plant-breeding will always be an 
 experimental process. It is this very experimental 
 uncertainty of the work that gives it much of its charm to 
 inquisitive and sensitive minds. 
 
 The plant-breeder should aim toward definite ideals. — 
 Now, plant-breeding is worthy of the name only as it sets 
 definite ideals and is able to attain them. Merely to 
 produce new things is of no merit ; that was done long 
 before man was evolved. A child can '^ produce" a new 
 variety, but it may learn nothing and contribute nothing 
 in producing it. In many ''new" things that are pro- 
 duced there may be dispute as to whether they are new, 
 and as to whether they are distinct enough to be named 
 and therefore to be ranked as varieties at all. This is not 
 science, nor even breeding : it is playing and guessing. 
 What does the world care whether John Jones produces 
 ''Jones' Giant Beardless Wheat" ? But it does care if he 
 produces wheat having a half of one per cent more protein. 
 We must give up the production of mere "varieties" ; we 
 must breed for certain definite attributes that will make 
 the new generation of plants more efficient for certain 
 purposes : this is the new out-look in plant-breeding. 
 
298 Plant-Breeding 
 
 Plant improvement a serious business. — In considering 
 the American achievement in plant-breeding, we must 
 divest ourselves at the outset of all idea of "wonder," and 
 "miracle," and other nonsense, which has been so much 
 written into the subject in very recent time. Plant- 
 breeding is a plain and serious business, to be conducted 
 by carefully trained persons in a painstaking and method- 
 ical way. It is not magic. There are persons who have 
 unusual native judgment as to the merits and capabilities 
 of plants and who develop great manual skill ; but they 
 are plain and modest citizens, nevertheless, and their 
 methods are perfectly normal and scrutable. The wonder- 
 mongers are the reporters, not the plant-breeders. 
 
 It is a curious psychological phenomenon that the popu- 
 lace, or a certain part of it, seems to lose its head now and 
 then. This phenomenon is not peculiar to politics. It 
 enters those domains that are compassed by fact and that 
 in ordinary times are dominated by common sense. 
 Plant-breeding has been seized of this sensationalism. 
 Newspapers, magazines, and books have spread the most 
 wonderful tales. The lay writers have at last awakened 
 to the fact that great progress is making in agricultural 
 subjects, and, with a fragmentary and superficial view 
 here and there, have written of the subjects with all the 
 enthusiasm and partiality of new discovery. We have 
 now in mind not only the inflated writing about plant- 
 breeding, which constitutes a regrettable contribution to 
 current horticultural literature, but also that general 
 tendency to exploit everything that is capable of high 
 coloring. The agricultural historian, when he takes ac- 
 count of the exploitations of the present day, will recall other 
 
The Forward Movement in Plant-Breeding 299 
 
 stages in which we seem temporarily to have lost our better 
 judgment, of which the Morus multicaulis craze and the 
 lightning-rod boom are examples in two past generations. 
 
 Having now warned our readers that we have nothing 
 , marvelous in store, we shall proceed to indicate some of 
 the ways in which American plant-breeders are working, 
 fully conscious that the space at our disposal is much 
 too httle to allow of any adequate presentation of the 
 subject. It may not be out of place to call the reader's 
 attention to the three foundations on which rests the in- 
 creased productiveness of crops and animals : — 
 
 The enrichment of the land; 
 
 The tillage and care ; 
 
 The producing of better varieties and strains. 
 
 We have long given careful attention to the first two ; 
 now we are studying the third with new enthusiasm aad 
 purpose. 
 
 The results of pla7it-hreeding effort. — Happily, we are 
 not without abundant accompHshment in this new field. 
 The last ten years has seen a remarkable specialization 
 in the producing of plants that are adapted to particular 
 needs. The days of merely crossing and sowing the 
 seeds to see what will turn up are already past ^dth 
 those who are engaged seriously in the work. The old 
 method was hit-and-miss, and the result was to take 
 what good luck put in our way : the new method proceeds 
 definitely and directly, and the result is the necessary 
 outcome of the Hne of effort. The crux of the new ideal is 
 efficiency in one particular attribute in the product of 
 the breeding. These attributes are measurable; the 
 kinds of results are foreseen in the plan. 
 
300 Plant-Breeding 
 
 State plant-breeding associations. — One of the most 
 significant advances in popular interest in plant improve- 
 ment is the banding together of persons in many of the 
 states and provinces in an organized effort to improve 
 plants, especially field crops. This line of effort has been 
 largely brought about at the suggestion of some officer 
 of the state agricultural college, who is often an expert 
 plant-breeder himself, and usually acts as secretary of the 
 association. These associations have done great good 
 in arousing interest in plant-breeding. 
 
 The Wisconsin Association, known as the Wisconsin 
 Agricultural Improvement Association, was estabhshed 
 Feb. 22, 1901, and now has a paid-up membership of 
 over 2000 persons, consisting of '^all former, present, and 
 future students and instructors of the Wisconsin College 
 of Agriculture," also ''any person residing within the state 
 having completed a course in agriculture in any college 
 equivalent to that given by the Wisconsin University." 
 More recently the county agricultural schools have been 
 admitted to membership and honorary members may be 
 elected by a majority vote at any annual or special meet- 
 ing of the association. 
 
 The association has organized some 44 county sub- 
 orders, which are smaller units conducting an active 
 work in more restricted areas. These county orders con- 
 tain approximately 4000 members. Any one interested in 
 agriculture may unite with the county order. They have 
 become live centers which stand behind all agricultural 
 activities and lend a helping hand in making agricultural 
 and other resources of the county known far and near. 
 As a result of the association there has been established 
 
The Forward Movement in Plant-Breeding 301 
 
 in the neighborhood of 2000 seed-grain centers where 
 pure-bred seed barley may be obtained. It is estimated 
 that over seventy-five per cent of the seed barley of Wis- 
 consin is of one distinct variety. 
 
 Another series of organizations, to be known as 'Hown- 
 ship organizations," has been planned. These are smaller 
 groups within the county orders. Three are already in 
 existence. This scheme of organization brings the activi- 
 ties of the association to practically every farmer of the 
 state. 
 
 Starting out primarily as breeding associations, their 
 activities have extended in many directions. An alfalfa 
 order has been established which is closely affiliated with 
 the main association : its object is 'Ho promote the alfalfa 
 interests of the state in general," 
 
 1st. By cooperating with the Department of Agronomy 
 and the Wisconsin Agricultural Experiment Association 
 in growing, experimenting, and in the wide dissemination 
 of alfalfa ; 
 
 2d. By having alfalfa exhibits at agricultural fairs ; 
 
 3d. By having annual meetings in order to report and 
 discuss topics beneficial to the members of the order ; 
 
 4th. By distributing Uterature and information bearing 
 upon the production of alfalfa for seed and forage. 
 
 The alfalfa order was organized three years ago and now 
 has a membership of 1200. In 1914, 50 tons of alfalfa 
 seed were sent out for experimental purposes. 
 
 The association receives state aid, $5000 a year, and 
 some of the county orders receive financial aid from the 
 county. The annual dues of members is fifty cents. 
 
 One of the principal aims of the Wisconsin association 
 
302 Plant-Breeding 
 
 is to place pure-bred seed on the market. This seed is 
 to bear the seal of the association. 
 
 It is estimated that members of the association sell 
 over three hundred thousand dollars' worth of pure-bred 
 seed a year. The members are in close touch with the 
 breeding work of the experiment station and test, propa- 
 gate, and disseminate the improved grains which are pro- 
 duced on the station farm. 
 
 The association prints an annual report of over one 
 hundred pages containing the progress of the members in 
 improving seed grain and much valuable information 
 concerning plant-breeding in general. Such titles as the 
 following appear in recent annual reports : — 
 
 Dissemination of Pure Bred Seed Grains, Through the Coopera- 
 tion of Students in the Country Schools, J. C. Brockert. 
 
 Necessity of Thorough Preparation of Pure Bred Seed Grain for 
 the General Trade, Wm. R. Leonard. 
 
 County Order of Experiment Association as Factor to Promote 
 Dissemination of Pure Bred Grain, R. A. Moore. 
 
 Importance of Testing Our Pure Seed Grains Previous to Sowing 
 Season's Crop, H. L. Post. 
 
 Importance of the Farm Inspection Work, and How Shall It Be 
 Carried Out? E. B. Skewes. 
 
 Growing and Preparing Seed Grains and Forage Plants for 
 Exhibition, O. R. Frauenheim. 
 
 Wheat Breeding — The Value of the Individual, F. H. Demaree. 
 
 In this connection, mention should be made of the 
 Wisconsin Potato Growers' Association, an active and 
 growing organization whose object is to improve the seed 
 and table potatoes of Wisconsin by breeding and to 
 
The Forward Movement in Plant- Breeding 303 
 
 guarantee variety shipments true to name and free from 
 disease. This association, Uke its sister organization, does 
 business on a large scale and has at present nearly 300 
 members. '' Potato Special " trains have been run through- 
 out the state under its auspices and that of the State 
 College of Agriculture, and several very successful potato 
 exhibits have been held. 
 
 This association has done much to standardize certain 
 commercial varieties of potatoes and to put seed on the 
 market which is true to name. Its members found our 
 varieties badly mixed up and containing many distinct 
 types. This purifying of varieties is the first step toward 
 careful and systematic breeding. 
 
 A Minnesota association, known as the ''Minnesota 
 Field Crop Breeders' Association," has been organized 
 with a similar plan and objects as the Wisconsin associa- 
 tions. It publishes an elaborate annual report giving 
 information concerning the work of the association as a 
 whole and the activities of the county sections, of which 
 there are many. One of the functions of the association, 
 besides encouraging the production and sale of pure-bred 
 seeds, is to stage elaborate exhibits of farm products at 
 the state and other fairs. 
 
 In some states, notably lUinois, Ohio, and New York, 
 associations of breeders have been established on a dif- 
 ferent membership basis. They have chosen to have 
 smaller associations consisting of persons who bind them- 
 selves to follow certain rules and regulations laid down 
 by the association. The IlUnois Seed-corn Breeders' 
 Association is such an organization. Its members grow 
 certain varieties of corn recognized by the association 
 
304 Plant- Breeding 
 
 and offer these for sale with the approval and backing of 
 the association. 
 
 The Ohio and New York associations laid out elabo- 
 rate plans of breeding for their members to follow, but it 
 was found that farmers were not ready for such work and 
 as a result the Ohio association has never been very large 
 and the New York association has abandoned this plan 
 and is turning its attention to bringing the farmers and 
 seedsmen into closer relations, encouraging the farmer to 
 demand a better product and the seedsmen to produce one. 
 
 Other plant-breeding associations. — The most notable 
 breeders' associations are the Canadian Seed Growers' 
 Association and the Swedish Seed Association. 
 
 The former has an elaborate system of inspection of all 
 seeds sold by members of the association under the su- 
 pervision of a permanent, salaried secretary. The results 
 are noteworthy. The standard of seed grain has been 
 tremendously raised in Canada and much better crops 
 are the result. Canadian seed grain is now in demand 
 all over the world. The Canadian experiment stations 
 are leading in this work by carefully and systematically 
 producing improved varieties on their experimental farms 
 and distributing them to members of the association who 
 grow them, keeping up a careful selection from year to 
 year and offering them for sale. 
 
 The Swedish association has an interesting history and 
 an enviable record. It has done more, probably, than 
 any other organization to reshape our conception and 
 methods of selection. Dr. Nilsson and his associates 
 have started on a large scale the principle of individual 
 selection in contrast to the older method of mass selection 
 
The Forward Movement in Plant- Breeding 305 
 
 which is now largely given up. The group of scientists 
 at Svalof have not only shown their ability to produce 
 practical results, but they have also elaborated scientific 
 principles. 
 
 The founding of the station at Svalof is wholly due to 
 the private initiative of a group of Swedish farmers. The 
 purpose of the association has always been to produce 
 practical results, to breed better grains for local use. 
 
 But the station has been fortunate from the first in 
 having in its employ expert botanists whose skill has not 
 only produced many noteworthy new varieties, but who 
 have elaborated scientific principles of far-reaching im- 
 portance. These men have been given a free hand to 
 pursue their work without such distracting activities as 
 teaching, comparative field trials, commercial analyses, 
 and the like. This fact together with an unrestricted 
 organization, a well-selected program, and an expert corps 
 of assistants accounts for the wonderful success of this 
 station. 
 
 This Swedish seed association has two groups of mem- 
 bers: those who are permanent after having paid $28 
 once for all ; and those who pay annually $1.40. 
 
 The association has an annual budget of about $40,000 
 derived from dues of members, contributions from agri- 
 cultural associations, government aid, and sale of pedigreed 
 seed. Funds from the last two sources have increased 
 very rapidly in recent years. Gifts of various kinds 
 amounting to $77,000 have been set aside for buildings. 
 
 Accordingly, the society now has at its disposal a large 
 and well-equipped establishment, comprising two con- 
 nected buildings serving as laboratories (Fig. 100), a house 
 
306 
 
 Plant-Breeding 
 
The Forward Movement in Plant-Breeding 307 
 
 for preparatory work, with a little farm and a dwelling 
 house ; it also owns 40 acres of land, of which special 
 cultures and seed multiplication plots occupy 25 acres. 
 Despite this, it has been found necessary to make most 
 of the cultural experiments on the wide fields of the huge 
 property adjoining, in order to give the different cereals, 
 occupying in all about 30 acres a year, their proper place 
 in the rotation of crops, which is found absolutely neces- 
 sary for a normal development. 
 
 The program of work in Sweden was, at first, vague 
 and uncertain. Theorizing scientists were attempting to 
 solve problems for practical farmers and nobody had 
 blazed the trail. The starting-point of the work was 
 naturally the method of selection in vogue at the time, 
 that is, the Darwinian method of ''methodical selection" 
 or of ''mass selection" as it is now called. By this system, 
 a selection of seed was made from a large number of plants 
 and the whole thrown together and sown "en masse" 
 in a single plot. But it soon became evident that this 
 method of selection was not yielding the results which the 
 Swedish farmers demanded — better varieties which would 
 be constant. The method of selection was therefore 
 changed and in two years the difficulties were being over- 
 come by the new method. 
 
 This new method consisted of testing individual plants 
 and their progeny instead of making, at once, a com- 
 posite test of many plants. This plan of individual 
 selection has proved itself. The results were convincing. 
 It left no doubt as to the fact that the only true starting- 
 point for the fixation of different types must be plants 
 taken one by one. 
 
308 Plant-Breeding 
 
 This Swedish discovery has changed the outlook on 
 the problem of plant-breeding, especially the methods of 
 selection. It could be easily demonstrated that there 
 existed in any cultural variety of plants a large number 
 of independent forms having widely divergent quahties 
 and a practical value that was quite useful. It was 
 found, moreover, that most of the descendants or ''pedigree 
 culture " of single individuals were constant. 
 
 In employing the old method of ''mass selection," 
 they were working bhndly without knowing how or when 
 or even whether they were going to reach a stabiHty of 
 type ; on the other hand the method of pedigreed culture 
 or "individual selection" ehminated the fear of failure 
 because of the appearance of the hitherto unsurmountable 
 variations. The varieties are already there, and fixed 
 from the beginning of the work ; the only difficulty is to 
 learn to recognize them and to place the proper valuations 
 upon them. 
 
 The success of this method of breeding at Svalof has 
 profoundly modified the method of selection in this 
 country. The principle almost universally applied now 
 is the method of individual selection. Thus we hear 
 about plant-to-row, head-to-row, ear-to-row, or tuber-unit 
 testing, depending upon the plant used. 
 
 This method of selection is by no means the only one 
 used for plant improvement at the Swedish station, hy- 
 bridization also plays an important part in the work. 
 
 The work has grown very rapidly and has now been 
 split up into different departments with an expert in 
 charge of each. 
 
 Commercial breeding agencies. — The chief among com- 
 
The Forward Movement in Plant- Breeding 309 
 
 mercial breeding agencies are, of course, the professional 
 seedsmen. The demand for '^ novelties " is ever present 
 and the seedsman must meet it. Therefore every seeds- 
 man's catalogue each spring features them, giving them 
 a prominent place and often painted in radiant colors. 
 Everybody knows that novelties are often no better 
 than the old standard sorts. But this demand for some- 
 thing new seems to be inherent. 
 
 It does not seem to be the common practice among 
 American seedsmen to produce their own novelties by 
 precise and recognized plant-breeding methods. Many 
 of them are purchased abroad and others are accidental 
 discoveries picked up here and there. 
 
 Our standard sorts of seeds of all kinds are being 
 gradually improved, but usually not by any particular up- 
 to-date methods, except in certain unusual or exceptional 
 instances. The seedsmen, however, carefully rogue their 
 fields to eliminate divergent plants in an attempt to pro- 
 duce seed of more importance. 
 
 Recently, however, the American Seed Trade Associa- 
 tion, consisting of the better class of seedsmen of the 
 United States, has begun a general movement for im- 
 proving crops by methods such as are used by careful 
 breeders at the agricultural experiment stations. A 
 committee on crop improvement has been organized 
 whose duties are to ascertain, so far as possible, how the 
 seed trade can be most helpful in these movements for 
 better bred seed, and to bring about a close harmony 
 between the seedsmen and the plant-breeding experts of 
 the agricultural experiment stations. 
 
 Many seedsmen feel, at present, that the extra cost 
 
310 Plant-Breeding 
 
 entailed in producing pedigreed seed will not be ade- 
 quately paid for by the average American buyer. There 
 is probably much justification for this feeling. Two 
 things should be done — to educate the buying public to the 
 importance of better seed and the justification for its 
 greater cost, and also to devise methods whereby this 
 seed may be more cheaply and economically produced. 
 The agricultural colleges through various channels are 
 doing much to solve these two difficulties. 
 
 Work of the council of grain exchanges. — The National 
 Council of Grain Exchanges is the associated body of the 
 various grain exchanges or boards of trade of this coun- 
 try. This organization is interested in a larger yield of 
 better grain. It has a crop improvement committee 
 which is very active in grain-improvement work, including 
 grain-breeding. This committee is conducting a very 
 extensive publicity campaign in an attempt to induce 
 farmers to use select seed and improve their crops. The 
 executive work is done by a secretary, who acts as general 
 manager, and an agronomist, who is an expert plant- 
 breeder and advises concerning the technical features of 
 the work, most of which is done through the county 
 agents. To aid in this work, the , committee publishes a 
 monthly publication called The County Agent, a paper 
 filled with terse information concerning all phases of farm 
 improvement work. The secretary and agronomist have 
 large funds at their disposal, which are being used to bring 
 about concerted action by farming communities for the 
 improvement of seed grain. 
 
 United States Department of Agriculture and state experi- 
 ment stations, — The most methodical plant-breeding is 
 
The Forward Movement in Plant-Breeding 311 
 
 now being clone by officers of the experiment stations in 
 the United States and Canada, and by the United States 
 Department of Agriculture. In most of the experiment 
 stations there is at least one person interested in improv- 
 ing horticultural plants and others interested in field 
 crops ; as there is an experiment station in every state 
 and territory and in the provinces of Canada, it will be 
 seen that there are several hundred persons who, by 
 their profession, are directly concerned in plant-breeding, 
 aside from a number of persons in the federal Department 
 of Agriculture who devote themselves exclusively to this 
 subject. The work is extended, also, into the hands of 
 various assistants in the different institutions ; so that it 
 is probably no exaggeration to say that three to four 
 hundred professional investigators are now giving atten- 
 tion, for a greater or less part of their time, to measures 
 for improving American crop production by means of 
 breeding. 
 
 The breeding enterprises of the federal Department of 
 Agriculture were formerly confined to investigators in the 
 Plant-Breeding Laboratory. But the work has grown to 
 such an extent and breeding now touches so many phases 
 of plant work that the former organization, as such, has 
 been discontinued, and breeding is taken up in connec- 
 tion with many other departments. There is now more 
 of a tendency for the administrative divisions to group 
 themselves around the crops such as corn, cotton, wheat, 
 vegetables, and so forth, rather than processes such as 
 plant-bre.eding, or culture. 
 
 The work of the federal investigators has been tre- 
 mendously important both from the standpoint of original 
 
312 Plant-Breeding 
 
 research and the production of improved varieties and 
 strains for dissemination. 
 
 The success of the cotton-breeding experiments is 
 noteworthy. These have been conducted with the object 
 of increasing the length and strength of lint ; and an early 
 variety to avoid the ravages of the boll-weevil is desired. 
 The famous long-stapled Sea Island Cotton has been 
 much used for hybridizing with the upland cottons to 
 increase the length of lint of the latter. The length has 
 been increased very considerably by this method and the 
 varieties have been made more uniform, an important 
 factor in ginning. 
 
 The work of Webber and Swingle in producing new 
 types of oranges which are resistant to cold is exceedingly 
 important. Various varieties of the common sweet 
 orange were crossed with Poncirus (or Citrus) trifoliata, a 
 hardy hedge orange, and hybrids have been produced which 
 are called " citranges." These will grow some four hundred 
 miles farther north than the present orange belt, which is 
 no small factor in orange-growing. These hybrids are too 
 bitter to be eaten out-of-hand, but they make an excellent 
 ade ; many of them have more juice than lemons. 
 
 A cross has also been made between the pomelo or 
 grapefruit and the tangerine. A hybrid was produced 
 which combines the easily removable rind of the tan- 
 gerine and has the flavor, not of the pomelo, but of the 
 sweet orange. A fruit of this kind, combining these char- 
 acteristics so well, bids fair to play an important part in 
 orange-growing of the future. 
 
 The division of Plant Introduction has contributed no 
 small part to breeding work. Through its activities, a great 
 
The Forward Movement in Plant-Breeding 313 
 
 many plants have been imported from all over the world 
 which have formed rich material for the plant-breeder to 
 take and improve, and many other varieties have been 
 introduced which have immediately become valuable 
 without further improvement. Such plants as durum 
 wheat, Japanese kinshu rice, Swedish select oats. Wash- 
 ington nave] orange, cold-resistant varieties of alfalfa, 
 Russian apples, varieties of dates for Southern Cali- 
 fornia and Arizona, drought-resistant olives, Egyptian 
 cotton, and very many others have added millions to our 
 agricultural wealth. 
 
 The work of Orton and his associates in breeding plants 
 resistant to disease forms an important chapter in this 
 work. They have been successful in Avaging war on wilt 
 of cotton, cowpeas, watermelons (see Figs. 55 and 56), and 
 other crops by means of breeding to obtain wilt-resistant 
 strains. The only successful method of combating certain 
 maladies seems to be in this way. Strains of disease-resist- 
 ant asparagus and of rust-resistant cereals have reached 
 economic importance. 
 
 Many great sections of the United States which are 
 now nearly barren could be made productive if varieties 
 of plants could be developed which are resistant to drought 
 and alkali. This work has occupied the attention of a 
 large corps of plant-breeders and not without results. 
 The experts from eighteen state experiment stations be- 
 sides the men from Washington are engaged in this work. 
 As a result, varieties of wheat and other cereals, alfalfa, 
 nuts, olives, and various fruits have been developed which 
 will grow in parts of this great region and are of considerable 
 economic importance. 
 
314 Plant-Breeding 
 
 Work of the state agricultural experiment stations. — 
 Investigators in the state experiment stations have always 
 taken an active part in plant-breeding work. Five years 
 ago, in an admirable editorial in the Experiment Station 
 Record, Dr. Allen says as follows: "The list of proj- 
 ects conducted by the experiment stations under the 
 Adams fund includes sixty-three which fall under the head 
 of investigations in breeding (eleven of these relate to the 
 breeding of animals). This relatively large number indi- 
 cates the popularity of the subject, and an evident feeling 
 that it not only presents large research possibility, but is 
 a line in which investigation is greatly needed. The 
 attention which is being given to breeding is encouraging 
 and the number of enterprises suggests the possibility of 
 material additions to the general understanding of its 
 various phases." 
 
 The experiments subsequent to that time have, to a 
 considerable extent, justified the hope of '^ material 
 additions to the general understanding of its various 
 phases." Numerous bulletins have been published which 
 have added to that knowledge, and the experiment station 
 men have written many articles which have appeared in 
 various serial publications. 
 
 The lines of work which have received the greatest 
 attention and in which the most constructive work has 
 been done are the application of Mendel's laws to economic 
 plants and the elucidation of individual selection and pure- 
 line breeding. Not only have important practical results 
 been obtained in improving our economic plants, but a 
 considerable amount of material of scientific value has 
 been accumulated. 
 
The Forward Movement in Plant- Breeding 315 
 
 The experiments with corn at the IlHnois and other 
 experiment stations and those with timothy at the Cornell 
 station stand out prominently as examples of pieces of 
 scientific research which, at the same time, have tre- 
 mendous economic importance. 
 
 There is scarcely an economic crop but is receiving 
 some attention by the plant-breeders of our experiment 
 stations, and bulletins are appearing frequently dealing 
 with this phase of the work. 
 
 Many experiment stations, such as Wisconsin, Minne- 
 sota, Ohio, New York, and Kansas, are also busily engaged 
 in producing superior varieties upon their own grounds 
 for distribution to their constituents. 
 
 The old-time very prevalent variety tests are still 
 made, but these are now supplemented by variety im- 
 provement and careful studies of variety adaptation. 
 
 Beside the large amount of practical work which most 
 of the stations are doing, there are a large number of 
 breeding projects prosecuted by them, and which are 
 destined to become of scientific importance. 
 
 The following projects have been reported by Dr. 
 Allen of the federal Office of Experiment Stations as 
 now conducted at the different stations : — 
 
 Breeding Corn — Alabama Station. 
 
 Breeding Experiments with Cotton — Alabama Station. 
 Breeding Oats — Alabama Station. 
 Wheat Breeding Investigations — Kansas Station. 
 Alfalfa Breeding Investigations — Kansas Station. 
 Analysis of Cellular Structure of Hybrids — Maine Station. 
 Experimental Modification of the Hereditary Process — Maine 
 Station. 
 
316 Plant-Breeding 
 
 Breeding Alfalfa with Reference to the Extreme and Sub-tropical 
 
 Conditions of Arizona — Arizona Station. 
 Cotton Breeding — Arkansas Station. 
 Nicotiana Hybrids — California Station. 
 Improvement of Dent, Flint, and Sweet Corn in Yield and 
 
 Feeding Value, by Breeding Work in Six Different Localities 
 
 — Connecticut Station (State). 
 Breeding Investigations with Tobacco — Connecticut State 
 
 Station. 
 Zenia in Maize and Hereditary Transmission of Various Char- 
 acters — Connecticut State Station. 
 The Effect of Variations in Physical Characters and Chemical 
 
 Composition of the Corn Kernel upon the Vigor of the 
 
 Plant — Delaware Station. 
 Plant Breeding — Florida Station. 
 Investigation of Mendelian Laws in Application to the Cotton 
 
 Plant — Georgia Station. 
 Inheritance of Contrasted Characters — Mississippi Station. 
 Study of the Correlation of Characters and of Inheritance in 
 
 Pure Lines and Varieties — Montana Station. 
 Degree of Close Breeding in Maize — Nebraska Station. 
 Plant Breeding Work with Pure Lines of Cereals — New Mexico 
 
 Station. 
 Place Variation with Cotton — North Carolina Station. 
 The Increase and Fixation of Desirable Properties in Plants — 
 
 Ohio Station. 
 Breeding Drought-resistant Corn ; Study of Qualities of Drought 
 
 Resistance — Oklahoma Station. 
 Breeding Sorghums, especially Kafir Corn, Milo Maize, and 
 
 Broom Corn, to secure more Drought-resistant Types — 
 
 Oklahoma Station. 
 Fundamental Study of Inheritance in Cotton — Texas Station. 
 Comparative Studj^ of Durum, Poulard, and Bread Wheats — 
 
 Arizona Station. 
 
The Forward Movement in Plant- Breeding 317 
 
 Study of Principles Underlying the Development of Disease 
 
 Resistance or Immunity in Farm Crops — North Dakota 
 
 Station. 
 Effects of Pollen from Barren Stalks of Corn — South Carolina 
 
 Station. 
 Breeding a Strain of Peaches resistant to Brown Rot — Alabama 
 
 Station. 
 Biological Analysis of Papago Sweet Corn for the Synthesis of 
 
 Desirable Characters — Arizona Station. 
 Principles relating to Transmission of Characters in the 
 
 Apple as affected by Selection and by Crossing — Illinois 
 
 Station. 
 Apple Breeding — Iowa Station. 
 
 Investigations upon Asparagus — Massachusetts Station. 
 Study of the Principles of Heredity underlying Disease and 
 
 Climatic Resistance in the Apple, Plum, and Strawberry — 
 
 Minnesota Station. 
 Heredity in Plants — Nebraska Station. 
 Studies of Heredity in Vegetables, especially Squashes and 
 
 Tomatoes — New Hampshire Station. 
 Carnation Breeding — New Hampshire Station. 
 Nature of the Inheritance and Correlation of Structural Char- 
 acters in Crosses — New Jersey Station. 
 Improvement of Mexican Chili by Breeding and Selection — 
 
 New Mexico Station. 
 Investigation of the Laws of Inheritance in Hybridization — 
 
 New York (Cornell) Station. 
 An Investigation of Mutation and Other Types of Variation 
 
 in Wild and Cultivated Plants, to determine their Value 
 
 in Plant Breeding — New York (Cornell) Station. 
 Influence of Environment in producing Variation of Value to 
 
 the Breeder — New York (Cornell) Station. 
 Study of Transmission of Characters in Hybrids of Rotundifolia 
 
 Grapes — North Carolina Station. 
 
318 Plant- Breeding 
 
 A Study of the Fecundation of the Rotundifolia Grapes — South 
 Carolina Station. 
 
 Improvement of Hardy Wild Fruits of the Northwest by Breed- 
 ing and Crossing — South Dakota Station. 
 
 The Breeding of Apple and Pear Varieties for Resistance to 
 Blight — Tennessee Station. 
 
 Breeding Work with Blackberry — Texas Station. 
 
 Breeding Experiments with Apples — Virginia Station. 
 
 Mendelism of the Hybrids of Blackberries and Raspberries, 
 particularly with Reference to Leaf Structure and Habits 
 of Growth — Washington Station. 
 
 Pollination of the Apple — West Virginia Station. 
 
 Investigation of Mendel's Law as applied to Hybridizing the 
 White with the Black Varieties of Muscadine Grape — 
 Georgia Station. 
 
 Apple Breeding Investigations — Idaho Station. 
 
 Effects of Fertilizers on Cell Structure of Crops and their Rela- 
 tions to Mutations in Fruits, Vegetables, and Flowers — 
 Maryland Station. 
 
 Investigations on "Double Flower" and Sterility in Blackberries 
 and Dewberries — North Carolina Station. 
 
 Pollination of the Apple and Conditions affecting It — Oregon 
 Station. 
 
 In addition to the work of the experiment station men, 
 very much highly valuable work is under way by such 
 men as East at Harvard, Shull at Cold Spring Harbor, 
 Harper and Stout at the New York Botanical Garden, 
 Bradley Moore Davis at the University of Pennsylvania, 
 B. M. Duggar at the Missouri Botanical Garden, and many 
 others. This research is undertaken by well-trained 
 specialists who are producing the very highest type of 
 fundamental constructive results. 
 
The Forward Movement in Plant- Breeding 319 
 
320 
 
 Plant-Breeding 
 
The Forward Movement in Plant- Breeding 321 
 
 Instruction in plant-breeding in the United States. — One 
 of the most, if not the most, significant advances that 
 plant-breeding has made in recent years is the increase in 
 the amount of instruction given in the agricultural colleges 
 and other agricultural schools. 
 
 Formerly, the only teaching of this subject was in 
 connection with a course of horticulture, probably, 
 and the breeding was likely to receive minor considera- 
 tion. 
 
 All of this has been changed. Strong courses are 
 given in this subject in all of the agricultural colleges. 
 Some go so far as to have separate departments or divi- 
 sions in which the staff devotes all of its time to plant- 
 breeding instruction and investigations. It is estimated 
 that over two thousand students receive regular plant- 
 breeding instruction each year in this country. This is 
 bound to have tremendous influence upon practical 
 plant improvement on the farms of the country. Plant- 
 breeding holds a very prominent place in the instruction 
 given to short-term students, as it should, and in the 
 form of various extension enterprises. 
 
 Luther Burhank. — In addition to the large number of 
 plant-breeders who have some official connection with 
 the state experiment stations or the federal government, 
 there has always been a number of men who have 
 maintained private plant-breeding establishments. Chief 
 among these is Luther Burbank. He will always be given 
 a prominent place in American horticulture because of the 
 many and valuable varieties which he has added to it. 
 
 The practical results, however, that Mr. Burbank has 
 secured have been praised by the writers beyond reason. 
 
322 
 
 Plant-Breeding 
 
 a 
 
 
 03 
 
 'a 
 
 CO 
 
 CO 
 
 o 
 
 
The Forward Movement in Plant-Breeding 323 
 
 His place abounds in interesting and surprising things, 
 just as would be expected of any man's place if conducted 
 under similar conditions (Figs. 101-103), and many of the 
 things will undoubtedly have great value. His work has 
 been so much written about that it is not necessary to 
 make any catalogue of the things that are under his hand. 
 It is not too much to hope that some of his productions, 
 as the plumcots, may be the starting-points of strong and 
 noble lines of evolution. Some of those that have been 
 much heralded are of doubtful economic value. 
 
 The value of Mr. Burbank's work lies above all merely 
 economic considerations. He is a master worker in mak- 
 ing plants to vary. Plants are plastic material in his 
 hands. He is demonstrating what can be done. He is 
 setting new ideals and novel problems. Heretofore, 
 gardeners and other horticulturists have grown plants 
 because they are useful or beautiful : Mr. Burbank grows 
 them because he can make them take on new forms. 
 This is a new kind of pleasure to be got from gardening, 
 a new and captivating purpose in plant growing. It is a 
 new reason for associating with plants. 
 
APPENDIX A 
 
 GLOSSARY OF TECHNICAL PLANT-BREEDING 
 
 TERMS 
 
 Allelomorph. — One of the pure unit-characters commonly 
 existing singly or in pairs in the germ-cells of mendelian hybrids, 
 and exhibited in varying proportion among the organisms them- 
 selves. Thus an allelomorphic pair of characters comprises the 
 opposed units, one of which comes from each parent in a hybrid. 
 For example, the roundness and wrinkledness found in two varie- 
 ties of peas is an allelomorphic pair. 
 
 Biometry. — The application of statistical methods to biological 
 problems. 
 
 Chromosome. — A term applied to certain minute bodies, in 
 the nuclei of the animal and vegetable cells which appear at 
 definite periods in the division of the cell ; they are constant in 
 number for each species of animal or plant, and are characterized 
 by the fact that they stain very deeply with certain dyes. The 
 chromosomes are supposed to be the bearers of heredity. 
 
 Dominant characters. — It often occurs, when* two varieties 
 or species are crossed, that the characters of one appear in the 
 first generation hybrid to the exclusion of the other. These 
 are called dominant characters. 
 
 Duplex. — The state of inheriting a character that is present 
 in both parents. 
 
 Epistatic. — Used to describe a color factor which, in hybrid- 
 ization, covers up or hides other color factors in the first genera- 
 tion hybrid (opposed to hypostatic). 
 
 325 
 
326 Plant-Breeding 
 
 Factor hypothesis. — An assumption that organisms may 
 contain various hereditary units which do not appear in their 
 body cells. This is especially applied to color units. Very 
 often these factors do not appear until the plant has been crossed 
 with another plant containing a complementary factor. 
 
 Fi. — A symbol introduced by Bateson, to designate the 
 first filial or hybrid generation. 
 
 F2. — A symbol for the second generation. 
 
 /^3. — A symbol for the third hybrid generation. And so on. 
 
 Galton curve. — A curve, devised by Galton, when the values 
 for all the individuals are recorded consecutively in an ascending 
 series. The class values are plotted on the vertical axis. 
 
 Gamete. — A mature sex- or germ-cell , which will produce a 
 new individual upon uniting with another such cell of the op- 
 posite sex. 
 
 Genetics. — A study of the phenomena of variability and 
 heredity, or of the physiology of descent, as affecting individuals 
 or races of plants, animals, or human beings. 
 
 Genotype. — A type represented by individuals of the same 
 germinal constitution. The nature of such a type can be 
 determined only by a breeding test, not by inspection. 
 
 Heterozygote. — An individual formed by the union of two 
 germ-cells of unlike constitution. 
 
 Homozygote. — An individual which is of a pure type in regard 
 to a certain character because both of its parents were of the 
 same gametic constitution. 
 
 Hybrids. — The offspring of crosses between individuals of 
 distinctly different natures. 
 
 Hypostatic. — Used to describe a color factor which is con- 
 cealed by higher color factors. (See Epistatic.) 
 
 Mutation. — A sudden variation, differing from its parents 
 in a distinct character or characters, and able to transmit its 
 new characters in full degree to its offspring. 
 
 Nulliplex. — A condition of an individual when it does not 
 
Appendix A 327 
 
 possess a character because neither of its parents carried the 
 possibilities for such a character in their germ-cells. 
 
 Phenotype. — The visible type of a group as expressed by 
 external characteristics. Opposed to genotype. There may be 
 several genotypes in a phenotype. 
 
 Plateation. — (From the Latin platea, meaning place.) A 
 physiological variation caused by external influences such as 
 locality, climate, soil, and so forth; sometimes called place- 
 variation. It IS what Darwin called " definite variation." This 
 word was coined to express in one word the third of the three 
 kinds of variation — fluctuation, mutation and plateation . (Here 
 first defined.— A. W.G.) 
 
 Qiietelet curve. — A curve which shows the relative frequency 
 with which individuals of a given lot, or population, occur in 
 certain classes. Class values are plotted on the horizontal 
 line and frequencies on the vertical. The mode is the highest 
 point of such a curve and represents the dominating type of 
 the character studied. 
 
 Recessive characters. — (See Dominant characters.) The 
 characters which are entirely covered up the first generation 
 but reappear the second and subsequent generations. 
 
 Segregation. — The reappearance in definite ratios, in the 
 second hybrid generation, of the characters of two forms crossed ; 
 and the first hybrid generation (when this differs from the 
 dominant character). 
 
 Simplex. — The condition of an individual which has inherited 
 a character from only one parent. 
 
 Somatic. — Of, or pertaining to, the body as opposed to the 
 germ-cells. 
 
 Xenia. — The results of a cross-fertilization between different 
 varieties of plants due to a double fertilization; found in such 
 plants a^ corn, peas, etc. 
 
 Zygote. — The result of the union of two gametes. (See 
 Gamete.) 
 
APPENDIX B 
 
 PLANT-BREEDING BOOKS 
 
 Following is a brief list of books containing material more or 
 less related to plant-breeding. This list is not intended to be 
 complete, but is designed to give the reader an idea of the more 
 important books on the subject. There are many books which 
 are not listed upon the general subject of botany, others upon 
 Heredity and evolution in their broadest phases, and still others 
 upon animal breeding which will contain much material which 
 is related to the subject of plant improvement by breeding. 
 
 American Breeder's Association Reports. Washington, D.C. 
 
 1905-1912. 
 Bailey, L. H., Cyclopedia of American Agriculture. Vol. II, 
 
 Crops. Macmillan Co. 1907. 
 Bailey, L. H., Standard Cyclopedia of Horticulture. 6 vols. 
 
 (Continuing) Alacmillan Co. 1914. 
 Bailey, L. H., Sketch of Evolution of Our Native Fruits. xiii + 
 
 472 pp., 125 figs. Macmillan Co. 3d edition. 1898. 
 Bailey, L. }i.,The Survival of the Unlike. 515 pp., illus. Mac- 
 millan Co. 1897. 
 Bateson, W., MendeVs Principles of Heredity, xiv + 396 pp., 
 
 9 pis., and 35 figs. Cambridge. 1909. 
 Baur, Dr. Erwin, Einfuhrung in die experimentelle Vererbungs- 
 
 lehre. 293 pp., 80 figs. Berlin. Gebriider Borntraeger. 
 
 1911. 
 
 328 
 
Appendix B 329 
 
 Castle, W. E., Coulter, J. M., Davenport, C. B., East, 
 E. M., Tower, W. L., Heredity and Eugenics. 315 pp., 
 98 figs. The Univ. of Chicago Press. 1912. 
 
 Castle, W. E., Heredity, in Relation to Evolution and Animal 
 Breeding. 184 pp. N. Y. and London. D. Appleton Co. 
 1911. 
 
 Crampton, Henry Edw., The Doctrine of Evolution; its Basis 
 and its Scope, ix +311 pp. N. Y, Columbia Univ. 
 Press. 1911. 
 
 Darbishire, a. D., Breeding and the Mendelian Discovery. 
 xii + 282 pp. Cassell & Co. London. 4 colored pis., 
 34 figs. 1911. 
 
 Davenport, E., Domesticated Animals and Plants, xiv + 
 312 pp., 49 figs. Ginn & Co. 1910. 
 
 Davenport, E., and Rietz, H. L., Principles of Breeding (by 
 E. Davenport). Appendix: Statistical Methods (by 
 H. L. Rietz). A treatise on thremmatology, or the prin- 
 ciples and practices involved in the economic improvement 
 of domesticated animals and plants, xiii + 727 pp. 
 Ginn & Co. Boston. 1907. 
 
 Fifty Years of Darwinism, v + 274 pp., 5 pis., 1 fig. N. Y. 
 1909. 
 
 Fruwirth, C, et al.. Die ZUchtimg der LandwirtschaftUchen 
 Kulturpflanzen. Vols. 1-5. 1904-1912. 
 
 JoHANNSEN, W., Elcniente der E.vakten Erblichkeitslehre. vi + 
 515 pp., 30 figs. Gustav Fischer. Jena. 1903. 
 
 JoiL\NNSEN, W., Ueber Erblichkeit in Populationen und in reinen 
 Linien. 68 pp., 8 figs. Gustav Fischer. Jena. 1903. 
 
 Kellogg, V. L., Darwinism To-Day. 403 pp. Henry Holt 
 & Co. N. Y. 1907. 
 
 Knuth, p., Handbook of Flower Pollination. Vol. I, xix + 
 382 pp. Oxford. Porter. 1906. 
 
 Lang, H., Theorie und Praxis der Pflanzenzuchtung. viii + 
 169 pp., 47 figs. 1910. 
 
330 Plant-Breeding 
 
 LoBNER, M., Leitfaden fiir Gdrtnerische Pflanzenzuchtung. 
 
 vii + 160 pp., 10 figs. Jena. 1909. 
 Lock, R. H., Recent Progress in the Study of Variation, Heredity, 
 
 and Evolution. 2d ed., xiv + 334 pp. Murray. London. 
 
 4 pis., 45 figs., and 5 portraits. 1909. 
 
 Newman, L. H., Plant Breeding in Scandinavia. 193 pp., 
 63 figs. The Canadian Seed Growers' Association. Ottawa. 
 1912. 
 
 PuNNETT, R. C, Mendelism. 192 pp. N. Y. Macmillan Co. 
 
 5 pis., 35 figs. 1911. 
 
 Reid, G. a., The Laws of Heredity. 548 pp. Methuen & Co. 
 
 London. 1910. 
 RuMKER, VON K., Ueber Organisation der PfianzenzUchtung. 
 
 56 pp. Berlin. 1909. 
 Seward, A. C. (Editor), Darwin and Modern Science, xvii + 
 
 595 pp., fig. and pi. 1909. 
 Stevens, W. C, Plant Anatomy from the Standpoint of the 
 
 Development and Functions of the Tissues and Handbook of 
 
 Micro-technic. xii + 349pp. Blakiston's Son & Co. Phila- 
 delphia. 136 illus. 1907. 
 Thomson, J. Arthur, Heredity, xvi + 605 pp., 49 figs. 2d 
 
 ed. 1912. 
 Vernon, H. M., Variation in Animals and Plants, pp. ix + 
 
 415, 30 figs. Henry Holt & Co. 1902. 
 Vries, Hugo de. Species and Varieties, their Origin by Mutation. 
 
 Edited by Daniel Trembly MacDougal. The Open Court 
 
 Pub. Co. Chicago. 1904. 
 Vries, Hugo de, Plant Breeding. Comments on the experiments 
 
 of Nilsson and Burbank. xiii + 360, figs. 114. 1907. 
 Vries, Hugo de. The Mtdation Theory. Vol. I, ''The Origin 
 
 of Species by Mutation." Engfish translation by Prof. 
 
 J. B. Farmer and A. D. Darbishire. xvi + 582 pp. The 
 
 Open Court Publishing Co. Chicago. 4 pis. and 119 figs. 
 
 1909. 
 
Appendix B 331 
 
 Vries, Hugo de, The Mutation Theory. Vol. II, ''The Origin of 
 Varieties by Mutation." English translation by Prof. 
 J.B.FarmerandA.D.Darbishire. viii+ 683 pp. Chicago. 
 The Open Court Publishing Co. 6 pis., 149 figs. 1911. 
 
 Walter, Herbert Eugene, Genetics. An Introduction to the 
 Study of Heredity, xiv + 264 pp. The Macmillan Co. 
 N. Y. 72 figs, and Diagr. 1913. 
 
 Wilson, E. B., The Cell in Development and Inheritance, xxi + 
 483 pp., 194 figs. Macmillan Co. 1900. 
 
 Yearbooks U. S. Department of Agriculture. 1894-1913. 
 
 Hybrid Conference Report (First International Conference). 
 London. Printed in Journal of the Royal Hort. Soc, April, 
 1900. 
 
 International Conference (Second) on Plant Breeding and Hybrid- 
 ization. Proceedings published as Memoir, Vol. I. Hort. 
 Soc. of New York. 1902. 
 
 International Conference {Third) on Genetics. London. Report 
 issued by Royal Hort. Soc. 1906. 
 
 International Conference {Fourth) on Genetics. Report pub- 
 lished in Paris, 1911, under Editorship of Ph. de Vilmorm. 
 
APPENDIX C 
 
 LIST OF PERIODICALS CONTAINING BREEDING 
 
 LITERATURE 
 
 We have attempted to include in this list such periodicals 
 as are most likely to contain breeding articles that may be of 
 interest to the general reader and the teacher and student of 
 Genetics. This list is not intended to be complete, but to in- 
 clude the principal publications. 
 
 Abbreviations : semi-a = semi-annual ; q = quarterly ; semi-q = semi- 
 quarterly ; m = monthly ; bi-m = bi-monthly ; semi-m = semi-monthly ; 
 w = weekly : semi-w = semi-weekly ; i = irregular. 
 
 American Naturalist. New York. m. 
 
 American Philosophical Society. Proceedings. Philadelphia. 
 3 nos. 
 
 Annales de la science agronomique. Paris, m. 
 
 Annales des science naturelles. Botanique. Paris. 
 
 Annals of Applied Biology. London. 
 
 Annals of Botany. London, q. 
 
 Archiv fiir Rassen- und Gesellschafts-Biologie. Leipzig, bi-m. 
 
 Archives des sciences biologiques. St. Petersbourg. 
 
 Association internationale des botanistes. Progressus rei 
 botanicae. Jena, semi-a. 
 
 Biological Bulletin, m. Wood's Hole, Mass. Marine Bio- 
 logical Laboratory. 
 
 Biologisches Centralblatt. Erlangen, Leipzig, semi-m. 
 
 Biometrika. Cambridge, Eng. i. 
 
 332 
 
Appendix C 333 
 
 Botanical Gazette. Chicago, m. 
 
 Botanische Zeitung. Abt. 1 and 2. Leipzig, w. 
 
 Botanisches Centralblatt. Jena. w. 
 
 Botanisches Centralblatt-Beihefte., Abt. 1 ; 3 nos. Anatomic, 
 
 Histologic und Physiologic der Pflanzen. Abt. 2; 3 nos. 
 
 Systcmatik, Pflanzengeographic, Augewandte, Botanik, etc. 
 
 Dresden. 
 Deutsche Botanische Gesellschaft. Berichte. Berlin, m. 
 Deutsche Landwirtschafts-Gesellschaft. Jahrbuch. Berlin, q. 
 Die Landwirtschaftlichen Versuch-Stationen. Berlin, semi-m. 
 Florists' Exchange. New York. w. 
 
 France — Institut national agronomique. Annales. Paris, i. 
 Gardeners' Chronicle. London, w. 
 Jahrbucher fur Wissenschaftliche Botanik (Pringsheini's). 12 
 
 nos. Leipzig. 
 Journal of Agricultural Research, m. 
 Journal of Agricultural Science. Eng. q. 
 Journal de botanique. Paris, m. 
 Journal of Genetics. Cambridge, Eng. q. 
 Journal of Heredity. Washington, m. 
 La Cellule. Lierre. i. 
 La Science agronomique. Paris. 
 Linnean Society : 
 Journal, botany. London, m. 
 Transactions, botany. London, i. 
 (The) Mendel Journal. London. 
 New Phytologist. London. 10 nos. 
 Physiological Researches. Baltimore, i. 
 Plant World. Tucson, Ariz. m. 
 Popular Science Monthly. New York. m. 
 Quarterly Journal of Microscopical Science. London, q. 
 Revue, generale agronomique. Uccle lez-Bruxelles. m. 
 Revue generale de botanique. Paris, m. 
 Royal Microscopical Society. Journal, bi-m. 
 
334 Plant-Breeding 
 
 Royal Society of London, Philosophical transactions. 1. 
 
 Science. New York. w. 
 
 Society de biologie, Comptes rendus. Paris, w. 
 
 Societe botanique de France. Bulletin. Paris, m. 
 
 Societe des agriculteurs de France. Bulletin. Paris, semi-m. 
 
 Society royale de botanique de Belgique. Bulletin. Bruxelles. 
 
 Torrey Botanical Club. Bulletin. New York. m. 
 
 United States Dept. of Agriculture, Office of Experiment 
 
 Stations. Experiment Station Record. Washington. 16 
 
 nos. 
 Zeitschrift fiir Planzenziichtung. Wien. 
 Zentralblatt fiir AUgemeine und Experimentelle Biologie. Leipzig. 
 
APPENDIX D 
 BIBLIOGRAPHY 
 
 Following is a list of miscellaneous references to writings on 
 subjects related to plant-breeding. It is not intended to be 
 either complete or comprehensive. This bibliography begins 
 with the year 1905. References to -earlier writings may be 
 found in the fourth edition of this work. 
 
 For reference to the literature of cross-fertilization, the reader 
 is directed to d'Arcy Thompson's list in Mueller's '' Fertiliza- 
 tion of Flowers," and an extensive bibliography to the rapidly 
 growing literature upon the heredity of color can be found in a 
 technical bulletin by the junior writer of this book. This bulle- 
 tin will soon be published by the Agricultural Experiment 
 Station of Cornell University. 
 
 1905. Balls, W. L., The Sexuality of Cotton. Khed. Agr. 
 Soc. Yearbook, 199-222. 
 
 1905. BiFFEN, R. H., Mender s Laws of Inheritance and Wheat 
 Breeding. Jour. Agr. Sci., Cambridge, 1 : 4-48, 1 pi. 
 
 1905. BiFFEN, R. H., The Inheritance of Sterility in the Bar- 
 leys {Hordeum sativum, etc.). Jour. Agr. Sci. 1 : 250-257, 
 Ifig. 
 
 1905. Butler, E. J., The Bearing of Mendelism on the Suscep- 
 tibility of Wheat to Rust. Jour. Agr. Sci. 1 : 361-363. 
 
 1905. CoNKLiN, Edwin G., The Mutation Theory from the Stand- 
 point of Cytology. Science, n.s. 21 : 525-529. 
 
 1905. Eastman, C. R., On the Spelling of " Clon." Science, 
 n.s. 22 : 206. 
 
 335 
 
336 Plant-Breeding 
 
 1905. Hurst, C. C, Notes on the " Proceedings of the Inter- 
 national Conference on Plant Breeding and Hybridisation, 
 
 1902r Roy. Hort. Soc. Jour. 29 : 417-433. 
 1905. Jones, L. R., Disease Resistance of Potatoes. U. S. 
 
 Dept. Agr. Bur. Plant Ind. Bull. 87 : (39 pp.). 
 1905. Jones, L. R., Concerning Disease Resistance of Potatoes. 
 
 Vermont Agr. Exp. Sta. 18 : 264-267. 
 1905. Klinck, L. S., Corn Breeding in the Corn Belt. Can. 
 
 Seed-Grow. Assoc. Rep. 2: 56-61. 
 1905. Pearl, Raymond, Investigation by Statistical Methods of 
 
 Correlation in Variation. Carnegie Inst. (Wash., D.C.), 
 
 Yearbook (1905) (No. 4) : 285-286. 
 1905. Pearl, Raymond, Note on Variation in the Ray Flowers 
 
 of Rudheckia. Am. Nat. 39 : 87-88. 1 fig. 
 1905. Petrunkevitch, Alexander, Natural and Artificial 
 
 Parthenogenesis. Am. Nat. 39 : 65-76. Bibliog. 
 1905. Pollard, Charles Louis, On the Spelling of " Clon." 
 
 Science, n.s. 22 : 87-88. 
 1905. Pollard, Charles Louis, " Clon " versus " Clone.'' 
 
 Science, n.s. 22 : 463. 
 1905. Shamel, a. D., The Effect of Inbreeding in Plants. U. S. 
 
 Dept. Agr. Yearbook, 377-392. 3 pis., 1 fig. 
 1905. Shamel, A. D., Tobacco Breeding Experiments in Conn. 
 
 Conn. (State) Agr. Exp. Sta. Ann. Rep. 331-343. 
 1905. Starnes, Hugh N., Japan and Hybrid Plums. Georgia 
 
 Agr. Exp. Sta. 68 (see pp. 1-40). 
 1905. Vries, H. de, Dauer der Mutationsperiode bei CEnothera 
 
 Lamarckiana. Deutsch. Bot. Gesell. Ber. 23 : 382-387. 
 1905. Vries, H. de. The Mutation Theory. Gard. Chron. 
 
 3d ser. 37 : 321-322. 
 1905. Webber, Herbert J., The Science of Plant Breeding. 
 
 Can. Seed-Grow. Assoc. Rep. 2 : 79-92. PL II., fig. 1 & 2. 
 1905. Webber, Herbert J., Pedigree or Grade Breeding. Can. 
 
 Seed-Grow. Assoc. Rep. 2 : 61-70. PL, Photo., Fig. 
 
Appendix D 337 
 
 1905. WiESNER, J., Untersuchungen uber den Lichtgenuss der 
 Pflanzen im Yellowstone Gebiete und in anderen Gegenden 
 Nordamerikas. Photometrische Untersuchungen auf pflan- 
 zenphysiologischem Gebiete {V. Abhandlung). Kais. kon. 
 Akad. d. Wiss. in Wien, mathem. naturw. Klasse, Sit- 
 zungsber. 114: (Part 1). Rev. in Am. Nat. 40:600-603. 
 
 1905. Williams, C. G., Pedigreed Seed Corn. Ohio Agr. Exp. 
 Sta., Circ. 42: 1-11. 
 
 1906. Andrews, F. M., Some Monstrosities in Trillium. Ind. 
 Acad. Sci. Proc. 187-188. 
 
 1906. Bateson, W., and Saunders, Miss E. R., and Pun- 
 nett, R. C, Inheritance in Sweet Peas and Stocks. Roy. 
 Hort. Soc. (London) Proc. B. 77 : 236-238. 
 
 1906. Bateson, W., Coloured Tendrils of Sweet Peas. Gard. 
 Chron. 39 : 333. 
 
 1906. BeaL; W. J., Improving Wild Potatoes by Selection. Soc. 
 Prom. Agr. Sci. Proc. 27 : 75. 
 
 1906. BiFFEN, R. H., Experiments on the Hybridization of 
 Barley. Phil. Soc. Proc. (Cambridge), 13:304-308. 
 
 1906. Blanchard, W. H., A New Dwarf Blackberry. Torreya 
 6 : 235-237. 
 
 1906. Buchanan, J., Some Effects in Varieties of Cereal Crops 
 arising from Different Conditions of Growth. Can. Seed- 
 Grow. Assoc. Rep. 3 : 74-77. 
 
 1906. Card, F. W., Blake, M. A., and Barnes, H. L., Rasp- 
 berry Score Card. Rhode Island Agr. Exp. Sta. 168-169. 
 
 1906. Card, Fred W., Apple Breeding. Rhode Island Agr. 
 Exp. Sta. 20:250-252. 
 
 1906. Card, Fred W., Corn Selection. Rhode Island Agr. 
 Exp. Sta. Ann. Rept. 20 : 216-220. 
 
 1906. Castle, W. E., hibreeding, Crossbreeding and Sterility 
 in Drosophila. Science, n.s. 23 : 153. 
 
 1906. Crocker, W., Role of Seed Coats in Delayed Germination. 
 Bot. Gaz. 42:265-291. Fig. 
 
338 Plant-Breeding 
 
 1906. DuvEL, J. W. T., The Germination of Seed Corn. U. S. 
 Dept. Agr. Farmers' Bull. 253 : (16 pp.), 4 figs. (Includ- 
 ing : Value of a germination test. Average yield of corn 
 to the acre. Testing individual ears. Selecting seed ears. 
 Numbering the ears. The germination box. Results of 
 tests.) 
 
 1906. Gager, C. S., De Vries and His Critics. Science, n.s. 
 24 : 81-89. Bibliog. in notes. 
 
 1906. Graenicher, S., Some Notes on the Pollination of Flowers. 
 Wis. Nat. Hist. Soc. Bull. 4 : 12-21. 
 
 1906. Griffon, E., Le greffage des Solanees. Acad. Sci. Compt. 
 Rend. 143:1249-1251. 
 
 1906. Haacke, Wilhelm, Die Gesetze der Rassenmischung 
 und die Konstitution des Keimplasmes. Arch. f. Entwick'- 
 mech. d. Org. 21 : 1-93. 104 tab. 
 
 1906. Halsted, B. D., Breeding Sweet Corn — Cooperative 
 Tests. New Jersey Agr. Exp. Sta. Bull. 192 : 1-30. Fig. 
 
 1906. Heckel, E., Variation in the Potato Tuber. Gard. 
 Chron. 3d ser. 39 : 88. 
 
 1906. Henslow, G., Evolution and Adaptation. Roy. Hort. 
 Soc. Jour. n.s. 31 : 159-163. 
 
 1906. Henslow, G., The True Meaning of " Natural Selec- 
 tion " and the "Survival of the Fittest " in Nature. Roy. 
 Hort. Soc. Jour. n.s. 31 : 90-96. 
 
 1906. Henslow, G., Species and Varieties; their Origin by 
 Mutation. Roy. Hort. Soc. Jour. n.s. 31 : 164-168. 
 
 1906. Hesketh, R. T., Apple Grafted on Hawthorn. Gard. 
 Chron. 3d ser. 39 : 347. 
 
 1906. Hurst, C. C., Mendelian Laws of Inheritance. Gard. 
 Chron. 3d ser. 39: 187. 
 
 1906. Le Clerc, J. A., The Effect of Climatic Conditions on the 
 Composition of Durum Wheat. U. S. Dept. Agr. Year- 
 book: 199-212, 2 pis. Same. Yearbook Separate, 417: 
 199-212, 2 pis. 
 
Appendix D 339 
 
 1906. Lock, R. H., Plant Breeding in the Tropics. III. Ex- 
 periments with Maize. Roy. Bot. Gard. Ann. 3:2: 95- 
 184. 
 
 1906. Macoun, W. T., The Improvement of the Potato. Can. 
 Seed-Grow. Assoc. Rep. 3 : 77-84. Photo., Fig. 
 
 1906. Morgan, T. H., Are the Germ-cells of Mendelian Hybrids 
 "Pure "f Biol. Centralbl. 26 : 289-296. 
 
 1906. MuNSON, W. M., Plant-breeding in its Relation to Ameri- 
 can Pomology. Maine Agr. Exp. Sta. Bull. 132 : 149-176. 
 
 1906. Ortmann, a. E., The Mutation Theory Again. Science, 
 n.s. 24 : 314-317. Bibliog. in notes. 
 
 1906. OsTERHOUT, W. J. v., Experiments with Plants, x + 
 493 pp. TheMacmillanCo.,N.Y. 252 figs. Rev. in Am. 
 Nat. 40 : 146-148. 
 
 1906. Pearl, Raymond, Variation in the Number of Seeds of 
 the Lotus. Am. Nat. 40 : 757-768. 4 figs. 5 tab. 
 
 1906. Raunkiaer, C, Transmission par heredite dans les 
 especes heteromorphes. Vid. Selsk. Overs. 31-39. 
 
 1906. Riviere, G., and Bailhache, G., Influence du porte- 
 greffe sur le greffon. Acad. Sci. Compt. Rend. 142 : 845- 
 847. 
 
 1906. Rosenberg, 0., Embryobildung in der Gattung Hieracium. 
 Deutsch. Bot. Gesell. Ber. 24: 157-161, 1 pi. 
 
 1906. Saame, 0., Kernverschnelzung bei der karyokinetischen 
 Kernteilung im protoplasmatischen Wandeelag des Embryo- 
 sacks von Fritillaria imperialis. Deutsch. Bot. Gesell. 
 Ber. 24 : 300-303, 1 pi. 
 
 1906. ScHARF, E., Keimkraft-Apparat. Deutsch. landw. 
 Presse 33 : 507-508, 514^516. 
 
 1906. Schulte, J. L, Corn Breeding Work at the Experiment 
 Stations. U. S. Dept. Agr. Yearbook, 279-294. 
 
 1906. Solms(-Laubach), H. Graf zu, Cruciferenstudien. 
 IV. Die Varianten der Embroyolage. Bot. Zeitung, 64: 
 1 : 15-43, 1 pi. 
 
340 Plant-Breeding 
 
 1906. Sperling, J., Korrelation zwischen Kornfarbe und Aehren- 
 
 formen beim Roggen. Fiihlings landw. Zeitung, 55 : 93-99. 
 1906. Stuart, W., Disease Resistance of Potatoes. Vermont 
 
 Agr. Exp. Sta. Bull. 122: (see pp. 107-136). Abstr. in 
 
 Exp. Sta. Rec. 17 : 1078. 
 1906. Van den Heede, A., Variation chez les vegetaux. Soc. 
 
 Nantaise d'hort. Ann. 79 : 97-103. 
 1906. Vries, H. de, Aelters und neuere Selektionsmethode. 
 
 Biol. Centralbl. 26 : 385-395. 
 1906. Vries, H. de, Die Svalofer Methode zur Veredelung land- 
 
 wirtschaftlicher Kulturgewdchse und ihre Bedeutung fur 
 
 die Selektions-Theorie. Arch. Rassenbiol. 3 : 325-358, 
 1906. Vries, H. de, Species and Varieties; their Origin by 
 
 Mutation. Second edition, xviii + 847 pp. 
 1906. Webber, H. J., New Citrus and Pineapple Productions 
 
 of the Department of Agricidture. U. S. Dept. Agr. Year- 
 book, 329-346. 8 pis., 1 fig. Same. Yearbook Separate, 
 
 427:329-346. 8 pis., 1 fig. 
 1906. Weismann, a.. The Evolution Theory. Translated with 
 
 the author's cooperation by J. A. & Margaret R. Thomson. 
 
 2 vols, xvi +416 pp. and 405 pp. E. Arnold. London. 
 
 Rev. in Am. Nat. 40 : 375-377. 
 1906. WiANCKO, A. T., Corn Improvement. Indiana (Purdue 
 
 Univ.) Agr. Exp. Sta. Bull. 110:79-120. 14 figs. 
 1906. WiLBRiNK, G., Deuxieme rapport sur les experiences de 
 
 selection faites avec Vindigotier de Natal. (In Dutch.) 
 
 Buitenzorg (1906), 1-20. 
 1906. Wilson, E. B., Mendelian Inheritance and the Purity 
 
 of the Gametes. Science, n.s. 23: 112-113. 
 1906. Wilson, Edmund B., Studies on Chromosomes. III. The 
 
 Sexual Differences of the Chromosome-groups in Hemiptera, 
 
 with Some Considerations on the Determination and Heredity 
 
 of Sex. Jour. Exp. Zool. 3: (No. 1). Rev. in Arch. f. 
 
 Entwick'mech. d. Org. 21 : 357. 
 
Appendix D 341 
 
 1906. Winkler, H., Morphologie und Biologie tropischer Bluten 
 
 und Fruchte. Bot. Jahrb. 38 : 233-271. 
 1906. Winkler, H., 'Parthenogenesis bei Wikstroemis indica 
 
 (L.), C. A. Mey, und ihre Bedeutung filr die Lehre der Be- 
 
 fruchtung. Jard. Bot. Ann. n.s. 5 : 208-276, 4 pis. 
 1906. WiTTMACK, L., Berichte ilber die internationale Konferenz 
 
 uber Hybridisation und Pfianzenzucht in London vom 30. 
 
 Juli bis 3. August 1906. Gartenflora 55: 481-486, 509- 
 
 511. 
 1906. WiTTMACK, L. The Influence of the Graft on the Rooting 
 
 of the Pear. Gard. Chron. 3d ser. 40 : 150. 
 
 1906. WiTTMACK, L. Sports. Gard. Chron. 3d ser. 40 : 223. 
 
 1907. Balls, W. R., Note on Mendelian Heredity in Cotton. 
 Jour. Agr. Soc. 2 : 216. 
 
 1907. Bessey, C. E., a Sijnopsis of the Plant Phyla. Univ. 
 Studies, Univ. of Nebraska, 7 : 275-373. 1-99. 
 
 1907. BiFFEN, R. H., Studies in the Inheritance of Disease Re- 
 sistance. Jour. Agr. Sci. 2 : 109. 
 
 1907. BiFFEN, R. H., The Hybridization of Barleys. Jour. 
 Agr. Sci. 2 : 183. 
 
 1907. BouLENGER, G. A., On the Variations of the Evening 
 Primrose, (Enothera biennis. Jour. Bot. 45 : 353-363. 
 
 1907. Brown, Arthur Erwin, Variation or Mutation. Science, 
 n.s. 25 : 107-108. 
 
 1907. Brownlee, John, Statistical Studies in Immunity. A 
 discussion of the means of estimating the severity of cases of 
 acute diseases. Biometrika, 5 : 423-435. Tab., Diagr. 
 
 1907. Butler, E. J., The Selection of Sugarcane Cuttings. 
 Agr. Jour. India, 2 : 193. 
 
 1907. Card, Fred W., Cherry Crosses. Rhode Is. Agr. Exp. 
 Sta. Rep. 258-259. 
 
 1907. Castle, W. E., On a Case of Reversion Induced by Cross- 
 breeding and its Fixation (guinea-pig). Science, n.s. 25: 
 151-153. 
 
342 Plant-Breeding 
 
 1907. CocKERELL, T. D. A., Is there Determinate Variation? 
 
 Science, n.s. 25 : 34. 
 1907. Cook, 0. F., Mendelism and Other Methods of Descent. 
 
 Washington Acad. Sci. Proc. 9 : 189-240. 
 1907. Crosthwait, G. A., Indian Corn. Its Production and 
 
 Improvement. Idaho Agr. Exp. Sta. Bull. 57. 
 1907. Davenport, C. B., Heredity and MendeVs Law. Wash- 
 ington Acad. Sci. Proc. 9 : 179-187. 
 1907. Davenport, E., and Rietz, H. L., Type and Variability 
 
 in Com. Illinois Agr. Exp. Sta. Bull. 119 : 1-29. 
 1907. Davidson, A., The Changes in our Weeds. So. Calif. 
 
 Acad. Sci. Bull. 6:11-12. 
 1907. East, E. M., The Relation of Certain Biological Principles 
 
 to Plant Breeding. Connecticut Agr. Exp. Sta. Bull. 158 : 
 
 1-93. Fig. 
 1907. East, Edward M., Some Essential Points in Potato 
 
 Breeding. Conn. (State) Agr. Exp. Sta. Ann. Rep. 429-448. 
 1907. East, Edward M., Inbreeding in Corn. Conn. (State) 
 
 Agr. Exp. Sta. Ann. Rep. 419-429. 
 1907. East, Edward M., Better Seed Corn in Conn. Conn. 
 
 (State) Agr. Exp. Sta. Ann. Rep. 397-406. 
 1907. East, Edward M., Practical Use of Mendelism in Corn 
 
 Breeding. Conn. (State) Agr. Exp. Sta. Ann. Rep. 406-419. 
 1907. Fletcher, S. W., and Gregg, O. I., Pollination of Forced 
 
 Tomatoes. Mich. Agr. Exp. Sta. Spec. Bull. 39. 
 1907. Fletscher, F., Mendelian Heredity in Cotton. Jour. 
 
 Agr. Sci. 281-282. 
 1907. Gager, C. S., An Occurrence of Glands in the Embryo of 
 
 Zea Mays. Torrey Bot. Club. Bull. 34 : 125-137. 
 1907. Gallardo, a., Estudios de Davenport sobre la herencia. 
 
 El Libro (Buenos Aires) 2 : 17-23. 
 1907. Gates, R. R., Pollen Development in Hybrids of (Enothera 
 
 lata X 0. Lamarckiana, and its Relation to Mutation. Bot. 
 
 Gaz. 43:81-115, 3 pis. Rev. in Am. Nat. 41:403-404. 
 
Appendix D 343 
 
 1907. Gregoire, v., Les fondements cytologiques des theories 
 
 courantes sur Vheredite Mendelienne. Soc. Roy. Zool. 
 
 et Malacol. Belgique Ann. 42 : 267-320. 4 figs. 
 1907. Gregory, E. S., Pollen of Hybrid Violets. Jour. Bot. 
 
 45 : 377. 
 1907. Gregory, R. P., On the Inheritance of Certain Characters 
 
 in Primula sinensis. British Assoc. Adv. Sci. Rep. 691- 
 
 693. 
 1907. Hatai, S., Studies on the Variation and Correlation of 
 
 Skull Measurements in Both Sexes of Mature Albino Rats. 
 
 (Mus norvegicus,vax. Albus.) Am. Jour. Anat. 7 : 423-441. 
 1907. Heckel, E., Sur Vorigine de la pomme de terre cultivee 
 
 et sur les midations gemmaires culturales des Solanum 
 
 tuberiferes sauvages. Facult. d. Sciences Marseille Ann. 
 1907. Hill, A. W., The Natural Hybrid between the Cowslip and 
 
 Oxlip. New Phytolog. 6 : 162. 
 1907. Hurst, C. C., MendeVs Law of Heredity. Roy. Hort. 
 
 Soc. Jour. 32 : 227. 
 1907. International Confererice on Plant Hardiness and Ac- 
 climatization. Science, n.s. 26 : 356-357. 
 1907. Johnson, E. W., Sage Brush and Cactus. Am. Bot. 
 
 12 : 59-63. 
 1907. Kammerer, Paul, Bastardierung von Flussbarsch [Perca 
 
 ftiwiatilis L.) und Kaulbarsch (Acerina cernua L). Arch. 
 
 f. Entwick'mech. d. Org. 23 : 511-551, 2 pis. & 1 fig. Bib- 
 
 liog. 
 1907. Klebs, Georg, Studien iiber Variation. Arch. f. 
 
 Entwick'mech. d. Org. 24 : 2^113, 15 figs. 4 tab. Bibliog. 
 1907. Lamb, A. B., A New Explanation of the Mechanics of 
 
 Mitosis. Jour. Exp. Zool. 5 : 27-33. 
 1907. Leveille, H., Un nouvel hybride de J uncus. Soc. 
 
 Botan. France Bull. 54 : 517-518. 
 1907. Lock, R. H., The Interpretation of Mendelian Phenomena. 
 
 Nature, 76 : 616, 77 : 32. 
 
344 Plant-Breeding 
 
 1907. Lock, R. H., On the Inheritance of Certain Invisible Char- 
 acters in Peas. Roy. Soc, Proc. London B. 79 : 28 pp. 
 
 1907. LuTZ, Anne M., The Chromosomes of (Enothera Lamarck- 
 iana and One of its Mutants, 0. gigas. Science, n.s. 26 : 
 151-152. Fig. 
 
 1907. MacDougal, D. T., Vail, A. M., & Shull, G. H., Muta- 
 tions, Variations, and Relationships of the (Enotheras. Car- 
 negie Inst. Pub. no. 81. 1-92. pi. 1-22. & Fig. 1-73. 
 
 1907. MacDougal, D. T., Hybrids among Wild Plants. Plant 
 World 10 : 25-37. Figs. 7-8. 
 
 1907. MacDougal, D. T., Hybridization of Wild Plants. Bot. 
 Gaz. 43 : 45-58. Figs. 1-4. 
 
 1907. MacDougal, D. T., Natural Hybrids. Plant World, 
 10 : 138-139. 
 
 1907. Martinet, M., Experiences sur la selection des cereales. 
 Annuaire Agr Suisse, 75. 
 
 1907. MuDGE, G. P., The Interpretation of Mendelian Phenom- 
 ena. Nature, 70 : 8. 
 
 1907. Noll, F. Uber eine Heegeri-dhnliche Form der Capsella 
 bursa pastoris Mnch. Niederrheinischen GeseU. f. Natur- 
 u. Heilk. z. Bonn. Sitzungsber. 
 
 1907. NusBAUM, JozEF, Kleiner Beitrag zur atavistischen 
 Regeneration der Sch ren bei Flusskrebse. Arch. f. Ent- 
 wick'mech. d. Org. 24 : 124-130, 2 figs. Bibliog. in notes. 
 
 1907. O'Mara, p.. Sports. Hort. Soc. N. Y. Jour. 1 : 39-43. 
 
 1907. Pearl, R., Variation and Differentiation in Ceratophyllum. 
 Carnegie Inst. Wash. Pub. 58: (136 pp.), 2 pis., 126 figs. 
 Rev. in Am. Nat. 41 : 404-405. 
 
 1907. Reid, a. G., The Interpretation of Mendelian Phenomena. 
 Nature, 7 : 566. 
 
 1907. Reitsma, J. F., Correlative variabiliteit bij planten. 
 Dissert. 98 pp. Amsterdam. 
 
 1907. RusBY, H. H., Some Little-known Edible Native Fruits 
 of the United States. N. Y. Bot. Gard. Jour. 8 : 175, 177-178. 
 
Appendix D 345 
 
 1907. RusBY, H. H., The Wild Grains and Nuts of the United 
 States. Jour. N. Y. Bot. Gard. 7 : 269-273. 
 
 1907. Shamel, a. D., and Cobey, W. W., Tobacco Breeding. 
 U. S. Dept. Agr. Bur. Plant Ind. Bull. 96 : 1-67, 10 pis. & 
 14 figs. 
 
 1907. Shamel, A. D., The Art of Seed Selection and Breeding. 
 U. S. Dept. Agr. Yearbook, 221-236, 5 pis. Same. Year- 
 book separate, 446 : 221-236 5 pis. 
 
 1907. Shepard, W. F., The Calculation of the Moments of a 
 Frequency Distribution. Biometrika, 5 : 450-459. Rev. in 
 Am. Nat. 42 : 418-422. 
 
 1907. Shull, G. H., Results of Crossing Bursa bursa-pastoris 
 and Bursa Heegeri. Intern. Zool. Congress, 7th Proc. 
 (6 pp.) Boston. Cambridge, Mass. 1910. 
 
 1907. Spalding, V. M., The Artificial Production of Mutants. 
 Science, n.s. 26 : 349-350. 
 
 1907. Spillman, W. J., Standardizing Breed Characteristics. 
 Soc. for Prom. Agr. Sci. Proc. 28: 116-120. 
 
 1907. Stoll, Ein interessanter Bastard zwischen einem Emmer 
 und Kolbenspelze. Deutsche Landw. Presse, 100. 
 
 1907. ViLMORix, Ph. de. Evolution et Selection, theories an- 
 ciennes et nouvelles. Paris. Soc. Agr. de France. 
 
 1907. Vries, H. de, Luther Burbank's Ideas on Scientific Horti- 
 culture. Century Mag. 73 : 674-681. Illus. 
 
 1907. Vries, H. de. Evolution and Mutation. The Monist, 
 17:6. 
 
 1907. Vries, H. de. On Twin Hybrids. Bot. Gaz. 44 : 401- 
 407. 
 
 1907. Webber, H. J., and Boykin, F. B., The Advantage of 
 Plantiyig Heavy Cotton Seed. U. S. Dept. Agr. Farmers' 
 Bull. 285: (16 pp.), 6 figs. 
 
 1907. Wight, W. F., The History of the Cowpea and its Intro- 
 duction into America. U. S. Dept. Agr. Bur. PI. Ind. Bull. 
 1026:1-21. PI. 1-3. 
 
346 Plant-Breeding 
 
 1907. Wilson, J. H., The Hybridization of Cereals. Jour. 
 
 Agr. Sci. 2:68. 
 1907. Winkler, H., tlber Pfropfbastarde und Uanzlichefl 
 
 Chimdren. Deutsch. Bot. Gesell. Ber. 25 : 568. Rev. 
 
 (Ger.) in Arch. f. Entwick'mech. d. Org. 28 : 163. 
 
 1907. Yule, U., Mendelism and Biometry. Nature, 76 : 152. 
 
 1908. Balls, W. S., Mendelian Studies of Egyptian Cotton. 
 Jour. Agr. Sci. 2 : 346-379. 
 
 1908. Beal, W. J., Mutations of Rudbeckia hirts. Am. Ass'n 
 Adv. Sci., Sec. Bot. Abstr. in Science, n.s. 27 : 207-208. 
 
 1908. Bennett, B. L., .4 Method of Breeding Early Cotton to 
 Escape Boll-weevil Damage. U. S. Dept. Agr, Farmers' 
 BuU. 314: (30 pp.), 16 figs. (Including: A description 
 of the distinguishing characteristics of early cotton, instruc- 
 tion for seed selection, crossing one plant with another, 
 treatment to insure a stand, experiments, etc.) 
 
 1908. BiFFEN, R. H., On the Inheritance of Strength in Wheat. 
 Jour. Agr. Sci. 3: 86-101. 1 fig. 
 
 1908. Bolley, Henry L., Observations regarding the Constancy 
 of Mutants and Questions regarding the Origin of Disease 
 Resistance in Plants. Am. Nat. 42: 171-183. Bibliog. 
 in notes. 
 
 1908. Briem, H., Naturliche Bastardierungen zwischen Zucker- 
 riXben und Futterruben. Oester.-rung. Zeitsch. f. Zuckerin- 
 dustrie u. Landw. : (4 pp.). 
 
 1908. Briem, H., Mitteilungen und Bemerkungen zu de Vries, 
 zilchtersichen Ansichten. Blatter f . Zuckerriibenbau, 15 : 
 309-312. 
 
 1908. Bristol, C. L., Otter Sheep. (Note.) Am. Nat. 42 : 282. 
 
 1908. Bull, C. P , Corn Breeding in Minnesota. Minnesota 
 Agr. Exp. Sta. BuU. 173-266. 
 
 1908. Burtt-Davy, J., How to Secure Good Seed-maize. Trans- 
 vaal Agr. Jour. 6 : 441-453. 5 pis. 
 
 1908. Cannon, W. A., A Redwood Sport. Plant World, 11 : 232- 
 234. 
 
Appendix D 347 
 
 1908. Clark, Charles C, Wheat Crops of the United States, 
 1866-1906. U. S. Dept. Agr. Bur. Statistics BuU. 57: 
 (39 pp.) (revised). 
 
 1908. Clute, W. N., The Boston Fern and its Sports. Fern 
 BuU. 15 : 73-74. 
 
 1908. Clute, W. N., A Remarkable Change of Color in Trillium. 
 Am. Bot. 14 : 33-35. lUus. 
 
 1908. Cobb, J. A., The Effect of Errors of Observation upon the 
 Correlation Coefficient. Biometrika, 6 : 109. 
 
 1908. Cockerell, T. D. A., Variation in Helianthus. Bot. 
 Gaz. 45 : 338. 
 
 1908. Cook, 0. F., The Mendelian Inheritance of Mutations. 
 Science, n.s. 28 : 86-88. 
 
 1908. Cook, 0. F., Reappearance of a Primitive Character in 
 Cotton Hybrids. U. S. Dept. Agr. Bur. Plant Ind. Circ. 
 18: (11pp.). 
 
 1908. CoRRENS, C, Die Bestimmung und Vererbung des De- 
 schlechtes nach neuen Versuchen mit hoheren Pfianzen. Ab- 
 stract presented before a recent meeting of the Medico- 
 Biological Journal Club of the University of Virginia, by 
 H. E. Jordan, adjunct professor of anatomy. Rev. in Am. 
 Nat. 42: 811. 
 
 1908. CoRREXS, C, Weitere Untersv^hungen iiber die Geschlechts- 
 formen polygamer Bliitenpfianze. Jahr. f. Wiss. Botan. 
 45 : 661-700. 
 
 1908. CoTTOX, J. S., The Improvement of Mountain Meadows. 
 U. S. Dept. Agr. Bur. Plant Ind. BuU. 127 : (29 pp.), 4 pis. 
 
 1908. Cramer, P. J. S., Mutaties bij Coffea robusta. Teys- 
 mannia (Batavia), 19 : 531-537. 
 
 1908. Cramer, P. J. S., De variaties van Coffea liberica in 
 Liberia. Teysmannia, 19 : 667-683. 
 
 1908. Cuenot, L., "Les Idees Nouvelles sur VOrigine des Es- 
 peces par Mutation.'' Abstr. in Science, n.s. 30 : 768-769. 
 Trans, from Rev. gen. Sci. pures et appUq. 19: (Xo. 21). 
 
348 Plant-Breeding 
 
 1908. CuENOT, L., and Mercier, L., Etudes sur le cancer des 
 Souris. Y a-t-il un rapport entre les differ entes muta- 
 tions connues chez les souris et la receptivite a la greffef 
 Acad. Sci. Paris Compt. Rend. 147 : 1003-1005. 
 
 1908. Cunningham, J. T., The Inheritance of Acquired Char- 
 acters. Nature, 77 : 367. 
 
 1908. Dachnowski, A., Type and Variability in the Annual 
 Wood-increment of Acer ruhrum L. Ohio Nat. 8 : 343-349. 
 Fig. 1. 
 
 1908. Danforth, C. H., Notes on Numerical Variation in the 
 Daisy. Bot. Gaz. 46 : 349-356. 
 
 1908. Darbishire, A. D., On the Result of Crossing Round with 
 Wrinkled Peas, with Especial Reference to their Starch-grains. 
 Roy. Soc. London Proc. B. 80 : 122-135. 
 
 1908. Davenport, C. B., The American Breeder's Association. 
 Science, n.s. 27 : 413-417. 
 
 1908. Davenport, C B., Determination of Dominance in 
 Mendelian Inheritance. Amer. Phil. Soc. Proc. 47 : 59-63. 
 
 1908. Davenport, C. B., Recessive Characters. Science, n.s. 
 28: 729. 
 
 1908. Davis, C. A., Some Interesting Variations of Common 
 Plants. Michigan Acad. Sci. Rep. 10 : 37-38. 
 
 1908. Dean, Bashford, The Lamarck Manuscript in Harvard. 
 Am. Nat. 42 : 145-153. Illus. 
 
 1908. Dix, W., Uher die Entstehung eines Squarehead bei Tri- 
 ticum turgidum Weizen. 111. Landw. Zeitg. 837-838. 2 figs. 
 
 1908. Druery, C. T., Natural Selection. Roy. Hortic. Soc. 
 Jour. 33: 114-118. 
 
 1908. Druery, D. T., The Origin of the Potato. Nature, 79: 
 305. 
 
 1908. East, E. M., Suggestions concerning Certain Bud Varia- 
 tions. Plant World, 11 : 77-83. 
 
 1908. FioRi, A., Un nuovo ibrido di Carduus {C. simplicif alius 
 X nutans Nol). Soc. Bot. Ital. Bull. 155-156. 
 
Appendix D 349 
 
 1908. Fyson, p. F., Some Experiments in the Hybridising of 
 
 Indian Cottons.^ India Dept. Agr. Mem. Bot. Ser. (29 pp.). 
 1908. Gain, E., Etude biometrique sur un hybride de prime- 
 
 veres, Primula flagellicaulis Pax. Assoc. Franc. Avanc. 
 
 Sci. Compt. Rend. 36 : 490. 
 1908. Gallardo, a., Sur Vepreuve statistique de la hi de 
 
 Mendel. Acad. Sci. Compt. Rend. 146 : 367-372. 
 1908. Gates, R. R., The Chromosomes of (Enothera. Science, 
 
 n.s. 27 : 193-195. Bibliog. in notes. 
 1908. Gates, R. R., A Preliminary Account of Studies in the 
 
 Variability of a Unit Character in (Enothera. Am. Ass'n 
 
 Adv. Sci., Sec. Bot. ; Abstr. in Science, n.s. 27 : 209. 
 1908. Geerts, J. M., Uber die Zahl der Chromosomen von 
 
 (Enothera Lamarckiana. Deut. Bot. Gesell. Ber 25- 
 
 191. 
 1908. Hansen, N. E., Neiv Hybrid Fruits. South Dakota 
 
 Agr. Exp. Sta. Bull. 108: (14 pp.), 9 pi. (Plums.) 
 1908. Hardy, G. H., Mendelian Proportions, in a Mixed Popu- 
 lation. Science, n.s. 28 : 49-50. 
 1908. Harris, D. F., The Functional Inertia of Living Matter. 
 
 A contribution to the physiological theory of life. 136 pp. 
 
 London. 
 1908. Henslow, G., The History of the Cabbage Tribe. Roy. 
 
 Hort. Soc. Jour. 34 : 15-23. 
 1908. HiLDEBRAND, F., Ubcr Samlinge von Cijtisus Adamii. 
 
 Deutsch. Bot. Gesell. Ber. 26a : 590-595. 
 1908. Hill, E. J., A Red Fruited Huckleberry. Torreya, 8 : 30- 
 
 31 pp. 
 
 1908. Iltis, H., Johann Gregor Mendel als Forscher und Mensch. 
 20 pp. Briinn. 
 
 1908. Jackson, H. S., Development of Disease-resistant Varie- 
 ties of Plants. Mass. Hort. Soc. Trans. 123-136. 
 
 1908. Jennings, H. S., Heredity, Variation and Evolution in 
 Protozoa II. Heredity and Variation of Size and Form in 
 
350 Plant-Breeding 
 
 Paramcecium, with Studies of Growth, Environmental Action 
 
 and Selection. Am. Philos. Soc. Proc. 47 : 393-546. 
 1908. KoRiBA, K., Variation in the Ray-flowers of Some Com- 
 
 positoB. Bot. Mag. Tokyo, 22: 109-112, 121-128. 
 1908. Kribs, H. G., Note on the Relative Variability of the 
 
 Sexes in Carabus auratus, L. Biometrika, 6 : 103-105. Tab. 
 1908. Leake, H. M., Studies in Experimental Breeding of the 
 
 Indian Cottons; and introductory note. Asiat. Soc. Bengal 
 
 Jour. 13-20. 
 1908. Lefevre, J., Contribution a Vhistoire des theories pro- 
 
 posees sur la variation des types vegetaux. Assoc. Franc. 
 
 Avanc. Sci. Compt. Rend. 36 : 426. 
 1908. LocHHEAD, W., The Problem of Breeding Disease-resistant 
 
 Plants. Can. Seed-Grow. Assoc. Rep. 4 : 64-70. 2 tabs. 
 1908. Lock, R. H., The Present State of Knowledge of Heredity 
 
 in Pisum. Roy. Bot. Gard. Peradeniya Ann. 4:93-111. 
 1908. LoLLi, A., Osservazioni su una varieta di Mais ramificato. 
 
 Staz. Sper. Agr. Ital. 41 : 761-767. 1 pi. 
 1908. MacDougal, D. T., First Crosses Breeding True. Plant 
 
 World, 11:42. 
 1908. McAlpine, D., The Improvement of Cereals by Selection 
 
 and Crossing. Dept. Agr. Victoria Jour. 6 : 282. 
 1908. Meyer, P., Les croisements et Vheredite des caracteres 
 
 {la hi de Mendel). Rev. Gen. des Sci. pures et appliquees, 
 
 27-31. 
 1908. MiNKiEwicz, R., Uetendue des changements possibles 
 
 de couleur de Hippolyte various. Compt. Rend. Acad. 
 
 Sci. 147 : 943-944. 
 1908. Moore, E., Abnormalities in the Radish, Clover, and Ash. 
 
 Torreya, 8 : 220 pp. 
 1908. O'Farell, H. H., The Interpretation of Mendelian Phenom- 
 ena. Nature, 77: 271. 
 1908. Ortmann, a. E., The Inheritance of Fluctuating Varia- 
 tion. Science, n.s. 27 : 545-546. 
 
Appendix D 351 
 
 1908. Orphal, K., Untersuchungen uher Korrelation-ser- 
 scheinungen bei mehreren. Sorten der Vicia Faba. Jena. 
 75 pp. 
 
 1908. Orton, W. a., The Development of Farm Crops Resistant 
 to Disease. U. S. Dept. Agr. Yearbook, 453-464. 2 pis. 
 Same. Yearbook separate, 494 : 453-464. 2 pis. 
 
 1908. Paulin, G., No Struggle for Existence, no Natural Selec- 
 tion. Critical examination of the fundamental principles 
 of the Darwinian theory. 284 pp. London. 
 
 1908. Pearl, Raymond (Reviewer), Biometrics. Recent con- 
 tributions to theory. (Review.) Am. Nat. 42 : 418-422. 
 Bibliog. in notes. 
 
 1908. Price, H. L., and Drinkard, A. W., Inheritance in 
 Tomato Hybrids. Virginia Agr. Exp. Sta. Bull. 177 : 15^ 
 54. PI. Fig. 
 
 1908. PuNNETT, R. C, Mendelism in Relation to Disease. Roy. 
 Soc. of Med. Proc. Epidemiol. Sect. 1 : 83-168. 
 
 1908. Reid, G. a., Mendelism and Sex. Nature, 77 : 236- 
 237. 
 
 1908. Reid, G. A., The Inheritance of "Acquired^' Characters. 
 Nature, 77 : 442. 
 
 1908. RoBBiNs, W. W., Variation in Flower-heads of Gaillardia 
 aristate. Biometrika, 6 : 106-108. Fig. Diagr. 
 
 1908. Rolfe, R. a., and Hurst, C. C., The Orchid Stud-book. 
 Enumeration of hybrid orchids of artificial origin, with 
 their parents, raisers, rate of first flowering, etc. xlvi 
 + 325 pp. Kew. 121 figs. 
 
 1908. RosENAu, J., and Anderson, J. F., Further Studies 
 upon Hyper susceptibility and Immunity. Jour, of Med. Re- 
 search, Vol. 16, pp. 381-418. Rev. in Am. Nat. 42 : 135. 
 
 1908. Seaver, F. J., Color Variation in some of the Fungi. 
 Torrey Bot. Club Bull. 35 : 307-314. 
 
 1908. Shimek, B., a Hybrid Oak. Iowa Acad. Sci. Proc. 15: 
 77-83, pis. 1-2. 
 
352 Plant-Breeding 
 
 1908. Shull, G. H., Dr. Baur on Variegation. Plant World, 
 
 11 : 147-151. 
 1908. Shull, G. H., The Pedigree Culture, its Aims and Methods. 
 
 Plant World, 11:21. 
 1908. Shull, G. H., Some New Cases of Mendelian Inheritance. 
 
 Am. Ass'n Adv. Sci., Sec. Bot. ; Abstr. in Science, n.s. 
 
 27 : 206. 
 1908. Shull, G. H., Some New Cases of Mendelian Inheritance. 
 
 Bot. Gaz. 45: 103-116, figs. 1-4. 
 1908. Shull, G. H., A New Mendelian Ratio and Several Types 
 
 of Latency. Am. Nat. 42: 433-451. Bibliog. in notes. 
 1908. Sutton, Arthur W., Brassica Crosses. Linnean Soc. 
 
 Bot. Jom\ 38:337-349. 12 pis. Rev. in Zeitsch. f. ind. 
 
 Abs. u. Vererb. 2 : 140. 
 1908. Terry, W. A., A New Variety of the Ostrich Fern. Fern 
 
 Bull. 16:3-4. 
 1908. Trail, J. W. H., Floral Variation in the Genus Veronica. 
 
 Scottish Nat. Hist. Soc. Ann. 68 : 158-259. 
 1908. TscHERMAK, E. VON, Die Mendelschen V ererhurgegesetze. 
 
 Schr. zur Verbr. Naturwiss. Kennt. (Wien.) 48 : 145-164. 
 1908. TscHERMAK, E. VON, Dcr Moderne Stand des Vererhungs- 
 
 proble^ns. Arch. f. Rassen- und Ges.-Biol. 5 : 305-326. 
 1908. Vries, H. de, Especes et varietes; leur naissance par 
 
 mutation. Trad, de I'angl. p. L. Blaringhem. Paris. 
 1908. Vries, H. de, Uber die Z willing sbastarde von (Enothera 
 
 nanella. Deutsch. Bot. Gesells. Ber. 26a : 667-676. 
 1908. Webber, H. J., Plant Breeding for Farmers. Cornell 
 
 Univ. Agr. Exp. Sta. Bull. 251 : 282-332. 
 1908. Webber, H. J., Improving Corn by Seed Selection. Cor- 
 nell Univ. Farmers' Reading Course Bull. 42 : 5. Figs. 
 1908. Werner, F., Nochmals Mimikry und Schutzfdrbung. 
 
 Biol. Centralbl. 28 : 567-576, 588-601. 
 1908. White, C. A., Aggregate Mutation of Gossypium. Science, 
 
 n.s. 27 : 193. 
 
Appendix D 353 
 
 1908. WiCKSON, E. J., Luther Burbank and his New Environment. 
 
 Sunset Mag. 27 : 151-162. 
 1908. WiLLisTON, S. W., What is a Species? Am. Nat. 42: 
 
 184-194. 
 1908. Winkler, Hans, Uber Parthenogenesis und Apogamie 
 
 im Pflanzenreiche. Prog. Rei. Bot. 2 : 293-454. Fig. 
 
 Bibliog. 
 1908. Winkler, H., Solanum tubingense, ein echter Pfropf- 
 
 bastard zwischen Tomate und Nachtschatten. Deutsch. 
 
 Bot. Gesell. Ber. 26a : 595-608. 2 illus. 
 1908. Winkler, H., Parthenogenesis und Apogamie im Pflan- 
 
 zenreich ( — in the plant kingdom), 166 pp. Reprint 
 
 from Prog. Rei. Bot. 2 ; Rev. (Ger.) in Arch. f. Entwick'- 
 
 mech. d. Org. 26 : 696. 
 
 1908. Zavitz, C. a., The Work of Plant Improvement at Home 
 and Abroad. Can. Seed-Grow. Assoc. Rep. 4 : 42-46. Tab. 
 
 1909. Aaronsohn, A., Contribution a Vhistoire des cereales. 
 Le ble, Vorge et le seigle a Vetat sauvage. Soc. Bot, France 
 Bull. 56 : 196-203, 56 : 237-245, 56 : 251-258. 
 
 1909. Aikman, p. J. A., Oii Some Hybrid Tuberous Solanums. 
 
 Roy. Hort. Soc. Jour. 35 : 53-55. 
 1909. Baco, F., Sur des variations de vignes greffees. Acad. 
 
 Sci. Paris, Compt. Rend. 148:429-431. 
 1909. Balls, Lawrence, Some Cytological Aspects of Cotton 
 
 Breeding. A. B. A. Rep. 5: 16-29. 
 1909. Bateson, W., Saunders, Miss E. R., Punnett, R. C., 
 
 Experimental Studies in the Physiology of Heredity. Roy, 
 
 Soc. London Evol. Com. Rep. 4 : (60 pp.). Rev. in Zeitsch. 
 
 f. ind. Abs.- u. Vererb. 2 : 17-19. 
 1909. Bateson, W., Mendel's Principles of Heredity. 396 pp. 
 
 G. P. Putnam's Sons, N. Y. Cambridge (England) Univ. 
 
 Press. 6 pis., 35 figs., 3 plates. Rev. in Science, n.s. 30: 
 
 481-483. 
 
 1909. Baur, E., Die Aurea-Sippen von Antirrhinum majus. 
 2a 
 
354 Plant-Breeding 
 
 Zeitsch. f. indukt. Abst.- u. Vererb. 1 : 124-125. Bibliog. 
 
 in notes. 
 1909. Bauer, E,, Pfropfbastarde. Periklinalchimdren und 
 
 Hyperchimdren. Deutsch. Bot. Gesell. Ber. .27 : 603-605. 
 1909. Beach, S. A., The Present Status of Apple Breeding in 
 
 America. A. B. A. Rep. 5 : 28-36. 
 1909. Bellair, G., L' hybridation en horticulture. 350 pp. 
 
 Paris, 123 figs. 
 1909. Benedict, R. C, N'eiv Hybrids in Dryopteria. Torrey 
 
 Bot. Club Bull. 36 : 41-49. Includes D. Cintoniana X 
 
 spinuloss, D. cristata X Goldiana, D. Goldiana X spinulos 
 
 and D. intermedia X marginalis hybb. nov. 
 1909. Blaringhem, L., Sur les hybrides d'orges et la hi de 
 
 Mendel. Acad. Sci. Paris, Compt. Rend. 148 : 854-857. 
 1909. Boas, Franz, Determination of the Coefficient of Correla- 
 tion. Science, n.s. 29 : 823-824. 
 1909. Broomall, cm., Flower Pigments. Delaware County 
 
 Inst. Sci. Proc. 4 : 81-84. 
 1909. Brown, Harry R., Selection of Seed Potatoes. Can. 
 
 Seed-Grow. Assoc, Rep. 5 : 103-105. 
 1909. Brozek, a., Variabilitdt bei Palcemonetes varians. 
 
 Bohm Ges. Wiss. Prag. S. B. 1-11. 
 1909. Burtt-Davy, J., Mendelism in Maize. Transvaal Agr. 
 
 Jour. 7 : 461-462. 
 1909. Bybowski, J., Regeneration des plajitations de cafeiers 
 
 par V introduction d'une espece nouvelle. Acad. Sci. 
 
 Paris, Compt. Rend. 148 : 232-235. 
 1909. Cannon, W. A., Studies in Heredity as Illustrated by the 
 
 Trichomes of Species and Hybrids of Juglans, (Enothera, 
 
 Papaver and Solajium. Carnegie Inst. Wash. Pub. 117. 
 
 Washington, D.C., pis. 1-10, and figs. 1-21. 
 1909. Carleton, M. A., Field Methods in Wheat Breeding. 
 
 A. B. A. Rep. 5 : 185-207. 
 1909. Castle, W. E., The Behavior of Unit Characters in Heredity. 
 
Appendix D 355 
 
 In Fifty Years of Darwinism, pp. 143-159. Bibliograph. 
 
 in notes. 
 1909. Chambers, Robert, Einfluss der Eigrosse und der Tem- 
 
 peratur auf das Wachsthum und die Grosse des Frosches 
 
 und dessen Zellen. Arch, fiir Mikroskopische Anatomic 
 
 und Entwicklungsgeschichte ? Vol. 72, pt. 3, pp. 607-661. 
 
 Rev. in Am. Nat. 43:57. 
 1909. Chamblise, Charles E., A Note on Rice Breeding. 
 
 A. B. A. Rep. 5 : 182-185. 
 1909. Clothier, Geo. L., Practical Possibilities of Grafting 
 
 and Building Forest and Nut Trees. A. B. A. Rep. 5 : 262- 
 
 265. 
 1909. Collins, G. N., The Importance of Broad Breeding in 
 
 Corn. Dept. Agr. Bur. Plant Ind. 141 (pt. 4) : 33-44. 
 1909. Cook, 0. F., McLachlan, Argyle, and Meade, Row- 
 land M., A Study of Diversity in Egyptian Cotton. U. S. 
 
 Dept. Agr. Bur. Plant Ind. Bull. 156: (60 pp.), 6 pis. 
 1909. Cook, O. F., Pure Strains as Artifacts of Breeding. Am. 
 
 Nat. 43 : 241-242. 
 1909. Cook, 0. F., Suppressed and Intensified Characters in 
 
 Cotton Hijhrids. U. S. Dept. Agr. Bur. Plant Ind. Bull. 
 
 147: (27 pp.). 
 1909. Cook, 0. F., The Superiority of Line Breeding over Narrow 
 
 Breeding. U. S. Dept. Agr. Bur. Plant Ind. Bull. 146: 
 
 (45 pp.). 
 1909. Criddle, N., The So-called White Wild Oats and What 
 
 they Are. Ottawa Nat. 23 : 127-128. 
 1909. Darbishire, A. D., An Experiinental Estimation of the 
 
 Theory of Ancestral Contributions in Heredity. Roy. Soc. 
 
 London Proc. 81 : 61-79. 
 1909. Darbishire, A. D., Recent Advances in the Study of 
 
 Heredity. III. New Phytolog. 7 : 157-181 ; 7 : 237-248. 
 1909. Davenport, Charles B., Mutation. In Fifty Years of 
 
 Darwinism, pp. 160-181. 
 
356 Plant-Breeding 
 
 1909. De Loach, R. J. H., The Problem of Fixation in Cotton 
 Hybrids. A. B. A. Rep. 5 : 130-138. 
 
 1909. Demoll, R., and Strohl, J., U influence de la tem- 
 perature sur le developpeinent des organismes et la duree 
 de la vie. Soc. Biol. Compt. Rend. 66 : 855-857. 
 
 1909. Dow, George, Some Results Obtained through the Careful 
 Selection of Seeds. Can. Seed-Grow. Assoc. Rep. 5 : 109- 
 111. 
 
 1909. East, E. M., A Study of the Factors Influencing the Im- 
 provement of the Potato. III. Exp. Sta. Bull. 127 : Rev. 
 in Zeitsch. f . ind. Abs.- u. Vererb. 2 : 142-143. 
 
 1909. East, E. M., Note concerning Inheritance in Sweet Corn. 
 Science, n.s. 29 : 465-467. 
 
 1909. East, Edward M., The Distinction between Development 
 and Heredity in Inbreeding. Am. Nat. 43 : 173-181. Bib- 
 liog. in notes. 
 
 1909-10. East, E. M., The Transmission of Variations in the 
 Potato in Asexual Reproduction. (Contr. from the Labora- 
 tory of Genetics, Bussey Institution of Harvard University, 
 No. 3.) Conn. Exp. Sta. Rep. 120-160, 5 pis. 
 
 1909. Emerson, R. A., Factors for Mottling in Beans. A. B. A. 
 Rep. 5 : 368-376. 
 
 1909. Emerson, R. A., Inheritance of Color in the Seeds of the 
 Common Bean, Phaseolus vulgaris. Nebraska Agr. Exp. 
 Sta. Rep. 22:65-101. 
 
 1909. Forbes, F. E., A New Hybrid Violet. Rhodora, 11: 
 15-15. V. Brittoniana X lanceolata. 
 
 1909. Garner, W. W., Breeding Tobacco for High and Low 
 Nicotine Conte7it. A. B. A. Rep. 5 : 299-303. 
 
 1909. Gates, R. R., A] Litter of Hybrid Dogs. Science, n.s. 
 29:744-747. Tab. ^ 
 
 1909. Gates, R. R., The Behavior of the Chromosomes in (Eno- 
 thera lata X 0. gigas. Bot. Gaz. 48 : 179-199, pis. 12-14. 
 
 1909. Gates, R. R., The Stature and Chromosomes of (Enothera 
 
Appendix D 357 
 
 gigas De Vries. Archiv Zellforsch. 3 : 525-552. Pis. 
 
 29-30. 
 1909. Gatin, M. C. L., La morphologie de la germination et 
 
 ses rapports avec la phylogenie. Rev. Gen. Bot. 21 : 147- 
 
 158. 
 1909. Geerts, J. M., Beitrdge zur Kenntnis der Cytologie und 
 
 der partiellen Sterilitdt von (Enothera Lamarckiana. Rec. 
 
 Trav. Bot. Neerlandais, 5: 1-114, 28 pis. 
 1909. Griffon, E., Recherches sur la xenie chez les Solanees. 
 
 Soc. Bot. France Bull. 55 : 714-720. 
 1909. Guthrie, C. C., Guinea Pig Grajt-hyhrids. Science, 
 
 n.s. 30 : 724-725. Bibliog. in notes. 
 1909. Hagedoorn, Arend L., Mendelian Inheritance of Sex. 
 
 Arch. f. Entwick'mech. d. Org. 28 : 1-34, 3 figs. 
 1909. Hansen, N. E., The Wild Alfalfas and Clovers of Siberia, 
 
 with a Prospective View of the Alfalfas of the world. U. S. 
 
 Dept. Agr. Bur. Plant Ind. Bull. 150: (31 pp.), 1 pi. 
 1909. Harris, J. A., Variation in the Number of Seeds per Pod 
 
 in the Broo7n, Cytisus scoparius. Am. Nat. 43 : 350-355, 
 
 2 tab. Diag. Bibliog. in notes. 
 1909. Harris, J. A., A Short Method of Calculating the Coefficient 
 
 of Correlation in the Case of Integral Variates. Biometrika, 
 
 7:214-218. 
 1909. Harris, J. A., Note on Variation in Adoxa. Biometrika, 
 
 7 : 218-222. 
 1909. Harris, J. A., The Correlation between Length of Flower- 
 ing Stalk and Number of Flowers per Inflorescence in Nothos- 
 
 cordum and Allium. Missouri Bot. Gard. Rep. 20 : 105-115. 
 1909. Harris, J. A., Variation and Correlation in the Flowers 
 
 of Lagerstroemia indica. Missouri Bot. Gard. Rep. 20 : 
 
 97-104. 
 1909. Harshberger, J. W., The Biologist's Part in Practical 
 
 Plant and Animal Breeditig. Amer. Vet. Rev. 35 : 254- 
 
 265. 
 
358 Plant-Breeding 
 
 1909. Meckel, M., Fixation de la mutation gemmaire culturale 
 du Solanum maglia. Soc. Nation. d'Agr. Bull. 69 : 874-877. 
 
 1909. HoLDEFLEiss, P., Bastardierimgsversuche mit Mais. 
 Landwirtsch. Inst. Halle a. S. Ber. 19 : 178-198, 1 pi. 
 
 1909. Holmes, S. J., The Categories of Variation. Am. Nat. 
 43 : 257-285. 
 
 1909. Howard, A., and Howard, G. L. C, The Varietal Char- 
 acters of Indian Wheats. India Dept. Agr. Mem. Bot., 
 Series 2: (66 pp.). 
 
 1909. Hy, F., Sur une forme sterile de Cardamine hirsuta. 
 Soc. Bot. France Bull. 56: 210-213. 
 
 1909. Jennings, S. H., Heredity and Variation in the Simplest 
 Organism. Am. Nat. 43 : 321-337. Bibliog. in notes. 
 
 1909. Jepson, Willis L., Spontaneous Hybrids of Native Cali- 
 fornian Trees. A. B. A. Rep. 5 : 259-262. 
 
 1909. Johannsen, W., Uber Knospenmutation bei Phaseolus. 
 Zeitsch. f. indukt. Abst.- u. Vererb. 1 : 1-10, 2 figs. Bib- 
 liog. \ p. 
 
 1909. Johnson, R. H., Variation in Syndesmon and Hepatica. 
 Ohio Nat. 9:431-436. 
 
 1909. JoRDON, D. S., and Kellogg, V. L., The Scientific As- 
 pects of Luther Burbank's Work, xiv + 115 pp. San 
 Francisco. 
 
 1909. Knuth, R., liber Bastardbildung in der Gattung Pelargo- 
 nium. Bot. Jahrb. f. Systematik usw. (Engler) 44 : 1-35. 
 4 figs. 
 
 1909. Leake, H. M., Studies m the Experimental Breeding of 
 Indian Cottons 2. On Buds and Branching. Asiat. Soc. 
 Bengal Jour., n.s. 5 : 23-30. 
 
 1909. Leavitt, R. G., A Vegetative Mutant and the Principle 
 of Homoeosis in Plants. Bot. Gaz. 47 : 30-68, figs. 1-19. 
 
 1909. Lee, F. E., Report of Wheat Improvement Committee. 
 Dept. Agr. Victoria Jour. 7 : 239-254. 
 
 1909. Lock, R. H., A Preliminary Survey of Species Crossing 
 
Appendix D 359 
 
 in the Genus Nicotiana from the Mendelian Standpoint. 
 Roy. Bot. Gard., Peradeniya Annals, 4 : 195-227, 12 pis. & 
 
 Ifig. 
 
 1909. Love, Harry H., Influence of Food Supply on Variation. 
 A. B. A. Rep. 5:357-365. 
 
 1909. Macallum, a. B., On the Origin of the Life on the Globe. 
 Canadian Inst. Trans. 8 : 423-441. 
 
 1909. MacDougal, D. T., The Direct Influence of Environment. 
 In Fifty Years of Darwinism, pp. 114-142, 2 pis. Bibliog- 
 raphy in notes. 
 
 1909. McAlpine, D., and de Castella, F., Bud-variation in 
 Corinth Currant Vine. Victoria Dept. Agr. Jour. 7 : 145- 
 149. 
 
 1909. McCallum, W. B., The Reciprocal Influence of Scion 
 and Stock. Plant World, 12 : 281-286. 
 
 1909. Marryat, (Miss) Dorothea C. E., Hybridisation Ex- 
 periments ivith Mirabilis Jalapa. Roy. Soc. London Evol. 
 Comm. Rep. 5 : 32-50, 2 pis. Tables. 
 
 1909. Martius, Fr., Das pathogenetische Vererbungsproblem. 4- 
 (letztes) Heft der " Pathogenese innerer Krankheiten.^' Nach 
 Vorlesungen fiir Studierende und Arzte. pp. 323-467. 
 Leipzig und Wien. 
 
 1909. Maynard, G. D., Variability in Shirley Poppies from 
 Pretoria. Biometrika, 7 : 227-230. Fig. 
 
 1909. Meisenheimer, Johannes, Experimenielle Studien zur 
 Soma und Geschlechts-Differenzierung. Erster Beitrag. 
 Jena, Gustav Fischer. Rev. in Am. Nat. 44 : 316. 
 
 1909. Merzbacher, L., Gesetzmassigkeiten in der Vererbung 
 und Verbreitung verschiedener hereditdrfamilidrer Erkran- 
 kungen. Archiv f. Rassen- u. Gesell.-Biologie, 6 : 172-198, 
 2 pis., 19 figs. 
 
 1909. Newman, L. H., Certain Biological Principles and their 
 Practical Application in the Improvement of the Field Crops 
 of Canada. Ottawa Nat. 23 : 85-91 ; 23 : 105-110. 
 
360 Plant-Breeding 
 
 1909. Paton, J. Airman, Notes on Some Hybrid Tuberous 
 Solariimis. Roy. Hort. Soc. Jour. 35 : 53-55. 
 
 1909. Pearl, Raymond, A Note on the Degree of Accuracy of 
 Biometric Constants. Am. Nat. 43 : 238-240. 
 
 1909. Pearl, Raymond, and Surface, Frank M., Selection 
 Index Nuynbers and their Use in Breeding. Am. Nat. 
 43 : 385-400. 
 
 1909. Pearl, Raymond, and Surface, Frank M., Data on the 
 Inheritance of Fecundity obtained from the Records of Egg 
 Production of the Daughters of "200-egg " Hens. Maine 
 Agr. Exp. Sta. Bull. 166: (34 pp.), 13 figs. 
 
 1909. Pearson, Karl, Determination of the Coefficient of Cor- 
 relation. Science, n.s. 30 : 23-25. 
 
 1909. Pearson, K., On the Ancestral Gametic Correlations of 
 a Mendelian Population Mating at Random. Roy. Soc. 
 London Proc. 81 : 225-229. 
 
 1909. Perriraz, J., Etude hiologique et biometrique sur Nar- 
 cissus angustifolius. Soc. Vaud. Sci. Nat. Bull. 45 : 153- 
 176. 
 
 1909. Piper, C. V., Alfalfa and its Improvement by Breeding. 
 A. B. A. Rep. 5:94-115. 
 
 1909. Plate, L., Darwinismus u. Landwirtschaft. 24 pp. 
 Parey, Berlin. 
 
 1909. Powers, H. J., Are Species Realities or Concepts Only? 
 Am. Nat. 43: 598-610. 
 
 1909. Price, H. L., and Drinkard, W., Inheritance in Tomato 
 Hybrids. Plant World, 12 : 10-18, figs. 1-2. 
 
 1909. Price, H. L., and Drinkard, A. W., Inheritance in 
 Tomato Hybrids. Virginia Agr. Exp. Sta. Bull. 177 : 17- 
 53, 10 pis. Rev. (English) in Zeitsch. f. indukt. Abst.- u. 
 Vererb. 1 : 402-403. 
 
 1909. RiTTER, G., tfber discontinuierliche Variation im Organis- 
 menreiche. Bot. Centralbl. Beih. 251 : 1-29. 
 
 1909. RiTTER, W. E., The Hypothesis of ''Presence and Ab- 
 
Appendix D 361 
 
 sence " in Mendelian Inheritance. Science, n.s. 30 : 367- 
 
 368. 
 1909. Rosenberg, 0., Uber die Chromosomenzahlen bei Taraxa- 
 cum und Rosa. Svensk Bot. Tidskr. 3 : 150-162. 
 1909. Roux, G., Les problemes de Vheredite. La Revue (Oct. 
 
 1): 375-383. 
 1909. RussEL, E. S., The Transmission of Acquired Characters. 
 
 Rivista di Scienza, 5: 192-203. 
 1909. Sandsten, E. P., Improvement of Wisconsin Tobacco 
 
 through Seed-selection. Wisconsin Agr. Exp. Sta. Bull 
 
 176. 
 1909. Sauer, L. W., Quercus Leana; a Hybrid Oak. Plant 
 
 World, 12: 198-201, figs. 1-2. 
 1909. Saxton, W. T., Parthenogenesis in Pinus Pinaster. 
 
 Bot. Gaz. 47 : 406-409, figs. 1-7. 
 1909. Seyot, p. M., Etude biometrique des pepins d'un Vitis 
 
 vinifera franc de pied et greffe. Acad. Sci. (Paris) Compt. 
 
 Rend. 149 : 53-56. 
 1909. Shoemaker, D. N., Report of the Committee on Breeding 
 
 Cotton. A. B. A. Rep. 5: 115-116. 
 1909. Shull, G. H., a Simple Chemical Device to Illustrate 
 
 Mendelian Inheritance. Plant World, 12 : 145-152. Illus. 
 1909. Smith, J. Russell, Elimination of the Gullied Hillside 
 
 through Tree Breeding. A. B. A. Rep. 5 : 265-269. 
 1909. Spillman, W. J. (Reviewer), The Nature of ''Unit'' 
 
 Characters. (Review.) Am. Nat. 43 : 243-248. Bibliog. 
 in notes. 
 1909. Spillman, W. J., The Effect of Different Methods of Selec- 
 tion on the Fivation of Hybrids. A. B. A. Rep. 5 : 341-347. 
 1909. Stevens, F. L., and Hall, J. G., Variation of Fungi 
 
 Due to Environment. Bot. Gaz. 48 : 1-30, figs. 1-37. 
 1909. Straugin, M. N., and Church, C. G., The Influence of 
 Environment on the Composition of Sweet Corn, 1905-1908. 
 U. S. Dept. Agr. Bur. Chemistry Bull. 127 : (69 pp.), 11 figs. 
 
362 Plant-Breeding 
 
 1909. SuDWORTH. Geo. B.. Prelim. Rep. Chairman Committee on 
 
 Breeding Xut and Forest Trees. A. B. A. Rep. 5 : 255-259. 
 1909. Tedix, H., Redogdrelse for arbetena pa Svalof med korn, 
 
 arter och vieker under ar. Sveriges Utsadesfor. Tidskr. 
 
 20:245-255. 1910. 
 1909. Trabut. Contribution a Vetude de Vorigine des avoines 
 
 cultivees. Acad. Sci. Paris Compt. Rend. U9 : 227-229. 
 1909. Tracy, J. E. ^A'.. Work conducted by the United States 
 
 Department of Agriculture in breeding Highgrade Strains 
 
 of Sugar Beet Seed and testing Important Varieties. A. B. A. 
 
 Rep. 5:284-2S5. 
 1909. Trow. A. H.. Forms of Senecio vulgaris. Jour, of Bot. 
 
 47 : 304-306. 
 1909. TscHER^L^K. E. v.. Der Moderne Stand der Kreuzungs- 
 
 zuchtung der landwirtschaftlichen Kulturpflanzen. Vortrag 
 
 gehalten in der Okonomischen Gesellschaft in Konigreich 
 
 Sachsen zu Dresden am 5. Feb. 19 pp. 
 1909. TscHER^L\K. E. v., Uber Correlationen. Landw. Um- 
 
 schaii, 1 : (2 pp.). 
 1909. Van Fleet. W., Report of the Committee on Breeding 
 
 Roses. A. B. A. Rep. 5 : 14-15. 
 1909. VoGT, O., Studien ilber das Artproblem. 1. ]\litt. Uber 
 
 das Variieren der Hummeln. 1. Teil. Ges. Xaturf. Freunde 
 
 Berlin Sitzungsber. 28-83, 1 pi. & fig. 
 
 1909. VoLL^L\xx. F.. Die Bedeutung der Bastardierung filr 
 die Entstehung von Arten und Formen in der Gattung Hiera- 
 cium. Bayer Bot. Gesell. Ber. 12 : 29-37. 
 
 1909. Vries. H. de, Fertilization and Hybridization. ^Monist, 
 19 : 514-555. 
 
 1909. Vries, H. de, On Triple Hybrids. Bot. Gaz. 47 : 1-8. 
 
 1909. Vries, H. de. Transformwme et mutation. Rev. du 
 
 Mois. (Sept.), 269-302. 
 1909. Wagx'er. a.. Die drei Elemente der Lamarckschen Lehre. 
 
 Zeitsch. Ausbau Entw. Lehre, 3 : 44-60. 
 
Appendix D 363 
 
 1909. Warburton, C. W., Improvement of the Oat Crop. U. S. 
 Dept. Agr. Bur. Plant Ind. Circ. 30 : (10 pp.). 
 
 1909. Waugh and Shaw, Variation in Peas. Mass. (State) 
 Agr. Exp. Sta. Ann. Rep. 167-173. 
 
 1909. Webber, H. J., Improving Corn by Seed Selection. Cor- 
 nell Univ. Reading-Course for Farmers, 42. 
 
 1909. Webber, H. J., Methods of Breeding and Improving the 
 Potato Crop. Cornell Univ. Farmers' Reading-Course 
 Bull. 43 : 3 figs. 
 
 1909. Webber, H. J., Clonal or Bud Variation. A. B. A. 
 Rep. 5:347-357. 
 
 1909. WEisiL\xx, August, The Selection Theory. Darwin and 
 Mod. Sci. pp. 18-65, pL, fig. Bibliog. in notes. 
 
 1909. Westgate, J. M., Methods of Breeding Alfalfa by Selec- 
 tion. A. B. A. Rep. 5 : 144-166. 
 
 1909. Westgate, J. M., Another Explanation of the Hardiness 
 of Grimm Alfalfa. Science, n.s. 30 : 18^186. 
 
 1909. Wheldale, (Miss) ]\I., The Colours and Pigments of 
 Flowers, with Special Reference to Genetics. Roy. Soc. 
 London Proc. 81 : 44-60. 
 
 1909. Wheldale, (Miss) M., Further Observations upon the 
 Inheritance of Flower-colour in Antirrhinum majus. Roy. 
 Soc. London Evol. Comm. Rep. 5 : 1-26. Tables. Bib- 
 liog. in notes. 
 
 1909. Wilson, Edmund B., Studies on Chromosomes V. The 
 Chromosomes of Metapodius. A Contribution to the Hypothesis 
 of the Genetic Continuity of Chromosomes. Jour. Exp. Zool. 
 6 : 147-205, 1 pi. & 13 figs. 
 
 1909. Wilson, Edmund B., The Cell in Relation to Heredity 
 and Evolution. In Fifty Years of Darwinism, pp. 92- 
 113. 
 
 1909. WooDHEAD, J. W., and Drierley, M. M., Development 
 of the Climbing Habit in Antirrhinum majus. Xew Pliy- 
 tologist, 8 : 284-298, 3 pis. & 5 figs. 
 
364 Plant-Breeding 
 
 1909. Woodruffe-Peacock, E. A., Heredity of Acquired 
 
 Characters. Jour, of Bot. 47 : 320-321. 
 1909. Wright, R. P., Potatoes, Effect of Planting Sprouted 
 
 Tubers on Yield. West. Scot. Agr. Coll. Ann, Rep. 9: 101. 
 
 Roy. Hort. Soc. Abs. in Jour. 35 : 557. 
 1909. Zavitz, Z. a., Fotmdation Stock on Plant Breeding. 
 
 A. B. A. Rep. 5: 167-171. 
 
 1909. ZiMMERMANN, W., Orckis coriophora X morio. Allg. 
 Bot. Zeitsch. 15: 150-151. 
 
 1910. Andrews, F. M., Twin Hybrids {Iceta and velutina) and 
 their Anatomical Distinctioris. Bot. Gaz. 50 : 193-201. 
 
 1910. Babcock, Ernest B., Walnut-Oak Hybrid Experiments. 
 
 Am. Breed. Mag. 1 : 200-202. Tab. 
 1910. Ball, Carleton R., The Breeding of Grain Sorghums. 
 
 Am. Breed. Mag. 1 : 283-293. 
 1910. Balls, W. L., Some Complications in Mendelian Cotton 
 
 Breeding. Inst. Egyptien Bull. 3 : 120-127. 
 1910. Baltzer, F., Uber die Beziehungenzwischen dem Chroma- 
 tin und der Eritwickelung und Vererbungs-richtung bei 
 
 Echinodermenbastarden. Arch. Zellforschung, 5 : 497-621. 
 
 5 pis. & 19 figs. 
 1910. Barus, C, Variations Graphically. Science, n.s. 31 : 
 
 867-868. 
 1910. Bataillon, E., Contribution a V analyse experimentale 
 
 des phenomenes karyocinetiques chez Ascaris megalocephala. 
 
 Arch, f . Entwick'mech. d. Org. 30 : 1 : 24-44, 1 pi. Bib- 
 
 liog. \\ pp. 
 1910. Baur, E., Pfropf bastards. Biol. Centralbl. 30:497-514. 
 
 7 figs. 
 1910. Benedikt, Moriz, Biomechanische Grundfragen. Of- 
 
 fenes- Sendschreiben an Herrn H of rat Ernst Ludwig. Arch. 
 
 f. Entwick'mech. d. Org. 31 : 164-174. 
 1910. Bernard, Noel, L'origine de la pomme de terre. 19 pp. 
 
 Soc. Franc. d'Impr. et de Librairie, Poitiers. Reprint 
 
Appendix D 365 
 
 from Soc. Acad. d'Agric, Belles] ettres, Sci. et Arts de 
 Poitiers Bull. 
 1910. Berthault, p., i propos de Vorigine de la pomme de 
 
 terre. Rev. G^n. Bot. 22 : 345-353. 
 1910. Berthault, P., Sur les types sauvages de la pomme de 
 terre cultivee. Acad. Sci. Paris, Compt. Rend. 150:47- 
 50. 
 
 1910. Bessey, E. a.. Air Drainage as Affecting the Acclimatiza- 
 tion of Pla7its. N. Y. Hort. Soc. Mem. 2: 25-28. 
 
 1910. Blanchard, Henry F., Improvement of the Wheat Crop 
 in California. U. S. Dept. Agr. Bur. Plant Ind. Bull. 178 : 
 (37 pp.), 10 figs. ^ 
 
 1910. Bordage, E., a propos de Vheredite des caracteres ac- 
 quis. Bull. Scient. France et Belgique 44: (Heft 1). 
 
 1910. Bornet, E., and Gard, M., Recherches sur les hybrides 
 artificiels de Cistes obterius par M. Ed. Bornet. I. Notes 
 inedites et resultats experimentaux. Ann. des Sci. Natu- 
 relles (Botanique) 12 : 71-116. 
 
 1910. Brand, Charles J., The Utilization of Crop Plants in 
 Paper Making. U. S. Dept. Agr. Yearbook, 329-340. 
 Same. Yearbook Separate, 541 : 329-340. 
 
 1910. Bruce, A. B., The Mendelian Theory of Heredity arid the 
 Augmentation of Vigor. Science, n.s. 32:627-628. 
 
 1910. Bruce, A. B., Self-fertilization and Loss of Vigour. Na- 
 ture. March 3. 
 
 1910. Buder, J., Pfropfbastarde und Chimaeren. Zeitsch. f. 
 allg. Physiol. 11: 15-31. 
 
 1910. Buder, J., Studien an Laburnum Adami. Deutseh. Bot. 
 Gesell. Ber. 28: 188-192. 
 
 1910. Burtt-Davy, J., A Note on the Correlation of Characters 
 in Maize Breeding. Transvaal Agr. Jour. 8 : 453-455. 
 
 1910. Burtt-Davy, J., An Experiment in Breeding a Neiv Type 
 of Maize. Transvaal Agr. Jour. 8 : 450-453. 
 
 1910. Chevalier, J., Influence de la culture svr la teneur en 
 
366 Plant-Breeding 
 
 alcaloides de quelques Solanees. Acad. Sci. Paris Compt. 
 Rend. 150:344-347. 
 
 1910. Clark, Chas. F., Variation and Correlation in Timothy. 
 Cornell Univ. Agr. Exp. Sta. Bull. 279 : 421-469, 40 figs. 
 
 1910. Clements, F. E., The Real Factors in Acclimatization. 
 N. Y. Hort. Soc. Mem. 2 : 37-40. 
 
 1910. Clothier, Geo. L., Breeding to Improve Physical Quali- 
 ties of Timber. Am. Breed. Mag. 1 : 261-263. 
 
 1910. CocKERELL, T. D. A., A New Variety of the Sunflower. 
 Science, n.s. 32: 384. 
 
 1910. CoiT, J. E., The Relation of Asexual or Bud Mutation to 
 the Decadence of California Citrus or Deads. Fruit Growers' 
 Cons. (Cal.) Proc. 37: 31-39. 
 
 1910. Collins, G. N., Increased Fields of Corn from Hybrid 
 Seed. U. S. Dept. Agr. Yearbook, 319-328. Same. 
 Yearbook Separate, 540: 319-328. 
 
 1910. Collins, G. N., The Value of First-Generation Hybrids 
 in Corn. U. S. Dept. Agr. Bur. Plant Ind. Bull. 191: 
 (45 pp.). 
 
 1910. CoTTE,' J., and Cotte, C, Sur Vindigenat du ble en 
 Palestine. Soc. Bot. France Bull. 56 : 538-540. 
 
 1910. CouPiN, H., Sur la vegetation de quelques moisissures 
 dans Vhuile. Acad. Sci. Paris Compt. Rend. 150:1192- 
 1193. 
 
 1910. Crosby, Dick J., and Howe, F. W., School Lessons on 
 Corn. U. S. Dept. Agr. Farmers' Bull. 409 : (29 pp.), 12 figs. 
 (This bulletin contains outlines for class studies and exer- 
 cises on the growth and structure of the corn plant, selection 
 and testing of seed corn, and the cultivation and breeding of 
 corn, with list of publications on the subject.) 
 
 1910. Crosby, Dick J., School Exercises in Plant Production. 
 U. S. Dept. Agr. Farmers' Bull. 408: (48 pp.), 39 figs. 
 (This bulletin describes the material needed for laboratory 
 exercises in plant production, and contains outlines of 
 
Appendix D 367 
 
 lessons in the structure and growth of plants, methods of 
 
 propagation, seed testing, etc., and a list of publications 
 
 on agriculture, of special interest to teachers.) 
 1910. Dachnowski, a., Physiologically Arid Habitats and 
 
 Drought Resistance in Plants. Bot. Gaz. 49 : 325-339. 
 1910. Derr, H. B., a New Awnless Barley. Science, n.s. 
 
 32 : 473-474. 
 1910. DiLLMAN, Arthur C, Breeding Drought-Resistant Forage 
 
 Plants for the Great Plains Area. U. S. Dept. Agr. Bur. 
 
 Plant Ind. Bull. 196: (40 pp. ), 4 pis. 
 1910. Dow, Geo., The Status of the "False " Wild Oats. Can. 
 
 Seed-Grow. Assoc. Rep. 6: 105-107. 
 1910. Drzewina, a.. La transmission des caracteres heredi- 
 
 taires chez les hybrides. Revue des Idees, 7 : 372-376. 
 1910. East, Edward M., ^ Mendelian Interpretation of Varia- 
 tion that is apparently Continuous. Am, Nat. 44 : 65-82. 
 
 7 tab. Bibliog. in notes. 
 1910. East, Edward M., Inheritance in Potatoes. Am. Nat. 
 
 44 : 424-430. Bibliog. in notes. 
 1910. East, E. M., Notes on an Experiment concerning the 
 
 Nature of Unit Characters. Science, n.s. 32 : 93-95. 
 1910. East, E. M., The Role of Hybridization in Plant Breeding. 
 
 Pop. Sci. Mo. 77 : 342-355, figs. 1-11. 
 1910. East, E. M., The Transmission of Variations in the 
 
 Potato in Asexual Reproduction. Conn. Agr. Exp. Sta. 
 
 Rep. 119-160, 5 pis. Rev. in Zeitsch. f. indukt. Abst.- 
 
 u.Vererb. 4:375-376. 
 1910. Emerson, R. A., The Inheritance of Sizes and Shapes in 
 
 Plants. Amer. Nat. 44:739-746. Rev. in Zeitsch. f. 
 
 indukt. Abst.- u. Vererb. 5: 193. 
 1910. Fletcher, S. W., Varieties of Fruit Originated in Mich. 
 
 Mich. Agr. Exp. Sta. Spec. Bull. 44. 
 1910. Frost, H. B., Variation as related to the Temperature 
 
 Environment. A. B. A. Rep. 6: 384-396. 
 
368 Plant-Breeding 
 
 1910. Frye, T. C, Height and Dominance of the Douglas Fir. 
 Forest Quart. 8 : 465-470. 
 
 1910. Gassner, G., tjber Solanum Commersonii und S. "Com- 
 mersonii violet " in Uruguay. Landw. Jahrb. 1011-1020. 
 1 pi. 
 
 1910. Gates, R. R., Abnormalities in (Enothera. Missouri 
 Bot. Gard. Ann. Rep. 21 : 175-184, pis. 29-31. 
 
 1910. Gates, R. R., The Earliest Description of (Enothera 
 Lamarckiana. Science, n.s. 31 : 425-426. 
 
 1910. Gates, R. R., The Material Basis of Mendelian Phenom- 
 ena. Am. Nat. 44 : 203-213. Bibliog., 1 p. 
 
 1910. Gauss, Robert, Acclimatization in Breeding Drought- 
 resistant Cereals. Am. Breed. Mag. 1 : 209-217. 
 
 1910. Griffon, E., Sur la variation dans le greffage et V hybri- 
 dation asexuelle. Acad. Sci., Paris, Comp. Rend. 150: 
 629-632. 
 
 1910. Griffon, E., Variations avec ou sans greffage chez les 
 Solanees et les Composees. Soc. Bot, de France Bull. 57 : 
 517-535, 2 pi. 
 
 1910. Groff, H. H,, Hybridizing the Gladiolus. Are its Lessotis 
 Possible of General Application? Can. Seed-Grow. Assoc. 
 Rep. 6 : 52-58. 
 
 1910. Guthrie, C. C, On Graft Hybrids. A. B. A. Rep. 6: 
 356-373. 
 
 1910. Haecker, Valentin, Die Radiolarien in der Variations- 
 und Vererbungslehre. Zeitsch. f. indukt. Abs.- u. Vererb. 
 2 : 1-17. Rev. in Arch. f. Entwick'mech. d. Org. 29 : 573. 
 
 1910. Hansen, N. E., Is Acclimatization an Impossibility? 
 N. Y. Hort. Soc. Mem. 2 : 69-74. 
 
 1910. Harper, J. N., Experiments with Hybrid Cottons. South 
 Carolina Agr. Exp. Sta. Bull. 148: (17 pp.). 
 
 1910. Hartley, C. P., Seed Corn. U. S. Dept. Agr. Farmers' 
 Bull. 415: (12 pp.), 3 figs. (This bulletin contains direc- 
 tions for the growing, selection^ and care of seed corn. 
 
Appendix D 369 
 
 the destruction of weevils or grain moths, the testing, 
 grading, and shelhng of the corn to be planted, with sug- 
 gestions to the corn grower as to the importance and re- 
 quirements of good seed, and adaptability of any variety 
 to his locality.) 
 1910. Henry, A., On Elm Seedlings Showing Mendelian Results. 
 
 Linn. Soc. Bot. Jour. 39 : 290-300. 
 1910. Henslow, G., The Origin and History of our Garden 
 Vegetables and their Dietetic Values — //. Royal Hort. Soc. 
 Jour. 36 : 345-357, figs. 120-125. Roots and tubers. 
 1910. Henslow, G., The Origin and Histonj of our Garden 
 
 Vegetables. Roy. Hort. Soc. Jour. 36: 115-127. 
 1910. Herre, a. C., Suggestions as to the Origin of California's 
 
 Lichen Flora. Plant World, 13 : 215-220. 
 1910. Heuer, W., Pfropfbastarde. Gartenflora, 59 : 434-438. 
 1910. Himmelbaur, W., Der Gegenwdrtige Staiid der Pfropfhy- 
 
 bridenfrage. Natw. Ver. Univ. Wien Mitt. 8 : 105-127. 
 1910. Hindle, Edward, A Cytological Study of Artificial Par- 
 thenogenesis in Strongylocentrotus Purpuratus. Arch. f. 
 Entwick'mech. d. Org. 31 : 145-163, 1 pi. Bibliog. li pp. 
 1910. Howard, Albert," and Howard, Gabrielle, Wheat 
 in India. Its Production, Varieties, and Improvement. 
 Calcutta. 288 pp., 7 maps, 4 figs., 7 pis. Rev. in Zeitsch. f. 
 indukt. Abst.- u. Vererb. 4 : 153-154. 
 1910. Humphreys, E. W., Variation among Non-lobed Sassafras 
 
 Leaves. Torreya, 10 : 101-108, figs. 1-8. 
 1910. HuRD, Wm. D., Corn Selection for Seed and for Show. 
 
 Mass. State Board of Agr. Ann. Rep. 58. 
 1910. Hurst, C. C., MendeVs Law of Heredity and its Applica- 
 tion to Horticulture. Roy. Hort. Soc. Jour. 36 : 22-52. 
 1910. Ikeno, J., Sind Alle Arten der Gattung Taraxacum 
 Parthenogenetischf Deutsch. Bot. Gesell. Ber. 28-394- 
 397. 
 
 1910. Javillier, M., Sur la migration des alcaloides dans les 
 2b 
 
370 Plant-Breeding 
 
 greffes de Solanees sur Solonees. Inst. Pasteur Annales, 
 
 24 : 569-576. 
 1910. Kearney, Thomas H., Breeding New Types of Egyptian 
 
 Cotton. U. S. Dept. Agr. Bur. Plant Ind. Bull. 200 : (39pp.) 
 
 4 pi. 
 1910. Keeble, Frederick, and (Miss) Pellew, C, The Mode 
 
 of Inheritance of Stature and of Time of Flowering in Peas. 
 
 Pisum sativum. Jour, of Gen. 1 : 47-56. 
 1910. Keeble, Frederick, and (Miss) Pellew, C, White 
 
 Flowered Vai^ieties of Primula sinensis. Jour, of Gen. 
 
 1 : 1-5. 
 1910. Keeble, F., Pellew, C., and Jones, W. N., The In- 
 heritance of Peloria and Flower Colour in Foxgloves {Digi- 
 talis purpurea). New Phytolog. 9 : 68-77, 1 fig. 
 1910. Kroll, H. G., tjher Polygamic bei Polygonatum officinale. 
 
 Bot. Ver. Brandenb. Verh. 52: 98^101. 
 1910. Lecaillon, a., La parthenogenese naturelle rudimen- 
 
 taire. Bull. Scientif . de France et Belgique, 7th ser. 44 : 
 
 235-272. 
 1910. Love, Harry H., Are Fluctuations Inherited? Am. Nat. 
 
 44 : 412-423, 9 figs. & 4 tab. Bibliog. in notes. 
 1910. MacDougal, D. T., Vail, A. M., and Shull, G. H., 
 
 Mutations, Variations, and Relationships of the (Enotheras. 
 
 Carnegie Inst. Wash. Publ. 81: (92 pp.) 1907. Rev. in 
 
 Zeitsch. f. indukt. Abst.- u. Yererb. 3 : 226-228. 
 1910. ]\Iaigre, E. F., Uheredite Mendelienne. Rev. des 
 
 Idees, 234-242. 
 1910. Moorehouse, L. A., Improvements of Bermuda Grass. 
 
 Am. Breed. Mag. 1 : 95-98, fig. 
 1910. Morgan, T. H., Chromosomes and Heredity. Am. Nat. 
 
 44 : 449-496, 3 tab. lUus. 
 1910. Nakano, H., Variation and Correlation in Rays and Disk 
 
 of Aster fastigiatus. Bot. Gaz. 49 : 371-378, figs. 1-4. 
 1910. Nash, G. V., Observations on Hardiness of Plants culti- 
 
Appendix D 371 
 
 vated at the New York Botanical Garden. N. Y. Hort. 
 
 Soc. Mem.2: 130-143. 
 1910. Xemec, B., Das Problem der Befruchtungavorgdnge. 
 
 526 pp. Borntraeger, Berlin. 5 pis. & 119 figs. 
 1910. Newman, L. H., The Correlation of Characters in Plants 
 
 and its Economic Importance to the Plant Breeders. Ottawa 
 
 Nat. 23 : 220-224. 
 1910. NiENBURG, W., Die Jungsten Ergebnisse der Pfropf- 
 
 bastardforschung. Gartenflora, 59 : 479-495. 
 1910. Nilsson-Ehle, H., Kreuzungsuntersuchungen an Hafer 
 
 und Weizen. Lunds Universitats Areskirft. N. F. Afd. 
 
 2. 5: 1-122. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 
 
 3:290-291. 
 1910. Nilsson-Ehle, H., Svalofs Pudelhvete. Sveriges Utsades- 
 
 for. Tidskr. 20 : 69-87. 
 1910. Oliver, George W., Neiv Methods of Plant Breeding. 
 
 Fig. Am. Breed. Mag. 1 : 21-30. 
 1910. Orchard, Harold, Potato Breeding in Manitoba and 
 
 Some Results Obtained. Can. Seed-Grow. Assoc. Rep. 6 : 
 
 103-104. 
 1910. OsTENFELD, C. H., Further Studies on Apogamy and 
 
 Hybridization of Hieracium. Zeitsch. f. Indukt. Abst. 3 : 
 
 (Heft 4). Rev. in Am. Nat. 44:750-762. Bibliog. in 
 
 notes. 
 1910. Paton, Alkman, Notes on Some Hybrid Tuberous Solanums. 
 
 Roy. Hort. Soc. Jour. 36: 127-133. 
 1910. Pearl, Raymond, and Surface, F. M., Experiments in 
 
 Breeding Sweet Corn. Maine Agr. Exp. Sta. Bull. 183 : 
 
 (66 pp.). 
 1910. Pearson, Karl, Darwinism, Biometry and Some Recent 
 
 Biology, I. Biometrika, 7 : 368-385. Tab. 
 1910. Pearson, Karl, On a New Method of Determining Cor- 
 relation when one Variable is given by Alternative and the 
 
 Other by Multiple Categories. Biometrika, 7 : 248-257, Tab, 
 
372 Pla7i t- Breeding 
 
 1910. Planchon, Mutation gemmaire dii Solanum Conimersonii. 
 
 Soc. Nation. d'Agr. Bull. 70 : 373-375. 
 1910. Rehder, a., a New Hybrid Cornus {Cornus rugosa X 
 
 stolonifera) . Rhodora, 12:121-124. C. Slavinii Rehder. 
 1910. RiCHTER, 0., PJropfungen, Pfropfbastarde und Pflanzen- 
 
 chimaeren. Lotos, 58: 1-22, 
 1910. RiETz, H. L., Correlation in Corn. 111. Agr. Exp. Sta. 
 
 Bull. 148: (25 pp.). 
 1910. Salaman, R. N., The Inheritance of Colour and Other Char- 
 acters in the Potato. Jour, of Gen. 1 : 7-46, 29 pi. Rev. 
 
 in Zeitsch. f. indukt. Abst.- u. Vererb. 5 : 192-193. 
 1910. Saunders, E. R., Studies in the Inheritance of Double- 
 
 ness in Flowers. I. Petunia. Jour, of Gen. Fig. 1 : 57. 
 1910. ScHRiBAux, Sur le Solanum Conmiersoiiii. Soc. Nation. 
 
 d'Agr. Bull. 70:798-801. 
 1910. Shepperd, J. H., Report of Co7nmittee on Breeding Fiber 
 
 Crops. Am. Breed. Mag. 1 : 197-199. 
 1910. Shoemaker, D. N., Report of Committee on Breeding 
 
 Cotton. Am. Breed. Mag. 1 : 293-294. 
 1910. Shull, George Harrison, Color Inheritance in Lychnis 
 
 dioica L. Am. Nat. 44 : 83-91, 3 tab. Bibliog. 
 1910. Shull, A. Franklin, The Artificial Production of the 
 
 Parthenogenetic and Sexual Phases of the Life Cycle of Hyda- 
 
 tina senta. Am. Nat. 44 : 146-150, 5 tab. 
 1910. Shull, George Harrison, Hybridization Methods in 
 
 Corn Breeding. Am. Breed. Mag. 1 : 98-107. Bibliog. 
 1910. Smith, Louie H., Increasing Protein and Fat in Corn. 
 
 Am. Breed. Mag. 1 : 15-21. Tab. 
 1910. Smith, J. Russell, Breeding and Use of Tree Crops. 
 
 Am. Breed. Mag. 1 : 86-91. 
 1910. Spillman, W. J., A Theory of Mendelian Phenomena. 
 
 Am. Breed. Mag. 1 : 113-125. Diagr. 
 1910. Spillman, W. J., Effect of Recent Discoveries 07i the Art 
 
 of Breeding. Am. Breed. Mag. 1 : 69-70. 
 
Appendix D 373 
 
 1910. Spillman, W. J., Mendelian Phenomena without de 
 
 Vriesian Theory. Am. Nat. 44 : 214^228, 4 tab. Bibliog. 
 
 in notes. 
 1910. Spillman, W. J. (Reviewer), Heredity. (Rev.) Am. 
 
 Nat. 44 : 504-512. Bibliog. in notes. 
 1910. Spillman, W. J., The Nature of "Unit'' Characters. 
 
 The American Naturalist, 43 : 243-248. Rev. in Zeitsch. 
 
 f. indukt. Abst.- u. Vererb. 3 : 110. 
 1910. Stevens, R. L., and Hall, J. G., Variation of Fungi 
 
 Due to Environment. Bot. Gaz. 48:1-30, fig. 37. Rev. 
 
 in Zeitsch. f. indukt. Abst.- u. Vererb. 3 : 343-344. 
 1910. SuDWORTH, George S., Report of Committee on Breeding 
 
 Nut and Forest Trees. Am. Breed. Mag. 1 : 185-193. Tab. 
 1910. Taylor, George M., The Cross Fertilization of the 
 
 Potato. Gard. Chron. 3d ser. 48 : 279. 
 1910. Tischler, G., Ujitersuchungen uber die Entwicklung des 
 
 Bananen-P aliens. Arch. f. Zellforschung, 5 : 622-670, 2 pis. 
 
 & 4 figs. 
 1910. Trabut, L., Sur une mutation inerme du Cynana Cardun- 
 
 culus. Soc. Bot. de France Bull. 57 : 350-354, 2 pis. 
 1910. Tracy, W. W., Breeding and Raising Garden Seeds. 
 
 Mass. State Board cf Agr. Ann. Rep. 58. 
 1910. Tracy, W. W., Report of Committee on Breeding Vege- 
 tables. Am. Breed. Mag. 1 : 110-113. 
 1910. TuTTLE, A. H., Mitosis in (Edogonium. Jour. Fxp. 
 
 Zool. 9: 143-157, 18 figs. 
 1910. ViLMORiN, Philippe de, Recherches sur Vheredite men- 
 
 delienne. Acad. Sci., Paris, Compt. Rend. 151 : 548-551. 
 1910. Vries, H. de, The Production of Horticultural Varieties. 
 
 Roy. Hort. Soc. Jour. 35 : 321-326. 
 1910. Waldron, L. R., a Suggestion regarding Heavy and 
 
 Light Seed Grain. Am. Nat. 44:48-56. 
 1910. Waldron, L. R., Heredity in Popidations and in Pure 
 
 Lines. Plant World, 13 : 1-12, figs. 1-5. 
 
374 Plant-Breeding 
 
 1910. Westgate, J. M., Variegated Alfalfa. U. S. Dept. Agr. 
 
 Bur. Plant Ind. Bull. 169 : (63 pp.), 9 pis. & 5 figs. 
 1910. Wheeler, Seager, Plant Breeding of the Farm. Can. 
 
 Seed-Grow. Assoc. Rep. 6: 107-109. 
 1910. Wheldale, M., Plant Oxydases and the Chemical Inter- 
 relationships of Colour-varieties. Prog. Rei. Bot. Vol. 
 
 3 : 457-473. Bibliog. in notes. 
 1910. Wilson, E. B., Studies on Chromosomes. Jour. Exp. 
 
 Zool. 9 : 53-79. 
 1910. Winkler, H., Uber das Wesender Pfropfbastarde. (Vor- 
 
 Idufige Mitteilung.) Deutsch. Bot. Gesell. Ber. 28 : 116-118. 
 1910. Winkler, H., Uber die Nachkommenschaft der Solanus- 
 
 Pfropfbastarde und die Chromosomes zahlen ihre Keimzellen. 
 
 Zeitschr. fiir Botanik. 2 : 1-33. Rev. in Zeitsch. f. indukt. 
 
 Abst.- u. Vererb. 3:223-224. 
 1910. Winkler, Hans, Weiters Mitteilungen ilber Pfropfbastarde. 
 
 Zschr. f. Botanik. 1 : 315-345, 1 pL, 4 figs. Rev. in Zeitsch. 
 
 f. indukt. Abst.- u. Vererb. 3: 111-113. 
 1910. Winkler, Hans, Zur Kritik der Ansichten von der Ent- 
 
 stegung der Angiospermenbluten. Schles. Ges. Vaterl. 
 
 Kult. Bteslau. Jahresber. 87 : 22-28. 
 1910. WiNSLOw, E. J., A New Hybrid Fern. Am. Fern Jour. 
 
 1 : 22-23, figs. 1-4. 
 1910. WiTTE, H., Vallvdxtfdrddlingen pa Svalof, dess nodvdndighet 
 
 och behafver af utstrdckt inhemsk froodling . Sveriges Utsades- 
 
 for. Tidskr. 20:317-331. 
 1910. Zavitz, C. a., Heredity in Plants and its Bearing on Agri- 
 cultural Problems. Can. Seed-Grow. Assoc. 6th Ann. 
 
 Meeting Rep. 49-52. 
 
 1910. Zeijlstra, H. H., On the Cause of Dimorphism in (E710- 
 thera nanella. Kon. Akad. Wetensch. Amsterdam Proc. 
 13 : 660, 1 pi. 
 
 1911. Agee, Hamilton P., Propagation of Seedlings of Sugar 
 Cane in Louisiana. A. B. A. Rep. 6: 178-183. 
 
Appendix D 375 
 
 1911. Atkinson, Alfred, Grain Investigations with Different 
 Varieties of Wheat, Oats, and Barley. (Types and variety 
 tests.) Montana Agr. Exp. Sta. Bull. 84 : 24 pp. 
 
 1911. Babcock, Ernest B., Walnut-Oak Hybrid Experiments. 
 A. B. A. Rep. 6: 138^141. 
 
 1911. Balls, W. Lawrence, The Inheritance of Measurable 
 Characters in Hybrids between Reputed Species of Cotton. 
 IV Inter. Conf. Genetique, Paris, 429-440, fig. 9. 
 
 1911. Bally, W., Cytologische Studein an Chytridineen. Jahrb. 
 wissensch. Bot. 50 : 95-156, 5 pis. & 8 figs. 
 
 1911. Barrus, M. F., Variation of Varieties of Beans in their Sus- 
 ceptibility to Anthracnose. Phytopathology, 1 : 190-195, 1 pi. 
 
 1911. Bateson, W., and Punnett, R. C, Reduplication of 
 Terms in Series of Gametes. IV Inter. Conf. Genet. Paris, 
 99-100. 
 
 1911. Bembower, W., Pollination Notes from the Cedar Point 
 Region. Ohio Nat. 11 : 378-383. 
 
 1911. Benedict, Ralph C., Do Ferns Hybridize ? Science, 
 n.s. 33 : 254-255. 
 
 1911. Bringham, E. S., a Yearns Work in Potato Breeding. 
 R. N. Y. 70 : 559. 
 
 1911. Blaringhem, L., L'etat present de la theorie de la mu- 
 tation. Soc. Bot. de France Bull. 58 : 644-652. 
 
 1911. Blaringhem, L., Sur Vheredite en Mosaique. IV Inter. 
 Conf. Genet. Paris, 101-151. 
 
 1911. Braem, F., Die Varoatio7i bei den Statoblasten von Pec- 
 tinatella magnijica. Arch. f. Entwick'mech. d. Org. 32 : 
 314-348, 8 figs., 2 tab. Bibliog. \ p. 
 
 1911. BuFFUM, B. C, Effect of Environment on Plant Breeding. 
 A. B. A. Rep. 6:212-225. 
 
 1911. Campbell, Douglas Houghton, The Nature of Graft- 
 Hybrids. Am. Nat. 45 : 41-53, 1 fig. Bibliog. in notes. 
 
 1911. Chubbuck, Levi, A Variety of Corn for Elevated Regions. 
 Am. Breed. Mag. 2:235, fig. 
 
376 Plant-Breeding 
 
 1911. Clements, Frederick B., Proposals for a System of 
 
 Tree Breeding. A. B. A. Rep. 6 : 275-282. 
 1911. Clothier, Geo. T., Breeding to Improve Physical Qualities 
 
 of Timber. A. B. A. Rep. 6 : 170-172. 
 1911. Clute, W. N., and Ferriss, J. H., A New Species of 
 
 Phlox. Am. Bot. 17 : 74-76. Phlox argillacea sp. nov. 
 1911. Collins, G, N., and Kempton, J. H., Inheritance of 
 
 Waxy Endosperm in Hybrids of Chinese Maize. IV Inter. 
 
 Conf. Genet. Paris, 347-357. Tab. X. 
 1911. Collins, G. N., Increased Yields of Corn from, Hybrid 
 
 Seed. U. S. Dept. Agr. Yearbook, 319-328. 
 1911. Cook, 0. F., Hindi Cotton in Egypt. U. S. Dept. Agr. 
 
 Plant Ind. Bull. 210 : 1-58, pis. 1-6. 
 1911. Cook, 0. F., and Meade, R. M., Arrangement of Parts 
 
 in the Cotton Plant. U. S. Dept. Agr. Plant Ind. Bull. 
 
 222 : 26, figs. 1-9. 
 1911. CouPiN, H., Sur la localisation des pigments dans le 
 
 tegument des graines de haricots. Acad. Sci. Compt. 
 
 Rend. 153: 1489-1492. 
 1911. Creed, Richard, The Growing of Turnip Seed in the 
 
 Maritime Provinces. Can. Seed-Grow. Assoc. Rep. 7 : 
 
 49-50. 
 1911. Dallimore, W., Notes on Trees suitable for Experimental 
 
 Forestry. Kew Bull. Misc. Inf. 1911 : 211-223. 
 1911. Daniel, L., Etude biometrique de la descendance de 
 
 Haricots greffes et de Haricots francs de pied. Acad. 
 
 Sci. Compt. Rend. 152: 1018-1020. 
 1911. Daniel, L., Recherches biometrique sur tin hybride de 
 
 greffe entre poirier et Cognassier. Acad. Sci. Compt. 
 
 Rend. 152: 1186-1188. 
 1911. Davenport, E., ^'Domesticated Animals and Plants.^' 
 
 Science, n.s. 34 : 715. 
 1911. Davis, Bradley Moore, Genetical Studies on (Enothera. 
 
 II. Some Hybrids of (Enothera biennis and 0. grandiflora 
 
Appendix D 377 
 
 that resemble 0. Lamarckiana. Am. Nat. 45: 193-233, 18 
 
 figs. Bibliog. f p. 
 1911. Decker, H., MendeVs Law as Related to Heredity and 
 
 Breeding. I-V. Horticulture, 13 : 635 ; 13 : 669 ; 13 : 705-706 ; 
 
 13 : 741-742 ; 13 : 780. lUus. Translated from Cosmos by 
 
 G. Thommen. 
 1911. Delacroix, G., Maladies des plantes cultivees dans les 
 
 pays chauds, publie par A. Maublanc, vol. 1., 605 pp. 
 
 Challamel. Paris. 
 1911. Emerson, R. A., Genetic Correlation and Spurious Allelo- 
 morphism in Maize. Neb. Agr. Exp. Sta. Ann. Rep. 24 : 
 
 59-90, 9 figs. 
 1911. Emerson, R. A., Latent Colors in Corn. A. B. A. Rep. 
 
 6 : 233-237. 
 1911. Emerson, R. A., Production of a White Bean Lacking the 
 
 Factor for Total Pigmentation. A Prophecy Fulfilled. 
 
 A. B. A. Rep. 6:396-397. 
 1911. Evans, G. W., Wheats and Wheat Breeding. Agr. Jour. 
 
 of Brit. East Africa, 3 : 348-356. 
 1911. EwiNG, E. C., Correlation of Characters in Corn. Cornell 
 
 Univ. Agr. Exp. Sta. Bull. 287 : 67-100, 14 tab., 2 figs. 
 1911. Fairchild, David, Plant Introduction for the Plant 
 
 Breeder. U. S. Dept. Agr. Yearbook, 411-422, 6 pis. & 
 
 1 fig. Same. Yearbook Separate, 580: 411-422, 6 pis. 
 1911. FooTE, E. H., A Study of the Supposed Hybrid of the 
 
 Black and Shingle Oaks. Sci. Lab. Denison Univ. Bull. 
 
 16:315-338, pis. 11-14. 
 1911. Freeman, E. M., Resistance and Immunity in Plant 
 
 Diseases. Phytopathology, 1 : 109-115. (Also published 
 
 in Publ. Bot. Soc. Am. 50: 17-26.) 
 1911. Freeman, G. F., and Jones, D. F., Plant Breeding. 
 
 Univ. Arizona Agr. Exp. Sta. Ann. Rep. 541-546. 
 1911. Gates, R. R., Mutation in (Enothera. Am. Nat. 45: 
 
 577-606. Bibliog. 
 
378 Plant-Breeding 
 
 1911. Gates, R. R., Studies on the Variability and Hentability 
 
 of Pigmentation in (Enothera. Zeitsch. f. indukt. Abst.- u. 
 
 Vererb. 4 : 337-372, pi. & o figs. Bibliog. | p. 
 1911. Gauss, Robert, Acclimatization in Breeding Drought- 
 Resistant Cereals. A. B. A. Rep. 6 : 147-156. 
 1911. Gauss, Robert, The Plant Breeding Problem. Am. Breed. 
 
 Mag. 2:259-263. 
 1911. Gautier, Armand, Sur le Principe de la coalescence des 
 
 plasmus vivants et Vorigine des races et des especes. IV 
 
 International Conf. Genetique, Paris, 79-90. 
 1911. Gexty, C, Note sur deux Carduus hybrides. iMonde 
 
 des Plantes, 14 : 26. 
 1911. Gilbert, Arthur W., Suggestions for an Undergraduate 
 
 Course in Plant Breeding. A. B. A Rep. 6:352-356. 
 1911. Gilbert, Arthur W., Suggestive Laboratory Exercises 
 
 for a Course in Plant Breeding. Am. Breed. Mag. 2 : 196- 
 
 212, fig. Tab. Bibliog. in notes. 
 1911. Granier, J., and Boule, L., Sur le phenomene de con- 
 
 jugaison des chromosomes a le prophase de la premiere 
 
 cinese reductrice {microsporogenese chez Endymion nutans 
 
 Bum). Acad. Sci. Compt. Rend. 152:393-396. 
 1911. Gregory, R. P., Experiments with Primula sinensis. 
 
 Jour, of Gen. 1 : 73. Illus. 
 1911. Gregory, R. P., On Gametic Coupling and Repulsion in 
 
 Primula sinensis. Roy. Soc. London Proc. 84 : 12-15. 
 1911. Griffon, E., Greffage et Hijbridation Asexuelle. IV 
 
 Internat. Conf. Genetique, Paris, 164r-196, figs. 24. 
 1911. Griffon, E., Observations et recherches experimentales sur 
 
 la variation chez le mais. Soc. Bot. France BuU. 57 : 604- 
 
 615. 
 1911. Groth, H. a.. The Fi Heredity of Size, Shape, and Number 
 
 in Tomato Leaves. I. Seedlings. N. J. Agr. Exp. Sta. 
 
 Bull. 238 : 3-38, 5 figs. & 1 pi. 
 1911. Groth, H. A., The Fi Heredity of Size, Shape, Number 
 
Appendix D 379 
 
 in Tomato Leaves. Part II. Mature plants. New Jersey 
 Exp. Sta. Bull. 239: 3-12, pi. 1-9. 
 1911. Hagedoorn, a. L., Facteurs Genetiques et Facteurs du 
 Milieu dans V amelioration et Vohtentian des races. IV 
 Internat. Conf. Genetique, Paris, 132-135. 
 1911. Halstead, B. D., Geometrical Figures in Plant Breeding. 
 
 Am. Breed. Mag. 2:217-220, fig. 
 1911. Haxsen, N. E., Some New Fruits. So. Dak. Agr. Exp 
 
 Sta. Bull. 130 : 163-200, 1 fig. 
 1911. Harris, J. Arthur, On the Formation of Correlation and 
 Contingency Tables when the Number of Combinations is 
 Large. Am. Nat. 45: 566-571, 2 tab. Bibliog. in notes. 
 1911. Harris, J. Arthur, The Biometric Proof of the Pure Line 
 
 Theory. Am. Nat. 45 : 346-363. Bibliog. in notes. 
 1911. Harris, J. Arthur, The Measurement of Natural Selec- 
 tion. Pop. Sci. Mo. 78 : 521-538, figs. 1-7. 
 1911. Hartley, C. P., The Corn Breeder's Problems. Am 
 
 Breed. Mag. 2 : 212-217. Diagr. 
 1911. Hatai, Shinkishi, The Mendelian Ratio and Blended 
 
 Inheritance. Am. Nat. 45 : 99-106. Bibliog. 
 1911. Hayes, H. K., and East, E. M., Improvement in Corn. 
 
 Conn. Agr. Exp. Sta. Bull. 168: 21, 4 pis. 
 1911. Hayes, H. K., Inheritance in Corn. Conn. (State) 
 
 Agr. Exp. Sta. Ann. Rep. 407-427. 
 1911. Heckel, E., Sur les mutations gemmaires culturales 
 du Solanum Maglia et sur les premiers resultats culturaux 
 de ces mutations. Acad. Sci., Paris, Compt. Rend 153- 
 417-420. 
 1911. Henry, J. L., Results obtained through the Use of Hand 
 
 Selected Seed. Can. Seed-Grow. Assoc. Rep. 7 : 79-80. 
 1911. Hill, E. J., (Enothera Lamarckiana: its Early Cultiva- 
 tion and Description. Bot. Gaz. 51 : 13&-140. 
 1911. HiLLMAN, F. H., Testing Farm Seeds in the Home and 
 in the Rural School. U. S. Dept. Agr. Farmers' Bull. 428: 
 
380 Plant-Breeding 
 
 (47 pp.), 32 figs. (This bulletin describes the seed-trade 
 condition, the seed used as adulterants, methods and ap- 
 paratus used in making tests, etc.) 
 
 1911. Honing, J. A., Die Doppelnatur der (Enothera Lamarck- 
 iana. Zeitsch. f. indukt. Abst.- u. Vererb. 4:227-278, 
 10 figs. Bibliog. in notes. 
 
 1911. Hopkins, L. S., A New Variety of the Cinnamon Fern. 
 Am. Fern Jour. 1 : 100-101. Osmunda cinnamomea auri- 
 culata var. nov. described and illustrated. 
 
 1911. Humbert, E. P., A Quantitative Study of Variation. 
 Natural and Induced, in Pure Lines of Silene noctiflora, 
 Zeitsch. f. indukt. Abst.- u. Vererb. 4 : 161-226, 12 figs. 
 Bibliog. in notes. 
 
 1911. Hurst, C. C, The Application of the Principles of Genetics 
 to Some Practical Problems. IV Internat. Conf. Genetique, 
 Paris, 210-221. 
 
 1911. Hus, H., and Murdock, A. W., Inheritance of Fascia- 
 tion in Zea Mays. Plant World, 14 : 88-96, 1 fig. 
 
 1911. Jansonius, H. H., and Moll, J. W., Der anatomische 
 Bau des Holzes der Pfropfhybrids Cytisus Adami und ihrer 
 Compomenten. Rec. Trav. Bot. Neerland. 8 : 333-368. 
 
 1911. Jennings, H. S., Computation of the Coefficient of Cor- 
 relation. Am. Nat. 45 : 413. 
 
 1911. Jennings, H. S., Pure Lines in the Study of Genetics in 
 Lower Organism. Am. Nat. 45 : 79-89. Diagr. 
 
 1911. Jesenka, F., Sur un hybride fertile entre Triticum 
 sativum {Ble Mold-Squarehead) and Secale Cereale. {Seigle 
 de Petkus.) IV Inter. Conf. Genetique, Paris, 501-511. 
 
 1911. JoHANNSEN, W., Mutotions dans des lignees pures de 
 haricots et discussion au subject de le mutation en general. 
 IV Internat. Conf. Genetique, Paris, 160-163. 
 
 1911. Kastle, J. H., and Haden, R. L., Color Changes in Blue 
 Flowers of Wild Chicory (Cichorium intybus). Amer. 
 Chem. Jour. 46:315-325. 
 
Appendix D 381 
 
 1911. Keeble, F., and Pellew, C, The Mode of Inheritance 
 
 of Stature and of Time of Flowering in Peas {Pisum sativum). 
 f Jour, of Gen. 1 : 47-56. Rev. in Zeitsch. f. indukt. Abst.- 
 
 u. Vererb. 5:331. 
 1911. KiJCK, G., Eine Mutation der Kartoffelsorte Up to Date. 
 
 Monatsh. f. Landw. 4 : 108-109. 
 1911. Kroemer, K., Uber das " Mendeln " und seine Bedeutung 
 
 fUr die gdrtnerische Pflanzenziichtung . Mollers Deutsche 
 
 Gartner-Zeitung, 26 : 50-52. 
 1911. Lacke, M., and Parr, A. E., The Problem of the Im- 
 provement of Cotton in the United Provinces of Agra and 
 
 Oudh. Agr. Jour. India, 6 : 1-13, 5 pi. 
 1911. Lang, H., Technisches aus dem Gebiete der Futterpfianzen- 
 
 ziichtung. IIlus. Landw. Zeitung, 704. 
 1911. Leake, H. M., Studies in Indian Cotton. Jour, of Gen. 
 
 1 : 205-272. Illus. 
 1911. Leidigh, a. H., Methods for the Improvement of Sorghum. 
 
 Am. Breed. Mag. 2 : 294-296. Port. 
 1911. LoTSY, J. p.. Hybrids entre especes d' antirrhinum. IV 
 
 Inter. Conf. Genetique, Paris, 416-428, figs. 9. 
 1911. Love, Harry H., Studies of Variation in Plants. Cornell 
 
 Univ. Agr. Exp. Sta. Bull. 297 : 593-677, 70 figs., 48 tab. 
 1911. MacDougal, D. T. , Climatic Selection in a Hybrid Prog- 
 
 eny Oak. Plant World, 14: 129-131, 1 fig. 
 1911. Mason, Silas C., Drought Resistance of the Olive in the 
 
 Southwestern States. U. S. Dept. Agr. Bur. Plant Ind. 
 
 Bull. 192: (60 pp.), 6 pis. & 20 figs. 
 1911. Mayer, A., Bemerkungen zu G. Lewitsky : Uber die 
 
 Chondriosomen in pflanzlichen Zellen. Deutsch. Bot. 
 
 Gesell. Ber. 29: 158-160. 
 1911. Mendel, G., Versuche Uber Pjianzenhybriden. Heraus- 
 
 gegeben von E. v. Tachermak. Ostwalds Klassiker der 
 
 exakten Wissenschaften, No. 121, 2d ed. Leipzig, Engel- 
 
 mann. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 182. 
 
382 Plant-Breeding 
 
 1911. Montgomery, E. G., Correlation Studies in Corn. Ne- 
 braska Agr. Exp. Sta. Ann. Rept. 24 : 109-158. 
 
 1911. Montgomery, E. G., Note regarding Maize Flowers. 
 Science, n.s. 33 : 435. 
 
 1911. Montgomery, E. G., Perfect Flowers in Maize. Pop. 
 Sci. Mo. 79 : 346-349, figs. 1-6. 
 
 1911. Morehouse, L. A., hnprovement of Bermuda Grass. 
 Figs. A. B. A. Rep. 6:60-63. 
 
 1911. Muller, R., Mutationen bei Typhus- und Ruhrhacterian. 
 Mutation als spezifischee Kulturmerkmal. Centralbl. f. 
 Bacteriologie, 58 : 1 : 97-106, 2 pis. 
 
 1911. Mundy, H. S., Maize Breeding and Seed Selection. Rho- 
 desia Agr. Jour. 8 : 385^390. 
 
 1911. Munson, T. v.. Single Character vs. Tout Ensemble Breed- 
 ing in Grapes. A. B. A. Rep. 6 : 183-189. 
 
 1911. Newman, H. H., Reply to E. Godlewski's " Bemerkungen 
 zu der Arbeit von H. H. Newman: 'Further Studies of the 
 Process of Heredity in Fundidus Hybrids.^ " Arch. f. 
 Entwick'mech. d. Org. 32 : 472-476. Bibliog. in notes. 
 
 1911. Newman, L. H., Plant Breeding in Sweden. Can. Seed- 
 Grow. Assoc. Rep. 7 : 89-99, 4 tab. 
 
 1911. Nilsson-Ehle, H., Mendelisme et Acclimatation. IV 
 Internat. Conf. Genetique, Paris, 136-157. 
 
 1911. Nilsson-Ehle, H., Svalofs Solhvete, Ny sort for sodra 
 Sverige. Sveriges Utsddesfor. Tidskr. 21 : 123-126, 1 pi. 
 
 1911. Nomblot, a., Recherches de varietes fruitier es nou- 
 velles. IV Inter. Conf. Genetique, Paris, 464-468. 
 
 1911. Oliver, George W., New Methods of Plant Breeding. 
 A. B. A. Rep. 6: 11-20. Figs. 
 
 1911. Orton, W. a.. Disease Resistance in Varieties of Potatoes. 
 Indiana Acad. Sci. Proc. 219-221. 
 
 1911. Orton, W. A., The Development of Disease Resistance 
 Varieties of Plants. IV Internat. Conf. Genetique, Paris, 
 247 : 265, figs. 9. 
 
Appendix D 383 
 
 1911. Owen, E. J., Inheritance Studies with Beans. N. J. Agr 
 
 Exp. Sta. Bot. Dept. Rep. 277-281, 1 pi. 
 1911. Parde, L., Enquete sur Vacclimation des essences exo- 
 
 tiques en France. Soc. Dendr. France Bull. 19 : 5-12. lUus. 
 1911. Pearl, Raymond, Biometrics. Am. Nat. 45:319-320. 
 1911. Pearl, Raymond, Biometric Arguments regarding the 
 
 Genotype Concept. Am. Nat. 45 : 561-566. Bibliog. in 
 
 notes. 
 
 1911. Pearl, Raymond (Reviewer), Some Recent Studies rni 
 Variation and Correlation in Agricultural Plants. (Review ) 
 Am. Nat. 45 : 415-425. Bibliog. 1 p. 
 
 1911. Pearl, R., The Personal Equation in Breeding Experi- 
 ments involving Certain Characters of Maize Biol Bull 
 21:339-366. 
 
 1911. Pearson, Karl, On a Correction to be made to the Cor- 
 relation Ration. Biometrika, 8 : 254-256, pi. 
 
 1911. Pole-Evans, J. B., South African Cereal Rusts with Ob- 
 servations on the Problem of Breeding Rust-resistant Wheats 
 Jour. Agr. Sci. 4 : 95-104. 
 
 1911. Redfield, R. L., Acquired Characters Defined Am 
 Nat. 45 : 571-573. 
 
 1911. Roberts, F. B., A Method of Corn Pollination. Am 
 Breed. Mag. 2 : 54-60. Fig. 
 
 1911. Roberts, Herbert F., Breeding for Type of Kernel in 
 Wheat. A. B. A. Rep. 6: 142-147. Figs. 
 
 1911. Rudolph, J., UAster cordifolius et ses varietes. Rev 
 Hort. 83 : 325-327. 
 
 1911. RuGG-GuNN, A., Sociological and Other Aspects of the 
 Unit-Character Conception. IV Inter. Conf. Genet., Paris, 
 
 1911. Salaman, R. N., Studies in Potato Breeding. IV Inter. 
 
 Conf. Genetique, Paris, 373-376. 
 1911. Saunders, Edith R., The Breeding of Double Flowers. 
 
 IV Inter. Conf. Genetique, Paris, 397-405. 
 
384 Plant-Breeding 
 
 1911. Saunders, Charles E., Production de varietes de hie 
 
 de haute valeur boulougere. IV Inter. Conf. Genet., Paris, 
 
 290-300. 
 1911. Saunders, E. R., Oji Inheritance of a Mutation in the 
 
 Common Foxglove {Digitalis purpurea). New Phytologist, 
 
 10 : 49-63, 1 pi. & 12 figs. 
 1911. Scudder, H., Similarity of Color in Bud and in Leaf. 
 
 Rhodora, 13 : 86-87. 
 1911. Shamel, a. D., a Study of the Improvemeiit of Citrus 
 
 Fruits through Bud Selection. U. S. Dept. Agr. Plant Ind. 
 
 Circ. 77 : 1-19, 5 figs. 
 1911. Sherff, E. E., Tragopogon pratensis X porrifolius. 
 
 Torreya, 11 : 14-15. 
 1911. Shull, G. H., a Pure-Line Method in Corn Breeding. 
 
 Amer. Breeders' Assoc. Rep. 5 : 51-59. Rev. in Zeitsch. 
 
 f. indukt. Abst.- u. Vererb. 5 : 331-332. 
 1911. Shull, G. H., Defective Inheritance-Ratios in Bursa 
 
 Hybrids. Naturf. Vereins Briinn Verb. 49: (12 pp.), 6 
 
 pis. 
 1911. Shull, G. H., Hybridization Methods in Corn Breeding. 
 
 A. B. A. Rep. 6:63-72, figs. 
 1911. Shull, G. H., Reversible Sex-Mutants in Lychnis dioica. 
 
 Bot. Gaz. 52 : 329-368, 15 figs. 
 1911. Smith, Louie H., Increasing Protein and Fat in Corn. 
 
 A. B. A. Rep. 6:5-11. 
 1911. Smith, Russell J., Breeding and Use of Tree Crops. 
 
 A. B. A. Rep. 6:51-56. 
 1911. Spillman, W. J., Heredity. Am. Nat. 45: 60-64. 
 1911. Strampelli, N., De V etude des characteres anormaux 
 
 presentes par les plantules pour la recherche des varietes 
 
 nouvelles. IV Internat. Conf. Genetique, Paris, 237-246, 
 
 figs. 11. 
 1911. Styan, K. E., Pollen Grains. Rev. in Am. Bot. 17:41- 
 
 44. Originally published in Selbourne Magazine. 
 
Appendix D 385 
 
 1911. Sutton, W., Compte Rendu. D'esperiences de Croise- 
 ments faites entre le pois sauvage de Palestine and les pois 
 de commerce dans le but de decouvris entre eux quelque 
 trace d'identite specifique. IV Inter. Conf. Genetique, 
 Paris, 558-567, figs. 4. 
 
 1911. Taylor, G. M., Disease Resisting Potatoes. Gard. 
 Chron., 3d ser. 49: 181. 
 
 1911. Tedin, H., Ar skalhalten hos arter en sortegenskap? 
 (With German r^sum^.) Sveriges Utsadesfor. Tidskr, 
 21 : 72-77. 
 
 1911. The Sugar-Beet Industry is based on Breeding. Am. 
 Breed. Mag. 2 : 234. 
 
 1911. Thoday, M. G., and Thoday, 0., On the Inheritance 
 of the Yellow Tinge in Sweet Pea Colouring. Cambridge 
 Phil. Soc. Proc. 16:71-84. 
 
 1911. Thomas, Rose Haig, Nicotiana Crosses. IV Inter. 
 Conf. Genetique, Paris, 453-461, figs. 6. 
 
 1911. Tower, W. L., The Determination of Dominance and the 
 Modification oj Behavior in Alternative {Mendelian) In- 
 heritance, by Conditions Surrounding or Incident upon the 
 Germ-Cells at the Time of Fertilization. Biol. Bull. 18 : 
 (No. 6). Rev. (Ger.) in Arch. f. Entwick'mech. d. Org. 
 31 : 345-348. 
 
 1911. Tracy, W. W., Report of Comniittee on Breeding Vege- 
 tables. A. B. A. Rep. 6 : 75-78. 
 
 1911. TscHERMAK, Prof. Erich VON, Examcu de le theorie 
 des facteurs par le recroisement methodique des hybrids. 
 IV Internat. Conf. Genetique, Paris : 91-95. Tab. VIIIc. 
 
 1911. ViLMORiN, p. DE, and Bateson, W., A Case of Gametic 
 Coupling in Pisum. Roy. Soc. London Proc. B. 84: 9-11. 
 
 1911. ViLMORiN, Philippe de, Fixite des races de Froment. 
 IV Inter. Conf. Genetique, Paris, 512-516. Tab. 3. 
 
 1911. ViLMORiN, Ph. de, Recherches sur Vheredite mendelienne. 
 
 Acad. Sci. Compt. Rend., 548-551. 
 2c 
 
386 Plant-Breeding 
 
 1911. VoGLER, Die Variationen der Blattspreite bei Cybisulabur- 
 
 num L. Bot. Zentralbl. Beih. 27 : 337-390. 
 1911. Vries, Hugo de, Intracellular Pangenesis. Translated 
 
 into English by C. Stuart Gager, Chicago. Open Court 
 
 Publ. Compt. Rev. in Zeitsch. f. indukt. Abst.-u. Vererb. 
 
 5:90. 
 1911. Vries, H. de, tjher doppeltreziproke Bastarde von (Eno- 
 
 thera biennis L. und 0. muricata L. Biol. Centralbl. 31 : 
 
 97-104. 
 1911. Waldron, L. R., Variegation of European Alfalfas. 
 
 Science, n.s. 33 : 310-312. 
 1911. Wheldale, M., On the Formation of Anthocyanin. Jour. 
 
 of Gen. 1 : 133. 
 1911. Wheldale, M., The Chemical Differentiation of Species. 
 
 Biochemical Jour. 5 : 445-456. 
 1911. WiTTMACK, L., Botanische Fragen in Beziehung zur 
 
 Kartoffelzuchtung. lllus. Landw. Zeitung, 51 : 289. 
 1911. Woodruff, Chas. E., Breeding for Color Adjustment, 
 
 under Certain Climates. Am. Breed. Mag. 2 : 313-000. 
 1911. Zavitz, C. a.. Report of Committee on Breeding Cereals. 
 
 A. B. A. Rep. 6: 141-142. 
 
 1911. Zeijlstra, H. H., CEnothera nanella de Vries, eine krank- 
 hafte Pfianzenart. Biol. Centralbl. 31 : 129-138. 
 
 1912. AcLOQUE, A., La genealogie du chrysantheme. Monde 
 des Plantes, 14 : 27-28. 
 
 1912. Ball, Carleton R., and Hastings, Stephen H., Grain- 
 Sorghum Production in the San Antonio Region of Texas. 
 U. S. Dept. Agr. Bur. Plant Ind. Bull. 237 : (30 pp.), 4 figs. 
 
 1912. Batchelor, Leon D., Carnation Breeding. A. B. A. 
 Rep. 7 : 199-205. 
 
 1912. Baur, Erwin, Vererbungs- und Bastardierungeversuche 
 mit Antirrhinum. II. Faktorenkoppelung. Zeitsch. f. in- 
 dukt. Abst.- u. Vererb. 6: 201-216, 3 tab. Bibliog. in 
 notes. 
 
Appendix D 387 
 
 1912. Beach, S. A., and Maney, T. J., Mendelian Inheritance 
 
 in Prunus Hybrids. A. B. A. Rep. 7 : 214-227, fig. 
 1912. Beach, S. A., Report of the Committee on Breeding Tree 
 
 and Vine Fruits. A. B. A. Rep. 7 : 213. 
 1912. Belling, John, Breeding Experiments with Forage Plants 
 
 in Florida. A. B. A. Rep. 8 : 438-440. 
 1912. Belling, John, Selection in Pure Lines. Am. Breed. 
 
 Mag. 3:311-312. 
 1912. Blaringhem, L., Les problemes de biologic appliquee 
 
 examines dans la quatrieme conference internationale de 
 
 genetique. Revue Scientifique, 50 : 50 : 265-269. 
 1912. Brainerd, E., Violet Hybrids between Species of the 
 
 Palmata Group. Torrey Bot. Club Bull. 39: 85-97, 3 
 
 pis. 
 1912. Burtt-Davy, J., Observations on the Inheritance of Char- 
 acters in Zea Mays. Roy. Soc. South Africa Trans. 2 : 
 
 261-270. 
 1912. Castle, W. E., The Inconstancy of Unit-Characters. 
 
 Am. Nat. 46 : 352-362. 
 1912. Christie, W., Untersuchungen iXber alte norwegische 
 
 Hafersorten. Fiihlings landw. Zeitung : 297. 
 1912. CocKERELL, T. D. A., The Red Sunflower. Pop. Sci. 
 
 Mo. 80 : 373-382. Illus. 
 1912. CocKERELL, T. D. A., The Word Genotype. Science, 
 
 n.s. 35 : 304. 
 1912. Collins, G. N., and Kempton, J. H., An Improved 
 
 Method of Artificial Pollination in Corn. U. S. Dept. Agr. 
 
 Bur. Plant Ind. Circ. 89: (7 pp.), 2 figs. 
 1912. Collins, G. N., Improvements in Technique of Corn 
 
 Breeding. A. B. A. Rep. 8 : 349-353. 
 1912. Cook, 0. F., Results of Cotton Experiments in 1911. 
 
 U. S. Dept. Agr. Bur. Plant Ind. Circ. 96 : (21 pp.). 
 1912. Davis, Bradley Moore, Genetical Studies on (Enothera. 
 
 Ill, Further Hybrids of (Enothera biennis and 0. grandiflora 
 
388 Plant-Breeding 
 
 that resemble 0. Lamarckiana. Am. Nat. 46 : 377-427, 
 
 15 figs. Bibliog. ^ p. 
 1912. Dean, A., The Potato and Floral Sterility. Gard. Chron. 
 
 3d ser. 51 : 13. 
 1912. Derr, H. B., The Breeding of Winter Barleys. Am. 
 
 Breed. Mag. 3: 103-113. 
 1912. DiLLMAN, A. C, Breeding Alfalfa as a Dry-land Crop. 
 
 A. B. A. Rep. 8:414-424. 
 1912. DoNCASTER, L., Sex-limited Inheritance in Cats. Science, 
 
 n.s. 36 : 144. 
 1912. Dorset, M. J., Variation in the Floral Structures of Vitis. 
 
 Torrey Bot. Club Bull. 39 : 37-52, 3 pi. 
 1912. Dorset, M. J., Variation Studies of the Venation Angles 
 
 and Leaf Dimensions in Vitis. A. B. A. Rep. 7 : 227-250, 
 
 fig. 
 1912. East, E. M., A Study of Hybrids between Nicotiana 
 
 Bigelovii and N. quadrivalvis. Bot. Gaz. 53 : 243-248, 
 
 4 figs. 
 1912. East, E. M., and Hats, H. K., Inheritance in Maize. 
 
 Conn. Agr. Exp. Sta. Bull. 167: (137 pp.), 25 pis. Rev. 
 
 in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 193-196. 
 1912. East, E. M., Inheritance of Color in the Aleurone Cells 
 
 of Maize. Am. Nat. 46 : 363-365. 
 1912. East, E. M., The Application of Biological Principles 
 
 to Plant Breeding. In Heredity and Eugenics, pp. 113- 
 
 138, fig. 
 1912. East, E. M., The Mendelian Notation as a Description 
 
 of Physiological Facts. Am. Nat. 46 : 633-655, 1 tab. 
 1912. FiNLOW, R. S., and Burkill, J. H., The Inheritance of 
 
 Red Colour and the Regidarity of Self-fertilization in Cor- 
 
 chorus capsularis L., the Common Jute-plant. India Dept. 
 
 Agr. Bot. Ser. Mem. 4 : 73-92. 
 1912. Frost, H. B., The Origiri of an Early Variety of Matthiola 
 
 by Mutation. A. B. A. Rep. 8 : 536-545. 
 
Appendix D 389 
 
 1912. Funk, Eugene D., Ten Years of Corn Breeding. Am. 
 
 Breed. Mag. 3 : 295-302, 4 figs. 
 1912. Gates, R. R., Early Historico-botanical Records of the 
 
 (Enotheras. Iowa Acad. Sci. Proc. 85-124, 6 pis. Rev. 
 
 in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 285-287. 
 1912. Gerner, W. W., Some Observations on Tobacco Breeding. 
 
 A. B. A. Rep. 8 : 458-468, fig. 
 1912. Gernert, Walter B., A New Subspecies of Zea Mays L. 
 
 Am. Nat. 46 : 616-622, 3 figs. 
 1912. Gernert, Walter B., Methods in the Artificial Pollina- 
 tion of Corn. A. B. A. Rep. 8 : 353-367. 
 1912. Gilbert, A. W., A Mendelian Study of Tomatoes. A. B. 
 
 A. Rep. 7 : 169-188. 
 1912. Gilbert, A. W., and Upton, G. B., An Algebra of Men- 
 
 delism and its Application to a Mixed Hybrid Population. 
 
 A. B. A. Rep. 7:312. 
 1912. Gilbert, A. W., Present Status of Plant-breeding In- 
 struction in the United States. A. B. A. Rep. 7:7-11. 
 1912. Glawe, M., Timotheezuchtung in Amerika. Deutsch. 
 
 Landwirtsch. Gesell. Mitt. 146. 
 1912. 'Groth, B. H. a.. The F2 Heredity of Size, Shape, and 
 
 Number in Tomato Fruits. N. J. Agr. Exp. Sta. Bull. 
 
 242 : 3-39, 3 pi. 
 1912. Hartley, C. P., Brown, E. B., Kyle, C. H., and Zook, 
 
 L. L., Cross-breeding Corn. U. S. Dept. Agr. Bur. Plant 
 
 Ind. Bull. 218: (72 pp.), 1 fig. 
 1912. Hartley, C. P., Brown, E. B., Kyle, C. H., and Zook, 
 
 L. L., Cross-breeding Corn. U. S. Dept. Agr. Plant Ind. 
 
 Bull. 218 : 5-72. 
 1912. Hartley, C. P., Productivity of Seed Corn as Influenced 
 
 by Factors Other than Heredity. A. B. A. 'Rep. 8 : 335-338. 
 1912. Hartley, C. P., The Seed-Corn Situation. U. S. Dept. 
 
 Agr. Bur. Plant Ind. Circ. 95 : (13 pp.), 2 figs. 
 1912. Hauman-Merck, L., Observations sur la pollination 
 
390 Plant-Breeding 
 
 d'une Malpighiacee du genre Stigmaphijllon. Rec. Inst. 
 
 Bot. Leo Errera, 9 : 21-28, 1 fig. 
 1912. Hayes, H. K., Methods of Corn Breeding. Ani. Breed. 
 
 Mag. 3 : 99-108, pi. Tab. Bibliog. 
 1912. IL\YES, H. K., Correlation and Inheritance in Nicotiana 
 
 Tabacum. Connecticut Agr. Exp. Sta. Bull. 171 : 3-45, 
 
 5 pis. 
 1912. Hedrick, U. p., and Wellington, R., An Experiment 
 
 in Breeding Apples. N. Y. (Geneva) Agr. Exp. Sta. Bull. 
 
 350. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 8 : 347. 
 1912. Hill, Arthur W., The History of Primula obconica, 
 
 Hance, under Cultivation, with Some Remarks on the History 
 
 of Primula siiiensis Sab. Jour, of Gen. 2: 1-20, 2 pis. 
 
 Bibliog. in notes. 
 1912. HousER, True, Certain Results in Ohio Tobacco Breeding. 
 
 A. B. A Rep. 8:468-479. 
 1912. Hunt, B. W., Fig Breeding. Univ. Georgia Bull. 12: 
 
 107-110. 
 1912. Johnson, Roswell H., The Malthusian Principle and 
 
 Natural Selection. Am. Nat. 46 : 372-376. 
 1912. Jones, W. Xeilson, Species Hybrids of Digitalis. Jour. 
 
 of Gen. 2 : 71-88, 3 pis., 45 figs. Bibliog. in notes. 
 1912. IL\JANUS, BiRGER, Geuctische Studien an Beta. Zeitsch. 
 
 f. indukt. Abst.- u. Vererb. 6 : 137-139. (Correction : 
 
 p. 268), 9 pis., 2 figs., 5 tab. 
 1912. Kellogg, Vernon Ly^vian, The Animals and Man. 
 
 An elementary text-book of zoologj^ and human physiology. 
 
 495 pp. Henry Holt & Co., N. Y. Rev. in Science, n.s. 
 
 35:270-272. 
 1912. Leake, H..M-, and Peyshad, R., Observations on Certain 
 
 Extra-Indian Asiatic Cottons. India Dept. Agr. Mem. 4: 
 
 93-112, 7 pis. 
 1912. Leighty, Clyde E., Correlation of Characters in Oats 
 
 with Special Reference to Breeding. A. B. A. Rep. 7 : 50-61, 
 
Appendix D 391 
 
 1912. Lewis, C. I., The Teaching of Genetics. A. B. A. Rep. 
 
 8:327-329. 
 1912. Lock, R. H., Notes on Color Inheritance in Maize. Royal 
 
 Bot. Gard. Peradeniya Abbls. 5: (part IV). Rev. in 
 
 Zeitsch. f. indukt. Abst.- u. Vererb. 8 : 347-348. 
 1912. Love, H. H., A Study of the Large and Small Grain Ques- 
 tion. A. B. A. Rep. 7 : 109-118. 
 1912. Love, H. H., Relation of Certain Ear Characters to Yield 
 
 in Corn. A. B. A. Rep. 7 : 29-40. 
 1912. Love, H. H., The Relation of Seed Ear Characters to 
 
 Earliness in Corn. A. B. A. Rep. 8 : 330-335. 
 1912. LuTZ, A. M., Triploid Mutants in (Enothera. BioL 
 
 Centralb. 32 : 385-435, 7 figs. 
 1912. Macoun, W. T., Apple Breeding in Canada. A. B. A. 
 
 Rep. 8 : 479-488. 
 1912. McLendon, C. a., Mendelian Inheritance in Cotton 
 
 Hybrids. Georgia Exp. Sta. BuU. 99 : 143-228, 20 figs. 
 1912. MoxTGOMERY, E. G., Wheat Breeding Experiments. 
 
 Nebraska Agr. Exp. Sta. Bull. 125 : 5-16, 7 pi. 
 1912. Moore, A. R., On Mendelian Dominance. Arch. f. 
 
 Entwick'mech. d. Org. 34 : 168-175, 9 figs. Bibliog. in 
 
 notes. 
 1912. Muller, R., Bahterienmutationen. Zeitsch. f. indukt. 
 
 Abst.-u. Vererb. 8 : 305-324. Bibliog. I p. 
 1912. MuNSON, T. v.. Problems in Breeding Tree and Vine 
 
 Fruits. A. B. A. Rep. 7 : 13-214. 
 1912. Myers, Clyde H., Effect of Fertility upon Variation and 
 
 Correlation in Wheat. A. B. A. Rep. 7 : 61-74. 
 1912. Newman, L. H., Principles Recognized in the Breeding 
 
 of Cereal Plants at Svalof, Sweden. A. B. A. Rep. 8 : 502-508. 
 1912. Norton, J. B., Asparagus Breeding. A. B. A. Rep. 8: 
 
 440-444. 
 1912. Park, J. B., and Smith, L. H., Experiment on the Methods 
 
 of Conducting Plot Tests. A. B. A. Rep. 8: 525-528. 
 
392 Plant-Breeding 
 
 1912. Planchon, L., Solanuin Commersonii et Solarium tubero- 
 sum. Soc. Bot. de France Bull. 59 : 70-77. 
 1912. Ramaley, Francis, Mendelian Proportions and the In- 
 crease of Recessives. Am. Nat. 46 : 344-351, 4 tab. Bibliog. 
 
 in notes. 
 1912. Roberts, H. F., Variation and Correlation in Wheat. 
 
 A. B. A. Rep. 7 : 80-109, figs. 
 1912. Shamel, a. D., Bud Selection as a Means of Improving 
 
 Citrus arid Other Fruits. A. B. A. Rep. 8 : 497-502. 
 1912. Shull, G. H., Defective Inheritance-ratios in Bursa 
 
 Hybrids. Naturf . Vereines in Briinn. Verhandl. 49 : 
 
 (12 pp.), 6 pis. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 
 
 6 : 281-282. 
 1912. Shull, G. H., "Genotypes;' "Biotijpes," "Pure Lines," 
 
 and "Clones.'" Science, n.s. 35:27-29. Bibliog. in notes. 
 1912. Shull, G. H., Hermaphrodite Females in Lychnis dioica. 
 
 Science, n.s. 36 : 482-483. 
 1912. Shull, G. H., '' Phenotype " and "Clone." Science, 
 
 n.s. 35 : 182-183. 
 1912. Shull, G. H., Reversible Sex-Mutants in Lychnis dioica. 
 
 Bot. Gaz. 52 : (No. 5). Rev. in Zeitsch. f. indukt. Abst.- u. 
 
 Vererb. 6 : 282-283. 
 1912. Smith, F. W., The Application of Mendelian Principles 
 
 to Sugar-cane Breeding. West Ind. Bull. 12 : 365-377. 
 1912. Smith, L. H., Occurrence of Natural Hybrids in Wheat. 
 
 A. B. A. Rep. 8:412-414. 
 1912. Snow, E. C., The Application of the Correlation Coefficient 
 
 to Mendelian Distributions. Biometrika, 8 : 420-424. Tab. 
 1912. Spillman, W. J., Chromosomes m Wheat and Rye. Science, 
 
 n. s. 35 : 104. 
 1912. Stockberger, W. W., A Study of Individual Performance 
 
 in Hops. A. B. A. Rep. 8 : 452-458. 
 1912. Sudworth, Geo. B., Annual Report of Committee on 
 
 Breeding Nut and Forest Trees. A. B. A. Rep. 7 : 250. 
 
Appendix D 393 
 
 1912. Vries, Hugo de, and Bartlett, H. H., The Evening 
 Primroses of Dixie Landing, Alabama. Science, n.s. 36: 
 599-601. 
 
 1912. Waldron, L. R., Breeding Certain Field-crop Plants in 
 the Cold Northwest. A. B. A. Rep. 8:429-438. 
 
 1912. Waldron, L. R., Hardiness in Successive Alfalfa Genera- 
 tions. Am. Nat. 46 : 463-469, 2 tab. 
 
 1912. Waldron, L. R., Influence of Variegation in Alfalfa 
 upon Hardiness. A. B. A. Rep. 8:424-429. 
 
 1912. Waldron, L. R., Value of Continuous Selection and its 
 Bearing upon Hardiness in Winter Wheat. A. B. A. Rep. 
 7:74-80. 
 
 1912. Watts, Francis, Work with Seedling Sugar-canes in the 
 British W. I. ayid British Guiana. A. B. A. Rep. 7 : 167-169. 
 
 1912. Webber, H. J., Preliminary Notes on Pepper Hybrids. 
 
 A. B. A. Rep. 7: 188-199, fig. 
 
 1912. Webber, H. J., The Cornell Experiments in Breeding 
 
 Timothy. Am. Breed. Mag. 3 : 85-99, tab., 4 pis. 
 1912. Webber, H. J., The Effect of Research in Genetics on 
 
 the Art of Breeding. Science, n.s. 35 : 597-609. 
 1912. Webber, H. J., The Production of New and Improved 
 
 Varieties of Timothy. Cornell Univ. Agr. Exp. Sta. Bull. 
 
 313:339-381, 10 pi. 
 1912. Wellington, R., Influence of Crossing in Increasing the 
 
 Yield of the Tomato. N. Y. (Geneva) Agr. Exp. Sta. Bull. 
 
 346 : 57-76. 
 1912. Williams, C G., Variation in Pure Lines of Wheat. A. 
 
 B. A. Rep. 8:409-412. 
 
 1912. Winkler, Hans, Untersuchungen ilber Pfropfbastarde. 
 
 Erster Teil : Die unmittelbare, gegenseitige Beeinflussung der 
 
 Pfropfsymbionten. 186 p. Jena, Gustav Fischer. 2 Illus. 
 
 Rev. in Zeitch. f. indukt. Abst.- u. Vererb. 7 : 77-80. 
 1912. ZooK, L. I., Tests with First Generation Corn Crosses. 
 
 A. B. A. Rep. 8 : 338-343. 
 
APPENDIX E 
 
 LABORATORY EXERCISES 
 
 The following laboratory exercises are intended to serve merely 
 as suggestions. It is impossible and inadvisable to attempt to 
 outline a rigid set of exercises for instructors to follow. It is 
 the hope that these may serve as hints or type exercises, capable 
 of all sorts of modification to suit conditions. An attempt has 
 been made to avoid elaborate laboratory equipment which is 
 expensive and unnecessary. The instructor should always aim 
 to arrange laboratory practicums so that the student's inquisi- 
 tive curiosity may be aroused and he may be induced to find 
 out things for himself from the material with which he has to 
 work. These exercises are not arranged with any particular 
 order or sequence. The sequence will depend on the time of 
 the year, material at hand, and so forth. The first group of 
 exercises is of a general nature, and the exercises on corn, 
 potatoes, and the cereals are grouped more or less together. 
 
 We wish to acknowledge the assistance of Professor E. E, 
 Barker in the preparation of these exercises, most of which 
 have been successfully used by him with large classes. A few 
 new ones have been added. 
 
 Exercise 1 
 
 Field Study of Variations by making an Herbarium of Variations 
 
 Have each student collect, press, and mount fifty variations 
 
 of plants. This is an excellent exercise, because it calls the 
 
 394 
 
Appendix E 
 
 395 
 
 Fig. 104. — A specimen herbarium sheet, showing variation in the leaves 
 
 of the mulberry. 
 
396 
 
 Plant- Breeding 
 
 Fig. 105. — A specimen herbarium sheets showing differences between two 
 leaves of the horse-i-adish. 
 
Appendix E 397 
 
 student's attention very effectively to the vast extent of varia- 
 tion in wild and cultivated plants. Since variation is the basis 
 of artificial selection as well as evolution in nature, it is highly 
 important that considerable time and attention should be given 
 to this study. 
 
 Material. — A botanical collecting case, 20 blotters, 12 X 18 
 inches ; 50 mounting sheets, 12 x 18 inches ; 50 labels, and glue. 
 
 The accompanying photographs represent specimens treated 
 as above (Figs. 104 to 107). The following directions may be 
 given to each student : — 
 
 Directions for collecting, pressing, and mounting an herbarium of 
 
 variations 
 
 1. Search for fluctuations, plateations, mutations, and bud- 
 variations of plant characters which have been discussed in the 
 lectures. 
 
 2. Collect as nearly the whole plant as practicable. The 
 size of the mounting sheets is 12 X 18 inches. When you collect 
 your specimens plan upon this size of sheet, and arrange them 
 accordingly when you are putting them into the blotters. 
 
 3. Do not mount large, woody branches showing different 
 degrees of thorniness, etc., upon the mounting sheets, but pre- 
 serve them in bundles properly labeled. 
 
 4. If you wish to show variations of berries, such as thorn- 
 apples, etc., dry the fruits and fasten them to the mounting sheets 
 by threads. 
 
 5. Leave specimens in the blotters until they are thoroughly 
 dry. If you do not have enough blotters, take out the speci- 
 mens which have been in the blotters for a week or more, and 
 put them between pieces of newspapers, under pressure, until 
 they become thoroughly dry. Then dry your blotters near a 
 radiator and put in the fresh material. 
 
 6. After the specimens have become thoroughly dry, stick 
 them to the mounting sheets, preferably with glue Put a small 
 
398 Plant-Breeding 
 
 ^f^U^n 
 
 Fig. 106. — a specimen herbarium sheet, showing variation in leaves of 
 
 the Persian lilac. 
 
Appendix E 399 
 
 band of adhesive tissue over the larger stems. Arrange the 
 specimens, if possible, so that you have at least one variation 
 on a sheet. 
 
 7. Put the label on the lower right-hand corner, leaving a 
 small margin. Attach the label to the mounting sheet with 
 glue or paste, putting it only on the left edge of the label, that 
 is, do not cover the back of the label with paste or glue. 
 
 Sample of Label 
 
 HERBARIUM OF VARIATIONS 
 
 DEPARTMENT OF PLANT-BREEDING. NEW YORK STATE 
 COLLEGE OF AGRICULTURE 
 
 Name 
 
 Locality Date 
 
 Habitat 
 
 Description of variation 
 
 Class of variation 
 
 Collector No. 
 
 8. Before the specimen is handed in, fill in as many of the 
 blank spaces on the label as possible. Place your name after 
 the word "Collector." Fill in both the scientific and common 
 names. 
 
 9. Absolute neatness is essential. 
 
 Exercise 2 
 
 The Statistical Study of Type and Variability 
 
 Making measurements. — The value and uses of the statistical 
 method of studying variation are explained in Chapter IV. In 
 dealing statistically with a group of organisms, or parts of them, 
 the first step in the procedure is, of course, to collect data. These 
 
400 
 
 Plant-Breeding 
 
 Fig. 107. — A specimen herbarium sheet, sho^vdng variations in leaves 
 
 of the blackberry. 
 
Appendix E 401 
 
 will consist of quantitative measurements of characters to be 
 studied. These data are later analyzed, certain constants are 
 derived therefrom, and, lastly, the constants are interpreted. 
 The conclusions of the breeder or the investigator are based on 
 his interpretations of these constants. The meaning of the 
 various constants is explained in Chapter IV. 
 
 In coUecting data, it is important that as large a proportion 
 as possible of the entire population should be measured. Fail- 
 ing this, the sample should be fairly representative of the whole. 
 The time or season during which measurements are taken is 
 important where populations are to be compared. It would 
 obviously be unfair to collect data one year on fully matured 
 plants and another year on immatured plants. It is not always 
 easy to avoid a selection, conscious or unconscious, but the 
 collector should try to take his data with absolute impartiality. 
 He should collect at random until he has obtained a represent- 
 ative sample. Much time and labor will be saved if he can 
 conveniently limit the number of individuals measured to a num- 
 ber whose square root is an integer. 
 
 ^ The frequency distribution. — Having measured a representa- 
 tive sample of the entire population, the next step is to sort the 
 data. All individuals of the same or nearly the same size are 
 grouped together in one order of magnitude. In order to give 
 a clear understanding of what follows, let us take, for example, 
 the data collected by a class of students on 500 bean plants! 
 The individual lengths range from 5 cm. to 95 cm. This is 
 known as the range of variability and the way in which the in- 
 dividuals are distributed along the successive equal intervals in 
 this range is spoken of as the frequency distribution of the vary- 
 ing character. For convenience, these lengths may be grouped 
 into classes, thus : 5-14; 15-24; 25-34 . . . 85-94. 
 
 It is desirable that the number of classes be limited to not 
 more than about a dozen, and thus the size of the class will 
 depend upon the nature of the material. For example bean 
 2d 
 
402 Plant-Breeding 
 
 plants may vary in height from 5 cm. to 95 cm. ; to make the 
 classes differ by only 1 cm. would give us 90 classes, which 
 would be very inconvenient to handle mathematically. 
 
 The class limits should be given in all cases, not the mid- 
 point of the class. The magnitude of a class is its value and is 
 designated by the sjonbol T"^. In calculations the mid-point of 
 a class is used as the class value. The number of individuals 
 falling into each class is termed its frequency and is symbolized 
 b}" the letter /. The accompanying table shows how the various 
 bean lengths are distributed throughout the range : — 
 
 V f 
 
 5-14 4 
 
 15-24 72 
 
 25-34 169 
 
 35-44 125 
 
 45-54 64 
 
 55-64 38 
 
 65-74 11 
 
 75-84 11 
 
 85-94 6 
 
 500 
 
 The graph or frequency polygon. — It is often desirable to 
 present the data in a graphic way so that the eye can take in at 
 a glance such information as would otherwise require an extended 
 and careful study of quantities of figures. For this purpose the 
 frequency polygon is used. Such a simple diagram or chart 
 presents a picture embodying the chief characteristics of the 
 given population. Its significance is apparent to the student at 
 once. The frequency polygon is made, as explained in Chapter 
 IV, by plotting the class range along the base-line or axis of 
 abscissas. On the vertical axis, or axis of ordinates, are plotted 
 the class frequencies. 
 
 When all the frequencies have been plotted in their proper 
 places on the chart they may be connected by a continuous 
 
Appendix E 403 
 
 line. This will form the frequency or distribution curve, knowii 
 also as the ^'probability curve." It will take the form of a 
 Quetelet curve rising from the lowest class value at the left end 
 of the base-line to an apex at the class of greatest frequency, 
 then dropping to the right end at the highest class value. Such 
 a curve shows at once four things about our data: (1) The 
 extreme values, or the extent of the range, (2) the way in which 
 the individuals are distributed throughout this range, (3) the 
 prevailing type, or class of greatest frequency, and (4)' whether 
 the curve is symmetrical, following the normal probability curve 
 or not. If the classes are arranged along the base-line"^ in the 
 sequence of their values instead of their frequencies, the curve 
 wiU ascend constantly from the lowest value on the left end to- 
 ward the highest value at the right end. This forms a Gallon 
 curve. The Galton type of curve shows merely a different 
 method of exhibiting the frequency distribution of a population 
 that is under study. 
 
 Mode.~T\\e class of greatest frequency, the most "popular " 
 or ''modish" class, so to speak, is known as the mode or modal 
 class. In our problem, the modal class is 25-34, or the mode is 
 29.5, the mid-value of this class. This is oneway, and an excel- 
 lent one, of expressing type. A tjijical bean plant of this popu- 
 lation, we can say, is 29.5 cm. long. 
 
 Modal coefficient. — It is desirable to know what proportion 
 of the population conforms to this tj^pe, or falls into this modal 
 class. This proportion, which is expressed as a percentage des- 
 ignated as the modal coefficient, is found by dividing the number 
 of individuals in the modal class by the total number of indi- 
 viduals measured. In our example, it would be iff = .3836 = 
 38.36 %, which is the percentage of the population in the class 
 of greatest frequency, hence, the modal coefficient. 
 
 Mean. — If one desires to know what an average individual 
 in the population is worth, the mean, sjnibolized by the letter 
 M, will show it. The mean shows the average value of the' 
 
404 Plant-Breeding 
 
 population, hence it is only another method of expressing type. 
 It 'is found by multiplying the mid-value of each class {V) by 
 the number of individuals in that class (/), then summing the 
 products and dividing this sum by the total number of individ- 
 
 uals. The formula for this operation is •' ^ 
 
 Thus : — 
 
 
 
 ^f — 
 
 
 n 
 
 V 
 
 
 / 
 
 
 Vf 
 
 9.5 
 
 X 
 
 4 
 
 = 
 
 38.0 
 
 19.5 
 
 X 
 
 72 
 
 = 
 
 1404.0 
 
 29.5 
 
 X 
 
 169 
 
 = 
 
 4985.5 
 
 39.5 
 
 X 
 
 125 
 
 = 
 
 4937.5 
 
 49.5 
 
 X 
 
 64 
 
 = 
 
 3168.0 
 
 59.5 
 
 X 
 
 38 
 
 — 
 
 2261.0 
 
 69.5 
 
 X 
 
 11 
 
 = 
 
 764.5 
 
 79.5 
 
 X 
 
 11 
 
 = 
 
 874.5 
 
 89.5 
 
 X 
 
 6 
 500 
 
 — 
 
 537.0 
 18970.0 
 
 189 
 
 70.0 
 
 = 37.94 
 
 cm. 
 
 500 
 
 We would get exacth^ the same result if we arranged the bean 
 plants, in order of size, in a single line, placing them end to end, 
 and then divided the total length of this line by 500, the number 
 of individuals in it. 
 
 Average deviation. — One way of expressing variability is to 
 find out by how much, on the average, any individual in the 
 population deviates from the mean, the constant thus secured 
 being termed the average deviation. This is ascertained as 
 follows : the amount by which each class differs from the mean, 
 or in other words, the deviation from the mean (designated by 
 D) is multiplied by the frequency of the corresponding class, 
 and then 'the sum of these products is divided by the total 
 
 1 The Greek letter capital "sigma" (S) indicates that the suru of 
 a series of values is to be taken. 
 
 The total number of individuals measured is designated by n. 
 
Appendix E 405 
 
 Ul lllU 
 
 IVIU 
 
 ua,ib. 
 
 XliL' 
 
 luniiuia lur ine op 
 
 ieraiion is ^ 
 
 n 
 
 our problem it \a 
 
 ould be found as shown 
 
 in the table : — 
 
 V 
 
 
 / 
 
 
 D 
 
 Dj 
 
 9.5 
 
 X 
 
 4 
 
 
 28.44 
 
 113.76 
 
 19.5 
 
 X 
 
 72 
 
 
 18.44 
 
 1327.68 
 
 29.5 
 
 X 
 
 169 
 
 
 8.44 
 
 1426.36 
 
 39.5 
 
 X 
 
 125 
 
 
 1.56 
 
 195.00 
 
 49.5 
 
 X 
 
 64 
 
 
 11.56 
 
 739.84 
 
 59.5 
 
 X 
 
 38 
 
 
 21.56 
 
 819.28 
 
 69.5 
 
 X 
 
 11 
 
 
 31.56 
 
 347.16 
 
 79.5 
 
 X 
 
 11 
 
 
 41.56 
 
 457.16 
 
 89.5 
 
 X 
 
 6 
 
 
 51.56 
 
 309.36 
 5735.60 
 
 
 
 5735.60 
 
 = 11.4712 cm. 
 
 
 500 
 
 Of course, the deviations below the mean (28.44, 18.44, 8.44) 
 are negative quantities, those above (1.56, 11.56, 21.56, 31.56, 
 41.56, 51.56) positive, but inasmuch as we are here concerned 
 only with deviation from type, we are correct in neglecting these 
 signs, and using the arithmetic sum, and not the algebraic. 
 
 We would secure the same result if we went along our line 
 of bean plants spoken of above with an average or mean indi- 
 vidual as a measure, added up the lengths by which each one 
 missed of being an average individual, and then divided this 
 total by 500, the number of individuals measured. Clearly this 
 would give the amount by which, on the average, each individual 
 missed of being the mean or the average individual. 
 
 Standard deviation. — Another constant expressing departure 
 from type, and one which is preferred by biometricians on mathe- 
 matical grounds, is standard deviation, designated by the Greek 
 letter small ''sigma " (o-). It is found by squaring the deviations 
 from the mean before multiplying by the frequencies, dividing 
 the summation of these products by the number of individuals, 
 
406 
 
 Plant- Breeding 
 
 and then extracting the square root of the quotient. The 
 formula is : — 
 
 
 
 
 
 m 
 
 
 
 
 
 
 cr 
 
 = \ n' 
 
 
 
 V 
 
 / 
 
 Vf 
 
 D 
 
 Df 
 
 D2 
 
 2)2/ 
 
 5-14 
 
 4 
 
 38.0 
 
 28.44 
 
 113.76 
 
 808.8336 
 
 3235.3344 
 
 15-24 
 
 72 
 
 1404.0 
 
 18.44 
 
 1327.68 
 
 340.0336 
 
 24482.4192 
 
 25-34 
 
 169 
 
 4985.5 
 
 8.44 
 
 1426.36 
 
 71.2336 
 
 12038.4784 
 
 35-44 
 
 125 
 
 4937.5 
 
 1.56 
 
 195.00 
 
 2.4336 
 
 304.2000 
 
 45-54 
 
 64 
 
 3168.0 
 
 11.56 
 
 739.84 
 
 133.6336 
 
 8552.5504 
 
 55-64 
 
 38 
 
 2261.0 
 
 21.56 
 
 819.28 
 
 464.8336 
 
 17663.6768 
 
 65-74 
 
 11 
 
 764.5 
 
 31.56 
 
 347.16 
 
 996.0336 
 
 10956.3696 
 
 75-84 
 
 11 
 
 874.5 
 
 41.56 
 
 457.16 
 
 1727.2336 
 
 18999.5696 
 
 85-94 
 
 6 
 
 537.0 
 
 51.56 
 
 309.36 
 
 2658.4336 
 
 15950.6016 
 
 
 500 
 
 18970.0 
 
 
 5735.60 
 
 
 112183.2000 
 
 M = 
 
 = 37.94 
 
 cm. 
 
 
 
 
 
 Av. 
 
 Dev. = 
 
 = 11.4712 
 
 ! cm. 
 
 
 
 
 (T = 
 
 14.9789 cm. 
 
 
 
 
 
 Performing the operations indicated by this formula, we find 
 the standard deviation in our problem to be 
 
 112183.2000 
 500 
 
 14.9789 cm. 
 
 The squaring of the deviations has the effect of exaggerating 
 the departures of the extremes, and thus the standard deviation 
 is always greater than the average deviation, so that the two 
 are not comparable. For the practical breeder the one is just 
 as good as the other and whether he employs the average devia- 
 tion or the standard deviation is of little practical importance 
 so long as he is consistent in the use of one to the total exclu- 
 sion of the other in the same piece of work. 
 
 Finding the mean and the standard deviation by the " short 
 method^ — Where large numbers are used, the derivation of the 
 mean and the standard deviation by the method presented 
 
Appendix E 
 
 407 
 
 above is a long and laborious process, in which the liability to 
 error is great. A much shorter, simpler, and at the same time 
 more accurate method has been devised. This consists in mak- 
 ing a guess at the mean (designated by G), and indicating the 
 difference between each class value and this guess in a column 
 marked {V-G). Each of these differences is then multiplied by 
 the corresponding frequency and the algebraic sum of the total 
 negative differences and the total positive differences is found. 
 This is the total amount by which our guess missed the mean 
 for the whole population, and hence we should divide this 
 quantity by n to find the average amount by which we missed 
 our guess. If this amount, which is called the '^correction," is 
 positive, then our guess has been too low by that amount, and it 
 is to be added to the guess. On the other hand, if it is negative, 
 then our guess has been too high, and it is to be diminished by 
 this amount. The formula for this procedure is : — 
 
 correction (c) = (Algebraic) —^^^^ ^ 
 
 M =G±c. 
 
 n 
 
 Length of Plants (Short Method) 
 
 V 
 
 / 
 
 (V-G) 
 
 KV-G) 
 
 
 /(F-G)2 
 
 5-14 
 
 4 
 
 -30 
 
 - 120 
 
 
 3600 
 
 15-24 
 
 72 
 
 -20 
 
 1440 
 
 
 28800 
 
 25-34 
 
 169 
 
 -10 
 
 -1690 
 
 -3250 
 
 16900 
 
 35-44 
 
 125 
 
 
 
 
 
 
 
 
 45-54 
 
 64 
 
 10 
 
 640 
 
 
 6400 
 
 55-64 
 
 38 
 
 20 
 
 760 
 
 
 15200 
 
 65-74 
 
 11 
 
 30 
 
 330 
 
 
 9900 
 
 75-84 
 
 11 
 
 40 
 
 440 
 
 
 17600 
 
 85-94 
 
 6 
 
 50 
 
 300 
 
 2470 
 
 15000 
 
 
 500 
 
 
 Sum 
 
 = -780 
 
 113400 
 
 c =- 
 
 - 780 
 
 1.56 
 
 c2 
 
 = 2.4336 
 
 
 500 
 
408 Plant-Breeding 
 
 M= 39.5- 1.56 = 37.94 cm. 
 
 o- =^^1^00 _ 2.4336 = V224.3664 = 14.9789 cm. 
 
 C= 1M785 ^ 39.48%. 
 37.94 
 
 In our problem, the mean as determined by this method, as 
 shown in the accompanying table, is exactly the same as was 
 found by the long method, 37.94 cm. 
 
 We would have secured the same result if, after a casual in- 
 spection of the line of bean plants spoken of above, we guessed 
 that the mean was 39.5, and taking an individual of this length 
 as a measure, we found the total amount which the short ones 
 lack of being equal in length to the assumed mean, or the guess, 
 and likewise the total amount which the long ones exceed the 
 guess. The algebraic sum of these two amounts would be the 
 total amount by which our guess missed of being the true mean, 
 and since 500 individuals were measured, the average amount 
 by which we missed on each individual would be found by 
 dividing this sum by 500. Our assumed length would then 
 be corrected by this amount, just as above. If we had guessed 
 that the mean was 37.94, and went through the same process, 
 then the sum of the negative differences would have exactly 
 counterbalanced the sum of the positive differences, since our 
 guess in this case coincides with the true mean. 
 
 It would have made no difference whatever had we made our 
 guess at 9.5. Indeed, this would have the advantage that 
 minus signs would be eliminated and thus a frequent source of 
 error removed, since students are prone to forget the algebraic 
 signs. On the other hand, larger numbers would be involved. 
 
 In finding the standard deviation by the short method, the 
 elements of the (V-G) column are squared before multiplying 
 by the corresponding class frequencies. The sum of these prod- 
 
Appendix E 409 
 
 ducts is then divided by n, just as in the long method. In find- 
 ing the mean a certain correction was appUed to the guess. 
 Now, since we are here dealing with squares, we must apply as 
 a correction the square of the correction found previously ; but 
 unlike the previous procedure, this square of the correction is 
 always subtracted from the quotient found as stated above. 
 (All this has been proven mathematically correct, but the proof 
 is beyond the scope of this study.) The square root is then found 
 as before. The fonnula for deriving the standard deviation by 
 this method is : — 
 
 • -4 
 
 n 
 
 Using this method, we find the standard deviation to be 
 exactly the same as before, as shown in the table above and the 
 
 following calculations : — 
 
 ^ =\/^^i^- (- 1-56)^ = 14.9789 cm. 
 
 A further considerable shortening of the short method can be 
 employed when the class values differ by amounts other than 
 unity or a simple multiple of it, such as 10. In such a case 
 the class differences arc to be treated as unity and a correction 
 made at the end of the calculation. The modified formulae are : — 
 
 M = G ± (ex True Difference between Classes) , 
 
 X True Difference. 
 
 V 
 
 f{V-GY 
 n 
 
 The short method, because of its simplicity and its labor- 
 saving features, recommends itself for general use. It is also 
 slightly more accurate than the long method because no deci- 
 mals are dropped until the very end of the calculation. 
 
 Coefficient of variability. — Standard deviation, as a measure 
 
410 Plant-Breeding 
 
 of variability, allows of comparison only between similar organ- 
 isms or parts, between such characters as are measured in the 
 same denomination, as tubers with tubers, or height measured 
 in inches with height in inches. This is because it is not an 
 absolute, or abstract constant, but really represents a certain 
 number of feet, pounds, centimeters, or what not. And just as 
 we cannot compare 5 pounds with 5 inches mathematically, so 
 we cannot compare standard deviation in inches with that in 
 pounds. 
 
 An undenominational abstract constant that will allow of com- 
 paring diverse variabilities, let us say, height with thickness, or 
 pounds with inches, is designated as the coefficient of variability. 
 It is found by dividing the standard deviation by the mean. 
 
 The formula is — X 100 and it is symbolized by C. It is really 
 
 only the standard deviation measured in terms of the mean. For 
 our beans the coefficient of variability for length is .3948 or since 
 it is usually read as percentage, 39.48 %. This constant is now 
 comparable with any other coefficient of variability for what- 
 ever character or in whatever denomination it may have been 
 measured. Thus we can compare the variability in the length 
 of beans in millimeters with their variability in breadth meas- 
 ured in millimeters or inches, or with height in men or sugar 
 content in beets, if we wish. 
 
 Probable error. — Probable error does not mean the amount 
 of error that an investigator is likely to make in his experiments 
 or measurements. It means that if he would measure another 
 random sample of a population similar in size and character to 
 the sample he had measured before, the chances are even that 
 the mean for the new sample would lie somewhere between the 
 limits denoted by the probable error. Thus, the mean as to 
 length of plants for our beans is 37.94 cm. with a probable error 
 of ± .4518. This means that the mean for the new population 
 would not be greater than 37.9400 + .4518 = 38.3918 cm., or 
 
Appendix E 411 
 
 less than 37.94 - .4518 = 37.4882 cm., but would fall some- 
 where in between these two Umiting values. It is sjrmbolized 
 by E with the initial of the constant to which it belongs attached 
 in smaller case type. Thus, the symbol for the probable error 
 of the standard deviation is E^; of the mean, Em', of the co- 
 efficient of variability, Ec. 
 
 The probable errors are based upon certain relations between 
 the standard deviation and the number of individuals. The 
 greater the number of individuals, the smaller will be the prob- 
 able error. In short, the probable error will indicate how much 
 confidence we can place in our constant, and should always 
 accompany the latter. It is really a part of the constant. 
 
 In finding the probable errors the constant .6745 is used. 
 This has been derived mathematically and is used by all biom- 
 etricians in the same way. 
 
 The following formulae will show how the various probable 
 errors can be found : — 
 
 ^^ = ±.6745^. 
 
 J^<.=±.6745-^. 
 
 V2n 
 
 Ec = 
 
 C 
 ± .6745—:=, where C is 10 % or less.^ 
 
 V2 
 
 n 
 
 V2n>' Vioo; 
 
 ± .6745 — =\ 1 + 2 -^^ ), where C is greater than 10 %.' 
 
 Our completed constants for length of bean plants are then 
 as follows : — 
 
 M = 37.9400 ± .4518 cm. 
 
 o- = 14.9789 ± .3195 cm. 
 
 C = 39.48 ± .96 %. 
 
 ^ In these equations the value of C in per cent is to be used. The prob- 
 able error will come out as a percentage. 
 
412 Plant-Breeding 
 
 In the accompanying table the constants for the number of 
 pods borne on these plants are likewise determined by the short 
 method. Note that the colmnn {V-GY is entirely omitted, a 
 short cut which is another considerable time saver. Instead, 
 the elements of column /( V-G) are simply multiplied by the cor- 
 responding elements of the {V~G) column since J{V-G) times 
 {V-G) equals /(F-G)2. 
 
 Number of Pods (Short Method) v 
 
 V f (V-G) f{V-G) j{V-GY 
 
 5-14 16 -20 - 320 6400 
 
 15-24 140 -10 -1400 -1720 14000 
 
 25-34 169 
 
 35-44 115 10 
 
 45-54 40 20 
 
 55-64 12 30 
 
 65-74 5 40 
 
 75-84 ^ 50 
 
 500 Sum = 940 74200 
 
 c =^= 1.88 c2 = 3.5344 
 
 500 
 
 Mode = 29.5 Modal Coefficient = 38.36 % 
 
 M = 29.5 + 1.88 = 31.38 ± .3631 (pods). 
 
 
 
 
 
 1150 
 
 
 11500 
 
 800 
 
 
 16000 
 
 360 
 
 
 10800 
 
 200 
 
 
 8000 
 
 150 
 
 + 2660 
 
 7500 
 
 .-V 
 
 74200 _ 3^3^^ ^ 12.0360 ± .2568 (pods). 
 500 ^ ^ 
 
 C = IM^ep ^ 3g3g ^ 33 3g g3 ^ 
 31.38 
 
 Exercise 3 
 Correlation 
 
 Certain characters in organisms tend to appear together 
 and the inference is that they are causally connected, that is, 
 
Appendix E 413 
 
 one is the cause of the other or else both are dependent upon 
 the same cause. 
 
 Two phenomena are causally connected if any one of the 
 following four cases is true : — 
 
 (1) If, when the first is present, the second is invariably present 
 also. 
 
 (2) If, when the first increases in amount, the second also in- 
 variably increases a proportional amount. 
 
 (3) If, when the first is absent, the second is invariably absent 
 also. 
 
 (4) If, when the first decreases in amount, the second also 
 invariably decreases a proportional amount. 
 
 Because a fixed or absolute relationship exists in each of the 
 four cases the correlation between the two phenomena is said 
 to be perfect, but in the first two cases it is positive in nature, 
 in the second two negative in nature. If absolutely no relation 
 existed between the two phenomena, the correlation would be 
 zero. 
 
 Now, in the bean problem used in the preceding exercise, it 
 might be asked, ''Is there any fixed relation between the length 
 of plant and its number of pods?" Suppose, for example, that 
 if on selecting a plant from the whole lot, it was found to be a 
 long one, could we then say, on this information only, that it will 
 be found to bear a great number of pods? If so, we are assum- 
 ing that some relation exists between the two characters. 
 
 Let us, for the sake of illustration, suppose that each bean 
 plant bears one pod for every centimeter in length. Because in 
 this case there exists a fixed or absolute relationship, the corre- 
 lation is said to be perfect, and is expressed by 100 %, or more 
 usually simply by unity (1). 
 
 Now, suppose, however, that on selecting 300 plants averag- 
 ing 80 cm. in length, we find the first 100 plants to bear an 
 average of 50 pods per plant, the second 25 pods, and the third 
 10, it is clear that if we select one more plant at random and 
 
414 Plant-Breeding 
 
 measure it to be 80 cm. also, we could no more predict the 
 number of pods it bears than if we had not. measured it at all. 
 Here, then, we say there is no relationship whatever between 
 length of plant and number of pods, or, in other words, the cor- 
 relation is 0. 
 
 Now suppose a third case, in which we ,find that invariably 
 the longest plant bears the fewest pods, and the shortest the 
 most. Here we could say the relationship is fixed or absolute 
 too, but in an opposite, or negative manner, and accordingly, 
 the correlation would be expressed by — 1. 
 
 But now turning back to the first supposition, where it was 
 assumed that one pod was borne for each centimeter length, 
 suppose that the relationship were not so definite. Suppose 
 that one pod occurs not for every centimeter, but sometimes for 
 a little more than a centimeter, sometimes for a little less ; then 
 the relationship, though not absolute, is high, and the degree 
 to which this relationship approaches the perfect 100 % relation- 
 ship will express the correlation between the two characters. 
 The correlation coefficient, in other words, would fall between 
 and + 1. 
 
 We rarely find characters or organs in an organism to be 
 absolutely related; usually they are associated in a more or 
 less intermediate degree, somewhere between and + 1, or 
 and — 1. The degree to which they are associated, or corre- 
 lated, if it can be determined in an exact manner and expressed 
 by a mathematical constant, should be an index of the degree 
 for which one is the cause of the other, or the probability of 
 finding the other when we know the first is present. This may 
 be of importance sometimes to the breeder because some easily 
 seen character may be responsible for, or indicative of, the 
 presence of a desired, but unseen character. Thus a certain 
 shaped kernel of corn (one with a large germ) is known to run 
 high in oil content, one with large endosperm high in starch. 
 To select kernels with large germs is much easier than to analyze 
 
Appendix E 
 
 415 
 
 many ears by chemical methods. Or if, after a relation had 
 been established, we could safely choose the longest or tallest 
 bean plants right in the field and know that they will bear the 
 greatest number of pods, it would be of great advantage to the 
 breeder. 
 
 Now, an exact determination of the degree of correlation can 
 be obtained by the biometrical method. Let us follow the pro- 
 cess step by step, using our bean data. 
 
 First of all, we take our data for the two characters for which 
 we wish to find the correlation, length of plant, and number of 
 pods. 
 
 Our original observations will be somewhat as follows : — 
 
 No. OF Observation 
 (or Plant) 
 
 Length of Plant in Cm. 
 
 No. of Pods 
 
 1 
 
 2 
 3 
 
 etc. 
 
 27 
 46 
 
 18 
 etc. 
 
 32 
 
 27 
 45 
 
 etc. 
 
 In finding the constants — mean, standard deviation, etc., for 
 each of these characters, the observations for length and those 
 for number of pods were distributed in separate tables. Now, 
 however, we distribute both sets of observations on one table, 
 in what are known as arrays of a correlation table. (See Table 
 1.) For example, the first observation tabulated above would 
 fall in the vertical array 25-34, as regards length, and in the 
 25-34 horizontal array, as regards number of pods. The second 
 observation would fall in the 5th column (vertical array 45-54) 
 and in the third row (horizontal array 25-34). 
 
 Thus each vertical array would be a frequency distribution 
 of length of plant with respect to number of pods, and each 
 
'416 Plant-Breeding 
 
 horizontal array would be a distribution of number of pods 
 with respect to length of plant. But if we add up all the fre- 
 quencies along each horizontal array, we will get the frequency 
 distribution with respect to the number of pods and it will be 
 exactly the same as that found in the preceding exercise (see 
 table on p. 404) ; likewise, if we add up the frequencies in the 
 vertical arrays, we will get the frequency distribution with 
 respect to length of plants. 
 
 The various steps by means of which the constants for length 
 of plant and those for number of pods were obtained were 
 given in the preceding exercise and need no repetition. They 
 are here secured by the "short method" and are given in the 
 correlation table. We are here concerned with the finding of 
 the constant which will express the degree of correlation between 
 these two characters. 
 
 The only new feature of this correlation table, aside from the 
 method in which the observations are distributed, is the column 
 marked 2P. Each element of this column represents the total 
 deviation (from the assumed mean, or guess) of the individuals 
 in each array with respect to both length of plant and number of 
 pods. Thus, taking the first horizontal array, the 5-14 class 
 as regards number of pods, we wish to find how much the in- 
 dividuals in this class deviate from the assumed mean for length 
 of plants. It is found as follows : — 
 
 3 individuals each deviated by — 30 = — 90 
 9 individuals each deviated by — 20 = — 180 
 3 individuals each deviated by — 10 = — 30 — 300 
 1 individual deviated by + 20 = 20 + 20 
 
 Algebraic Sum = — 280 
 
 All the individuals in this array deviate from the assumed 
 mean for length of plants by the algebraic sum of the total minus 
 deviations and the total plus deviations, which is — 280, as 
 indicated. But each individual in this array with respect to 
 
Appendix E 417 
 
 length deviated by — 20 from the assumed mean with respect 
 to number of pods, and hence we must multiply — 280 by — 20 
 to find the total deviation from both assumed means and this 
 gives us + 5600. 
 
 All the elements in the 2P column are secured in exactly the 
 same way. The third element is zero, since the deviation from 
 the assumed mean for number of pods is zero in this case. The 
 fourth element comes out a minus quantity according to the 
 following calculation : — 
 
 1 X - 30 = - 30 18 X 10 = 180 
 
 11 X - 20 = - 220 5 X 20 = 100 
 
 42 X - 10 = - 420 2 X 30 = 60 
 
 33 X 1 x40 = 40 
 
 -670 2 X 50 = 100 
 
 480 
 
 - 670 + 480 = - 190 X 10 = - 1900. 
 
 The algebraic signs for each quantity must be carefully ob- 
 served throughout the calculations. 
 
 Finally, the algebraic sum of all the elements in the SP column 
 is determined.^ This will give us the grand total deviation from 
 both assumed means for all the individuals, and hence to find 
 the deviation for each individual we must divide by 500. Per- 
 forming the operation we get = 66.20. 
 
 ouu 
 
 Now all along we have been working from an assumed mean, 
 or guess, and we must apply a correction, which, mathematicians 
 tell us, must be the product of the correction for length by that 
 
 1 The elements of the SP column can be obtained by finding the total 
 deviation of each vertical array with respect to number of pods and 
 multiplying by the deviation of that array with respect to length, instead 
 of vice versa. The elements will be different, but their sum will be 
 exactly the same by either method. 
 2e 
 
418 
 
 Plant-Breeding 
 
 
 oi 
 
 02 " 
 
 o 
 
 K 
 
 n 
 P 
 
 X 
 
 Eh 
 < 
 
 Ah 
 O 
 
 o 
 
 y « 
 
 % .2 
 
 K 
 O 
 O 
 
 Ph 
 
 
 
 o o 
 
 o o o o o o 
 
 o 
 
 
 
 
 
 
 o o 
 
 o o o o o 
 
 o 
 
 ULI 
 
 ft. 
 
 o o 
 
 05 O CD 00 o 
 
 y—{ 
 
 w 
 
 lO o 
 I— I 
 
 —( lo CO -* CO 
 
 1 
 
 CO 
 CO 
 
 '^ a 
 
 ^ 
 
 
 
 s 
 
 o o 
 
 o o o o o o 
 
 o 
 
 $S 'CO 
 
 o o 
 
 o o o o o 
 
 o 
 
 '^ -M o -H 
 
 TjH ^ CO ^ 
 
 fcL 
 
 Ttl O 
 
 lO O 00 o >o 
 
 C^l 
 
 CO Tt< 
 
 --H CD O QO 1> 
 
 TfH 
 
 ^^ 
 
 rH 
 
 I— 1 1— 1 I— 1 
 
 t^ 
 
 
 
 
 
 T}H 00 CO CO 
 
 
 
 
 
 00 CO CO O CO r^ 
 
 «5 "^ rH* d 00 3 
 
 
 
 
 
 
 
 o 
 
 o 
 
 o 
 
 rH CO CO rH CO >^ 
 
 
 
 (M 
 
 o 
 
 '^ 
 
 
 
 
 t^ 
 
 CD 
 
 Oi 
 
 i i 
 
 ^^^ 
 
 
 r— 1 
 
 CI 
 
 
 o 
 
 S 
 
 1 
 
 
 
 
 CD 
 CO 
 
 o 
 
 ^_ 
 
 o o 
 
 o o o o o 
 
 
 ^^g ^ 
 
 2 ^ 
 
 «*i 
 
 (M O 
 
 lO O CO O lO 
 
 
 ^~^ . CO 
 
 c =^ 
 
 
 00 TfH 
 
 1-H X CO (M 1-H 
 
 
 q 
 
 
 I— 1 
 
 I— 1 
 
 
 
 
 1 1 
 
 
 
 ^ocd-^SB^ Jl 
 
 i^H 
 
 
 
 
 
 1^2???^^ § 
 
 o 
 
 s ^ 
 
 
 
 
 ;5 
 
 o o 
 
 (M T-H 
 
 1 1 
 
 o o o o o o 
 
 rH (M CO Tfl »0 
 
 
 ff) 1 . t^ ■^ Oi CO 
 
 ^ 1 <M CO rH CO CO 
 
 o 
 
 lO 
 
 S^ 
 
 1 1 
 
 
 
 II II II II II II II 
 
 
 
 
 
 
 CD O 
 
 05 lO O (N lO CO 
 
 o 
 
 
 
 1—1 Tjl 
 
 CO i-H rJH rH 
 
 Q 
 
 
 
 1— 1 
 
 rH »— 1 
 
 ■^005 
 
 1 08Z -| 00^811 
 
 
 
 
 
 
 
 
 
 <M rH r-H (M 
 
 9 
 
 og 
 
 008 OLfZ + 
 
 00051 
 
 00 
 
 
 
 
 
 
 
 ■* 
 
 
 
 
 oo 
 
 1— 1 
 
 ■^ rH CO (M 
 
 n 
 
 0^ 
 
 0^^ 
 
 009ZI 
 
 t> 
 
 
 
 
 
 
 
 ;^ 
 
 
 
 
 
 
 t>. (M rH rH 
 
 IT 
 
 08 
 
 088 
 
 0066 
 
 CD 
 
 
 
 
 
 
 
 •># 
 
 
 
 
 CO 
 
 rH CD 
 
 TtH lO CO CO CO 
 
 88 
 
 OS 
 
 091 
 
 00S51 
 
 »o 
 
 
 
 
 
 
 
 :t 
 
 
 
 
 1 
 
 I— t 
 
 CO 00 LO rH oq 
 
 ^9 
 
 01 
 
 0^9 
 
 00^9 
 
 •* 
 
 
 
 
 
 
 
 •* 
 
 
 
 
 1 
 
 O 
 
 CO 
 
 iO CO CO CO i-H 
 
 rfl CO rH 
 
 gsT 
 
 
 
 
 
 
 
 CO 
 
 
 
 691 
 
 01 - 
 
 
 
 •<* 
 
 CO 
 
 CO •* 
 
 O <M O rH 
 lO •* rH 
 
 
 0691 - oes8 - 
 
 00691 
 
 <N 
 
 
 
 
 
 
 
 ■<** 
 
 
 
 
 
 CO 
 
 TtH rH rH 
 rH rH 
 
 Zl 
 
 os- 
 
 O^^T - 
 
 0088S 
 
 I— 1 
 
 
 
 
 
 
 
 ■* 
 
 
 
 
 i-H 
 J. 
 
 CO 
 
 f-H 
 
 f 
 
 08 - 
 
 051 - 
 
 0098 
 
 
 -* Tt^ 
 
 ^ ^ ^ ^ ^ ^ 
 
 
 
 
 
 > 
 
 1 1 
 
 T-H 
 
 CO '^l lO CD t>- 00 
 1 1 1 1 1 1 
 
 lO lO lO »o lO »o 
 
 (M CO ■* iCl CO J^ 
 
 i 
 
 0-A 
 
 (D-A) } 
 
 ziO-A)} 
 
 
 
 
 spoj JC 
 
 jaqiur 
 
 ^N 
 
 9'Q2 = D 
 
 
 
Appendix E 419 
 
 for number of pods. This product is always subtracted from the 
 quotient of — 
 
 66.20 - (1.88 X - 1.56) = 69.1328. 
 
 Now this corrected deviation must be secured in terms of the 
 standard deviations for each character, and hence this quantity 
 69.1328 is to be divided by the product of both standard devia- 
 tions : — 
 
 69.1328 
 
 14.9789 X 12.0360 
 
 = . 3835. 
 
 We have now finally arrived at our correlation coefficient, 
 designated universall}^ by the letter r, the fomiula for the deter- 
 mination of which is as follows : — 
 
 -^ - Ci C2 
 
 Correlation Coefficient (r) = 
 
 0"l 0"2 
 
 Like all other constants the correlation coefficient must be 
 accompanied by its probable error, the formula for the finding 
 of which is as follows : — 
 
 ^ ^ ^ .6745 (1 - r^) 
 
 Vti 
 
 Solving this for our correlation coefficient, we ffiid the prob- 
 able error to be ± .0257. 
 
 The amount of confidence which can be placed in the corre- 
 lation coefficient depends upon the size of its probable error 
 largely. Biometricians saj^ that in order to be of much value, 
 the coefficient must be from five to ten times as great as its 
 probable error. But whether the coefficient shows a high, low, 
 or intermediate degree of correlation between the two charac- 
 ters measured depends entirely upon its position with reference 
 to its two limits, and + 1 or and - 1. According to the 
 
420 
 
 Plant-Breeding 
 
 size of r found jor the data used in our problem, the correlation 
 existing between the length of plant and its number of pods is 
 not great. 
 
 Exercise 4 
 Statistical Study of Apples from Different Trees 
 
 Object. — To study the individuality of fruit trees. 
 
 Materials. — Apples representing the total product of different 
 trees ; scales ; calipers. 
 
 Fill in the following form for each tree. Plot curves repre- 
 senting the entire population of trees. 
 
 Name of Variety 
 
 Tree no. 
 
 Age of tree 
 
 Condition of tree ... 
 
 Total number of apples 
 Number of marketable apples 
 Total weight of apples 
 Weight of marketable apples 
 Average width of 50 apples 
 Average length of 50 apples 
 
 Color 
 
 Any other noticeable differences 
 
 Exercise 5 
 Statistical Study of Branches of Different Trees 
 
 Object. — To continue the study as outlined in Exercise 4, 
 to test the individuality of trees. 
 
 Materials. — Fruit trees of different kinds, preferably dwarf 
 trees; tapes. 
 
 Measure the new growth of various parts of each tree and of 
 different trees. Plot curves of each tree and of all of the trees 
 
Appendix E 
 
 421 
 
 Fig. 108. — A common form of ragweed. 
 
422 
 
 Plant-Breeding 
 
 Fig. 109. — Another form of ragweed. 
 
Appendix E 423 
 
 as a population, to show graphically the extent of bud variation 
 present. 
 
 Exercise 6 
 
 Statistical Study of the Quantity of Grapes from Different Grape 
 
 Vines 
 
 Use the same general method as in Exercise 4. 
 
 Exercise 7 
 
 Study of Variation in Pressed Specimens of Ragweed or Some 
 Plant showing Many Different Types 
 
 Object. — Careful study of the large and small variations among 
 different biotypes of ragweed {Ambrosia artemisiifolia) . 
 
 Materials. — Specimens of many different types of the above 
 plant or any species of plant which is rich in biotj'pes. These 
 specimens should be carefully pressed and mounted. (See Figs. 
 108 and 109.) Have each student make detail drawings to show 
 minute differences. 
 
 Exercise 8 
 
 Study of Bud Variations and Reversions in Ferns 
 
 Object. — To determine the nature and amount of reversion 
 from the parental type, and if possible to find some cause for 
 the same. 
 
 Material. — Obtain specimens of the sword fern {Nephrolepis 
 exaltata) and Boston fern {Nephrolepis bostoniensis) and as many 
 of the other ferns named below as possible. 
 
 Study the trueness to type of each variety' and any reversions 
 which they may contain. Draw typical specimens. 
 
 The following is the history, according to Cogswell, of some 
 of the fern varieties. This is not a complete list but gives 
 an idea of the origin of a few common horticultural varie- 
 ties. 
 
424 
 
 Plant-Breeding 
 
 Nephrolepis bostoniensis .... 
 
 Nephrolepis Piersonii 
 
 Nephrolepis elegantissima 
 
 Nephrolepis Scottii 
 
 Nephrolepis Barrowsii .... 
 Nephrolepis Whitmanii .... 
 Nephrolepis todeaoides .... 
 Nephrolepis superbissima 
 
 Nephrolepis Scholzelii 
 
 Nephrolepis Pruessneri .... 
 Nephrolepis magnifiea .... 
 Nephrolepis elegantissima eompaeta 
 
 Sport of 
 
 nephrolepis 
 
 exaltata 
 
 (sword fern) 
 
 bostoniensis 
 
 Piersonii 
 
 bostoniensis 
 
 Piersonii 
 
 Barrowsii 
 
 Whitmanii 
 
 Scottii 
 
 Scottii 
 
 Whitmanii 
 
 Whitmanii 
 
 elegantissima 
 
 Exercise 9 
 Study of the Morphology of Different Kinds of Flowers 
 
 Object. — To acquaint the student with floral parts and their 
 functions. To determine the proper condition of the buds and 
 flowers for emasculation, crossing, etc. 
 
 Material. — Buds and flowers of various kinds and in different 
 stages of development ; microscope or hand lens ; set of dis- 
 secting instruments. The material should represent different 
 natural families or orders. 
 
 Have the students make careful drawings of the floral organs, 
 of various types of flowers. Take special care to distinguish 
 the stamens and pistils. 
 
 The following outline by Dr. M. J. Dorsey may be found 
 helpful in this exercise : — 
 
Appendix E 425 
 
 Study of Flowers (prerequisite to crossing) 
 
 Flower — 
 Non-essential organs — 
 
 Calyx — composed of sepals. 
 Corolla — composed of petals. 
 
 Essential organs — 
 
 Pistil — f carpels. 
 
 a, style ; b, stigma ; c, ovary { placenta. 
 
 I ovules. 
 
 Stamens — composed of 
 
 £1 , , , , f loculus or cell. 
 
 a, filament ; b. anther < 
 
 I pollen. 
 
 Degree of cross-relationship. — 
 
 1. Self- or close-fertilization. (Occurring in perfect or her- 
 maphrodite flowers.) 
 
 2. Cross-fertilization. (Between individuals of same species 
 or variety.) 
 
 3. Hybridization. (Between species and sometimes between 
 varieties which are very distinct.) 
 
 Causes of sterility. — 
 
 1. Stamens and pistils maturing at different times. (Di- 
 chogamy.) 
 
 2. Lack of affinity between pollen and stigma. 
 
 3. Scanty or insufficient pollen. 
 
 4. Lack of viability of pollen. 
 
 Relative position between stigma and anthers. — 
 L Stigma and anthers the same height. 
 
 2. Stigma above anthers. 
 
 3. Stigma below anthers. 
 
426 Plant-Breeding 
 
 Relative maturity of pistil and anthers. — 
 
 1. Both maturing at same time. 
 
 2. Stigma matures first — protogyny. 
 
 3. Anthers mature first — protandry. 
 
 Methods of pollination. — 
 
 1. Insects. 
 
 2. Wind. 
 
 3. Water. 
 
 4. Self-pollination. 
 
 Types of plants in regard to sex. — 
 
 1. jSIonoecious (both sexes on same plant). 
 
 2. Dioecious (each sex on different individuals within the 
 species or variety). 
 
 3 . Polygamous (perfect and imperfect flowers on the same plant) . 
 
 Types of flowers in regard to sex. — 
 
 1. Imperfect (1) Staminate — bearing only stamens. 
 
 (2) Pistillate — bearing only pistils. 
 
 2. Perfect or hermaphroditic — bearing both stamens and 
 pistils. Determine the following : — • 
 
 {a) Number of parts of flower. — 
 
 a, sepals ; b, petals ; c, stamens ; d, pistils. 
 (6) Type of flower — perfect (hermaphrodite) or imperfect, 
 (c) Relative position of stigma and anthers. 
 {d) Relative maturity of pollen and stigma, 
 (e) Is the flower pollinated by insects, wind, or selfed? 
 (/) Draw the essential organs and label each part. 
 
 Exercise 10 
 
 Technique of the Cross-pollination of Plants 
 This exercise may be carried out in the winter in a green- 
 house or conducted in the fall and spring out of doors, where 
 
Appendix E 427 
 
 additional expense is not involved in growing the plants under 
 glass. 
 
 The following suggestive directions may be given to each 
 student : — 
 
 Materials. — 1. Instruments: tweezers; scalpel; small, sharp- 
 pointed scissors, hand lens, etc. 
 
 2. For covering flowers : ^Manila bags, waxed paper bags, 
 cheese cloth, etc. Wire labels, stringed tags, fine copper wire 
 or twine cut into short lengths may be used to fasten the bags. 
 
 Preliminary study of -plant. — 
 
 Before attempting to cross plants, it is necessary' to know the 
 structure of the flower to be used. To do this {A) locate 
 all parts — sepals, petals, anthers, filaments, stigma, style, 
 ovar\^; {B) determine whether the flowers are perfect or 
 imperfect; (C) learn to recognize the "ripe'' or receptive 
 condition of the stigma and pollen. 
 
 Technique. — 
 
 {A) Emasculation. (Unnecessary' where stamens and pistils 
 are borne on different flowers.) For crossing purposes 
 select flowers in which the anthers have not opened. Re- 
 move the anthers with tweezers or scalpel, taking care not 
 to injure the stigma. It may be necessary' to remove part 
 or all of the petals in some flowers in order to get at the 
 anthers, but it is best to remove only the anthers, if possible. 
 
 {B) Bagging. After the anthers have been removed, the 
 flower should then be covered with some material, as a 
 manila or oil paper bag, to prevent the entrance of foreign 
 pollen. When the stigma is receptive, remove the covermg, 
 pollinate with the desired pollen of known purity, and im- 
 mediately cover again, leaving cover on until fertilization 
 has taken place — as indicated by withered or broAisTiish 
 stigma. It is desirable to remove the covering when the 
 cross has "set." 
 
428 Plant-Breeding 
 
 (C) The record. The record should include a description of 
 each parent, giving particular attention to the contrasted 
 characters. Colors may be recorded by comparing with a 
 standard color chart. The female parent should always be 
 mentioned first. The record on the label should include 
 variety name or number of each parent, date of emascula- 
 tion, and pollination. (Name of worker can also be placed 
 on the label.) As far as possible reciprocal crosses should 
 be made. 
 
 Exercise 11 
 
 Embryological Studies from Slides showing Cell Division at Dif- 
 ferent Stages, Chromosomes, Pollen Mother-cells, Development 
 of the Embryo-sac, etc. 
 
 Provide each student with a high-power microscope and mi- 
 croscopic slides mentioned above. Careful drawings of each slide 
 should be made. 
 
 Exercise 12 
 
 Study of Pollen Germination and Fecundation 
 
 Materials. — Fresh and preserved flowers showing structure 
 of carpels in cross and long section ; microscopic slides showing 
 growth and penetration of pollen tubes into ovary, fecundation, 
 etc. For study of germinating pollen, fresh pollen may be 
 germinated in sugar solutions of various strengths mounted in 
 the cells of hanging-drop slides. If this is done at the beginning 
 of the practicum, the germinated pollen will be ready for ex- 
 amination before the end of the period. 
 
 Careful drawings of all stages observed should be made. The 
 drawings should show all the differences in the length and size 
 of the pollen tube in various degrees of concentration of the sugar 
 solutions. Note also the effect of temperature and other external 
 influences upon germination. 
 
Appendix E 429 
 
 Exercise 13 
 
 Practice in the Cross-pollination of Apples, Pears, Peaches, 
 
 Plums, etc. 
 To be carried on in the spring, when the trees are in bloom. 
 For general methods of procedure, see Exercise 10. 
 
 Exercise 14 
 
 Purpose. — To teach the Laws of Probability; dominance 
 and recessiveness; segregation and recombination; presence 
 and absence hypothesis; inhibitory factors; complementary 
 factors ; inversed ratios, etc. 
 
 Materials. — Coins, wrinkled and smooth peas, both yellow 
 and green m equal numbers for two character pairs ; yellow and 
 white kernels of both dent and flint corn ; a pack of playing 
 cards; and chemicals. 
 
 Program. — The instructor should take special care to make 
 clear the significance of each step in the exercise and their con- 
 crete application to problems of plant-breeding and genetics. 
 
 1. The Law of Probability is taught by tossing coins. Each 
 student should toss one coin for 2 or 3 minutes and record the 
 number of times it faUs head, and th6 number of times tail. 
 Then the total for the whole class is summed up. It will be 
 found that the latter count, including more tosses, approaches 
 the theoretical ratio much more nearly. This should be ex- 
 plained by the instructor. 
 
 2. Then in the same way two coins may be tossed by each 
 student. He now records heads ; heads and tails ; tails. 
 
 The application of this law in the formation of gametes should 
 be made clear by the instructor. 
 
 3. Now the material may be changed by way of illustration. 
 Peas or corn comprising two allelomorphs may be used for this 
 exercise. They are mixed together in equal numbers in a bag 
 
430 Plant-Breeding 
 
 and each student draws blindly from the bag one seed at a time, 
 recording his draw. This exercise illustrates segregation and 
 the formation of gametic cells. 
 
 4. Now each student may remove simultaneously one pea 
 from each of two bags, and lay them down side by side to illus- 
 trate the mating of gametes in an Fx hybrid and the subsequent 
 recombination of characters. He should record only the domi- 
 nant characters present in each pair taken and his record will 
 show the phenotypes of his F^ hybrids. 
 
 5. The same principles can be illustrated by the use of a pack 
 of playing cards. Draw at random two cards at a time. Record 
 each combination observed. Two blacks coming simultaneously 
 represent a homozygous black individual; a black and a red 
 represent a heterozygous form appearing as black, two reds 
 represent a pure recessive. For illustrating the combination of 
 two character pairs, four cards may be drawn at a time. 
 
 6. Some simple chemical reactions ^ afford an excellent series of 
 demonstrations illustrating the main features of Mendelism. 
 The following apparatus and chemicals are required : — 
 
 4 500 cc. flasks 3 dozen test tubes 
 
 1 100 cc. flask 4 small funnels for burettes 
 
 1 100 cc. graduate 1 iron stand and clamps 
 
 4 50 ee. burettes 3 test tube racks 
 
 1 2 cc. pipette 1 pipette dropper 
 
 500 cc. 10% ep. NHaOH 500 cc. 5% cp. HCl 
 
 500 cc. 25% cp. NH4OH 100 cc. 2% litmus powder 
 
 500 cc. 10% cp. HCl solution 
 
 10 cc. phenolphthalein 
 
 While the burettes are not absolutely necessary, they will 
 greatly facilitate the demonstrations. The solutions are to be 
 made up beforehand by the instructor, who should try some pre- 
 
 1 This portion of the exercise is based on an article by G. H. ShuU, 
 " A Simple Chemical Device for illustrating Mendelian Inheritance," 
 Plant World, 12: 145-153, 1909. 
 
Appendix E 
 
 431 
 
 n 
 
 nEMO/V5T/lAT/DN O^ ALLeLLDMDffrti/^ 
 AND OF COMrLETE UOM/NANCE 
 
 n7=f IT 
 
 /7 
 
 vn n 
 
 O'^rnE^s 
 
 TJ 1 
 
 nn T 
 
 JJFf 
 
 nn 
 
 m 
 
 ■ 
 
 Ff 
 
 77 
 
 77/7 
 
 Fig. 110. 
 
432 
 
 Plant-Breeding 
 
 OEMON5rF?Ar/ON UF FF7E5ENCE AND ABSENCE HrFOrHE5/5 
 AND nF /NTEFMEO/ACr 
 
 I 
 
 cf 
 
 r A 
 
 m 
 
 r A 
 
 r a 
 
 a. T 
 
 v^ 
 
 A A 
 
 FT 
 
 A a 
 
 A a 
 
 a a 
 
 ^ 
 
 EDMFLEMENTAFr FACTOFS 
 
 TTT A 
 
 \^ 
 
 A 3 
 
 I 
 m 
 F \ 
 
 Fig. 111. 
 
 G TTT 
 
Appendix E 433 
 
 liminary experiments to see whether or not the strengths of the 
 solutions are correct. They may have to be varied slightly. 
 The contents of each test tube representing a gamete (labeled in 
 the accompanying figures) are given below. In order to secure 
 the simple 3 : 1 or 1 : 3 ratio in F^, eight test tubes representing 
 the gametes of Fi are necessary in each case. It is of course 
 impossible to represent the phenomenon of segregation in Fx 
 by using the test tube labeled Fi. The instructor will have to 
 explain that after segregation the gametes are exactly the same 
 in nature as those of the original parents of the cross, and that 
 the hybrid Fi now forms gametes similar to those of both parents, 
 in equal numbers. 
 
 {a) Demonstration of Allelomorphism and of Complete 
 Dominance (Fig. 110). 
 
 D contains 10 cc. 10% HCl-\- 2 cc. litmus solution. 
 
 R contains 10 cc. 10% NH4OH + 2 cc. litmus solution. 
 
 The dominance of blue over red can be shown by substituting 
 5% HCl for the 10 %. 
 
 (6) Demonstration of the Presence and Absence Hypothesis 
 and of Intermediacy (Fig. Ilia). 
 
 A contains 10 cc. 10 % NH4OH + 2 drops Phenolphthalein. 
 a contains 10 cc. 5% HCl. 
 
 (c) Demonstration of Complementary Factors (Fig. 111b). 
 A contains 10 cc. 10% NH^OH. 
 B contains 10 cc. H>0 -\-2 drops phenolphthalein. 
 
 Dominance of a character has usually been taken to be indica- 
 tive of the presence of a positive factor determining that char- 
 acter. But in some cases the absence of a factor, e.g. cases of 
 awnlessness in wheat, or hornlessness in cattle, seems to be 
 dominant over its presence. To say that the absence of a thing, 
 
 in other words a purely negative condition, is dominant over its 
 2f 
 
434 Plant-Breeding 
 
 a^MONSrmT/ON DF T^/E Ff9£5ENCe nr an /N/i/S/rOfJ FATTOff 
 
 r A 
 
 AI 
 
 ^ 
 
 cf 
 
 A / 
 
 A i 
 
 m 
 
 A i 
 
 W 
 
 fi Zyga/es 
 A A // '" 
 
 M 
 
 ^ m 
 
 r A i 
 
 A / 
 
 A All ] 
 
 A Ali 
 
 (^ 
 
 AI 
 
 AI 
 
 F. ^ 
 Fig. 112. 
 
 A All 
 
 W 
 
Appendix E 435 
 
 presence seems an absurdity. However, to make the facts 
 consistent with the presence and absence hypothesis, two expla- 
 nations are offered. One consists in assuming the presence of a 
 positive inhibitory factor, which prevents the production of the 
 character concerned. The other consists in assuming that one 
 ''dose" of the factor concerned is insufficient to produce the 
 result, hence in its simplex or heterozygous condition, the char- 
 acter determined by the factor fails to appear, and it is only 
 when the factor is in the duplex or positively homozygous con- 
 dition that it does appear. The first of these explanations is 
 embodied under demonstration (d). The last is embodied 
 under the demonstration entitled ''Explanation of So-called 
 ' Dominance of Absence.' ". 
 
 (d) Demonstration of the Presence of an Inhibitory Factor 
 (Fig. 112). 
 
 A contains 10 cc. 2.5 % NH4OH + 2 drops phenolphthalein. 
 Ai equals A + 5 cc. 10 % HCl. 
 
 (e) Explanation of So-called "Dominance of Absence" 
 (Fig. 113). 
 
 A contains 10 cc. 10% NHaOH -\-Q drops phenolphthalein. 
 a contains 10 cc. 10 % HCl. 
 
 After the zygotes of F2 are obtained, in this last demonstration, 
 the instructor should add 10 cc. - 10 % NH^OH to each Aa 
 zygote of F2 to show that another "dose " of factor A will now 
 produce the result. 
 
 Exercise 15 
 A Study of Mendelian Characters in Timothy and Oats 
 
 Purpose. — To afford the student concrete illustrations of 
 Mendel's laws ; to find unit characters in plants and to see their 
 segregation and recombination. 
 
 Materials. — Mature timothy plants of various strains, com- 
 
436 
 
 Plant-Breeding 
 
 exrLANAT/DN 0/= 50-CALL^0 VOM/NANC^ D^ A33e/VC€'' 
 
 r -4 
 
 /7 w 
 
 a. 1 
 
 'v'^ 
 
 Cf 
 
 DAme/es 
 
 ? 
 
 /T Zygo/es 
 
 A 
 
 ■^ 
 
 A A 1 
 
 - ii 
 
 w 
 
 w 
 
Appendix E 437 
 
 prising as great a variety of unit characters as possible. A small 
 bundle of stems for each student containing samples from different 
 plants. Photographs and mounted specimens. Varieties of 
 oats comprising various unit characters that may be readily 
 distinguished in hybrid plants, such as black and white grains, 
 side and panicled types of inflorescence; also bearded and 
 beardless varieties of wheat or barley. Specimen plants of 
 parent types should be available for inspection, also specimens 
 of the Fi plants. A large number of F^ plants resulting from each 
 cross studied should be available for examination by the class. 
 
 Program. — 1. The instructor should first explain the purpose 
 of the afternoon's exercise and outline the order of procedure. 
 Unit characters are to be studied and illustrated with timothy 
 and oats or barley. Dominance, recessiveness (or presence and 
 absence), segregation, and recombination can be illustrated here. 
 
 2. At this occasion a talk may well be given on artificial 
 crossing of small cereals for the purpose of creating new varieties. 
 The instructor may describe the inflorescence of the oat plant, 
 and the technique of making crosses in these plants. He should 
 illustrate the talk with charts and with diagrams made on the 
 blackboard. 
 
 3. Mounted specimens of oat types together with the Fi and 
 F2 progeny resulting from their crossing may be handed around 
 for examination by the class. If enough mounts are available, 
 the specimens may be drawn and described by each student. 
 
 4. Composite samples of timothy should be handed to each 
 student. He should study them to see what diversity of unit 
 characters can be found there, in the nature of differentiating 
 botanical characters. A list should be made of all the unit 
 characters observed. Drawings of timothy heads may help to 
 train his observation and fix the idea. 
 
 5. A large progeny of F2 oat plants should be distributed 
 among the class after the parent types have been shown and their 
 differentiating characters discussed. The class may now examine 
 
438 Plant-Breeding 
 
 the plants given to them, and sort out the segregated characters. 
 When sorting has been completed, the counts for the whole class 
 may be ascertained. It should serve to illustrate the expected 
 theoretical mendelian ratio. 
 
 Remarks. — Timothy affords very good material for this prac- 
 ticum, especially when bundled and mounted specimens, together 
 with photographs, are available. 
 
 Oats exhibit excellently contrasted unit characters, but expe- 
 rience shows them rather poorly adapted for class study, except 
 when mounted specimens are used. The reasons for this are : — 
 
 1. Side and panicled characters — the specimens are often 
 pressed out of shape, due to drying and storing, and are, therefore, 
 difficult to distinguish, 
 
 2. Color. — Black oats crossed with white give oats of inter- 
 mediate color which are often difficult to distinguish from black. 
 White and yellow are impossible of being distinguished by the 
 inexperienced student. Moreover, color in oat hulls varies 
 greatly with the seasonal conditions under which it was grown. 
 
 3. Plants are likely to become broken up in handling, thus 
 spoiling the count when mendelian ratios are expected. The 
 first two of these objections can be obviated by using mounted 
 specimens. Other characters such as naked, hulled, awned, and 
 awnless can be illustrated in this way. Probably a better exer- 
 cise would be given by substituting corn for oats. 
 
 Exercise 16 
 
 Mendelian Problems 
 
 Purpose. — To enable students to become familiar with what 
 might be called the mechanics of mendelism by working out 
 mendelian problems by the method of squares. 
 
 Problem. — Given : Two pairs of contrasted characters — 
 Tall vine (J"), dwarf vine (t) ; Yellow seeds (Y), green seeds (y) . 
 Tallness and yellowness are completely dominant characters. 
 
Appendix E 
 
 439 
 
 1. What gametes will be formed by an Fi hybrid individual 
 from the cross between tall, green and dwarf, yellow ? 
 
 2. How many offspring will it be necessary to grow in order 
 to allow every combination to appear in the second generation ? 
 
 3. How many genotypes will there be? 
 
 4. How many phenotypes will appear? 
 
 5. In what ratio will the phenotypes appear ? 
 
 6. How many pure dominant individuals ? 
 
 7. How many pure recessive individuals? 
 
 8. If the combination T X t gave plants of medium height 
 when a tall plant with yellow seeds is crossed with a dwarf plant 
 with green seeds, how many genotypes will appear in i^2? How 
 many phenotypes ? In what ratio ? 
 
 Illustrative 'problems. — The following problems may be studied 
 by way of illustration. These are taken from actual cases with 
 the tomato, but will apply in principle to other plants, by sub- 
 stituting other unit characters : — 
 
 Problem 1 . — 
 
 Tall, homozygous (T) X dwarf, homozygous {t) = Tt; Fi 
 Fi gametes = T ; t 
 Fi selfed = 
 
 Pollen-grains 
 
 T 
 
 Egg-cells 
 
 TT 
 
 tT 
 
 Tt 
 
 tt 
 
440 
 
 Plant-Breeding 
 
 1 tt. 
 
 Phenotypes (visible types) (2'») = S TT ; 1 tt. 
 Genotypes (actual types) (3") = 1 TT ; 2 Tt 
 
 Problem 2. — 
 
 Heterozygous Tall (Tt) X homozygous dwarf (tt). 
 
 Whenever a plant which is already heterozygous is used as a 
 parent, its gametes will become segregated during their formation, 
 and when the crossing takes place more than one kind of progeny 
 will be produced. In this case the female parent will produce 
 two kinds of egg cells, namely, tall and dwarf. 
 
 Graphically, this cross may be represented as follows : — 
 
 Pollen Grains 
 t t 
 
 Egg Cells 
 
 Tt 
 
 Tt 
 
 tt 
 
 tt 
 
 The male parent is pure dwarf, therefore all of the pollen grains 
 will represent dwarfness only. 
 
 Phenotypes = 2 Tt; 2 tt. 
 Genotypes =2 Tt; 2tt. 
 
 If the female parent were crossed with a homozygous tall 
 instead of a dwarf, the visible types the first year after crossing 
 would all appear the same (tall) instead of two kinds as above. 
 There would be 
 
 Phenotypes = 4 f T. 
 Genotypes = 2 TT ; 2 Tt. 
 
Appendix E 
 
 441 
 
 Problem 3. — 
 
 The cases which have been considered hitherto show perfect 
 dominance of one unit over another. This is not always the 
 case. It frequently happens that the first generation hybrid 
 is intermediate between the two parents, and in the second gen- 
 eration the heterozygote forms differ from either homozygous 
 form. Thus when large, round tomatoes are crossed with small, 
 plum-shaped ones, the Fi hybrid is intermediate between the 
 parents. If L represents largeness and (Z) small, plum-shaped, 
 then Fi hybrids (LI) will not be the same as (LL), but will be 
 distinctly different. The formulae previously given, 2", 3", etc., 
 will not hold in cases of incomplete dominance. This will be 
 more fully explained later. Large (L) x small, plum-shaped 
 (l) = LI, an intermediate type of fruit. 
 
 Fi gametes = L, I. 
 Fi self ed = 
 
 Pollen Grains 
 
 L I 
 
 Egg Cells 
 
 LL 
 
 LI 
 
 LI 
 
 11 
 
 Phenotypes = 1 LL; 2 LI; 1 II 
 Genotypes = 1 LL; 2 LI; 1 II. 
 
 Problem 4. — 
 Intermediate {LI) X Large, round {LL) 
 
442 
 
 Plant- Breeding 
 
 Pollen Grains 
 L L 
 
 Egg Cells 
 
 LL 
 
 LL 
 
 LI 
 
 LI 
 
 Phenotypes =2 LL] 2 LI 
 Genotypes = 2 LL ; 2 LI. 
 
 Problem 5. — 
 
 Tall, smooth (Th) X dwarf, Hairy (tH) = Tall, Hairy (TtHh) 
 
 Fi gametes = TH; Th; tH; th. 
 
 Fx self ed = 
 
 Pollen Grains 
 
 TH Th tH th 
 
 TH 
 
 '% Th 
 
 H 
 
 o 
 
 ItH 
 
 th 
 
 TT 
 HH 
 
 TT 
 Hh 
 
 Tt 
 HH 
 
 Tt 
 Hh 
 
 TT 
 Hh 
 
 TT 
 
 hh 
 
 Tt 
 .Hh. 
 
 Tt 
 hh 
 
 Tt 
 HH 
 
 Tt 
 Hh 
 
 tt 
 HH 
 
 tt 
 Hh 
 
 Tt 
 Hh 
 
 Tt 
 hh 
 
 tt 
 Hh 
 
 tt 
 hh 
 
' Appendix E 
 
 443 
 
 Phenotypes (2«) = 9 TH ; 3 Th; S tH ; 1 th. 
 Genotypes (3«) = 1 TTHH, 1 TThh, 1 UHH, 1 tthh, 2 TTHh 
 2 UHh, 2 7^^/i/i, 2 r^Fiy, and 4 7^^^/^. 
 
 Problem 6. — 
 
 Tall (Heter) i smooth (T^^/i) x dwarf, Hairy (tH). 
 Female gametes = Th, th. 
 Male gametes = tH. 
 
 Pollen Grains 
 tH 
 
 Egg Cells 
 
 Th 
 
 th 
 
 It will be seen that two types are produced the first year after 
 crossing instead of the one where pure parents are used. Segre- 
 gation takes place immediately in the female parent because of 
 its hybridity, and two kinds of gametes will be produced. 
 
 In order to get a comparison with the F. when pure parents 
 are crossed, it is necessary to self both types as follows : — 
 
 (a) TtHh produces gametes as follows, Th, Th, tH, th. These 
 are the same as in problem 5 and hence the resulting plants will 
 be: — 
 
 Phenotypes =9TH,S Th, 3 tH, 1 th. 
 
 Genotypes = 1 TTHH, 1 TThh, 1 ttHH, 1 tthh, 2 TTHh, 
 2 ttHh, 2 Tthh, 2 TtHH, and 4 TtHh. 
 
 (b) ttHh produces the following gametes: tH, th. 
 
 ^ "Heter " is used for short in place of heterozygote, similarly "homo " 
 is used for homozygote. 
 
444 
 
 Plant-Breeding 
 
 Pollen Grains 
 tH th 
 
 IH 
 
 Egg Cells 
 
 th 
 
 It 
 
 tt 
 Hh 
 
 tt 
 Hh 
 
 tt 
 hh 
 
 Phenotypes = ttHH, ithh. 
 Genotypes = tlHH, 2 UHh, 1 tthh. 
 
 Problem 7. — 
 
 Tall, large-round (TL) X dwarf, small plum-shaped (tl) = Tall 
 intermediate (TtLl). 
 
 Fi gametes = TL; Tl; IL; tl 
 
 Pollen Grains 
 TL Tl tL 
 
 tl 
 
 Egg Cells 
 
 TL 
 
 Tl 
 
 tL 
 
 tl 
 
 TTLL 
 
 TTLl 
 
 TILL 
 
 TtLl 
 
 TTLl 
 
 TTll 
 
 TtLl 
 
 Ttll 
 
 TILL 
 
 TtLl 
 
 ItLL 
 
 ttLl 
 
 TtLl 
 
 Ttll 
 
 ttLl 
 
 till 
 
 It must be remembered in this problem that we have incom- I 
 plete dominance in one allelomorphic pair, therefore the number 
 of visible types is different than in cases where both units exhibit 
 dominance. 
 
Appendix E 
 
 445 
 
 Phenotypes = 3 TTLL, 6 TTLl, 3 TTll, 1 ttLL, 2 ttLl, 1 ttll. 
 
 Genotypes = 1 TTLL, 1 TTll, 1 ^^LL, 1 ttll, 2 TTL/, 2 Ttll, 
 2 r^^/, 2 «L/, and 4 T^L/. 
 
 What visible types would be produced if incomplete dominance 
 occurred in both characters? 
 
 Problem 8. — 
 
 Self-fertilize-Tall, intermediate (TTLl). This is a pure tall, 
 hence all of its progeny will be tall. 
 
 Pollen Grains 
 TL Tl 
 
 Egg Cells 
 
 TL 
 
 Tl 
 
 TTLL 
 
 TTLl 
 
 TTLl 
 
 TTll 
 
 Phenotypes = 1 TTLL, 2 TTLl, 1 TTll. 
 Genotypes = 1 TTll, 2 TTLl, 1 TTll. 
 
 EXEECISE 17 
 
 Ear-to-Row Test with Corn 
 Field Practicum 
 
 Purpose. — To demonstrate to the student the method of 
 testing out the transmitting power of individual plants; to 
 show him how a breeding plot should be arranged for corn ; to 
 teach him how to harvest the corn and make notes on which 
 to base his selections. A practical demonstration of the method 
 of pure line selection. 
 
 Materials. — For each student a sack for holding ears, wired 
 tags and strings for tying sacks, and sheets for taking data. A 
 wooden rack with spikes for drying ears of corn. Grocery scales 
 for weighing the ears from each row. 
 
446 
 
 Plant-Breeding 
 
 Data Sheet for Corn Selection 
 (Ear-to-Row Method) 
 Mark Dent (+) ; mark Flint (F). 
 
 No. of row 
 Total no. of hills 
 Total no. of stalks 
 No. barren stalks 
 Total no. of ears 
 Total wt. of ears 
 No. mature ears 
 Wt. mature ears 
 No. immature ears 
 Wt. immature ears 
 Percentage mature ears 
 Percentage immature ears 
 
 Choose 10 of the best-looking ears from one row on which to 
 take the following data : — 
 
 Wt. of ears 
 Length of ears 
 Circumference ^ of ears 
 No. of rows per ear 
 Wt. of shelled corn 
 Wt. of cob 
 
 A field plot planted by the ear-to-row method, saving unused 
 half of each ear for comparison with its progeny. It should 
 contain two or more rows, as space permits, for each student. 
 Each row should contain 50 hills. The rows should be planted 
 
 ^ Circumference should be measured at a point about ^ of the distance 
 from the butt toward the tip. 
 
Appendix E 447 
 
 and cultivated under regular field conditions. Two buffer rows 
 should be planted completely around the plot. These should 
 be cut and discarded before the interior rows of the plot are 
 studied. Their purpose and use should be explained to the 
 class. 
 
 Program. — After the instructor has explained the purpose of 
 the practicum, and the manner of procedure for the afternoon, 
 the class may be taken to the field. Each student should have 
 one or two rows for himself. Students may be permitted to 
 work in pairs, if desirable. Careful and detailed notes should 
 be made on each row and recorded on data sheets provided for 
 that purpose. The corn may be taken back to the laboratory 
 for weighing. Statistics for the whole plot should then be 
 compiled, so that the individuality of different rows can be 
 compared. The student should select 10 of the best ears from 
 each of his rows and put them on the drying rack provided. 
 These ears are to be used later for a study in the laboratory. 
 
 EXEKCISE 18 
 
 Corn-judging 
 
 Students of plant-breeding should be trained to have a critical 
 judgment of agricultural and horticultural plants. Exercises 
 in comparative judging are the best way to attain this end. 
 Utility should be kept constantly in mind. 
 
 Details of corn judging will not be given here ; they are too 
 well known to need emphasis. For the East, both dent and 
 flint varieties should be used. The ears which are judged in 
 this exercise may be the ones the student himself has previously 
 harvested from the ear-to-row plot. The best ten ears should 
 be used for Exercise 19, which should always accompany exer- 
 cise 18. 
 
 Object. — To encourage critical judgment of corn and, by the 
 same means, of other crops. 
 
448 Plant-Breeding 
 
 Materials. — Ten ears of different races and types of corn to 
 each student ; tape, scales, charts, etc. 
 
 Each student should score a sample of flint corn according to 
 the following score card : — 
 
 New England Flint 
 
 Points 
 
 Maturity and seed condition 20 
 
 Uniformity (or regularity of single ears) 15 
 
 Kernels 15 
 
 Weight of ear 10 
 
 Length and proportion 10 
 
 Tips 5 
 
 Butts 10 
 
 Sulci (space between rows) 10 
 
 Color _5 
 
 Total 100 
 
 Exercise 19 
 
 Statistical Study of Ears of Corn 
 
 This should accompany or follow Exercise 18. 
 
 Object. — (a) To study critically and statistically the various 
 parts of ears of corn, (b) To work up these data by biometrical 
 methods, drawing curves, and ascertaining mean, standard 
 deviation, coefficient of variability, etc., for the various parts 
 of the ear. (c) To illustrate testing for germination. 
 
 Materials. — Each student should be given the same ears of 
 corn which he had for Exercise 18 ; tapes, scales, etc. 
 
 The following form should be filled in by each student : — 
 
 Note. — This should not be merely a mechanical process, but 
 the student should give each step very careful thought. These 
 tables are given to assist in organizing the student's method and 
 his thinking, but not to replace them. Do not study the method 
 but the plants. Consider carefully the significance of each step. 
 
 ■' A 
 
Appendix E 
 
 449 
 
 Study of Corn 
 Variety: Dent, flint, sweet, pop. (Underline.) 
 
 Where grown 
 
 (a) Length of ear in cm. 
 
 (b) Circumference of ear in cm. (^^ butt to 
 
 tip) 
 
 (c) Weight of ear 
 
 (d) Number of rows 
 
 (e) Circumference of cob (l buti to tip) 
 (/) Weight of shelled corn 
 
 (g) Weight of cob 
 (h) Percentage of shelled corn 
 (?■) Total number of kernels 
 (j) Average weight of kernel 
 (/c) Width of kernels in cm. (taken at ran- 
 dom) 
 (/) Compute average width 
 (m) Length of 50 kernels in cm. (taken at 
 
 random) 
 (n) Compute average length 
 
 Exercise 20 
 Study of Correlations of Characters in Corn 
 
 Use the same data as employed in Exercises 17 and 19. Make 
 correlation tables by accepted biometrical methods of such 
 characters as length and circumference ; length and number of 
 grains ; weight and number of grains ; length and weight ; etc. 
 Work out correlation coefficients. 
 
 Object. — To find out if certain characters are associated so 
 that a measurement of one will give an indication of the other. 
 
 Materials. — Data from Exercises 17 and 19 ; cross-section 
 paper. 
 
 2g 
 
450 Plant-Breeding 
 
 Exercise 21 
 
 Corn Selection — Laboratory Study 
 
 Purpose. — To give the student an understanding of the 
 qualities that constitute a good ear of corn ; to teach the bene- 
 fits and dangers of cross-pollination. 
 
 Material. — For each student : 1 tape measure ; 1 scalpel ; 
 1 hand lens; 10 ears of corn selected from a row in breeding 
 plot; samples of various types and colors of corn. These 
 should have been shelled and soaked in water for 24 hours pre- 
 vious to this laboratory period in order to render them easy to 
 dissect. Cobs of corn bearing mixed kernels to illustrate zenia ; 
 scales ; data sheets ; germinator. 
 
 Program. — The instructor should first explain the purpose 
 of the practicum and outline the afternoon's work. He should 
 explain the structure of a kernel of corn, calling attention to 
 the difference between the various types of corn and the ad- 
 vantage of certain shaped kernels. Fecundation should be 
 thoroughly discussed, and its effect in causing zenia. Illustrate 
 with diagrams, charts, and specimens. 
 
 Discuss the dangers of mixing varieties by close planting. 
 The danger of close fertilization and the stimulus resulting from 
 cross-fertilization should also be discussed. 
 
 The advantage and manner of making germination tests 
 should be explained. 
 
 The student should remove 6 kernels from each ear and place 
 them in the germinator to be examined later, at which time he 
 should record the percentage of germination. 
 
 Questions and problems concerning zenia printed on the 
 outline sheet should be answered in a written report. 
 
 Laboratory Directions for Corn Study 
 
 1. Complete taking data on 10 ears of corn. Compare with 
 remnant half of parent ear. From your data select the best 
 3 ears for breeding purposes. 
 
Appendix E 451 
 
 2. Remove 6 kernels from each ear for germination test, 
 along a spiral line from 1 inch of butt to near the top, revolving 
 the ear twice. 
 
 3. Draw a typical kernel. 
 {a) Face aspect. 
 
 (6) Side aspect. 
 
 4. Make and draw longisections through the middle line 
 both ways of the kernel, showing the following structures : — 
 
 (a) Mass of starch or endosperm. 
 
 (6) Crescent-shaped body, the germ or scutellum near the 
 
 smaller end of the grain, 
 (c) Remaining portion of embryo lying in the depression 
 
 between scutellum and seed-coat. 
 {d) In sample kernels where does color lie, in the pericarp, 
 
 aleurone layer, or endosperm ? 
 (e) Note relative amount and position of starchy and 
 
 horny endosperm in 
 
 1. flint kernel, 
 
 2. dent kernel, 
 
 3. pop-corn kernel, 
 
 4. sweet-corn kernel. 
 
 5. How would an i^i kernel of corn appear in a cross between 
 
 white sugar X yellow flint ? 
 
 yellow flint X white sugar ? 
 
 white flint X purple flint ? 
 
 purple flint X white flint ? 
 
 red sweet X purple flint ? 
 
 purple sweet X red flint ? 
 
 Dominant Characters. — 
 
 Colored over white. 
 Yellow over non-yellow. 
 
452 Plant-Breeding 
 
 Red pericarps may conceal purple aleurone. 
 Purple in aleurone over red in aleurone. 
 Starchy over non-starchy. 
 
 Exercise 22 
 
 A Study in Potato Selection 
 
 Purpose. — 1. To teach the essential characteristics of a good 
 tuber and a good tuber-line. 
 
 2. To teach the principles of selection by a study of variability 
 in pure tuber-lines. 
 
 3. To demonstrate the tuber-unit method of potato selection. 
 
 4. To study variability by means of biometrical data, and 
 the interpretation of constants and curves derived therefrom. 
 
 5. To fix in mind how the hills of different weights look. 
 
 6. To calculate the theoretical weights per acre when given 
 certain weights per hill. 
 
 First Exercise 
 
 Materials. — Printed directions and sheets for recording data. 
 Manila paper bags, size 12, for containing product of each hill. 
 Cloth bags for carrying a number of these small bags when filled. 
 
 A breeding plot planted by the 4-hill tuber-unit method, 
 that is, each four hills having the same progeny-number should 
 come from the same mother tuber, and they should be planted 
 and staked so that the progeny of each hill and unit can be 
 distinguished. 
 
 This plot should be planted in good soil and given excellent 
 care throughout the season as its usefulness to the class will 
 depend entirely on the condition of the crop at harvest time. 
 The rows and tuber-units should be labeled carefully and accu- 
 rately in a convenient way, so that they may be made an object 
 lesson in record-keeping. 
 
Appendix E 
 
 453 
 
 a 
 o 
 
 <J 
 
 O 
 pin 
 
 « 
 O 
 
 H 
 
 a 
 
 Eh 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 - 
 
 
 
 
 
 
 
 
 
 
 
 ""'] 
 
 
 
 
 
 6 
 
 •<* 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ' 
 
 CO 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 09 
 
 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 = 
 
 -= 
 
 
 
 
 1 
 i 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 6 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 eo 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 j 
 
 
 1 
 
 
 
 
 
 1-1 
 
 
 
 
 
 i 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 _ 
 
 
 Unit 
 No. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 .2 
 
 c 
 
 o 
 S3 
 
 s 
 
 O 
 
 o 
 
 
 
 ce 
 
 c 
 
 c 
 a 
 
 3 
 O 
 ii 
 
 o 
 '> 
 
 c 
 
 >> 
 
 -d 
 
 c3 
 (0 
 Xi 
 
 03 
 
 a: 
 
 a 
 
 w 
 
 g 
 
 a 
 6 
 
 a 
 
 15 
 a 
 
 u 
 
 Ci 
 
 3 
 
 <V 
 
 Si 
 
 £ 
 
 "o 
 
 6 
 'Z. 
 
 aj 
 
 a 
 
 a: 
 
 03 
 
 s 
 
 2 
 
 a 
 
 IS 
 _c 
 
 t- 
 
 o 
 
 'c 
 3 
 
 a 
 
 o3 
 
 x: 
 
 IS 
 c 
 
 _^ 
 5c 
 
 a 
 
 ^5 
 '*^ 
 -5 
 
 G 
 
 o 
 
 o 
 
 S 
 
 "5 
 
 en 
 
 c 
 .S 
 
 O 
 
 o 
 o 
 
 1 
 re 
 
 Ih 
 
 3 
 X 
 
 u 
 
 T 
 
 13 
 
 is 
 c 
 
 1 
 
 s 
 
 1 
 
 5 
 
 3 
 
 'a 
 
 ca 
 
 d ' 
 o 
 
 u 
 
 _d 
 
 o 
 i-< 
 
 X! 
 
 <a 
 >, 
 W 
 
 r. 
 ?; 
 
 o 
 
 H 
 O 
 
454 Plant-Breeding 
 
 Enough hills should be provided so that each student may 
 have for himself several tuber-units. Five to ten units to each 
 student will be enough if the student is required to observe and 
 compare a large number as they lie in the field. The complete 
 data for the whole field should be compiled by the class as a 
 whole, and distributed to each student for a comparative study. 
 
 Program. — Just prior to the exercise, each hill should be 
 dug carefully and the tubers replaced where they grew, but 
 exposed to sight, especial care being taken that no labels be mis- 
 placed nor lost. The class may then be taken to the field. 
 The instructor should explain the purpose of the exercise, the 
 principles of pure-line selection as illustrated here, and the 
 method of planting a potato-breeding plot by the tuber-unit 
 method. He should give careful instructions for the after- 
 noon's work. The class may then examine and compare the 
 units as they lie exposed in the rows. The instructor should 
 point out such differences as occur. A certain number of tuber- 
 units should then be assigned to each student, and he should 
 be required to take data from these units, as directed on the 
 printed sheets provided. Such data-taking as involves the use 
 of apparatus will necessarily have to be postponed until the 
 following period, when it can be done in the laboratory. 
 
 Each student should carefully preserve his tubers properly 
 labeled for the next laboratory exercise. 
 
 Second Exercise 
 
 Materials. — Data taken in Exercise 1 ; the tubers collected 
 in Exercise 1; scales; paper plates (6 for each student). 
 
 Program. — The instructor should first outline the afternoon's 
 work. He should explain the qualities that constitute a good 
 tuber ; also how that ideal form, size, and color differ in various 
 varieties. He should explain a score-card. 
 
 The students may now proceed to finish taking the data on 
 the tubers that they collected at the previous laboratory period. 
 
Appendix E 455 
 
 When the data are complete, they can all be summed up for 
 each tuber-unit and the units compared. 
 
 Each student should next make out a score-card embodying 
 the points of his ideal unit, and score his units by it. The 
 instructor may now give out a score-card by which the whole 
 class may score their units alike. 
 
 Make up hills weighing i 1, H, 2, 3, and 4 pounds, and 
 draw them natural size. 
 
 Compute the yield per acre from the above weights per hill, 
 assuming the hills to be planted in rows 3 feet apart and 18 
 inches apart in the rows. One bushel weighs 60 pounds. 
 
 Directions for Report on Potato Selection 
 
 1. Distribute the data for the number of tubers per hill into 
 
 classes. 
 
 2. Determine the mode, modal coefficient, mean, standard 
 deviation, coefficient of variability, and their probable errors for 
 the number of tubers per hill. 
 
 3. Determine the mode, mean, standard deviation, and co- 
 efficient of variability for the number of marketable tubers per 
 hill, weight of tubers per hill, and weight of marketable tubers 
 
 per hill. 
 
 4. Draw Quetelet curve, showing frequency distributions for 
 number of tubers per hill, number of marketable tubers per 
 hill, weight of tubers per hill, and weight of marketable tubers 
 
 per hill. 
 
 5. Distribute into classes the data for the number of tubers 
 per four-hill-unit, number of marketable tubers per four-hill- 
 unit, weight of tubers per four-hill-unit, and weight of market- 
 able tubers per four-hill-unit. 
 
 6. Draw Quetelet curves, showing frequency distributions for 
 number of tubers per four-hill-unit, number of marketable tubers 
 per four-hill-unit, weight of tubers per four-hill-unit, and weight 
 of marketable tubers per four-hill-unit. 
 
456 Plant-Breeding 
 
 7. Make a transmission curve from the data on the accom- 
 panying sheet. Which progeny units would you select for breed- 
 ing purposes? How do you account for the apparent discrep- 
 ancies which occur, such as the cases where the offspring give a 
 very different yield from their parents ? 
 
 8. Taking into account the number of tubers per hill, weight 
 of tubers per hill, number of marketable tubers per hill, and 
 weight of marketable tubers per hill, select the best 25 four- 
 hill-units. Tabulate these, giving their progeny number and 
 data for number of tubers per four-hill-unit, number of market- 
 able tubers per four-hill-unit, weight of tubers per four-hill-unit, 
 and weight of marketable tubers per four-hill-unit. 
 
 9. Give briefly your reasons for selecting the above four-hill- 
 units. Draw Galton curves for these 25 four-hill-units, showing 
 variation in the number of marketable tubers per four-hill-unit 
 and weight of marketable tubers per four-hill-unit. 
 
 10. Determine the possible yield of marketable tubers from 
 an acre of the highest and lowest yielding of the 150 four-hill- 
 units, also for the highest and lowest and for the average of the 
 25 selected units. 
 
 11. Give a short summary of results as shown by the con- 
 stants and curves and their bearing on your final selection. 
 
 12. Give direction for starting a potato breeding-plot.^ 
 
 Potato Data for making a Transmission Curve 
 
 The following data have been obtained by the method out- 
 lined above. They represent the weights in grams of parent 
 hills and the average weight of their corresponding progeny. 
 The parent hills have been listed in the order of their weight 
 from lowest to highest (forming a Galton curve). 
 
 1 Reference : H. J. Webber, "Plant Breeding for Farmers." New 
 York Agr. Exp. Sta., Cornell University, Ithaca, N. Y., Bull. 251 : 
 162-171, 1908. 
 
Appendix E 
 
 457 
 
 Nos. 
 
 Parents 
 
 Progeny 
 
 Nos. 
 
 Parents 
 
 Progeny 
 
 1 
 
 1077 
 
 1463 
 
 26 
 
 1588 
 
 1454 
 
 2 
 
 1106 
 
 1080 
 
 27 
 
 1588 
 
 1615 
 
 3 
 
 1106 
 
 1240 
 
 28 
 
 1616 
 
 1175 
 
 4 
 
 1361 
 
 1881 
 
 29 
 
 1616 
 
 1575 
 
 5 
 
 1361 
 
 837 
 
 30 
 
 1644 
 
 1775 
 
 6 
 
 1361 
 
 1136 
 
 31 
 
 1644 
 
 1807 
 
 7 
 
 1361 
 
 1536 
 
 32 
 
 1644 
 
 1917 
 
 8 
 
 1361 
 
 1605 
 
 33 
 
 1758 
 
 2250 
 
 9 
 
 1361 
 
 1660 
 
 34 
 
 1814 
 
 1660 
 
 10 
 
 1361 
 
 1800 
 
 35 
 
 1871 
 
 1275 
 
 11 
 
 1361 
 
 1895 
 
 36 
 
 1871 
 
 1.80 
 
 12 
 
 1389 
 
 1972 
 
 37 
 
 1871 
 
 1665 
 
 13 
 
 1418 
 
 1696 
 
 38 
 
 1871 
 
 1688 
 
 14 
 
 1418 
 
 1904 
 
 39 
 
 1871 
 
 1750 
 
 15 
 
 1471 
 
 1440 
 
 ' 40 
 
 1874 
 
 1555 
 
 16 
 
 1474 
 
 1086 
 
 41 
 
 1874 
 
 1861 
 
 17 
 
 1474 
 
 1215 
 
 42 
 
 1874 
 
 1889 
 
 18 
 
 1474 
 
 1480 
 
 43 
 
 1928 
 
 1440 
 
 19 
 
 1531 
 
 711 
 
 44 
 
 1928 
 
 1481 
 
 20 
 
 1531 
 
 1294 
 
 45 
 
 1928 
 
 1620 
 
 21 
 
 1531 
 
 1574 
 
 46 
 
 1928 
 
 1982 
 
 22 
 
 1531 
 
 1725 
 
 47 
 
 1984 
 
 1575 
 
 23 
 
 1531 
 
 1755 
 
 48 
 
 2041 
 
 1236 
 
 24 
 
 1588 
 
 1320 
 
 49 
 
 2041 
 
 1880 
 
 25 
 
 1588 
 
 1365 
 
 50 
 
 2098 
 
 2365 
 
 Exercise 23 
 
 Study of Citrus Hybrids 
 
 Object. — (a) To study the possibility of obtaining valuable 
 kinds of citrus fruits by means of hybridization. (6) To study 
 the structure of citrus hybrids as compared with their parents. 
 (c) To study the economic value of these hybrids. 
 
 Materials. — Obtain from some of the extreme southern ex- 
 
458 Plant-Breeding 
 
 periment stations, or from nurserymen or growers, samples of 
 citrus hybrids, such as citranges, tangelos, and the like, and 
 samples of Citrus trifoliata. Purchase oranges, lemons, grape- 
 fruits, and tangerines from the fruit stores. Provide also for 
 each student, or group of students, a glass, spoon, sugar, and 
 water. 
 
 Compare the hybrids with their parents, with special reference 
 to the following points : — 
 
 (a) Fruit — size, shape, color, amount of juice, quality of 
 juice, condition of segments, etc. 
 
 (b) Trees (if branches or photos are available) — size, shape, 
 branching, kind of leaves, etc. 
 
 (c) General — length of season, resistance to cold, etc. 
 Squeeze out the juice from several fruits, add sugar and water, 
 
 and test the adaptability for beverage and other economic 
 purposes. 
 
 Exercise 24 
 
 Study of the Results of the Plant-to-Roio Tests of Wheat, Oats, 
 Cabbage, Onions, or any Crop where Data are Available 
 
 Exercise 25 
 
 Studies of Origin of Varieties — Corn, Wheat, Apples, Plums, 
 
 Grapes, Etc. 
 
 Literature study of the history of varieties. Methods em- 
 ployed to originate varieties should be carefully noted. 
 
 Exercise 26 
 
 Field Trip to Experimental Grounds 
 
 Most experiment stations have plant-breeding experiments 
 under way, and if a fall inspection of the plats would be in- 
 structive to students, they should be taken on such a trip early 
 
Appendix E 
 
 459 
 
 in the fall and required to make careful notes, to be written up 
 later in the form of a report. 
 
 Exercise 27 
 
 Working Plans for Practical Breeding Experiments 
 
 Object. — To familiarize the student with field methods of 
 breeding plants. 
 
 Outline for Timothy Breeding 
 
 First Year. — Select 10 heads of timothy and grow 50 plants 
 from each. 
 
 100 ft. 
 
 10 rows. 
 
 40 ft. 
 
 500 plants in 10 rows 100 ft. 
 long. Plants 2 ft. apart in 
 the rows. 
 
 Second Year. — Cultivate. 
 
 Third Year. — Choose several of the best plants from the best 
 two rows, and the one best plant from each of the other rows — 
 14 or 15 in all. With the seed from these, plant a ''test plat," 
 and plow up the original seedling plat. 
 
 60 ft. 
 
 60 ft. 
 
 15 rows. 
 Rows 4 ft. apart — plants 2 ft. 
 apart in the rows. 
 
 Fourth Year. — Cultivate the test plat. 
 
 Fifth Year. — Choose 2 or 3 or more of the best rows and save 
 separately the seed from each. Plow up the remainder of the 
 rows and plant to vegetables. 
 
460 
 
 Plant-Breeding 
 
 60 ft. 
 
 60 ft. 
 
 4 selected rows. 
 Plant I acre multiplication 
 plat from each select row. 
 Seed them broadcast at the 
 rate of 16 pounds per acre. 
 Remainder of the plat utilized 
 for vegetables. 
 
 Sixth Year. — Use seed from multiplication plats to plant a 
 fairly large-sized field. Continue selection of seedlings, if de- 
 sired, from select rows according to above scheme. 
 
 Outline for Selective Breeding of Timothy 
 
 First Year. 1 . Manner of procuring seed from starting a selec- 
 tion. — When timothy is ripening, go over a field and choose a 
 number of good ripe seed-heads from tall, robust culms which 
 appear to come from good plants. Also look for exceptionally 
 good plants from along the roadsides and fences, and whenever 
 they are found, preserve good heads for seed. Choose good seed- 
 heads from at least 10 or 12 of these good plants. Thresh the 
 seed from these heads, keeping the seeds from each plant sepa- 
 rate, and sow them immediately. No time should be lost. 
 
 2. Planting the seed. — The seed should be planted early in 
 August. Take small boxes about 2 feet long by 1^ feet wide 
 and 4 inches deep ; fill them with good soil from some locality 
 where there has been no timothy and thus where there is little 
 likelihood of timothy seed being in the soil. Pack the soil down 
 slightly in the box and smooth off the top, removing all lumps. 
 Plant the seed in the boxes in short rows, placing the rows about 
 2 to 2| inches apart. In planting the seed open shallow furrows 
 in the soil and sow the seed by hand, arranging so that the seed 
 will be only very lightly covered. Sow the seed as thinly as 
 possible in the rows and thin out later so that the plants will 
 
Appendix E 461 
 
 stand about 1 inch apart. Sow enough seed in rows of sufficient 
 length, so that when properly thinned there will remain about 
 300 plants. If thinned to 1 inch apart, this will require rows 
 aggregating 25 feet long. Be careful to keep the seeds from 
 each head or plant separate from one another and plainly labeled. 
 
 After the seed is sown, water the seed boxes carefully, using a 
 fine spray, in order to prevent washing the seed out. A good 
 method is to cover the soil with an open mesh cloth, such as 
 cheese cloth, and sprinkle the water on this until the soil is 
 thoroughly wet. Then place the seed box in the shade in a moist 
 place, such as the north side of the house. It is a good practice 
 to keep the boxes covered with paper or glass, until the young 
 plants begin to appear. It is important to keep them moist at 
 all times. When the young plants are well up, thin them to 
 about one inch apart in the rows, leaving the strongest plants. 
 
 The plants should be kept in boxes until about the 20th of 
 September, when they should be planted in the field. About a 
 week before transplanting they should be gradually exposed to 
 the full sunlight in order to harden them up. At this time each 
 plant should have 2 or 3 leaves, 3 or 4 inches long. 
 
 3. Transplanting into the field. — Choose a place in the field 
 where the plants may remain for at least two years without 
 being disturbed. Set the plants two feet apart in rows that 
 are four feet apart. By this method the greater part of the 
 cultivation can be done with a horse cultivator. In transplant- 
 ing the seedlings from the boxes, a time must be chosen shortly 
 after a rain, when the soil is well moistened. The plants should 
 be set out about the 20th of September, if possible, so that they 
 may become well rooted before winter comes on. It may be 
 necessary to hoe them before winter, but this is not likely if the 
 land is well prepared before planting. 
 
 If 10 heads were originally chosen and 50 plants are grown 
 from each head, there should be 10 rows 100 feet long, which 
 would occupy a piece of land 40 X 100 feet. 
 
462 Plant-Breeding 
 
 4. Second Year. Cultivating the seedlings. — In the spring 
 the seedlings must be cleaned out very eariy before they are 
 hidden by other grasses. The cultivation and hoeing must be 
 done at sufficient intervals to keep the ground free from weeds 
 and in good condition. These plants will produce a few culms 
 each the first summer, which should be cut as soon as they have 
 bloomed, in order that the strength shall go into the general 
 growth. Do not attempt to select the best plants the first 
 season. A safe judgment cannot be rendered until the second 
 season. 
 
 5. Third Year. Selecting the best plants. — When the plants 
 reach the stage for cutting in the second summer, that is, when 
 they are in full bloom, the final selection of the best individuals 
 can be made. Examine each row critically in order to determine 
 which head or heads have given the best progeny as a whole. 
 If any one or two rows are markedly superior to the others, 
 choose several of the best plants in each of these rows. Also, 
 choose the one best plant in each of the other rows. 
 
 6. Testing the selected plarits as clonal varieties. — In order to 
 make a further test of the 14 or 15 best plants, choose another 
 uniform plat of fairly good soil between the 5th and 20th of Septem- 
 ber and prepare for planting an area of slightly over 60 feet square. 
 This plat should be located at some distance from any other 
 timothy, preferably 200 to 300 feet. Dig up each selected 
 plant ; divide it into slips or clons and plant this new plat with 
 them as before, in rows 4 feet apart. Plant one row with slips 
 from each selected plant, placing the plants 2 feet apart in the 
 rows. Transplant about 30 slips from each of the selected 
 plants, so there will be a single row from each about 60 feet long. 
 This plat may be designated as "the clonal test plat." 
 
 As soon as this clonal test plat is planted from the selected 
 plants, the seedling test plat may be plowed up and used for 
 other purposes. 
 
 7. Fourth Year. Cultivation of "clonal test plat.'' — The 
 
Appendix E 463 
 
 clonal test plat should be cultivated and hoed sufficiently to 
 keep the weeds down and to allow the full development of the 
 
 plants. 
 
 8. Fifth Year. Selecting the best clonal rows. — When the 
 plants are well headed and are about to begin blooming, the 
 final examination can be made. Go over each row carefully, 
 and examine it with reference to yield and desirability of type, 
 and select the superior row or rows. It will be best to retain 
 at least 2 or 3 of the best rows ; or more, if there is but little 
 difference in them. Good early-maturing and late-maturing 
 rows should be retained if both are present in the test plat. 
 When this selection has been made, cut the crop on the dis- 
 carded rows immediately so that the pollen from these dis- 
 carded rows will not contaminate, by cross-fertilization, the seed 
 which is being developed in the selected rows. At any con- 
 venient time these discarded rows may be dug up and the space 
 filled with new plants grown from cuttings of the chosen plants. 
 By a little care and cultivation these select rows can be retained 
 5 or 6 years as a source of supply of seed of a superior kind. As 
 the rows of selected types begin to run out, or become impure 
 by ordinary timothy plants around them, or by other grasses 
 growing in the clumps, other or more extended clonal rows 
 could be planted from them. 
 
 9. The multiplication plat. — The seed from the select rows 
 of the clonal test plat should be sown in the early fall, sometimes 
 before the 15th of September in broadcast plats, as large as the 
 amount of seed obtained will permit. Sow these plats, at the 
 rate of about 16 pounds to the acre. There should be enough 
 seed from each row to plant about | acre. 
 
 Sixth Year. — The seed from these broadcast multiplication 
 plats can be utilized the next year to plant a fairly large field 
 which, if desired, may be harvested for seed to plant still larger 
 areas.' These plats may be utilized for seed for several years 
 before they run out. 
 
464 Plant- Breeding 
 
 10. Continuation of the selection. — If the farmer has in mind 
 the continuous selection of his seed, with the view of selling his 
 seed as improved seed, he should plant small samples of seed 
 from each of the selected rows in the clonal test plat. Their 
 treatment and subsequent selection should be a repetition of the 
 original scheme outlined above. ^ 
 
 General Directions and Questions for Report on Corn 
 
 Breeding 
 
 Suppose you buy a farm of 200 acres on which are growing 
 the following crops : potatoes, corn, timothy, and one of the 
 three cereals, wheat, oats, or barley. There are 50 acres of 
 pasture and woodland. You wish to continue growing these 
 same crops, and at the same time to improve them by a scheme 
 of selective breeding. Plan the arrangement of fields and breed- 
 ing plots for the first 6 years, using the following directions. 
 Timothy breeding plots should be 200 to 300 feet from any 
 other timothy. Corn plots 1200 feet from any other corn. 
 (Why?) Each year should be planned separately, using 
 maps and diagrams, but should be included in a definite 
 six-year scheme. Observe proper rotations for crops where 
 desirable. 
 
 1 . In selecting plants for breeding purposes, why do we choose 
 individual plants? 
 
 2. In breeding work, why do we test out the selected individ- 
 uals by breeding each one separately? 
 
 3. Why is it most satisfactory for the breeder to work with 
 plants that are self-fertilized? 
 
 4. Why do we plant border rows around breeding plots? 
 
 5. Why do we detassel alternate halves of adjacent rows in 
 corn breeding plots? 
 
 1 For more detailed directions for timothy breeding, see Webber, H. J., 
 " Production of New and Improved Varieties of Timothy." Cornell 
 University Agr. Exp. Sta. Bull. 313, 1912. 
 
Appendix E 465 
 
 6. Why should corn breeding plots be isolated? What is a 
 safe distance? 
 
 7. Why should timothy breeding plots be isolated ? What is a 
 safe distance? 
 
 8. Is it necessary to isolate breeding plots of the small cereals? 
 
 9. In selection work, what three rules should the breeder 
 follow who understands the principles of pure-line breeding ? 
 
 Scheme for Potato Breeding Plots ^ 
 First Year. — Choose 500 good tubers. Plant them in a 
 breeding plot by the tuber-unit method. Rows should be 3 
 feet apart, hills l\ feet apart in the rows. At harvest time 
 choose the best 50 units. Save the best 10 from each of these 
 units for planting a breeding plot the next year. 
 
 Second Year. — Plant the selected tubers in a breeding plot 
 as in the first year. At harvest time discard all poor units. 
 Select the best 50 units. Save 10 of the best tubers from each 
 of these units for planting the third year's breeding plot. Use 
 the rest for planting a field crop the next year. 
 
 Third Year. — Use these 500 tubers to plant a breeding plot. 
 Plant your field crop with the remaining choice tubers. How 
 
 1 For details of the following schemes read Cornell University Exp. 
 Sta. Bull. 251, "Plant Breeding for Farmers," 1908 ; also Bull. 313, "The 
 Production and Improvement of New Varieties of Timothy." 
 
 For cotton breeding, see Webber, H. J., "Improvement of Cotton by 
 Seed Selection," U. S. Department of Agr. Yearbook, 1902, pp. 365- 
 386. 
 
 16.5 ft. = 1 rod ; 160.0 sq. rd. = 1 acre. 
 
 Plant: Corn, 8-12 qt. per acre; Oats, 2-3 bu. per acre; Wheat, 
 2-3 bu. per acre ; Barley, 2-3 bu. per acre ; Potatoes, 12-15 bu. per acre; 
 Timothy, 6-8 qt. or 16 lb. per acre. 
 
 Standard weights: Corn, 1 bu. = 70 lb. shelled, or 56 lb. on cob; 
 Oats, 1 bu. = 32 lb. ; Wheat, 1 bu. = 60 lb. ; Barley, 1 bu. = 48 lb. ; 
 Potatoes, 1 bu. = 60 lb. ; Timothy, 1 bu. = 45 lb. 
 
 Average yield per acre in United States for 1002: Corn, 20.2 bu. ; Wheat, 
 15.9 bu. ; Oats, 37.4 bu. ; Barley, 50.4 bu. ; Potatoes, 113.4 bu. 
 2h 
 
466 Plant-Breedings 
 
 large a field can be planted if the yield has been at the rate of 
 200 bushels per acre? 
 
 Fourth and Subsequent Years. — Continue this same scheme, 
 constantly discarding the poor units and selecting the best for 
 breeding. 
 
 Estimate how large your breeding plot should be in order to 
 supply a 5-acre field with seed in the third year, supposing the 
 yield from your selected units to be the same as the average 
 yield given by the 25 best selected units in your former report^ 
 i.e. about 370 bu. per acre. 
 
 Scheme for Corn Breeding Plots 
 
 All corn breeding and increase plots should be at least 1200 
 feet from any other corn. Why? 
 
 First Year. — Select from the field 100 ears. From these 
 choose the best 50 for planting a breeding plot the next year. 
 
 Second Year. — From these 50 ears, plant a breeding plot 
 by the ear-to-row method. Rows should be 4 feet apart, hills 
 3 feet apart in the row, each row to contain 100 hills. Surround 
 the breeding plot with 2 or more border rows planted with seed 
 from the unused select ears. Why? Detassel alternate halves 
 of adjacent rows. Why? Select from the best 10 or 12 rows 
 50 to 100 of the best ears, choosing the best 50 for the next 
 year's breeding plot. Save the seed from the other best-yielding 
 rows for an increase plot, or the general field. 
 
 Third Year. — ■ Plant your breeding plot as before, with the 
 best selected 50 ears. With the other selected ears plant an 
 increase plot or general field. Select as before the best 50 ears 
 from the breeding plot for the next year's breeding plot, saving 
 the remainder for a new increase plot. Save ears from this 
 year's increase plot for planting next year's field. 
 
 Fourth and Subsequent Years. — As before, plant your breed- 
 ing plot, increase plot, and field, using a continuous and pro- 
 gressive scheme of selection. 
 
Appendix E 467 
 
 Scheme for Wheat Breeding Plots 
 
 First Year. — Choose 100 fine heads for starting your improve- 
 ment work. 
 
 Second Year. — • Plant seed from these select plants in short 
 rows b^' the plant-to-row method. Space the rows 1 foot apart. 
 Select a few rows, say twenty, to furnish seed for a breeding plot 
 in the third year. 
 
 Third Year. — Plant seed from each of these select rows in a 
 breeding plot. Do not mix the seed from different rows. Plant 
 as many 17 foot rows in each plot as the amount of seed saved 
 will permit. This is at the rate of 1| bushels per acre. The 
 rows should be 1 foot apart. 
 
 Fourth Year. — Find average yield of progeny rows that came 
 from the selected rows of the third year. Select several of the 
 best strains which may yield about 24 bu. per acre. With this 
 seed plant increase plots from each kind of seed. Save seed from 
 2 or 3 of the best jdelding plots for more extensive trials in the 
 5th year. The rest of the seed can be used for planting a field. 
 Make new selections of heads in the fields and repeat the whole 
 program as before. There may be many more valuable types 
 in the fields that can thus be isolated. 
 
 Fifth Year. — Test out your select strains and choose one or 
 two of the best for increase plots and for planting your field. 
 Plant the field this year with seed from last year's increase plot 
 and from the test rows. 
 
 Scheme for Oat or Barley Breeding Plots 
 
 The principles of selection and methods of breeding these 
 cereals are the same as for wheat. 
 
INDEX 
 
 Absence factors, 192. 
 
 Acquired characters, 17. 
 
 Adami, M., 145. 
 
 Adams fund, 314. 
 
 Adam's laburnum, 142. 
 
 Adaptation, 7, 37, 106. 
 
 Alfalfa, 313. 
 
 Alkali resistance, 313. 
 
 Allelomorph, 325. 
 
 Allen, Dr., 314, 315. 
 
 American Seed Trade Association, 
 309. 
 
 Anemone coronaria, 57, 58. 
 
 Animals, breeding, 217. 
 
 Anthers, 276. 
 
 Anthocyanin, 186. 
 
 Antirrhinum {see snapdragon). 
 
 Apples, 212, 255, 295 ; hybrid, 235. 
 
 Arthur, 228, 239. 
 
 Artificial selection, 37. 
 
 Asexual propagation and hybridi- 
 zation, 125. 
 
 Asparagus, 313. 
 
 Associations, plant-breeding, 300. 
 
 Atavism, 211, 231. 
 
 Average deviation, 47. 
 
 Barker, E. E., 394. 
 
 Bartel, T. C, 254. 
 
 Barteldes, 264. 
 
 Bateson, 155, 183, 187, 192. 
 
 Beans, 260 ; Emerson's experiments 
 
 with, 189. 
 Bibliography, 335. 
 Biometry, 41, 325. 
 Biotypes, conception of, 19. 
 Blackberries, hybrid, 136. 
 
 Blackberry, 253. 
 
 Books, plant-breeding, 328. 
 
 Braun, Alexander, 20. 
 
 "Breaking the type," 22, 219. 
 
 Breeding periodicals, 332. 
 
 Breeding plants, rules for, 222. 
 
 Broughton, Mr., 91. 
 
 Browne, Dr. Thomas, 56. 
 
 Bruant, 237. 
 
 Brunella vulgaris, 80. 
 
 Brussels sprouts, 243. 
 
 Budd, Professor, 258. 
 
 Buds, methods of emasculation, 
 291. 
 
 Bud-selection, 39, 242. 
 
 Bud-sports, 210, 241. 
 
 Bud-variation, 11, 29. 
 
 Bud-varieties, 242. 
 
 Burbank, 112, 321. 
 
 Burpee, 264. 
 
 Burr, "Field and Garden Vege- 
 tables," 295. 
 
 Cabbage, evolution of, 267 ; savoy, 
 244 ; shapes, 245 ; wild, 240. 
 
 Camerarius, 110. 
 
 Canadian Seed Growers' Associa- 
 tion, 304. 
 
 Cannas, 237, 265. 
 
 Capsella Heegeri, 80. 
 
 Car ex, little natural crossing in, 
 103. 
 
 Carnation, 179. 
 
 Carri^re, 58, 223, 239, 296. 
 
 Castle, 180. 
 
 Cauliflower, 248. 
 
 Cavalier, wheat, origin of, 91. 
 
 469 
 
470 
 
 Index 
 
 Cereals, disease-resistant, 313. 
 
 Change, of seed, 28 ; of stock, results 
 from, 105, 107. 
 
 Chelidonium, 55, 56. 
 
 Cherries, hybrid, 235. 
 
 Chimaera, 146, 148. 
 
 Chromoplasts, 186. 
 
 Chromosome, 325. 
 
 Chrysanthemum, 251, 252, 253, 
 256, 257, 258, 259, 262, 263, 264, 
 267, 268, 269; carinatmn, 226; 
 indicum., 250 ; inodorum plenis- 
 simum, 87 ; morifolium, 249 ; sege- 
 tum, 86, 89 ; segetum plenum, 86, 
 88. 
 
 Citranges, 132, 312. 
 
 Citrus trifoliata, 312. 
 
 Climate, as factor in variation. 25, 
 26 ; man's control over, 27. 
 
 Coefficient of heredity, 152 ; of va- 
 riability, 49. 
 
 Collard, 242. 
 
 Color, mendelian inheritance of, 185. 
 
 Commercial breeding agencies, 308. 
 
 Compositae, 223. 
 
 Compositous flowers, 279. 
 
 Corn breeding, 216. 
 
 Correns, 155. 
 
 Cotton, 213, 214, 312, 313. 
 
 Council of grain exchanges, 310. 
 
 County agent, the, 310. 
 
 Cowpeas, disease resistance, 220. 
 
 Cross, function of, 101, 230. 
 
 Crosses, characteristics of, 123. 
 
 Crossing, a means not an end, 232 ; 
 and change of seed, 103 ; effects 
 on the species, 97 ; from stand- 
 point of plant improvement, 108 ; 
 how to overcome antipathy to, 
 121; limits of, 97. 98, 99; process 
 of, 281 ; refusal result of natural 
 selection, 100 ; vigor as result of, 
 112, 115. 
 
 Crossing animals, 216. 
 
 Crossing plants, philosophy of, 92. 
 
 Crozy, 237. 
 
 Cucumber pollinations, 141. 
 Cultivation, philosophy of, 24. 
 Cupid sweet pea, 77. 
 Curled kale, 241. 
 Cytisus Adami, 142, 145. 
 
 Darwin, 20, 34, 52, 59, 73, 105, 107, 
 
 111, 113, 209, 240, 242, 244, 296, 
 
 307. 
 Dates, 313. 
 
 Davenport, C. B., 183. 
 Davenport, E., 149. 
 Davis, Bradley Moore, 318. 
 Deviation, average, 47 ; standard, 48. 
 de Vries, Hugo, 52, 53, 59, 62, 63, 
 
 72, 73, 74, 76, 79, 155. 
 Dewberry, 253. 
 Dihybridism, 171. 
 Dioecious flowers, 278. 
 Disease resistance, 219, 220, 313. 
 Dominance, 165 ; incomplete, 179. 
 Dominant characters, 325. 
 Dorsey, M. J., 424. 
 Double flowers, experiments in 
 
 production of, 86 ; history of 
 
 appearance of, 56. 
 Downing' s "Fruits and Fruit 
 
 Trees," 295. 
 Draba, 73. 
 
 Drought-resistant plants, 313. 
 Duggar, B. M., 318. 
 Duplex, 325. 
 Durum wheat, 313. 
 
 Ear-to-row, 308. 
 East, E. M., 318. 
 Eckford, 237. 
 Egg-plant, 128, 141. 
 Egyptian cotton, 313. 
 Elderberry, 217, 218. 
 Elementary species, 63, 80. 
 Emasculation, 282. 
 Emerson, 189. 
 
 Environment as a cause of varia- 
 tion, 16, 216. 
 Epistatic, 325. 
 
Index 
 
 471 
 
 Error, probable, 50. 
 Evening-primrose {see (Enotbera). 
 Evening-primroses, laws of muta- 
 bility of, 72. 
 
 Factor hypothesis, 326. 
 
 Fairchild, Thomas, 110. 
 
 Fertilization, 270. 
 
 Flowers, structure of, 270. 
 
 Fluctuating variations and muta- 
 tions, 54. 
 
 Focke, 232. 
 
 Food supply, as cause of variation, 
 20, 21 ; of different branches, 23. 
 
 Frequency curve, 42. 
 
 Fultz wheat, origin of, 91. 
 
 Galton curve, 326. 
 Gametes, 168, 326. 
 Garden varieties, origin of, 18. 
 V Gartner, C. F., 110, 111. 
 Genetics, 326. 
 Genotype, 326. 
 
 Germ-plasm, action of environ- 
 ment upon, 17. 
 Gibb, 258. 
 
 Gideon, Peter M., 233. 
 . Gladiolus, 237. 
 Glossary, 325. 
 Gmelin, J. G., 110. 
 Goff, 228, 229. 
 
 Gold Coin wheat, origin of, 91. 
 Gourds, 140. 
 Graft-hybrids, 142. 
 Grain exchanges, council, 310. 
 Grapes, 212, 235 ; hybrid, 133. 
 Gray, Asa, 35. 
 Green, Ira W., 91. 
 
 Hallock & Son, 247. 
 Harper, R. A., 318. 
 Head-to-row, 308. 
 Helianthemum, 73. 
 Henderson, 264. 
 
 Heredity, 149; coefficient of, 152.; 
 studied collectively, 149. 
 
 Heterozygote, 326. 
 
 History of mutation, 55. 
 
 Homozygote, 326. 
 
 Hopetown wheat, origin of, 91. 
 
 Hurst, 192. 
 
 Husk-tomato pollination, 141. 
 
 Hybridization and asexual prop- 
 agation, 125. 
 
 Hybridized, what plants can be, 
 111. 
 
 Hybrids, 326 ; history of, 1 10 ; defini- 
 tion of, 108 ; influence of sex on, 
 138 ; production of, 101 ; vari- 
 ability of, 122. 
 
 Hyper-chimsera, 148. 
 
 Hypostatic, 326. 
 
 Ideal, 220. 
 
 Illinois Seed Corn Breeders' Associa- 
 tion, 303. 
 
 Immature seeds, 228. 
 
 Implements of pollination, 292. 
 
 Improvement of plants, systematic, 
 295. 
 
 In-breeding, 127. 
 
 Indeterminate varieties, 209. 
 
 Individuality, fact of, 2. 
 
 Individual selection, 308. 
 
 Inhibitor, 180. 
 
 Inter-crossing, swamping effects of, 
 98. 
 
 Ipomoeas, 229. 
 
 Kinshu rice, 313. 
 
 Knight, Thomas Andrew, 110. 
 
 Kohl-rabi, 248. 
 
 Kolreuter, J. G., 110. 
 
 Kumerle, J. W., 265. 
 
 Laboratory exercises, 394. 
 
 Lamar k, 59. 
 
 Lemoine, 237. 
 
 Lettuce, improvement in, 221. 
 
 Linaria vulgaris {see toad-flax). 
 
 Linaria vulgaris peloria, 84. 
 
 Linnaeus, 110, 138. 
 
472 
 
 Index 
 
 Locke, 180. 
 Lupines, 231. 
 
 Maize, 224. 
 
 Mass selection, 307. 
 
 Mean, 45; use of, 46. 
 
 Measurement of, 41. 
 
 Mendel, 155. 
 
 Mendelian inheritance of color, 185. 
 
 Mendelian ratio, 179. 
 
 Mendelism, application to plant- 
 breeding, 202, 225 ; in wheat, 194 ; 
 limits of, in the production of 
 new varieties, 204 ; of tomatoes, 
 203 ; summarized, 200. 
 
 Mendel's experiments, 156. 
 
 Mendel's law, explanation of, 158. 
 
 Methodical selection, 307. 
 
 Minnesota Field Crop Growers' As- 
 sociation, 303. 
 
 Mirdbilis, 112. 
 
 Modal coefficient, 45. 
 
 Mode, 44. 
 
 Monoecious flowers, 277. 
 
 Monotypic genera, 224. 
 
 Moore, Jacob, 235. 
 
 Morning-glories, Darwin's experi- 
 ments with, 114. 
 
 Morse & Company, 77. 
 
 Morus multicaulis, 299. 
 
 Munson, Professor, 117, 235. 
 
 Munting, Abraham, 57. 
 
 Mutability, laws of, with evening- 
 primroses, 72. 
 
 Mutants, how produced in the 
 garden, 71. 
 
 Mutation, history of, 55 ; first use 
 of word, 56. 
 
 Mutations, 40, 52, 326 ; economic 
 significance of, 90 ; and fluctua- 
 tions, 54 ; can they be produced 
 artificially ? 200 ; examples of, 76 ; 
 experimental study of origin of, 
 84 ; frequency of occurrence of, 79 ; 
 mutations resulting from men- 
 delian segregation and recombi- 
 
 nation, 193 ; mutations which 
 mendelize are constant, 193. 
 
 Natal and post-natal variations, 18. 
 
 Natural hybrids, rarity of, 102. 
 
 Natural selection, 34, 93 ; as cause 
 of variation, 14. 
 
 Navel oranges, 313. 
 
 Nectarines, 241. 
 
 New York Plant Breeders' Associa- 
 tion, 304. 
 
 Nicotiana pollinations, 142. 
 
 Nilsson, Professor, 304. 
 
 Nulliplex, 326. 
 
 Oats, Swedish select, 313. 
 
 (Encthera albida, 63, 67, 71, 74 
 analytical table of seedlings 
 68-69 ; brevistylis, 63, 64, 71, 74 
 de Vries' experiments with, 59 
 elliptica, 64, 68, 71, 74; gigas 
 
 63, 65, 66, 71, 74; loevifolia, 63 
 
 64, 71, 74 ; Lamarkiana, 59, 60 
 61, 64, 71, 74; lata, 64, 67, 71 
 74 ; muricata, 60 ; nanella, 60 
 63, 64, 71, 74; oblonga, 63, 67 
 71, 74 ; rubrinervis, 63, 65, 71 
 74; scintillans, 64, 68, 71, 74 
 variations in stature of, 53. 
 
 Ohio Plant Breeders' Association, 
 
 304. 
 Olives, drought-resistant, 313. 
 Ononis repens, 80. 
 Organs, essential, 274. 
 Orton, 313. 
 
 Palmer, Asa, 264. 
 
 Peaches, 212. 
 
 Peas, Mendel's experiments with, 
 
 157. 
 Pedigree culture, 308. 
 Pelargoniums, 237. 
 Peloric toad-flax, 79. 
 Pepino pollination, 141. 
 Pepper pollinations, 141. 
 Peppers, 222. 
 
Index 
 
 473 
 
 Perennial plants, 241. 
 
 Periclinal chimaera, 148. 
 
 Periodicals, breeding, 332. 
 
 Phenotype, 327. 
 
 Physalis, 104. 
 
 Pineapple hybrids, variation of, 123. 
 
 Pistils, 271. 
 
 Plant-breeding : associations, state, 
 300; books, 328; by selection, 
 218; defined, 212; forward 
 movement in, 294 ; instruction, 
 321 ; laboratory, U. S. Dept. 
 Agri., 311; projects, 315; use 
 of term, 296. 
 
 Plant improvement a serious busi- 
 ness, 298. 
 
 Plant introductions, division of, 
 312. 
 
 Plants, differences compared with 
 animals, 10. 
 
 Plant-to-row, 308. 
 
 Plateation, 397 ; defined, 327. 
 
 Plums, 212, 294. 
 
 Pollen, 280. 
 
 Pollen storage, 289. 
 
 Pollination, 270 ; process of cross, 
 281, 289; uncertainties of, 140. 
 
 Poncirus trifoliata, 312. 
 
 Population, 41. 
 
 Potatoes, 241. 
 
 Presence-and-absence hypothesis, 
 181. 
 
 Pride Butte wheat, origin of, 91. 
 
 Probabilities, theorem of, 169. 
 
 Probable error, 50. 
 
 Punnett, 183, 184. 
 
 Quetelet curve, 44. 
 
 Radishes, division of, 239. 
 Raspberries, hybrid, 235. 
 Recessive characters, 327. 
 Recessiveness, 165. 
 Regel, cited, 295. 
 
 Reproduction, difference between 
 plants and animals, 10. 
 
 Retrograde varieties, 65. 
 Rogers' grape hybrids, 235. 
 Roguing, 251. 
 Russian apples, 212, 258, 295. 
 
 Savoy cabbage, 244. 
 
 Score card, use of, 236. 
 
 Sea Island cotton, 312. 
 
 Sectional chimaera, 148. 
 
 Seed, change of, 28. 
 
 Segregation, 327. 
 
 Selection, accumulative, 209 ; ar- 
 tificial, 37, 243 ; individual, 308 ; 
 mass, 307 ; methodical, 307 ; 
 plant-breeding by, 218. 
 
 Sex, a factor in variation, 15, 215; 
 influence on hybrids, 138 ; origin 
 and function of, 95. 
 
 Shirley poppy, 76. 
 
 Shull, 190, 318.- 
 
 Simplex, 327. 
 
 Snapdragon, 83. 
 
 Snyder blackberry, 255. 
 
 Solanaceous plants, 222. 
 
 Solarium darwinianum, 147; Gdrt- 
 nerianum, 147 ; graft-hybrids, 146 ; 
 kolreuterianum, 147 ; proteus, 147 ; 
 tubingense, 146. 
 
 Somatic, 327. 
 
 Species, definition, 8. 
 
 Species-formation, 8. 
 
 Spencer, 105. 
 
 Spillman, 180, 194. 
 
 Sport, 39. 
 
 Sprenger, 55. 
 
 Squares, method of, 169. 
 
 Squashes, 128, 140. 
 
 Stamens, 271. 
 
 State experiment stations, 310. 
 
 State plant-breeding associations, 
 302. 
 
 Statistical methods (see biometry). 
 
 St. Hilaire, Geoffroy, 58. 
 
 Stout, A. B., 318. 
 
 Struggle for life, a cause of varia- 
 tion, 30. 
 
474 
 
 Index 
 
 Sturtevant, 228. 
 
 Sugar beets, variation in amount 
 
 of sugar in, 54. 
 Swede turnip, 248. 
 Swedish Seed Association, 304. 
 Swedish select oats, 313. 
 Swingle, Walter, 312. 
 Systematic improvements of plants, 
 
 295. 
 
 Tangelo, 133, 312. 
 Teas' Weeping mulberry, 233. 
 Teosinte, 137. 
 Thomson, 149. 
 Thymus vulgaris, 80. 
 Timothy, variability of, 3. 
 Toad-flax, 79, 81, 82. 
 Tobacco pollinations, 142. 
 Tomato, 215, 222, 228, 244, 246; 
 ignotum, 246; pollinations, 141. 
 Trihybrid, 177. 
 Tschermak, 155, 188. 
 Tuber-unit, 308. 
 Type, 43. 
 
 Unit-characters, 9, 154. 
 United States Dept. Agri., 310. 
 Uses, breeding for specific, 224. 
 
 Variability, biometrical expression 
 of, 43, 47; coefficient of, 49. 
 
 Variation, action of natural selec- 
 tion upon, 14 ; and adaptation, 7 ; 
 causes of, 13, 30, 94 ; caused by 
 environment ; caused by sex 
 differences, 15 ; in climate, 25 ; 
 choice and fixation of, 34 : de 
 Vries' classification, 53 ; fluctuat- 
 ing, 54 ; in food supply, 20 ; 
 
 measurement of, 41 ; natal and 
 post-natal, 18. 
 
 Varieties, "coming true," 210, 211 ; 
 how they originate, 209 ; inde- 
 terminate, 209 ; non-uniformity 
 of, 19 ; outright production of, 
 by crossing, 118 ; retrograde, 63 ; 
 spontaneous appearance in wild 
 state, 79. 
 
 Variety, what is it ? 35. 
 
 Verlot, 244, 296. 
 
 Vigor as result of crossing. 112, 115. 
 
 Vilmorin, 226, 230, 231, 269. 
 
 Vitis, 122. 
 
 Vries, de, Hugo (.sec de Vries). 
 
 Walker, Ernest, 243. 
 Wallace, 105, 123. 
 Watermelons, wilt-resistant, 219. 
 Wealthy apple, 233. 
 Webber, 133, 156, 312. 
 Weismann, 16, 17. 
 Wheat, Durum, 313. 
 Wheatland fife wheat, origin of, 91. 
 Wheat-rye hybrid, 136. 
 Wier, D. B., 233. 
 Wild cabbage, 240. 
 Wilks, Rev. W., 76. 
 Willis, 117. 
 
 Wilson, strawberry, 248. 
 Wilt-resistant watermelons, 219. 
 Winkler, Professor, 146, 148. 
 Wisconsin Agricultural Improve- 
 ment Association, 300. 
 
 Xanthein, 187. 
 Xenia, 327. 
 
 Zygote, 327. 
 
The following pages 
 
 contain advertisements of books by the same 
 
 author or on kindred subjects 
 
CYCLOPEDIA OF 
 AMERICAN AGRICULTURE 
 
 Edited by L. H. BAILEY 
 
 With 100 full-page plates and more than 2,000 illustrations in the 
 text; four volumes; the set, $20.00 net; half morocco, $32.00 net. 
 
 Vol. I — Farms Vol. Ill — Animals 
 
 Vol. II— Crops Vol. IV— The Farm and the Community 
 
 This is unquestionably the most important agricultural cyclopedic 
 work published in this country. The leading experts in the United 
 States and Canada, both investigators and practical farmers, con- 
 tribute to its chapters, which are arranged not alphabetically, but 
 topically, each subject being treated in its various aspects by men 
 especially familiar with it. It contains advice for the city man who 
 is seeking a home in the country, as well as for the professional 
 farmer. The book is strictly new and up-to-date in its methods and 
 advice, thoroughly readable, and a standard work of reference. It 
 is profusely illustrated, about one-third of the total space being 
 assigned to illustrations — all original. 
 
 "Indispensable to pubhc and reference libraries . . . readily 
 comprehensible to any person of average education." — The Nation. 
 
 "The completest existing thesaurus of up-to-date facts and 
 opinions on modern agricultural methods. It is safe to say that many 
 years must pass before it can be surpassed in comprehensiveness, 
 accuracy, practical value, and mechanical excellence. It ought to 
 be in every Ubrary in the country." — Record-Herald, Chicago. 
 
 THE MACMILLAN COMPANY 
 
 PUBLISHERS 64-66 Fifth Avenue NEW YORK 
 
'''■The Bible and Britannica of the Garden-folk'' — The Nation 
 
 The Standard 
 Cyclopedia of Horticulture 
 
 Edited by L. H. BAILEY 
 
 With the assistance of over 500 collaborators 
 
 New edition, entirely rewritten and enlarged with many features, with 24 plates 
 
 in color, 96 full-page half-tones and over 4,000 text illustrations. 
 
 To be complete in six volumes. 
 
 Each volume: Cloth, $6.00; Leather $10.00. 
 Sold only in sets by subscription. 
 
 Two opinions of Volume I of the new Cyclopedia: 
 
 "No one who knows anything at all about the hterature of garden- 
 ing needs to be told that the Cyclopedia is unique. It is the Bible 
 and Britannica of the garden-folk, amateur and professional alike. 
 And the remarkable thing is that, while it is fundamentaly a work 
 of reference, it also contains limitless quantities of good reading of 
 the sort dear to the heart of the garden enthusiast." — The Nation. 
 
 "It is no exaggeration to state that Bailey's new work is the best 
 cyclopedia obtainable for all who are connected, either remotely or 
 intimately, as amateurs or professionals, with horticultural pursuits. 
 It is the best for the student of botany who is investigating the subject 
 in a purely scientific way; best for the commercial grower who Ukes 
 to be well informed on matters in general and his own trade in par- 
 ticular, and best for the other sort of commercial grower, who does 
 not bother himseK particularly about hunting for any information 
 except such as will give him immediate help in producing a better 
 crop." — The Florist's Review. 
 
 THE MACMILLAN COMPANY 
 
 PUBLISHERS 64-66 Fifth Avenue NEW YORK 
 
 f 
 
THE RURAL MANUALS 
 
 Edited by L. H. BAILEY 
 MANUAL OF FRUIT INSECTS 
 
 By MARK VERNON SLINGERLAND and 
 CYRUS R. CROSBY 
 
 Of the New York State College of Agriculture, at Cornell University 
 
 Illustrated, 12mo, 503 pages, $2.00 net; postage extra. 
 
 A MANUAL OF WEEDS 
 
 By ADA E. GEORGIA 
 
 Assistant in the Farm Course, New York State College of Agriculture, 
 
 Cornell University 
 
 With 385 Illustrations by F. SCHUYLER MATHEWS 
 
 Illustrated, cloth, Vlmo, 593 pages, index, S2.00 net: postage extra. 
 
 MANUAL OF FARM ANIMALS 
 
 A Practical Guide to the Choosing, Breeding and Keep of 
 Horses, Cattle, Sheep and Swine 
 
 By MERRITT W. HARPER 
 
 Assistant Professor of Animal Husbandry in the New York State 
 College of Agriculture, at Cornell University 
 
 Illustrated, V2mo, 545 pages, index, $2.00 net; postage extra. 
 "A book deserving of close study as well as being handy for lefeience, 
 and should be in the possession of every farmer interested in stock." — ■ 
 Rural World. 
 
 MANUAL OF GARDENING 
 
 A Practical Guide to the Making of Home Grounds and the 
 Growing of Flowers, Fruits and Vegetables for Home Use 
 By L. H. BAILEY 
 
 Illustrated, cloth, 12mo, 544 pages, $2.00 net; postage extra. 
 
 This new work is a combination and revision of the main parts of 
 
 two other books by the same author, "Garden-Making" and "Practical 
 
 Garden Book," together with much new material and the result of the 
 
 experience of ten added years. 
 
 THE FARM AND GARDEN RULE BOOK 
 
 By L. H. BAILEY 
 
 Revised and enlarged edition — Illustrated, cloth, 12mo, $2.00 net. 
 
 It is essentially a small cyclopedia of ready rules and references 
 
 packed full from cover to cover of condensed, meaty information and 
 
 precepts on almost every leading subject connected with country life. 
 
 THE MACMILLAN COMPANY 
 
 PUBLISHERS 64-66 Fifth Avenue NEW YORK 
 
The Rural Outlook Set 
 
 By L. H. BAILEY 
 
 Four Volumes. Each, cloth, 12ino. Uniform binding, attractively boxed, 
 $5.00 net per set; carriage extra. Each volume also sold separately. 
 
 In this set are included three of Professor Bailey's most popular books 
 as well as a hitherto unpublished one, — "The Country-Life Movement." 
 The long and persistent demand for a uniform edition of these little 
 classics is answered with the publication of this attractive series. 
 
 The Country Life Movement 
 
 Cloth, 12mo, 220 pages, $1.25 net; postage extra 
 
 This hitherto unpublished volume deals with the present movement 
 for the redirection of rural civilization, discussing the real country-life 
 problem as distinguished from the city problem, known as the back-to-the- 
 land movement. 
 
 The Outlook to Nature (New and Revised Edition) 
 
 Cloth, l2mo, 195 pages, $1.25 net; postage extra 
 
 In this alive and bracing book, full of suggestions and encouragement, 
 Professor Bailey argues the importance of contact with nature, a sympa- 
 thetic attitude toward which "means greater efficiency, hopefulness, 
 and repose." 
 
 The State and the Farmer (New Edition) 
 
 Cloth, 12mo, $1.25 net; postage extra 
 It is the relation of the farmer to the government that Professor 
 Bailey here discusses in its varying aspects. He deals specifically with 
 the change in agricultural methods, in the shifting of the geographical 
 centers of farming in the United States, and in the growth of agricultural 
 institutions. 
 
 The Nature Study Idea (New Edition) 
 
 Cloth, 12mo, $1.25 net; j^ostage extra 
 "It would be well," the critic of The Tribune Farmer once wrote, "if 
 'The Nature Study Idea' were in the hands of every person who favors 
 nature study in the public schools, of every one who is opposed to it, and 
 most important, of every one who teaches it or thinks he does." It has 
 been Professor Bailey's purpose to interpret the new school movement 
 to put the young into relation and sympathy with nature, — a purpose 
 which he has admirably accomplished. 
 
 THE MACMILLAN COMPANY 
 
 PUBLISHERS 64-66 Fifth Avenue NEW YORK 
 
RURAL TEXT- BOOK SERIES 
 
 Edited by L. H. BAILEY 
 Each volume illustrated. Cloth, 12mo. 
 
 While the RURAL SCIENCE SERIES is designed primarily for 
 popular reading and for general use, this related new series is designed 
 for classroom work and for special use in consultation and reference. 
 The RURAL TEXT-BOOK SERIES is planned to cover eventually 
 the entire range of pubUc school and college texts. 
 
 DUGGAR, B. M. 
 
 Physiology of Plant Production $1 bU net 
 
 DuGGAR, John Frederick 
 
 Southern Field Crops I 7iy net 
 
 Gay, C. Warren i -r^ * 
 
 Principles and Practice of Judging Live-Stock . 1 ^0 net 
 
 Harper, M. W. ^ ^ -, ^r^ , 
 
 Animal Husbandry for Schools 1 ^0 net 
 
 Hitchcock, A. S. i en / 
 
 Grasses i c>V net 
 
 Livingston, George 
 
 Field Crop Production I 4i) net 
 
 Lyon, T. L. and Fippin, E. O. . ^. , 
 
 Principles of Soil Management 1 7d net 
 
 Mann, A. R. 
 
 Beginnings in Agriculture io net 
 
 Montgomery, G. F. , ^.r^ . 
 
 Corn Crops , • • • ' 1 60 ne« 
 
 Piper, Charles V. , __ , 
 
 Forage Plants and Their Culture I 7b net 
 
 Warren, G. F. i m / 
 
 Elements of Agriculture i lu net 
 
 Warren, G. F. ^ -^ 
 
 Farm Management i io net 
 
 Wheeler, H. J. i ah / 
 
 Manures and Fertilizers i ou net 
 
 WiDTSoE, John A. ^ _^ 
 
 Principles of Irrigation Practice l ^o net 
 
 THE MACMILLAN COMPANY 
 
 Publishers 64-66 Fifth Avenue New York 
 
RURAL SCIENCE SERIES 
 
 Edited by L. H. BAILEY 
 Each volume illustrated. Cloth, 12mo, 
 
 A series 6f practical books for farmers and gardeners, sold as a set or separately. 
 Each one is the work of a competent specialist, and is suitable for consultation alike 
 by the amateur or professional tiller of the soil, the scientist or the student. Illus- 
 trations of marked beauty are freely used, and the books are clearly printed and 
 well bound. 
 
 ON SELECTION OF LAND, ETC. 
 
 Isaac P. Roberts' The Farmstead $1 50 net 
 
 T. F. Hunt's How to Choose a Farm \ 7b net 
 
 E. S. Cheyney and J. P. Wentling's The Farm Woodlot . . . I 5Q net 
 Glenn W. Herrick's Insects Injurious to the Household ... 1 75 net 
 
 ON TILLAGE, ETC. 
 
 F. H. King's The Soil 1 50 net 
 
 Isaac P. Roberts' The Fertility of the Land 1 50 net 
 
 F. H. King's Irrigation and Drainage 1 50 net 
 
 Edward B. Voorhees' Fertilizers \ 25 net 
 
 Edward B. Voorhees' Forage Crops \ bO net 
 
 J. A. Widtsoe's Dry Farming 1 50 net 
 
 L. H. Bailey's Principles of Agriculture 1 25 net 
 
 S. M. Tracy's Forage Crops for the South 1 50 net 
 
 ON PLANT DISEASES, ETC. 
 
 E. C. Lodeman's The Spraying of Plants 1 25 net 
 
 ON GARDEN-MAKING 
 
 L. H. Bailey's Garden-Making 1 50 net 
 
 L. H. Bailey's Vegetable-Gardening 1 50 net 
 
 L. H. Bailey's Forcing Book 1 25 net 
 
 L. H. Bailey's Plant Breeding , . . (New edition preparing) 
 
 ON FRUIT-GROWING, ETC. 
 
 L. H. Bailey's Nursery Book 1 50 net 
 
 L. H. Bailey's Fruit-Growing (New Edition) I bO net 
 
 L. H. Bailey's The Pruning Book I bO net 
 
 F. W. Card's Bush Fruits 1 50 net 
 
 W. Paddock & O. B. Whipple's Fruit-Growing in Arid Regions . 1 50 net 
 
 ON THE CARE OF LIVE-STOCK 
 
 Nelson S. Mayo's The Diseases of Animals \ bQ net 
 
 W. H. Jordan's The Feeding of Animals 1 50 net 
 
 I. P. Roberts' The Horse I 2b net 
 
 M. W. Harper's Breaking and Training of Horses 1 75 net 
 
 George C. Watson's Farm Poultry. New edition \ bO net 
 
 John A. Craig's Sheep Farming 1 50 net 
 
 ON DAIRY WORK, FARM CHEMISTRY, ETC. 
 
 Henry H. Wing's Milk and Its Products. New edition . . . . \ bO net 
 
 J. G. Lipman's Bacteria and Country IJfe 1 50 net 
 
 ON ECONOMICS AND ORGANIZATION 
 
 William A. McKeever's Farm Boys and Girls 1 50 net 
 
 I. P. Roberts' The Farmer's Business Handbook 1 25 net 
 
 George T. Fairchild's Rural Wealth and Welfare 1 25 net 
 
 H. N. Ogden's Rural Hygiene \ bQ net 
 
 J. Green's Law for the American Farmer 1 50 net 
 
 G. H. Powell's Cooperation in Agriculture 1 50 nei 
 
 THE MACMILLAN COMPANY 
 
 PUBLISHERS 64-66 Fifth Avenue NEW YORK 
 
\.. 
 
LIBRARY OF CONGRESS 
 
 oDDmaaa^ES 
 
 ,i<l']v:f il