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Geobos Hinslow, M. A., F. L. S., F.Q.S. With 88 nioBtratiomi. THE INTERNATIONAL SCIENTIFIC SERIES THE ORIGIN OF FLORAL STRUCTURES THROUGH INSECT AND OTHEK AGENCIES BY THE REV. GEORGE gENSLOW, M. A., P. L. S., F. G. S. PBOFESSOR OP BOTANY, QUEEN^S COLLEGE, AND LXCTDBJCR TO ST. BARTHOLOKEW^S HOSPITAL MEDICAL SCHOOL, LONDON AUTHOR OF "EVOLUTION AND BELIOION,^^ "CHRISTIAN BELIEFS BECONBIDBBED/' " BOTANY FOB CHILDBEN," " FLOBAL DISSECTIONS," ETC. WITH EIOBTY-EIGHT ILLUSTRATIONS NEW YORK D. APPLETON AND COMPANY 1888 1-3 r^.TV ' ii, 6S-3 PREFACE. The belief that we must look mainly to the environment as furnishing the influences which induce plants to vary- in response to them — whereby adaptive morphological (including anatomical) structures are brought into exist- ence — appears to be reviving. To illustrate the progress of this belief, I will give a few cases. In 1795, Geoffroy Saint Hilaire "seems to have relied chiefly on the conditions of life, or the ' monde ambiant,' as the cause of change." * In 1801, Lamarck "attributed something to the direct action of the physical conditions of life " as the means of modification, " something to the crossing of already existing forms, and much to use and disuse," In 1831, Mr. Patrick Matthew (who, like Dr. W. C. Wells in 1818, anticipated Mr. Darwin in the theory of "natural selection") "seems to have attributed much influence to the direct action of the conditions of life." • I quote from Mr. Darwin's " Historical Sketch " in his Origin of Species, 6tb ed., 1878. VI PREFACE. In 1844, the " Vestiges of Creation " appeared. The author suggests that " impulses '' were imparted to the forms of life, on the one hand advancing them, and on the other hand tending to modify organic structures in accordance with external circumstances ; the effects thus produced by the conditions of life being gradual. In 1852, Mr. Herbert Spencer " attributed the modifi- cations [of species] to the change of circumstances." In 1859, "The Origin of Species" appeared. Mr. Darwin did not at first seem to lay so much stress as his predecessors upon the action of the environment as a cause, for he says: "It is curious how largely my grandfather. Dr. Erasmus Darwin, anticipated the views and erroneous grounds of opinion of Lamarck." Again, in speaking of the constancy of some varieties, he says, "Such considerations incline me to lay less weight on the direct action of the surrounding conditions, than on a tendency to vary, due to causes of which we are quite ignorant." * He had, however, previously said, " Changed conditions of life are of the highest importance in causing variability. ... It is not probable that vari- ability is an inherent and necessary contingent under all circumstances." t With regard to my own opinion, having been early and greatly interested in Paley's "Natural Theology," as well as the "Vestiges" when Mr. Darwin's work • Or. of 8p., p. 107. t ^«i'. P- 31- See also Desc. of Man, u., p. 388. PEEFACE. V;i appeared, the great difficulties I felt in accepting natural selection as any real origin of species lay, first, in the seeming impossibility of the histological minutiae of the organs in adaptation having been selected together; and, secondly, in the idea that all those wonderful and "purposeful" structures which Paley thought could only have been " designed," could be the ultimate result of any number of accidental and appa- rently at first "purposeless" variations. In a broad sense natural selection seemed obviously true ; for Geology had revealed the fact that the world had been peopled over and over again by old forms dying out and new forms coming in ; so that although it might account for the extinction of the former, it did not seem to me capable to account for the origin of the latter. I, there- fore, still looked to the environment as afibrding a better clue to the source of variations.* In 1869, when watching a large humble-bee hanging on to the dependent stamens of Epilobium, angusti- folium, the idea first occurred to me that insects them- selves might be the real cause of many peculiarities in the structure of flowers. The thought passed through my mind that the way the stamens hung down might perhaps have become an hereditary effect from the repeatedly applied weight of the bees. In 1877, I advanced, this idea as a speculation • See Letter to Nature, vol. v., p. 123. VUl PREFACE. ■when suggesting the origin of nectaries and irregu- larities of flowers in my paper on " Self-fertilisation of Flowers." * In 1880, Mr. A. R. Wallace reviewed Dr. Aug. Weis- mann's " Studies in the Theory of Descent." t In this work the author says : " According to my view, trans- mutation by purely internal causes is not to be enter- tained. . . . The action of external inciting causes is alone able to produce modifications." Mr. Wallace adds that he had "arrived at almost exactly similar con- clusions." In 1881, when reviewing Paul Janet's work on "Final Causes,"*[: I took occasion to remark that "I regarded the environment as by far the most important "cause" of variations, in that it influences the organ- ism, which, by its inherent but latent power to vary, responds to the external stimulus, and then varies accordingly." In 1881, appeared the first really systematic treatise that I know of, by Dr. C Semper, § which dealt with the origin of variations in animals as being referable to the environment. In 1884, Dr. A de Bary's " Comparative Anatomy of the Vegetative Organs of the Phanerogams and Ferns," * TroTis. Lin. 8oc., 2nd ser., Bot., vol. i., p. 317. t Natwre, xxiL, p. 141. % Modem Review, IflSl, p. 53. § The Natwal Conditione of Existence as they affect Animals," Intern. Sci. Ser., toI. xxxi. PREFACE. IX was published in English. In the Introduction, the author writes as if it were a perfectly well understood thing that species have arisen by adaptations to the iufluences of the environment.* In 1886, Mr. Herbert Spencer contributed two articles on " The Factors of Organic Evolution " to the Nineteenth Ceniv/ry.^ In these he showed, from many passages in Mr. Darwin's works, especially "Animals and Plants under Domestication " and in his later volumes, that he became much more favourably inclined to the belief that the effects of the environment were accumulative, and that in the course of some generations the variations set up tended to cease and become fixed. Mr. Spencer par- ticularly notes the change of view, as illustrated by the expression " little doubt " being replaced by " no doubt " in the following sentence: "I think there can be no doubt that use in our domestic animals has strengthened and enlarged certain parts, and disuse diminished them ; and that such modifications are inherited." J It may be added that in " The Cross and Self Fertilisation of Flowers" (1876), and in "Forms of Flowers" (1877), Mr. Darwin makes many observations upon the effects of the external conditions upon plants as influencing and modifying them in various ways. It is curious to note that the three influences upon which Lfimarck laid * See, e.g., p. 25. t See p. 570 and p. 749. X "tJse" and "disuse" in animals corresponds to what I have called " hypertrophy " and " atrophy " in plants, in this work. X PEEFACE. emphasis are just those which Mr. Darwin himself latterly, though often indirectly perhaps, laid stress upon in his experiments, viz. crossing, use and disuse, and the physical conditions of life. In 1886, also appeared an article in Nature, entitled, " Plants considered in Relation to their Environment." It was not signed, but the author alludes to the external conditions as bringing about all sorts of changes in the vegetative system. He stops short of discussing floral structures. In 1886, Dr. Vines' " Physiology of Plants " appeared. After discussing various views and theories of reproduc- tion, he observes, that " variability was first induced as the response of the organism to changes in the conditions of life." * . . . We conclude, then, that the production of varieties is the result of the influence of the conditions of life, t -In the last page of his work. Dr. Vines calls attention to Naegeli's view as foUows : " Naegeli suggests, and his suggestion is worthy of serious consideration, that there is an inherent tendency to a higher organisation, so that each succeeding generation represents an advance, ... as in cases of what is termed saltatory evolution." Thus, * Page 676. Dr. Vines here uses almost identically the same words as myself in 1881. I hare just found that Mr. St. G. Mivart said much the same in 1870, Genestg of Species, p. 269. See also O. Schmidt's Doctrine of Descent and Darwinism, p. 175. t Page 679. PREFACE. XI while Mr. Darwin seems at last to have tacitly accepted Lamarck's ideas, at least to a considerable extent, we have here a return in 1887 to the views of the author of the " Vestiges " of 1884. 1888. I have attempted in the present work to return to 1795, and to revive the " Monde ambiant " of Geoffroy Saint Hilaire, as the primal cause of change. My object is to endeavour to refer every part of the structures of flowers to some one or more definite causes arising from the environment taken in its widest sense. To some extent the attempt must be regarded as speculative ; and, therefore, any deductive or db priori reasonings met with must be considered by the reader as being suggestive only. CONTENTS CHAPTER PAOE I. GEHXUMi PbCNCIFLEB ... ... ... ... 1 II. The Pbinciple of Ndmbee ... ... ... 7 III. The Pbinoiplb of NxnHBBE — Continued ... ... 25 IV. The Pkinciplb of Aeeangement ... ... 39 V. The PBOfciPLE of Cohesion ... ... ... 48 VL The Pbinoiplb or Cohesion— Contt»»«d ... 54 VIL The Pbinciple of Cohesion— ConWnued ... ... 62 VIII. The Pbinoiplb of Adhesion ... ... ... 78 IX. The Cause of Unions ... ... ... ... 84 X. The Eeceptacular Tube ... ... ... 89 XI. The Fobms of Flobal Obsans ... ... ... lOl XII. The Obigin of " Ztgomoephism " ... ... H6 Xin. The Effects of Stbadjs on Stsuctdbes .., ... 123 XIV. AcQuiBED Eegulabitt and "Pelobia" ... 128 XV. The Obigin of Floeal Appendages ... ... 133 XVL Secbetive Tissues ... ... ... ... 140 XVIZ Sensititeness and Iebitabilitt of Plant Obganb ... 151 XVIII. Obigin of Conducting Tissues ... ... 164 XIV CONTENTS. CHAPTER PAGE XIX. CoLOUBE OP Flowers ... ... ... ... 174 V XX. The Emergence op the Floral Whobls ... 184 XXI. The Detelopment op the Floral Whorls ...' 191 XXII. Heterogamy and Autogamy ... ... ... 198 XXIII. Hbterostyusm ... ... ... ... ... 203 XXrV. Partial Dicldiism ... ... ... ... 220 XXV. Sexuality and the Ehvirokment... ... ... 230 XXVI. Degeneracy op Flowers ... ... ... 251 XXVn. Degeneracy op Flowers — CorUimied ... ... 273 XXVIU. Pbogresbite Metamorphoses ... ... ... 285 XXIX. Eetrogresstve Metamorphoses ... ... ... 295 XXX. Phyllody of the Floral Whorls ... ... 301 XXXI. The Varieties or Fertilisation ... ... ... 311 XXXII. Fertilisation and the Origin op Species .:. 329 LIST OF ILLUSTRATIONS. FIGUBB FAGS 1. Diagram of a typical flower composed of six whorls ... 3 2. Diagram of the positions of opposite leaves, illastrating the method of passage to alternate arrangements ... ... 11 3. Diagrams of floral ffistiTations, showing the passage from the two-fifth or qnincnncial, to the contorted 15 4. Diagram of flower of Qaridella, with stamens superposed to petals ... ... ... ... ... ... ... ... 21 5. Diagram of flower of Hellehorus niger with stamens super- posed to twenty -one nectaries ... ... ... ... 22 6. Diagrams illastrating the anatomy of the floral receptacle of a Wallflower, showing the origin of the floral members ... 82 7. Diagram of the leaf-traces in the stem of Arahii albida ... 39 8. Vertical and transverse sections of the wall of the inferior ovary of Campanula medium, showing how the eepaline cords originate those of the rest of the floral organs (see fig. 15, p. 71) 43 9. Flower of Phyteuma, showing cohesion by contact and con- genital, in the corolla ... ... ... ... 50 10. Flower of Iftmutut undergoing " dialysis " 51 11. Stamens of OentoAirea, showing syngenesions anthers ; method of fertilisation by "piston-action" (b), nectaiy and direc- tion of insect-proboscis, etc 60 12. Anatomy of the floral receptacle of Hellebore, showing the changes in orientation of the cords ... 64 13. Anatomy of the floral receptacle of Pelargonium, showing changes in the orientation, -in the separation and in the union of the cords ... 65 68 xvi LIST OF ILLUSTRATIONS. FIGUEE 14. Anatomy of the floral receptacle of Ivy, showing the multi- plication and difEerentiation of the cords, etc. 15. Anatomy of the floral receptacle of Campanula medium, showing the distribution of the cords, etc. (see fig. 8, p. 43) 71 16. Origin and development of the ovule in Beta 73 17. Carpels of Acer, showing the thickened bases, preparatory for ovules ... ... .'.. ... ... ... ••■ ••• 75 18. A separate carpel of Primula sinensis, with marginal ovnles and a " heel-like " process, the origin of the free centi'al placenta 76 19. Anatomy of the floral receptacles of Lysimachia and Primula, showing the cords of five carpels ... 77 20. Echitim, showing declinate stamens and protandroos condition 82 21. Ovary, stamens, and stigmas of Aristolochia ... 83 22. Vertical sections of buds of Pyrus and Cotoneaster, shovnng degrees of adhesion or undifferentiated condition between the ovary and receptacular tube ... ... ... ... 90 23. Orchis Morio (?), with arrest of pistil, the receptacular tube represented by a rod-like pedicel. Two anthers are deve- loped instead of one (a) 92 24. Receptacular tube of Rose, bearing a leaf and a stipnlar sepal 93 25. Vertical section of the receptacular tube of Hawthorn, with supernumerary carpels arising from the snmmit ... ... 93 26. Leaves of Fear with hypertrophied and snb-fasciate petioles 94 27. Fuchsia with f oliaceons sepals, partly detached from the ovary 94 28. Anatomy of the receptacular tube of Primus, showing the origin of the petaline and staminal cords ... 95 29. Part of the receptacular tube of Cherry, showing the distri- bution of cords in the sepaline lobes 97 30. Anatomy of inferior ovary of Alstriemeria, showing the junc- tion between the ovary and the tube ... ... ... 97 31. Mower of Duvemoia, showing its adaptability for intercrossing 107 32. Flower of Calceolaria, shovring thickened ridges, etc., and adaptability for intercrossing .. . ... ... ,„ ... 109 33. Flower of Dictarrmus, showing declinate stamens and displace- ment of petals ... 110 34. Flower of Epilobium angustifolium, showing dependent sta- mens and displacement of petals ... ... Ill LIST OF ILLtrSTEATIONS. XVU FIGURE PAGE 35. Flower of Veronica Chamced^s, showing method of fertilisa- tion by insects, and degeneracy of anterior peta.1 ... ... Ill 36. Flower of Teucrium, to show efifeot of weight of insect with exposure of atamens ... ... ... ... ... ... 117 37. Diagrams of Narcissus cemuiis, to show instability in the heterostylism and lengths of stamens ... ... ... 121 38. Basal end of a Pear, to show cause of thickening in response to forces 124 39. Diagram of & declinate bongh, showing distribntion of forces 125 40 a. A diagram of declinate stamens, to show distribution of forces 126 40b. Flower of Lamtufli oZImm, to shew distribntion of forces ... 126 41. Base of fiower of Amaryllis, showing the honey-protector ... 134 42. Adhesive epidermal cells of roots of Orchids 137 43. Stipules of jTopatisTis, showing nectariferous tisane ... ... 140 44. Petals passing into nectariferons stamens of .^A'agene ... 141 45. Cells of hair of Tradeacantia, showing the state of protoplasm before and after excitation by electricity 152 46. Climbing peduncle of Uncaria, thickened aftOT irritation by the support ... ... ... ... ... ... ■■• 156 47. Flower of Genista Unctoria, before and after mechanical irritation j the claws of the keel and wing petals being in unstable equilibrium 160 48. Flowers of Lopezia in three stages, showing movements of the staminode and stamen 161 49. Flower of Medicago sativa, before and after mechanical iirita- tion, the staminal tube being in unstable equilibrium ... 162 5a Transverse sections of conducting tissues of Fumaria, Eubus, and of a Cmcifer ... 164 61. Diagram of emergence of the petaline stamens of Peganum outside the eepaline ... ... ... ... ... •■• 189 62. Flower-bnd, and same opened, of Stellaria media, showing conditions of degeneracy and adaptations for self-fertili- sation ... ... .-■ ••• ..• •■• ••• •■• 255 53. Flower-bud, and essential organs of Epilobvu/m montanum, showing positions for self -fertilisation 255 54. Styles and stigmas of the two forms of Pansy, showing the conditions which (a) prevent and (b) secure self-ferti- lisation, respectively 255 XVIU LIST OF ILLUSTRATIONS. FrctTRE PAGE 55. Styles and stigmas of self-fertilising forma of Pansy ... ... 257 56. Details of structure of cleistogamous Violets ... ... ... 258 57. Details of structure of cleistogamous Oxalis Acetosella ... 260 58. Flower-bud and stamens of cleistogamous Impaftens .. . ... 261 59. Flower-bud and section of cleistogamous Lamium amplexi- caule ... ... ... ... ... ... ... ... 261 fiO. Corolla, stamens, and style of Salvia clandestina, showing adaptations for self -fertilisation ... ... ... ... 262 61. Transitional forms between bracts and leaves of Relleborus viridis ... ... ... ... ... ... 286 62. Inflorescence of Oor»«8^ortda, showing floral mimicry ... 287 63. Inflorescence of Daruiinta, showing floral mimicry ... ... 287 64. Involuoral bract of Nigella, bearing an anther ... ... 288 65. Glumes of Lolium, both antheriferous and stigmatiferous ... 288 66. BamMncttZits with a f oliaceous sepal ... ... 289 67. Foliaceous calyx of Trifolium repens with stipulate leaves, borne by the receptaoular tube ... ... ... ... 289 68. Flower and leaf of 3fMss(»7ida ... 290 69. Linona with one sepal petaloid ... ... ... ... ... 291 70. Calyx of Garden Pea with oarpeUary lobes ... ... ... 292 71. Ovuliferous sepal of Violet ... ... ... ... ... 292 72. Corolla of Foxglove with filamentous processes, some being antheriferous ... ... ... 292 73. .iguikgio, the corolla with poUeniferous spurs 293 74. Ovuliferous petals, etc., of BejroMta 293 75. Ovuliferous anthers of Sempeniiuum 294 76. Stigmatiferous and ovuliferous stamens of Begonia 294 77. Carpels and ovules originating from a placenta of Carnation, the carpels again ovuliferous (o) 295 78. Stameniferous carpels of Willow and Ranunculus auricomus 296 79. Petaliferous placentas of Cardamine pratensis and of Rhodo- dendron ... ... ... ... ... ... ... 296 80. Metamorphosed snb-petaloid carpel of PoVywnthus 297 81. Foliaceous connective of Petumia 298 82. Petalody, or " hose-in-hose " form, of connective in a double Columbine (.4}Mi%»a) 298 83. FoUaceons stamen and petal of the Alpine Strawberry and stamen of the Green Bose 302 LIST OF ILLUSTRATIONS. XIX FIG17BB PAGE 84. Stamen of Jatropha Pohliana, with foliaceous membranes to the anther-cells ... 302 85. Metamorphosed and foliaceous ovules of Mignonette 305 86. Metamorphosed and foliaceous orules of Sisymbrium Alliaria 306 87. Tubular excrescence on the labellum of Cattleya, homologous -with an OTule 306 88. Multifold carpels, with oruliferous margins, from a malformed Primrose 308 THE OEien OE FLOEAL STEUCTUEES THEOUGH INSECT AND OTHEE AGENCIES. CHAPTER I. GENERAL PEINCIPLES. Introductory. — MncL. has been -written on the structure of flowers, and it might seem almost superfluous to attempt to say anything more on the subject ; but it is only within the last few years that a new literature has sprung up, in which the authors have described their observations and given their interpretations of the uses of floral mechanisms, more especially in connection with the processes of fertilisation. Moreover, there is a considerable amount of scattered litei'atnre on special points which seems never to have been collated, so as to show the reletive significance of the dif- ferent classes of observations to which the authors have devoted themselves respectively. The consequence is, that, good as each in itself may be, it often requires the help of other classes of facts to enable one to fully elucidate any question to be discussed. Now, the primary object of the first really scientific study of plants was their classification, and no longer vrith the sole view of ascertaining the real or imaginary medicinal uses of herbs ; as had been the case in Gerarde's time, when a botanist and a herbalist were one and the san:e. 3 2 THE STRUCTURE OF FLOWERS. Systematic botanists, however, have hitherto invariably contented themselves with observing differences of structnre only ; and paid little or no attention to the " why '' and the " wherefore " of the differences they seized upon as being more or less important for the purpose of distinguishing species. When, however, the desirability of a more thorough knowledge of the origin of parts of plants as interpreting mor- phological characters was felt, developmental history began to be studied ; a method strongly insisted upon by Schleiden, for example ; and the most elaborate result of this method of investigation is undoubtedly Payer's Traite d' OrganogBnie Com- paree de la Fleur, published in 1857 : but if it be thought sufficient to limit the study of flowers to tracing their mor- phological development alone, one soon begins to see that it is far from being so, and, taken by itself, it may lead one into false interpretations, so that to the study of development must be added that of anatomy, To Ph. van Tieghem we are indebted for an elaborate treatise, entitled Becherches sur la Structure du Pistil et swr VAnatomee ComparSe de la Fleur (1871), dealing with the more minute details of floral struc- tures. This treatise, however, Btill leaves much to be desired. Besides these methods, analogy and especially teratology furnish assistance of no mean value. Here we are especially indebted to Dr. M. T. Masters for his standard work on Teratology * Now, any one of these methods taken alone would be insufficient, and in many cases would be far from thoroughly accounting for particular points under consideration. Hence to arrive at a complete interpretation of the origin of every sort of structure to be found in flowers, it can only • A Gei-man edition, Fflamen Teratologic, ed. Eaicmer, 1886, haa nomeroiu additiong. GENERAL PRINCIPLES. be done by calling in the aid of each and all these methods to the very ntmost extent possible. Lastly, to attempt any theoretical exposition of the evo- lutionary history of flowers, considerable caution is required ; for the causes of variation are generally so obscure, the chances of seeing them in activity so small, and experimental methods of verification well-nigh impossible, that specula- tions on this subject cannot altogether escape the bounds of hypothesis so as to become demonstrable facts. Hence observations which I shall make later on, with reference to the origin of existing floral structures, will not profess to be anything more than theoretical, and at most only a " work- ing hypothesis " for future investigations. The Steucttjre of a Typical Flowee. — Before consider- ing how the innumerable forms of flowers deviate from one another, it is advisable to assume some typical form or plan as a preliminary basis to start from, or to which aU flowers, if pos- sible, may be referred as a standard. It would be quite possible to adopt some kind of flower -as it exists in nature, but as this would be arbitrary, it may be better to take an ideal type, and the diagram (Fig. 1) will answer the purpose, in which the outermost circle is supposed to represent a cross section of the five Sepals constituting the Calyx. The second circle is that of the five Petals of the Corolla. The third stands for the Anthers of the five Stamens superposed to the sepals ; the fourth being those of five Stamens super- posed to the petals. These two whorls of stamens together Fig. 1.— Diagram of a typical flower. 4 THE STRUCTURE OF FLOWERS. constitute the Androecinm. Lastly, there are represented two * whorls of Carpels forming the Gjnoacium f or Pistil. The outermost whorl of carpels is superposed to the sepals, the innermost to the petals. There may be additional structures in flowers, such as disks, honey-glands, etc. ; but as these, when they occur on the floral-receptacle, are merely cellular protuberances and form no part of the floral whorls proper — not being foliar in their origin — they may be omitted, especially as their posi- tion is by no means constantly the same in all flowers.J The Principles of Variation. — Having thus assumed an ideal type, we may at once consider the "Principles of Variation," as I propose to call them, in accordance with •which the difFerent members of flowers can be altered; so that by means of various combinations of these principles all the flowers in the Vegetable Kingdom can be brought under this one fundamental plan. There are five principles which require special considers^ tion. They are usually designated by the terms Number, Arrangement, Cohesion, Adhesion, and Form. "Number" refers to the number of whorls and the number of parts in each whorl. If two or more whorls contain the same number of parts or be multiples of one another, they are said to be " symmetrical " or " isomerous." If they differ in the number of parts they are " unsym- metrical " or " anisomerous." "Arrangement" refers to the relative positions of the ♦ Why I assume two whorls for the pistil, instead of one only, as is generally done, will be nnderstood hereafter. I have since fonnd that Robert Brown came to the same conclusion (Col. Works, i. 293). t I adopt the spelling GyruBcium for the sake of nniformity ; it may be regarded as a shortened form of Gyncecaecium. $ I do not here allnde to certain glandular structures, which may be the homologues of arrested organs. GENERAL PRINCIPLES. 5 difFerent whorls, as well as of those of the individual members of the whorls with regard to each other. " Cohesion " signifies the union of parts of any, but of the same whorl. The original or ancestral condition of the parts composing every whorl is presumed, on the principles of evolution, to have been one of entire freedom ; so that the members were as completely separate or free as, for example, they are in a Buttercup. Reversions to this con- dition of freedom may occur, and then the process is called " dialysis , " as in the case of a polypetalous Campanula occasionally cultivated as a garden plant. " Adhesion " signifies the union of parts of different whorls ; as well as that between the ovary and the recepta- cular tube, constituting the so-called inferior ovary. I regard adhesion as representing a more advanced or a more highly differentiated state than that of cohesion. Reversions may occur by " solution," which brings about a freedom of parts normally united, as in the abnormal cases of Apples, double Saxifrage, members of the Umbelliferoe, etc., which have all their parts perfectly free, though with inferior ovaries under ordinary circumstances. " Form " refers to the shape of the organs ; such as those of sepals and petals upon which generic characters are so often founded, the length of the filaments, and other peculiarities. If all the parts of any whorl be exactly alike, it is said to be " regular ; " if not, the whorl will be " irregular." The above five principles constitute the most important in accordance with which Nature has brought about the infinite diversity which exists in the Floral world. There are minor distinctions, hereafter to be considered, such as colours, scents, etc. ; but they are of less importance in investigating the causes at work which have evolved specific and generic differences amongst flowering plants. 6 THE STRUCTURE OF FLOWERS. There is another point which may be here noticed. That a flower-bud is a metamorphosed leaf-bud is now an accepted fact ; bnt an obvious difference between them consists in the arrested state of the axis of the former, constituting the floral receptacle ; and the question arises, how has this arrest been brought about ? Like all other peculiarities of structure to be described, I would attribute the arrest primarily to the altered nature of the foliar organs on becoming members of flowers. Thus, a Fir-cone and a Buttercup are arrested branches ; but when the parts of a flower are reduced in number, and instead of being in a continuous spiral are grouped in " compressed cycles," * I would then (hypo-, thetically) attribute this further reduction of the axis, as well as other features hereafter to be described, to the irritation of insects in probing for juices, and causing nectaries to be formed, f It is the commonest thing for leaf- buds to be arrested, and sometimes metamorphosed as well, by insects puncturing and depositing their eggs in them. Such may be seen on the terminal shoots of Tews, Thyme, and in certain kinds of Oak-galls, etc. In all such cases the immediate effect is the total arrest of the axis, though the leaves may be but slightly altered, as in the Tew. How the various metamorphoses of leaves into petals, etc., has followed will be discussed later on. It mnst not be forgotten, however, that the tendency to shorten the axis is primarily, in some cases, due to the altered structure of the foliar organs, as in Gymnosperms ; whereby they undertake the reproductive functions. At the same time, I think insects have had a good deal to do with it, in many other phanerogams, which have but few parts to their whorls. Each of the above principles must now be considered in detail. • See pp. 41, 42. f See p. 140, seqq. CHAPTEE II. THE PBINCIPLE OF NUMBER. Number — General Obsbrtations. — The first principle of Variation to be considered is that of the number of parts composing the different -whorls of flowers. There are good reasons for considering that six whorls, consisting of five, four, three, or two parts each, as the case may be, should be regarded as the theoretically complete number of verticils of any flower. Anatomical investigations prove that the rule is for the pedicel to contain — at least, immediately below the flower, — if the latter be pentamerous, ten more or less distinct fibro- vascular cords, five of which belong to the sepals and five to the petals ; if it be hexamerous, there will be six cords, three for each whorl of the perianth. Each of these cords can give rise by branching, first, to a whorl of stamens and subsequently to a whorl of carpels, furnishing at least two marginal and one dorsal cord for each of the latter. In many flowers both whorls of stamens are present, and the androBcium is then isomerous with the entire perianth. More often one whorl is arrested, and then it may be either one ; but most usually it is the petaline. On the other hand, the calycine may not be developed as in Primroses, Bhamnus, etc. The absence of the petaline stamens is possibly attribu- 8 THE STRUCTUEli OF FLOWERS. table to the law of compensation, in consequence of tlie enhanced growth of the corolla, the petals thereby abstract- ing the nourishment that would be required by the stamens superposed to them. That the number of staminal whorls should be two in verticillate flowers, i.e., equal to the perianth, is apparent from the fact that two whorls prevail in Monocotyledons and are not at all uncommon in Dicotyledons ; and when the petaline whorl alone exists, as in Primulacece and Myrsineoe, calycine staminodia are sometimes present which tend to restore the complete number, as in the genus Samolus in the former and in the tribe Theophrastece of the latter order. The reduction of the number of carpels is very generally carried to a greater extent than that of the stamens. Assum- ing two complete whorls of carpels as the primitive number, not only are both rarely to be found in the same flower, as in Butomvs, but a portion only of one whorl is commoner than even a single entire whorl. Thus, two are characteristic of Gruciferoe, FolygahcB, and of most of the gamopetalous orders ; while one carpel only prevails in Legitminosce and elsewhere. That the absence of parts of, as well as of entire whorls of flowers as they now exist does not represent primitive conditions, is testified to by the frequent occurrence of varions kinds of degradations, such as were alluded to above in the case of the staminodia of Samolus, etc. Thus, with regard to the calyx, it is a noticeable fact that when the inflorescence consists of a large nnmber of flowers, especially if small and closely compacted, there is a strong tendency for the sepals to become partially arrested and remain rudimentary, or even not to be developed at all. This is particularly observable in some epigynous orders as UmbelUfercB, AraliacecB, Capri- foUacecB, Buhiacece, Oompositm, etc. THE PRINCIPLE OF NUMBEE. 9 The degradation of the corolla is likewise very common. As its enhancement has been due to insect agency, so, conversely, its reduction in size, colour, etc., is presumably often the result of the neglect of insects. Consequently inconspicuousness becomes a characteristic feature of self- fertilising flowers. By increased degradation the corolla may disappear entirely, as in Sagina apeiala, some cleistogamons flowers, and in the Incomjpletce generally. Such degradation is also characteristic of wind-fertilised flowers. As both calyx and corolla may be degraded and disappear, BO may the stamens and carpels, unisexual and neuter flowers being the result. Further observations, however, will be made upon this subject when teeating of the several whorls respectively, and especially when discussing the phenomenon of degeneracy. The Obigin op Diffeeent Numbers. The number of parts constituting the floral whorls is, without doubt, primarily due to phyllotaxis ; and therefore, to understand why certain numbers, such as fives, fours, and threes prevail, it is needful to give some preliminary remarks on the principles of leaf arrangement. It has long been observed that these are referable to two kinds — one in which two or more leaves are situated on the same node, when they are decussate,* that is to flay, each pair or whorl of three or more leaves alternates in position with the whorl immediately above and below it. The second system is when only one leaf occui-s at a node ; the leaves are then said to be alternate. The leaves are then arranged on a continuous spiral line, and can be represented by the fractions of the well-known series ^, ^ , f , |, y\, /^, etc. Of these fractions the' denominator represents the number of • Bare ezceptions occur in species of Potamogeton, in which alternate intemodeB between the distichonsly arranged leaves are Buppressed, so that they become opposite, bat are all in the same plane. 10 THE STRUCTURE OF FLOWERS. leaves in a "cycle," and the nnmerator the number of times a spiral line, passing through the position of the leaves, coils round the stem in forming a cycle ; thus, with the f arrange- ment, any leaf being taken as number 1, the sixth leaf will be first that falls in the same vertical line with number 1, the leaves 1 to 5 constituting the cycle. The portion of the spiral line which passes through the leaves 1 to 6 coils ttcice round the stem, and if projected on a plane forms two circles. The angular distance, measured from the centre of the stem or circles, between any ^^T0 successive leaves is always found by multiplying 360° by the fraction : thus f X 360° = 144°. Tbe interpretation, therefore, of the prevailing numbers 3 and 5 in floral whorls is that they are, in most cases, cycles of the 3^ or -I types respectively ; while 4 i^ primarily due to the union of two pairs of opposite and decussate parts. 6, 8, 10 are merely the doublen of the preceding, and mostly represent two pairs of whorls or cycles blended together, thus forming one whorl, or so closely approximated as scarcely recognizable as two ; though tbe rare number 8, in some cases, such as Nigella, and Selleiorus foeiidus, may repre- sent a cycle of the ^ type. Similarly, the still rarer numbers 7, 9, and 11 in flowers correspond to the absence of these numbers as denominators of any fractions of the above prevailing series. With the exception of dimerous and tetramerons whorls, all the rest are presumably due to alternate arrangements. Now, opposite leaves present a more primitive type than alternate ; that this is so, is not only reasonable from the primordial condition of the cotyledons of Dicotyledons, but the transition from an opposite to an alternate condition may be often witnessed on rapidly growing stems, such as of the Jerusalem Artichoke. Whenever this plant bears opposite leaves below, and alternate leaves above, it will be THE PRINCIPLE OF NUMBER. 11 found that the arrangement of the latter is almost invariably represented by the ^ type. It is secured by developing inter- nodes between the two opposite leaves of each pair, and by shifting their positions so as to acquire ultimately an angular divergence of 144°.* The feature to be especially observed in the transitions from opposite to alternate arrangements is the order in which the opposite leaves separate so as to assume successive positions on the continuous spiral line passing through their insertions, when they have become alternate. This will be understood from the accompanying diagram, in which the numbers represent the order which the leaves will ultimately assume on the f type ; though they ai-e placed as if still opposite and decussate. The numbers 1 and 2, 3 and 4, 5 and 6, etc., represent the successive p.iirs of opposite leaves, the arrows showing the direction of the spiral. It will be at once ob- -^ 2 served that the numbers 6, 5 9, 14, and 22 are in the ^^ same row, and correspond to -.q a the divergences f, |, -r»j, 21 /y. No. 17 falls into the 3 8 11 16 19 20 15 12 7 4 series f , and completes the 22 second cycle of that type V 17 (= 2 X 8 + 1) from No. 1. q It may be observed 6 here, as occasion will arise 1 — ^ for a fuller allusion to the Fig- S— Opposite leaves passing into .Itemate. significance of the fact, that, with the sole exception of the * I have fnlly explained this in my paper, On the Tariationa of the Angular Divergences of the Leases of Helianthns Taberosns, Trans. Lin. Soe., vol. ixvi., p. 647. See also On the Origin of the Prevailing Systems of Phyllotaxis, I.e., 2nd series, vol. i. p. 37. 12 THE STRUCTURE OF FLOWERS. distichous or ^ type, every other arrangement always has three leaves in every projected circle. It may be noticed that No. 4 not only does not occur in the row 1, 6, 9, etc., — a fact which corresponds with the rarity of a ternary arrangement occurring amongst flowers of Dicotyledons, — but in order to fall over No. 1 it would have to pass through 270°, that is from right to left, practically an impossibility; so that when "threes" are met with in Dicotyledons we must look for some other interpretation than to refer them to the J- type. The numbers 7 and 11, as stated, are extremely rare in flowers, and this is in accordance with the fact that they belong to another series, viz. j, I, f, tVi t5> etc , which is rarely represented in nature. Examples, however, will be found in the leaves of Sedum reflexum, on some branches of Araucaria imhricata, and sometimes in the Jerusalem Artichoke. In the last case, it will be discovered that the heptastichous or y type arises out of verticils of threes, in precisely the same way as the pentastichous or f type does from an opposite and decussate an-angement ; and as there are always four leaves in every projected circle, for every type of this series, except- ing the first or ^, it can only occur where the leaves are narrow or are short, or do not occupy too much space so as to overshadow one another. Variations in the Tloral Symmetry. — Besides the fact that certain numbers are often characteristic of certain species, genera, or even orders, great variations in the sym- metry exist, iiot only in different genera of the same order, but in different species of the same genus.* Now, with reference to this latter fact, it mnst be borne in mind that flowers are so highly differentiated from the * See note by the author, On the Causes of the 'Numerical Increase of Paris of Plants, Joam. Lin. Soc. Bot., xvi. p. 1. THE PRINCIPLE OF NUMBER. 13 leaf type, that they have undergone such wonderful transfor- niations and adaptations to insect and other agencies and to their environing conditions, so that the simple and original laws governing the arrangement of the leaves, here pro- pounded for the origin of what may be called the " primitive symmetry " of the floral organs, have become in many cases masked or interfered with. Hence, to deduce those original laws from the present structure of flowers, it is not only neces- sary to consider the floral symmetry of an immense number of genera, and so ascertain what are the relative proportions of certain numbers when associated with alternate and oppo- site leaves respectively, but to discover what may have been the interfering causes which have modified what would have been the immediate effects of the fundamental laws of phyllotaxis. Thus, it will be found that the numbers of the parts of whorls are liable to vary on their own account, while the arrangement of the foliage varies independently at the same time ; so that where the floral symmetry of a plant does not tally with the leaf arrangement, the discrepancy may be due either to subsequent changes occurring in the flowers or in the leaves, or perhaps in both. For example, a quaternary floral type may be, and often is, associated with alternate leaves ; where there is reason to suspect that the former was established from a primitive opposition in the leaf organs, but that the foliage has subse- quently differentiated into a spiral arrangement, leaving the original 4-merous symmetry of the flowers unaffected, as in many of the Onagraeece ; Epilobium, indeed, often furnishing ocular demonstration, as, while the lower leaves may be opposite, the upper are often alternate. On the other hand a quinary arrangement is often associated with what may be called a persistent opposition 4 14 THE STRUCTURE OF FLOWERS. in the leaves, as in GaryophyllecB and Labiates. This may be due either to an abrupt change from opposite leaves or bracts to a spiral one in the flower, or by a reversion from an alternate to an opposite position of the leaves,' the floral organs retaining the arrangements due to their spiral origin. The symmetry is based on Calyx, Corolla, and in many cases the Androecinm also ; but the carpels are not generally regarded, for it does not usually extend to the gyncecium, though it is very frequently retained in the andrcecinm, which is often some multiple of that of the perianth whorls. In presenting the reader with what may be regarded as ostensible grounds for the interpretation proposed, attention will be first directed to the more obvious correlations be- tween floral symmetry and leaf arrangements, as appear from certain numerical proportions ; and, in the next chapter, to significant facts observable in the symmetry of particular plants. Commencing with genera possessing alternate leaves and a quinary floral type, the prominent fact becomes at once apparent that this correlation far exceeds in nnmerical proportion any other. Thus, of above eighty Dicotyledo- nous orders* examined in all, no less than 1285 genera have quinary flowers associated with alternate leaves, and this is exactly what (5ne wonld expect according to the theory advanced that 5-merons whorls are cycles of the % type- As a corroboration is the fact that such whorls often have their parts arranged quincuncially in aestivation (Fig. 3, a) ; and when they are not so they can be referred to * I conanlted the first volume of the Qenera Plantarum for this purpose, which embraces the Thalamifiorce and Calyciflor(e. THE PRINCIPLE OF NUMBEE. 15 it, as I have explained elsewliere : * thiis Fig. 3 shows how the varieties of imbricate asstivations are deducible from the f type (a), by shifting the edge of the 2nd member under the 4th (b, " vexillary "), the 3rd under the 5th (c, " imbricate proper "), and the 1st under the 3rd (d, " contorted "). Similarly ternary ortrimerous whorls are almost universal amongst flowers of Monocotyledons, and the ^ type of phyllo- taxis is equally common in the foliage. It has been seen that the J type cannot be deduced from opposite leaves, and consequently never occurs, as fur as I know, amongst the foliage of Dicotyledons. The comparatively few genera in this class with ternary flowers is therefore in accordance with the views herein expressed; and where they occur, as -©OQO a h c ct Fig. 3.— Floral Jilivatloiw. in Berheris, there are special features which lead one to believe they are not due to the -J- type at all, but to the breaking up of a high continuous spiral into groups of threes, as will be explained hereafter. If, however, we take a theoretical departure from a single cotyledon, as occurs in Monocotyledons, then the next leaf can be at either of the limiting positions of the angnlais.^ distances of 180° or 120°, but not less ; for if it were less than 120°, there would be four leaves in any projected circle, and this would immediately introduce a member of the series ^, ^, f , etc., as shown above. The consequence is * See my paper, On the Origin of Floral Estivations, Trans. Lin. Soo., 2nd series. Botany, toL i. p. 177. 16 THE STRUCTURE OF FLOWERS. that the ^ and ^ types are exceedingly common in the foliage of Monocotyledons, while the |, as far as I am aware, is entirely wanting in that class, whether in foliage or flowers. Of genera having alternate leaves but associated with a binary or quaternary floral symmetry, there are about 270 in number of about 30 orders. Now, the co-existence of alternate leaves with 2- or 4-merons flowers appears at first sight to negative the theory ; but, as mentioned above, these and other irregularities have been brought about by subsequent differentiations in the foliage or flowers. On the other hand, opposite leaves with quaternary flowers are not at all in- frequent, though not quite so common as when they are alternate ; thus, Oleacem and Onagraceoe are so conditioned. Again, in Bosacece, which is an order characterized by having alternate leaves and 5-merous flowers, three genera alone out of seventy have opposite leaves, and these three also are accompanied by 4-merous flowers ; viz. Bhodotypus, Goleogyne, and Eucryphia. These three genera thus acquire their importance from being isolated amongst others to which they are allied, and which are generally otherwise charac- terized. Many orders have both foliage and floral symmetry remarkably inconstant, and all four combinations, viz. 4- merous and 5-merous flowers with opposite or alternate leaves almost indiscriminately, as in the tribes Diosmece and Borosmece of Butacece ; and it is a noticeable fact that, associated with this inconstancy of correlation, there is an inconstancy in the leaf arrangement, opposite and alternate leaves being often in species of the same genus, and even on the same individual plant. The total number of genera noticed as having 4-merous flowers and opposite leaves was 110 in 25 orders ; whereas 1 noticed 276 genera of 30 orders as having 4-merous flowers associated with alternate leaves. This, I believe, is due to THE PRINCIPLE OF NUMBER. 17 subsequent differentiation in the foliage to an alternate condition, the quaternary condition of the flowers remaining unaltered. Similarly with the last condition, I found 212 genera of 30 orders with a quinary arrangement of the flowers corre- lated to an opposite condition of the leaves, this being an apparent anomaly of the same kind, but which is, however, to be interpreted in the same way. Thus the Lahiatce are con- stantly 5-meron8 in the flowers, but with as constantly opposite leaves. Now, if we contrast this order with Scro- phularinece, we find a similar constancy in certain genera only, as in Bhinanthus, etc. ; while other genera have alter- nate leaves as Linaria, Digitalis, etc. There is an alternative of interpretations of this fact, for both can be illustrated in nature. Either all the pentamerous flowers have been deduced from alternate leaves (as may have been the case with Bhinanthus and Labiatce), the leaves having subsequently reverted to the original or ancestral state of opposition ; or else, the 5-merous character of the flowers has arisen by a sudden change (possibly due to the stimulus of insect agency) from opposition in the leaves or bracts to an alternate arrangement in the parts of the flower. As an illustration of this latter process may be mentioned the development of the five sepals of Deutzia as compared with the four of the allied genus Philadelphus. In this latter genus the anterior and posterior sepals appear together, subsequently the two lateral arise simultaneously. In Deutzia, however, the two anterior sepals correspond to Nos. 1 and 3 ; two sepals are lateral, viz., Nos- 4 and 5 ; and the posterior sepal is No. 2. Thus the opposite and decussate pairs of sepals of Philadelphus would be repre- sented by the figures 1 and 2, 3 and 4. If these were to break up into a quincuncial spiral and shift their positions. 18 THE STRUCTURE OF FLOWERS. t.hey would, ■with the addition of one more sepal, asstune those represented by Beutzia. Exactly the same procedure occurs in the change from opposite to alternate arrangements of leaves ia the Jeru- salem Artichoke, as I have explained in treating of the varieties of leaf -arrangement in that plant. Galycanthus is another instance illustrating an abrupt change from an opposite condition of the leaves to the ^\ type in the bracts enveloping the flowers, and which then pass insensibly into sepals and petals. Symmetrical Increase and Deceease in Plokal Whorls. — As another instance of variability adding further complica- tions, it may be observed that in both kinds of arrangements, namely, of those plants possessing alternate and those pos- sessing opposite leaves, there are many genera- whose floral symmetry ranges from one to some higher number in the different species of the same genus. Thus 4-5-merous flowers are especially common. I found it so in more than 100 genera of 23 oi'ders examined among alternate-leaved plants ; and 58 genera of 19 orders among those with opposite leaves. Again, some genera have species the whorls of whose flowers range from 3 to 6 or 6, or from 4 to 6 in the number of parts ; others from .5 to 7 or 5 to 8, etc. In these cases it is often quite impossible to explain what has been the immediate causes producing such variations. The only interpretation that can be given is that the primary sym- metry having been originally determined by phyllotazis, it THE PRINCIPLE OF NUMBER. 19 changes, whether in the individual or in its descendants, through the law of " symmetrical increase or decrease." By this I mean that the number of sepals, petals, and stamens often vary together from the typical number by the addition or subtraction of a member. Thus, in a single corymb of an Elder, 4-, 5-, 6-merous flowers may be often found ; simi- larly, while early blossoming Fuchsias may bear 3-merons flowers, they are replaced later by the regularly 4-merous ones. Although these changes frequently occur in the same plant, they usually are not permanent. Yet they occas,ionally appear to haye become so, as in the terminal flowers of Adoxa and Monotropa. On the other hand, the constant occurrence and, therefore, specific character of 4-merons flowers in Potentilla Tormentilla, and 3-merous in Tillcea muscosa, I should be inclined to attribute to the fixation of a symme- trical reduction which has taken place from the permanent 5-meroiis type so characteristic of Potentilla, and many genera of the Grassulacece. Not infrequently the difference of number is pronounced by systematists as generic; thus, while Eubia has 5-merous flowers, Galium has 4-merous. A similar difference lies between Buta and Saplophyllum.* If a cause be looked for, it would seem to be merely a question of nutrition. If the symmetry varies in the same plant, it is obvious that a corolla of four petals could not have been pi-ovided with the same amount of nutritive material as a 5-merous one. But if it be a specific character, as in Tormentil (which, it may be observed, affectB the more or less barren soil of heaths), then the change has become fixed and is now hereditary. * By running the eye through the artificial keys at the commence- ment of the Orders in the Oenera Plantarum of Bentham and Hooker, it will be seen how frequently these authors regard the namber of parts in the Calyx and Corolla as a prominent generic character. 20 the structure of flowers. TJnstmmeteical Deceease in certain Tloeal Whorls. — Another modifying cause of the change of symmetry ia the adaptation to insect or other agency for fertilisation. This I believe to have played a most important part in modi- fying flowers, as Tvill be explained more fully hereafter, more especially in affecting the Andrcecinm and Gynoecium, than the Perianth, as far as " number " is concerned, this latter organ being altered by their agency, more especially in Form. Thus, the loss of one or more stamens is very characteristic of certain groups, as in the Labiatoe, when the remaining mem- bers of the andrcecium become altered in length and position so as to facilitate the intercrossing of distinct flowers. On the other hand, with inconspicuous and cleistogamous flowers, there is a strong tendency to reduce the number of stamens, as in Cbickweed to three, the allied species Stellaria Holostea having ten. Similarly, in the cleistogamous flowers of Violets they are sometimes reduced to three or two ; since a very small amount of pollen is really quite sufiBcient to fertilise a considerable number of ovules. The gynoecium has very frequently a less number of carpels than the other whorls have parts. Now, the primary effect of intercrossing is to enhance the size of the corolla and to give a preponderance to the andrcecium. On the other hand, one result is to check for a time the growth and development of the gyncEcium of most insect-visited herma- phrodite flowers, i.e. to render the flower protandrons; and I strongly suspect that the generally reduced number of carpels in highly differentiated flowers — as of the GamopetalcB, in comparison with the Thalamiflorce and Calyciflorce — is cor- related to the fact that they have been for many generations visited by insects. This idea is supported by the fact that bicarpellary genera sometimes tend to restore the ancesti'al number of the five carpels, as is occasionally the case in Gesneria. THE PBINCIPLE OF NUMBER. 21 In some cases, nature seems, as it were, to try and com- pensate for the loss of the carpels by an increase in the quantity of seeds. Thus, while no Labiate flower has more than four seeds, it has been ascertained that a Maxillaria bore 1,700,000 seeds ; and I found by calculation that a single plant of Foxglove yielded a million and a half apparently good seeds. The relative advantages of having many or few seeds will be discussed later on. Illustrations from Ranunculacej;. — Certain genera of the ManuneulacecB are particalarly instructive in showing how members of the floral whorls originate in phyllotactical methods, but are more or less altered in their positions by the lateral union of their fibro-vascular cords ; so that they become ar- ranged in superposition instead of being alternate, or vice versa. Thus, in Garidella (Fig. 4) (with which Helleborus foetidus partly agrees), the sepals and petals are both arranged, and arise succes- sively, in quincnncial order; the ' petals being (correctly, in accord- ^'«- *-»"Eram of Garidella. ance with phyllotaxis) superposed to the sepals. The an- droecium forms a whorl of eight stamens, and represents a cycle of the f arrangement ; the proper angular divergence of 135° is, however, not retained, in consequence of the fibro- vascular cords being intimately connected with those of the petals. Having thus established the first whorl of eight, the rest of the staminal series follow on the same radial lines. By referring to the diagram (Fig. 4) it will be seen how the stamens of the outermost whorl gproup themselves in super- 22 THE STRUCTURE OF FLOWERS. position to the petals and sepals. Similarly, in Nigella saliva the petals are eight in number, and occupy the same positions as the outermost -whorl of stamens of Garidella. They have, then, the eight stamens of the outermost -whorl of the andrcecium superposed to them. In Delphinium the stamens and carpels form a continuous .spiral, represented by |, or approximately by f. In some cases Braun* found 16 stamens, and the first carpel being the 17th organ, 'stood superposed to the stamens No. 9 and No. 1. In another case 18 stamens -were developed, so that the first carpel stood superposed to stamen No. 11. Helleborus tiiger (Fig. 5) has five sepals which emerge and are arranged in quin- cuncial order. There are twenty-one nectariform pe- tals, i.e. one cycle of the -^ arrangement, grouped as in the accompanying dia- gram. The petals 1 to 8 and 9 to 16 would correspond approximately to two cycles of the'f type. Radial rows of stamens then follow on the same lines as the petals. Eranfhis hyemalis has, as usually regarded, a 6-8-merons colojired calyx. A pair of staminodes stand superposed to each member of the outer whorl. Stamens follow along the radial lines, of which six terminate in carpels. Aguilegia vulgaris, or the Columbine, has the sepals, as .«! 99 -Q 0\-J :::-^ oh •> g o o o o. .^ 1 Fig. 5.— Diagram of SdlehoTut niger. • Al. Brann on Delphinium (Pringsheim's Jahrb. f. Wiss. Bot., 1857, i. 206), referred to by Henfrey, Morphol. of Balsaminene, Journ. of Liu. Soc, iii. 159. THE PRINCIPLE OF NUMBER. 23 usual, quincnncially arranged. The petals appear simul- taneously, alternating in position to the sepals. The stamens occur in ten rows, 6 being superposed to tbe petals and 5 to the sepals ; and, lastly, 6 carpels appear superposed to the petals. This flower, then, adopts the more usual character of alternation in the whorls. Bat it may be noticed that while the corolla alternates with 'the calyx, each of these outer whorls gives rise to a radial series of stamens. From the preceding illnstrations, it will now be seen that phyllotaxis lies at the foundation of the arrangements of the members of floral whorls ; that the -f type prevails in the sepals and petals, with a strict angular divergence of 144°. The divergences are, however, subsequently modified in the stamens and carpels. Thus, in Hellehorus niger the petals clearly represent a whorl of 21 parts, i.e. they are pre- sumably arranged according to the -^j type. They are, how- ever, so far modified in position as to become superposed to the sepals in groups. Similarly the stamens fonn series of 21, each being superposed in radial lines to the petals. The interpretation of these displacements from what would be due to strict, phyllotactical laws is that the [ individual cords of the stamens and carpels are not inde- I pendent as they are in the " leaf traces " of an axial cylinder, I where the cord or cords belonging to each leaf are simply intercalated side by side with those of the leaves most nearly approaching the same vertical line, and constitute together the common fibro-vascular cylinder of the stem. In thfi pedicel, however, the rule is that this should contain at least the same number of cords as there are leaves to the perianth, or sepals and petals together. These, usually six or ten cords, on reaching the floral rf ceptacle are sent off respec- tively as the cords of the sepals and petals ; whereas, it is 24 THE STRUCTURE OF FLOWERS. these latter which by lateral or radial " chorisis " supply the cords required for the stamens and carpels The consequence is that the essential organs have their cords issuing from a common stem with those of the perianth. Thus they are compelled to stand superposed to them. Perhaps the word " compelled " requires a word of ex- planation. The cord of any organ superposed to another may be given ofE either by radial, i.e. lateral, or tangential chorisis from the cord of the latter. Instead, however, of the new lateral branch giving rise to an organ by the side of the former, it results, partly from the close proximity of the two and partly from the tendency of the remaining cords of the cylinder to " close up," that the new member finally takes np a position in front of, i.e. supei'posed to, the one whose cord has given rise to it. When a cord is separated by tangential chorisis, as is so often the case with staminal cords, then the resulting organ must necessarily be super- posed to the one, from the cord of which it has been detached. CHAPTER III. THE PRINCIPLE OP NUMBER — Continued. Illustrations op Special Numbers. — It will now be advisable to give examples of particular numbers occurring in flowers, and attempt to account for tbem. One-membered Whorls. — "Where one part to a whorl is only found, it may in nearly every case be regarded as a degradation from some higher number. The only instances I am aware of in which the calyx seems to consist of a single member are some species of Aristolochia. In Musscmda one out of the five sepals is greatly enlarged to become an attractive organ.* One petal is occasionally found. Thus, four genera of Vochysiacece have each only one petal to their flowers ; but as the sepals are five in each of the seven genera of this order, and the petals range from one to five in number, the inference is clear that the solitary petal of these four genera is due to the arrest of the others. One stamen occurs more frequently ; as in Hippuris, Gentranthus, Euphorbia, Casuarina, Orchis, Ganna, Lilcea, Lemna, etc. As allied genera have more than one, and it is accompanied by other signs of degradation or metamorphosis, * If there be one external foliar organ only, it is regarded as a bract, as in Willows and Aponogeton. 5 2G THE STRUCTUEE OF FLOWEES. there is no doubt but that similar processes will account for one stamen as for one petal. Thus Eippuris with one, is allied to Myriophyllum with four ; while Centranthus has one, Fedia has two and Valeriana three. Casuarina alone seems to raise a doubt of its being degraded and possibly a primitive form ; but this is solely because it has no living allies (excepting perhaps Mynca). The terminal stamen would not be of itself a point of importance, as it has a parallel in Euphorbia ; but it is its isolation without afiSnities, its peculiar equisetum-like habit, which seem to indicate great antiquity, so that no inference can fairly be drawn to interpret its present monandrous condition. Amongst Monocotyledons, Canna is clearly monandrous by petalody of the other stamens. Orchis by metamorphosis also. Lastly, Naias, Gaulinia, Zostera, Zannich£ell/3,, and Lemna are in all probability greatly degraded forms' from higher plants, degradations being the usual effect of an aquatic life, and not primitive types of Monocotyledons. One carpel is not at all uncommon, as in the Leguminosa. As Affonsea has five, the absence of four in this order is no doubt due to arrest. In the tribe Berbereoe, however (if my interpretation be correct, of the origin of the seven whorls of three each constituting the flowers of Berberis, as explained below), the one carpel may be the last of an originally \ \ continuous spiral, formed from eleven pairs of opposite leaves, ' ' now broken up into seven ternary whorls, with one over. It may, however, be the remaining one of three, which possibly constitutes a ternary gyncecial whorl, which is characteristic of the tribe LardizdbalecB of the same order Berberideoe. Dimerous Whorls. — A dimerous arrangement is not par- ticularly common, though a quaternary calyx is dimerous in its development, as the sepals emerge from the axis in sue- THE PRINCIPLE OF NUMBER. 27 cessive pairs.* The following may be taken as illustrative instances. The sepals of Papaver and Fumaria, the outer stamens of Crucifercn. In Gircma all the whorls are dimerous, in Oleacece the essential organs alone, as also in Pinguicula, Salvia, Veronica, and Salix diandra. The question arises, is this number two an original one, or has it arisen by arresting some parts of a more numerous whorl ? It is obviously so with Salvia and other genera of the Lahiaice, where rudimentary stamens are present. So also with Senebiera didyma where the two stamens take the place of the four larger ones of other genera of the Gruciferce. It is probably so with the two imbricate sepals of Poppies, those of P. orientate being often increased to three, which seems to be a tendency to revert to a more primitive and higher number. With sach plants, however, as Circcea, the Ash, and Vero- nica, which have retained opposite leaves, the dimerous whorls may be a primitive condition. This idea is ostensibly supported by the fact that the outer whorls of the flowers are quaternary and not quinary, since, when this is the case, the sepals always issue in pairs from the axis, and not simultaneously as do the petals ; but as long as no rudi- mentaiy organs exist, there is nothing to disprove the idea that in these genera the number of stamens may not be due to degradation. Indeed, atU analogy would lead one to suppose so in most cases, as of Circcea and Veronica: the binary whorls of the former genus, and the quaternary outer and binary inner whorls of the latter, being presumably due to " symmetrical reduction " from the prevailing quaternary * Though the antero-posterior Bepals of cmciferons flowers are regarded as the most external, it is really the lateral ones which are first provided with fibro-vascnlar cords from the complete oblong cylinder in the pedicel, jnst as iu Cleome (see Fig. 6, p. 32). 28 THE STRUCTURE OF FLOWERS. type of the Onagracem and quinary of the Scrophularinece respectively. Teimeroits Whorls. — The number three is strongly characteristic of Monocotyledons, and appears to be in this class the immediate result of the ^ phyllotaxis. In Dicoty- ledons, however, there are certain orders in which it prevails, and it will be noticed that the number of parts in those orders is generally much increased ; as in Magnoliacece,* AnonacecB, Berberis, Laurus Gamphora, Bumex, etc. In some the andrcBcium and gynoecium are so increased in number that they cease to be whorled, but have become spirally arranged on a more or less elongated receptacle and are represented by the fractions f'g- or ^j* It has been demonstrated above that a pentamerous arrangement is undoubtedly due to the f phyllotaxis, each ■whorl constituting a cycle ; but if the fraction be a higher one, as -j-*^ or t^, then the number of parts in a cycle are too great to be compressed into a whorl. Natare appears then to adopt another method. Falling back upon the law that with these arrangements no part of the continuous spiral, of sufficient length to constitute a complete circle when pro- jected upon a plane, ever contains more or less than three leaves (excepting the ^ type), the series is now broken up into a succession of ternary whorls, the whole forming the complete flower, and, being taken together, corresponds to about or exactly one cycle of a high type. Thus Barberry has 3 bracts, 3 -\- S sepals, 3-1-3 petals, 3 + 3 stamens and one carpel ; that is, seven whorls of threes or twenty-one * In Magnolia an individnal complication is introdaced, in that the immense nnmber of stamens and carpels is secured by donbling the whole number attribntable to the I'j arrangement.- _ Consequently, instead of there being five and eight " secondary spirals," there are ten in one direction and sixteen in the other. THE PRINCIPLE OF NUMBER. 29 ■parts, and one over. If these seven whorls were broken up and arranged spirally, they would be represented by -j^i- ; and then there would be eight coils in the cycle. The presence of seven and not eight whorls is due to the fact that in rearranging them, so to say, in a verticillate manner, and by necessarily shifting the position of the parts, a certain por- tion of the spiral line is lost in forming each whorl, as the angular divergence between two parts in a whorl is 120°, but on the spiral it is nearly 123° ; so that by the time the twenty-first organ is arrived at, only seven circles have been completed. Similarly, in Itumem, if we supply the theoretically lost corolla, the flower would consist of twenty-one parts exactly.* Another and somewhat frequent origin of the number three in Dicotyledons is due to what 1 have called sym- metrical reduction : when not only the different species of a genus may have the number of parts of their floral whorls ranging from 5 to 4 or 3 ; but such variations may occur on the same plant. Thus RutaceoB (following the Gen. Plant.) has 34 genera with 5-merou8 flowers ; 18 genera with species varying from 5 to 4-merous ; 16 are 4-merou8 ; 3 range from 5 to 3-nierous ; 2 from 4 to 3-meroas, and 1 is 3-merous. Tetrameeous Whoels. — That a true quaternary arrange- ment is due to an opposite condition of the foliage seems borne out by statistics, though quinary flowers are not at all uncommon as well. Thus of Butacece there are 6 genera with opposite leaves and 4-merous flowers; 2 only with 5-merous, and 2 with 4-5-merous flowers. On the other hand, there are 25 genera with alternate leaves and 6-merous flowers. * High spirals can be otherwise treated, as in the case of Chimoncm- thus, where whorls of fires are made out of a spiral system of j\ (see below, p. 38J. 30 THE STEUCTUKE OF FLOWERS. Another correlation with a quaternary arrangement is a not nnfrequent valvate condition of the sepals at least, or of the sepals and petals as well. These conditions prevail, for example, in Oleacece, Onagracece, and, with the exceptional genns. Clematis, of the Banunculaceoe. Too much stress must not be placed upon this coincidence, as, if the petals be enlarged through insect or other agency, the valvate aestivation is often lost, and the petals become imbricate, as in Fuchsia, Godetia, etc., though it is there retained in the sepals. This valvate condition is foreshadowed in the ver- nation of the foliage ; m that opposite leaves are almost invariably valvate, having the two upper surfaces of the leaves pressed together, as may be seen in Hypericum and Vinca ; or else with the edges indnplicate, as is characteristic of Caprifoliacece, resembling the sepals of Clematis.* Though the Onagracece have a preponderance of genera with 4-merous flowers, there is in this order great variation in the foliage. It is strictly opposite in Fuchsia and others, but 14 genera out of a total of 22 have alternate leaves, while with some, like Epilohium, it varies on the same stem. This, I think, reveals the fact that the 4-merous condition has been first established in the flowers, and subsequently the foliage has varied from an opposite to an alternate condition in certain genera, just as it does in an individual plant of Fpilohium. That symmetrical reduction has elsewhere played an important part in the origin of 4-merous flowers, is a sup- position fully borne out by facts. In some cases it has seemingly established itself as a permanent character, so that systematists recognize it as generic or specific, accordingly, • See a paper by the author, On Vernation and tJie Methods of Development of Foliage as protective against Radiation, Journ. Lin. Soo. Bot., vol. zxi., p. 624. THE PEINCIPLE OF NUMBER. 31 as the case may be; this, Haplophyllum may be compared with Biuta, Bubia with Galium, or, again Potentilla reptans with P. Tormentilla, etc. On the other band, I repeat, when one observes that of the 71 genera of Bosacece three only arc recorded in the Gen. Plant, as having opposite leaves, and these three are characterized as having 4-meroas flowers, viz. Bhodotypus, EucrypMa, and Coleogyne, there appears to be a significant correlation between quaternary flowers and opposite leaves. A quaternary arrangement is found very exceptionally in Monocotyledons, as in the order Naiadacece, e.g. Tetron- cium and Potamogeton. As the numbers 6 {i.e. 2 X 3), 4, 2, and 1 are found in different genera, the quaternary as also binary arrangements may, I think, be reasonably referred to symmetrical reduction. Perhaps of all orders the quaternary arrangement (at least in part) of Crucifers has raised more discussion than any other kind of floral symmetry.* Without entering here upon any lengthened discussion I would only add that, as far as investigations into the anatomical structure of the pedicel is concerned, there is a decided difference from what occurs in most flowers having a definite number of parts, and where the whorls are regularly superposed to one another, in that the members of the whorls not being for the most part on common radial planes, they have not their cords fused together in the usnal manner in a radial direction. A section at some distance below the flower reveals four or five cords forming a circle. These rapidly increase in number by branching laterally, till between ten and twenty are found arranged in an oval just below the flower. Two • See my paper On the Structure of a Cruciferous Flower, Trans. Lin. Soc, 2nd serieSi Botany, vol. i. p. 191. 32 THE STRUCTURE OF FLOWERS. cords, one at each end of the long axis, now part company from the rest, and enter the lateral sepals (Pig. 6 (a) l.s.), the antero-posterior sepals next receiving their cords (a.s. andjj.s.). The cylinder tends to close np, and four groups situate at the comers of the oblong cylinder supply cords for the petals, p. The two honey-glands next put in an appear- ance, G. They are merely cellular expansions of the floral I receptacle, and are entirely devoid of cords, and therefore I not rudiments of appendages. The two lateral stamens next receive their cords, l.st., while four other cords are given off from beside the petaline for the taller pairs of stamens, st. G *^ m.c. Fig. 6.— Anatomy of Wallflower. Fig. 6 (6) shows how their cords diverge below and spring from the siae of the petaline cords, while extra cords arise between them to form the marginal cords of the carpels (m.c). From this it will be seen that tlie longer stamens cannot be formed by " chorisis " of a common intermediate cord ; but, like those of all other members of the flower, their cords are separated from the common fibro-vasculax cylinder of the stem. The conclusion suggested by this investigation, and by a comparative study of Ccupparidece, is that a cruciferous flower is not reducible to an originally quaternary type at all, but to some higher one. In my paper referred to, I suggested a THE PEINCIPLfi OF NUMBER. 33 quinary ; but I am now more inclined to refer it primarily to an indeBnite spiral series referable to the /^ or ^ type, which has been reduced, perhaps through insect agency, by symmetrical reduction to the present anomalous condition. The process of transition from a hypothetical indefinite number of stamens to the present hexandrous state may be, perhaps, seen by comparing the three genera of Capparideoe — Gapparis, Polanisia and Cleome., The first has many stamens and six placentas, ■which are sometimes reduced to two. Polanisia has eight stamens, or more rarely six. Their situations correspond exactly -with those of the Oruciferce, except that, when there are eight, there are four on the anterior side instead of two. Lastly, Gleome brings us to the same structure as in the CrucifercB with even the tetradynaraous condition of the stamens ; the elongated torus below the pistil being about the only " capparidaceous " feature left. It is not at all uncommon to find more than six stamens in cultivated plants of the Oruciferce, and when this is the case I should be inclined to regard it as a tendency to a reversion to a higher ancestral number. On the other hand, the close proximity of the two taller ones on each, side not infrequently brings about some degree of cohesion between them, with an occasional arrest of half an anther. This has led some to suppose that the pair have resulted from cborisis. Since, however, their cords diverge downwards to the right and left, and run down beside the petalline cords (Fig. 6, 5), this clearly proves that the union is a result of close contact, and that the normal separation is not due to chorisis, but to a primitive freedom, which has been retained from a multistaminate condition. Pentambeous Whoels. — These are by far the commonest amongst Dicotyledons. And as an enormously greater pro- 34) THE STRUCTURE OF FLOWERS. portion of plants in this class have alternate leaves and 5-merous flowers, this correlation alone would be almost sufiBcient to prove that the latter issued out of the com- monest or f type of phyllotaxis. But since the sepals are sometimes decidedly qnincuncial, as are those of Digitalis, and the petals frequently so, we have undoubted proof that they represent cycles of this angular divergence. As with other numbers, fives may arise by symmetrical increase from fours, or decrease from sixes ; though in by far the greater number of instances it is a primitive number, as stated above. As a rare instance of symmetrical decrease may be mentioned Lythrum Salicaria, which has usually the central floret of each axillary cyme 6-merous, bat the lateral ones only 5-merons. As an instance of five parts to a whorl amongst Monocotyledons, may be mentioned the stamens of Strelilzia regina; but this number is obviously due to the suppression of a stamen. Although whorls of fives are cycles of the f divergence, and usually follow after an alternate arrangement in the foliage, yet it is quite possible to change abruptly from opposite leaves or bracts to whorls of fives in the flower, as may be seen in Hypericum and Dicmthus. This arrangem.ent, as I have elsewhere shown, is that- most easily acquired when opposite and decussate leaves become alternate by the development of internodes (see pp. 11 and 18). Hexameeohs Whorls. — A floral whorl of six parts is, in most cases, as amongst Monocotyledons, the result of the combination of two whorls of three each — as the androecium of Berheris, Tulip, or perianth of the Lily of the Valley. It may, however, arise from symmetrical increase, as, for example, in the orders Meliaceoe and OlacinecB. In the former, there are 18 genera with alternate leaves and 6-merou3 flowers; 9 with 4-5-merous; 4 with 4-meronsj THE PRINCIPLE OF NUMBER. 35 4 with 5-6-meroas, and 1 with 4-6-merons whorls in the difEerent species. In Olacinece, of 36 genera, 17 have alter- nate leaves and 6-merous flowers ; 7 have 4-5-inerous ; 4, 6-6-merous ; 2, 6-merous, and 1, 4-6-merous. As six leaves cannot form a cycle of any of the ordinary kinds of phyllotaxis, this will account for its rarity in nature ; and indeed it may probably, without exception, be divisible into two whorls of three members each, except in the case of symmetrical increase from five. Heptamerous Whoels. — Like the number 6, 7 is a very rare one ; and when present appears to be due to its being a primitive number or to symmetrical change. If any whorls are deducible from decussating verticils of threes, a cycle may contain seven parts, as the phyllotactical series arising from the breaking up of such verticils into a continuous spiral arrangement is represented by ^, ^, f-, -^y, etc. So that if leaves on a plant were in whorls of threes, as occurs in some instances, and not opposite, as in the primitive type amongst Dicotyledons, then a heptamerous arrangement would occur. If, therefore, there be any existing illustra- tion, it must, by the very nature of the case, be exceedingly rare. It sometimes occurs in Trientalis ; and when this is the case, it may possibly have arisen as here suggested. According to the description given of this plant in the Genera Plantarum, the numbers of the three outer whorls range from 5 to 9, the capsule being 5-valved. The leaves, on the other hand, are " saepe tot quot petala subverti- cillata." A second cause is arrest. This obviously accounts for the 7 anthers in Pelargonium, for the 10 filaments are present. A third cause is symmetrical change. I/ythrum Salicaria illustrates this as already mentioned. This flower is some- times described as 6-merous, but it is not always so. The 36 THE STEUCTUKE OF FLOWERS. ceatral floret of the cyme has often a higher number than that of the lateral ones ; so that if they be 6-merous, the central flower -will be 7-merous. Agapanthus, amongst Monocoty- ledons, is another instance, its flowers ranging from 6 to 8 in the number of parts in the whorls. OcTAMEEOUS Whoels. — A whorl of eight parts is not common ; but it .appears in GMora and in the corolla of Dryas oetopetala, in which it may be a cycle of the f phyllotaxis. In other oases it is a combination of two whorls, which, as a rule, can be easily distinguished as the stamens in the Ona- gracece, or it may be due to symmetrical change. Enneameeotjs "Whorls. — The number 9, like 6, 7, and 11, corresponds to no cycle of any one of the usual forms of leaf- arrangement, and is proportionately rare. It may occur as a combination of three cycles of three each, and perhaps this wiU account for it when it occurs in Trientalis, and the androecium of Mercurialis. The stamens of ButoTnus are also nine in number. Decameeous Whoels. — The number 10 never occurs except as the union of two whorls of five in each, as in the androecium of LeguminoscB. Endecameeous Whoels. — Like 7, the number 11 might occur if the series J, i, f , -^, etc., was as frequently repre- sented as ^, I, I, f, etc., when "sevens " would be as abun- dant as " fives " are now. I do not know of a case where it could reasonably be referred to such an origin. "When it does occur, as in CupJiea, it is clearly due to an arrest of one stamen through insect agency. Brownea is said also to have sometimes 11 stamens ; if so, this would undoubtedly be due to numerical increase. DoDECAMEEOUS "Whoels.— The number 12 closely verges on the "indefinite," which simply means a more or less numerous series of cycles of the same kind. Neverthe- THE PRINCIPLE OF NUMBER. 37 less, it occurs as a " definite " number in several instances. The 12 stamens of Lythrum are, of course, two series of six each. Both 12 and 24 are found in the Grassulacece, as in Sempervimim, in which genus the petals vary from 6 to 20, and the stamens from 12 to 40. This seems to show that in the one case they are combinations of cycles of threes, in the other, of fives ; just as Berheris illustrates the former, Chimo- nanthus the latter instance. Indefinite Whorls. — As soon as we pass from twelve to some higher number, then flowers cease to be whorled, and the parts are arranged spirally, and follow more or less exactly the laws of alternate phyllotaxis ; interferences occur in consequence of the want of space, some secondary spirals being often incomplete. Moreover, since the fibrovascular cords become fused, in other words bi-anch by chorisis, and are not independent as of ordinary foliage, parts take up slightly different positions to what they would if they could strictly follow phyllotactical laws. I have alluded to what I call " symmetrical increase and decrease " as causes of variation in the number of parts of whorls ; and what brings about these variations in number, is an excess or deficiency of nutriment and vital activity respectively. There are innumerable examples of all the above kinds of changes in number. In fact, if any one or series of whorls of a flower be w-merous, it may become n ± a;-merons, and will give rise to symmetrical increase or decrease accordingly ; or again, three whorls of the same flower may become n ± x, n ± y, n ± g-merous ; when all numerical symmetry between them will be destroyed. Similarly, if the parts be spirally arranged, the number may vary from the prevailing one by increasing or decreasing the length of the spiral, both in flowers of the same plant or in different species of the same genus ; as, for example, may 6 38 THE STKUCTUEE OF FLOWERS. be seen by comparing the nnmber of stamens in a large- flowered form of Banunculus aquatilis, with the small- flowered Bi. hederaceus ; or one genus with an allied one, as Ranunculus with Myosurus, in which the stamens are reduced, often to one whorl of five only. Lastly, just as high spirals can be broken up into ternary whorls, so can the arrangement ^^y be separated into whorls of a lower series, as of 13, 8, or 5 parts respectively. Thus, of the two genera, which have opposite leaves, comprising the order GalycantJiacece, Galycanthus illustrates an abrupt change from opposite leaves to the -j^ arrangement in the bract-like sepals of the flower; but no distinction between bracts, sepals, and petals can really be made. Ghimonanthus, however, would seem to be a more highly difEerentiated type, in that, not only is the calyx distinguishable f A)m the corolla, but five exterior stamens constitute a distinct whorl by them- selves, and the indefinite barren ones of Galycanthus are here reduced to five ; so that, omitting the pistil, the flower con- sists of four distinct pentamerous whorls. CHAPTER IV. J3 S THE PRINCIPLE OF AEEANGEMENT. SuPEEPOsrrioN and Alternation of Whorls. — It has been already observed that leaves are arranged on two methods, either being on the same plane, i.e. opposite and verticillate ; or with only one at a node, i.e. alternate. If the fibro-vascular cords passing from the leaves into the stem be traced downwards, >« ^^- mmis km , those belonging to the leaves i^- situate in one and the same ver- to tical line always have their lower extremities inserted laterally and not actually confluent in that line, as will be seen in Fig. 7, taken from Hanstein's researches.* This fact is tme, not only for foliage and bracts, but also to some extent for sepals and petals. When, however, we trace the az -* a/ a 3.a.s. fiT-iCTiTi nf stampriR nnr) fjlTnpla wo Fig- ' —Wogram of the foliar conjB in origin 01 siamens ana carpeis, we ^^^ ^^^ ^j ti,^ ArabU aUMa (after find that their cords, instead of ^Hanstein). being inserted separately into the fibro-vascnlar cylinder, generally arise by branching, or by the so-called "chorisis" • De la Connexion qui existe entre la Disposition des Feuillea et la Structure de la Zone Ligneuse des Dicotyledons, Ann. des. Soi. Nat., 4" ser., torn. 8. 40 THE STRUCTURE OF FLOWERS. of the cords belonging to the sepals or petals, or from both ; and similarly the dorsal cords of the carpels branch off from the same stem as that of the sepals or petals, very rarely from both at once. Simultaneously with the dorsal, two marginal cords pass up directly into the placentas, having originated in the same way; and, in so doing, the floral re- ceptacle usually becomes extinct, and takes, as a rule, no further part in the construction of the central portion of the pistil. Starting, then, with these two fundamental sources of the various arrangements of the parts of flowers, we may first observe that of opposition or superposition and alternation, the former, if represented by decussate pairs of appendages, is the most primitive type. This is seen in many quaternary flowers in which the sepals emerge in successively decus- sating pairs. Such opposite leaves being foreshadowed in the cotyledons of exogens. The next, or rather the first stage of differentiation is seen in the spiral condition which obtains in many flowers, mostly represented by the ^ and | types : thus, e.g., ^ repre- sents the arrangement prevailing in petaloid Monocotyledons ; and all pentamerous calyces issue in a quincuncial manner. In Sahia, the petals follow continuously with the sepals in the same spiral line, so that the first petal is superposed to the first sepaL These whorls accordingly represent two cycles of the f type, as seen above in Oaridella (p. 21). By far the commoner condition is to break up the spiral into cycles, say of five parts each, and then to shift their positions, so that they become alternate instead of superposed. Now, such a decussate arrangement is usually described as a fundamental law, not only governing opposite and verticillate leaves, but floral whorls as well ; and particular stress is laid upon the usual presence of the petaline whorl of carpels, THE PRINCIPLE OF AEEANGEMENT. 41 inasmuch as the law of alternation is thus carried out completely, and which may be represented as follows — the hyphens indicating the parts superposed to one another — Sepal-stamen ; Petal-carpel. Prom what has been stated above, the true order of arrangement and superposition would be — Sepal-stamen- carpel; Petal-stameit-carpel ; and either one of the staminal and either one of the cai-pellary whorls may be suppressed. Thus, for example, Oxalis, Zygophylliim, Geranium, and Euta have Sepal-stamen ; Petal-stamen-carpel : while Limnanthes, Coriarea, and Agrostemma have Sepal-stamen-carpel ; Petal- stamen. As instances where there is but one whorl of sta- mens. Campanula and Hermannia have Sepal-carpel; Petal- stamen ; whereas Idnum and Biosma have Sepal-stamen ; Petal-carpel. Of these variations, although Sepal-stamen is commoner than Petal-stamen, and Petal-carpel than Sepal-carpel,* yet these are, so to say, rather matters of accident than otherwise, in that it is probably due to certain exigencies of nutrition, and especially insect agencies, that such variations of arrangement exist The important fact mentioned above, that floral whorls are projected cycles and not primitive whorls, has, as far as I know, been entirely overlooked by botanists. Thus, for example, Professor Asa Gray remarks on the presence of whorls in flowers as follows : " Cycles alternating with each other are simply that of verticillate phyllotaxy," f to which he refers the opposite, temate, quaternate and quinate verti- cils. J In the case of leaves, verticils represent usually more primitive types, such as twos and threes, and, from an evolutionary point of view, sxxcla. precede alternate and spiral arrangements. • I.e. in Bxogens. t Bot. Text-Book, p. 175. % i.e., p. 120. 42 THE STEUCTUEE OF FLOWEBS. On the other hand, whorls of threes, and fives, and others in flowers are com'pressed cycles of spiral arrangements. They are, therefore, attempts at simulating ancestral or the verti- cillate conditions, but cannot possibly be primitive whorls themselves. That the petals can thus become decussating with the sepals is a result of the fact that their cords are not strictly superposed to and confluent with those of the latter. "The total number of cords in the pedicel being usually limited to the same number as there are parts in the perianth, i.e. the calyx and corolla together, there is ample room for them to arrange themselves at equal angular distances around the central medulla of the pedicel. Then from the vascular cylinder thus formed, they pass off into the sepals and petals respectively.* The sepals and petals or the two whorls of a perianth being thus provided for as to their fibro- vascular cords, the stamens and carpels, as already stated, generally depend upon these latter for their positions, and various arrangem.ent9 arise according as the cords of the perianth-leaves give off new members or not. Theoretically there should be at least one whorl of stamens superposed to the sepals, another superposed to the petals, and two whorls of carpels as well ; but while many flowers have both staminal whorls {Caryophyllece, Leguminosce, Ericaceae, etc.), many others, as the Gamopetalae retain only one, and more generally the first formed or sepaline, but sometimes it is the petaline, as in Primulacece; the probable cause in each case being certain exigencies in • That foliar organs posses^ this power of rearranging themselves according to requirements is evident from other considerations ; thus, many plants having freely growing erect shoots — as, for example, the common Laurel — have their leaf-arrangements represented by tho fractions | or J, but when extending horizontally, as in the usual con- dition, they are distichous. Similar features are seen in the Jeroaalem Artichoke, which often changes its phyllotaxis on the same stem. THE PRINCIPLE OF AEEANGEMENT. 43 tt. fft. the flower, througli which nourishment is withdrawn at certain places to produce hypertrophy elsewhere. Thus the sepaline cord, instead of bearing an anther in Primula, bifur- cates at the angle, and each branch proceeds up the margin of a lobe of the corolla, and aids in nourishing the latter. As a converse instance of the sepaline cord undertaking a considerable amount of work, may be mentioned Gampanula ■medium. In this plant the 5-lobed fibro- vascular cylinder of the pedicel sends ofE five cords intended for the calyx (Fig. 8, sep.) ; but, before reaching the base of the superior sepal, it sends ofB an inner- most and lowest cord to become the dorsal one of the carpel (d. car.), which, in this flower, is thus super- posed to a sepal. It also sends off two, right and left, one for each petal alternating with it (pet.) ; so that each petal receives two cords, one from each adjacent sepal, — a -^ most unnsual condition of things, O . , — vOZT^^, „, for petals have almost invariably /^ II \ their own cords issuing from the ^x n_7 ^ pedicel. Lastly, the same sepaline Fie- S—Vcrtical and transverae aec ^ . tions of the wall of the inferior cord provides that of the stamen ovary of campanula medium -,^ ji-i Til- (*"*"■ ^^^ Tieghem). (St.) superposed to it. In this flower, therefore, we can understand why there is no petal- ine whorl of stamens ; simply because the corolla does not possess its own proper fibro-vascular cords to give rise to them. On the other hand, in the Malvacece after the axis has supplied cords for the sepals, others furnish those of the corolla ; these latter, however, by radial division form two ^ft. 44 THE STRUCTUKE OF FLOWERS. to each petal, subsequently dividing into several; for the same pair by repeated tangential division gives rise to the series of stamens (which have been thus doubled) superposed to each petal, both having arisen from a common cord. With regard to the numerous carpels of Hollyhock, I find that the axial cylinder which has given rise to the five sepals continues on, and by radial division again supplies cords to the carpels, which are grouped into five sets super- posed to the sepals, as may be easily seen if the pistil be examined from below. Hence, as the sepaline or petaline cords in these flowers each undertake to form a large number of extra parts — many stamens in the one case, and many carpels in the other — it is presumable that neither sepaline stamens nor petaline carpels could be formed. With regard to the presence, and consequently the relative position, of one whorl rather than the other of the gynoecium, it is due to the fact that sometimes the sepaline cord will give rise to the dorsal carpellary, as in Althcea and Campa- nula; at others, it is the petaline, as in Fuchsia, Sedum, Ivy, etc. ; so that the carpels become superposed to the sepals or petals accordingly. As instructive instances of variations in this respect occun-ing in the same family, it may be mentioned that all species of Campanula which have five carpels, as also Wahlenbergia capensis, Michauxia, Ganarina, and Lightfootia subulata, have their carpels superposed to the sepals and stamens. On the other hand, Musschia (^Campanula aurea, L.) Platycodon (G. grandiflora, Jacq.), and Microcodon have the carpels superposed to the petals. * The fact that either the sepals or the petals can have the carpels superposed to them respectively, just as they can each have a whorl of stamens, and that, in some few orders, the two whorls are actually present, as in Butomece and Jtmcaginece, led me to assume two whorls as the primary THE PEINCIPLE OF ARRANGEMENT. 45 or ancestral number of carpels in an ideally complete flower. Besides the usual alternation of whorls resulting from a regular and equal displacement of every part of the whorl, there may be unequal displacements ; thus, while Cistus has a pentamerous flower, with strict alternation of its whorls, Helianthemum has a tendency to be trimerons ; first, in the two outer sepals being reduced in size, and the pistil to three carpels instead of five. In this flower there are five petals, but in correlation with the preceding irregularities, it will be found that two pairs of petals stand superposed to the sepals, Nos. 3 and .5, while a single petal is over No. 4 ; Nos. 1 and 2, therefore, have none superposed to them. With regard to the stamens, it may be added that those of Cistus consist, first, of one whorl of five, the most interior and first developed superposed to the sepals ; and a second whorl superposed to the petals, in which the stamens are grouped into five clusters. The staminal whorls arise centrifugally. Another cause of a change of order in the whorls results from substitution of one kind for another. Thus, in the female flower of Zanthoxylon, the five carpels are superposed to the five sepals. In the male, five stamens now occupy exactly the same place as the carpels, the corolla alternating with the sepals in both kinds.* The interpretation I would suggest is that the sepals, being the only whorl of the perianth developed, the calyx is the only source for supplying the dorsal cords of the carpels which thus become necessarily superposed to them. From what has now been said, it will be. seen that the arrangement of the essential organs of a flower is, as a general * See Figs, in Le Maont and Decaisne's Descriptive and Analytical Botany, p. 324. The female flower is described as apetalous, but Payer discovered rndiments of the petals. 46 THE STRUCTURE OF JFLOWEKS. i rnle, most intimately connected with the union of their fibro- I vascular cords with those of the perianth ; and as parts of flowers are often multiplied, as the petals of Camellia, perianth-leaves of DafBodils, etc., such has given rise to the idea of chorisis or dedoublement of French authors ; as if one organ had split into two or more. That vascular cords can become repeatedly bifurcated is abundantly observable, whether radially, as in the case of the carpels of the Holly- hock, or tangentially, as in producing the stamens of the same flower. The more correct way, therefore, of regarding the process would seem to be, first, to recognize the phyllo- tacticai origin of the perianth as the basis to start from, and then to regard each fibro-vascular cord as an instrument for furnishing any number of appendages, whether they be additional petals, stamens, or carpels, by the process of chorisis, not of the complete organ, as generally meant, but of the cord belonging to it. To summarize these remarks — we find that the cause of the alternation of the whorls of the perianth, or of the calyx and corolla, is due to their being made up of cycles of spiral arrangements, which are projected on to the same plane, and so form verticils. Their positions are then shifted so that the parts of each whorl bisect the angles between the parts of the whorl succeeding or preceding it. Secondly, having laid this foundation, the stamens and carpels follow in superposition to one or other or both of the preceding whorls in consequence of the branching of^the fibro-vascular cords. And this accounts for super- position. It may be still further inquired why in some cases the sepaline, and why in others it is the petaline cords which give rise to a whorl of stamens or carpels, as the case may be. The reply at present must be speculative, for there may THE PRINCIPLE OF ARRANGEMENT. 47 be more than one influence at work to determine what whorl shall follow each of those of the perianth. The immediate cause is nutrition ; but the deeper question, what directs the nutrition to one cord rather than another, can only be guessed at in most cases : but as the petaline stamens are generally absent from at least the gamopetalx, it would seem that the enhancement of the corolla through the agency of insects has caused the whorl of stamens in front of it to be atrophied through compensation. Some special circumstance, however, we know not what, have interfered to retain that whorl in Primulacece, and some few other plants. The reader must be reminded, however, that this method of branching in order to give rise to stamens and carpels from the cords of the perianth is not universal. When they are many, it is done by the fibro-vascular cylinder of the pedicel becoming much enlarged, and consisting of a great number of cords, all arising by lateral chorisis, it is true, but long before they enter the floral members ; so that by the time the latter are about to emerge they each receive their own cords from the general axial cylinder. This is what happens e.g., in Banunculacece and Oruciferce. 48 THE STRUCTURE OF FLOWERS, CHAPTER V. THE PEINCIPLE OP COHESION. Cohesion. — General Obseeyations. This term signifies the miioii between parts of the same kind or whorl ; and the prefix gamo- is nsed in conjunction with the terminations -sepalons, -petalous, and -phyllous, — to indicate that the parts of the calyx, corolla, and perianth respectively cohere. In the case of the stamens, they are said to be mon-, di-^ tri-, or poly-adelphons, according as the filaments cohere into one, two, three, or more groups ; while syngenesious is nsed for the coherence of anthers, and, lastly, syncarpous denotes that the carpels of a pistil cohere. There are two kinds of cohesion, congenital and by con- tact.* Congenital cohesion I regard as an advance npon freedom, or a further state of difEerentiation ; for, according to the principles of Evolution, freedom or separation of parts must precede their union ; just as, for example, bones are free in the embryo which become " ankylosed " in the adult ; or always free in a fish, while their homologues cohere in higher types of vertebrates. Congenital cohesion applies to by far the greater number of cases of union amongst the parts of the different whorls • We might appropriately distingnish these two kinds of union by the terms connate or " bom together," and coherent or " sticking together." THE" PKINCIPLE OF COHESION. 49 of flowers, respectively. Cohesion by contact is the cause of the anthers being syngenesious in the Compositm. It applies, sometimes at least, to the two margins of each carpel when in contact up the axis of an ovary, as of that of a Lily. The stigmas of Asclepias are at first free, but later in their deve- lopment they become coherent by contact. Congenital cohesion takes place almost from the very commencement of grovf^th and development of the parts, so that when full-grown there may be no trace of the line of cohesion. Fibro-vascnlar cords, indeed, often occur in the f very position of it, not unfrequently branching ofE in various ways, as, e.g., at the fork to nourish the adjacent free portions ; of the limb. This occurs in the calyx of Stachys and the, corolla of Primula, etc. In Campanula rotundifolia the fibro- vascnlar system of the corolla becomes completely altered, and instead of representing that of distinct leaves in contact by their edges, the veins ramify and anastotnose all over the general space between the two adjacent dorsal ribs, com- pletely obliterating all trace of the line of union between them. In the case of the Primrose, however, the calyx has I the exact appearance of five pinnately nerved leaves being | united by their thin and impoverished edges, where there is ' nothing but translucent tissue without any cords at all. It is important to observe this more or less complete modification of the fibro-vascular system under congenital cohesion, as it shows how much more highly differentiated a condition has been acquired than when the parts are free. In the latter case they represent more closely the forms and venation of distinct foliar organs. As a curions instance of cohesion of both kinds in the same organ, may be mentioned the corolla of Phyteuma ; the basal portion of which consists of five petals congenitally united ; but the five portions of the limb cohere by contact 7 5U THE STRUCTURE OF FLOWERS. at the apex, and so form a tube which collects the pollen shed into it by the five free anthers, which are included within this corolla-tube (Fig. 9). They thus form the "cylinder" for . the " piston " action of the pistil which continues to grow, and so sweeps out the pollen beyond the extremity of the tube, just as it does from the syngenesious anthers of the Com- positcB and Lobelia. The five portions of the corolla thus cohering by con- tact subsequently become more or less free. The rationale of Cohesion lies in its adaptation to insect agency, and Fig. 9. — Phyteuma (after Muller). • t . j j. ■ t ^ ' implies a greater degree of specializa- tion than when the parts of the whorls are free. Thus in Thalamijlorce, of such an order as Ranunculacece with regular flowers and with all the parts of the perianth whorls free, the flowers are usually visited by a much greater number and variety of insects than are those of orders of GorolliflorcB. For example, Muller records sixty-two species of insects as seen by him to visit Eianunculus acris; whereas the humble-bee alone enters the gamopetalous tub^of the Foxglove. This adapta- tion oiform to insect visitors will -be better appreciated when we come to. discuss that principle of Variation, which so powerfully affects floral structure. It occasionally happens that parts normaUy united become free : the process is called " dialysis," and may be regarded as a reversion to an ancestral free condition. Fig. 10 repre- sents a flower of Mimulus in this condition. The rationale of cohesion in the sepals, petals, and stamens, I regard as the immediate result of hypertrophy set up by insect agency, THE PRINCIPLE OF COHESION. 51 Fig. 10. — Mimuluv undergoing "Dialysis" (after BaiUoo). aided by the close proximity of the parts; and as a resulting efEect, is the ever-increasing adaptation to the requirements of insects, which are more and more specialized for them, so that, for example, Lepidoptera are almost solely adapted to long tubular flowers like the Honeysuckle. An analogous process of congenital cohesion is well seen in the f asciation of stems which occcrs particularly often in snccnlent shoots, as Asparagus, Cabbage, Lettuce, and the young shoots of the Ash tree. This is most reasonably referred to hypertrophy coupled with the close proximity of the buds which ought to have developed into independent shoots. Again, cohesion between the sepals or petals of Orchids is not uncommon abnormally under cultivation ; and would also seem to be due to the stimulating conditions under which they are artificially cultivated. Hypertrophy in an organ is due to a special flow of nutriment to it ; and cohesion may result from the close proximity of the parts of the whorl to one another ; but the influence which brings about the determination of sap to a particular point, I take to be the mechanical strains induced by the insect visitors when alighting upon the flower in search for nectar or pollen. If this principle bo correct, that the tubular structure of calyces and corollas, as we see them now, has arisen through the requirements of those organs to meet strains thrown npon them ; I think it will furnish the solution to many a question that may arise as to the peculiar shapes of corollas, etc., besides explaining the veiy principle of cohesion itself. An 52 THE STEUCTURE OF TLOWEES. insect alights on one or two petals. In order to support it, an immense gain is secured if the flower can call in the aid of the other petals ; and this is obviously obtained by their cohesion into a tube, just so far as the required strength is wanted. Nothing would be gained by the portions of the limb being united, as far as additional strength was required to bear the burden. The tubular structure is the strongest possible, and when short, as in rotate corollas, little extra aid is required ; but if it be long and visited by heavy insects and not by Lepidoptera, which hover in front of the flower and ODly insert their long and slender proboscides, then the tube finds additional support in the calyx being tubular as well. At other times mutual suppoi-t is gained by the close contact of the flowers, as in a capitulum of the Compositoe, from which the calyx vanishes. Of course, every degree conceivable is met with between short, stout, and strong tubes with no additional aid, and slender ones supported by a strengthened gamosepalous calyx. These are adapted to insects which alight upon the corolla limb ; while for .Lepidoptera the tube is more elongated, and, as no weight is thrown on the anterior petals, no extra support is required. That this is the true interpretation of the origin of a gamopetalous corolla, appears from such negative evidence as is seen, for example, in Lonicera Peri- clymenum and Asperula tcmrina* which have greatly elongated and contracted tubes, deriving no support from the arrested calyrx; and although somewhat two-lipped, the anterior member is no larger than the others ; the reverse being always the case when a heavy insect is the regular visitor. These two species are exclusively fertilised by the Lepidoptera, such as the Hawk-moth, which only hovers in front of the orifice, but throws no weight upon the corolla. • See Mailer's figures, Fertilisation, etc., pp. 296, 303. THE PRFNCIPLK OF COHESION. 53 We may see, as it were, Nature's first attempt to form a tubular process in the Cruciferce. Here it is obtained by simple approximation of the slender claws of the petals, which are supported by the erect and closely imbricated sepals. A step further is gained in Dianthus, in which the sepals cohere but the petals are stiU free. The third and last stage is arrived at when both calyx and corolla are tubular. Subsequent to this state of cohesion many additional structures may arise as they are required in the formation of ribs, etc., as already explained ; while the very form of the tube may change from a purely straight cylinder to a curved or expanded funnel, etc., according as special strains have to be met, which the original form was not well calcu- lated to sustain. These changes of Form will be more fully discussed when I treat of that principle of Variation. 54 THE STRDCTtJRE OF FLOWERS. CHAPTER VI. THE PEINCIPLE OF COHESION — Continued. Cohesion of the Sepals, or Gamosepalous Calyx. — This is congeniial, and may be free, as in the Carnation and Primrose, or associated with a " receptacular tube," as in Leguminosce and Bosacece. As sepals mostly represent the petioles of leaves, the tubular part of a gamosepalous calyx consists really of the fusion of the expanded petioles, the teeth of the limb being all that remains to represent the blades which are usually suppressed. The main fibro-vascular cords correspond to the mid-ribs, while the interspaces are either without additional " marginal " cords, as in the Primrose, or with single or double cords in the line of junction, as in the Labiatce ; or they may be covered with anastomozing reticulations without any linear cord at all, as in Mimulus. With regard to the presence of linear cords in the line of suture, if there be five sepals, there will be at least ten ribs to the calyx ; i.e., if there be only one marginal cord ; but as there are two margins which cohere, they may have a separate cord apiece ; and then there may result fifteen cords in all. Thus Stachys has five dorsal cords with barely traces of five marginal ones ; Ballota has ten, and Nepeta fifteen. The above arrangements may be modified by the separa- tion of the two marginal cords in certain places but not in THE PRINCIPLE OF COHESION. 55 others, while supemumerary cords can be formed, which appear to have for their function to strengthen the calyx to meet the strain upon it wfcen an insect alights upon the flower. In the calyx of some species of Salvia, which is strongly bi-lobed, though retaining its five teeth, three dorsal (d) are posterior and two are anterior. There are two single marginal (m) cords between the three posterior and dorsal, which corre- ^ g spond to the mid-ribs of three sepals. The tn m two lateral and marginal cords are each in m double; while a supernumerary cord (s) lies " * beneath the lip of the corolla between the *"■ '"' two anterior marginals. The accompanying diagram of the sepaline cords of 8. Verhenaea will illustrate the arrangement. The arrangement of the cords (m and s) shows that the strain being greater on the anterior side, the calyx has, as it were, stretched in that direction, the two marginals having separated so widely in front, as to require an extra cord (s). The two lateral ones have not separated to so great an extent, while on the posterior side, where little or no strain is felt, the marginal cords have remained single. As the cord (s) shows how Nature can add a fibro-vascular cord if required, so one or more can be subtracted by atrophy where no stress occurs. Thus the petals of the Compositce have no dorsal or median cords, the five sepaline only being present below, but pass up the margins of the petals. Con- [ versely, in the Primrose, the calyx, giving no support to the , corolla, has no marginal cords. The aljove diagram will represent the distribution of the sepaline cords of 8. glutinosa and other species, as well as 8. Verbenaca, but in S. pratensis the strain has apparently 56 THE STRUCTURE OF FLOWERS. been not so great, consequently the supernumerary cord («) has not been developed. Such slight differences are ^gnificant, because they show- how readily an organ can respond to different degrees of force brought to bear upon it by different insect visitors ; and the cords are invariably placed just where the strains are greatest. The number of ribs to the calyx has been • adopted by systematists as generic characters in some of the Labiatce, as well as the tubular or campanulate shape of it. Now, it will fee found that the shape corresponds with the requirements of the corolla ; so that if the tube of the latter be compara- tively short and slender, the calyx completely encloses it, and has its surface strengthened by a variable number of ribs according to the genus ; though they are not always constant on the same plant. As examples, may be mentioned, Mentha and Melittis, which have a broad campanulate calyx, and a broad tube to the corolla. Stachys has 5-10 ribs surrounding the cylindrical corolla-tube. Galeopsis versicolor has 10 prominent ribs, and 10 othei-s which reach from the base of the calyx-tube to about half-way up. Melissa has a very narrow elongated calyx, which fits the slender tube of the corolla exactly, and has 13 or 14 ribs.* Similarly Nepeta Cataria and N. Glechoma support the contracted slender basal •part of the corolla-tube, and have 15 ribs to the calyx. Teucrium Scorodonia has only 5 dorsal ribs and 2 (posterior) marginal. The calyx is very broad compared with the slender corolla-tube, and scarcely, if at all, supports it. This flower, is visited both by bees, and nocturnal Lepidoptera which suck without throwing any weight upon the flower. Cohesion of Petals, oe Gamopetalous Coeolla. — As • This difference in the nnmber of ribs depends npon the lateral and marginal being single or double. THE PRINCIPLE OF COHESION. 57 already stated, this is congenital, and, as mth the calyx, so with the corolla, the line of junction may be marked by a marginal cord, or the interspace covered with reticulations as in Campanula rotundifolia. As in the calyx of many Labiates, so there may be super- numerary cords in the corolla, until they may be greatly increased in number, as in Gonvolvulus Sepium, Digitalis, etc. The cords being straight in the tube may ramify in the lobes, adding thereby marginal veins to the latter, as in Primula and the Gompositce. In this last, the petals are devoid of median nerves, hence the importance of the mar- ginal with their branches up the edges of the corolline lobes. It would be superfluous to multiply examples if the principle be understood ; and what I particularly wish the reader to realize is the, so to say, extraordinary plasticity which resides in these organs of flowers, in that they evidently have the power of altering their structure to meet a variety of requirements ; so that if we might compare them to architectural buildings, we might say that the floral Architect at one time saw not only a chance of some orna- mental improvements in a frieze at some particular place, gi-aceful lines of colour or curvature in another ; or, again, flutings, depressions, and elevations, etc., all breaking up any chance of monotony : but cunningly adds elegant buttresses without, as well as runs up ribs of masonry within the walls ; which, while intended to meet particular strains, only add additional charms to the general and harmonious beauty of the entire fabric. Cohesion op Stamens — (1) " Adelphous " Filaments. — This occurs in various degrees, from a comparatively slight union at the base, as in Linum usitatissimum, to a short distance from the anthers, as in MalvaceoB and Leguminosce. It is undoubtedly an adaptation to insect agency. 58 THE STRUCTURE OF FLOWERS. If the stamens be monadelplions, and the union be extended, it may completely enclose the usual honey-secreting surface characteristic of allied genera, the result being that it can secrete none at all. In such cases, insects are deceived in visiting the flower, as in Genista, and some other mona- delphons genera of LeguminosoB. Otherwise, the honey is secreted by some other source external to the staminal tube, as iu Idnum catharticum ; in which flower five inconspicuous glands occur on a fleshy ring, just opposite the stamens. In Malva, the honey is found in five pits between the bases of the petals, and in Pelargonium in a long tube formed by one sepal, the insertion of which remains far below that of the others, which are carried up by the growth of the pedicel. In Laburnum* as in Orchis, instead of a secretion, the fluid is only to be secured by piercing succulent tissue which is found in front of the vexillum in the form of a cellular cushion. In diadelphous species of the Leguminosm, the honey may be secreted by the inner basal portion of the staminal tube,* or else, and perhaps more usually, by an annular disk which surrounds the short pedicel of the ovary, as in Pisum. In this case the honey is easily secured by the proper insects as the superior stamen is free, and there is also an additional facility of access by means of an oval space formed by the widening of the staminal tube just above their base. In Gercis, the disk is very large, and the 10 stamens stand in depressions around it. Consequently they are entirely free. The staminal tube, together with the petals, which are more or less interlocked together, protect the honey from being rifled by the wrong insects,! ^^ i* •'^^ ^^J ^ secured • According to Miiller. + A cnrions additional protection occurs in Eippocrepis comosa, in that the claw of the vezillom, which is elevated in a remarkable manner, THE PRINCIPLE OF COHESION. 59 by such as have proboscides of sufficient lengtb to reach it, corresponding, of course, to each species or genns. Papilionaceous flowers being irregular, and visited in but one way, it is only the superior stamen which is free; but the staminal tube is often imitated in other flowers where there may be no cohesion at all, as by the tribe Ocimoidem of Labiates, Collinsia hicolor of the Scrophularinece and Polygala, etc. Similarly, in the case of regular flowers, the mona- delphous condition may be closely mimicked by filaments which are stout and sufficiently rigid to form a column. This occurs in Gruciferm, Viola, Convolvulus, Crocus, etc. In some cases, as in Crambe and Deutzia, the filaments are pro- vided with wing-like structures which render the tube more complete. In orange flowers, a certain amount of cohesion is actually obtained between some of the filaments. (2) Stngenesious Anthers. — These, as stated, are not congenitally united, but by simple contact. As with fila- ments, so with these, it is an adaptation to insect fertilisation. Jasione montana famishes a good instance for an incipient stage where they just unite at their bases only. This cohesion is completed in the genus Synanthera of the same order GampanulacecB, as well as in the sub-order LoheliecB. In other cases of true syngenesious anthers there is a complete lateral fusion, as in Lobelia and Compositce, in Gloxinia and Im- patiens. In all these cases the cohesion is by lateral con- tact only, and not congenital ; that is to say, the papillae of the future anthers on emerging from the axis grow to a somewhat considerable stage of development as incipient anthers before coming into contact. They then coalesce, apparently by a slight solution of the surface of the cellular carries a triangular flap, which exactly covers the orifice leading to the honey. A somewhat similar flap occnrB in the petals of Phaseolus and Delphinium, which likewise keeps out unwelcome guests. 60 THE BTRUCT0BE Of FLOWEKS. walls whlcli touch. ; so that when they are fully grown the cohesion is firmly secured. An imitative cohesion is seen in the anthers of the Heartsease, which arises from the interlocking of marginal hairs down the sides of the cells. Anthers, when thas closely approximate without actual cohesion, are usually called " connivent," as in Ericaeece, and the word is perhaps appropriate to those of Solanum Dulcamara; but in this plant the union is very close, and might even be considered as syngenesious. The rationale of the close approximation of anthers, or of actual cohesion between them, is the effect of insect agency, just as for the filaments ; but the method of extraction of the pollen varies. In Viola, the proboscis is thrust through a small orifice between the connectival appendages of the lower pair of stamens, in order to reach the end of the honey-collecting spur. In Heaths and some of their allies, the anther- cells are at first in contact, and so prevent the pollen from escaping ; but each anther is provided with two auricles which extend to the corolla. A bee on entering first strikes the projecting stigma, but its proboscis soon turns one of the auricles aside, which, acting as a lever, dislocates the rest, and a shower of pollen falls out. In Gompositce and Lobelia there is a trne piston action. The style continuing to elongate drives the pollen out of the cylinder formed by the anthers, and elevates it above the flower, thereby rendering it easy to be dispersed by insects. This is well seen in Centaurea (Fig. 11) ; (o) represents the stamens with the anther-cells closed above by the connectival appendages. The arrow shows the direction of the insertion of the proboscis of a bee to reach the annular Fig. 11 CejUaurea. Stamena of THE PEINCIPLE OF COHESION. 61 honey-disk at the base of the style ; in 6, the style-arms have spread after protrusion through the separated connectives. The hrush-like tuft of hairs has svrept the pollen oat by means of the piston-action of the style. In Ca-mpanula, the action is different, for the anthers though connivent, have not yet become syngenesious, as in allied genera, e.g. Ijdbelia. They at first closely surround the style, which is provided with long collecting hairs upon which the pollen is caught. The anthers then shrivel and fall down. Subsequently a bee enters the expanded bell, grasps the style with her legs, and so transfers the pollen to the abdomen. This method is identical with that followed by bees in getting honey from Crocus, though in this genus the anthers remain erect, and, being extrorse, at once discharge the pollen upon the insect without the interven- tion of the style. 62 THE STRUCTURE OF FLOWERS. CHAPTER VII. THE PEiNCiPLE OP COHESION — Continued. Cohesion of Cakpels, or Syncakpous Pistil. — The accepted doctrine tliat the carpels are metamorphosed leaves, will be considered more fully when teratological modifications come to be discussed ; and the proof that an ordinal^ carpel, such as a legume, is merely a leaf folded upon itself in a condnplicate manner with the margins coalescing and then metamorphosed into a new organ, requires no special evidence now. That a syncarpous pistil consists of two or more carpellary leaves coalescing is equally admitted; and there are two methods of cohesion. Either the carpels may be ah initio composed of unclosed leaves, which cohere by their edges * respectively in contact, thus forming a single cavity provided with parietal placentas, — such a union implying a more primitive or arrested condition, from an evolutionaiy point of view ; f or they may be individually more or less closed before coalescence takes place, in this case by their lateral surfaces. The axile placentation is the result. The • The theory that the placentas are, at least in part, azial, will be seen to be erroneona in conseqnence of the orientation of their rascnlar cords (e.g. Pig. 12, c, p. 64; and Fig. 13, a, h, p. 65). f Thns the parietal placentation of Orobanche ia probably a result of degradation through parasitism, from the azile, of the Scrophuiarinea. It may be compared to a " cleft palate " and " hare-lip " in man. \ THE PEINCIPLK OF COHESION. 63 margins show every degree of union from a mere contact without real cohesion, thence, cohesion by contact, to a solid central axial stmcture formed by congenital cohesion. Laatly, the ovary may be one-chambered, with a free-central placenta, as in CaryophyllecB and Primulacem ; or with one or more ovules attached at the base, as in Bumex, Compositas, GraminecB, etc. It is these latter kinds especially which have given rise to much discussion as to the real nature of the placentas, and as to how far the axis enters into their construction. To ascertain this latter point, a study of the distribution and structure of the fibro-vascular cords of the -axis and of the carpels would seem to afford the most promising clue to the interpretation. It has been already mentioned that the dorsal cords of carpels generally arise by lateral division from those of the sepals or petals ; and then the carpels will be superposed to the one or the other of these organs respectively ; * or, a group may emerge from the axial cylinder in a horse-shoe form, as seen in section ; the outermost cord becoming the dorsal- carpellary, and the ends of the curve the marginal. This is the case, for example, in Cyclamen. The point, then, at which the carpellary cords branch off- from a common stem in the first case may be regarded as marking the termination of their axial character ; and in the latter case, at the separation of parts of the " horse-shoes " to form groups of threes. With regard to those cords which become marginal and placentary, it is important to notice the position of their spiral vessels.f If they are situated on the side of the cord nearest to the medulla, the cord may • See pp. 23, 24, and 42, 43, 44. t The cords are, of coarse, reduced to vessels and soft bast only, the former being mostly spiral, but occasionally becoming more ol: less reticulated. I shall adopt the UBoal word Trachew. 64) THE STRUCTUEE OF FLOWERS. generally be regarded as axial ; if, on the other side, i.e. nearest to the ovary-cell, and if transverse sections exhibit intermediate positions, in which they are central or scattered irregularly within the phloem, they are then marginal and placentary. They may change their position from one side to the other of the cord, as far as I have observed, in three different ways. The whole cord may twist to the right or left, as in Hellebore (Fig. 12) ; or, secondly, it may divide into two, and each half turn towards an adjacent half of another cord andnnite with the latter, as in Pelargonium zonale (Fig. 13, 6) ; or, thirdly, the tracheae may traverse the phloem and so pass out at the opposite side at a higher level, as in Ivy (Fig. 14,/, p. 68). In any case, as soon as the tracheae are so placed as to effect their object of nourishing the ovules, they may be pronounced to be unquestionably and strictly carpellary. I will take Hellebore as illustrating the first case. Fig. 12 represents a section of the floral receptacle taken imme- b Fig. 12. — Hellebore: sectionaat baseof ovazy. diately above the insertion of the innermost stamens. There are nine cords* oriented as axial, three of which are beginning to curve outwards to form the dorsal cords of the three carpels. Sections made a little higher show that the three pairs of cords have spread out and revolved so as to bring their spiral vessels into a radial direction (5, c). In this ' The tracheae are indicated by black lines or dots, the phloem being inclosed within the thin lines. THE PRINCIPLE OF COHESION. 65 position the tracheae of each pair of cords face each other. At this point, then, they have quite lost their strictly axial character of facing the centre, and the axis is therefore no longer concerned in the structure. A little higher the cayities of the ovaries (indicated by the dotted lines) appear between the dorsal cord and the pair of marginal ones ; and now the latter turn their spirals completely towards the ovary cells, having rotated through 90° in all. The object of this rotation is to enable them to send off cords to the ovules. The second method is well seen in Geraniitm, Pelwrgonium zonale, and Impatiens. A section of the receptacle of the first two, made between the insertion of the stamens and the pistil, shows five groups of three cords each, airanged as in Fig. 13, a. Small portions of the ten staminal cords are SD Fig. 13,— Pelargonium : sections at baae of ovary (a, b, after Van Tiegbem). seen on the circumference of the section. The outermost one of each group of three will form the dorsal cord of the carpel. The two inner hare their vessels already turned 66 THE STRUCTURE OF FLOWERS. towards each other, as described in Hellebore, and are in part required for the placentas. They are, therefore, no longer oriented as in an axis, i.e. with all the vessels arranged on the inner edge of the cord and facing the central medulla. A short distance above the base of the pistil, the inner- most cords divide in a somewhat irregular manner, but rearrange themselves symmetrically round the centre of the ground tissue in ten cords, as soon as the ovary cells have put in an appearance. The method by which this condition is arrived at was described by Van Tieghem in Geranium hngipes, and with slight modifications it -will apply to Pelargonium zonale. Each of the lateral cords divides into two (Fig. 13, 6), the two interior and adjacent branches unite to form a single marginal cord with the tracheae within or on the outer side (Fig. 13, c). The two outermost branches pass ofE to the right and left, and proceed to join the corresponding halves from the neighbouring systems. The pairs uniting thus form five cords of double origin, alternating with the crescent-shaped marginal cords of the carpels (c). There are thus formed five in front of the ovary- cells, and five in fi-ont of the septa ; " which," Van Tieghem observes, "one would regard as axial, if one did not pay attention to the mode of formation of the cords and to their orientation." In his description of Iwpatiens Boyleana, he says that the two innermost branches (Fig. 13, b) unite at first end to end, i.e. like an 8, with the tracheae at the extremities in contact; they then form one cord with the spiral vessels ■ towards the circumference of the section, by rotating through 90°, accompanied by complete fusion. In Pelargonium zonale, the tracheae become plunged, as it were, within the phloem-tissue of the cords, as shown in Fig 13, c, which then fuse together laterally. THE PKINCIPLE OF COHESION. 07 Above the ovary-cells, at the base and thicker part of the style, a section (Fig. 13, d) shows five solid circular buttresses, the tissue of which is continuous with the central paren- chyma, in the middle of which a lacuna (Z) is formed by rupture. In the depression between the buttresses, a small portion of the style and conducting tissae forms a bridge, as in Fig. 13, d, showing a cavity below it. It is in this homogeneous mass of ground tissue that we have a complete fusion of the hypertrophied borders of the carpels which have thus entirely lost their individuality. The axis proper disappeared as soon as the spiral vessels became oriented, as in Fig. 13, a. Hence the dotted lines radiating from the centre (c) mark the ideal boundary of each carpel, and the line across the base of the ovary-cell is the place where rupture will take place when the fruit is mature. The column, or so- called "carpophore," remaining is therefore entirely car pellary in its origin. The third method by which the tracheae pass from one side to the other of a cord is partly seen in the preceding ; and 1 suspect that this is the commonest method of all ; for though, when axial, the cord has its spiral vessels fixed at the inner angle, as soon as a change of position occurs or whenever it has to branch, the fixity of the position of the tracheae becomes relaxed, and they readily become enveloped in the rest of the tissue of the cord, and so pass from one side to the other with perfect facility, as will be seen in the case of the Ivy. When a syncarpous pistil has its ovary inferior — that is, imbedded in the receptacular tube — the real state of cohesion between the several carpels is masked in consequence of their partially undifEerentiated state ; the ovaries of which then have the appearance of being simply isolated cavities 68 THE STBUCTUKE OF FLOWERS. sunk within a mass of parenchymatoas tissue. In fact, they might often be called " falsely syncarpous," a term applied to the Pomece, but which is equally applicable to Ivy and Fuchsia. In the pedicel of a flower of Ivy, there are, at a distance of about three-quarters of an inch from the tapering base of the inferior ovary, four fibro-vascular cords (Fig. 14, a). A little higher these split up into an irregular circle (6), and shortly above the base of the receptaculartube there are fifteen (c), ten being more towards the circumference than the other five. The outer ten are for the sepals and petals. The five inner will appear superposed to the sepals (d), having been already separated off by radial chorisis rather low down ; these are for the stamens. Then from the petal- ine cords, by a similar method of chorisis, a small cord runs up the dorsal part of the ovary-cell and another up the axis. This fixes the position of the five carpels (if so many be present) as superposed to the petals (d). There are often only four, or even three, Fig. 14.— Ivy : sections tram pedicel to sammlt of ovaiy. THE PRINCIPLE OF COHESION. 69 ovaiy-cells developed. When this is the case, the cords of the centre become fused into four or three (2 -)- 2 + 1) (e), and take np a position alternating with the ovary-cells. They become even more welded together higher up ; but they separate again, to fonn twice as many as there are ovary- cells (/). If there be three, then each cord may bifurcate, though they do not all do so in every instance ; so that out of 12 cords, three ovular cords are given off to nourish the ovules (/), and the rest run up the styles, though the total number of cords may be less than 12, as variations seem to take place. The ground tissue consists of a loose merenchyma, except- ing three or four layers of cells below the epidermis, which are more compact ; the ovary-cells — seemingly reduced to a thickened epidermal layer only — are plunged freely into this tissue (e). The cords run up the centre perfectly independent of the ovary-cells (e) with their spiral vessels on the inside, surrounding a central medulla. Were it not for the presence of the dorsal cord, there is nothing to hinder one from calling them axial. It is not until they reach the top of the ovary-cells that these cords bifurcate and send off one branch each into the pendulous ovules, the other branches being conveyed upwards into the styles (/). The above description will give a fair example of the distribution of the cords for supplying the several members of the whorls. The reader can estimate how far the central cylinder should be called axial. The fact is, that the whole of the tissue of the carpels, excepting the thickened internal epidermis covering the ovules, is totally lost in the general spongy mass in which they are imbedded. But since the petaline cord gives rise to the small dorsal-carpeUary and one axial, theoretically these two belong to the earpellary leaf ; and on this ground we should feel inclined to regard the central cords not as axial but marginal and earpellary, 70 THE STKUCTUEE OF FLOWERS. notwithstanding the fact that the tracheae are oriented inwards ; since it is not until they reach the level of the insertion of the ovules that they pass either to the middle or opposite side of the cord. The rest of the carpellary tissues are undifEerentiated, as stated above, and it is this very common condition in the case of inferior ovaries that has led botanists to regard the lower parts of the carpels as being of an axial nature and not foliar. The Foemation op Septa. — ^With regard to the union of the surfaces of the carpels to form the septa, the rule is for the adjacent epidermides to be altogether wanting ; and, if the median tissue be thick, the walls of two adjacent ovary- cells may be very wide asunder, as in the Ivy. On the other hand, the septa may be reduced to the two epidermal layers alone, and then they are often scarcely coherent at all, as in Balsam and Lemon. In some cases, the epidermides are not in contact through- out their entire surfaces, and whenever this is the case the characteristic epidermal cells reappear, as in lAUacece and AmarylUdacece. Similarly, as soon as the carpels of Hellebore become free, the epidermides of the margins appear in their proper character, which now cohere only by contact. It is the same with the axile placentas of the Lily. As instances where the axis seeTns to be more decidedly prolonged up the centre, are Lychnis and allied members of the SilenecB. Ph. Van Tieghem has also shown how an axial cylinder ascends up the middle of the flower of Campanula medium, for about two-thirds of the height. Thus Pig. 15, a, represents a section of the fluted pedicel ; 6 shows the lobes isolated, each containing a portion of the fibro-vascular cylinder. In c, the broken central cylinder has again closed np, a section showing a complete circle of an axial character. The triangular basal portions of the ovary-cells have now THE PKINCIPLE OF COHESION. 71 appeared, d represents a section of two-thirds of the height of the inferior ovary; but now the fibre-vascular cylinder is dissociated, and forms fifteen separate cords — two being marginal to each placenta and one belonging to each septum. As the cords have their spiral vessels reversed in position, i.e. facing outwards and not inwards towards the centre, their axial character has ceased.* ng. IB.— Oimponula medium (after Van Tleghcm). The rule appears to me to be that as soon as, or even before the level of the insertion of the ovules is reached, the internal position of the tracheae is abandoned. This is the case with Lychnis. In some cases there is an apparently axial formation, * I do not find that matters can be really expressed quite so "diagram- matically " as, e.g., in his figure d ; for Van Tieghem does not pay mnch attention to the central wnd scattered positiona of the tracJiew, which I take to be qnite aa significant as their outward orientation ; for as the ovules are approached they become dispersed, thoagh a medulla remains. 72 THE STKUCTURE OF FLOWERS. which has proved to be misleading. Thus, in Oeranium an d allied genera, the beak-like process from which portions of the carpels separate when ripe is not axial at all, but simply the coherent placentas of an entirely carpellary origin.* This will be understood from the description I have given of Pelargonium (p. 66). The mericarps of the fruit of an umbellifer are also supported on a carpophore, which is likewise usually described as axial ; but anatomical investigations do not warrant the conclusion. The commissural surfaces are obviously merely the result of rupture between the two carpels which have cohered ; and, in consequence of this union, each epidermis fails to develop its true character, but remains in an arrested condition, having the cells somewhat smaller than the rest of the ground tissue. This enables the mericarps to separate readily on maturity. A double fibro-vascular cord runs up the centre to supply ovular cords at the summit of the ovary-cells. If one traces the cords from the pedicel, there will be found in the latter a complete fibro- vascular cylinder. This spreads out at the base of the inferior ovary into ten clearly defined cords which run parallel to each other from base to apex, to furnish the petals and stamens ; while two only coalesce and form the axial cord. It is this cord which constitutes the stylopod when the fruit is ripe. Hence it is not axial, but simply the combined marginal cords of the two ovary-cells. Feee Cbnteal Placentas.— The position of an ovule or ovules on a central support, free from the wall of the ovary, or directly on the base of the chamber, and apparently quite * Prof. A. Gray (I.e., p. 213) and Henfrey (El. Course of Bat., ith ed. p. 100) both speak of it as axial ; thongh it waa quite correctly described and figured by M. Seringe so long ago as 1838 (Mem. sur la Fruit des GSraniaciea) : " Les bords de chaque carpel placentaires sont Testes et forment la colonne." THE PRINCIPLE OF COHESION. 73 central, has given rise to a good deal of discussion. Two views have been taken, one being that such ovules are, in some cases at least, axial in their origin, and not carpellary at all ; others would refer all ovules, without exception, to a carpellary source. Analogy, indeed, would, if taken alone, seem to justify the latter conclusion, since the numerical proportion of ovules having a decidedly carpellary origin is unmistakably very great; and any doubt upon the matter seems to me to have arisen from a want of due appreciation of the arrest of development, or rather failure of a complete differentiation which has taken place between the ovary and axis at the place where the ovule or ovules appear. This arrest is particularly apparent, as already stated, in the case of inferior ovaries, as of the Ivy. Thus, ia the Composite^, the ovular papilla seems to arise at the base of a cavity in the axis, and might easily be thought to be axial ; but a slight eccentricity may be dis- cerned at a certain epoch which is the 6rst indica- tion of its carpellary origin. In Beta the basal ovule arises in a very similar manner, but as the ovary becomes more developed, the ovule is carried up so as finally to become pendulous (Fig. 16, a, h. much the same in Typha and allied genera. 9 Fig. 16.— Beta (after Payer). C.) It is The same 74 THE STRUCTURE OF FLOWERS. gradual elevation of the ovule occurs in Bicinus and other Euphorbiaceous plants. Similarly, if we compare the differences in allied genera, as Eanunculus and Thalictrum ; in the former genus the ovule arises at the very base of the carpel, close to its point of attachment to the axis, and remains there. In Clematis and Thalictrum, the marginal cleft of the carpel appears a little more decidedly above the base, so that the ovule from its earliest period is situated somewhat higher up, and by a further development is carried to a yet higher position, and 80 ultimately becomes pendulous. Exactly similar differences occur between the orders Compositce and Bipsacem. Hence, it would seem that basilar ovules owe their positions to corresponding degrees of arrest of the growth and development of the carpels, and especially of the basilar portions of the carpellary margins. I think, therefore, we may draw the following conclusion, that the particular form of energy which would cause a carpel to emerge out from and be developed freely and entirely from an axis, is more or less potential than actual.* Consequently, it develops the ovule just where that portion of the carpellary margin would have appeared had it been formed ; so that the tissue whence the ovular papilla emerges may be considered to be, strictly speaking, neither axial nor carpellary, but undif- ferentiated merenchyma, and potentially carpellary. From a single ovule we may now pass to pluri-ovular' ovaries. Dioncea gives ns an instance where many ovules arise at the base perfectly free from the ovarian wall. In this flower the pistil consists of five carpels, which emerge congenitally out of the axis, first as a circular rim, which * It may be noted that it is more actuaX in Clematis, etc., in that eeveral ovnlar papillss are prodaced in genera with pendulons ovules, besides being more elevated in position ; but only one in RanuncuUui. THE PRINCIPLE OF COHESION. 75 then becomes a cup, ■which finally contracts above to form the style, just as in Primulacece. It is, therefore, unilocular, while a circle of ovules appeal's on a tbick ring of tissue within the base of the ovary. Other circles of ovules appear concentrically and centrifugally. It might be questioned, therefore, whetLier the ring which carries them were axial or not. I«think, however, the same interpreta- tion will apply here as elsewhere ; that is to say, the ovules arise from the place where the bases of the carpels would have appeared had they been differentiated out of the axis. In the allied genus Drosera the placentas are strictly parietal, and the ovules, commencing to emerge half-way up the wall, appear successively, both upwards and downwards. Now, as they are centrifugal in Bionoea (coiresponding to the upward development in Drosera), it looks as if only a portion of the upper half of the carpels were really repre- sented at all. In this genus there is a barren central space within the ring of ovules, perhaps representing the termination of the axis. That the basal portion only of syncarpous pistils should bear ovules is common enough, and the pla- centas often swell out there to form bosses which we may reasonably conceive as coa- lescing to form the continuous ring character- istic of Dionoea. Thus^cer illustrates how each of the two carpels gives rise to two globular protuberances on which the ovules are borne ^ (Fig. 17). Anemiopsis, as figured by Payer, has a confluent protuberance bearing several basifugal ovules. Similar multiovular bosses Fig. n —Carpels of occur in Solanece and ScropTiularinece, giving the characteristic dumb-bell shape in a transverse section. Now, if we imagine these swollen ovnliferous placentas / 76 THE STRUCTURE OF FLOWERS. arising from the basal portions of the carpellary leaves to reach the centre of the ovarian chamber, and be there fused together into a solid mass, we should obtain the apparently- axial structure of Primulacece, Santalacem, etc., with the few or numerous ovules badpetal in order of development, cor- responding to the centrifugal order in Dioncea and the ascending order in Drosera, The probability that this is the correct view is supported by a case I have met with in which the carpels of Primula sinensis were dissociated, and more or less foliaceous with rudimentary ovules, not only along the margins, but with several borne on heel-like processes,* which extended towards the centre of the ovary, as represented in Fig. 18. Anatomical investigations entirely corrobo- j,, jg rate the carpellary nature of the central placenta of Primulacece. The circle of cords, usually ten in number, which pass up the column to nourish the ovules are originally separated from the sides of the sepaline by radial chorisis, and become superposed to the sepals ; the dorsal cords (abont ten) having also parted company from the five sepaline and five petaline. The latter, however, do not give rise to any placentary cords ; hence there are really five carpels superposed to the sepals. With regard to the position of the, spiral vessels, they are not oriented as if axial, but are completely embedded in the phloem, and consequently central. Moreover, the ; cords in section are circular in form, and not wedge-shaped. The central (if not external) position of the tracheae and the ! circular form of the cords are both eminently characteristic • Van Tieghem, thongh once regarding the central placenta as axial (Eechfrches gur la Structure du Pistil, 1868), lias more recently arrived at the same conclosion as myself (Traits de Bot., 1884). THE PEINCIPLE OF COHESION. 77 features ■when they first cease to be axial and become appen- dicular. The accompanying diagrams (Fig. 19), (a) Lysi- niachia nemorum and (&) Primula veris, will illustrate these a. Fig. 19. — a, Lysimachia nemorum ; b, Primula veris, remarks. The sections are taken on planes * where the pistil is emerging from the receptacle ; «. represents the sepaline cords ; ab. st. abortive staminal cords ; p. the petal- ine and staminal (combined) ; d.c. dorsal carpellary ; pi. c. placentary cords. A free central placenta may result from the destruction of the septa of an originally axile placenta, as occurs in the CaryophylleoB. Thus, the ten rows of ovules in Lychnis sufficiently indicated their marginal origin. I may add that a careful investigation into the origin and distribution of the cords has convinced me that the axis in flowers of the Caryophylleoe early ceases to take any part in the structure of the pistil. • Tig. a represents a section taken rather lower down than in Fig. i ; as the cords in the latter are still nndiSerentiated in Fig. ai ■y 78 THE STRUCTUEE OF FLOWERS. CHAPTER VIII. THE PRINCIPLE OP ADHESION. Adhesion op Organs. — This tei-m is distinguisbed from cohesion by limiting its application to the union of different whorls. Thus, if the petals or stamens be united to the calyx, they are called episepalous, a term usually sycony- mons with perigynous ; and if the stamens be adherent to the perianth or corolla, they are epiphyllous or epipetalous respectively, sometimes also described as perigynous. On the other hand, if the stamens and pistil be in close con- junction, showing an adhesion between the filament and the style, so that the anther and stigma are brought together, the term g^nandrous is applied to them. Adhesion may be safely regarded as an advance upon cohesion; and there is, I think, a great probability of its being — perhaps, originally, in most if not all cases — a result of adaptation to insect agency. With regard to the perigynous condition which involves a more or less degree of adhesion of the petals and stamens to the calyx, this is in many clearly a result of the develop- ment of the receptacular tube with its honey-disk lining it, as in Bosacece. This causes the free portions of the petals and stamens to be carried away from the central axis, and placed in a ring "around the pistil," i.e. perigynotts ; while the more or less amount of adhesion of them to the calyx THE PRINCIPLE OF ADHESION. 79 has suggested the term episepalous. In the Rose, however, which secretes no honey, the sepals are almost, if not entirely free, and articulate readily ; whereas, in other rosaceous plants, if the receptacular tube does not itself fall off, as in Primus, the calyx remains persistent. Although it is usual to regard perigynous petals and stamens as episepalous as well — that is, " upon the sepals " — when the receptacular tube is well pronounced, it is more strictly in accordance with anatomical structure to regard the former as brought into close proximity to the calyx, rather than being really inserted upon it. In many other cases, as in Lythrum and Daphne, the whole of the tube has all the appearance of being truly ctilycine and not recepta- cular ; so that " episepalous " will then best describe their condition of adhesion. It is rare to find a gamopetalous corolla adhering to the calyx, but it is so in Cucurhitaceoe, as in the genera Cucumis And Bryonia, where the two outer whorls are united. Ph. Van Tieghem observes* that the union may be the result of the fusion of the respective parenchymas alone, leaving the cords proper to each organ distinct. I think, however, that it will be found to be more frequently the case that when the cords are superposed, they are fused together below, but separate when the organs become free. This is well seen in Prunus. The sepaline and petaline- cords branch, by tangential chorisis, about half-way up the receptacular tube, and thus give rise to ten stamens. Each of the petaline cords branches on either side again, at a different level, by radial fission, and gives rise to ten more.f So that if we retain the term " episepalous " for the stamens, we must understand that, while the actual stamen is practically free • Traile Botanigue, p. 390. t This will be described more fully below (see Fig. 28, p. 95). 80 THE STRUCTURE OP FLOWERS. from the calyx, yet its cord is common with that of the latter below. The epiphyllous or epipetalons condition of the stamens is almost invariably associated with a state of cohesion of the perianth-leaves and petals of the corolla ; as exceptional instances are Scilla and Lychnis, which have the parts of the perianth and corolla free, but with the stamens adherent to them ; while, conversely, Campanulacece and Ericaceoe have gamopetalons corollas, but the stamens not adherent to them.* The rationale is primarily, in many, perhaps in every case, an adaptation to insect agency. In the majority of gamopetalons corollas, the honey usually lies somewhere between the insei-tion of the corolla and pistil, being secreted by one or more glands or an annular disk round the base of the ovary. There are two positions in which the antters may be placed in regular gamopetalons flowers with reference to the visits of insects for the honey; either around the tube, as in the Primrose and Scilla, or close around the style, as in Convolvulus, Campanula, and Crocus. In the former case, when an insect passes its head or proboscis down the tube, it touches the anthers on one side of it and the stigma on the other ; but as the proboscis may pass on either side of the pistil in the same and different flowers, that is on the near or remote side, with reference to the position of the insect, such flowers have every facility of being crossed. If they be heterostyled, as the Primrose, then of course each kind has the greater chance of being crossed by the other sort. » The distribution of the cords in the floral receptacle of Azalea, between the insertion of the corolla and pistil, is ve>7 anomalons, having no symmetrical arrangement aronnd the centre ; while the cords of the corolla of Oampanula, as described above, are pecnliar for other reasons. This mayi perhaps, have something to do with the exceptional freedom of the stamens from the corolla. THE PRINCIPLE OF ADHESION. 81 la the case of Orocus, Convolvulus, and other flowers with a contracted base to the corolla or perianth, the anthers are situated close round the style. In these flowers, tlie insect alights on the stigmas, as already described, grasps the central column and sucks the honey head downwards, and so gets dusted on the abdomen, the pollen from which is thus trans- ferred to the next flower visited. The adhesion of the stamens to the corolla or perianth thus seems to give a rigidity and firmness, as well as leverage in some cases, so that the action of the insects is more accurately secured, and some one particular spot on their bodies invariably struck and dusted with pollen ; which would scarcely be the case if the filaments were free and at liberty to oscillate or swing about in any direction. In many flowers with irregular corollas, the stamens are declinate ; and their adhesion to the tube is then of manifest advantage, for the basal part of the filaments thus acquires an additional strength to act as a fulcrum, which enables the filaments to support the weight of the insect. In Echium, for example (Fig. 20, p. 82), the corolla is even strengthened by a rib where the stamen is inserted. This part constitutes the fulcrum. The line of force from the fulcrum intersects a line perpendicular to the filaments, corresponding to the weight of the insect ; while the third and upward force is that exerted by the filaments to counteract the resultant of the two former.* The origin of the adhesion between the stamens and the outer whorls is revealed by anatomical investigations ; for the rule is, as described in the case of Prunus, that the fibro- vascular cords of the stamens arise by division from those of the outer whorls whenever they are superposed to them. In other words, when adhesions are seen between the floral whorls, by being superposed to one another, then a • See also Figs. 38, 39, and 40, pp. 124-126, and consult text. 82 THE STEUCTUEE OF FLOWERS. f nsion of their respective cords will be found. Tf the members arise freely, as in lianunculaeem and CruciferoB, then their cords are inserted into the axis, having arisen by radial division or lateral chorisis. In the case of the gynandrous pistil, the stamens have their fibro- vascular cords more or less imbedded in the recep- Fig. 20. — ^Ei:hiniu ; a, side view ; b, before, and c, a'ter shedding poUen ; showing protundry. tacnlar tube, or rather the common tissue resulting from the fusion of the ovary and the tube together ; the anther then stands on the summit, and if there be a short or no style, but only the stigmas terminating the ovary, then the anther is in close contact vrith it, as in Sippuris, Orchis, etc. When there is a style, the filament may be prolonged in adhesion with it, as in most orchids possessing the so-called Column. It is not ■ THE PRINCIPLE OF ADHESION. 83 80, however, in Aristolochia, according to Van Tiegliem, though often described as such.* To summarize the above remarks, it seems clear that all adhesions between the two whorls of the perianth, to be found mostly in the Calyciflorce, is an accidental occurrence due to the hypertrophied condition of the axis in forming a receptacular tube ; so that the term " perigynous " is more strictly applicable than," episepalous." Adhesions betv^een the filaments and corolla, or calyx if the former be wanting as in Bapline, is an adaptation to insect fertilisation ; whereby a more rigid position is acquired for the stamens, coupled with a gain of leverage, etc. Lastly, adhesions between the stamens and pistil only occur where there is a receptacular tube, or " disk," as in Nymphcea ; and the fusion of filaments with the style, or between anthers and stigmas, is brought about by the very close proximity of the organs when in an early and undif- ferentiated state. • Dnchartre, EUm. de Bot., p. 648 ; Henfrey, I.e., p. 125 j Benth. and Hooker, Gen. PL, vol. iii., pt. 1, p. 123 ; Yan Tieghem, TraiU de Bot, i., p. 422. Van .Tieghem's description and fignre (Fig. 21) is as follows : — " The styles and stigmas are abortive, iind the six carpels are reduced to their ovaries. It is, then, the thickened connectives of the anthers, coherent laterally into a tube and covered above with stigmatic papillae, which now play the part of stigmas and of the style." To judge from Payer's fignres {Organoginie, pi. 91 and pi. 109), the stigmas appear to rise from the inner side of the verv short filwments, and might be interpreted as truly car- pellary stigmas, bnt fused to the former. A further investi- gation of the distribution of the fibro-vasoular cords should Fig. ai.— Aris- be made. Moreover, Asarum does not appear to have any. yan rleghem')' thing so abnormal. 84. THE STRUCTUEE OF FLOWERS. CHAPTER IX. THE CAUSE OF UNIONS. Having now noticed the different kinds of unions, we may ask what has brought them about. We have seen how progressively complex conditions can be traced from entire freedom, as in Buttercups, through forma of Cohesion, such as the gamosepalous, gamopetalons, monadelphous conditions, etc. -, to cases of Adhesion, as of the perigynous and epipetalons states ; and, lastly, to the adhesion of the ovary to the receptaeular tube. As stated above, these conditions are correlated with greater and progressive differentiations of the floral organs, which have been brought about by insect agencies. The above-mentioned and other terms do not, however, explain how or what the immediate influences are which induce unions of various kinds amongst the parts of flowers ; but some researches of Mr. Meehan on the ConifercB * will perhaps give us a clue. There is a well-known and a very generally prevailing feature amongst certain genera of Conifers — as of the GupregsinecB, for example — that the foliage can appear under two forms, the leaves being either free from their bases, or more or less adherent to the axis. The two forms of leaves have been recognized as specific characters in Jtmiperus, ' On the Leaves of the Coniferm, Proo. of the American Association for the Advancement of Science, 1869, p. 317. THB CAUSE OF UNIONS. 85 Retinospora, etc. ; bat both kinds of foliage not infrequently appear together on the same plant; and, when this is the case, the spinescent and free leaves are borne on relatively less vigorous branches, the adherent foliage being charac- teristic of the more vigorous and quick-growing terminal shoots. It has been also noticed by Dr. M. T. Masters that not only do the broad and free leaves of Juniperus and Betinospora not occur on the leader shoots, but when the plant is varie- gated then free leaves (on the stem with arrested growth) are much more variegated than they are on the quick-grow- ing leader shoot.* The last-mentioned observer has also noticed that the free foliage is characteristic of the younger condition of the plant, the adnate foliage that of the adult state. The conclusions arrived at by Mr. Meehan are as follows : (1) The true leaves of Coniferce are usually adnate with the branches. (2) Adnation is in proportion to vigour in the genus, species, or in the individuals of the same species, or branches of the same individual. (3) Many so-called dis- tinct species of Coniferce are the same, but with their leaves in various states of adnation. Another very common form of adhesion, to which I have already alluded and which is most probably due to hyper- trophy through sncculency at an early stage, is fasciation.f Under this condition the fibro-vascular cylinder of at least two " axes," which would be normally separate, coalesce, and form an oval cylinder with, it may be, only a slight * Oard. Chron., 1883, vol. xix., p. 657. t For remarks on this phenomenon the reader is referred to Dr. Masters's Teratology. It is particniarly common in herbaceous plants, as Lettuces, Asparagus, etc., and not unfrequent in Ash-trees. I observed a trailing plant of Cotoneaster growing over a rockery by the side of a stream in a garden, almost every branch of which was fasciated. 10 86 THE STRUCTURE OF FLOWERS. constriction indicating the nnion. The medullas, cortical and epidermal layers, are also continuous throughout and common to the whole. Now, the nnion of two opposite "appendages " to an axis, as in the case of connate leaves, may take place. This may be called foliar fasciation in which the fibro-vascular cords of each " leaf " are embedded in a common parenchyma, and all encased together within a common epidermis. If we regard the receptacular tube of, say. Fuchsia and Narcissus in the same light, though adherent to the ovary like a decnrrent leaf of a thistle or Sedum, I see no argument against the supposition that the tube, in such cases as these, may be regarded as the fasciated petioles of the sepaline and perianthial leaves, now adherent to the ovary within them. A pear would seem to combine both axis and petioles, as the base of the ovaries is situated much above the commence- ment of the expansion of the pedicel (see Fig. 22, p. 90, and Fig. 26, p. 94, and consult text). Each case must, however, be interpreted on its own merits ; and I think there will be little difficulty about this, if we recognize the fact that both the pedicel and floral receptacle on the one hand, and the petioles or their floral equivalents on the other, can alike assume all the features of the so-called receptacular tube. . Now let us apply these principles of nnion through \jiypertrophy to flowers, and we have an interpretation Recording to the theory advanced in this book : that differ- ences of floral structure depend largely upon different dis- ' tributions of nutrition in the several organs ; and that the ' irritation set up by insects themselves is one of the most ; potent causes of a flow of sap to certain definite places, which encourages local growths, thereby inducing these THE CAUSE OF CTNIONS. 87 unions to take place between the parts of any whorl, form- ing " cohesions," and also between different whorls, or "adhesions." Other causes may determine them, for hypertrophy may set in through a purely vegetative stimulus ; for it is not unfrequent to see abnormal cohesions and adhesions in cul- tivated orchids, such as petals or sepals adhering to the column, etc. Such may, with a good deal of probability, be referred to the artificially stimulated conditions under which they are grown. These abnormal cohesions between members of the perianth, and adhesions to the column, have been observed both in this country and America.* As a particular instance of the latter kind, Mr. Meehan had observed several dozens of flowers of Phaius grandiflorus which had the dorsal sepal united to the column, all being confined to separate spikes from those which have perfect flowers. In some cases, of the same plant two of the petals were united so as to form a hood over the column. Another peculiarity of Orchids is the tendency to convert sepals or petals into labella, and to multiply the spurs when an orchid is characterized by them so as to render them peloric, a sure sign of hypertrophy.f All these " monstrosities " seem to point to an excessively unstable condition of equilibrium in the flowers of Orchids ; and that they are peculiarly sensitive to the effects of nutri- tive stimuli, whether brought about by visits of insects or by artificial cultivation. So that the order Orchidem is particularly interesting, as furnishing indirect or even direct * Ab by Mr. T. Meehan. Proc. Acad. Nat. 8oc. Phil, 1873, pp. 205, 276. t The remarkable inflnence of the presence of a "plant-bng," causing . the normally irregular corolla of Clerodendron to become hypertrophied and peloric, will be described hereafter (p. 130). 88 THE STEUCTURE OF FLOWERS. proof for my theory — that the forms and structures of flowers are the direct outcome of the responsive power of protoplasm to external stimuli.* • We may, perhaps, see some analogy between these unions amongst floral organs, which thus occur abnormally in orchids and normally in so many flowers, and inflammatory adhesions in the human subject. It is well known that certain, otherwise abnormal, unions may be con. genital, which usually only occur through inflammation set up by abnormal excitation, but they are not hereditary. I have alluded to hypertrophy and atrophy as causes of the struc- tures of flowers, and shall have more to say about them. I would here add the following analogous phenomena between the animal and vege- table kingdoms. Sir James Paget remarks : — " Constant extra-pressure on a part always appears to produce atrophy and absorption ; occasional pressure may, and usually does, produce hypertrophy and thickening. All the thickenings of the cuticle are the consequences of occasional pressure ; as the pressure of shoes in occasional walking, of tools occa- sionally used with the hand, and the like : for it seems a necessary con- dition for hypertrophy, in most parts, that they should enjoy intervals in which their nutrition may go on actively " {Led. on Surg. Path., i. , p. 89). The reader will perceive the significance of this passage when recalling the fact that insects' visits are intermittent. Atrophy by pressure and absorption is seen in the growth of embryos ; while the constant pressure of a ligature arrests all growth at the constricted place. On the other hand, it would seem to be the persistent contact which causes a climber to thicken (see p. 156). CHAPTER X. THE EECEPTAC0LAE TUBE. The Calyx oe Recepi'aculae Tobe. — This organ consists of a cellalar sheath of varying degrees of thickness, free from or adherent to the ovary. Much discnssion has arisen as to the true nature of it, whether it should be regarded as axial or foliar. The older view generally maintained was that it consisted of the lower part of the outermost whorl of the perianth or calyx — in other words, that the basal or petiolar portions of the sepaline leaves were coherent ; and if the ovary were inferior, then they were supposed to be adherent to the latter as well. Schleiden appears to have been the first botanist who j propounded the view that it was axial and not foliar. He f was followed by others ; but this idea took two forms. According to one, it was thought that everything below the summit of the inferior ovary — that is to say, the outer wall, \ the septa and placentas — was axial, and only the free portion ' of the summit of the ovary, together with the styles and stigmas, were foliar. According to the other view, it was maintained that the ovaries, styles, and stigmas were foliar, and the superficial covering to the ovary alone was axial. The first view was held by Schleiden, A. de Saint Hilaire, Tr6cul, Payer, Prantl, and Sachs ; * the latter by Decaisne, * E.g. Sachs' Text-Boolc of Botany, Eng. (2ad) ed., p. 566. 90 THE STJltrCTURE OF FLOWERS. Naudin, Ph. Van Tieghem, and, I think, English botanists in general.* There are three methods of investigation, ■which conjointly may gnide us to the discoveiy of the real nature of the tube. The first is that of following its development ; the second is teratological, and the third anatomical. Morphological Investigations. — In tracing the morpho- logical development of flowers of the Eosacece, where the receptaeular tube is a characteristic feature, one notices how a border, surrounding the domelike termination of the axis which soon produces carpellary papillae, rises upwards and elevates the sepals and the papillae of the petals and stamens. This border ultimately forms the tube ; and the question is, whether it should be regarded as the basal part of the calyx or a development from the axis. In the Pomece we find the apocarpous condition of the pistil, characteristic of all the other members of the Bosacece still retained at first ; but in consequence of the growth and close proximity of the tube with the carpels, various degrees of adhesion are brought about between them ; thus, in Pyrus (Fig. 22, a), the bases only of the carpels are from the first fused into the axis. In Gotoneasier (b) the fusion Fig. 22.-<,,rj/™.; 6, ftto.e«,«er (after Payer), g^^g^^^ ^^ ^ ^.^^^^ j^^^j on the ovaries. Such " half- inferior " ovaries occur in other genera, as Saxifraga granulata, Gloxinia, etc. From such we pass to completely inferior states, as in Gompositce * Bentham and Hooker describe the inferior ovary of the Pomew in the terms, " Calycia tnbna ovario adnatns." THK RECEPTACULAK TUBE. 91 and TJmbelliferce, while Onagracece furnish illustrations of an extension of the receptacular tube to considerable distances beyond the summit of the ovary, as in Circcea, and probably Fuchsia and (Enothera are similar cases. A like prolongation is seen in some Composite with "stipitate" pappus, as the Dandelion, Tragopogon, Eypochceris, etc. In tracing the development of the inferior ovary of the CompositcB, the cavity of the ovary appears to be sunk below the level of the first emergence of the corolla and stamens ; and it is this which has suggested the view that the ovary is part of the axis, and that only the style and upper portion of the ovary which is exposed is foliar. On the other hand, since there are abundant cases of transitional conditions ; as, for example, between species of Saxifrage, — S. umbrosa having an entirely superior ovary ; S. granulata, one that is half-superior, and S. tridactylites, a completely inferior ovary ; and moreover, if we compare the PomeoB with the other tribes of Rosacece, comparative morphology does not tend to favour the above view held by Sachs, but rather inclines one to the impression that the basal part of the ovary must be carpellary a-nd not axial, though there may be no visible line of demai'cation between the canline and foliar structures.* The existence of the above-mentioned facts, and many cases of reversion to entire freedom by " solution," supply good reasons for believing that the development of the carpels is more or less arrested below, wherever they are in contact with the receptacular tube ; yet they retain their power of developing at least one ovule, as is often the case in * To regard the septa of an inferior ovary " as the prolongations of the margins of the carpels downwards on the inside of the ovary " (Sachs' Text-Book, p. 567), seems to be a vety strained interpretation in order to fit the axial theory. 92 THE STRUCTURE OF FLOWERS. ganjopetalous epigynous orders. Moreover, the ovule is not strictly basilar and central, bat is really situated laterally. Anatomical investigations, as we shall see presently, entirely confirm this view. Teratological Investigations. — Teratological evidence of the axial, or in some cases, perhaps, petiolar nature of the so-called receptacular tube is tolerably abundant. Thus, in monstrous forms of flowers normally possessing inferior ovaries, the pistil is sometimes completely arrested, when the latter is replaced by a long pedicel which is usually wanting or else is very short, as in Honeysuckle, Epilohium,- Orchis, etc. (Fig. 23).* Pears not unfrequently furnish similar instances, as in the case of the so-called "Bishop's Thumb Pear, which sometimes occurs of an elongated form, destitute of core and seeds. These fruits, which are merely swellings of the flower-stalk, are produced from the second crop of blossoms, which have not energy enough to produce carpels (core) with ovules or ripe seeds.'' t There is little doubt that the recepta- cular tube is, in these cases, converted into the jforii,'^f^m^. '■°'^^^^® structures in consequence of the total absence of the carpels from within it. In other words, it is axial. There are other indications of the tube being axial in its nature rather than foliar ; thus, it frequently becomes " pro- liferous ; " that is to say, flowers, or even branches, may grow out of it, as is often the case with Roses, Prickly Pear, UmbellifercB, etc.f Again, certain kinds of Fears, Medlars, * a ia the interior of tbe flower, consisting of a cnp-like dopreBsion with two anthers. t Gcurdener'i Chronicle, Oct. 9, 1886, p. 464. J Teratology, p. 100, seq. THE EECEPTACULAR TUBE. 93 Roses (Fig. 24), etc., occasionally bear foliage on the external surface of the tube, and when the calyx of the Rose becomes abnormally folia- ceous, stipules (Fig. 24, st.) may appear at the summit of the tube, indicating that Fig. 24.— Leaf-bearing recpptaculflr tube of Rose (after blasters). Fig. 25.— Hawthorn with super- numeraiy free carptls (after Masters). point to be the base of the sepal. Sometimes supernumerary carpels are borne freely on the top, as in the Hawthorn (Fig. 25). On the other hand, a tendency to hypertrophy is some- times discovered in the petioles of leaves of Apples* and Pears (Fig. 26, p. 94) ; and a not infrequent monstrosity is Been in Fuchsias, where one or more of the sepals become foliaceous, and then their petioles are formed but often remain more or less adherent to the ovary if present, which seems to imply that the tube in this plant might be formed * Mr. Meehan describes a similar instance of an Apple-tree .which never bore flowers but always had an abundance of fruit. The latter, how. ever, were composed of metamorphosed and fleshy floral whorls. He adds, however, that cork-cells were formed abundantly on the outside of the apples ; remarking, " It would seem, therefore, that with the lack of development in the inner series of whorls necessary to the perfect frnit, those which remained were liable to take on somewhat the character of bark structure " (Proc. Acad. Nat. Sc. Phil., 1873, p. 99). 94 THE STRUCTURE OF FLOWERS. by, or at least is homologous with, the petiolar portion of the calycine leaves (Fig. 27). Phyllomes, however, are after all but modified portions of caulomes, and petioles are still less de- partures than are blades from the nature of an axis ; so that while in some cases one is inclined to regard the tube as more strictly axial, in others it seem to be more homologous with a sort of fasciation of petioles. We shall see directly that the receptacnlar tube of Prunus contains the basal portions of the cords proper to the calyx and corolla, so that we might regard the latter as, on the one hand, axial cords preparatory to forming the perianth; or, on the other, perianthial cords not yet differentiated into petioles. Similarly, in the case of monoootyledonous flowers, as the Daffodil, since petioles are less dif- Flg. 26.— Pear *Uh hypcrtropbied and sub-fasciate petioles. Fig. 27.-<~Fiictasta with follaceons eepals and petals (alter Masters). THE RECEPTACULAE TUBE. 95 ferentiated from blades in this class than in Dicotyledons, the inferior ovary may be due to the combination of the pistil with the united sheath-like portion of the perianth, which is prolonged above the summit of the ovary just as it is in Fuchsia, though it is not so prolonged in the Snowdrop. Anatomy of the ReceptaculaeTubb. — Tracing the course of the fibro-vascular cords from the pedicel below the flower, say of Prunus Lauro-cerasus, the common laurel, there will be found to be ten, corresponding to the sepals and petals. The cortical tissue and epidermis are continuous throughout, from the pedicel to the summit of the tube. It is well seen also in the tapering end of a pear, from which the cortex gradually widens, while the fibro-vascular cords run verti- cally up the middle. Before the cords arrive at the border of the free tube of the Laurel, they have given rise to the staminal cords by chorisis, as shown in Fig. 28, a, h. Fig. a St J gijsty ■^...st^ ate fi stz Fig 28.— Receptacular tube of Prunui (after Van Tlegbem). represents a section near the edge of the tube in which both the sepaline (s) and the petaline (ji) have given rise by tan- gential chorisis to a whorl of stamens {st. 1) ; but the petaline by r adia l chorisis to another whorl (st. 2), i.e. to twenty stamens in all. Fig. 5 represents a vertical view of the same.* * The single carpel is represented in Fig. a to show the position of its three cords, one being dorsal, and the other two marginal. 96 .THE STRUCTURE OF FLOWERS. As Ion? as the cords are simple, i.e. up to the horizontal lines in Fig. b, there is nothing to distinguish them from cords of an axis, as in the pedicel. If, therefore, we reg^d the branches above those levels as belonging to the floral whorls, then the " axis " would terminate at different heights up the receptacular tube — which would seem to be rather too forced a view to be acceptable. Hence it would seem preferable to regard it entirely as axial until the portions of the perianth issue freely from the upper part of it. We might compare these branches of the fibro-vascular cords embedded in the axis to those belonging to ordinary leaves, which traverse the stem for varions distances downwards till they ultimately vanish ; only in the case of leaves they are not coherent into a common cord below, but remain free from each other. Moreover, other members of the Bosacem show that they cannot be always petiolar ; because in the rose the sepals reveal their foliaceous character, first by always bearing rudimentary leaflets, and sometimes stipules as well at the top of the tube (Fig. 24, p. 93). Further complications in the distribution of the cords sometimes arise. Thus, in the tube of the Cherry, I find that the petaline cords assist in furnishing the calyx-limb with vascular cords, just as those corresponding to the arrested stamens of the Primrose enter the corolla of that plant. They either do not branch till they reach the. angle between the sepals, or else from a point lower down. The small secondary branches are mainly directed outwards towards the margin, as represented in Fig. 29 ; s being sepaline, and JO the petaline cords. In examining transverse sections of inferior ovaries, what one almost invariably observes is an inner' epidermis, on some part or parts of which are placentas with ovules. THE RECEPTACULAE TUBE. 97 an outer epidermis, and an intermediate ground tissue, apparently nearly uniform in character, from one epidermis to the other (as in Fig. 14, a to e, p. 68). A definite number of fibro-vascalar cords penetrates this ground tissue. Theo- retically, if this structure consist of two parts, viz. the interior carpels and the exterior "tube," some line of demarcation might be expected to be traceable ; but in the majority of cases it would seem that, as neither the inner epidermis of the tube nor the outer one of the carpels are required, they are not developed at all ; and so the internal tissues of the two organs become confluent and uniform, and this accounts for the fact that the dorsal cords at least are simply embedded in this common tissue. Nevertheless, in some cases there actually is a certain differentiation in the tissue, as Van Tieghem has shown in the case of Alstroemeria versicolor (Fig. 30), where a yellow band of cells marks the Fig. 29. — Receptacular tube and calyx-limb of Cherry. Fig. iO.—AUtraimiria (after Van Tieghem). junction or congenital fusion of the two parts (indicated by the line in the figure). From the preceding descriptions, it will be seen, with regard to the sources of the cords belonging to the inner whorls, that they arise by division, radial or tangential as the case may be ; and then the secondary cords thus parted off are generally included within the tissue of the tube. 11 / 98 THE STETTCTURE OF FLOWERS. These cords of the inner whorls may be given off at the terminal point of the pedicel; that is, at the base of the flower. In this case they may all ran parallel from the base to the summit of the receptacular tube ; or they may branch at various heights within the tube itself, as in Prunus, described above ; or, lastly, they may not arise until the summit of the ovary is reached, when they pass off and enter their respective I floral organs directly. These variations occur in both free receptacular tubes as well as when coherent to ovaries. As an example of the first case may be mentioned Alstroe- meria versicolor ; of the second, Galanihus nivalis, or Snowdrop; and of the third, Narcissus. In Alstroemeria, all the floral appendages have their cords distinct and independent, but invaginated by the tube of parenchyma throughout (Fig. 30). In the Snowdrop, the carpellary cords are distinct, but the perianth and androecinm are inserted in the pedicel by a single verticil of cords, which becomes double higher up. Lastly, in Narcissus, all the parts of the flower are originally inserted in the pedicel by six cords, of which three give rise by successive tangential fission to a radial series composed of the dorsal cords of the carpels, the stamens opposite to the sepals, and the sepals themselves. Similarly, the other three form the petals together with the whorl of stamens opposite to them.* In Campanula, and to some extent in Lobelia, the cords * Ph. Van Tieghem, to whose researches I am indebted for the above, but which I have also paralleled in other cases, represents them neatly by the foUowing formnlas, wherein. ( ) signifies vascnlar nnion, and [ ] the cellular nnion of the receptacular tube ; while (d) stands for the dorsal and (to) the marginal cords of the carpels. St, signifies petaline and St. Bepaline stamens. Alstr(xmeria—[i S + 3 P + 3 St, + 3 Stp + 3 C,]. Galanthus—[3 (S + St.) + 3 (P + St,) + 3 OJ. Nardssua— 13 (S + St. + d C.) + 3 (P + St,) + 3 CJ. THE EECEPTACULAK TUBE. 99 belonging to the petals are given off by radial ehorisis from the sepaline, either quite from the base of the ovary or from about midway up the tube; they then diverge right or left at an acute angle, and, as soon as they have reached the summit of the ovary, pass up into the corolla.* As a rule, however, the petaline cords of flowers are quite distinct from the sepaline ; the six or ten, common to Monocotyledons and Dicotyledons respectively, forming the fibro-vascular cylinder in the pedicel. In all these and other cases the cords running up the receptacular tube proceed originally from the petiole, and are, so to say, even there intended for the appendages above. Normally they retain their axial character, in being arranged in a circle round the centre; abnormally an appendicular character can be revealed, by their becoming free and assum- ing a foliaceous aspect, as in Roses or Fuchsia, as mentioned above ; so that as long as the tube is normal, i.e. a cylinder of cortical parenchyma with cords, it is of the nature of axis, and can develop extra phyllomes and even bnds ; but abnor- mally, the foliar nature, usually limited to the floral members at the summit, is extended to a greater distance lower down and the cords may now be converted into petioles, etc. Hence it appears undesirable to call it either a calyx tube or axial ; for these terms would seem to bind one to consider it permanently and in all cases as being either of one nature or the other. The term receptacular tube is therefore best, as it certainly " receives " or supports the whorls of the flowers ; and Teratology clearly shows that it can be either foliar (petiolar) or axial according to circumstances. • This reminds one of the way in which stipnlar appendages of Qalivm, etc., are supplied with cords — not by their intercalation into the common fibro-vascnlar cylinder of the stem, bat — from a horizontal circular zone of fibres which connects the cords of the opposite leaves. 100 THE STRUCTURE OF FLOWERS. Just as the two complete vascular cylinders 6f two separate floral peduncles can become fused into one oval cylinder when the latter are " fasciated," so, too, would it seem that the cords belonging to the separate parts of a floral whorl, where there is no receptacular tube, can form a single united cylinder, which one then designates as the receptacular tube. In the case of the inferior ovary, 1 would again emphasize the fact that the difficulty felt as to what is axial and what carpellary is entirely removed if the undifferentiated con- dition of the carpels be thoroughly understood. Indeed, whenever two organs are congenitally in union the epidermis of each is undeveloped, and the two mesophyls become one ; so that the dorsal cords of the carpels and those proper to the axis are alike plunged into a common tissue, which, regarded as one, is neither wholly axial nor wholly carpeUary. CHAPTER XI. THE rOEMS OF FLOEAL OKGANS. The Form of the Perianth — General Observations. — It requires but a most cursory observation of flowers to notice how great is the variability in the forms of all their organs ; and the questions now before ns are, how these morphological characters are correlated to the one process of pollination in order to secure the fertilisation of the flower, and how this infinite diversity of form has arisen. Most important differences in this respect follow from the fact of flowers being regular or irregular, and, when adapted to insects, according as the honey is easily accessible or not. Regular * flowers when borne singly are almost always tei-minal ; t and when they are arranged in racemes, etc., they either stand out erect at the ends of their pedicels so as to be readily approached at any point of their circumference, as in the Wallflower, or else they are pendulous ; under which conditions, as a rule, no particular part is favoured by the • It is nsnal to speak of a flower as being regular or irregolar ; but the term shonld be, strictly speaking, confined to one whorl at a time ; thongh when the corolla is irregular, the calyx and stamens are asoally somewhat irregular as well. t The central and terminal flowers of many plants which elsewhere bear irregnlarflowers are often regular, as in Horse-chestnut.PeSor^omuTn, several of the Scrophidarinem, as Snapdragon, Lmaria, Pentstemon, etc. 102 THE STEUCTUKE OF FLOWERS. insect more than another. It is only -when the flower is situated laterally and projects horizontally, or approximately 80, with its limb or border ia a vertical plane, and, moreover, is more or less closely applied to the axis, that an insect is compelled to alight upon it on one side only, -when approach- ing it directly from the front. It then throws all its weight upon the organs on the lower or anterior side of the flower, as is the case with the keel petals of papilionaceous flowers, with the lips of Labiates, etc. ; or else its weight is sustained by the stamens or style, or by both together, as in Epilobium angustifolium, Gircma, Veronica, Larkspur, and Monkshood; and whenever the stamens are declinate, as in Horse-chestnut, Bictaimms, Echium, Amaryllis, etc. Flowers which have irregular corollas mostly show various degrees of "bilateral" form in their different whorls, and, have been called " zygomorphic.'' Such flowers, as a rule, do not receive the visits from so many difEerent species of insects as regular flowers. These latter, not being charac- terized by the possession of any very definite contrivances for securing special insect agency, are accordingly visited by a much greater number and variety than those flowers which have become markedly adapted, and consequently restricted to particular visitors. It must not be forgotten, however, that regular flowers, if the tabe leading to the honey be very contracted and more or less elongated, may become almost as mnch exclusive as very irregular ones ; for such flowers are mainly restricted to Lepidoptera. The following examples may suffice to illustrate these facts. ILanunculuB acris, which is perfectly regular and with no specialized structure, is visited, according to Miiller, by more than sixty difEerent species of insects ; whereas species of Aconitum and BeVphinium, the two most highly differentiated THE FORMS OF FLOBAL ORGANS. 103 and the only genera with irregular flowers of the same order, are adapted to, and mainly visited by the larger species of bees. Similarly of conspicuous and regular flowers of RosacecB, Primus communis has twenty-seven visitors ; Spirma Uhnaria, twenty-two ; Euhus fruticosus, sixty-seven ; Fragaria vesca, twenty-fivej-Orate^Ms oxyacantha, fifty-seven. On the other hand, of irregular flowers, Digitalis purpurea has only three useful visitors ; Linaria, nine or more species of bees, and Orchis mascula only eight. As an instance of a long-tubed regular flower, Lonicera ccBTulea may be mentioned. It is adapted to humble-bees, by which it is chiefly visited. Similarly, the flower of the Honeysuckle, the lobes of which are scarcely if at all unequal, admits only a few lepidopterous insects which can reach the honey. So, too, Asperula taurina, which has a tube 9 to 11 mm. long, is visited by nocturnal Lepidoptera. The Origin of Ieeegulaeitt. — "With reference to the theoretical origin of irregular whorls, I assume that they have all descended from regular ones through external influences.* With regard to terminal, regular flowers the &ow of sap is directed equally, radially, and in all directions on reaching the floral receptacle, and there is no inherent cause to make a terminal flower zygomorphic, or to induce one or more parts of any whorl to grow difBerently from the rest. Hence the primary cause of irregularity must come from without, and I regard this cause as issuing from the insect itself ; namely, the mechanical influence of its weight and pressures. To this external irritation the protoplasm of the cells responds, and gives rise to tissues which are thrown out to withstand the strains due to the extraneous pressures * The fibro-rascnlaT oords of the pedicel are arranged at regular interrals,. aad are perfectly Bjmmetrical around the medulla in iiregnlar flowers, just as they are in the case of regular ones. 104 THE STRUCTURE OF FLOWERS. of the insect, and so the flower prepares itseM to maintain an equilibrium under the tensions imposed upon it, and irregu- larities are the result. Such, for example, occur in bilobed calyces, as of Turze and Salvia ; in the many forms of " lips," or labella,* and enlarged anterior petals ; in dependent stamens, as of Aconite and Epilobium angustifoUum, or in the more usually declinate condition, as of Biciamnus, Amaryllis, etc. In these latter instances, in which the andrcecium. bears the burden, the anterior petal is either, as a rule, unaffected, and shows no increase in size, or else there is a tendency to atrophy, so that it is reduced in size, as are the keel petals in Amherstia. It is sometimes even wanting altogether, as in the Horse-chestnut.f * If the flower be resnpinate, then it is the posterior organ which, now being in the front, has become enlarged ; as in Viola and Orchis. + There has been more than one investigation into the causes of zygomorphism (as by Vdchtang, Ber. Deutsch. Bot. Qessell., iii. (1885), p. 341 ; and Pringsheim's Jahrb.f. Wiss. Bot,, xvii. (1886), p. 297 : also, by Dr. F. Noll, Arbeit. Bot. Inst. WUrzburg, iii. (1887), p. 315). H. Vochtnng distinguishes three different sets of causes as producing zygomorphism, viz. gravitation only; gravitation acting on the.consti. tntion of the organs ; and the constitution of the organs alone. Au objection to gravitation pure and simple is, that all flowers would be more or less subject to it, and become more or less zygomorphic accordingly. It does not account for the infinite diversity in the forms of zygomorphic organs; nor for the many correlations for insect fertilisation which exist between all parts of the flower. If to gravitation, however, we add the weight of the insect, which simply intensifies it, and couple with this the pressures exerted by the insect in various directions, then we have an adequate theory, which gravitation alone could not supply. When VSohtung speaks of " consti- tution alone" as a cause, I presume he means hereditary effect. If so, I would quite agree with him, as zygomorphic flowers now grow to be such from purely hereditary influences. When, however, he would attribute the form of Epilohium wngustifolium to geotropism, as the supposed cause of the lowermost petals bending upwards, and the stamens and style downwards (see Fig. 34, p. Ill), I do not see how THE FORMS OF FLORAL ORGANS. 105 Compensating processes thus come into play, so tbat while some parts are enlarged others are diminished, the former always having to bear the strains, while the latter are free from them. Thus the lip of Lamium consists of one much-enlarged petal, which forms an excellent landing-place, but the two lateral petals, not being required, are atrophied to mere points. Similarly, while the two posterior petals enlai'ge to form the hood, presumably due to the backward thrust of the insect's head, the posterior stamen has vanished altogether. The gamosepalons calyx now furnishes its aid to support the slender tube of the corolla, not only by doubling its number of ribs, but by uniting them all together by means of a sclerenchymatous cylinder within the mesophyl. If the tube of the corolla bo very strong and well able alone to support the insect, the adhesion of the filaments being also a powerful addition to its strength, then the calyx often remains polysepalous, as _ occurs in the Foxglove, Snapdragon, Petunia, etc. If, instead of the anterior petal forming the laading- place, the tube of a gamopetalous corolla has enlarged so as to admit the ingress of an insect which partly or entirely crawls into it; then it is this tabular part which, more especially having to bear the strain upon it, bulges outwards, or becomes more or less inflated in form ; while the lip or anterior petal, not having to bear the entire burden, is not particularly enlarged, if it be at all. The Toxglove and Gloxinia, as well as Petunia to a slight extent, illustrate this adaptation in irregular flowers, while "campanulate" flowers afford examples amongst regular ones. gravitation can act in any other way than " downwards.'' Bnt if one observes how a hnmble-bee suspends itself on the stamens while its body, so to say, thrusts the petals aside and upwards, we find a mnoh more satisfactory interpretation in the theory I have proposed. 106 THE STRUCTURE OF FLOWERS. If no more than the head of an insect enter the flower, then the corolla shapes itself to fit it. Thus Snowberry, Scrophularia, and Hpipactis only admit the heads of wasps, which are the regular visitors of these plants. Other instances in which the limb is not much, if at all, enlarged occur in flowers especially adapted to Lepidoptera. Hovering, as they generally do, before the flowers, and in- serting their long proboscides while on the wing, there is no tendency to develop larger anterior petals, but the irritation affects the tube only, which thus elongates and contracts, resulting in little or no irregularity in the flowers, as in (Enoihera biennis, in which the calyx tube has contracted, or in Honeysuckle, which has a tubular corolla. If bees or other insects visit the flower as well, then some degree of obliquity may result, as in Teucrium Scorodonia. Thus, then, may we get a rationale of the structure and form of floral organs, and their great diversity corresponds to a similar diversity in the insect world ; for the flower, if it be visited by niany, will presumably take a form correspond- ing to the resultant of the forces brought to bear upon it ; if visited by 'few, it will shape itself in accordance with the requirements of its principal visitors ; and thus is it that while some easily accessible flowers receive many classes of insects, others are restricted to few, or even one ; and then the insect and the flower are so closely correlated as to almost impress upon one the idea that they were mutually created for each other ! The accompanying figures of Duvemoia adhatodoides * may illustrate my meaning. Looking at Fig. 31, a, alone (sup- posing we know nothing of insect visitors), one might ask. For what use is this great irregularity ? why and how has it • From a paper by Mrs. Barber, Journ. Lin. Soc. Bot., vol. xi., p. 469. THE FOKMS OF FLORAL ORGANS. 107 Fig. 31 Duvervoia adkatodoides. come into existence ? And no answer is fortlicoming. Now turning to Fig. 31, l, we see one use at least. The weight of the bee must be very great ; and the curious shape of the lip, with its lateral ridges, is evi- dently not only an ex- cellent landing-place, but is so constructed as to hear that weight. Moreover, the two walls slope off, and are gripped by the legs of the bee, so that it evidently can secure an excellent purchase and can thus rifle the flower of its treasures at its case. Irregular corollas are very numerous, but certain prin- ciples, traceable to insect action, govern their forms. In the first place, the side upon which the insect rests, or at least upon which its weight is thrown, is always enlarged, and mostly forms the landing-place. It is almost always the anterior petal ; if, however, the pedicel or ovary has been too slender to support it, then it has sometimes hecome twisted, and the flower is said to be rcsupinate, so that the posterior petal becomes anterior in position, and is now the larger one, since it supplies the landing-place for insects, as in Orchis. Fumaria might be called semi-resupinate, as the corolla has only rotated through 90°. A slight modification occurs in the "Bee-orchis," Ophrys apifera, which is usually described as having a twisted ovary like a true Orchis ; but in this species it has scarcely if any twist at all ; the flower, however, is bent over to the opposite side of the stem, so that ■while the posterior petal is still the labellum, the ovary has itself remained perfectly straight. 108 THE STEUCTFRE OF FLOWEES. The next point to notice is that when the anterior petal is enlarged, the posterior one or more often enlarges also, while a corresponding tendency to atrophy affects the lateral ones. This is seen in many species of Leguminosm, Bcrophu- larineoB, &ni,Lahiatoe, and in zygomorphic flowers generally. It occurs thus in the wing petals of many papilionaceous flowers, as is particularly well seen in Onohrychis. The immediate causes, I repeat, I would recognize in the weight of the insect in front, the local irritations behind, due to the thrust of the insect's head and probing for nectar, coupled with the absence of all strains upon the sides. In some papilionaceous flowers the wing petals form a landing-place, as in Indigofera and Phaseolus. Whenever this is the case, they too are enlarged, as the lateral ones are in Fig. 31, and undertake the duty impressed upon them. When, therefore, one finds as an invariable rule how the front petals enlai'ge when flowers are compacted and visited only from the front, and thus become irregular; and as such often occur in orders where flowers are normally regular, as Iberis, Gentawrea, Heracleum, etc. ; and, moreover, when the same phenomena appear in orders having no affinity between them, as in Labiatce and Orchidece; and are, indeed, to be found throughout the length and breadth of the floral world, one is justified in attributing such irregularities to a common cause, that being, according to my theory, the responsive power of protoplasm to the irritations from with- out, set up by insect and other agencies. Many other special cases might be described from the different orders of plants, but the above will suffice to illus- trate this principle of responsive action with resulting correla- tions to insect agency. I would here, however, call the reader's attention to the mechanical arrangement of forces as shown in Lamium and Echitmi, where it will be seen that *he THE FORMS OF FLOBAL ORGANS. 109 adhesions of the stamens to the corolla furnish the fulcra, the cohesion of the petals into a tube aifording a greatly increased power of resistance ; the weight of the insect on the labellum or declinate stamens is, of course, vertically downwards, and the line of the resultant, which the lip in Lamium and the stamens whenever declinate have to exert, passes through the point of meeting of the first two, and so sustains the insect while visiting the flower. Other and analogous instances will be described here- after. Good illustrations of the occurrence of great thickenings just where the strain will be most felt, Etay be seen in the slipper-shaped flowers of Calceolaria (Fig. 32), Coryanthes, and Cypripedium. Thus Calceolaria Pavonii possesses a thick ridge along the upper edges of the curved basal part, which carries the inflated end upon which the bee stands, and which it depresses to get the honey. In this species it may be noticed the anther-cells are separated (a), so that they can oscillate as they do in Fig. 32.— calceolaria Pa- Salvia. In Cypripedium the edge is folded "™" ^^^' ^"''"'• inwards, thus strengthening the same part; while in Cory- anthes the lower portion is enormously enlarged, thus acting as a powerful spring which forces the anterior end of the labellum to be in close contact with the column. The Origin of Ieeegulaeitt in the Andrcecidm. — As it is with the perianth, so is it with the andrcecium : if the petals are regular the stamens are usually regular also ; but when irregularity occurs in the corolla the staminal whorl follows suit, and the position and form of the stamens are equally correlated to the efEectnal pollination of the flower. Thus, as hypertrophy affects the anterior side of the 12 110 THE STEUCTURE OF FLOWERS. flowers of Labiates, the anterior stamens are almost invariably the larger pair. On the other hand, atrophy has affected the posterior side of the staminal whorl, causing the total loss of the fifth stamen, and, to some extent, a reduction in length of the next pair of filaments. When the weight of the insect is thrt)wn npon the stamens, they either hang downwards, and the insect is suspended upon them, as in Epilohium angustifolium, or else they become declinate and then the anterior petal, being relieved, does not enlarge, either remaining of the same size as the rest, or else diminishes, and may even vanish alto- gether. Thus Vallota, with its perfectly i-egular perianth and spreading stamens, may be compared with Amarj^lUs, which has declinate stamens and a small anterior petal. The terminal flower of a " thyrse " of the Horse-chestnut, like the terminal flower of a "truss" of Pelargonium, is often regular with spreading stamens, whereas the normal flowers have declinate stamens, and usually only four petals, the fifth or anterior one being altogether suppressed. In some flowers the sta- mens are dependent at first, but their anthers rise up when dehiscing, and so the fila- ments become declinate in the pollinating stage. This is the case with Delphinium, Epilobiiim angustifolium, and Fig. 33.-Dtctamnus (after Tieghem). ^iotammus (Fig. 33) . In this flower the anterior petal is of much the same size as the others, but is often displaced (Fig. 33), and not immediately below the stamens, — this THE FORMS OF FLORAL ORGANS. Ill lateral displacement of the anterior petal being not always carried out, as it is in the next flower to be described. In Epilobium angtistifoUum (Fig. 34) and Oodetia, which have no anterior petals, the bees cling to the dependent stamens, while the petals have become permanently displaced, the two lower being somewhat raised, so that the angular distances are not the same. In Azalea and Jthododendron there is no anterior petal, but the posterior one is slightly enlarged, and this alone possesses extra colouring and the " path-finder." The stamens, being declinate, carry the insect without the aid of the corolla, so that the antero-lateral Fig. it.—^>CUiUma onguitifMum. fig. 35.— Feronico Chamadryt (after Mttller). pair of petals, not sharing in the support of the insect, are not enlarged at all. In Gircoea and Veronica Ghamoednjs (Fig. 35), the insect clings to the two stamens and style ; and the anterior petals are not enlarged, while in the latter flower it is, as usually the case, the smallest, the stamens of Veronica being attached to the lateral petals have to supply the fulcra for leverage, and consequently these have now become relatively hyper- trophied. In many flowers which have sub-declinate stamens, the latter lie in a more or less boat-shaped anterior petal, show- ing that the action of the insect has somewhat affected both the whorls together, as they have each some share in carry- 112 THE STEUCTUKE OF FLOWERS. ing the insect. Such is the case in the Ocimoideoe of Lahiatce, in Gollinsia bicolor, the " Letnon-scented " Pelargonium, etc. Correlation of Growth. — I have only referred to the forms of flowers as grouped under the terms "regular" or " irregular," and alluded to a few instances ; for it is not my object in this work to merely give illustrations of various kinds, -which are presumably well known to the reader, but to ofBer a rationale of the whole, without, however, attempt- ing to say how each individual shape has actually come into existence. To do this, it would be impossible in the present state of our knowledge of the history of flowers ; my object being to suggest a probable cause, namely, the mechanical influence of insects, without excluding others which we cannot trace. Nutrition, however, must be always borne in mind as an important one, hereditary influences as others — as, for example, in the restoration of an irregular flower to a condition of regularity, as occurs in Linaria, Lamium, Glox- inia, etc. The point, however, which I ■would specially emphasize is the correlation existing between the several parts of the organs, so that, regai-ded collectively, they all conspire to secure one and the same end, that being the pollination of the flower. Thus, as I have shown above, the calyx of Salvia has a form and structure correlated to the tube of the corolla; the corolla has a form in strict adapta- tion to the weight and pressures of the insect which rests upon the lip. The stamens are, again, correlated to the pres- sures brought to bear upon them, and have grown in response, forming the remarkable lever-processes, 'which are also found in species of Calceolaria. Lastly, the style and stigma ai'e correlated to the position of the anthers. Hyper- trophy in one direction has brought about atrophy in another, so that the two posterior stamens, are rudimentary, while the fifth has vanished altogether. THE FOEMS OF FLOEAL OEGANS. 113 Now, it might he argued, that when one organ changes its form others miist do so in obedience to the " laws of cor- relation of growth," as Mr. Darwin showed to be the case with the feet and bills of pigeons. In plants, however, the connection between various parts, even in close proximity, is by no means so intimate as between different organs of the higher animals ; while the theory advanced here gives a common interpretation for the whole of the so-called correla- tions found in any flower. That one is justified in saying that correlated growths are much restricted in plants, is clear from the experience of horticulturists ; thus, while, e.g., the varieties of pease are infinite, they having been the object of selection alone, the flowers which produce them have virtually remained unchanged. A single coincidence has little or no scientific weight as indicating cause and effect. It is only when coincidences can be multiplied that they furnish a probability of a high order ; which, even if they do not admit of a verifiable ex- periment, still furnish a mwal conviction, which, by the rules of philosophy, is equivalent to a demonstration. Now, this is exactly the case with irregular flowers. They always occur in similar positions ; they are always constructed so that the insect in adaptation to them can gain access to the honey in the easiest way ; their organs are so situated that the pollen should be transferred accurately to the stigma, etc. And when we find them distributed every- where throughout phanerogamous plants, the probability that the same or analogous causes have brought them about is of a very high order indeed Moreover, since we have abundant evidence of the re- sponsive power of protoplasm .to build up tissues wherever they are required, I am not assuming an influence on the one hand without ample evidence of the probability of the 114 THE STRUCTURE OF FLOWERS. responsive action on the other, coupled, of course, with here- ditary and other influences which fix the variation. Thus, then, aa I believe, all flowers as we have them now, which are in perfect adaptation to insect agency, are the outcome of the resultant of all the forces, external and internal, which the insect has actually brought into play or stimulated into action by visiting them for their honey or pollen. The belief that such processes may have gi-own in response to mechanical irritations is supported by some interesting experiments made by Mr. O'Brien, of Harrow, who has kindly favoured me with the following remarks: " With reference to impressions conveyed by ' nervous ' force in Orchid flowers, whereby the expansion of the sepals and petals signifies to the reproductive organs that the time for fertilisation has arrived, I have observed that the periods of maturing and of decay may be either arrested or hastened in certain orchids by artificial means. With reference to arrest- ing decay, I took such flowers as Stanhopea and Goryanthes, which have large membranous sepals, and which, in the ordinary course of events, become reflexed soon after the opening of the flowers, and shortly afterwards wither. These are then followed by the other parts. By seizing the opportunity as soon as they expand, and by passing a thread round them, so as to keep them in the condition of the flower when just on the point of expansion, they may be kept good for a long time, the flowers evidently, as it were, not realizing the increased lapse of time, and being unaware that they had passed the period when they would have been ready for fertilisation. When so secured, a flower of Goryanthes speciosa on my table kept fresh three times as long as it would have done on the plant. The dripping of the water from the horns above the bucket is also arrested. Finally, on releasing the ligature, the broad wing-like sepals imme- THE FORMS OF FLORAL ORGANS. 115 diately became reflexed, and the water commenced to drip. Shortly afterwards the wings shrivelled up, and the flower decayed in the same manner as it would have done a week before if left to itself on the plant. " I will now give an example of deceiving a flower by artificial means, by making it believe that its fertilisation has been accomplished without its having taken place at all. Miltonia Russelliana carefully guards the approach to the column by closing the petals over it ; but on pushing these petals aside with a pencil, I always found that the labellum faded, and withdrew upwards very soon afterwards. The showy portion of the flower, evidently having had it con- veyed to it that its duty was performed, then followed suit. On carrying the deception still further to the reproductive organs, by placing small pieces of grit on the stigma, I found that the ovaries would swell in many cases, just as though the flower had been properly fertilised by pollen. This same result often takes place in Orchid flowers under cultivation, and seed-vessels are obtained of full size, but, of course, with no vitality in the grains within." As an analogous instance, I will add that it is the belief of M. O. Beccari that ants are not only responsible for the remarkable growths in Myrmeccdia and Hydnophytum, etc., but that they have become indispensable for the healthy development of such plants. The investigations of M. Treub on Bischidia, the pitchers of which are frequented by ants, like the stipules of Acacia sphoBrocephala, seem to justify one in concluding that genus also to be one of these so-called "Ant-plants " {Ann. du Jard. Bot, de Buitenzorg, in., p. 13). Dr. Lundstrom also believes that the habit of producing " domatia " is now hereditary, without the actual presence of the insects (see Joum. Boy. Micr. Soc. 1888, p. 87.) ll(j THE STRUCTURE OF FLOWERS. CHAPTER XII. THE ORIGIN OP " ZTGOMOEPHISM." BiiiATBEATi Symmetry. — A feature abTindantly illustrated through the flowering world, in the construction of irregular flowers which are highly specialized for insect agency, and of which the Ldbiatce and Scrophularineoe, for example, fur- nish many instances, is the hypertrophy of the corolla in the direction of an antero-posterior plane, giving rise to a bilateral structure. On the one hand, the lips of various kinds, as also the keel, and often the wing petals too, where they help to sup- port the insects in papilionaceous flowers, are accounted for by the weight of the insects bringing about a responsive action in the protoplasm, thus determining a flow of nutriment to the parts demanding it, which now grow into the forms re- quired. On the other hand, the opposite or posterior side is often influenced as well, so that, as in Lamium, the lobes of the two posterior petals have grown into the enlarged hood. The cause of this I take to be the powerful thrust which insects exert against the posterior side while their weight is expended on the anterior. If a humble-bee be watched, as represented in Fig. 31 (p. 107), it will be seen how eagerly and determinedly it forces its way into a corolla-tube if it expand upwards, as in Duvernoia or Lamium,. All the pres- sure is exerted along the median plane, like an oblong wedge THE ORIGIN OF " ZYGOMOKPHISM." 117 thrust into a circular tube. The corolla then " gives," as it were, and expands along the antero-posterior plane. The calyx follows suit, and often assumes a bilobed funnel-shaped tube as well ; while the lateral lobes of the corolla tend to atrophy, since they do not lie along the line of the pressure due to the weight of the insect (see Fig. 40&, p. 126.) If the floral organs be imagined to consist of some plastic, extensible, but not elastic substance, and be subjected to various pressures, strains, thrusts, etc., in imitation of the motions of insects, it is readily conceivable how the parts would yield, stretch, or bulge, and become fixed into shapes very closely resembling what has actually taken place in nature. In reality, of course, the ability to grow in response to the fmxes applied is to be substituted for the theoretical plasticity and extensibility of the imaginary material. Compensatory degenerations occur in various directions, as in the atrophy of the lateral petal-lobes of Lamium, the loss of the fifth posterior stamen, the reduction in length of the filaments of the posterior pair of stamens. In this latter respect Nepeta differs from other genera , but as we can readily conceive how all sorts of differences may and do exist in the direction and degree of the forces applied to flowers, some exceptional ones must have occurred in that genus which has favoured the growth of the posterior pair, so that they have become the longer ones ; for there is no rule without an exception. As another illustration, Teucrium may be taken. In this genus the "hood" is entirely wanting; but here, again, F,g. 36._.Fiower of the interpretation is that, no hypertrophy ^wrium (after having been applied to them, the two petals of which it is composed have become reduced in size and "cleft," as shown in. Fig. 36, of T. {Teuaris) orientals. Bees, 118 THE STEUCTUEE OF FLO WEES. when visiting the flowers, hang downwards upon the corolla, as the lip and adjoining lohes are in one vertical plane, and give no thrust upon the posterior side. All weight, therefore, is thrown upon the front, just as it is on the stamens of Epilobium angustifolium, described ahove. Their weight has consequently, so to say, " split " the hood in twain, and the stamens now stand erect in the cleft. The peculiar form of the corolla, with the whole of the limb dependent in a vertical direction, must throw the weight of the insect so much to the front, that the leverage will be at a considerable disadvantage — much more so than when the insect stands more directly over the tube of a corolla; which latter, in that case, is often strengthened by that of the calyx. To meet this difificulty the pedicel is curved over at the top, as may be readily seen in our common Wood- sage, and forms a spring, while hypertrophy has attacked the posterior side of the calyx, in that it now carries two extra ^ marginal ribs, one on either side of the pos- 7)2, ^ terior dorsal one, as shown in the accompany- d d ing diagram. This is exactly the reverse of d d what occurs in Salvia, and others which are much more strengthened on the anterior side, when the insect stands more directly over the centre of the flower. Additional aid is also gained by the tube of the corolla of Teucrium being resilient ; the anterior pair of stamens form two thick ridges, much aiding it in this respect ; the posterior pair, however, are, so to say, " sunk " into the tissue of the corolla as to be invisible in a transverse section. Transitional Poems. — We may sometimes, as it were, catch the formation of irregular and zygomorphic flowers in the process of formation ; for it not infrequently happens that one genas will be irregular amongst its allied regular ones. Thus Verbascum and Petunia are transitional genera, THE ORIGIN OF " ZYGOMOEPHISM." 119 and stand intermediate between Solanacece and Scrophula- rinece. The former genus has a less zygomorphic corolla than many of the latter order, and also retains the fifth stamen in varying degrees of utility. We might regard both these genera as Solanaceous, and on the road to acquiring zygo- morphism, but to which neither has yet fully attained. " The short-tube [of VerbascuTn, nigrurn] widens out into a flat, five-lobed limb, which takes up an almost vertical position ; the inferior lobe is the longest, and the two superior are shorter than the lateral lobes, so that an insect settles most conveniently upon the inferior. The stamens project almost horizontally, but curve slightly upwards from the tube, and diverge slightly from one another ; they alternate with the petals, and again the superior is the shortest, and the two inferior longer than the lateral ones. . . . The style is shorter than the inferior stamens, and bent down slightly below them " From this description, taken from Miiller's work,* which, with slight modifications, would describe Petunia as well, the reader will see how these flowers fulfil the requirements of self -adaptation to insect agency ; and in every point of detail are they responding to the forces impinged upon them. Tho weight of the insect being well to the front, hypertrophy is commencing on the anterior side, while atrophy follows on the others, there being no special thrust as yet on the posterior side of the flowers There are many other genera and species which stand in intermediate positions between others, and it has always been a matter of doubt to systematists as to which they should be referred. The interpretation of their existence I take to be as here described, namely, that they are in an actual transitional state, brought about by insect agency, if * Fertilisation, etc., p. 429. 120 THE STRUCTURE OF FLOWERS. they be flowers visited; or by fluctaating conditions of nutri- tion, if not ; and then, arrested in that state. A further remark on a significant point may be added on Petunia. In this flower, as in Verbascum, the limb of the corolla 'stands in a vertical plane, the anterior lobe is a trifle larger than the others, the five stamens have a slight tendency to be atrophied on the posterior side, while the stigma has become just so much displaced as to hinder self- fertilisation. This property is, however, by no means yet lost. Florists are aware of it, and find it necessary to self- fertilise, but not to cross, these flowers artificially to secure plenty of seed ; Mr. Darwin corroborates this {Cross and Self, etc., p. 193). We have, then, here a case, but by no means an isolated one, in which the forms of the floral organs are undergoing a change, but the physiological characters of the essential organs have not yet been influenced by the external stimulus, so as to become more or less inert upon one another, as is sometimes the case in highly differentiated flowers. Indeed, it would seem to be a universal rule that morpho- logical changes are more readily acquired than physiological barrenness ; as by far the great majority of plants have retained their self-fertilising powers ; and, when they have lost it, it is easily and rapidly reacquired when the necessary conditions are supplied. Echium is another instance of almost a single genus amongst others of the same order characterized by great and persistent regularity. Bhododendron and Azalea may be compared with, other genera of Ericaceae, and the reader will readily suggest others. Sometimes the irregularity is confined to the stamens or style, or both, which may have a tendency to become decli- nate, as in Calluna, in some Liliaceous and Amaryllidaceons THE ORIGIN OF " ZYGOMORPHISM. 121 plants, as Narcissus Corbwlaria. In Anagallis arvensis and Lycium barharum there is nothing bat an obliquity in the style observable. In all the flowers which tend to show irregularities the rule is that the corolla-limb stands in a vertical plane, so that the flowers are visited from the front. This I take, as mentioned above, to be generally a primaiy necessity for bringing about irregularities of all kinds. There are some campanulate and pendulous flowers where irregularity occurs in the lengths of the filaments or the size of the anthers. Thus, I have observed great fluctuations in the stamens of Narcissus cernuus : some of these I have illustrated in Fig. 37. I noticed that a peduncle always bore the same form in every flower of its umbel. There were mostly three flowers in each, as of a, h, and d; one specimen of a and one of e had only a single flower; and one of c had two flowers. In a, b, c, d, the three short stamens, as well as the three long ones, were all of the same height, respectively ; but in e one of the shorter set was taller than the rest. Similar flactaations are not at all uncommon in cultivated heterostyled plants, as Primroses ; as will be alluded to again in discussing the conditions of heterostylism. In Fritillaria Meleagris, though no irregularity occurs in the perianth leaves, it often appears in the androecium, and is more especially obsei-vable in the lengths of the anthers. This would seem, therefore, to be another instance of incipient change. Calluna vulgaris is likewise just commencing to be 13 Fig. 37. — yarcissus cernuus. 122 THE STRUCTURE OF FLOWERS. irregular. The flowers are almost horizontal, closely com- pacted against the axis, and consequently not readily visited on any side except from the front. The style and stamens curve upwards, so that " the smaller bees and flics thrust the head or proboscis from the front into the flower, and the upward curvature of the style and stamens causes the insect to enter by the lower half of the flower, and so to get dusted with pollen from above." * Miiller also notices, about this flower, that " the style, which even in the bud overtops the stamens, grows very markedly after the flower opens, as the flower itself does. As a rule, it attains its full length only after the anthers have completely shed their pollen, at which time also the four-lobed stigma reaches its full development." He gives five figures of Saxifraga Seguieri to show the progressive stages of development. In the first or female (protogynous) condition the stigmas only are mature, the anthers, petals, and sepals being far from having attained their full size. It is not until half the anthers have shed their pollen, and the others ready to do so, that the flower attains its complete dimensions f I refer to these facts, which are equally applicable to many other flowers, to show that growth normally continues after insects have commenced to visit flowers ; so that there is plenty of opportunity for the petals, stamens, etc., to respond to the insect's action before reaching maturity. Dr. F. Noll has investigated the various movements of zygomorphic flowers during growth, resulting in the external position of the flower; and he finds that the excess of weight on one side is, when necessary, counterbalanced by active tensions (see Jl. B. Mic. Soc, 1887, p 612 and reffs.). • Fertilisation, etc., p. 379. + Ihid, p. 244. CHAPTER XIII. THE EFFECTS OP STRAINS ON STRUCTURES. Vegetative Organs. — In explaining the origin of irregular flowers by insect agency, it will not be amiss to fortify the theory by describing other instances apart from flowers, and to add further results which I believe to accrue from the persistent action of insects on the one hand, and a ready response on the part of the organ on the other. , Researches into the anatomy of stems have proved the existence of this responsive power. Thus, a tree will develop wood in a particular direction if it be compelled to meet special strains imposed upon it ; for Andrew Knight fonnd that when trees were allowed fi-eedom in one direction only, and were thus made to oscillate in definite directions, either east and west or north and south, the stem became elliptical in section, the long axis corresponding to the direction of oscillation. Mr, Herbert Spencer has also described how Cactuses, if submitted to particular strains, develop wood to meet them. The various kinds of the supporting tissues of pedicels, such as collenchyma, sclerenchyma, the so-called liber-fibres as well as true woody fibre, are all so many contrivances of the stems to support the weight of the flowers and fruits, and to overcome gravity, So, again, in the case of apples and pears, if they hang vertically downwards they grow as 124 THE STRUCTURE OF FLOWERS. symmetrically round the insertion of the stalk as an orange ; but if the pedicel projects obliquely from the branch, they then thicken along the upper side, forming a sort of buttress running down into the stalk, -which also itself tends to thicken. This enlargement, which gives the peculiar " lop- sidedness " to several kinds of pears especially, and in a lesser degree to some sorts of apples, is simply due to the fact that the force required to counteract the resultant of the two forces, gravity and tension — which act vertically downwards and along the stalk, respectively — must be increased in proportion as the direction of the stalk ap- proaches the horizontal one. The accompanying diagram (Fig. 38) represents the basal end of a Dr. Jules Guyot pear . and in the position in which it-hangs upon the tree. The letter w (weight) is in the line of gravity, t (tension) acta along . the stalk, while r coun- teracts the resultant, which tends to tear the pear from the stalk at the upper side. This strain must be met, and the increased thickness Fig. 38.— Dtegram of the end of a along this Upper side enables the pear Dr. Jules Guyot pear. , • j. -j. j j.-l i j.i- to resist it, and thus prevents the fruit, especially if it be a large and heavy kind, from being wrenched from the stalk. A somewhat similar development often occurs with plums and lemons ; only, as there is no receptacular tube in either case, the weight of the fruit causes them to produce a thick fold in the carpel on the under side, together with some degree of hypertrophy on the upper, where the tension occurs. It is not uninteresting to notice how branches of trees similarly sustain the strain produced by their own weight. This is done by growing at an acute angle (originally caused THE EFFECTS OF STBAINS ON STRUCTURES. 125 by arising in the axil of a horizontally inserted leaf), mucli more often than in a strictly horizontal direction. The branch, after growing for a short distance upwards, generally bends downwards, assuming just the same curvature as of declinate stamens which have to support the weight of insects. If the vertical line in the adjoining diagram (Fig. 39) represent the trunk, and the curved line a branch, the insertion at /sup- plies the fulcrum, w is the weight of / the branch, and acts in a vertical line, p is the power required to counteract the resultant of these two forces. *' When the bough breaks, either '^'l^f:-^^,';^™^, \,Hi,r through an additional weight of snow """<"' »"»''=««• or by its own weight on decay, it snaps off at the point p, i.e. the place where the force acts, as it can no longer over- come the resultant of / and w. Reproductive Oegans. — Applying these principles to floral structures, we have already seen in how many ways the strain to which parts of flowers are subjected, through the weights and pressures of insects, are met and overcome. In a large number of instances the organ becomes curved, and assumes the character of a spring, yielding on pressure, but recovering its position when pressure is removed. It is often so with the claws of the petals of papilionaceous flowers, the stamens of Dicenira, Corydalis, and Veronica Chamcedrys. Similar structures are seen in many styles, as those of Pansy (Fig. 54), and in genera of Polygalaceoe. All declinate stamens partake of it to a more or less degree. The distribution of the forces brought into play to support the insect is exactly the same as when a bough 126 THE STKUCTUEE OF FLOWERS, has to support its own weight, as will be easily understood from what has been described, and by referring to the diagram (Fig. 40a). If the tissue does not remain firm nnder pressure, then the lever-action of a spring may fail to be secured, and the organ will oscillate freely, as on a pivot. This I take to be another result of a constant, but of course unconscions, effort of the insect Fig. 4oa.-DiagraTn of deciinate to P^^h the Organ in a Certain direc- S"of fOTccs"""'^ "" *'""■ tion- It 'S thus that anthers become versatile, and oscillate, and may become even inverted in position, when pollination is being effected by insects. Consequently anthers normally introrse can be made to assume a pseudo-extrorse position. This happens with some Cruciferm as Cardamine pratensis, Tulips, etc. A similar cause I would attribute to the formation of the oscillating anthers of Salvia, and of the species of Calceolaria, as G. Pavonii, which form the section Aposecos of that genus, as shown m Fig. 32, a, p. 109. As an example of an entire flower illus- trating the distribution of forces, the accom- panying figure of Lamium album (Fig. 406) will explain how the forms of the calyx and corolla are adjusted to bear the weight of the insect. The bee alights on the lip and then partially crawls into the expanded mouth of the corolla, so that its weight now lies in the direction of w. The fulcrum will be at /, and the resultant of these is in the opposite direction to r. This is where the strain will be felt ; so that it is just at this Fig. 40b Lamium al- bum, showing distri- bution of forces. THE EFFECTS OF STEAINS OK STRUCTUEES. 127 point Tvhere the backward curvature tates place which gives strength to the corolla-tube. This latter is also greatly supported by the tube of the calyx, -which, as stated, has a curiously thickened cylinder within the mesophyl. Filially, if we may admit the existence of this adaptability to strains and other external forces, and that the various structures of flowers will grow in response to them and develop themselves accordingly, "we have a clue to the interpretation of every one of the most diverse forms which may be found in flowers adapted to insect agency. Similarly, with regard to several classes of cell structure which are now recognized as having a supportive f unction, snch as collenchyma, sclerenchyma, wood fibres, etc., I would con- tend that such are not foroied originally and anteriorly to the requirements of the plant; but that strains have beenresponded to, and the tissues formed accordingly. Then, subsequently, hereditary influences have come into play, so that now theymay appear even before there is any actual necessity for them. 1 find that M. J. Baranetzki's observations * on the thick- ening of cell-walls tend to corroborate this view ; for he, too, has arrived at the conclusion that the secondary formations on the interior of the cell-walls are always in adaptation to protect the cell- wall against the pressures exercised upon it. In alluding to the above instances of levers and mecha- nical powers in plants, one mentally recalls how abundant they are in the distribution of the bones and muscles in vertebrates. These latter are, of course, situated only and exactly where they are required. I cannot help thinking, therefore, that the old view was fundamentally correct; that snch have been gradually brought into existence by the efforts to meet the strains put upon them. If this be true, then one and the same law has prevailed in the evolution of organs in both the animal and vegetable kingdoms. * Ann. des Sci. Nat. (Bot), iv. (1886) p. 135. 128 THE STBUCTURE OF FLOWERS. CHAPTER XIV. ACQUIEED EEGULAEITT AND " PELOEIA." Reversions to REonLAEiTT. — Dr. Masters observes that "in cultivated Pelargoniums, the Geaj^l. flower of the nmbel or ' truss ' frequently retains its regularity of proportion, so as closely to approximate to the normal condition in the allied genus Geranium; this resemblance is rendered greater by the fact that, under such circumstances, the patches of darker colour characteristic of the ordinary flower are com- pletely wanting, the flower being as uniform in colour as in shape. Even the nectaiy, which is adherent to the upper surface of the pedicel in the normal flower, disappears, some- times completely, at other times partially. The direction of the stamens and style, and even that of the whole flower, becomes altered from the inclined to the vertical position. In addition to these changes, which are those most commonly met with, the number of the parts of the flower is sometimes augmented, and a tendency to pass from the verticillate to the spiral arrangement manifested." * All the differentiations in an ordinary iateral blossom of Pelargonium brought about by insect agency are, in the above instances, reversed in consequence of the terminal position of the flower. A more complete illustration of the effect of manner of growth and the distribution of nutrition could not * Teratology, p. 221. ACQUIRED EEGULARITY AND "PELORIA." 129 well be given, showing how all the features of irregularity acquired by the ordinary form must have been induced or impressed upon the flower when growing laterally and easily visited, but that they are readily lost as soon as the sap can be distributed radially and so cause the parts to grow symmetrically round the now vertical axis. Besides the occasional appearance of one or more terminal and regular flowers among a truss of irregular ones, it is the object of florists to induce all the blossoms of many irregular flowers to become regular. Thus cultivated Pelargoniums, Gloxinias, Azaleas, Pansies, etc., which are normally irre- gular, tend to become regular under cultivation, and lose their characteristic features. In all these cases I am inclined to recognize negative evidence in favour of the theory advanced ; in that, presuming the characteristic irregularities to have been brought about by the agency of insects and through the crossing of distinct flowers by these creatures, and that the ii'regularities have arisen under the various pressures, etc. ; then, under cultiva- tion, though they may be repeatedly crossed by man — the process, however, not being effected in the same way as by insects, and consequently the causes of irregularity being w&,nting — the flowers now revert to their ancestral forms ; while ample supplies of nutriment doubtless play an important part in the process. Moreover, though any irregular flower may become regu- lar, it is a significant fact that normally regular flowers are never known to suddenly assume any definite irregular form. That the change from irregularity to regularity is an acquired constitutional afEection is seen in the fact that, when the flowers of a drooping Gloxinia are fertilised with their own pollen, a large number of the seedlings will bear the erect regpilar form of flower. 130 THE STRUCTURE OF FLOWERS. In the preceding cases the regularity oocnmng in normally irregular flowers is due to the non-development or arrest of the usually characteristic features which give rise to the irregularity ; so that the resulting form is a reversion to, or a restoration of, the ancestral conditions of the flower which is assumed to have been perfectly regular. As insects, by their mechanical actions, are here believed to have brought about irregularities in flowers ; so, con- versely, regularity can be reacquired through their agency in another way. Glerodendron is a plant in the corollas of which certain members of the family Tingidce take up their abode as pupee. The irritation induced by their presence brings about a hypertrophy of the corolla, which now assumes a regular form, while the filaments and style are likewise affected, becoming much thicker than in the normal, irregular flower. Reversions to regularity may, therefore, I think, be safely referred to nutrition as the immediate agent, though such extra flow of nutriment may be brought about by diverse causes. "Peloeu." — Regularity may, however, arise in another way, by the members of the whorl or whorls normally irregular being all exactly alike. Instead of there being any arrest, there is here an excess of development. Thus, if, instead of the anterior petal of lAnwria being the only one provided with a spur, all the petals become spurred, then the corolla will become regular ; but there is no other tendency io revert to the ancestral form. This variety constitutes the form called " Peloria " by Linnaeus. There are, then, two factors, which appear either singly or together, in this process of change. First, a terminal position, as this tends to produce regularity in consequence of an equable ^ovi of sap in all directions : just as this also ACQUIRED REGULARITY AND " PELORIA." 131 determines the persistenfc regularity of all flowers which are normally so situated and are visited from all directions. It will be often found that when Snapdi-agons have pelo- rian blossoms they are in three-flowered cymes as in Cal- ceolarias, instead of a raceme, of which the central one is regular, while the lateral flowers are irregular. Secondly, whether terminal or not, the influence which first brought about the change in the anterior part of the flower spreads to and effects aU the rest. This statement, of course, only expresses what one sees, without explaining the process ; but the fact that the energy peculiar to the formation of one organ can affect others is so common, that we may recognize the process as a principle of growth; just as stamens may become petaloid, on the one hand, or pistiloid on the other ; showing that " petaline energy '' can affect the androecium in the first case, and "pistiline energy " in the latter. That the true pelorian form is correlated to vegetative energy is seen in the fact that such a flower obviously requires more material than a normal one, and that petalody of the stamens frequently accompanies the modification. Moreover, although of course usually sterile under such circumstances, yet pelorian Linarias have been reproduced when the seeds were sown in a rich soil. Mr. Darwin also raised sixteen seedling plants of a pelorian variety of Antirrhinum artificially fertilised by its own pollen, all of which were as perfectly pelorian as the parent plant. That peloria is due to hypertrophy is also seen in the fact that it always arises by multiplication of the normally enlarged organ. Thus, in Linaria and Antirrhinum all the petals are spurred or pouched ; in pelorian Larkspurs and Aconites it is the spurred and hooded sepal which is repeated ; and in papilionaceous flowers it is the standard which is multiplied five times, etc. An abnormal increase in the number of petals 132 THE STRUCTURE OF FLOWERS. and stamens often occurs in pelorian Pelargoniums, Horse- chestnut, etc. If pelorian forms were equally constant as the one-spurred condition, botanists would undoubtedly have recognized them as species, or perhaps genera, as it is the comparatively slight difference in the length of the spur upon which they separate Linaria from Antirrhinum. Similarly Gorydalis has normally but one spur and one nectary. It, however, bears occasionally two spurs and has two nectaries, as in Dicentra. " Peloria, then," as Dr. Masters observes,* " is especially interesting, physiologically as well as morphologically. It is also of value in a systematic point of view, as showing how closely the deviations from the ordinary form of one plant represent the ordinary conditions of another ; thus the peloric 'sleeve-like' form of Calceolaria resembles the flowers of Fabiana, and De Candolle, comparing the peloric flowers of the ScrophulariacecB with those [the normal ones] of Solanacece, concluded that the former natural order was only an habitual alteration from the type of the latter. Peloric flowers of Fapilionacem in this way are undistinguishable from those of RosacecB. In like manner we may trace an analogy between the normal one-spurred Delphinium and the five-spurred Aqiiilegia, an analogy strengthened by such a case as ihat of the five-sparred flower of Delphinium." * Teratology, p. 236. CHAPTER XV. THE OEIGIN OF FLOEAL APPENDAGES. Epidermal Trichomes, etc. — While all conspicuous flowera invite insects of some sort or another to visit them, which, by so doing, pollinate their stigmas, it is an important thing to be able to exclude those which would rifle the flower of its treasures and yet not transfer the pollen from one flower to another. Dr. Kemer, in his interesting work entitled Flowers and their Unhidden Guests, has described and figured a large number of instances of the forms of flowers in which he detects yarious processes, some of which produce sticky secretions, others occurring as hairy " wheels " and " tangles " of wool, etc. ; all of which tend to stop the ingress of ants and other small insects, and thus prevent them from getting at the honey. The question at once arises. How have these processes been caused ? Without attempting to account for all, the theory I offer will, I maintain, be answerable for a good many, especially for several cases of secretive processes and for the hairy obstructions. All these I would suggest as the immediate results of the irritations set up by insects ; so that, as a consequence, they occur just and only where they are wanted ; so that, while they form no hindrance to the larger and stronger insects which have presumably caused them to be developed, they, however, may effectually prevent the smaller ones from entering. 14 134 THE STRUCTURE OF FLOWERS. In many cases the capability of the flower to restrict itself to its proper visitors, and at the same time to exclude the ■wrong ones, is a common result of the differentiations which have taken place. Thus, an elongated tube, as in Evening Primrose, and in some species of Narcissus, etc., is a direct result of and adaptation to the long proboscides of Lepidoptera, and in proportion as the tube is elongated so does it prevent the ingress of short-tongued insects, or of those with short proboscides. Apart, however, from such and other general results of adaptations, whereby flowers have become, for example, irregular, and consequently their insect visitors are more and more restricted in number, there are innumerable out- growths of various kinds which act as special obstructions to the entry of small insects which would not be able to pollinate the flower. Thus, while many regular flowers, such as Gentians, have developed horizontal hairs all round the entrance to the tube of the corolla. Honeysuckle and Veronica Chamcedrys, which are irregular and approached from one side only, have developed them in the anterior side alone. In Amaryllis belladonna Kemer describes and figures (Fig. 41) a one-sided flap growing out of the perianth, and so folded as to famish a very small orifice for the entrance of a proboscis. There is no such growth on the anterior side, but only on that one, the posterior, which is probed by an insect. In Gentiana Bavarica there are Fig. 41. — Base of flower of .^mo- ,,,,., ryttis showing honey-protector tooth-like processes at the entrance of (after Eerner). _n j i i • i . t ,> t the tube, which remind one of the appendages to the corolla of some of the Silenece. Monotropa glabra and Daphne Blagayana agree in having a large circular THE OBIGIN OF FLORAL APPENDAGES. 135 stipma nearly blocking up the tube ; and while in the former the irritation set up by the proboscis of an insect has (presumably) given rise to a glutinous secretion, in the latter it has caused a development of hair.* Did we but know what the insects were, and how they have poised themselves upon the flower, and in what way their proboscides and tongues have irritated the different parts, one might be able to describe more accurately the whole process ; but that such has been the cause and effect, as above described, seems to me to be too probable a theory to be hastily discarded in the absence of a better one. It is one of those arguments of deduction that escape the opportunity of verification, and can only rest for support upon the number of coincidences which can be found, and which collectively furnish a probability of a high order. When, then, we find that these processes always occur just where we know the heads, legs, bodies, and proboscides or tongues of insects habitually are placed and irritate the flower, we are justified in recognizing, not only a coincidence, but a cause and effect, though we may not be able to trace the action in each individual case. Thus, it may be asked, * The remarkable fact of Heliotrope being the solitary exception oat of the order Apocynacea, with the stigma forming a circalar rim below the summit, may meet with its interpretation from a like caose. The corolla is so folded round the style that it leaves no space between it and the latter. Hence it may, perhaps, have been dae to a similar "Tabbing," that has transferred the stigmatic surface from the now abandoned apex to a lower level, just where the style-arms ought to begin to diverge. The papilte, too, difEer from the ordinary form in being pointed like fine hairs. The relative differences in the distribntion of the papillae on the style-arms of the Compositw, I would also suggest as having been brought about by different insects which irritate them in various ways. So, too, the diverging stigmas of insect-fertilised cruciferous flowers may be compared with the small globular form of self -fertilising species of the Cruciferae. 136 THE STRUCTURE OF FLOWERS. Why are tlie three anterior petals of Tropceolum fringed, but the two posterior, which stand a long way behind, not so ? Why are hairs produced on the anterior side of a Honey- suckle and Veronica, but all ronnd the mouth of the regular Geniiana ? And many other questions of a like sort might be raised. If we watch the habits of insects with their tongues, we may easily see how they irritate the various parts by licking them, not solely where the honey is secreted, but the filaments, etc. Thus Miiller often watched Rhingia rostrata licking the staminal hairs of Verhascum phceniceum, and in many cases the hairs on the filaments offer a foothold to the insects while visiting the flowers, as in species of Mullein ; such hairs, if my theory be true, being the actual result of the insects clutching the filaments or rubbing them with their claws. In Gentaurea, the epidermal cells of the filaments have produced projecting processes just where the proboscis rubs against them when searching for honey in the little cup (see Fig 11, p 60), from the middle of which the style issues, as shown by the direction of the arrow. These filaments also exhibit their extreme irritability by contracting, and so assisting in the " piston action " by dragging the anther-cylinder downwards over the style. While recognizing the coincidence between the localiza- tion of outgrowths, enations, trichomes, etc., and the position of the parts of insects in contact with flowers when searching for honey, one must not forget that a great number occur where such contacts do not take place. Hence we must look for other possible causes for their origin as well. One of the commonest forms of trichomes is glandular hairs, and, as Dr. Kerner has pointed out, when they occur on sepals, pedicels, etc., they form admirable barriers to the approach of ants and other creeping insects, which might rifle the flower and yet not fertilise it. We must be on our guard, however, in THE ORIGIN OF FLORAL APPENDAGES. 137 asserting that nature has produced them in order to keep ants oS ; for that line of reasoning' is pretty sure to land us in faulty teleological methods. What causes them is not at present known in all cases ; though we may perceive that certain conditions, as growth in water, can bring about their disappearance, as Dr. Kerner remarked in the case of Polygonum amphibium, which only has them when growing on land. If, however, we ask, for example, why the Sweet-briar has them all over it, and why the Dog-rose has none, I do not know how to reply to the question as yet. We may notice certain coincidences, that hairy herbaceous plants are com- moner in dry situations and smooth ones in watery; just as root-hairs occur in a loose sandy soil and their absence is noticeable in a heavy one ; but we do not know how these difEerent media actually bring about these changes, though we may feel assured that it is solely due to the environment. If we, thus, look elsewhere than in flowers for any analogous processes they are by no means wanting. For example, it is simply the mechanical iri'itation brought about by contact with a foreign body, probably aided by moisture and a lessened de- gree of light, that causes the epidermal cells of the aerial roots of the Ivy and Orchids (Fig. 42) to elon- gate into adhesive or clasp- ""^ j, ing hairs, so as to grasp the r,g 42._Adheslye epiderm.l cells of roots of body for support. This is J^'ei^'^^Sy '"'*'• *• ™'>'«"^«»-' (»«" only a form of the ordinary root-hairs which are immediately developed when the tip is in contact with a moist soil, and each hair grips and glues itself 138 THE STRUCTURE OF FLOWERS. to the partiules of soil.* Chatin noticed the production of hairs when the roots came in contact with any obstacle ; t but Dr. M. T. Masters observes that the obstacle alone in their case is insufficient without moisture, for he found that the roots of Mustard-seed could penetrate a stiS clay, but did not develop any root-haii-s until they came in contact with the sides of the pot — " Wherever there was a thin film of water investing a stone or the sides of a porous flower-pot or a plate of glass, there the root-hairs abounded." Besides a nutrient or moist medium, actual growth in water may enormously increase the length and quantity of root-hairs ; as may be seen in the dependent roots of floating plants of Hydrocharis, etc. ; or in the hypertrophied con- ditions of the roots of grasses when growing in water. That epidermal trichomes may be due to the irritation of insects is clearly seen by their appearance within the cavities of certain galls. J In the case, for example, of a very com- mon one on willows, the leaf bulges out below and foi-ms a sort of bag, open or closed above. , The tissues become hypertrophied though the epidermis and palisade cells are still recognizable lining the cavity. The leaf has scattered hairs on both sides ; but within the cavity much larger hairs, rich with protoplasmic or other matters, project from all sides into the interior. Some are straight, others carved, club-shaped, or with irregularly swollen ends, not unlike the forms produced on climbing roots by contact with a foreign body. Again, the crimson "spangles," so common on the underside of Oak-leaves, are covered with stellate clusters • Sachs' Pkys. of PI. (Eng. ed.), 1887, fig. 12, p. 19. t Mem. Soc. Nat. Sci., Cherbourg, 1856, p. 5 ; referred to by Dr. M. T. Masters in Notes on Boot-hairs, ei 41 44 3 P. Auricula [Scott] >i 73 §98 25 P. Sikkimensis „ 11 35 §42 7 P. cortDsoides „ 11 51 §61 10 P. involucrata „ t> 66 69 3 P. farinosa „ ») 52 56 4 Hottonia pal. [MuUer] it +91-4 66-2 25-2 Pnlmonaria ofi. [Hild.] tt 1-3 1-57 0-27 Mitchella repens »» +4-6 41 0-5 Linnm grandiflorum it 5-6 4-3 1-3 L. perenne tt 7 8 1 L. flaTum (3 flowers produced capsules) 1 3 2 * Forms, etc., p. 20. HETEROSTYLISM. 205 The first observation is that in twelve cases the short- styled are in excess of the long-styled, and in four cases (f) this is reversed. Hence Mr. Darwin's conclusion is not absolute ; and it is a somewhat remarkable fact that Primula veris (the Cowslip) is the identical species from which he deduced the conclusion that the short-styled was the more feminine of the two forms. The conclusion now arrived at from this species would be, that when it is left to itself the short-styled form sets most seed ; but when artificially crossed it is the long-styled form which bears best. The cause of the former result is that some pollen in the short-styled form can fall upon the stigma and so secure self-fertilisation, which is impossible in the latter case. The same results occurred with Mr. Scott.* Hence Mr. Darwin's first conclusion, that the short-styled was the more feminine, was drawn from a wrong premise; as it was not a question of sex so much as of union. When the results of self-fertilisation are compared, as given in the table on next page, it appears that the long-styled form of the Cowslip is the more feminine of the two, in the pro- portion of 42 to 30. Of that table, three cases of Primula sp. (f) only show the short-styled bearing more seed than the long-styled when illegitimately fertilised ; viz., with Mr. Scott, P. vulgaris, var. alba, and P. Auricula (i.e. forms more or less modified by cultivation) ; and with Hildebrand, P. Sinensis, when crossed • Journ. Linn. 8oc. Bot., vol. viii., 1864. This case may be taken to illustrate one of the disadvantages often accruing through great differenti- ation and adaptation to insect visitors. Though it appears proved that legitimate crossing sets most seed when carefully and artificially effected ; yet, when the process is left to the capricious visits of insects, Mr. Darwin's experiments show how nature fails to derive the full benefit of intercrossin!; ; so that the Cowslip has to be contented with the results of the illegitimate union of the leaft fertile of the two forms. 20 206 THE STRUCTURE OF FLOWERS. by distinct plants. The difference, however, being only two in each ease, is practically inappreciable. Of the other genera, Linum shows a slight inclination in favour of short-styled; but as this genus is exceedingly barren when illegitimately fertilised, the results here given of that plant are insufficient for deducing conclusions ; at all events, these tables show that the long-styled form is certainly more prolific when illegitimately fertilised, than the short-styled form vyhen similarly treated.* ILLEGITIMATE OR HOMOMORPHIO UNIONS. Long- Short- Differ- etyled. styled. ence. Primula veris ( V7t. of seeds of 100 capsules ) 42 30 12 P. elatior (Av. No. of seeds per capsule) 27-7 121 15(5 P. vulgaris )• 52-2 18-8' 3-4 „ var. alba [Soott] „ It tl3 2 F. Sinensis „ J) 35 25 10 „ [Hild.] (plants distinct) )> 18 t20 2 „ „ (same flower) J» 17 8 9 P. Auricula [Scott] IJ 12 tl4 2 P. Sikkimensis „ ft 14 8 6 P. cortuEoides „ „ 41 38 3 P. involncrata „ »> 38 28 10 P. farinosa „ 1* 30 19 11 Holtonia palustris [Miiller] (plants distinct) it 77-3 18-7 58-8 „ „ (same flower) St 15-7 6-5 9-2 Pulmonaria off. [Hild.] it Mitchella repens ti 2-2 2 0-2 Linum grandiflorum tt 2o +4-2 1-7 L. perenne It +3 3 I t „ mid-styled » .. 65 Mid-styled ... 92 „ „ long-styled )] .. 127 »5 ... 100 ,, „ short-styled )) .. 108 »» ... t25 illegi b. „ long sta. of mid-sl. ») ,. 55 » ... 93 „ „ long sta. of short-st. »j .. 69 it ... 54 ii „ short sta. of long-st. )» .. 47 »1 ... to )j „ short sta. of mid-st. »> From these resalts Mr. Darwin concluded that each form of pistil is as fully fertile as possible, only when it receives pollen from the stamens of the same length as itself, these being legitimate unions. It will be seen that the mid-styled form is the most fertile of the three when legitimately fer- tilised ; and as all illegitimate unions of the long- and short- styled forms vrere too sterile for any averages, the mid-styled form is also the most fertile when illegitimately crossed, and is least fertile with its own stamens, as indicated above by the (t). Hence self -fertilisation in this species is at a very low ebb. A few more remarks deduced from Mr. Darwin's observa- tions t ni3'y he added here. From the three forms occurring in approximately equal numbers in a state of nature, and from the results of sowing seed naturally produced, there is reason to belief that each form, when legitimately fertilised, repro- duces all three forms in about equal numbers. When they are illegitimately crossed with pollen from the same form, they evince a strong but not exclusive tendency to reproduce the parent form alone. * Farms of Flowers, p. 152. t i-c- P- 203. 212 THE STRUCTUKE OF FLOWERS. When the short or mid-styled forms were illegitimately crossed by the long-styled, then the two parent forms alone were reproduced, but in no case did the third form appear. When, however, the mid-styled form was illegitimately fertilised by the longest stamens of the short-styled, the seed- lings consisted of all three forms. This illegitimate union was noticed as being singularly fertile, and the seedlings themselves exhibited no signs of sterility, but grew to the full height. Finally, of the three forms, the long-styled evinces some- what the strongest tendency to reappear amongst the ofE- spring, whether both, or one, or neither of the parents are long-styled. Although L. Salicaria has not, as far as I know, shown any signs of variability in the lengths of its filaments and styles, yet, as is perhaps generally the case with heterostyled plants, there are one or more species of the same genus which are normally homostyled. Thus L. hyssojaifoKum, which is not social, and is a dwarf form and an annual, bears only six to nine stamens, the anthers of which surround the stigma, which is included within the calyx. The three stamens, which vary in being present or absent, correspond with the six shorter stamens of L. Salicaria. The stigma and anthers are upturned as in the last species, and so indicate the fact that it is a degenerate form from L. Salicaria or some other intercrossing species, though it has now reacquired its self- fertilising properties. Oxalis is a genus having trimorphic species. Many of them are extremely infertile with their " own form '' pollen. Such are the long-styled form of 0. tetraphylla, versicolor, Brasiliensis, and compressa. On the other hand, in the long-styled form of 0. incarnata, rosea, and Piottce, and in the mid-styled form of 0. camosa, no self- Bterility occurs.* • According to Hildebrand, Bot. Zeitg., xlv., pp. 1, 17i 33. HETEEOSTYLISM. 213 Origin of Heterosttlism. — The question may be now asked, How has heterostylism arisen ? We have seen, in the first place, that in many cases there is a certain instability in the length of the filaments of the stamens and of the styles, in that they are liable to alter spontaneously, and especially under cultivation.* In the case of Primula Auricula, the homomorphic form has the anthers and stigma at the orifice, while in P. Sinensis they are often both low down ; it is clear that either might arise in two vi^ays. In the case of the former, the stamens, while resembling in position that of the stamens in the short-styled form, have pollen like that of the long- styled, the pistil being of that kind. Hence it is reasonable to assume that the anthers have been uplifted. In the Chinese Primrose it is the reverse ; so that the pistil of a long-styled form has been lowered to the level of the stamens ; the stigmas, too, are that of the short-styled. Recognizing this instability of the essential organs, it is reasonable to assume that it may be due to varying degrees of nutrition which can readily bring about such changes, a relatively strong vegetative vigour elevating the stamens in the one case, while a slight tendency to degeneracy with lessened vital vigour tends to suppress the pistil in the other. Assuming a homomorphic form to have been the primitive and ancestral state, we can realize how dimorphism has been brought about by such varying degrees of stimulus having been applied to the stamens and pistil. Insect agency I take to have been this cause, which, at the same time, has by selection fixed the heights of the stamens and style so * See the description, given above, of Narcissus cemuva, Fig. 37, p. 121. Mr. Uarwin found Gilia to vary ninoh in this respect. It may be added that it is a not nucommon featiu'e in flowers which are not heterostyled, as e.g. cultirated Qladioli and Croci, Fntillaria Meleagris, etc. 214 THE STHUCTURE OF FLOWEKS. as to render them permanently dimorphic for legitimate fertilisation. The predominant insect or insects were (as I surmise) the direct cause of arresting the fluctuations which they themselves, as well as accidental sources of nutriment, had set up in the lengths of the essential organs, thus compelling them to retain their anthers and stigmas at the correct height. If there were from one to three prominent kinds of insect-visitors the flowers might become adapted to them, and trimorphism he the result ; if four, tetramorphism ; and there is no li priori reason why there should not be polymor- phic flowers as well, in the strict sense of the prefix of that term, provided a flower could furnish a suflaciency of stamens. It is further to be noticed that the rule holds good with heterostyled plants, as with all other kinds of differentiation, that in nature, whenever self-fertilisation can be effected, more seed is borne than by the forms requiring intercrossing. First, whenever it can be brought about mechanically; as has been observed in P. Sinensis, by the corolla, when falling off, dragging the anthers over the stigma in the long-styled form, which consequently yields more seed.* In P. veris, it does not do so ; but as pollen can fall in the short-styled form, in this species that form is thus the most fertile (see above, p. 205). Secondly, when these plants are artificially and legiti- mately fertilised, and not left to the chance visits of capricious insects, then the results are as they should be ; but if self-fertilisation be artificially and repeatedly practised, then nature responds to the act ; the anthers and pollen may in part degenerate, but what is left good is ample to secure abundant seed, and the self-fertilised form surpasses even the • Darwin found that, in the absence of insects, the long-styled form of P. Sinensis waa twenty-fonr times as productive as the short-styled. HETEROSTYLISM. 215 legitimately fertilised heteromorphic unions in fertility. Thus, Mr. Darwin observes, " The self-fertility of Primula veris increased after several generations of illegitimate fertili- sation, which is a process closely analogous to self-fertilisa- tion." * Lastly, if homomorphic forms occur spontaneously, as is often the case with species of Primula, Mr. Darwin has shown they are not only " capable of spontaneous legitimate fertilisation, but are rather more productive than ordinary flowers legitimately fertilised." f It was Mr. Scott who suggested that the equal-styled varieties arose through reversioa to a former homostyled condition of the genus. Mr. Darwin supported this view in consequence of observing " the remarkable fidelity with which the equal-styled variation is transmitted after it has once appeared." J ♦ Cross and Self Fertilisation, p. 351. t Forms of Flowers, p. 273; and Cross and Self Fertilisation, p. 352. J Forms, etc., p. 274 ; Mr. Darwin was bo profoundly impressed with the supposed advantages of intercroBsing, that he again and again asserts most positively that self-fertilisation Is injurious, often in diametrical opposition to his own statements and experiments. Thns, while speaking of heterostyled trimorphio plants, he says, " As I have elsewhere shown (The Effects of Cross, etc.), most plants, when fertilise^ with their own poUen, or that from the same plant, are in some degree sterile, and the seedlings raised from such unions are likewise in some degree sterile, dwarfed, and feeble." Yet, in the work quoted, he has not only shown that, when he persevered with self-fertilisation for several generations, he found it was just the reverse ; as e.g. with " Hero" Ipomcea, the white Mimulus, etc., and with Primula, as stated above ; but he more than once draws an opposite conclusion, as' when speaking of self- fertile varieties (I.e., p. 352): "It is difficult to avoid the suspicion that self-fertilisation is in some respects advantageous. . . . Should this suspicion be hereafter verified, it would throw light on the existence [of cleistogamy]." It is this " suspicion" which I have completely veri- £ed ; and, indeed, anj idea of " injurionsness " is refuted by the majority 216 THE STEUCTUBE OF FLOWERS. Besides the more obvious differences in the relative lengths of the styles and filaments* of heterostyled flowers, the rule is for the stigmas of the long-styled to be larger or longer than those of the short-styled,t and to have their papilla longer and broader. Thus in the nine species of Primula described by Mr Darwin, in two only were the stigmas nearly alike in both. Of three species of Linum, L. flavum alone had an appre- ciable difference in the stigmas. In Pulmonaria officinalis and Polygonum fagopyrum, Forsythia suspensa and ^giphila elata, it was not, or scarcely appreciable. Again, besides those mentioned there were twenty species in which the stigmas of the long-styled were markedly superior to those of the short-styled. of plants in a wild state being constantly self-fertilised, as Hiiller, and, indeed, Mr. Darwin himself has shown to be the case. Thus, he gives two lists, of forty-nine species in each, {Gross and, Self Pert., etc., pp. 357 and 365), one of self-sterile, the other of self -fertile plants, and adds, " I do not, however, believe that if all known plants were tried in the same manner, half would be found to be sterile within the specified limits; for many fiowers were selected for experiment which presented some remarkable structure ; and such flowers often require insect aid " (I.C., p. 270). The proportion of self -sterile plants is, in fact, extremely small. Mviller remarks, e.g., of the highly differentiated order Scrophu- larinece, that " in default of insect-visitors, self -fertilisation takes place in most forms ; and in only a few are insect-visits, and consequently cross-fertilisation, so far insured that self-fertilisation is never required and has become impossible." Similarly of Lahiatw he says, " Self- fertilisation seems to he rendered impossible only in the species of Nepeta, Thymus, Mentha, and Salvia described " {Fertilisation, etc-, pp. 464 and 503). Moreover, while Mr. Darwin includes the Fox-glove and Linaria vulgaris among his sterile plants, Miiller considers them both to be self -fertilising. * Exceptions occur, thus Cordia and Linum grancUfiorwm have little or no difference in the length of the stamens. f Leucosmia Bwrnettiana is remarkable for having the stigma of the ahort-styled form the more papillose {Foi-ms of Flowers, p. 114). HETEROSTTLISM. 217 Oa tbe other hand, the anthers of the short-styled are usually longer and contain larger pollen grains than those of the long-styled, the pollen of which is also often more translucent and smoothei-. Of all the species included in the above-mentioned thirty- six species, only five seem to have the pollen of both forms of the same size, and two in which it was reversed. The five species are Leucosmia Burnettiana, Linum grandiflorum, Cordia, Gilia pulchella, and Coccocypselum. The two in which the pollen grains of the long-styled form were the larger, were Gilia micrantha and Phlox subulata. The presence of cases where the usual differences are not pronounced is just what one expects to find, in accordance with the laws of differentiation ; whereby intermediate conditions are to be looked for. Thus some species of Primula afford great differences in the shapes of the stigmas, P. veris being globular in the long-styled, and depressed in the short-styled; while in P. Sinensis it is elongated: but in other species, as P. Sikkimensis and P. farinosa, there is but little difference between the stigmas of the two forms. In some cases the differences reside entirely in the stamens or pollen grains, as in Forsythia suspensa, in which, although (contrary to the rule) the anthers of the long-styled are in length as 100 : 87 compared with the short-styled, yet the pollen grains are as 94 : 100, which agrees with the rule. 'Wiih Linum grandiflorum and Cordia and Gilia pulchella, etc., the difference lies in the pistil. On the other hand, the difference may reside in the stamens, as in ^giphila elata, the pollen grains being as 62 : 100, i.e. in the long-styled as compared with the short-styled. ^giphila obdurata has the stigmas of the long-styled in length 100 : 55 as compared with the short- styled ; and the length of the anthers as 44 : 100. This is, therefore, 21 218 THE STRtJCTTJRE OF FLOWERS. apparently truly heterostyled, but from Mr. Darwin's obser- Tations lie thinks the short-styled incapable of fertilisation ; moreover the anthers of the long-styled form were " brown, tough, and devoid of pollen." He considers that, from having been heterostyled, it has now become dioecious, or else gyno- dioecious. M. W. Burck has shov^n * that several genera of RubiacecB are heterostyled in form but quite dioecious. Faramea affords another curious difference. In the long- styled form the stigma is short and broad ; in the short- styled, it is long, thin, and curled. The anthers of the short-styled are a little larger than those of the long-styled, and the size of their pollen grains are as 100 : 67. But the most remarkable difference (of which no other instance is known) is in the fact that while the pollen grains of the short-styled forms are covered with sharp points, the smaller ones are quite smooth. The anthers, moreover, rotate outwards in the short-styled, but do not do so in the long-styled flowers. A similar rotation takes place in some of the Cruciferce, and facilitates intercrossing. A somewhat analogous torsion occurs in some styles and stigmas, as of Linum perenne, Luzula arvensis, Begonia, etc. The smaller and smooth pollen, in the more degenerate condition of the long-styled form, is suggestive of the origin of that of wind-fertilised flowers, which has sometimes acquired the same form. Indeed, the two forms of pollen (figured by Mr. Darwin at p. 129 of Forms of Flowers) exactly correspond to the very common spinescent form in inter- crossing species of Compositce, and to that of the anemophilous Artemisia of the same order, respectively. The general conclusion, therefore, derived from the com- • Sur V Organisation Florale chez quelques Hvhiaciea. Ann. Jard. Bot. Bnitenzorg 3, p. 105. HETEROSTYLISM. 219 parison of these minute details, is that the long-styled form of flower represents a more fally developed pistil, and therefore a more female condition ; while the short-styled is more male : and, as we have seen above, this is borne out by the comparison of the offspring ; and, lastly, by the probable dioecious condition of ^giphila ohdurata, as well as by the actual dioecism of some species of Musscenda and Morinda umhellata; while Musscenda cylindrocarpa and certain other species of Morinda are hermaphrodite without heterostylism (Burck, I.e.). 220 THE STRUCTUEE OF FLOWERS. CHAPTER XXIV. PARTIAL BICLIKISM. Gtnodkecism and Gynomokcecism. * — In accounting for the origin of certain floral structures, it must be borne in mind that the habits and constitutions of plants are so infinitely various, that the interpretation given for that of a structure in one case may fail to be satisfactory when tested by another ; and an argument apparently sound for the expla- nation of a special phenomenon in a particular plant or plants may not at all apply to that of others. Thus, while the Hazel may mature its stamens before the pistils on a slight rise of temperature in early spring, there are many herbs, if they happen to blossom in spring earlier than is their custom, in summer, or what may be their optimum period, may have the staminal whorl more or less deranged, as such plants require a relatively higher temperature to develop them perfectly.t This is particularly characteristic of gynodicEcious plants. Thus, e.g., most of the distinctly protandrous species of the Alslneai are in this condition, and * Gynodiascifm signifies that the same species may have both female and hermaphrodite plants. Gynomoncecism signifies that the same plant may bear both female and hermaphrodite flowers. t This will be discussed more fully in the next chapter. PARTIAL DICLINISM. 221 the plants with small, usually pistillate flowers are chiefly in blossom at the beginning of the flowering period of the larger-flowered hermaphrodite plants of this section of the CaryophyllecB. Similarly, Caffea arahica produces small pis- tillate flowers in Guatemala at the beginning of the season. * It is the same with Geranium macrorhizon and many species of Pelargonium, €tc. f Gynodioecism also prevails in the Labiatoe, but both female and hermaphrodite plants for the most part blossom simul- taneously in summer. It may be noticed that the corolla is almost invariably reduced in size in female flowers, whether the species be strictly dioecious as in Bryony, or gynodioecious as Thyme, showing the close interdependence between the corolla and stamens. X That climatal conditions are likewise connected with the Gynodioecism of the Labiatoe seems probable from the behaviour of Thymus Serpyllum ; for Delpino found that it was trimorphic in the warmer region of Florence, having flowers with greatly developed stamens and the pistil in every stage of abortion or even absent (see Chapter XXV.) ; other flowers showed the exact converse ; and, lastly, others were hermaphrodite. Miiller, however, on the other hand, in Westphalia and Thnringia; Ascherson, in Brandenburg; Hildebi-and, in the Rhine provinces ; and Mr. Darwin, in England, never met with the purely male form ; though Dr. Ogle found some with the pistil permanently immature. § Similarly, Eriophorum angustifolium is gynodioecious in Scotland and the Arctic regions.|| Besides temperature, the character of the soil has most probably much effect in bringing about this kind of partial • Miiller, Fertilisation, etc., p. 304. + L.c, p. 158. J See Forms of Flowers, pp. 307-309. § Miiller, I.e., p. 474. || Forms of Flowers, p. 307. 222 THE STRUCTURE OF FLOWERS. diclinism. Mr. Darwin thought " a very dry station apparently favours the presence of the female form,"* i.e. a lessened vegetative vigour tends to check the development of the corolla and stamens, especially if a love temperature accompanies it ; just as, conversely, we have seen how a high temperature enhances it. Mr. Hart thus found that, with Nepeta GlecJwma, all the plants which he examined near Kilkenny were females ; while all near Bath were hermaph- rodites, and near Hertford both forms were present, but with a preponderance of hermaphrodites. f Both Miiller and Mr. Darwin offer theories to account for the origin of these gynodioecious plants. Miiller, after quoting Hildebrand's view, which he rejects, J says,§ " Of the flowers of the same species gi-owing together, the most conspicuous are first visited by insects, and if the flowers on some plants are smaller than on others, perhaps owing to scanty nourishment, they will generally be visited last. If the plant is so much visited by insects that cross- fertilisation is fully insured by means of protandrous dicho- gamy, and self-fertilisation is thus rendered quite needless, then the stamens of the last-visited small-flowered plants are useless, and Natural Selection will tend to make them disappear, because the loss of useless organs is manifestly advantageous for every organism. " This explanation rests upon the hypotheses, (1) that the flowers of those species in which small-flowered female plants occur together with large-flowered hermaphrodite plants are plentifully visited by insects and are markedly • Forms of Flowers, p. 301 + Nature, 1873, p. 1G2 ; and see below, p. 239. Z Fertilisation, etc., p. 473. § i.e., p. 484. Compare his remarks on Scahiosa arvensis, I.e., pp. 310, 311. PARTIAL DICLINISM. 223 protandrous ; (2) that variation in size of the flowers has always taken place, not among the flowers on a single plant, but between the flowers on different individuals.'' Mr. Darwin suggests another view : * " As the production of a large supply of seeds evidently is of high importance to many plants, and . . . the females produce many more seeds than the hermaphrodites, increased fertility seems to me the more probable cause of the formation and separation of the two forms." " S. M.," reviewing Mr. Darwin's work in the Journal of Botany, 1877, p. 375, "felt compelled to differ from the author, and adds, " For ourselves we cannot help thinking that gynodioBcism can be better explained on the view of a sufficiency of pollen for the fertilisation of all the individuals of a species being produced by only a few of the flowers, so that instead of some of the anthers of all the flowers becoming abortive — a very common occurrence — we see here abortion of all the anthers of some of the flowers. . . . All known instances of gynodioecism relate to species which have the maximum of stamens possessed by the orders to which they relatively belong, and are without any complex entoraophilous structure. ', . . We may also remark on the pauciovulate condition of gynodioecious species, and ask why do we not see this form of sexual separation in multiovulate ones ? " In reply to this writer's suggestions, I would remark that ia all entoraophilous flowers far too much pollen is produced and wasted ; that Mr. Darwin's observation, that a bee could fertilise ten pistils with pollen from one flower of Satureia, might readily apply to hundreds of cases where no gynodioecism exists ; and as long as insects visit flowers the tendency is not to contabescence and abortion of the * Forms of Flowers, p. 304. 224. THE STKUCTUBE OF FLOWERS. anthers, but to higher differentiations and an increase in the quantity of pollen. Secondly, that the orders, with gyno- dioecism have the maximum of stamens, is not universally true, Pelargonium having only seven out of ten. Again, the Lahiatce are especially characterized by " entomophilous structures." Lastly, the order Oaryophyllece is multiovulate. In the first two interpretations, those of Miiller and Darwin, Miiller suggests scanty noarishment as a cause for the diminished size of the female flowers, which might apply to any or every protandrous plant and so give rise to gyno- dioecism ; for if it be a sufficient cause in one family, why has it not brought it about in all ? This cause alone does not touch the question. Why is gynodicecism peculiarly common in the Alsinew of the CaryophylleiB and in Lahiatoe ? Mr. Darwin thinks that an increased fertility of the female may be the cause ; but he seems to forget that no flower of the LabiatcB can bear more than four seeds, so that, supposing a female plant to have the same number of flowers as a her- maphrodite, if it bears more seeds it must be due to the decrease in fertility of the latter, and not to any increase in the foi-mer. * It is, in fact, a very common occuiTence for a flower of any member of the Lahiatce to bear one, two, or three only, as well as four nutlets in an individual fruit. Mr. Darwin " doubts much whether natural selection has come into play,'' and notices that " the abortion of the stamens ought in the females to have added, through the law of compensation, to the size of the corolla," as is the case in the ray florets of the gynomonoecious Compositoe. He, however, recognizes the • In his experiment with Satureia hortensis, Mr. Darwin collected seeds from the finest of ten female plants, and they weighed 78 grains ; while those from the single hermaphrodite, which was a rather larger plant than the female, weighed only 33'2 grains ; that is, in the ratio of 100 to 43 (Forme of Flowers, -p. 303). PARTIAL DICLINISM. 225 intimate connection between the corolla and androecium, and thinks that " the decreased size of the female corollas is due to a tendency to abortion spreading from the stamens to the petals." In noting all the plants mentioned by Miiller and Mr. Darwin as gynodioecious, there are besides the two well- marked groups already mentioned, viz., Alsinece and Labiatce, the following isolated genera or species, Pelargonium, Gera- nium macrorhizon, Sherardia arvensis, Valeriana montana, Scabiosa, Cnictis, Echium vulgare and Plantago ; to the Compositce, I can add Achillcea millefolium; and I think also Vines may be included in the list. The first and important point to note about the flowering of the Alsinem is that the female flowers are the first to open, at the beginning of the season* It is the same with Geranium macrohizon. Pelargonium, and Cofiee in Guatemala. Now, we have already seen how sensitive the androecium and the corolla are to a low temperature, so that we have here a direct cause •which will account for the check upon the growth and development of these two whorls. Applying this principle to the Labiates, we must remember that as a group they are correlated to a warmer climate, their " home " being the Mediterranean and even warmer regions ; hence I assume their greater hereditary sensitiveness to a low temperature in those descendants which occupy a cooler temperate zone. This may, I think, account for the predominance of purely female forms, as well as the presence of stamens in every degree of degeneracy. How far the same principle will apply to the other gynodioecious genera and species, I will not pretend to offer an opinion, as not enough is yet known about them ; * See Hildebrand's observation, p. 234, and SEiUALlTir and Tempeea- TUEE, p. 237. 226 THE STRUCTURE OF FLOWERS. only we must always remember that there may be a variety of causes which may equally well bring about the same result. It may be also borne in mind here that another result of low temperature is, while retaining the function of the androeciura, to arrest the expansion of the corolla and to render the flowers self-fertilising. This is peculiarly the case with the Alsinece ; while Lamuim amplexicaule fails to open its earliest small- flowered flowers at all, being strictly cleistogamous. The preceding cases of gynodicecism are all associated with a more or less degree of protandry. It is rarer to find it accompanied with protogyny ia the hermaphrodite form. MuUer records it in Plantago lanceolata in England, which I can corroborate, and in P. media in Germany. These plants are anemophilons, and in a state of passage from an ento- mophilous ancestry ; s^j that it may have been retained from an early condition. Gynomonoecism is not particularly common, except in the Compositce, where the ray florets are often female, while the disk florets are hermaphrodite. This is due to com- pensation ; for transitional states may be seen in flowers which are passing into the " double " condition ; for as the corolla changes its form and becomes ligulate, the stamens are suppressed, and the style arms alter their shape. Anemone hepatica is said to be gynomoncecious,* and also Syringa Persica.f I have seen no case, and no description is given of these two, so that I can only suggest that it may be a result from degeneracy, perhaps on the road to a petaloid condition of the stamens. Sach a state I have found in a Planiago which was gynodioecious. " Dr. S. Calloni, Arch. Sci. Phys. et Nat, xiii., 1883, p. 409. f Miiller, Fertilisation, etc., p. 393. PARTIAL DICLINISM. 227 Andbodkecism and Andromoncecism.* — These conditions do not appear to prevail to the same extent as the female forms of flowers. Both of these kinds are not at all un- common in the Umhelliferoe, and are a result of exhaustion, for the umbels produced at the end of the season are often entirely male ; or, if at other periods, it is generally the central florets which develop no pistils, as in Astrantia minor. Miiller has noticed how " the -weaker plants usually bear but one umbel consisting only of 'male flowers." This would make it androdioecious, I find that andromoncecism prevails in Astrantia major, Carum, Smyrnium, and in Trinia vulgaris. This last, growing on the Clifton downs, bore umbels which were altogether male, after the hermaphrodite ones had formed their fruit. Daucus grandiflora is remarkable for having three kinds of flowers. According to Miiller, the central ones are male ; at the edge of the umbellule the flowers are neuter, with the outermost petal greatly enlarged; lastly, at the margin of the whole umbel, are female florets in which the outer petals attain to a gigantic size.f * Androdioicism eignifies that the same species has both male and hermaphrodite plants. Andromoncecism signifies that the same plant bears both male and hermaphrodite flowers. t I wonld here remind the reader that the interpretation given above (Chapters XI.-XIII.) of the origin of irregular corollas, applies equally well to those cases where it is only in the outermost florets of a clnster where the petals are enlarged, as in lieris, many of the Com- positae, and Umbellifei-ce, as well as in Hydrangea, Guelder Rose, etc. In all these, when insects first approach the umbel and alight on the border of it, any or each individual floret on the margin may have to carry the burden. As soon, however, as the insect passes the edge of the cluster, its weight is distributed over several florets ; so that they are not sub- mitted to any special strains upon one, i.e. the outer side only. The same remarks apply to Mentha, as compared with Lammrn. The insect visits one flower at a time in the latter, but scrambles over several in the former, which has (presumably) degraded in consequence. 228 THE STEUCTURE OF FLOWERS. Galtha palustris is said to be androdicEcions, but no details are giveu by the observer.* Besides the VmhelUfercB,] wbere andi-omonoecisra seems to be a characteristic feature, Miiller mentions Asperula taurina and Galium Crueiaia, Pulmonaria offidnalis, Coriaria myrtifolia,a.nd Diospyrus Virginiana as being andromonoecious. The hermaphrodite flowers of these species are protandrons. In Galium Gruciata, Mr. Darwin noticed that the piatil is suppressed in most of the lower flowers, the upper remainiug hermaphrodite. Heterostylism may tend to produce the same result when the stamens of the long-styled forms degenerate so far as to become atrophied without the pistil losing its functions. Pulmonaria angustifoUa and Phlox suhulata give hints of this condition.J Asperula scoparia was at first thought by Mr. Darwin to be heterostyled, but finding the anthers to be des- titute of pollen, he considered it to be dioecious. A. taurina, as figured by Mii]ler,§ shows great variability in the lengths of the filaments and styles, and he pronounces it to be andro- monoecious. Hence, as so many of the Buhiaceoe are hetero- styled, there seems every probability of one result of this peculiarity, being one or other kind of this incompletely afEected or partial diclinism. In the case of Coriaria myrti- foUa, Hildebrand found that it was the first flowers which were male only. In Maples, as in Galium Gruciata, the rule is for the three or more flowered corymb to have the central one hermaphrodite, and the lower or outer ones male. This * Lecoq, Geog. Bot., torn, iv., p. 488. t Miiller says that in Sanicula Europwa the- outer flowers are male, and derelop after the inner ones, which are hermaphrodite. This is so anomalons, that one suspects an error somewhere. I hare not had any opportunity of examining fresh flowers. X Forms of Flowers, p. 287. § Fertilisation, etc., p. 303. PARTIAL DICLINISM. 229 clearly is a question of the distribution o£ mitrition ; the loieer, being the later ones to expand, are the weaker.* Muller mentions Horse-chestnuts as being also andro- monoecions ; and what is exceptional is that the hermaphro- dite flowers are protogynous. This, however, may be due to the early period of flowering, like species of Fnmus and CratcBgus. The reader will now perceive that there may be several causes at work to produce these kinds of " partial diclinism ; " and tliat what is required is to ascertain, if possible, by observation and experiment, which is the one peculiar to each species. Secondly, when any one or more causes has been suflBciently persistent, the results become hereditary ; so that certain species, genera, and orders become more or less chai-acterized by these peculiar features. * Compare the observations on Adoxa, p. 188. 22 230 THE STRUCTURE OF FLOWERS. CHAPTER XXV. SEXUALITY AUD THE ENVIRONMENT. General Observations. — As the environment is now known to have most potent influences on the anatomical structure of the .vegetative system of plants, thereby affecting their outward and visible morphological characters as well ; so are there many causes which affect the reproductive system, at one time influencing the androecium, at another the gjncB- cium, favouring them or the reverse as the case may be ; so that either sex or even both may be entirely suppressed, and a hermaphrodite flower become male, female, or neuter. With regard to the most general agency, there seems to be a tolerably uniform consensus of opinion that the female sex in plants is correlated with a relatively stronger vital vigour than the male ; and this is just what an d priori assumption would look for, as the duration of existence and the work to be done in making fruit require a greater expenditure of energy than the temporary function of the stamens. We must, however, distinguish between a healthy vital vigour, and any excessive vegetative growth, as occurs under high cultivation, and as is often the result of intercrossing. If this latter surpass the requisite or optimum conditions for the healthy performance of the functions of all the organs SEXUALITY AND THE ENVIRONMENT. 231 of a plant, then either of the sexual organs mav begin to deterioriate, till they become metamorphosed into petals or leaves, or else degenerate and vanish. It is true enongh that we know nothing of the real nature of life ; bnt it is easy to see that, of the various phases of development, from germination to the production of seed, each should have the proper amount of energy at its disposal, and no more ; for if any one organ be stimulated beyond the optimum degree, others suffer through atrophy. The first and well-known distinction to be noticed lies, of course, between the " vegetative energy," by means of which roots, stems, branches, and foliage are developed, and the "reproductive energy," which brings about the formation of flowers, fruit, and seed. If either of these be unduly excited, the other diminishes. Thus, as long as fruit trees are developing much wood and foliage, they either bear fruit badly or not at all. Plants which ai-e propagated largely by vegetative means of multiplication, such as bulbs, corms, tubers, etc., are notorious for failing to set seed as well. As an instance in nature, Hanunculus Ficaria maybe mentioned. This plant propagates itself by " root-tubers " and by aerial corms, and rarely produces much fruit, for the pollen often remains in an arrested state.* Conversely, if vegetative energy be checked by root and branch pruning, bark-ringing, etc., the reproductive energy is promoted, and an abundance of fruit is the reward. Similar results follow a decrease of energy through impoverishment, when enormous crops of fruit may be borne by trees, as I have seen in Portugal Laurels, when the roots had penetrated a bed of gravel and the branches became decayed. Apart from these general considerations certain special conditions are found to favour one sex more than the other, * See Van Tieghem on E. Ficaria, Ann. dea Set. Nat., v., ser. 5, p. 88. 232 THE STRUCTURE OF FLOWERS. SO that normally hermaphrodite flowers may become uni- sexual, and every possible degree between these two extreme cases can be met with in nature and cultivation. The problem, therefore, is to discover what the immediate causes may be in each case which stimulate or suppress the energy required for the proper development of the stamens and pistil respectively. There appears to be a closer bond between the stamens and corolla than between the two kinds of essential organs themselves ; * thus, if the corolla degenerate, the antipetalous stamens at least tend to follow suit, as in the Alsivece. On the other hand, the first tendency towai-ds " doubling " appears in a more or less pronounced petalody of the androecium. As petals are a nearer approximation to foliar organs, the above means that vegetative energy is more prone to affect the stamens, when from some cause they have first begun to lose their proper function, than the pistil. The pistil may-fail in its development from two classes of causes : either from an undue display of the vegetative vigour, as in completely double flowers — though it may be unaffected in a partially double one ; or else from excessive feebleness, under which a flower may succeed in making the andrcBcium, but has not sufficient energy to develop the gynoecium ; as, e.g., often takes place in the flowers of the Umbelliferce at the close of the season. There is no absolute rule in these matters, and differences result from various degrees of energy at the disposal of the • A etndy of the vascular system of flowers and their axes bears this out, as the provision made for the stamens osnally arises from the periantbial cords, while that for the pistil is mostly isolated off in rather a, more marked and independent manner. Exceptions occur, as in llallota nigra, in which the four stamens originate from the same oorda as those of the placentas. SEXUALITY AND THE ENVIRONMENT. 233 whorls, giving rise to corresponding results of different degrees of development in the respective sexes. The points to be clearly perceived are that a plant should be able to develop all its organs in perfection ; that there is an optimum degree of energy for each ; and that, though it is customary to group these energies under the two expres- sions, vegetative and reproductive, yet the principle may be carried out ia detail : so that, e.g., an enlarged corolla tends to destroy the stamens, as of the ray florets of Dahlia, or even the pistil too, if it be very large, as in Oentaurea. A stimu- lated andrcecium brings about an arrest in the pistil, and causes protandry ; and if the perianth be highly developed, as in orchids, the enhancement of the former may cause degeneracy in the ovules. Sexuality and NuTRiTioif. — Assuming, for the present, that the ancestral condition of all iiowers, excepting, perhaps, those of the Gymnosperms, was hermaphrodite, many instances exist of the same species having male, female, and herma- phrodite flowers, such as the Ash, Silene infiata, etc., where the aborted organs often remain more or less rttdiraentary. It cannot be pretended as yet that the cause or causes can be at all positively asserted, in each case, for the tendency to abortion either in the stamens or pistil ; but there are certain well-ascertained facts which can undoubtedly play a part in the processes of degeneration or exaltation of the staminal and carpellary energies respectively. If they be sufficiently persistent the subsequent generations can, then, become completely diclinous, without a trace of the other sex remaining ; yet, as is well-known, any diclinous plant may reprodace by reversion the lost sex, thereby revealing its. original hermaphroditism. In endeavouring to trace the present condition of diclinous flowers back to an ancestral hermaphrodite condi- 234! THE STRUCTURE OF FLOWERS. tion, it will be as well to consider certain signiBcant facts which may help ns in ascertaining the cause of their present diclinism. "Hildebrand has shown," writes Mr. Darwin, " that with hermaphrodite plants which are strongly protandrous the stamens in the flowers which open first sometimes abort, . . . Conversely the pistils ia the flowers which open last sometimes abort." Similarly Gartner observed that "if the anthers on a plant are contabescent (and when this occurs it is always at a very early period of growth) the female organs are sometimes precociously developed." * A reason for this is that, on the one hand, since a higher temperature, is correlated with protandry, the first flowers open when the optimum temperature has not arisen ; so that the stamens are checked, a cooler temperature being less inimical to the development of the gynoecium. On the other hand, the last flowers of the seasop are produced when the vital energy is waning, and although the flowers may expand, they are too feeble to develop the pistil. Now exactly the converse may occur; thus Mr. W. Gr. Smith called attention f to the seemingly unobserved fact that Euphorbia amygdaloides always bears terminal male flowers alone at first, and subsequently the two sexes together on lower lateral "flowers." This agrees with Castanea Ainerica,na,% as noticed by Mr. Meehan. In these two cases, • Forms of Flowers, p. 283. I hardly think this can be always the case ; for, of Vines growing side by side, some will occaaionally have the anthers utterly devoid of sonnd pollen, bnt with the pistil normal ; while others will be entirely hermaphrodite with no sign of oontabescence. I have examined such, supplied to me by Mr. Barron from the gardens of the Royal Horticultural Society at Chiswick. The cause is at present very obscure. t Journ. ofBot, 1864, p. 196. X Proc. Acad. N. Sci. of Philadel., 1873, p. 290. SEXUALITY AND THE ENVIRONMENT. 235 therefore, we have instances of the plants flowering and bearing male organs only before the highest effort of vital energy is displayed — the preliminary and feebler effort being capable of developing tbe androeciiim alone. With regard to diclinous trees, many examples could be found to illustrate the principle that the female flowers are normally produced by stronger shoots than the male. Mr. Meehau has particularly called attention to this fact. For instance, " Juglans nigra* exhibits three grades of growing buds. The largest make the most vigorous shoots. These seem to be wholly devoted to the increase of the woody system of the tree. Lower down, the strong last year's shoots arise from buds not quite so large. These make shoots less vigorous than the other class, and bear the female flowers on their apices. Below these are numerous small weak buds, which either do not push into growth at all, or when they do, bear simply the male catkins." Again, Castanea Americana bears two crops of male flowers, the first of which disarticulate and are useless ; the second appear about ten days later, accompanied by clusters of females. Occasionally a tree will be entirely female. Mr. Meehan also calls attention to the fact that isolated trees of Birch, though producing an abundance of male and female flowers, very often have not a perfect seed. Hazels are sometimes protogynous, sometimes protandrous ; and if the latter condition prevail, there may be little or no fruit, as often occurs in Pennsylvania. After making analogous observations on American Maples, he summarizes his remarks on the latter as follows : — " Male flowers do not appear on a female Maple- tree till some of its vital power has been exhausted. • Laws of Sex in J. Nigra, Proc. Acad. N. Sci. of Phil., 1873, p. 290. 236 THE STKUCTUEE OF FLOWERS. " Branch-bo da bearing female flowers have vital power suflBcient to develop into branches. "Branch-buds bearing male flowers have not vital power enough to develop into branches, but remain as spars, which ever after produce male flowers only. "Buds producing male flowers only, are more excited by a slight rise of temperature than females, and expand at a low temperature under which the females remain quiescent " [i.e. when the winter temperature begins to give way to the rise in early spring, the males are more easily excited into maturity]. * As another authority, I would refer to a paper by Mr. Moore, upon the appearance of male flowers on female trees, such as the Papaw, etc- He alludes to Dr. Wight's views, in that he attributes these changes " to the modifying power of the soil and climate acting on the dormant energies of the rudimentary ovaries and developing them into prolific fruit, but at the cost of the male organs." In another case of the Papaw one fertile flower was produced, and that the first which expanded, others being all male " It would seem that fertile flowers in these instances have only been de- veloped when the greatest vital energy is present in the plant, which is the case when they first begin to expand. Other instances," Mr. Moore adds, " might be quoted to show that vigour and healthiness increase the female line of vital force in vegetables, whilst weakness is more conducive to the male development." This view was corroborated by a case of a young plant of Nepenthes distillatoria, raised from seed. Mr. Moore describes and figures it in the same paper. The lowermost flowers of the raceme bore both stamens and pistil, the • On the Relation of Heat to the Sexes of Flowers, Proc. Acad. Nat. Soi. of PhiL, 1882, p. 1. SEXUALITY AND THE ENVIRONMENT. 237 carpels of which were somewhat dissociated. On the upper half they were entirely male. He did not succeed in impreg- nating any of the numerous and well-foi'med ovules. He observes : " This well -authenticated case also favours the theory that vigour in the plant is productive of the female line of vital force." * It is a common phenomenon for diclinous trees to change their sex in different places or seasons. Ashes and Maples, as well as Palms, have been known to do this. The only in- terpretation being apparently the difference which occurs in the climatal conditions from year to year, or the modifications of temperature, soil, etc., consequent on different environing circumstances. Sexuality and Tempeeature. — Temperature has a marked influence on the sexes. A relatively high temperature favours the corolla and androecium, while a comparatively lower one the gynoecium. A. Knight long ago found that Water- melons grown with a maximum of 110° by day, usually varying from 90° to 105°, with a minimum of 70° at night, grew with luxuriance, but bore no fruit, though it had a profusion of minute male blossoms. This experience is corroborated by present horticulturists. He was not sur- prised, as he had for many years previously succeeded, by long-continued low temperature, in making cucumber plants produce female flowers only. Mr. Meehan's observations on tha development of buds on certain trees appeared to corroborate this view of Knight's. He remarks that, in the year 1884, after a winter of uniformly low temperature, the male and female flowers of the nut appeared together ; but in other years it was * Trans. Irish Acad., rxiv., p. 629; see also a paper on " Sexnality," by Dr. M. T. Masters, Pop. 8ci. Rev., xii., p. 363, 1873, and his Teratology, p. 190 J also, Proc. Acad. Nat. Sci. of Phil., 1873, p. 290. 238 THE STRUCTURE OF FLOWERS. found that a few warm days in winter would advance the male flowers, so that they would mature some weeks before the female flowers opened. Hence the latter were generally unfertilised.* That the stamens are much more sensitive to and pre- cocious in their development under a rise of temperature, is seen in the behaviour of plants in different countries. Thus it is asserted f that Stratiotes aloides produces its carpels with greater abundance towards the northern limit of its geographical distribution, and its stamens, on the contrary, are more frequently developed in more southern districts. J These tendencies to check one or the other sex, may lead to monoecious diclinism ; and even complete dicecism seems, at all events to some extent, due to climate, as differences occur in widely separated countries ; thus Honchenya peploides is frequently hermaphrodite in America, but usually sub- dioecious in England. § Mr. Darwin, in his experiments, found that Mimulus luteus was very sterile in one year ; and he attributed the fact partly to the extreme heat of the season. || * Proc. Acad. Nat. Sci. of Phil., 188 1, p. 116. t Teratology, p. 196. t Perhaps the propagation by apogatny of the female plants of Chara crinita may be a resonrce to which this plant has been driven in consequence of the male plants not thriving in a cool region. Sachs says that the female is fonnd thronghont the whole of Northern Europe, bat the male is only known to occur in Transylvania, South of France, and by the Caspian {Phys. of Plants, p. 801). The idea is suggested by this that when temperature airests the male without checking the vegetative system, a plunt may adopt vegetative methods of multiplication. Thus, instead of regarding the " root-tnbers " and atrial corms of Ranunculus Ficaria as the cause of the degeneracy of the pollen in that plant ; perhaps it would be more correct to reverse the process. § Teratology, p. 196. || Cross and Self FeH., etc., p. 68. SEXUALITY AND THE ENVIRONMENT. 239 Mr. Darwin also records * how " a tendency to the separation of the sexes in the cultivated Strawberry seems to be much more strongly marked in the United States than in Europe ; and this appears to be the result of the direct action of climate on the reproductive organs." Quoting from the Gardener's Chronicle, f he adds, " Mary of the varieties in the United States consist of three forms, namely, females, which produce a heavy crop of fruit, — of hermaphro- dites, which ' seldom produce other than a very scanty crop of inferior and imperfect berries,' — and of males which pro- duce none. . . . The males bear large, the hermaphrodites mid-sized, and the females small flowers. The latter plants produce few runners, whilst the two other forms produce many; ... we may therefore infer that much more vital force is expended in the production of ovules and fruit than in the production of pollen." Conversely, as runners were more abundant with male and hermaphrodite plants, we see here an instance of vege- tative growth correlated with the male elements at the expense of the female. Sexuality and the Soil. — Miiller has given two instruc- tive cases where it is pretty certain that the soil was a chief cause of the separation of the sexes.J Dianthus deltoides, near Lippstadt, offers interesting gradations from her- maphroditism to gynodioecism and gynomonoecism. " On the border of a meadow, of some hundred stems examined by myself, all the flowers, without exception, proved to be pro- tandrous, with a normal development of the anthers and stigmas. On the grass-grown slope of a sandy hill likewise, all the stems produced protandrous flowers, but on many stems the stamens, although emerging above the petals ♦ Varms of Flowers, p. 293. t 1861, p. 716. J Natiure, vol. xxiv., p. 532. 240 THE STRUCTURE OF FLOWERS. before the development of the styles and stigmas, bore diminished whitish anthers, not opening at all, and containing also some shrivelled pollen-grains. Lastly, in a ban-en sandy locality, many of the stems produced female flowers, with stamens aborted in the same degree as in D. superbics, and not infrequently snch female flowers and protandrons her- maphrodite ones are found on the same stem." Wiegman also found the Bianihus had contabescent stamens when growing on a dry and sterile bank. The conditions here mentioned are very like those more than once described as associated ■with double flowers, in which the stamens have also de- generated but taken the petaloid form. Hence I think we may directly trace the degeneracy of the anthers and pollen to atrophy ; since chemical analyses of pollen prove that the most important constituents required are potash, nitrogen, and phosphorus pentoxide,* probably wanting in the localities mentioned. " Centaurea Jacea " Miiller describes f " as having its flower-heads of the same stem always of the same form, but difBerent stems of the same locality often present astonishing differences in their flower-heads. " In the most common and apparently original form, the flower-heads consist of florets which are all of the same tubular shape, and all contain both fully developed anthers and stigma, the divergence of the outer florets giving to the whole head a diameter of 20-30 mm. From this original form variation has gone on in two opposite directions, the final effects of this variation being, on the one side, very conspicuous male flower-heads of 50-55 mm. diameter ; and on the other side less conspicuous female flower-heads of * From an analysis of Ash blossoms, by Professor Church, Journal of Botany, 1877, p. 364. t Nature, vol. xxv., p. 24X. SEXUALITY AND THE ENVIKONMENT. 241 30-35 mm. diameter. In both these extreme forms the outer row of florets possesses greatly enlarged radiating corollas which are sexually functionless, but useful in making the flower-mass more conspicuous. In the male flower-heads, anthers and pistils of the disk-florets are well-developed, but the style-branches never open so as to expose their stigmatic surfaces, and in their basal portion are grown together. In the female flower-heads, on the contrary, only the pistil of the disk-florets is fully developed, the anthers being pollenless, shrivelled, and brownish coloured " These two extreme forms are linked with the original one by a continuous series of gradations When in the original form variation begins in one direction, the outer row of florets gradually becomes longer and more radiating, and in the same degree their sexual organs diminish in size and become functionless, the anthers first aborting, and then the pistil. Finally, the barren ray-florets continuing to increase, the pistils of the disk-florets, too, become function- less, and the conspicuous male flower-head is accomplished. " In the contrary variation some of the outer florets of the original form begiu to diminish in size, while their anthers become brownish and pollenless, and this change step by step proceeds inwards and seizes a greater and greater number of disk-florets, until the whole flower-head is female, and reduced to a diameter of 15-18 mm. This state being reached, the corollas of the marginal flowers recommence to increase and become radiating, while at the same time their anthers disappear without leaving any trace, and their style-branches remain closed together." Calendula officinalis furnishes another instance of com- plete change of sex, most probably caused by varying con- ditions of nutrition supplied by the soil. In the normal " single " form the disk florets are male, but with club- 23 242 THE STRUCTUEE OF FLOWERS. shaped stigmas. The two style arms, being fnsed together and strongly papillose, are only useful for thrusting out the pollen from the anther cylinder. In " double " forms the corollas all become lignlate, the stamens disappear altogether, and the style arms of the pistils assume the normal form characteristic of the ray florets. They now set seed, so that the entire capitulum is female, and forms fruit.* Polygamoas states often occur in trees growing apparently under the same conditions, and although we cannot doubt that they are due to different degrees of nutrition, yet they cannot be readily correlated to visible differences in the environment. Mr. Darwin thus describes the Ash : f "I examined fifteen trees growing in the same field ; of these, eight produced male flowers alone, and in the autamn not a single seed ; four produced only female flowers, which set an abundance of seeds ; three were hermaphrodites, and two of them produced nearly as many seeds as the female trees, whilst the third produced none, so that it was in function a male. The separation of the sexes, however, is not com- plete in the Ash; for the female flowers include stamens, which drop off at an early period, and their anthers, which never open or dehisce, generally contain pulpy matter instead of pollen. On some female trees, however, I found a few anthers containing pollen-grains apparently sound On the male trees most of the flowers include pistils, but these likewise drop off at an early period , and the ovules, which ultimately abort, are very small compared with those in female flowers of the same age." It may be added that the stamens are sometimes sub- • I found no difference whatever between the plants raised from the larger seeds of the ray florets and the smaller ones of the disk florets. They all gave rise to the " single " form of capitnlnm. t Forms of Mowers, p. 11. SEXUALITY AND THE ENVIRONMENT. 243 petaloid forming staminodia — another hint that " conta- bescence " is closely akin to petalody of the androecium. Sexuality and Heterogamy. — Another source of diclinism may theoretically be attributed to protandry and protogyny carried to such a degree that the opposite sex is arrested altogether. Many plants have their flowers hovering about homogamy, some individuals being protandrons, others proto- gynous, according to locality, etc. Thus Saxifrages and species of Bibes are in this condition. We know that as soon as a flower is fertilised, the corolla fades and mostly falls. This means that the nourishment is now directed into the pistil. In a protogynous flower the petals and stamens may be in a very undeveloped state, while the stigma is ready for pollination.* If it be fertilised it no longer requires other organs, and nourishment may be abstracted from the corolla and stamens, which therefore vrould tend to abort. Let this procedure become hereditary, and we get passages to female flowers. Moreover, the more female forms tend less to degeneracy, plant for plant, than the hermaphrodites, as Darwin showed with Satureia, and as is known to be the case with Strawberries in the United States, and again as is the case with the Ash, described above. Therefore female plants might be produced abundantly which would keep that form permanent. Conversely, plants growing in the open with an increase of temperature, and readily seen and visited by insects, become strongly protandrous ; consequently the pistil is at first delayed in development with a corresponding tendency to enfeeblement in comparison with the more purely female plants. The results of crossing these conspicuous flowers — and • See e.g. Miiller's fignres of Saxifraga Seguieri in different stages, Fertilisation, etc., p. 244. 244) THE STRUCTURE OF FLOWERS. the more conspicuous the more masculine is the flower, and the more attractive will it be — one with another, would not therefore be so advantageous as crossing the more female plants with the conspicuous. The former, too, produce relatively more offspring, and might tend to oust the others, and reproduce both the "more masculine" and the "more female " sorts. Intercrossing, therefore, coupled with en- vironing conditions, may together bring about dicecism, as in Strawberries. As this reasoning is rather deduclive, it must be only considered as a suggestion. Sexuality and Heterostilism. — This undoubtedly is another source of diclinism, as already alluded to. Mr. Darwin alludes * to Goprosma and Mitchella as indicating this fact. " Coprosma is dioecious, and in the male flowers the stamens are exserted, and in the female flowers the stigmas-, so that, judging from the affinities of these genera, it seems probable that an ancient short-styled fonn, beai-ing long stamens with large anthers and large pollen-grains (as in the ease of several Bubiaceous genera), has been converted into the male Coprosma; and that an ancient long-styled form, with short stamens, small anthers, and small pollen- grains, has been converted into the female form. According to Mr. Meeban,t Mitchella repens is dioecious in some districts ; for he says that ore form has small sessile anthers without a trace of pollen, ihe pistil being perfect ; while in another form the stamens are perfect and the pistil rudi- mentary. Mitchella, therefore, would seem to be heterostyled in one district and dioecious in another," and this can scarcely be due to anything but environment. * Forms of Flou'ers, etc., p. 285. See also above, p. 228. t Proc. Acad, of Sci. of Philadelphia, July 28, 1868, p. 183. I do not gather from Mr. Meehan's account that he found any difCerence as to locality. Dicecism appears to be a constant character. SEXUALITY AND THE ENVIRONMENT. 245 Summarizing the varioas influences of the environment as climatic — such as temperature and light, shade and obscurity, humidity and drought, as well as varieties of soil and degrees of nourishment, and possibly others — we soon see how careful one must be in attributing a result to any one or special cause alone. What we can do is, as it were, to pick out of them, as tolerably well-ascertained, condi- tions which seem to favour, say, the female as compared with the male organs or flowers — such as, e.g., a mean or optimum condition of vegetative energy, a relatively low temperature, no excess of nutriment, a due amount of light, humidity, etc.; or again, on the other hand, a relatively higher tempera- ture, which favours and stimulates the staminal energies, the androBcium being more keenly sensitive and more readily responsive to slight increments of temperature than is the gynoecium. The duration of the male elements being shorter than that of the female, they can come more quickly to maturity and perish earlier, as seen, for example, in the first flowering deciduous male catkins of Gastanea Americana mentioned above. These, having been formed at the close of the preceding year (like many male flowers of the Umbelliferce late in the season), may represent the ex- piring energy of the year's growth. They open first, as soon as a sufficient though slight increment of temperature occurs, but quickly fall off, quite useless, as no female flowers are open to be benefited by them. Again, many, if not the majority of gynodioecious plants would seem to be produced by the first flowers opening before the temperature was sufficiently high to allow of the corolla and stamens to develop properly ; and though many female flowers of the Ldbiatce now blossom simultaneously with the hermaphrodite flowers of the same species ; this may be, perhaps, accounted for by hereditary influences, as 246 THE STRUCTURE OP FLOWERS. Mr. Darwin showed that seeds of tlie female plants of Thyme yielded both female and hermaphrodite plants. Although, therefore, we are unable to fathom all the mysteries of Nature's procedure, we can detect some of the lines upon which she works, and perceive how, in all cases, it is the environment — but sometimes one set of influences, sometimes another — which, being brought to bear upon the plant, the latter responds to it; and some form of what may be called "incipient diclinism " is the first result. If, then, these influences be kept up, hereditary conservatism comes into play, and such slight beginnings towards a separation of the sexes becomes fixed — only temporarily, however, — which constitute the first step, to be followed by others, till absolute and almost irrevocable dioecism is the final result. Dr. M. T. Masters has collected seveial cases in vyhich one or other of the sexes has been arrested, apparently in consequence of the nature of the soil and other conditions of the environment. I refer the reader to his " Teratology," as my object is not merely to enumerate all the instances known, but sufiBcient to establish the theory advanced, — that it is the environment that first influences the organism, which then responds to it ; and that, secondly, all adaptive variations thus set up — provided the environment continue to exert its influences — can become fixed by heredity. The consequence is that they are ultimately recognized as constant and specific characters. The Okigin of Sex. — If now the environment has been proved to exert potent effects upon the development of the sexual apparatus of flowers, there still remains the ques- tion how far is either sex or both present, or at least poten- tial, in the embryo. Marked diilerences have resulted from Bowing fresh or well-matui-ed and older seeds of melons. SEXUALITY AND THE ENVIRONMENT. 247 M. Arbaniaoiit found that young seeds gave rise to plants of extraordinary vegetative vigour ; moderately aged ones gave rise to corresponding moderately vigorous plants with both male and female flowers ; while older seeds gave rise to still less vigorous plants, but which, when properly nourished, formed female buds.* M. F. Cazzuolaf also foUnd that melons raised from fresh seed bore a larger proportion of male flowers than female ; while older seed bore more female flowers : and this has been confirmed. Another interesting result was obtained by M. Triewald, who grew twenty-one out of twenty-four melon seeds which were forty-one years old. The branches were very narrow, yet they produced early and plenty of good melons. J A cause of the difEerences of vigour in the plants raised from seeds of different age is, perhaps, connected with the fact that fresh melon seeds contain a neutral oil, which becomes more and more acid by keeping. This increased acidity coincides with a diminished germinative power ; § and proportionately, therefore, less liable to ran into excessive vegetative growth. The next condition to be observed is that resulting from sowing seeds of diclinous plants thickly or thinly. Hoff- man's experiments || in this direction showed that 283 male * Bull, de la Soc. de Bot. de Fr., 1878, p. 111. + Bull, de Tuscan. Hort. Soc, 1877. I Gard. Chrcm., 1879, p. 470. § M. LadnreaD in Ann. Agronomiques. Mr. Darwin also fonnd that fresh seeds of Iberis grew at first more vigorously than others {Orosa and Self-fertilisation, etc., p. 103). II Gard. Chron., 1879, p. 762; see also Bot Zeit, xliii., 1885, p. 145, seqq. ; also Jenaisch Zeitschr. f. Naimrwiss, xix. (1885), snp. ii., pp. 108- 112. The following were the plants with which he experimented : Lychnis diurna, L. vespertina, Valeriana dioica, Mercurialis annua, Rumex AcetoseUa, Spinacia oleracea, and Cannaiis sativa. 248 THE STEUCTUEE OF FLOWERS. plants appeared, and 700 female, in the thickly sown plot, while only 76 males occurred -when thinly sown. This has been paralleled in America, where Mr. Meehan, of Phila- delphia, has noticed how Ambrosia artemisisefolia, if growing vigorously, has a prdportion of female flowei-s largely in excess of the males ; bat in fields where the grain has been cut, and this " Rag-weed " comes tip in thick masses late in the season, the individual plants nearly starving each other, male flowers are very numerous, and some are wholly male. Prantl also observed that the crowded prothallia of Ferns gave rise to more antheridia, and scattered ones more pistillidia. Pfeffer, too, noticed the same fact with Equisetum. In these cases we seem to have results exactly the reverse of those of the melon seeds : but while in the latter the male flowers were accompanied by the precocious and excessive vegetative energy, the female were prevented from, appearing at all ; for it must be remembered that normally male flowers of melons appear before the females. In the case of thin sowing, the plants were in a natural and healthy condition: but when ci'owded they were starved, and the vital energy, being just enough to develop male flowers, proved insufficient for the female ; and, conversely, when thinly sown, "vitality" was not checked, and females were abundant. The question arises, are all seeds potentially bisexual, and one sex rather than another determined either by an inherent vigorous constitution or by the conditions of the environment during germination and growth f or is there, so to say, a determination of sex, or at least a predisposition, at an earlier stage still ? Dr. Hoffman, judging from his experiments, is inclined to the opinion that sex does not reside in the seed, but depends on conditions of germination. Mr. W. G. Smith arrived at the same conclusion, for he says SEXUALITY AND THE ENVIRONMENT. 249 in his Remarlis on some Diceeious Plants* " I think seeds themselves are probably not either male or female, but that after influences produce the sex ; as in animals the sex is not developed in the early embi'yo life of the creature, nor till the embryo has attained a certain age." On the other hand, F. Heyer thought sex was determined at an earlier period than the ripening of the seed.f Some differences which have been noticed in seedlings of Nutmegs seem to countenance this idea; thus Mr. Prestoe, in his report on the Trinidad garden, J says that "the leaf of the female seedling is most perfectly elliptical, with straighter primary veins. In the male plant it is broader towards tho point than at the middle, i.e. obovate, and furnished with a point much longer than that of the female. The vein.s are also curved in towards the point much more roundly than in the latter." An interesting experiment by Mr. I. Anderson-Henry, recorded in the Gardene^-'s, Chronicle of 1876, may be quoted. He says, " I raised a seedling Begonia having female flowers only. It resulted from an experiment I made on the seed- bearer by catting ofE two of the three lobes which compose the stigma, and fertilising the remaining lobe. I repeated this experiment ; and all of the progeny which have yet bloomed, consisting of four or five plants, have likewise all come with female flowers only." This seems to show that the female seedlings were due to concentration of energy to a limited number of seeds. On the other hand, a hybrid Begonia, ''Adonis," raised by Mr. Veitch from a summer- flowering tuberous variety, " John Heal," crossed with a winter-flowering variety (itself obtained from B. Socotrina crossed by a dwarf-flowering tuberous variety), bore nothing * Journ. ofBot, 1864, p. 232 (note), t Joum. Micr. Soc, 1884, 251. 4 Qard. Chron., 1884, p. 315. 250 THE STRUCTURE OF FLOWERS. but male flowers — presumably in conBeqnence of Bome weak- ness of constitution due to hybridisation. It would be quite foreign to my purpose to trace the origin of sexes throughout the vegetable kingdom, as I am solely concerned with that of flowers. But what appears to be pretty certain is that the absorption of the pollen-nucleus by the " egg-cell " involves a special form of nutrition, coupled with certain excitant effects. Uuion between nuclei occurs elsewhere ; and as illustrative analogies, one recalls the fact of fusion being normal in the Oonjugatce, and among zo6.spores, where no sexual differentiations are observable. Again, in the embryo-sac there Occurs the union of two nuclei, one from each tetrad, their function being then apparently to form endosperm. As another case, Mr. Gilburt has described the union of the nuclei of cells constituting a "cell-group," which forms a wood-fibre after the absorption of the septa.* Of course one of the most essential properties of the pollen-nucleus is to transmit to the offspring characteristics of the male parent : but even this is paralleled in the vegeta- tive system ; for an engrafted scion can transfer its peculi- arities to the stock, as has occurred with Cytisus Adami, variegated Abutilons, etc. If, however, we ask what are the actual differences which exist between the male and female energies, and how they have arisen, we at once find that we are completely baffled, and that all speculations are at present futile. • Morph. of Veg. Ties., Jonm. Roy. Micr. Soo., 1879, p. 806 (note). Scbacht observed a similar origin of liber-fibres in the Fapaw, each of which was originally composed of three or fonr cells, bat the septa become absorbed; their original positions being only indicated by clusters of pores on the walls {Les Laticif. du Carica Papaya, Ann. des Sci. Nat., 4 ser., viii., pi. 8, figs. 9, 10). Treub, on the other hand, dis- covered the laticiferoos vessels and liber-fibres of the Nettle, etc., to have arisen by repeated division of the nnclens, the partitions not having been formed at all {Arch. Neerl. des Sci. Exac. et Nat., torn, xy., 1880, p. 39). CHAPTER XXVI. DEGENEEACY OP FLOWEBS. Inconspictious and Cleistogamous * Flowers. — Degeneracy in plants is as of frequent occun'ence as in animals ; and just as it implies no pathological or anything of a constitutionally injurious character in them, so, it must be distinctly borne in mind, does it imply nothing of the sort in plants. The word means " down from the genus ; " like " degradation," it is only a "step downwards." It implies retrogressive or at least arrested conditions ; but a degraded flower often acquires new features, qualifying it for securing self-fertili- sation with a far greater certainty than was the case with its more conspicuously flowering ancestors. There are several causes which can bring about degrada- tions in the various organs of plants, such as growth in water, subterranean habits, parasitic and saprophytic states, freedom from strains, compensation, etc. Though it would be interesting to trace out the cause and efl'ecfc in each case, I must content myself with flowers, and particularly the essential organs. There are two principal causes which may be styled the rationale of degradation in flowers. The first is compensa- tion, when the vegetative system is in too great activity to * Cleistogamous, "a closed union," i.e. when flowers are self, fertilising without openiog. 252 THE STRUCTURE OF FLOWERS. allow of the proper amount of nutrition being at the service of the flowering process. This is so well known that I need not dwell upon it now. The second is the cessation of insect fertilisation. The effect of fertilisation operates in two directions. On the one hand, if it be the result of inter- crossing by insect agency, it stimulates the flowers till they become thoroughly adapted to their visitors, and highly differentiated in certain ways in consequence, but more especially as regards the perianth and stamens ; while, in many cases, some degree of degradation occurs simultaneously in the pistil. Conversely, self-fertilisation and anemophily, consequent upon the neglect of insects, are accompaaied by corresponding degradations in the perianth, stamens, and pollen, correlated with a regained ascendancy in the powers of reproduction. The limits of degradation, with an increase of fertility, are seen in many cleistogamous flowers. In tracing the progress of degeneracy from a species with large flowers to one with inconspicuous blossoms, I do not mean to imply that we can actually witness the process in activity • but we can see this represented, as it were, in many a series of what we call species of a genus ; but which we might call transitional forms of one kind. It is only because we cannot trace the actual process going on that we regard them morphologically as distinct species. Thus, if a verifiable demonstration be unattainable, it is a " moral conviction " not only that Geranium pratense is as much and obviously adapted to insect agency as G. pusillum is to fertilise itself, but that the latter species has been derived from the former or from some kindred plant, through some such transitional forms as G. pyrenaicum and G. molle. This process of degradation from insect to self-fertilising conditions, not only affects the size of all parts of the flower, but the entire plant. Mr. Darwin showed how the stimu- DEGENERACY OF FLOWERS. 253 lating effect of crossing generally increased the heights and weights and, for a time, the fertility of the plants experi- mented upon. Conversely, self-fertilised species are alto- gether smaller than their allied intercrossing species. Thus Stellaria Holostea may be compared with S. medium, Gerastium arvense with G. tetrandrum and G. glomeratunn, Gardamine pra- tensis with G. Mrsuta, Polygonum amphibium with P. aviculare, etc. Besides being thus dwarfed, self-fertilising plants are mostly annuals. But while conspicuous flowering plants blossom during a limited period in summer only, their smaller, less conspicuous, and regularly self-fertilising allies may, and often do, flower and set seed all the year round. In my essay on " The Self-fertilisation of Plants," * I drew np the following list of peculiarities of habitually self- fertilising plants, all of which indicate points of degeneration or arrest. 1. The inconspicuousness of the flowers, even when fully expanded. 2. The calyx and corolla are often only partially expanded, or not at all. 3. The white or pale colours of the corollas ; while specially coloured streaks, specks, "guides," and "path- * I mnst refer the reader to the above essay for a full discussion of this subject. The evidence there given proves conclusively that self- fertilising and anemophilons plants are in every way the most widely dispersed of flowering plants, and best fitted to maintain themselves in the struggle for life. I will add here that Mr. H. 0. Forbes came independently to a similar conclusion when studying cleistogamy in orchids ; and remarks, at the close of his paper (Joum. Lin. 8oc., vol. xxi., BoT., p. 548), " The observations above given would seem, therefore, to support the Rev. G. Henslow's conclusions so ably given in his ' Memoir on the Self -fertilisation of Plants,' already published in the Transactions of the Lihnean Society. My absence abroad prevented my seeing this paper till quite recentlv. and after I had completed these notes." 24 254 THE STRUCTURE OF FLOWERS. finders " peculiar to intercrossed flowers are more or less reduced, if not absent. 4. The partial or total arrest of the corolla. 5. The mature stamens of the expanded flower retain in many cases the incurved, i.e. an arrested position, which they had in bud ; the anthers thus remain in contact with the stigmas. 6. The stamens are often reduced in size and number, and the pollen in quantity. 7. The pollen tubes may often be seen to be penetrating the stigmas, either from grains still within the anther-cells, or evidently derived from those of the same flower. 8. The styles are shortened, and the stigmas are situated appropriately for direct pollination from the anthers of the same flower. 9. The partial arrest of the corolla and stamens in their rates of development, allows the pistil to mature with com- parative rapidity. 10. The consequent early maturation of the stigma, so as to be ready before or simultaneously with the dehiscence of the anthers. 11. Little or no scent, 12. Decrease in size or total absence of honey glands, with corresponding little or no secretion of honey.* Notwithstanding these various indications of degradation, such flowers are often correlated with special alterations which secure self-fertilisation without a chance of failure — a precariousnesa which almost always exists in flowers adapted to insects. Thus — contrary to the old but erroneous • Miiller, in his "General Retrospect" (Fertilisation, etc., p. 591), also gives a number of modifications, mostly referred to in the text above, of what he describes as " the conntless ways in which plants revert to self-fertilisation in default of sufficient insect visitors." DEGENERACY OF FLOWERS. 255 dictum that, whether flowers were pendulous or erect, the stigma was always helow the anthers, so that pollen could fall upon it — the anthers are always closely applied to the stigmas, as may be seen in Chickweed (Fig. 52), and small- Fig. 52. — Flower-bud, closed and expanded, of Stellaria media, showing petals reduced in size; stamens, tbree only; anthers closely adpressed on stigmas. a h Fig. 63. — Stamens and stigmas of EpUoMum montanum, the bud scarcely open, while anthers are closely applied to the stigmas. flowered Willow Herbs (Fig. 53), and especially in cleistoga- mous flowers (Figs. 56-59, pp. 258-261). The structure of the anthers and stigmas is often greatly altered in form, besides being merely reduced in size. As an illustration of the above remarks, the genus Viola is interesting as furnishing two " forms " of the same species, Y. tricolor, or Pansy, the one being adapted to insects, the other to self- fertilisation ; while other species, such as F. odorata, the Violet, bear cleistogamous buds on the same plant as the ordinary violet blossom. The dimorphic flowers of Viola tricolor were first noticed by Miiller, who described them as follows : * "In the large- flowered form, the stigmatic cavity (Fig. 54, a, st) lies some- • Nature, Nov. 20, 1873, p. 45. Fig. 54. — Styles and stigmas of the two forms of Pansy - a, that of the larger and Intercrossing ; b, that of the self- fertilising form. 256 THE STRUCTURE OF FLOWERS. ■what more towards tke top of the skull-like end of the style than in the small-flowered one (6). When the skull-like knob in the two forms is pressed against the lower petal, in the large-flowered form the opening of the stigmatic cavity is directed outwards, so that the pollen-grains which have fallen oat of the anther-cone can never spontaneously fall into the stigmatic cavity, and must be carried there by insects ; whereas in the small-flowered form the opening of the stigmatic cavity is directed inwards, so that pollen-grains falling out of the anther-cone spontaneously, fall directly into the stigmatic cavity. " In the large-flowered form, the opening of the stigmatic cavity (d) bears, on its lower side, a labiate appendage (I) provided with stigmatic papillsB, so that a proboscis inserted into the flower when charged with pollen from a previously visited flower, rubs off this pollen on to the stigmatic lip, thus regularly effecting cross-fertilisation; whereas, when withdrawn out of the flower, charged with pollen, the proboscis presses the lip (I) against the stigmatic opening (sf), thus preventing self -fertilisation. This nice adaptation to those visitors provided with a long proboscis (Lepidoptera, Apidae, Ehingia) is completely wanting in the small-flowered form (6). " In the large-flowered form, there is a black wedge-shaped streak (g) on the front of the style, to which Mr. A. W. Bennett first called attention, and which he has interpreted as a guide-mark for those visitors which are diminutive enough to crawl entirely into the flower. This streak is also wanting in the small-flowered form. " In the large-flowered form, pollen-grains do not spon- taneously fall out of the anther-cone before the flower has been fully developed for several days ; whereas, in the small- flowered form, in bb far the majority of cases, a great number DEGENERACY OF FLOWERS. 257 of pollen-grains fall spontaneously oat of the anther-cone into the stigmatic cavity and there develop long pollen- tubes, even before the opening of the flower, in much rarer cases a short time after it has opened. " When the visits of insects are prevented by a fine net, the flowers of the small-flowered form wither two or three days after opening, every one setting a vigorous seed- capsule ; those of the large-flowered form remain in full freshness more than two or three weeks, at length withering without having set any capsule ; when fertilised they, too, wither also after two or three days." I have met with several variations in minor details of structure in the smaller-flowered kind. Thus iu some the stigmatic lip, probably representing one of the three stigmas, formed a globular knob protruding from the orifice, as shown in Fig. 55, a, b. In another, it protruded like a tonerne, C. The lateral ng BS.— styles and stigmas of Belf-fertlHslng forms , , of Pausy. (For description, see text.) fringes,* which help to keep the pollen back from reaching the stigmatic chamber in the larger flowers, are more or less retained in these ; as is also the bent-base to the style which forms the spring,* which keeps the globular head in a downward position. The accompanying figures will illustrate the cleistogamons flower-buds of Violets. They are very minute, about one- eighth of an inch in length (Fig. 56, /). The petals are reduced to linear and pointed structures, green or purplish green, (a) ; or they may be altogether wanting. The spur alone of the larger petal is sometimes present in strong- • For the theoretical origin of " fringes '' and " springs," see Chap. XV., p. 133, and Chap. XXII., p. 123, respectively. 258 THE STRUCTURE OF FLOWERS. growing garden plants (6). The stamens are five or less in number, having spoon-shaped connectives, and not pointed as in the normal form, bearing very minute oval anther-cells at the base (c, g) * Small bundles of pollen-tubes may be traced from the anthers into the stigma (g). The pistil has a short curved style, and truncated stigma (d) concealed beneath the anthers which lie imbricated over the top of the pistil. The anthers are usually devoid of appendages, though they are sometimes present, like the spur ; though f e 9 Fig. 56. — Cleistogamous Violets. (For deBcription, see text.) both organs are now useless. As the ovary swells it raises the stamens up with it (e). The capsules of the violet, Mr. Darwin observes, bury themselves in the soil, if it be loose enough, and there ripen ; but they certainly are very, if not more frequently not buried at all, but only concealed beneath the foliage. As another interesting case of a plant showing transi- tional conditions may be mentioned Scrophularia arguta, Ait.f " The two lowermost opposite and axillary branches bend backwards and penetrate the soil. The next pair do • (c) r. odorata; (g) V. cwnina. t Bull. 8oc. Bot. de Fr., iii., p. 669. DEGENEEACr OF FLOWERS. 259 the same, but do not always reach the ground, or else pene- trate it veiy slightly. They all bear fertile flowers. The lowest are apetalous, if completely hypogean [and pre- sumably cleistogamous]. Those which just reach the soil have a corolla of four lobes nearly equal, and resemble the corolla of Veronica. A little higher up, the irregularity of the bilabiate character of Scrophularia is pronounced." The preceding quotation is interesting, first in showing how the subterranean cleistogamous form is derived from the conspicuous flower, and also supplies a hint as to the origin of Veronica, in that it is a 4-merous degradation from a primitive 5-merous genus, which is lost or unrecognizable now, unless it be some member of the subgenus Pygmma, which has five parts to the corolla.* As an illustration where geographical conditions favour the development of autogamous forms of flowers, the follow- ing passage may be quoted : — "Herr C. A. M. Lindman has examined the very rich flora of the Dovrefjeld in reference to the arrangements for fertilisation. He finds a distinct tendency to a deeper colour in the flowers than is displayed by the same species in the lowlands, red and blue predominating. The great length of daylight appears to increase the size both of leaves and of flowers, though in some species, on the other hand, the flowers are diminntive in consequence of the low tempera- ture. Crowded masses of small flowers are very common. The number of scented species is comparatively small, though the fragrance is sometimes powerful. The scarcity of insects necessitates that there should almost always be a provision for possible self-fertilisation ; and many species, elsewhere heterogamous, are here homogamons. Notwith- • For Miiller's theory of the origin of Veronica, see Fertilisation, etc., p. 465. 260 THE STRUCTURE OF FLOWERS. standing the cold and wet summer (1886), the plants observed almost invariably bore fruit."* As an example of pure cleistogamy I vpill take Oxalis Acetosella, as having special peculiarities. Mr. Darwin alludes to M. Michalet's description of the cleistogamous flowers of this species,t and adds some observations of his own.J He quotes an observation of Michalet's, that the five shorter stamens are sometimes quite aborted. This fact, which I have also ob- served (Fig. 67, d), is quite in keeping with ^^MPA lUI IW the common process of ^«-^W ^W the redaction of the Fig. 57.— cieistoRamous flower-buds of oxaiii number or parts of sta- Acetosaia. (For description, see teu.) ^^^^ ^^ self-fertilising flowers. He also adds this interesting observation : " In one case the tubes, which ended in excessively fine points, were seen by me stretching upwards from the lower anthers towards the stigmas, which they had not as yet reached. My plants grew in pots, and long after the perfect flowers had withered they produced not only cleistogamic, but a few minute open flowers, which were in an intermediate condition between the two kinds.'' This last remark is quite in accordance with the true origin of these flowers, that they are in all cases degra- dations from the conspicuous forms normally characteristic of the species which produce them. Fig. 57, a, clearly shows that in Oxalis Acetosella the cleistogamous state is simply a flower-bad which has become adapted to self-fertilisation ; and the intermediate conditions alluded to by Mr. Darwin I should suspect were analogous to • Joum. Boy. Micr. Soc, 1887, p. 615, and note. See below, pp. 270, 271. t Bull. Soc. Bot. de Fr., vii. (I860), p. 465. J Forms of Fiowem, p. 32]. !\ )6 DEGZyCRACT OF FLOWEES. 261 the pemanent forms of the flowers of O. eomiculata, which I at first inferred, from tte wide distribntion of this species, must be habitually self-fertnisin?. From Fi?. 57, a, it will be seen thai the corolla jnsi protrndes from the closed sepals, and alwajs remains as a '• cap," b. Of the ten anthers, £-.-e are often abortiTe or wanting, d; the fertile anthers are placed over the xery short stigmas, and are bonnd toeether by fine threads. Th^ie appear to play some part, bat the nature of their function ig ofcscore, c. Impatiens fulva and I. Xoli-me-tangere have also cleisto- gamoos flowers. Fi?. 58, a, represents a bud, and 6 two metamorphosed sta- mens. Lamium amplexicauU will fnmish " V r \, ^ another example of cleistogamy. Th^s tig. ».— «, asiaopaaaaa gen OS has usually flowers highly differen- /..ic?,- b, aun^s^^ tiated, and adapted to insect fertilisation. ^-""''O- That the cleistogamons flowers of this, as of all other species, are degraded forms of the normal kind is obvijas from the presence of the "lip," as weU as by there being four and didynamons stamens. The style elongates very much, and under the pressnre of the closed summit of the corolla becomes bent, so that the stigmas lie between the anther-cells, and thns readily become fertilised. Fig. 59, a, represents a flower-bnd ; b, the corolla in section ; and c, the pistil removed. This Fic. sa.—a. aestuetmoaa Bower- ..^ ... . . , . bpd of jjOmUmm amf i nicam te; t^ condition of CleiStOgamy is fonnd in Totial ttctioa at mae; c. piadL the earlier-flowering plants, so that it is probably a mere result of check through a colder temperature. Salvia dandegtina th&j be compared with the last described, as it is a self -fertilising form of, perhaps, 8. pro- 262 THE STRUCTURE OF FLOWERS. tensis. Fig. 60,* a, represents a corolla, whicli is very small, but open ; 6 represents the two fertile stamens ; the anther- lobes instead of being horizontal are erect, and face each other. The , I stigmas curl back be- „.„._,., ^ ,. „ I .,, tween them, and are re- Fig. 60.~Salvia elandeshna : a, corolla j 6, anthers j ' c, style and stigmas. markably long, C. The Origin of Cleistogamt. — We are now in a position to trace the causes of cleistogamy. Cleistogamous flowers nearly always occur on plants otherwise, or at least their allied species are, adapted for intercrossing, and include four genera of anemophilous plants. The first cause or influence is the arrest of the reproductive energy in the conspicuous flowers, which often set no seed at all. "Whatever the primary cause of that may be, a very common result in perennials is to increase the power of vegetative methods of multiplication, as in the case of many bulbous and tuberous plants. This, however, is not a special feature of the plants which bear cleistogamous flowers. It would seem, therefore, that the reproductive energy being checked in one form of flower, it, so to say, breaks out in another. But there are several influences at work, and a very obvious one is temperature ; for the same species may behave very differently in one country with a high mean annual temperature, from what it does in another with a lower one. Thus, Yiola odorata does not produce cleistogamous flowers in one part of Liguria, where the conspicuous flowers are perfectly fertile ; while they are mostly barren in England. On the other hand, cleistogamous flowers are produced by Violets near Turin, * From a specimen growing at Kew. It ib cleistogamons at Halle (see below, p. 263). DEGENERACY OF FLOWERS. 263 and abundantly in all parts England. Viola nana bears normal flowers in its nafcire borae in India, but only cleisto- gamous ones in England. Viola palusiris bears only the larger flowers near Paris, wbicb are perfectly fertile, but when it grows on mountains it bears cleistogamous flowers. Similarly Impatieiis fulma bears both kinds of flowers m Eng- land, but the larger are usually barren. After midsummer, in its native home in the United States, these flowers will produce capsules. Salvia clandestina, when transplanted from Africa to Halle, bore only cleistogamous flowers for five years, according to Ascherson, who considered the plant to afBord an example of continuous self-fertilisation. He, however, afterwards observed ordinary open flowers. It is a species particularly common on the Continent. Again, plants vary according to the season. Thus Mr. Darwin found that Vandellia nummularifolia bore no perfect flowers in one season ; so, too. Ononis colwmnm bore none in 1867, yet it had both kinds in 1868. The time of the year also influences the production of cleistogamous flowers. Thvts Ononis minutissima, parviflora, and 0. colurrmoB, according to Mr. Bentham, produce them early in the spring. Oodetia Gavanillesii and Lam/ium am- plexicaule do the same ; while some bear a fresh crop in the autumn, as 0. columnoe. Two cases are mentioned by Mr. Darwin in which the period is the reverse of the above. Viola Boxburghiana bore abundance of cleistogamous, but no perfect flowers, in Mr. Darwin's hothouse ; and it bears the perfect flowers in India " only during the cold season, and these are quite fertile. During the hot, and more especially during the rainy season, it bears an abundance of cleistogamous flowers." * * Forms, etc., p. 320. 264) THE STRUCTURE OF FLOWERS. The other example is RuelUa tuherosa, of which Mr. Darwin i-emarks, " It produces both open and cleistogamons flowers; the latter yield from 18 to 24, whilst the former only from 8 to 10 seeds : these two kinds of flowers are pro- duced simultaneously, whereas in several other members of the family the cleistogamons ones appear only during the hot season." From this one would infer that an excess of heat may be a cause of cleistogamy, just as too low a temperature appears to bring it about. I think it probable that other influences than tempera- ture may be brought to bear upon a plant ; which, indeed, we may see in our own Violets. The larger flowers of this species are not produced in the hottest time of the year, while the cleistogamous buds are only borne in the summer. On the other hand, the foliage is only developed fully, con- temporaneously with the dwarfing of the floral organs. Again, a poor soil has been noticed as associated with cleistogamy by Torrey and Gray, in the case of North American species of Helianihemum. Temperature, however, seems to be the most important agent; thus, while the climate of South Italy can develop the perfect flowers and render them fertile, there cleistogamy is suppressed; here, in England, the climate is seemingly not sufficiently warm to do so, and the cleistogamons buds appear in compensation. The vegetative energy, however, comes to the fore during the summer, and perfect flowers are not produced simultaneously with it ; so that it is not until the vegetative period has ceased, and the materials are remade for their development, that larger flowers are again borne later in the year, as in November, as well as in the following spring. With regard to the anemophilous genera, Mr. Darwin mentions Hordeum, Oryptostachys, Leersia oryzoides, and Junctn hufonim in Bussia. DEGENERACY OF FLOWERS. 265 Now, the three genera of Grasses here mentioned are characteristic of warmer regions, and even tropical, Leersia oryzoides being the sole species of that genus which reaches Europe, where it becomes cleistogamous. Therefore climatal conditions may, with some reasonable presumption, be sug- gested as the immediate cause in these cases. With regard to Hordeum murinum, which is, perhaps, almost habitually cleis- togamous in this country, it may be an hereditary result issuing from a similar cause. This may also apply to Viola ; for not only are some species tropical, but all the genera most nearly allied to Viola are tropical also. This is analo- gous to what I have suggested as the origin of gynodicecism in LabiatcB, which it may be noticed has at least two genera with cleistogamous flowers in this country or Europe. Juncus iufonius, according to Batalin, is exclusively cleistogamous in Russia, hence the same cause suggests itself for this species ; for, according to Ascherson, at Halle it has ordinary open, lateral, hexandrous flowers in addition to terminal cleistogamous triandrons ones.* This seems to show that lessened vigour has also a hand in the process in this case : the mean temperature of Halle is probably higher ; if so, it may cause the plant to bear the open flowers there. From the above-mentioned facts, it will be seen that there may be more than one cause to account for cleistogamy. Hence, it must be regarded as an inevitable result whenever those influences are brought to bear upon the plant which are capable of producing it ; and there is every reason to believe that whatever effects are produced in plants by external stimuli, if the latter be permanently kept up they will become hereditary, and then will be recognized by systematists as specific or generic characters. Anemophilous, oe Wind-feetilised Plants. — The general • Muller, he, p. 561. 25 266 THE STRUCTUKE OF BLOWEES. characters preTailinej in this group consist of elongated papillose or plumose stigmas, or else they spread out into laminae (Eupliorhia) . The filaments are usually slender and movable, with vei'satile anthers, bearing incoherent and often smooth pollen-grains. In some cases the filaments are elastic, and project the pollen outwards ; or the whole flower may oscillate on a slender pedicel or peduncle, as the catkins of the Amentiferce, the flowers of Rumex, etc. Long, slender filaments are seen in Grasses, Sedges, Rushes, Hemp and Hop, Plantains, Littorella, and Poterium. Nettles and their allies are remarkable for their elastic filaments, which materially aid in the dispersal of the pollen. On the other hand. Palms, Bulrushes, etc., have more or less rigidly fixed flowers and floral organs. There is little doubt but that all wind-fertilised angio- sperms are degradations from insect-fertilised flowers. This is obviously so when many of the allies of an anemophilons genus or species are constructed for insects. Thus, Miiller says that Thalictrum minus * is anemophilons, while T. flavum is visited by several species of insects. Poterium Sanguisorha is anemophilons; and Sanguisorba officinalis presumably was so formerly, but has reacquired an entomo- philous habit; the whole tribe Poteriem being, in fact, a degraded group which has descended from PotentilleoB. Plan- tains retain their corolla, but in a degraded form. Juneece are degraded Lilies ; while Cyperacece and Qramineoe among monocotyledons may be ranked with Amentiferae among dicotyledons, as representing orders which have retrograded very far from the entomophilous forms from which they were possibly and probably descended. • I do not know on what reason j for the stigmas are not charac- teristic of snch flowers. On d priori grounds I shonld have inferred its being self-fertilising, as the anthers completely conceal the few and email carpels. DEGENERACY OF FLOWERS. 267 What, then, have been the causes which have given rise to the features generally characteristic of anemophilous flowers ? In the fii-st place, it must be remembered that such are far from absolute. Smooth and easily scattered pollen,* Miiller remarks, is the only positive character common to these plants. Mr. C. F. White, F.L.S., however, tells me that from his researches he very much distrusts the division so generally accepted between wind- and insect- borne pollens. It is his opinion that there is no pollen-gi-ain so smooth but that the hairs on the limbs of a bee or fly can hold it. Moreover, no pollen, however massed together, can possibly be heavier than, say, a thistle seed and its down attached, which the wind can carry with perfect facility ; so that to draw any distinction on that score seems to me to be very far-fetched.t With respect to the pollen of Grasses, Mr. White observes that it is perhaps forgotten that, although smooth in water, when dry they are notably wrinkled into sharply angled and irregular shapes. Mr. Bdgeworth J has figured many forms of pollen of anemophilous genera, several of which show no signs of smoothness or rotundity, such as Alopecurus pratensis, Carex arenaria, and 0. panica, which, like Juncus effusus, is oblong, with sharp edges, all of which are at right angles or nearly so. Again, Typlia latifolia and Cupressus have octahedral pollen; Areca Baiteri, Geratozamia, Rheum, Mercurialis, Oak, etc., have more or less sharply pointed spindle-shaped grains. * See Mr. A. W. Bennett's paper, On the Form of Pollen-grains in Reference to the Fertilisation of Flowers, Brit. Absoo. Rep., 1874. t 1 would here allade to another d. priori assamption. It has been thought that the two pouches on the pollen of the Fir aid it in trans- portation; but unless they were filled with some gas lighter than air they only increase the weight of the grain. X Pollen, by Mr. M. Pakenham Bdgeworth, F.L.S., 1877. 268 THE STRUCTURE OF FLOWERS. In Corylus, Alnus, and Plantago media, they are polygonal, while Beech has them deeply three-grooved, etc. Mr. Edgeworth, in fact, states that the different kinds of pollen of anemophilous plants " are by no means all globular, as Mr. Bennett asserts." He notices, however, that " the grasses and Gyperacece, and perhaps the Plantaginece are without the sticky nature of the outer coat, which obtains through all other pollen grains." With regard to the versatile condition of the anthers in grasses, and their consequent facility of oscillating on a point, this feature seems to be only the result of the extremely slender filament due to degradation ; * and not quite the same thing as the antero-posterior oscillation which the action of bees has set np in the connectives of Salvia, species of Calceolaria, and Gurcuma Zerumhet.-f Remembering how the rigidity of the filaments of intercrossing flowers is corre- lated to the retention of some well-defined positions for the anthers, so that insects can be struck by them accurately, and be again struck on the same spot by the stigmas of other flowers, we see that when the stimulus due to intercrossinc has been long withheld, the filaments have become slender, easily waved about by the wind, and versatility of the • Plantago media, which is visited, has motionless anthers j but in the anemophilous species of Plantain they are versatile. + Mr. H. 0. Forbes has described and figured a very analogous case in this species of Curcuma of Somatra. The two anthers project for- wards in contact, they are provided with terminal processes like horns. The style passes between them. When a bee enters the flower it depresses these horns with its head, and so forces the anthers down- wards on to its thorax. The anthers bring the style and stigma down also. In a similar way do some species of Salvia canse the style to be brought down from the hood (4 Naturalises Wanderings in the Eastern Archipelago, p. 247). DEGENERACY OF FLOWERS. 269 anthers has followed. Those wind-fertilised plants with stiff filaments have presumably not yet degraded to a similar state. With regard to the pistil, since of heterostyled plants the stigmatio papillae are larger and longer in the long-styled forms, we seem to get a hint as to the origin of the papillose and plumose characters of many wind-fertilised plants ; in that such may be due to compensatory processes on the loss of the corolla, honey-secreting organs, etc., which have thus favoured the development of the pistil generally, such deve- lopments becoming emphasized in certain directions. Protogyny or homogamy generally accompany anemo- phily.* Thus Miiller mentions Thalictnim minus, Plantago, Luzula, OallUriche, Myriophyllum, and many Grasses as being protogynous ; and a common characteristic feature of such flowers is frequently noticed by Muller, viz., that they have all " long-lived stigmas." This seems clearly to point to a relatively increased amount of vigour in the develop- ment of that organ in protogynous flowers ; which becomes especially noticeable in their enhanced size, as seen in most anemophiloDS flowers. Poterium he regards as homogamous, as well as Rye and Wheat. These conditions all agree with the total suppression of the corolla, and may be regarded as signs of degradation : and I have elsewhere shown, when treating of emergence and development of the floral organs, how a compensatory process accompanies the formation of the corolla and stamens on the one hand, and of the pistil on the other ; so that when the former tend towards degra- dation, the pistil gains the ascendancy, and matures earlier. * Artemisia vulgaris seems to be protandrons. The style arms are provided with papillose rosettea in the central florets, bnt are very elongated, and terminate in points in the oircnmferential florets. In no case oonld I detect pollen-tubes in nnopened florets, though the grains were shed. 270 THE STBUCTUBE OF FLOWERS. Hence, to find its stigmas enlarging under anemophily is all in keeping with the above facts. The Origin of Anemophilt. — With regard to the origin of anemophilous flowers, there is every reason to believe them to be due to the neglect or absence of insects : that as these have brought about brilliant colours or other kinds of conspicuonsness, so their absence has allowed flowers to degenerate and become inconspicuous, the result being either self-fertilisation or anemophily. As two examples of districts which illustrate this fact, are the Galapagos Islands, visited by Mr. Darwin, and Greenland, the flora of which is described by M. Warming. The former observer, on landing, thought that there were few or no flowers, but, on stricter search, discovered niany to be inconspicuous. A specimen before me of Solanum nigrum, which he brought from those islands, has flowers much smaller than our own native plant, and illustrates the wide dispersion of self -fertilising plants. M. Warming found Greenland, like the Galapagos Islands, to be poor in insects, and "the flowers display a corresponding increased tendency to autogamy. One hundred and thirty-eight species of anemophilous plants are also named by him, exclusive of Willows. The flowers appear to decrease in size with the increase of latitude ; and the brilliancy of colour certainly does not become greater." * This last observation does not agree with M. Flahault's observations ; f and possibly M. Warming is here intimating a wrong cause of degeneracy, which I should incline to regard as the absence of insect stimulation, with the consequent tendency to inconspicuonsness, anemophily, and autogamy. * Overs. K. Damske Tidensk. Belsk., 1886, p. zxv. (quoted from Journ. Bm/. Micr. Soc, 1887, p. 433). See also above, pp. 177 and 259. t Arm. des Sci. Nat, 6 ser., t. vii. (1877), et t. ix. (1879). DEGENERACY OF FLOWERS. 271 Where, however, insects are abundant, -whether in high latitudes or greater . altitudes, as in the Alps, there two causes will be at work to enhance the brightness of flowers ; viz. insect stimulation and prolonged sunlight. For Sachs has shown that the ultra-violet and invisible rays are specially eflicacious in the development of flowers; and as the foliage grows more vigorously with prolonged light so it is presumable that the flower-forming substances will be more abundant as well.* The genus Plantago, like Thalietrum minus, Poterium, and others, well illustrates the change from an entomophilous to the anemophilous state. P. lanceolata has polymorphic flowers, and is visited by pollen-seeking insects, so that it can be fertilised either by insects or the wind. P media illustrates transitions in point of structure, as the filaments are pink, the anthers motionless, and the pollen-grains aggregated, and it is regularly visited by Bombus terrestris (Delpino). On the other hand, the slender filaments, versatile anthers, powdery pollen, and elongated protogynous style are features of other species indicating anemophily ; while the presence of a degraded corolla shows its ancestors to have been ento- mophilous. P. media therefore illustrates, not a primitive antomophilous condition, but a return to it ; just as is the case with Sanguisorba officinalis and Salix Caprea; but these show no capacity of restoring the corolla, the attractive features having to be borne by the calyx, which is purplish in Sanguisorba, by the pink filaments of Plantago, and by the yellow anthers in the Sallow Willow. Plantago aVpina is self-fertilising, as the stigma does not wither until after maturing the anthers. If we may speculate as to why some degraded flowers * See La Y4gHation du Oloie, par Grisebach, t. i., p. 155 (trad. fran. de Tchihatchef). 272 THE STRUCTURE OF FLOWERS. have become regularly autogamoas, while others are now anemophilous, it may be due to the fact that, if a flower has been entomophilous and even strongly protandrons, the first stage of degradation is to bring the essential organs to a homogamous state. If they stop there, and become autoga- mous as well, whicb is the usual result, then the flower will remain persistently self-fertilising, as, e.g., Shepherd's-purse, Chickweed, Knot-grass, etc. If, however, the flower had been protogynous, such as early-flowering HeHebores, Prunus communis or some Alpine species, with " long-lived stigmas," then this protogyny, associated with other degradations of the corolla, etc., which only tend to increase it, has ended with anemophily. In the first case the androecium of protandrous flowers has come down from its previous highly differentiated state, so as to be homogamous with the stigmas. From the other or protogynous condition, the gyncecium has not been brought back again so as to be homogamous with the anthers and pollen, butj on the contrary, it may have become even further differentiated, and so has now no fertiliser to depend upon except the wind, CHAPTER XXVII. DEGENEEA.CT OP FLOWERS (continued). Degeneracy of the Andececium. — The number of stamens may decrease, as well as the quantity of pollen ; while the form of the anthers may change and the character of the pollen may alter ; and lastly, the position of the stamens may not be the same as in intercrossing flowers, — all these forms of degradation being so many adaptations or adjustments for self-fertilisation. They are well seen in Violets and the Wood-sorrel. As examples, in Stellaria Holostea there are ten stamens, in S. media only three; and in cleistogamous Violets they vary from five to three or two. In the latter, the anthers become spoon-shaped with a rounded connective and much reduced anther cells ; in the cleistogamous flowers of Oxalis Acetosella the pollen is almost deliquescent. Lastly, in all flowers especially adapted for self-fertilisation the anthers are in contact with the stigmas in consequence of their arrest in growth. It must be noted here that this degeneracy in the stamens in no way impairs their functional value. The fact is that a very small amount of pollen is really quite sufficient for fertilising a considerable number of ovules. For convenience I call it degeneracy, but another view would be to regard it as the conservation of energy, instead of 274 THE STRUCTURE OF FLOWERS. wasting it in the production of a great deal more pollen than is usually required. An interesting experiment of Mr Darwin's proves this. He placed a very small mass of pollen-grains on one side of the large stigma of Ipomcea purpurea, and a great mass of pollen over the whole surface of the stigmas of other flowers, and the result was that the flowers fertilised with little pollen yielded rather more capsules and seeds than did those fertilised with an excess.* That normally intercrossing flowers produce a great snperfluity of pollen is well known. Thus Kolreuter found that sixty grains were necessary to fertilise all the ovules of a flower of Hibiscus, while he cal- culated that 4863 grains were produced by a single flower, or eighty-one times too many.f Mr. Darwin says, "In order to compensate the loss of pollen in so many ways, the anthers produce a far larger amount than is necessary for the fer- tilisation of the same flower ; . . . and it is still more plainly shown by the astonishingly small quantity produced by cleistogene flowers, which lose none of their pollen, in com- parison with that produced by the open flowers borne by the same plants ; and yet this small quantity suffices for the fertilisation of all their numerous seeds." Mr. Darwin observed that when flowers were artificially self-fertilised for several successive generations, a degeneracy sometimes took place in the anthers and pollen ; and he seems to attribute this to what he called the " evil effects " of self- fertilisation ; but from the above-mentioned facts, which occur so abundantly in nature, I am inclined to regard it as an experimental verification and illustration of a universal principle in nature, namely the preservation of energy wherever possible, and that such cases as appeared under his • Cross and Self Fertilisation of Plants, p. 2S. t Ibid., pp. 376, 377. EEGENERACY OF FLOWERS. 275 experiments were instances of this principle at work, as the flowers became habituated to self-fertilisation, and were then fullj fertile. We have, then, in such cases an actual demonstration of the first step of the changes induced by self-fertilisation continually enforced ; and thereby a witness to one cause of the origin of certain, and indeed, a very large number of species. It is the converse process to that of insect fertilisation, which itself I take to be the vera causa of the origin of intercrossing species. It is, perhaps, worthy of note that, while both the number of stamens and the quantity of pollen are thus often much reduced in some flowers the capsules of which produce many seeds, yet in others which set but one, as Fumaria, or at least but few seeds, the number of stamens may remain unaltered. This seems to me to be an additional proof that such flowers are degradations from forms originally adapted to intercrossing when much more pollen was requisite. Hence the present forms are retentions of former ancestral conditions. The following cases will illustrate this : — Scleranthus perennis and species of Medicago have ten stamens and one seed; Daphne Laureola has eight stamens and one seed; Chenopodium has five stamens and one seed; similarly is it the case with the large orders Compositoe and Graminece. The phenomenon called " contabescence " by Gartner* would seem to have its rationale in this adaptation to self- fertilisation in some cases, and to diclinism in others, though there are other causes which may bring it about, when it is a purely pathological phenomenon. Mr. Darwin observes, " The anthers are affected at a very early period in the flower-bud, and remain in the saine state (with one recorded exception) during the life of the • An. and PI. under Dnm., i!., p. 165. 276 THE STBUCTURE OF FLOWEES. plant. The affection cannot be cared by any change of treatment, and is pi-opagated by layers, cuttings, etc., and perhaps evea by seed. In contabescent plants the female organs are seldom affected, or merely become precocions in their development. The canse of this affection is donbtful, and is different in different cases. . . . The contabescent plants of Bianfhus and Verbascitm found wild by Wiegmann grew on a dry and sterile bank." * " Cases of an opposite nature likewise occur — namely, plants with the female organs struck with sterility, whilst the male organs remain perfect." The constancy or prevalence of this condition of conta- bescence seems to be the first indication of diclinism, what- ever the cause ; and Silene inflata may be mentioned as frequently furnishing good examples of both kinds of contabescence. Degeneracy of the Pollen. — As this is a feature of importance in the general degradation of flowers, a few words may be added in reference to it. It is of frequent occnn-ence in cultivated plants ; thus Potatoes are notorious for failing to produce fruit ; and some varieties are much less liable to do so than others, Mr. C. F, White, F.L.S., tells me he regards this plant as furnishing the most conspicuous example of a form of degradation of pollen ; the pollen grains of a normal character are very generally not to be found at all, but round, square, and polygonal forms abonnd. On the other hand, he gathered many flowers, in a large field in the Isle of Thanet, with scarcely a grain imperfect in shape or reduced in size. Mr. White has noticed, in his numerous researches among pollens, that degeneracy by dwarfing is mostly or veiy frequently induced by inclement weather. He mentions • A like cause prodnoea petalody of Btamens, see p. 299. DEGENEKACY OF FLOWERS. 277 the case of " Ononis, growing and flowering abundantly on the ' Sand-totts ' near Burnham, on the Bristol Channel, in which plant scarcely a grain of normal form was to be found ; many were absolutely united into grotesque groups and utterly deformed. At the commencement of the cold weather of autumn, although the corolla may appear unin- jured, the pollen grains are often ' dirty,' unable, as it were, to throw off the residual tissue surrounding them, and are often irregularly reduced in size." This sensitiveness of pollen to barren soil, inclement weather, etc., at once throws light on a probable origin of diclinism, such as of gyno-dioeceons plants already mentioned; and simply confirms the idea that these differences in the sexual systems of plants must not be looked upon as so many beneficial arrangements, but simply inevitable results which must follow such circumstances as give rise to them, whether they may prove advantageous or not. The injurious effect of over-crossing, abundantly proved by florists, Mr. White recognizes in the character of the grains of Rhododendrons and Ericas, which exhibit a shrivelling up and occasionally a complete " dissolution " of one and the uppermost grain of the group i>i four. Arid this observer adds, that in more than one species of Erica and also of Vaccinium the injury, he thinks, has become chronic. If the " vegetative " system be too energetic the " repro- ductive " is sure to suffer, and one of the primary causes of the injury is the arrested state of the pollen, as Van Tieghem has described and figured it in Ranunculus Ficaria.* A like result occurs in many cultivated plants, as Mr. Darwin has pointed out when describing the " contabescence of anthers." J * See above, p. 231, note. f An. and PI. under Dom., vol. ii., p. 165. 26 278 THE STRUCTURE OF FLOWERS. Degeneracy in the Gyncecium — If the theory be true that a typical flower should contain two whorls of carpels, or, if spirally arranged, several cycles, then it is an obvious fact that these conditions are not the prevailing ones in nature. In a simple type, like Ranunculus, we find the pistil of many carpels, but with one ovule in each alone developed, except in monstrous conditions ; if the ovules be numerous, then the carpels are reduced in number, as in the Selleborece. This is a primary result of Compensation. And when carpels have become whorled —a condition I take to be primarily due to adaptations to insect agency, causing an arrest of axial growth by the enhancement of the corolla, etc., (see p. 6) — then degeneracy begins to play an important part, in that, firstly, (theoretically, be it observed) one of the two whorls of carpels goes altogether, sometimes the calycine (e.g. Fuchsia), at others the petaline (e.g. Cam- panula). Secondly, the number of carpels diminishes, as in the Gamopetalce, where less than five prevail The following table will show with tolerable accuracy the proportional number of carpels and ovules that prevail in the first three divisions of Dicotyledons. Thakm. Calyc. Gamop. a) Orders with many carpels or Ord. p.c. Ord. p.c. Ord. p.c. many ovules 12 or 19 6 or 7 Oor (2) Orders with 5 carpels and many ovnles 12 or 19 10 or 12 7 or 12 (3) Orders with 5 carpels and 5-10 ovules 12 or 19 14 or 17 3 or 5 (4) Orders with less than 5 carpels and less than 5 crales 14 or 21 30 or 36 23 or 40 (5) Orders with less than 6 carpels and many ovnles 17 or 25 22 or 27 25 or 43 Observations. — (1) The first-mentioned correlation has two DEGENERACY OF FLOWERS. 279 conditions, either many carpels having one or few orales in each, or a few carpels with many seeds, as in the RanunculaceoB. This primitive condition rapidly vanishes in passing to CalyciflorcB and Ganwpetaloe. (2) Having reduced the nuraher of carpels to a definite quantity, five, i.e. one cycle of the prevailing f type, this number remains tolerably persistent, but does not show a large percentage. (3) The combination of five carpels with a reduced number of ovules, i.e. one or two in each cell, or 5-10 ovules in all, is pretty uniform for the first two divisions, but almost disappears under Gamopetalm, the orders Sapntaceae, Nolanece, and one or two Euhiacece, (e.g. Erithalis) representing this condition. (4) and (5). Here we see a steady increase in the percentages in passing from Thalamifloree to Gamopetalce, in which the number of carpels is still further reduced ; but the number of ovules runs in two directions, being either numerous or few. Two questions arise at this point. If one result of insect agency is to bring about increased specialization in flowers (yet, in proportion as they become specialized, so, inversely, is the number and variety of insect visitors diminished), how is it that some (e.g. Foxglove and Orchids) produce an enormous number of seeds ; while others (e.g. Labiata, Coinpositce, etc.) produce few or only one in each flower ? The second question is whether a plant is better ofE for having so many more seeds than another. Recognizing reproduction as the sole end of plant life, so that a plant should bear as many good seeds as possible, it is noticeable that the two largest orders, Compositoe and Gramineas have never more than one seed to each flower. Again, comparing Labiaiae with Scrophularinece, according to the Genera 280 THE STRUCTURE OF FLOWERS. Plantarum of Bentham and Hooker, while the former has 2600 species, the latter has only 1900. Lastly, comparing two orders with regular flowers and two carpels, Boragineae has 1200 species, and Solanece, 1250 ; while the former order never has more than four seeds to a fl.ower, in the latter they are numerous. If it were possible, we should procure statistics as to the relative degrees of abundance in individuals of two kinds at any place where they thrive. Casnal observations certainly have not led one to notice any such proportional abundance of the many-seeded plants as theoretically ought to exist if all their seeds germinated and grew to maturity ; for I have calculated the number of appai-ently good seeds in a large plant of Foxglove, and found it was one and a half millions. If we take a typical case, that of Orchids, whose flowers are certainly of those most highly adapted to insect agency, it is now well known that the proportion of seedlings to seed is infinitesimally small. Mr. Fitzgerald speaks of a Dendrohium speoiosum, which bore 40,000 flowers open at the same time ; but though the plant was growing in the open air and was exposed to the visits of insects, only one ■flower produced a seed pod* Mr. H. 0. Forbes found the same thing to occur in the terrestrial orchids of Portugal, and the tropical ones of Borneo.f Exactly the same diffi- culties are met with in cultivating plants, and especially Orchids (with few exceptions), as Mr. Veitch has testified. Now, when we examine the structure of the essential organs of Orchids microscopically, their degeneracy at once becomes apparent. First, with regard to the pollen. Instead of its being in well-formed distinct grains, each with its * Referred to by Mr. Veitch, Heport on Orchid Conference, Joarn. Boy. Hort. Soo. Bot., vol. vii., p. 47. t Journ. Lin. 8oc. Bot., vol. xxi., p. 538. DEGENERACY OF FLOWERS. 281 extine and intine, their development is arrested and, while still in contact, a common extine clothes the whole of each massula. Moreover, it is only after the pollen mass has been placed upon the stigma that the development is con- tinued.* With regard to the pistil the first sign of degeneracy is seen in the parietal placentation which prevails, and more especially in the rudimentary character of the ovules, every part of which is degraded. Even after fertilisation the embryo cannot grow to maturity, but remains in the arrested pro-embryonic condition. Having no albumen or nucellus- tissue wherewith to nourish the embryo, the suspensor does its best by elongating and escaping from the micropyle, and then, fastening itself like a parasite upon the placentas, ex- tracts nourishment therefrom — the result being that myriads of seeds never succeed (at least in cultivation) in developing even the pro-embryo ; and one can only infer that such is the case in nature.f In the cultivation of other flowers analogous phenomena are met with. The more highly cultivated a florists' flower may be, the less good seed is procurable ; while the poorer ones — that is, from a florist's point of view — or " weedy '' looking plants furnish plenty, and are highly prolific. The rationale of these facts, whether taken from nature or from cultivation, I believe to be fundamentally the same, viz. the adaptation to insect agency and the result of repeated intercrossing, which enhances the development and form of the perianth especially, and generally of the stamens as well. At least the kinds of energy which are concerned in the manufacture of these whorls are more especially forced into activity by the stimulus received from without. On the other hand, the pistil suffers proportionately in all its parts * Mr. B. T. Lowne, Orchid Conference, etc., I.e., p. 48. t M. Guignard hae drawo Bimilar conclusionB. See above, p. 172. 282 THE STRUCTURE OF FLOWERS. throagh compensation and atrophy, the ovules being appa- rently particularly sensitive. To meet this difiBculty nature seems, to speak metaphorically, to have tried two methods, either to make an immense number of seeds, so that at least a few might be perfect, or else to attempt no more than four or even one, so that at least they should be vigorous, and survive in the struggle for life during the critical periods of germination and seedling existence. To judge by results, this latter method turns out to be the best. The interpretation, then, I would offer of iuconspicaons- ness and all kinds of degradations is the exact opposite to that of conspicuousness and great differentiations ; namely, that species with minute flowers, rarely or never visited by insects, and habitually self-fertilised, have primarily arisen through the neglect of insects, and have in consequence assumed their present floral structures. The external stimulus or irritations derived from the weights, pressures, and punctures of insects being no longer applied, the secretion of honey has failed, the corolla ceasing to be subject to hypertrophy has atrophied. A like procedure has obtained with the stamens, while a large proportion of pollen has become effete, the anthers being partly contabescent, as it is called. What remains, though often altered in cha- racter, is amply sufiBcient to set an abundance of seed. With regard to the pistil, however, the reverse of this has in some respects taken place. The corolla and andrcecium no longer putting a check upon the rapid development of the gynoecium, the latter has a strong tendency to gain the ascendancy ; so that the result is homogamy or protogyny, with an extraordinary fertility of all plants which have inconspicuous and regularly self-fertilising flowers. If the seed be not always in great quantity in one and the same capsule, an ample progeny is secured by the DEGENERACY OF FLOWEES. 283 extremely rapid maturation of the fruits in succession ; as may be remarkably well seen in Chickweed. The general result is that all these " weed-like " plants, with which wind-fertilised herbs must be associated as equally independent of insects, of all flowering plants are by far the most widely dispersed, and are, in fact, cosmopolitan ; * and although they be small and annuals, are yet best capable of holding their own in the great struggle for life. KuDiuENTAKT ORGANS. — These are the ultimate result of atrophy and degeneracy in flowers. They are so well known as occurring in all parts of plants, vegetative and repro- ductive, that I need not describe them now. The reader will doubtless gather from all that has been said about hypertrophy and atrophy as causes of development and degeneration respectively, that they are just what one would expect to flnd. Indeed, every organ can be met with \ in every stage of degeneration till it has completely vanished ; i and even when all visible trace is wanting, the vascular cord | belonging to it may in some cases still be detected. Last of I all, this vanishes as well. These differences, for instance, can be witnessed in the presence or absence of the " trace " of the fifth stamen of the Labiatae. It is thought by some that a rudimentary organ may become a honey-secreting gland, as Robert Brown suggested for some Cruciferous plants. Glands mostly consist of epider- mal and sub-epidermal tissues only, and if they occupy the place of an organ, the latter has the vessels arrested before they reach into the gland, which therefore is still of the same nature. In the male flower of Lychnis dioica the disk sur- rounds the rudimentary pistil, which in no way contributes * In my essay referred to, I have given a long list of self -fertilising plants which have been discovered in widely distant localities over the northern and sonthern hemispheres. 284 THE STRUCTURE OF FLOWERS. to it. On the other hand, a gland may have its own proper vascular system, as in Lamium album, in which fease a circular horizontal ring of vascular cords is formed from the piatillary cords ; from this are given o£E a series of vertical cords, running up into the gland itself. There can he no d priori objection to the supposition that an organ, when degenerating and becoming rudimentary, may acquire a new form and function ; for such, indeed, is not infrequently the case. But what perhaps may be more usual, is that some other organ becomes more highly de- veloped through compensation. Thus, for example, the leaflets of the Pea, in becoming tendrils, lose all trace of a blade, retaining only their mid-ribs. These, however, now elo:ngate and acquire sensitiveness, for the use of climbing. On the other hand, in compensation for the loss of a certain amount of leaf surface, the stipules are very broad and foliaceous. Again, in the ray florets of Gentaurea the essen- tial organs have vanished altogether, but the corolla is greatly enlarged in comparison with those of the disk florets.* • For a disonssion upon " rudimentary organs," and their bearing npon the theory of Evolution, I would refer the reader to my work on Evolution and Religion (the " Actonian " Prize Essay for 1872), chap, xiii., p. 197. CHAPTER XXVIII. PROGRESSIVE METAMORPHOSES. Homology. — The theory of homology has long been main- tained, and has met with such an overwhelming mass of evidence in its favour, that it is now regarded as a well- established morphological doctrine. The belief that every individual member of a flower, whether sepal, petal, stamen, or carpel, may be interchangeable with a leaf, and that they are therefore all phyllomes or foliar appendages to the axis, scarcely requires proof. Secondly, any one organ may theoretically be sub.stituted for any other, so that although a sufficient number of interchanges has not yet been met with to make a complete series of permutations, yet they have ■gone far towards strengthening the probability that such might be possible.* I propose giving a very abbreviated series to illustrate, first, progressive changes from leaves through bracts to • The metamorphosis, with the exception of the sabstitntion of petals for other organs, is rarely more than tentative ; for it is, as it were, a mere attempt to effect a change, so that wherever a " monstrous " organ bears ovules they are almost always rudimentary and quite incapable of being fertilised. I have said "rarely," for M. Brongniart BDCceeded in obtaining fertile seeds from artificial impregnation of ovnliferous stamens in Polemonium cmvleum (Bull. Soc. de Bot. Fr., t, viii., p. 286 THE STRUCTURE OF FLOWERS.' carpels ; and, secondly, a retrogressive series from carpels to bracts, and thence to leaves ; finally deducing some important conclusions. Progeessive Changes in Bracts.— Bracts are in many cases very obviously modifications of leaves, being sometimes simply complete leaves reduced only in size, as in Epilobium ; or a bract consists either of tbe blade alone, as in Buttercups, or else of the petiole only, but now expanded and blade-like in form, as may be well seen in Hellebores, where transitional states occur between the normal pedate leaf and tnie lan- ceolate bracts (Fig 61, (I, h, c). When bracts are coloured otherwise than green, they then approach nearer to members of the repro- ductive or floral series rather than the vegetative, and in many cases are actually continuous in a spiral series with the sepals and petals, as in Cactus, Calycanthus, etc., and so assist in rendering the flower attractive. Several species of the genus Salvia, e.g. S. splendens, S. Bruantii, as well as of Bromeliaceoe, are remarkable for having brilliantly coloured bracts at the base of the flower. In some cases the bracts may be so arranged as to mimic a corblla, and indeed func- tionally replace it, as in species of Oornus (Fig. 62), Danoinia (Fig. 63), and the so-called Everlastings. The presence of bright colours in bracts, as also in sepals, to be described, I take to be due to the same influence as of the normal attractiveness in corollas; viz., the visits of insects : the immediate cause being nourishment ; the Fig. 61.— Transitional forms, a, b, from a leaf to a true bract, c, of HdUborUi viridis. PROGRESSIVE METAMORPHOSES. 287 stiTOulns required to bring the extra flow to the bracts, etc., being presumably the irritation induced by insect visitors. The next progressive state is for bracts to assume a more Fig. 62 — Infloreecence of Cdrntts fiorida, with fuur white petaloid bracts. Fig. 63. — ItifloresceDce oF Darviinia, with coloured petaloid bracts. or less staminoid character. This is rare, but it has been noticed in Abies excelsa* A substitution of anthers for bracts has been seen in Melianthtis major, f concerning which Sig. Licopoli remarks that the flowers of chiefly the terminal racemes were imperfect, the summit of the floriferous axis bearing a tuft of perfect and imperfect anthers the petals and the two carpels of the flower having been atrophied or aiTested. -* Pig. 64 represents an involucral bract of Nigella, bearing an anther on one side of it; while Fig. 65, a, is that of a glume of Lolium perenne with an anther. That bracts should ever assume a pistilloid character is, d priori, still more unlikely, as being further removed from the central organ of the flower. Dr. M. T. Masters has, however, described J a * Teratology, p. 192. + Bull. Soc. de Bot. Fr., Rev. bib., t. xiv., p. 253. t Journ. of Lin. Soc. Bot, vol. vii., p. 121. 288 THE STRUCTURE OF FLOWERS, malformed Lolium perenne, in which the flowering glumes had styles and stigmas (Fig. 65, a, b) ; the essential organs being absent, were replaced by a tuft of minute scale-like a b Vlg. 64.— Involncral Iwact of Fig. 65.— Glumes of Lolium, with anther Nigella, with autber (after and stigmas (after Masters). Masters). organs, some of which were prolonged into styliform pro- cesses, the sexual organs being otherwise suppressed. la a proliferous case of Delphinium elatum described and figured by Cramer,* the parts of the flowers were all metamorphosed into open rudimentary carpels. The axis was elongated and terminated above, in one case, by a similar abortive flower; in another, by an umbel of such flowers, every part of which was more or less carpellary ; while all the bracts on the prolonged axis, even those out of the axils of which the branches of the umbel sprang, were similarly made of open carpels. Peogeessite Changes in the Calyx. — The sepals are usually homologous with the petiole of a leaf. This is obvi- ously the case with the Rose, where the rudiments of the ♦ Bildungsahweichungen, etc., heft, i., taf. 10. The figure is repro- duced in Teratology, p. 126. PROGBESSIVE METAMORPHOSES. 289 compound blades are retained (see Fig. 24, p. 93). In Pedicularis the blades are present as a minute fringe on the edge. In Ranunculus, Potentilla, etc., the broad base of the petiole is the only part present, for in abnormal conditions the blade may be borne above (Fig. 66). Similarly, in a gamosepalons calyx the teeth as a rule seem to be all that remain to represent the blades ; for in Trifolium, repens, when virescent, trae unifoliate blades are developed on elongated pedicels, all arising from the border of the calyx-tube (Fig. 67), in which the teeth become pinnately nerved blades. Fig. 66. — Ranunculus with folioceous aepal. Fig. 6t.— Foliaceons calyx of Trifolium repens, with Etipulate leaflets (after Bailion). The venation may in some cases assist in furnishing a clue as to the real nature of a part. Thus in Hellebore, as already seen (Fig. 61), the bracts are homologous with petioles, their venation being palmate, and not pinnate as in the divisions of the blades of the leaves. It is the same in the sepals, which are presumably therefore homologous with petioles as well. The sepals of Oaltha resemble them in their venation, but in this plant the leaf is of a more primitive type, not being lobed, and has also a palmate venation. A similar difference between the venation of the sepals 27 290 THE STRUCTURE OF FLOWERS. and blades of the leaves is seen in Bipterocarpus and Mus- scBnda (Fig. 68). Transitional states from a single to a double flower of Saxifraga decipiens, described and figured by M. C. Morren,* shows that the newly foi-med petals in the place of stamens, as also the normal petals of the flower, exactly correspond, both in shape and venation, with tbe cotyledons. Palmate venation thus simply represents a more primitive type ; and, since flowers are constructed out of metamorphosed leaves — ^the vegetative being replaced by reproductive energies, — one naturally expects to find the calyx and corolla, which more nearly approach leaves in structure, to show arrested foliar con- ditions, as, e.g., are seen in palmate nervation and absence of blade or petiole, as the case may be. In Musscenda (Fig. 68) the teeth of the sepals are usually subulate and acuminate ; but in the one foliaceous and snbpetaloid sepal it is drawn out into a long petiolar form, which then expands into a palmately nerved lamina. The fact that a "tooth" is in this case prolonged into a " petiole " seems to imply that the sepal arises at once from the receptacnlar tube, which, therefore, one would infer to be axial. A somewhat analogous pro- cedure is in the monstrous Trifolium, where the unifoliate blades, supported on long pedicels with stipular appendages as well, all arise from the border of tbe so-called calyx-tube (Fig. 67). There the inference would be the same, only that the receptacnlar tube is free from the • Les Bull, de I'Acad. Ray. de Bruxelles, t. xvii., p. i., p. 415. Fig. 68.— Flower and leaf of PROGRESSIVE METAMORPHOSES. 291 pistil, and not adherent as in the case of Mmsmnda. In both instances it will presumably be purely axial in character. Progressive changes in the calyx are not uncommon by its assuming a petaloid character. This is normal in some genera of Banunculacew, in Fuchsia, Bhodochiton, as well as in some members of the Incompletce, as in Mirabilis, Polygonum, Daphne, etc. Normally coloured sepals are most frequent in polysepalous genera. Abnormal colorisation, with or without any metamorphosis of the organ, is most frequent in gamosepalous flowers, as in the cultivated " hose-in-hose " varieties of Primula, Mimulus and Azalea. The calyx may be petaloid either wholly or in part only. In Musscenda (Pig. 68), one sepal only is normally sub-petaloid. Calceolaria has occasionally one or more sepals petaloid. Similarly Linaria (Fig. 69) and other in- stances might be mentioned. These condi- tions, brouEfht about by cultivation, clearly rig. et.— Linaria. , . , ji . 1 ■ 1 • > ''"'' "OS sepal show the important part that high nounsb- petaloid. ment plays as an external stimulus or factor in the produc- tion of colour. Staminoid sepals appear to be very rare. It is recorded by M. Gris that they have occurred in Philadelphus speciosus.* Pistiloid sepals are nearly equally as rare as staminoid. They have been observed by Mr. Laxton in double flowers of the Garden Pea (Pig. 70), in which there was a. five or six-leaved calyx, some of the segpients of which were of a carpellary nature, and bore imperfect ovules on their mar- gins, the extremities being drawn out into snb-stigmatiferous styles.f * Bull. 8oc. de Bot. Fr., t. v., p. 330. t Qard. Chron. 1886, p. 897 i and Teratology, p. 302. 292 THE STEUCTUEE OF FI.OWEES. I have also found the sepals ovuliferons in a monstrons form of Violet, which was almost entirely virescent (Fig. 71). Progeessive Changes of the Coeolla. — For petals to become staminoidis far from uncommon. It is a normal con- dition in Atragene (Fig. 44, p. 141), which illustrates the transition, and in "Water-lilies, where a gradual development of the anther cells is accompanied by a gradual reduction of the petal to a filament. As abnormal instances may be men- tioned, a case of Foxglove which I have elsewhere * described as having the corolla split up into strap-shaped antheriferous processes (Fig. 72), and a Columbine in which the spars Fig. 10 Calyx of Garden Pea, with carpellary lobes (after Masters). Fig. 71. — Ovullferous sepaL of Violet. Fig. T2.— Corolla of Fox glare, with staminate tube. became curionsly coiled and bore pollen within the tissue of the coils (Fig. 73). Pistiloid petals are of rare occurrence. As an example is Begonia (Fig. 74, a), in which the apex of the petal was green and stigmatiform, the basal part being broad, coloured, and ovnliferous. Fig. 74, bj shows a petal, ovuliferons below, stigmatiferous at the summit, and antheriferous midway ; c is a rudimentary ovule. Peogeessive Changes in the Stamens. — The only change * Journ. Linn. Soc. Bot., vol. xv., p. 86, tab. 3. PEOGRESSIVE METAMORPHOSES. 293 that stamens can undergo in this direction is to be more or less converted into pisfcillary structures. This is by no means uncommon. Either the filament alone, or the anther alone, or both together may be affected. The reader is Fig. 13, — Aquilegiat with poUeniferous spurs (alter W. G. Suiitli). Fig. 74. — Ovuliferous petals, etc. , of Begonta (after JUasterBJ. referred to Dr. Masters's Teratology for a description, with figures of several kinds.* It is more usual for the filament to become enlarged into the ovarian part bearing rudimentary ovules ; but when the anther is involved, it may be partially or wholly transformed. In these cases the connective is usually prolonged into a stigmatiferous process, f As an example often described is that of the Honseleek, in which the margins of the anther cells become ovuliferous in various degrees ; as in Fig. 7-5, where ovules are borne by the pos- terior sides only, instead of pollen. In other cases the filament bears rudimentary ovules as well. Dr. Masters points out that " where there is a combination of the • Page 303. ■|- In Anstolochia this change seems to be permanent and functional. See above, p. 83. 294 THE STRUCTURE OF FLOWERS. attributes of the stamen and of the pistil in the same organ, the pollen is formed in the upper or inner surface of the leaf organ, while the ovules arise from the opposite surface from the free edge." Begonia is a genus which is peculiarly liable to produce malformations in the stamens (Fig. 76).* Rosa Fig. 75. — Ovuliferous anthers of Sempervivum (after Masters). Fig. 76. — St)[;matfferous and ovuliferous staiiieus of Jitgonia. arvensis'\ affords a case in which the ovules were borne by the anthers, and then they themselves produced pollen. In these cases, where the anthers are ovuliferous, the connective is often more or less stigmatiferous, as in Begonia (Fig. 76), which shows various degrees of metamorphosis in this way ; but the anthers may sometimes be stigmatiferous, as in Poppies, X or styliform as well, as in Bamboos. § The complete substitution of carpels for stamens occurs in many plants, as in Mains apetala,\\ Tulips, etc., and is extremely common in Wallflowers,^ while it is by no means an uncommon occurrence to find male plants of normally dioecious or monoecious character bearing female organs, though perhaps in these cases it is often an addition, rather than a substitution of one organ for another. of Lin. Soc, xi. 472; Bot. Zeit. (1870), vol. xxviii., X Teratology, p. 304. * See Joum. p. 150, tab. ii. t Joum. of Bot., 1867, p. 318, tab. 72. § Col. Mnnro, Trans. Lin. Soc, vol. xxvi., p. 7. I Poiteau et Turpin, Arhr. Fruit., t. xxxvii., referred to by Moquiii' Tandon, TSratologie, p. 220. ^ Called " Rogues " by the market-gardeners, as the corolla is want- ing or green. See Ann. des 8ci. Nat., 5 b6t., xiii., p. 315, pi. 1. CHAPTER XXIX. RETROGRESSIVE METAMORPHOSES. The Pistil. — Commencing -with the pistil, there may be changes in the ovary, ovules, style, and stigmas, separately or collectively. Instead of one or more ovules, a pistil may be formed within an ovary, as sometimes occurs in Wall- flowers, Grapes, Oranges, etc.* A sin- gular instance is described by Dr. Masters t of a Carnation, " the placenta of which bore not only ovules but also carpels, the latter originating in a per- verted development of the former ; so that many intermediate stages could be traced between the ordinary ovule and the ovary. Some of these carpels, thus derived from ovules, themselves bore secondary ovules on a marginal pla- centa " (Fig. 77, a, carpel and section), the secundine, how- ever, being the only part developed (6). Stamens within an apparent ovary have occurred in • Teratology, p. 182. t L.C., p. 267. Perhapa the supposed " ovule within an ovule " may have been the nucellns only, more or less free from the Becnndine. Fig. 11. — Carpels and ovules on placenta ot CarnatioQ (after Masters). 296 THE STRUCTURE OF FLOWERS. Bcpchia diosmoefolia ; * but as they grew on the interior of the wall and not on an axile placenta, as is the normal con- dition, in the Myrtacece, I expect that it was due to the staminal vascular cords branching off and coming out of the tissue within instead of at the summit of the hollow recepta- cnlar tube, the carpels being more or less arrested. A not t uncommon instance is to find the pistils of Willows with open ovaries and bearing one or more anthers on the margins (Pig. 78, a). I have met with a similar occurrence in Banunculw auricomus (Fig. 78, 6). Pistils of other flowers Fig. 78 StameniferouB carpels of Willow (a) and Banunculus auriccmus (b). Fig. 19. — a, Petaliferous placeritas of Car' damine pratensis; b, of Rhododtndron. way, have been known to bear anthers in a similar Ghamcerops humilis, Trunus,^ etc. Pollen within ovules has been met with occasionally, as in Passiflora and Rosa arvensis.X In some members of the Orucifera, as Gardamine pratensis (Fig. 79, a), round pods are formed instead of the usually * Teratology, p. 184. Possibly the ovary wag entirely absent, and the stamens would then be growing on the interior of a closed receptacnlar tube, just as carpels grow upon the inside of the hip of a rose. t See Weber, Verhamdlung des Nat. Hist. Vereinea der Preuss Bhein- v/nd Westph., 1860, p. 381. J Teratology, p. 185. RETROGRESSIVE METAMORPHOSES. 297 long siliqnas. These are full of petals, and if carefully- examined appear to be whorled, with traces of stamens and pistil within them ; so that they represent flower-bnds, but of which petals form the greater part ; similarly, Rhodo- dendrons and other flowers are known to bear imperfect flower-buds within the ovary (Fig. 79, 6). Anthers occupying the place of stigmas appear to have occurred in Campanula,* Snowdrop, and double Tulips. The substitution of stamens for the entire pistil is of a less usual occurrence than the staminody of its parts : for cases, the reader may consult Masters's Teratology.'^ In a species of Orchis, probably 0. Mario, the ovaries were wanting altogether, a long pedicel taking their place, and within the reduced and regular perianth were two anthers on opposite sides (Fig. 23, a, p. 92), an apparent compensation in lieu of the pistil. The next and most frequent case of metamorphosis is that of conversion of carpels, and usually the stamens as well, into petals, or the so-called "doubling" of flowers. This is usually accompanied by a change from whorls to spirals with a multi- plication of the parts. Thus, in a double Wallflower, I have counted more than fifty petals spirally arranged. With regard to the petalody of the pistil, as Dr. Masters observes, " this is much less common than the corresponding change in the stamens. ^'^i.„',2i^J!^Sd It generally affects the style and stigma J^J^p^' of /■ofjian- only, as happens normally in Petalostylis, Iris, etc." J Fig. 80 illustrates a metamorphosed carpel of Polyanthus, with a broad coloured appendage to the style. In some double flowers the carpels only are petaloid. • Teratology, p. 300. t lUd., p. 299. J Ibid., p. 296. 298 THE STRUCTURE OF FLOWERS. This has been observed in Anemone nemorosa, cultivated varieties of Ranunculus, Violet, and Gentiana Amarella. Retrogressive Metamorphoses of Stamens. — For the stamens to become petaloid, it is extremely common, as in double flowers, and such a change may represent what is normally the case in Water-lilies, Canna, and Atragene (Fig. 44, p. 141). Changes may apply to the anther lobes, connective, or filament, or to all together. Fuchsias often bear filaments with petaloid expansions of the apex, at the base of which are one or two anthers showing varying degrees of degeneration. This is a very similar condition to one in Petunia, described by Dr. Masters, in which the con- nective had developed into a green roundish blade bearing two anther cells at the base (Fig. 81).* In such cases, it seems to be the connective which has expanded outwards and become the blade of the petal or leaf. Similarly, in the Fig. 81. — Foliaceous connective of Petunia Fig. 82. — Petalody, or ••lio8e-in-hose"forin, (after Masters). of counectives in a double Columbine. double Columbine petalody of the connective sometimes takes place (Fig. 82). f Commelina alba has also furnished a case of an anther lobe becoming petaloid. Causes of " Doubling." — There can be no doubt that petalody results from a weakened reproductive energy, espe- cially that of the androecium, which can become constitn- tional and may be hereditary and transmissible by crossing. * Teratology, p. 254. + Ibid., p. 293 RETROGRESSIVE METAMORPHOSES. 299 Cases seem clearly to show that a barren and dry soil, as well as a very dry atmosphere, are prominent causes for its appearance. Thus Mr. Darwin described a double Oentiana Amarella* growing " on a very hard, dry, bare, chalky bank." T. S. speaks f of a double Potentilla as "grow- ing along a high wall, on a dry raised bank close to a beaten path, adjoining a gravelly field." Again, a writer in Gartenzeitung J alludes to the raising of double Stocks, and says that they should only have " jast enough water for their preservation," and that " the starved state of the plants " causes doubling. He allades to Camellias, also, as becoming double when grown in a dry soil. Kerria Japonica becomes double in Europe, in consequence of its missing the wet season of Japan. It is well known that double flowers are more easily raised on the continent than in England, probably from a like cause, as our atmosphere is considerably more charged with moisture than a continental one. In raising double Stocks, it is customary to procure seed from the flowers on axillary shoots which have a weaker repro- ductive energy than those growing on the primary or central axis, the seeds being smaller and often misshapen. The above causes are, therefore, suggestive ; in that if a some- what elevated, dry, and poor soil, one devoid of phosphates, etc., be provided, the probability is that petalody will ensue. Having once shown a trace of the malady, florists know how to proceed in order to propagate and transmit the afEection. There remains one other floral metamorphosis, and that is of petals into sepals. This condition approximates to virescence of the corolla, so that in many cases such a change could scarcely be called sepalody. But M. Godron has shown that when Eanunculus auricomus appears to be • Gard. Chron., 1843, p. 628 t Ibid., 1866, p. 973. J Ibid., 1886, p. 197. 300 THE STRUCTUUE OF FLOWEKS. apetaloas or to have a corolla consisting of a few petals only, it is dae to the fact that the petals which are wanting are really present, but have become calycine. Oeigin of Homologt. — Though we cannot penetrate into the arcana of life, nor trace the workings of its forces which bring aboat the development of any organ whatever, I think we can at least reach the physiological starting-point, so to say, of all these changes which I have briefly described. I have already mentioned that we may consider a vascular cord as the fundamental " floral unit," and as all cords are identical in character as long as they are within a pedicel, and, as far as one can observe, identical also in character even when they have penetrated the different organs, we at once see that there is a common source for each and all. Secondly, when we trace these cords from the receptacle or axis into the floral membel-s, we soon discover that any cord can supply two, three, or more totally difEerent organs with their respective branches, as in the case of Campanula medium described above (p. 43). Indeed, starting, say, with five cords in a pedicel, they can snpply any number of organs ad libiium, however diverse in character and however numerous they may be. Hence, although normally each whorl is stamped with its own individuality, it is easy to imagine, in accordance with the principles of evolution, that others may partake of it ; and so the characteristic features peculiar to one whorl can transcend its limits, and influence others as well. Beyond some such interpretation as this, I do not think it is possible to go. In saying that a fibro- vascular cord can "give rise" to a sepal, or petal, or other organ, I need hardly remind the reader that I am only speaking metaphorically, in describing what one observes in studying the anatomy of flowers. CHAPTER XXX. PHYLLODI* OF THE FLORAL WHORLS. VlEESCENCE AND FOLIACEOHS CONDITIONS — SePALS, PeTALS, AND Stamens. — The last changes to be described, which are,, commoii to all the members of a flower, are virescence, when they retain their normal forms, but are simply green ; and foliaceous conditions, when they assume more or less a truly leaf -like form. Dr. Masters has giveu descriptions t of several of each kind of floral members as well as of foliaceous bracts, to which I must refer the reader for details. There are certain particulars, however, to which I would especially draw attention as throwing light upon the ordinary structure of floral whorls, and especially that of ovules. Taking the Alpine Strawberry as an illustrative case, the petals, stamens, and carpels are often more or less foliaceous ; but the petals retain a palmate venation, though the three leaflets of the ternate leaf are pinnately nerved (Fig. 83, a, b). In the case of stamens the connective may be foliaceous, as in Petunia (Fig. 81) ; J also in the Alpine Strawberry (Fig. 83, a) and in the " Green Rose " the anthers are often persistent on either edge of a leaf-like intermediate part * The abnormal assumption of a leaf -like character. t Teratology, p. 241, seqq. t lUd., p. 254. 28 302 THE STRUCTURE OF FLOWERS. (Fig. 83, c). A curious foliaceous modification is described by Miiller and figured by Masters,* in which the metamor- Fig. 83.— o, Foliaceous stamen, and h, petal of the Alpine Strawberry (after Le Maout and Decaiene) ; c, stamen ol " Green Rose." phosed stamen had the appearance of two leaves united by their mid-ribs. It occurred in JatropTia Pohliana (Fig. 84). This will be alluded to again, as pecu- liarly significant. Phtllodt op the Carpels and Ovules. — This is of much more frequent occurrence than of the stamens. The first condition of change is to leave the ovary open and to expose the ovules ; the style may still be stigmatiferous. The ovules then undergo phylloidal changes of different degrees, and much discussion has arisen as to whether the coats of ovules should be regarded as homologous with leaves, the nucellns being axial, or not, etc.f Since, however, anatomical observations clearly prove that both the primine and secundine issue out of tangential • Teratology, p. 255. + i.e., p. 262. Fig. 84.— Foliaceous i^atnen of Jatropha Fohliana (after Masters). PHTLLODY OF THE FLORAL WHOKLS. 303 divisions of the epidermal layer of the nucellus, one can hardly consider these of themselves as homologous with a true phyllome. But when we find that each of the two sides of an anther cell can develop into a foliaceous structure, as in the case of the Jatropha alluded to above (Fig. 84), we seem to have discovered a power of converting what is originally and simply an epidermal layer into a truly folia- ceous structure. Moreover, this process is not infrequent in certain monstrous states of ovules, so that it would appear that any question of homology is, strictly speaking, out of court in these cases. When the whole of an appendicular organ becomes foliaceous, then, of course, a true case of homology may be recognized. Oeigin, Development, and Homologies of Ovules. — Tera- tology, here, I think, assists us greatly. With regard to the structure of an ovule, it first appears as a papilla upon the placenta, the cellular tissue of which, with its epidermal layer, constitutes the first stage. Such may, perhaps, be considered as the rudimentary condition of the funicle alone, as the true ovule is formed at the summit of it. One or more of the apical sub-epidermal cells gradually develop into the nucellus, while the secundine is first formed by tan- gential division of the epidermis commencing at a certain place below the apex ; the primine, if present, subsequently following suit in the same manner.* It is a noticeable fact that while an ovule thus complete is elsewhere general in flowering plants, the Gymnosperms and most orders of the Gamopetalce form remarkable exceptions, as having only one coat to the ovule. In the former of these two groups it is doubtless due to a primitive condition being accompanied by other features showing aflSnities with cryptogams. In ♦ See paper by Warming, De VOvule, Ann. des Sci. Nat., v. (1877), p. 177. 304 THE STRUCTURE OF FLOWERS. the latter, it is due to reversion by arrest, and is likewise accompanied by a simpler origin of the nncellus and embryo- sac, as Warming has shown. The suggestion I would offer to account for this anomaly is that such ari'est is due to compensation. The Gamopetalce, as a whole, are the most advanced of all flowers through adaptations to insect agency ; and as this invariably brings about an exalted condition of the corolla and stamens, the consequence is that the pistil has to suffer ; the first visible result being protandry, accom- panied by a temporal arrest in the development of the pistil. If this tendency to arrest be carried to the ovule, it may be affected too, and the result is that one, the last-formed coat, may be arrested altogether. Orchids, as shown above, illustrate this principle remarkably well, as their ovules, though possessing two coats, are as degenerate as in many parasitic plants (see above, pp. 172 and 281). Tracing the origin of an ovule, then, from its birth, it first appears as a papilla on the placenta of the carpel. A branch from the marginal fibro-vascular cord of the carpel enters it from below, and reaches afc least as far as the cbalaza, or base of the nucellus. It may go no further, as in rudimentary ovules of Orchis ; or be arrested in the form of cambium in the degraded state seen in the parasitic Thesium. On the other hand, as the ovule becomes a seed and the coats go to form the seed-skin, fibro-vascular branchings may occur all through the l^itter, being developed from the original cord. Such may be well seen in Mustard, Acorns, Beans, and the Coco-nut. Although the coats of the ovule were originally formed by tangential division of the cells of the epidermis of the nucellus, when united to form a seed-skin, this has become thickened by a cellular growth between them, through which the cords then ramify. PHYLLODY OF THE FLORAL WHORLS. 305 Pistils -whicli have reverted to a more or less foliaceons character bear ovules whicli often become foliaceons as well ; and then a not nncommon proceduro is the develop- ment of a cup-like structure, probably composed of the two ovular coats, on an elongated stalk, with a rudimentary nucellus within, but more or less perfectly free from it ; or it may not exist at all. The late Professor Henslow described a monstrous con- dition of Mignonette with figures of ovules in this condition.* They were sometimes replaced by minute leaves (Fig. 85, c) ; or else in the place of each was a cnp-like structure, elevated on a long stalk, with an egg-like nucellus within, but quite free from it. He likened it to tbe theca of a pig. 55 Follaceous and metamorphosed ovulea of Mlgno- moss with its central °'"' ('"*' ^°^- •'■ ^- Hensiow). columella. Comparing these two modifications, represented by Fig. 85, a and h with c, — or, again, those of Fig. 86, a and 6, — the interpretation seems to be that the fibro-vascnlar cord passing up the funicle of the omle becomes a petiole, and its prolongation constitutes the mid-rib. The secundine and primine with intermediate tissue become the blade, as seen in the foliaceous states of ovules, and constitute the " cup " when they assume that form. A similar process, I think, quite explains the origin oE tbe foliaceous processes of the stamen of Jatropha, repre- sented by Fig. 84. The entire stamen is, of course, really * Trans. Camh. Phil. Soc, vol. r. 306 THE STRUCTUKE OF FLOWERS. homologous with one leaf alone ; but the membranes belong- ing to each anther, being of, at least, two layers of cells, have become foliaceons, just as the epidermis of the nucellus has done in the cases herein described; so that, in the Jatropha, two leafy expansions were developed out of one. Other instances are known of ovules being represented by leaves, as Primula Sinensis, Synvphytum officinale,* and Sisymbrin/m Alliaria (Fig. 86). Theoretically, it might be objected that a leaf (carpel) should give rise to a leaf (ovule or, at least, ovular coat) ; but foliaceous excrescences from a leaf- Fig. se.-Metamorphosed ovules surface are not at all uncommon, as, ^r'Sr^romtt for example, fi-equently occur in Cab- lum, xTii., t. 20). bages,f where, in consequence of high nourishment inducing hypertrophy, any " rib " or " vein " may throw off a branch which can form a leafy expansion, which not at all infrequently becomes funnel-shaped, like the abortive ovules of the Mignonette. Similar funnel-shaped or tubular productions are found on corollas of semi-double flowers, as in Primulas, Cyclamens, Antirrhinum, etc., sometimes externally. Fig. 87 represents a like out- cence'on the labeiium of growth from the labellum of Gattleya * "■ MossieoB; and I have seen the posterior sepal of Vanda coerulea replaced by a pedicel with a cup at the apex exactly like the terminal process in Fig. 85, a. In all these cases I would regard such productions as due to hypertrophy. Teratology, p. 263. t Ibid., p. 312, fig. 166. PHYLLODT OF THE FLORAL WHOELS. 307 As another carious instance a remarkable form of the Sun-dew, Drosera rotundifolia, may be allnded to here, as throwing additional light upon the origin of ovules. It has been described and figured by Naudin,* and also by Plan- chon.'l" In this monstrosity the ovular coats were represented by " tentacles." These, as is well known, are not epidermal trichomes, but structures issuing from branches arising from the fibro-vascular cords of the leaf, and are therefore strictly homologous with the "funnels " on cabbage leaves. J The conclusion, therefore, which seems deducible from the foregoing observations is that an ovule is simply an appendage (not a bud) to the fibro-vascular cord of the margin of the carpel, and under monstrous conditions can grow into foliaceous excrescences to the carpellary leaf. It is not, therefore, axial in its character. Since all that is required to start from is a fibro-vascular cord, this may be furnished by any cord, even the mid-rib ; and such is the case in some monstrous states of Primula, in which rudiments of ovules are found on the mid-ribs as well as on the margins of separate carpels. As the " funnels " on the mid-ribs and lateral veins of cabbage leaves are due to an abnormal condition of hyper- trophy, so ovules I consider as arising in a similar way, and take them to be due to the same influence, though of course it is normal in their case. The very presence of the large cords running up the margins of carpellary leaves, direct from the axis below, — being often, indeed, larger than the dorsal cord, — which then ramify, not only into each ovule, but often backwards within the carpellary walls till they reach and * -47111. des Sci. Nat., 2° s^r., vol. xiv., p. 14. t Ibid., 3' ser., vol. ix., p. 86, tab. 5, 6. X The " pitchers " of Nepenthes, perhaps, originate in much the same way, from the original water-gland at the apex of the leaf. 308 THE STRUCTUEE OF FLOWERS. anastomose with the dorsal cord ; these, together with the greatly thickened cellular margins now constituting the placentas which supply the conducting tissue for the pollen- tubes, all show a form of hypertrophy in the edges of the carpellary leaves, a condition of things widely different from the usually thin and more or less impoverished margins of true leaves. If we may recognize a fibre- vascular cord as the " funda- mental unit," and as a basis for the construction of any organ, and moreover as also containing within it poten- tially the power of evolving any number of similar organs by repeatedly branching ; then, when hypertrophy affects such a " unit," it may branch once, twice, or any number of times, when each branch passing off to the surface can lay the founda- tion of a repetition of the organ from which it takes its rise.* Attention has already been called to this origin of the numerous stamens of the MaVoacece, and how certain forms of double flowers originate from the multi- i Psl r~^ plication of the petaline cords, each branch of which issues in a distinct petal, as, in Snowdrops. Similarly for carpels and ovules, the process of multiplication can be witnessed both normally and .abnormally. On the Fig. 88.— Multifold carpels one hand, that of carpels into five groups withovuliferousmargiDS , _^.,_, ., ^ from a malformed Prim- occurs in the Hollyhock through the chorisis of the original carpellary cord ; on the other. Fig. 88 represents a multifold carpel of a Prim- rose, due, there is no doubt, to a like chorisis of the cords belonging to one individual carpel. Similarly for ovules, while two only are normally charac- * I mnst again remind the reader tbat I am here Bpeaking meta- phorically J as we do not know wherein this potentiality really lies, but can only describe what is actually visible. PHYLLODY OF THE FLOEAL WHORLS. 309 teristic of the Plum, and Orchis has an innumerable qnantity arising by repeated chorisis of the original placentary cords, so in monstrous Primroses, etc., as represented in Fig. 88, many additional ovular processes may be formed, not only on the margins, but even, as stated, on the mid-ribs. One other point may be here noticed, d propos to the following curious discovery by M, Baillon. I have regarded a vascular cord as a " unit," as being capable of giving rise to any appendage whatever ; and as long as it is in an axis as a " trace," the cords of all organs are absolutely indistin- guishable. Further, there is no difEerence between a cord which will enter an appendage and one which will form a pedicel from a peduncle. In the latter case, several cords are usually required for the pedicel ; while one, the most external of the " horseshoe " group given off at one side of the peduncle (i.e. as seen in a transverse section), enters the bract. In Erodium, cicutarium, which has three flowers to the umbel with, very slender pedicels, one single cord is all that the peduncle contributes to supply each of the pedicels, and one very small cord for a bract. The cord for the pedicel increases by radial chorisis, and so passes from the form of a wedge to that of a fan, when the outermost parts increase till they meet, aind so a circle is established. This shows that an "axis" and an "appendage" are fundamentally due to the same kind of " unit." The reader will now see that in the following case * the funicular cord, which is normally that of a foliar, i.e. appendicular organ, supplied an axial cord ; just as many leaves can give rise to buds which are often utilized for pro- pagative purposes. * 8v/r le Diveloppement et la Germination des Grains Bulbifm-nves des Ama/ryUid4es, par. M. Baillon, Bnll. Soo. de Fr., t. xxi., 30 (pub. en Sevue des Oours Sci. Lyon, Aotit 30, 1873). 310 THE STRUCTUBE OF FLOWERS. " Les bulbilles des Amaryllidees ne sont pas toujours des graines veritables modifiees seulement quant a I'epaisseur et a la consistance de leurs diyerses conches naturelles, notam- ment des plus exterieures. Temoin le Calostemma Cunning- hamii. Ici, par une singuliere transformation de I'ovnle en bulbe, la cbalaze, en s'epaississant, joue le r61e d'un veritable plateau, sur lequel se produisent une, puis plnsieurs racines adventives. Les enveloppes ovulaires tienne alors lieu d'ecailles bulbaires tandis qu'il s'eleve dans le sac embryon- naire un veritable bourgeon parti de la chalaze comme support et s'echappant par son sommet de la cavite ovnlaire pour se comporte ensnite comme une plante complete.'' An analagous case of bulbs arising from a foliar organ occurred with Scilla Sibirica. Some plants dug up in October, 1887,* were found to have taken the form of the so-called " droppers " not uncommon in tulips. Their peculiarity resides in the fact that the tubular leaf-sheath bends and grows downwards, thereby carrying the axillary bulbil to a greater depth in the soil than usual. In February, 1888, on re-examining them, Dr. Masters discovered that from one to four bulbils had been developed at different heights within the tissue of the tubular sheath, being in connection with the cords of the latter by means of a transverse nexus of tracheids. I refer to these cases as being curious instances of axial structures proceeding from foliar — i.e., by the change of icharacter of the fibro-vascular cords from being at first jfoliar and then axial. They support the theory of homology jof leaf and axis, which is, of course, otherwise quite efficiently substantiated by such plants as Xylophylla, Buscus and the Oactacem. * Gwrd. Chron. for Got. 15, 1887, p. 475, fig. 98, " droppers ; " also, for March 3, 1888, p. 276, fig. 45, ditto, with bulbils. CHAPTER XXXI. THE TAEIETIES OF FERTILISATION. There are at least seven kinds of union : — (1) self-fertilisa- tion, or tte fertilisation of a pistil by the pollen from the same flower (Autogamj) ; (2) crossing different flowers on the same plant ; (3) crossing flowers on different plants of the same stock ; (4) crossing flowers of different plants, hut of different stocks ; all the preceding being of exactly the same form or variety of species ; (5) crossing varieties of the same species ; (6) crossing different species of the same genus ; (7) crossing different genera of the same order. When a knowledge of the floral sexes was first acquired, the idea maintained was that hermaphrodite flowers were specially adapted for self-fertilisation ; but it was, I believe. Dean Herbert who first observed the importance of crossing, in his work on the Amaryllidacece (1836). He says, " I am inclined to think that I have derived advantage from im- pregnating the flowers from which I wished to obtain seeds with pollen from another individual of .the same variety, or, at least, from another flower rather than its own, and espe- cially from an individual grown in a different soil or aspect." Mr. Darwin's work. On the Cross and Self Fertilisation of Plants (1876), placed on a scientific basis, by means of experimental verifications, the exact values of such crossings. His conclusions, however, require considei-able modifications. 312 THE STEUCTXJEE OF FLOWERS. They are trae for at least the first few years ; as in but foui' or five cases only did he exceed the third genei'ation ; and when he prolonged them to seven generations, as in Mimulus luteus, and ten in Ipomcea purpurea, his results began to assume a very different complexion. The inference deducible from his experiments is that careful and artificial crossing generally introduces a remark- able stimulas for a time; but the effects are not permanent. On the other hand, a perseverance in self-fertilisation pro- duces results which are much more stable ; so that, finally, self-fertilised plants (i.e the successive off-spring of this process) outstrip their competitors. Florists also find that by continued crossing the flowers of a species they soon reach the end of their tether, and no further progress is obtainable. Secondly, Mr. Darwin failed to realize the fact that self- fertilisation predominates in nature with the vast majority of hermaphrodite plants, whether they be adapted to insects or are inconspicuous and adapted for autogamy. Thirdly, he misinterpreted the meaning of degeneracy, which often accompanies self-fertilisation ; thinking that it involved constitutional injuriousness, of which there is no trace whatever in nature. Lastly,* he, and other writers who have followed him, wrongly inferred that adaptations to insect agency implied a converse "purpose," viz. to avoid self -fertilisation, instead of regarding them as the inevitable results of the stimulus of intercrossing and of the visits of insects. The danger of this o priori, deductive, or teleological reasoning, without any attempt at verification, lies in the fact that it is untrust- • I mnet refer the reader to my paper on The Self-fertilisation of Plants, in which. I have dealt with these points. It was written in 1877, but I have met with nothing since to invalidate the above couolusions, but, on the contrary, very much in support of them. THE VARIETIES OF FERTILISATION. 313 worthy. It may or may not be trae ; but it is of no value unless thoroughly tested by experiment aud verified. Thus, for example, Mr. Darwin, in speaking of the movements of the stigmatic lobes of Mimulus, says " Mr. Kitchener has ingeniously explained the use of these movements, namely, to prevent the self-fertilisation of the flower." He, however, experimented with this plant, and then discovered that " if insects are excluded the flowers fertilise themselves perfectly, and produce plenty of seed." * Again, it has been argued that we are justified in assum- ing that the remarkable adaptations to insects, which are so obvious in many flowers, must he of some use to the plant, even though we may not be able to discover it. This state- ment, however, is just as much an d priori and deductive assumption as the preceding, and is quite valueless until verified ; and it is only by means of such experiments as Mr. Darwin laboriously carried out, that the real value of inter- crossing and self-fertilisation or other kind of union can be ascertained. Thus, e.g., the Garden Pea is undoubtedly adapted to insects, like other irregular flowers ; but experi- ments proved that " a cross between two individuals of the same variety does not do the least good to the offspring, either in height or fertility." f * Cross and Self Fertilisation, p. 64. Ab another iDstance of an d prion deduction, Sachs says of Epipactia latifolia, " The flower left to itself does not get fertilised, for the pollen-masses do not spontaneonsly fall out of the anther ; and eren if they did, woald not come on to the stigmatic surface " (,Veg. Phys., p. 796). Mr. A. D. Webster, however, has observed that E. latifolia is very imperfectly fertilised, for, although visited by insects, cross-fertilisation seldom takes place j that "self- fertilisation by the pollen "falling spontaneously on the stigma is not nncommon, as the pollen-masses . . . become friable, and before the plant withers, either spontaneously or by the action of the wind fall on the stigma" (Bot. Oaz., xii., p. 104). t L.C., p. 264. 29 314 THE STRUCTURE OF FLOWERS. Moreover, however greatly we may feel impressed with the truly wonderful adaptations of flowers, a careful and critical study of them reveals many features which seem to counterbalance, to some degree at least, the " good " we may in the first instance be inclined to assume as self- evident. Indeed, the disadvantages accruing from great differentiations in adaptation to insect agency are really too important not to have been frequently noticed. Such are, "hercogamy," or the mechanical obstruction to self -fertilisa- tion, as in Orchids ; the physiological barrier, as in Linuni perenne ; the absence of insects required to fertilise a flower, as is the case with Convolvulus septum in England, which rarely sets seed, as Sphinx Convolvuli is a rare insect ; the frequent absence of bees, etc., in inclement weather, when Clover sets but little seed, to the great loss of the farmer ; when certain flowers are neglected for greater attractions, as may be often seen when bees keep persistently to one species of plant and pass over others ; the frequency with which bees perforate tubular flowers without pollinating them at all. Again, Muller points out * that while honey- seeking insects may legitimately cross heterostyled plants, pollen-seeking insects have no need to thrust their heads or probosoides down to the stigma of the shoi-t-styled forms ; hence such tend to bring about illegitimate unions of the long-styled forms only. This, he thinks, may be a cause of the greater fertility of that kind of union f Lastly, the more highly differentiated a flower Is, the less is its number of insect visitors and the rarer may it become in nature. Thus orders of plants with easy access to the honey are some of the most abundant, as Banunculaaece, GomposU(B,X * Fertilisation, etc., p. 387. f See above, p, 206. J The enormous numbep of species and vid© diSnsion of the Com- posite are proofs of the advantages accruing to it from the (jecnliar THE VARIETIES OF FERTILISATION. 315 and UmheUiferce ; as well as are those dependent upon the wind, which never fails, such as Willows, Gyperacece, and Grasses. On the othei* hand, all regularly self-fertilising plants are abundant, and, together with certain wind- fertilising plants, are cosmopolitan. Although the idea that self-fertilisation is injurions is certainly not held now by botanists in so absolute a form as Mr. Darwin often stated it, yet it will not be amiss to point out the want of agreement between his conclusions and his own experiments. In a chapter on " General Results," * he commences by saying : " The first and most important of the conclusions which may be drawn from the observations given in this volume, is that cross-fertilisation is generally beneficial, and self-fertilisation injurious. This is shown by the difl'erence in height, weight, constitutional vigour, and fertility of the offspring from crossed and self-fertilised flowers, and in structure of the flowers ; first, in being adapted to a great variety of insects. Thus, on ten species of plants, Miiller detected 54S species of insects, in the following proportions, Lepidoptera, 15 p.c. ; Apidse, 41 p.c. ; Diptera, 27 p.c. ; other short-tongned insects, 17 p.c. Bees, therefore, are the chief visitors. This is almost invariably the rule : the only species mentioned by Miiller in his table in which short-lipped insects surpass in number the Apidse is Chrysanthemum leucanthemum, which has a corolla tube, 3 mm. in length, in which the honey rises up into the widening throat and is easily accessible. The number of Lepidoptera is in the proportion of 6'9 p.c. ; Apidffl, 16"6 p.c. ; Diptera, 38"9 p.c. J others, 37'5 p.c. In Achillea Millefolium, with a corolla tube of 3 mm., Lepidoptera are 6"9 p.c. ; Apidae, 34'5 p.c; Diptera, 24'1 p.c, and others, 34 '5 p.c. Lastly, in Centaurea Jacea, with a tube of 7 to 10 mm., the Lepidoptera rise to 27 p.c. ; Apidse, 58*7 p.c. ; while Diptera sink to 12'5 p.c, and other short-lipped insects are only 2 p.c. The CompositcB thus well illustrate the fact that tubes are propor- tionate in length to the more specialized insects, u universal feature seen in all other orders as well. * Cross amd Self Fertilisation of Plants, p. 436. 316 THE STRUCTXJBE OF FLOWERS. the number of seeds produced by the parent plants. With respect to the second of these two propositions, namely, that self-fertilisation is generally injurious, we have abundant evidence. The structure of the flowers in such plants as Lobelia ramosa. Digitalis purpurea, etc., (1) renders the aid of insects almost indispensable for their fertilisation ; and bearing in mind the prepotency of pollen from a distinct individual over that from the same individual, such plants will almost certainly have been crossed during many or all previous generations. So it must be, owing merely to the prepotency of foreign pollen, with cabbages and various other plants, the varieties of which almost invariably in- tercross when grown together. The same inference may be drawn still more surely with respect to those plants, such a.s Beseda (2), and Eschscholtzia (3), which are sterile with their own pollen, but fertile with that from any other individual. These several plants must therefore have been crossed during a long series of previous generations, and the artificial crosses in my experiments cannot have increased the vigour of the offspring beyond that of their progenitors. Therefore the difference between the self-fertilised and crossed plants raised by me cannot be attributed to the superiority of the crossed, but to the inferiority of the self- fertilised seedlings, due to the injurious effects of self- fertilisation." Mr. Darwin then proceeds to discuss the first proposition, " that cross-fertilisation is generally beneficial," so that we may conclude that the preceding quotation represents the author's reasoning and conclusions on the idea of there being some " injuriousness " in self-fertilisation. In the first place, it may be observed that the reason why Mr. Darwin's crossings yielded at first more marked results in height, fertility, etc., is because plants are never THE VARIETIES OF FERTILISATION. 317 80 carefully crossed in nature, nor self-fertilisation so carefully prevented, as was the case in his experiments. The probability is that the two processes are much more mixed in nature in the case of most plants. Therefore, by his experiments the more unalloyed influence of crossing brought about a much more enhanced stimulus than ever occurs in the wild state. Moreover, the prepotency of foreign pollen, upon which he lays stress, is a purely relative phenomenon ; for whenever self-fertilisation yields more seeds than intercrossing, as is often the case, it is a just inference that the pollen "of the saoie flower " is then prepotent, in its turn. Indeed, Mr. Darwin actually found that in some cases intercrossing did no " good " at all, as in the case of the Garden Pea mentioned above, and in Oanna Warscewiczi, etc. I will now add some observations upon certain points I have numbered in this paragraph. (1) That Lobelia ramosa and Digitalis purpurea, and many others given in a "List of Plants Sterile without Insect-aid," * cannot readily fertilise themselves unless the flower be disturbed in some way, is, per se, no proof that self-fertilisa- tion is injurious ; for the flowers of many of such plants are fully self-fertile when artificially assisted. Thus, Mr. Darwin says that although Lupinus luteus and L. pi-losus seed freely when insects are excluded ; yet Mr. Swale, of Christchurch in New Zealand, found Lupins only formed pods of seed when the stamens were artificially released, as they are not there visited at all by bees.f The interpretation of this fact, so well known that the term " hercogamous " J has been invented for it, I take to be an immediate result of * Cross and Self Fertilisatian, etc., p. 357. t L.c, p. 150, note. J If I remember rightly, by Brrera ; see BuU, de la Soc. Bot. de Beilg., rrii. (1887). The term means a " fenced-off union." 318 THE STRUCTURE OF FLOWERS. the action of insects. I have given reasons for believing, and the reader can readily suggest other instances, that structural peculiarities have grown in response to pressures and thrusts made upon the floral organs by the insects themselves ; and that such have sometimes produced protuberances or obstructions in the way of the emission of the pollen upon the stigma of the same flower, is no more than might be anticipated to be extremely probable. Thus one of the most remarkable is the rostellum of Orchids, believed to be a modified stigma now converted to a new use. In nearly all Orchids this blocks up the way of access to the stigmatio chamber, while the pollen masses recUne on the roof over it, so to say; but when Orchids become self-fertilising or even cleistogamous as well, this is often brought about by the degradation of the rostellum ; so that the pollen masses can then easily slide over the summit of the stigmatic chamber and fall into it at once. When they do so they are fully self-fertile, as Mr. Henry 0. Forbes has shown.* Some few plants are quite barren with their own pollen, even when artificially placed upon the stigma ; though Lobelia and Digitalis do not belong to the group. These, as shown elsewhere, can and often do become fully fertile at other places and seasons, and are thereby benefited by acquiring the possibility of setting seed by self-fertilisation, as otherwise they might set none at all. There are, then, three kinds of barriers to self -fertilisation : one mechanical, as in Orchids ; a second, that of time, when e.g. a flower is so strongly protandrous that the pollen is all shed before the stigmas are mature ; and, thirdly, a physiolo- gical one, when the pollen is actually impotent on the stigma of the same flower, even though it be homogamous. • On the Contrivances for insuring Self-fertilisation in some Tropical Orchids, Jonm, Linn. Soc, xzi., p. 538. THE VAEIETIES OF FERTILISATION. 319 In no case is it logical to say that such, arrangements are to prevent self-fertilisation. We may well ask why are a comparatively few plants thus provided for, and yet the vast majority are not. If, however, we regard them as results of differentiation brought about by the stimulus of insect agency — so that in certain places hypertrophy has set in and rendered the flower hercogamous, in others the andrcBcium is so stimulated and its development so hurried on that the flower becomes protandrous, or its pollen so highly differentiated as to become like that of a distinct species, — we have a reasonable interpretation for these phenomena. Moreover, not one of them is absolute or stable. Thas a hercogamous Orchid can become self-fertilising ; * • Since the above was in type, Mr. H. N. Eidley has read a paper, at a meeting of the Linnean Society (Feb. 16, 1888), on "The Self- fertilisation of Orchids," in which he arrives at the same conclnsions as Mr. H. 0. Forbes (see above, p. 253, note), finding that the process is effected in several ways, especially, perhaps, by the degeneration of the rostellum. Moreover, the Orchids which he discovered to be capable of fertilising themselves are not only the most nnmerous in individuals, but are also the most widely dispersed of the genera to which they respectively belong. He also corroborates Mr. Forbes's observations, that Orchids set bnt a small percentage of their fmit, although fully exposed to the visits of insects. Mr. H. Veitch has also contributed a, valuable paper on the " Hybridisation of Orchids," in which he appears to corroborate M. Gnignard's observations in every particular (see above, Chap. XVIII.). The reader will take note of the significance of the fact that when Mr. Darwin published his work on " The Fertilisation of Orchids," it was thought that no flowers could equal them in their remarkable adaptations for securing the benefits of intercrossing by insect agency, and in their methods of "preventing self-fei-tilisation." Yet, of all flowering plants, evidence now tends to show that they set the least amount of seed, even when fully exposed to insects ; while the order has furnished materials for two important papers on the many forma and ways by which self -fertilisation is secured in different genera. 320 THE STRUCTURE OF FLOWERS. the strongly protandrous Carnation can be made to be highly self -fertile, as Mr. Darwin showed; and Linum perenne can have its pollen so modified as to set seed abundantly in the same flower, as occurred -with Mr. Meehan in Philadephia, though it was physiologically impotent in England. It is, in fact, so to say a mere accident that mechanical and physiological barriers exist at all ; and it is only by experiment that one can discover whether a flower so conditioned may not be really capable of self-fertilisation all the time. Indeed, Mr. Darwin's experiments have abundantly shown that self-fertilising properties are quickly reacquired, whenever the process is persevered with. For example, EschscholUia Galifomica was "absolutely self-sterile" in Brazil. Mr. Darwin, however, by self-fertilising it in Eng- land, raised the fertility in two generations to nearly 87 p.c. When he asserts that his artificial crossings could not have increased the vigour of the offspring, and therefore all differ- ences must be attributed to the inferiority of the self-fer- tilised, this argument wonld apply to a certain number of his experiments in different degrees, viz., with plants normally self-sterile ; but he ignores the fact that, as soon as he tried to raise a stock of self-fertilised plants, the latter steadily gained upon the offspring of the crossed, till they equalled or surpassed them, or else would have done so had the experiments been continued. Thus, with regard to Lobelia ramosa, the ratio of heights of the " intercrossed " to the " self-fertilised " offspring of first generation was 100 : 82 ; and the proportion of seeds as 100 : 60. In the second year, those growing under what he had proved to be the most disadvantageous condition for self-fertilised seedlings, namely, being crowded, the ratio of the heights became as 100 : 883. The experiment, unfortunately, was not continued further. THE VAEIETIES OF FERTILISATION, 321 Comparing this plant with L. fulgens, which is also quite sterile without aid, and, according to Gartner, is "qnite sterile with pollen from the same plant, though this pollen is efficient on any other individual," * Mr. Darwin suc- ceeded in raising self-fertilised plants by keeping the pollen of a flower in paper till the stigmas were ready, as it is strongly protandroas. The heights of the offspring were as 100 : 127, and Mr. Darwin adds, " the self-fertilised plants [in two out of four pots] were in every respect very much finer than the crossed plants." In the next generation he used pollen from a different flower on the same plant to represent self -fertilisation. In this case those " self-fertilised " were only 4 p.c. below the crossed, the ratio being as 100 : 96. The conclusion, then, is that self-fertilisation pure was the best ; intercrossing distinct plants, less so ; and crossing on the same plant, the least. Dianthus, like Lobelia fulgeni, is strongly protandrous ; but in the third generation the proportional number of seeds per capsule was as 100 ; 125. " This anomalous result is probably dae to some of the fertilised plants having varied so as to mature their pollen and stigmas more nearly at the same time than is proper to the species " (p. 135). Exactly so. The conclusion I would draw is, therefore, not that self- fertilisation is per se in any way injurious, but that flowers which are normally sterile, by having become so highly differentiated through insect stimulation, do not now spon- taneously set seed ; and self-fertilisation is not so efficient as crossing. As soon, however, as the former process is persevered with, signs are not wanting of nature's showing even an eager response to it, till the results are often far superior to those normally obtained by intercrossing. • Cross and Self Fertilisation, etc., p. 179. 322 THE STRUCTURE OF FLOWERS. If flowers, unlike the preceding, are normally very self- fertile, as Ipomoea and Mimulus proved to be, then it appears that intercrossing supplies a remarkable stimulus, and the intercrossed beat the self-fertilised for a time. Sooner or later, however, the efFect of the stimulus gi-adually dis- appears, and self-fertilisation reasserts itself. Thus with IpomoBa purpurea Mr. Darwin raised crossed and self- ferti- lised plants for ten generations ; and the heights of the latter were 24, 21, 32, 14, 25, 28, 19, 15, and 21 p.c.,* respec- tively, less than the crossed. Grouping these into threes, the ratios become 100 : 74-3 ; 100 : 77-6 ; 100 : 81-6. That is to say, the intercrossed were steadily declining ; for if the self- fertilised be regarded as 100, then the ratios of these to the crossed appear as follows : 100 : 134 ; 100 : 129 ; 100 : 121 Similarly with regard to fertility, the ratio of that of the intercrossed plants to the self-fertilised was for the first and second generations as 100 : 93 ; for the third and fourth, as 100 : 94 ; for the fifth, as 100 : 106 ; and the eighth, as 100 : 113. Hence the self-fertilised were superior. Mimulus luteus gave analogous results. The crossed plants (i.e. offspring of crossings) surpassed the self-ferti- lised until the fourth generation, when several plants of the latter assumed a taller character, with whiter blossoms. This self -fertilising form " increased in the later self -ferti- lised generations, owing to its great self-fertility, to the com- plete exclusion of the original kinds." f " It transmitted its character faithfully, and as the self -fertilised plants consisted exclusively of this variety, it was manifest that they would always exceed in height the crossed plants." J • These numbers correspond to the first nine years. The tenth gives 46; bnt Mr. Darvrin thinks this number to hare been accidental (p. 41). t Gross and Self Fertilisation, p. 67. J Ibid., p. 70. THE VARIETIES OF FERTILISATION. 323 (2) With regard to Reseda and EschschoUzia, his observa- tions are also somewhat misleading. Mr. Darwin experi- mented with a. lutea and B. odorata. They are both very- capricious. Of Bi. lutea some individuals were absolutely self-sterile, whether left to themselves or artificially polli- nated, while a few produced self-fertilised capsules. Simi- larly with Bi. odorata, when protected by a net some plants were loaded with self -fertilised capsales, others produced a few, and others, again, not a single one. Miiller,* however, found that " plants which are kept protected from insects, yielded capsules filled with good seed." The inference from this variability in the fertility of difierent individuals in the same year, is that it is an accidental peculiarity of some to be more or less self -fertile than others ; and that it was due to varying degrees of nutrition affecting the essential organs. We know now that plants frequently vary in their degrees of fertility, both at different seasons of the year,t and in different years or localities, according to climate, con- ditions of soil, etc. In any case, the self-sterility of these plants is by no means so absolute as to justify the belief of their having never been self-fertilised for years. Let us now turn to Mr. Darwin's experiments. Beseda lutea. The ratio between the heights "of the crossed plants and those of the self -fertilised were as 100 : 85, the weights as 100 : 21, when the plants were grown in pots. When grown in open ground they were nearer equality, viz., in height, as 100 : 82, and in weight (a better test than height), as 100 : 40. Differences in fertility are not given, and, therefore, presumably not striking. * Fertilisation, etc., p. 116. t Mr. Darwin says Papaver vagum, included in the list of plants Bterile without insect aid, produced a few capsules in the early part of the summer ; see above, Ohap. SXT., on Sexuality and Environment. 324! THE STEUCTURE OF FLOWERS. Beseda odorata. The results of plants grown in pots were as follows, the proportions being taken as before. The heights were as 100 : 82; weights as 100 : 67; while their heights when the plants were grown in the open were as 100:105.* He next raised seed by crossing some flowers and self- fertilising others on the same plant of a particular semi- self-sterile individual. From these the seedlings gave the following results : heights as 100 : 92 ; weights as 100 : 99 ; fertility as 100 : 100. These results show that the difEerences have practically vanished ; the weight being a much better test than height, as it points to greater assimilative powers, and leaves nothing to be desired. It is difficult, then, to see how Beseda furnishes data for any argument raised to prove the existence of injurionsness in the self-fertilisation of plants. Indeed, Mr. Darwin him- self observes : " I expected that the seedlings from this semi-self-sterile plant would have profited in a higher degree * Mr. Darwin remarks upon this result as follows : " We have here the anomalous result of the self-fertilised plants being a little taller than the crossed, of which fact I can offer, no explanation. It is, of course, possible, but not probable, that the labels may have been inter, changed by accident " (Cross, etc., p. 121) . In my paper (p. 383) referred to I have shown that it was most generally the case that while a close competition in the same pot proved disadvantageous to the self-fertilised seedlings, yet, when they had no competition, the differences were not nearly so marked. There are apparently but two alternatives to appeal to in order to account for the fact that intercrossed plants are not so greatly superior to the self-fertilised when planted in open ground, as when in competition in pots ; viz., either the intercrossed plants become deteriorated on being planted in open ground, which is absurd, or else the self-fertilised must regain or acquire vigour in a relatively greater degree than do the intercrossed, and thus would seem to evince what might be called u greater " elasticity '' of growth than their intercrossed competitors. THE VARIETIES OF FERTILISATION. 325 from a cross than did the seedlings from the fully self-fertile plants. But my anticipation was quite wrong', for they profited in a less degree : " * — really not at all, for the self- fertilised were superior. " An analogous result followed in the case of Eschsclioltzia, in which the offspring of the plants of Brazilian parentage (which were partially [said to be " absolutely " so, on p. Ill] self-sterile) did not profit more from a cross, than did the plants of the far more self-fertile English stock." * Mr. Darwin commenced his experiments by saying, " This plant is remarkable from the crossed seedlings not exceeding in height or vigour the self-fertilised. On the other hand, a cross greatly increases the productiveness of the flowers on the parent-plant, and is sometimes necessary in order that they should produce any seed. Moreover, plants thus de- rived are themselves much more fertile than those raised from self-fertilised flowers ; so that the whole advantage of a cross is confined to the reproductive system." t Twelve flowers crossed produced eleven good capsules, containing 17'4 grains of seeds ; eighteen self-fertilised flowers produced twelve good capsules, containing 13'61 grains: therefore the ratio of fertility was as 100:71. In the first season the heights were as 100 : 86. Being cut down, the next season, they were reversed, " as the self- fertilised plants in three out of four pots were now taller than and flowered before the crossed plants." " In the second generation, eleven pairs were raised and grown in competition in the usual manner. The two lots were nearly equal during their whole growth, or as 100:101. Thei'e was no great difference in the number of flowers and capsules produced by the two lots, when both were left freely exposed to the visits of insects." • Cross and Self Fertilisation, p. 121. t i-c, p. 109. 30 326 THE STEtJCTUKE OF FLOWERS. This conclades his experiments with English plants ; and though crossing did little or no good, and the first average of heights, viz. 100 : 82, he thinks were accidental, the conver.se proposition, that self-fertilisation was injurious, is in no way proved. It would be just as logical to say that, since the self-fertilised plants grew more vigorously after both were cut down, that crossing must have weakened the constitution of the crossed seedlings. Or, again, from the second year's results, we might justly conclude that the two effects were quite identical. He next experimented with seed the parents of which had been cultivated in Brazil, in which country Fritz Miiller had found them to be "absolutely self-sterile with pollen from the same plant, but perfectly fertile when ferti- lised with pollen from any other plant." Seeds raised from these in England " were found not to be so completely self- sterile as in Brazil." The average number of seeds prodnced in the capsules borne on the intercrossed and self-fertilised plants of Brazilian origin were 80 and 12 respectively in the first year; that is in the ratio of 100 : 15. With regard to the second generation, or grandchildren, next raised, Mr. Darwin observes : " As the grandparents in Brazil absolutely required cross-fertilisation in order to yield any seeds, I expected that self-fertilisation would have proved very injurious to these seedlings, and that the crossed ones would have been greatly superior in height and vigour to those raised from the self -fertilised flowers. But the result showed that my anticipation was erroneous ; for as in the last experiment with plants of the English stock, so in the present one, the self-fertilised plants exceeded the crossed by a little in height, viz., as 100 : 101." In the next year the average number of seeds per capsule of the crossed and self-fertilised was as 100 : 86-6 ; so that the THE VARIETIES OF FERTILISATION. 327 relative fertility of the self-fertilised had risen from zero in Brazil to 15, and then to 86'6 p c, in comparison with the crossed regarded as 100. He now made crossings between the offspring of the Brazilian plants and the English-grown plants, with the following results : — First, as to heights, — The English-crossed to the self -fertilised plants 100:109 The English-crossed to the intercrossed * plants 100: 94 The intercrossed to the self -fertilised plants ... 100:116 Secondly, as to weights, — The English-crossed to the self-fertilised plants 100:118 The English-crossed to the intercrossed plants ... ... 100:100 The intercrossed to the self -fertilised plants 100:118 Three rows of plants of each kind grew in the open ; and here also the self-fertilised grew taller than the others. Moreover, all except three of the self-fertilised were killed by the winter. " We thus see that the self -fertilised plants which were grown in the nine pots were superior in height (as 116 : 100) and in weight (as IIS : 100), and apparently in hardiness, to the intercrossed plants derived from a cross between the grandchildren of the Brazilian stock. The superiority is here much more strongly marked than in the second trial with the plants of the English stock, in which the self- fertilised were to the crossed in height as 101 : 100. It is a far more remarkable fact . . . that the self-fertilised plants exceeded in height (as 109:100), and in weight (as 118 : 100), the offspring of the Brazilian stock crossed by the English stock." • "Intercrossed" signifies the offspring of the Brazilian plants crossed with one another. 328 THE STRUCTURE OF FLOWERS. "WTien we look back and remember that the plant was " absolutely self-sterile " in Brazil, and compare that fact with these final results, it is difficult to see how self-fertilisa- tion can be charged in any way with injuriousness. Though the results may have shown little or no advantage from crossing, it does not follow " that the differences," namely greater height, weight, or fertility of the self-fertilised, were attributable " to the inferiority of the self-fertilised seedlings, due to the injurious effects of self -fertilisation." On the other hand, the facts appear to warrant the conclusion that this north-temperate plant became barren in Brazil in consequence of the hot climate ; that the recovery of its self-fertilising powers was due to the English climate better suiting it ; that it at once responded to the effort, so that its self-fertility rose in two generations from to 86'6 p.c. The plants, too, thus raised showed nothing to indicate any constitutional derangement that might, with any show of reason, be attributable to self -fertilisation. From the preceding observations upon Mr. Darwin's reasoning, I think the reader will now see that it is not so conclusive in proving the existence of any injuriousness in self-fertilisation as he appeared to think. This chapter was already in type when I met with the following passage in " The Life and Lettei'S of C. Darwin," written in May, 1881 : " I now believe . . . that I ought to have insisted more strongly than I did on the many adap- tations for self-fertilisation, though I was well aware of many such adaptations." With regard to the values of other kinds of fertilisation, 1 must refer to Mr. Darwin's works ; for it is beyond my purpose to discuss them, as they have no special bearing upon the origin of floral structures. CHAPTER XXXII. FERTILISATION AND THE ORIGIN OF SPECIES. The Origin of Species by Insect Agency. — The attractive features of flowers being now well recognized as correlated with insect agency in fertilisation, the question arises, How have they come into existence ? We may suppose that a plant bore seedlings, some of which had, we will say, the corolla accidentally (that means from some unknown cause arising from within) larger on one side than another ; and then such a flowex', being selected by insects, left offspring which, by gradual improvement through repeated selection, ultimately reached the form it now possesses. As an alternative, we may suppose that the first impulse came from without, and induced by the insect itself; so that the variation once set up in a definite direction, went on improving under the constantly repeated stimulus of insect visitors until the form of the flower was actually con- formable to the insect itself. The process of evolutionary development might perhaps be much the same under either supposition, but the latter hypothesis has more than one advantage. First, in the assignment of a direct physical cause for the incipient change, instead of some incidental and unaccountable variation, which must be assumed by the former. Secondly, the theory does not require the plant to make an indefinite number of 330 THE STEUCTUBE OF FLOWERS. less useful changes or variations, only to be discarded at each generation for the one form that was wanted. Thirdly, as a great number of flowers would be visited, both on one plant and on many surrounding individuals in the neigh- bourhood, great numbers might bear offspring advancing more or less in the same direction ; and there would be no fear of extermination, even if some happened to be crossed by the parent form. Indeed, the varying offspring would largely supersede the parent form in number altogether, if they sprang up at one place without emigration. If we supply the additional aid of isolation, many other influences would be brought to bear upon them, and they would be free to vary without any interference from the parent stock. Mr. Darwin has abundantly shown that when a plant is crossed, and its seedlings strugijle in a confined place with those derived from flowers which have not been crossed but artificially self-fertilised, they generally succeed in mastering the latter ; so that if there be any struggle with the seedlings of a self-fertilised parent, such a struggle for life is mainly during the early period of growth, before any varietal or specific characters of the flowers have put in an appearance at all. For it is only in the youthful stages that the greatest contest is maintained ; and the result depends largely upon constitutional, and not at all upon specific, that is morpho- logical characters, mostly taken from the flowers. Now, Mr. Darwin has shown that such constitutional vigour does very generally accompany at least the first few years of crossing. So that we have a vera causa of the success of such newly crossed plants in the preliminary struggle for life. It need hardly be remarked that if insects thus start a new variety, they are crossing the flowers at the same time. It is trae that the stimulus of crossing does not last for FERTILISATION AND THE ORIGIN OF SPECIES. 331 many years ; but it is probably all tliat is wanted to give the crossed plant the ascendancy wben starting ou an evolu- tionary career. As an illustrative case of a struggle between two varieties, I took the same quantity of English-grown " Revett's " wheat and Russian " Kubanka," the former having a pre- ponderance of starch and the latter of gluten, being a smaller and harder grain. I sowed them as thickly as possible on a square yard, the two kinds having been previously well mixed together. They all germinated, and the struggle of course became intense. About twenty ears only were pro- duced, which were all Kubanka. The experiment was repeated a second year, with the same result. This is what I would consider as, therefore, doe to " constitutional selection." Survivors, however, are by no means entirely dependent upon constitution, much less on specific differences ; for seeds which fall on the circnmferenoe of the crowd, or on a better soil than that upon which others may happen to lie, as on stony ground, are thereby " selected," but it is through no merit of their own, as in any way being the fittest, for they survive only because they are the " luckiest ; " just as out of the thousands of eggs of a salmon a few only escape the jaws of their enemies : so that simply " good luck " plays an important part in determining which shall survive and come to maturity in both kingdoms alike. Hence, during the period of life when the straggle for existence is most intense, there are varions circumstances which determine what plants shall survive ; and in probably few cases, generally no case, have the morphological variations or specific characters any voice in the matter of selection whatever, excepting indirectly, as stated above, whenever constitutional vigour is correlated with first crossings. 832 THE STRUCTURE OF FLOWERS. The diflBculty which Mr. Romanes has felt in the struggle for fife through the swamping effect of a varying offspring being crossed with the parent form, seems to mc to be illusory as far as most flowering plants are concerned.* For not only do the majority of new forms arise through transport of seeds to a new and distant locality, but even at home, if the plant be at all responsive, so many seedlings, perhaps all, will tend to be differentiated at the same time and in the same way, that the parent form will soon be in a minority, and if now neglected by insects may die out through " insect- selection " of the new form. According to the old view, that plants are varying spon- taneously in all directions, and that only a few are selected by insects, the difficulty has long been felt that dangers of all sorts must surround the offspring of those few. Let us reverse the process, however, and let the insects themselves be the cause of changes set up in the flowers in the adaptive directions, and the responsive power of the flower itself will soon develop the best forms. These run no risk of being lost, through the multitude of offspring. Hence, if my theory be true, physiological selection, which I cannot find horticul- turists are inclined to accept, is not needed at all. Suppose some prevailing insect to have begun to set up incipient changes for a new variety, which then becomes dis- persed ; since many of the offspring will possess the new adaptation, and several other kinds of insects will visit the flower in different places, as the seeds happen to get trans- ported, the result will be, that while the original species of insect induces the descendants of the plant at home to vary in adaptation to itself, others are at work elsewhere, • Fritz Miiller found the genus Abutilon and a species of Bignonia to be more or less sterile with parental pollen. See Miiller's FeriiUsation, etc., pp. 145, 466. FERTILISATION AND THE ORIGIN OF SPECIES. 333 modifying the same incipient alterations to suit themselves. Hence, as sooq as isolation by migration has taken place, it is the presence of other insects which determines the develop- ment of other varieties. All, however, are based on the same plan of departure. In this way many vai-ietal and subsequently specific forms of the same genus will arise; and the further they travel from the parental home the greater, perhaps, will be the specific differences; and thus can representative species be accounted for, especially among conspicuously flowering plants. On the other hand, the perpetually self-fertilising species which alone, as a rule, are cosmopolitan, are almost identical in form, or at least have a minimum of differences between them, and snch as may possibly be accounted for by climatal causes alone. DiFFiCDLTiES OF NATURAL SELECTION. — The greatest difiB.- culty I have always felt in the idea that a plant was selected because it had some floral structures more appropriate than others, lay first in the fact that the principal period of the straggle for life takes place in the seedliug stage, before any varietal and specific characters have appeared ; and, unless there were a large number of the seedlings which would ultimately bear the improved flower, or else a superior con- stitutional vigour be guaranteed to be correlated with the particular varietal characters to be preserved, these alone could have nothing to do with the survival of the fittest. Secondly, granting that the plant has succeeded in sur- viving till the flowering period, then why should so many minute details of floral structure be necessarily correlated ? If the loss of three out of five carpels in the LdbiatcB were due to natural selection, why should this go hand-in-hand with a multiplication of the ribs of the calyx, and the 334 THE STRUCTURE OF FLOWERS. pecnliar lipped and hooded corolla with the lateral position of the flower, etc.? We find in selecting peas arid beans great varieties among them, but next to none in the calyx and corolla, to which the horticulturist pays no attention. In nature, however, we often find in flowers regularly visited by insects innumerable and minutely correlated adap- tations in all the whorls, which must have all varied together to form such existing flowers. Now, the difficulty of their doing so without some common cause, which affects them all simultaneously, seems to me insuperable. If my theory, however, be accepted, it solves the whole mystery at once, as all the changes are set up by one prime cause, namely, the irritations of the insect in the case of all flowers adapted to insect-fertilisation ; while the absence of insects in regularly self-fertilised flowers, as well as anemo- philous ones, is sufficient to account for the atrophy which has afiected them, the present condition of such flowers having been the inevitable result. Hence, instead of speaking of the Origin of Species of Plants by Natural Selection, I would regard the survival of the fittest as first issuing from " Constitutional Selection ; " * while the origin of the floral specific characters is the result of the responsive power of protoplasm to external stimuli. These latter are infinitely various in kind and degree, as has been shown in the early part of this book. The result is, that while high differentiations occur in some directions, degrada- tions are met with in others, sometimes seen in different parts of the entire plant ; but not at all infrequently are both features observable simultaneously in one and the same floral • Of oonrse the cbances of less competition by growing on the oircum- ference of the batch of seedlings, by receiving a little more light, etc., aid in selecting, and Bometimes may determine, as stated above, those which shall sorvire. FERTILISATION AND THE ORIGIN OF SPECIES. 335 whorl. The phrase " natural selection " will therefore have been noticed as conspicuoas by its absence throughout this book. This is not because I would in the least deny tlie fact that vast numbers of seedlings perish while others sur- vive through that form which I have called " constitutional selection," which are thus " selected," and arrive at the flowering and fruiting stages; and, again, that of these latter many may set no seed through the neglect of insects, etc., and so perish entirely and leave no offspring, while others again survive and are selected. Why, however, I do not refer any particular structure to the action of natural selection is because I have always felt or perceived a danger in doing so. Natural selection is, as thus styled, an abstraction; and as long as we hide our ignorance of its concrete representatives, that is to say, the real causes at work to induce a change, we may fancy we understand all about it, while we may be in reality in profound ignorance. Professor Huxley remarked, in his lectures on the Origin of Species, that what we want is " a good theory of varia- tion." It is in the attempt to fill this hiatus that I have, step by step throughout this book, preferred to give what seemed to me a direct cause, mechanical, physiological, climatal, etc., for every structure ; which may bring us nearer to a comprehension of the direct interaction of cause and effect than the vague term " natural selection " seems capable of doing Thus, to take an example, Miiller refers the loss of the fifth stamen in Labiates to natural selection, but makes no statement how he supposes selection to have done it. On the other hand, I would prefer to attribute its absence to atrophy, in compensation with the hypertrophy of the corolla on the posterior side. I may be wrong, of coarse, but at all events I give a reasonable cause, which is a fertile one in bringing about alterations in the structure 336 THE STRUCTURE OF FLOWERS. of flowers; whereas "natural selection" leaves us exactly where we were before. Moreover, natural selection is made to cover exactly opposite processes ; for the formation of the enlarged lip, on the one hand, would be attributed to it, just as much as the elimination of a stamen altogether, on the other. Instead, therefore, of using this term as the cause of anything and everything, I prefer to attribute effects to hypertrophy, atrophy, resistance to strains, responsive action to irritations, and so on. If it be thought that natural selec- tion somehow underlies all this, the reader is at liberty to substitute the phrase; but, I must confess, it conveys nothing definite to my mind, while the others undoubtedly do. I do not wish the reader to suppose that my theory is altogether in opposition to Mr. Darwin's ; for it must not be forgotten that he himself laid great stress on the environ- ment as a cause of variability upon which, when once brought about, natural selection could then act. Thus he remarks : "To sum up on the origin of our domestic races of animals and plants. Changed conditions of life are of the highest importance in causing, variability, both by acting directly on the organisation, and indirectly by affecting the reproductive system. It is not probable that variability is an inherent and necessary contingent, under all circumstances. . . . Vari- ability is governed by many unknown laws, of which corre- lated growth is probably the most important. Something, but how much we do not know, may be attributed to the definite action of the conditions of life. [Under this I would include the definite action of insects exerted mechanically upon the organs of flowers.] Some, perhaps a great, effect may be attributed to the increased use or disuse of parts. [Compensation plays undoubtedly a very important part]. . . Over all these causes of Change, the accumulative action of Selection, whether applied methodically and quickly, or FEETILISATION AND THE ORIGIN OF SPKCIES. 337 unconsciously and slowly, but more efficiently, seems to have been the predominant Power." * If thus the variations of floral structures can be reasonably referred directly to external agencies, and we may speak of each as a cause instead of using the abstract expresssion " natural selection," there still remains the question. What has brought into existence the primary flowers themselves, which insects have subsequently modified into their present conditions ? The Origin op Flowees. — There are good reasons for regarding Gymnosperms — ^both from their extreme antiquity, as well as from points of structure showing affinity with the higher Cryptogams ; such, for example, as the Lycopodi- acece — as standing in some sort of way intermediate between the latter and Dicotyledons. Yet the connecting links are much wanted on both sides of them. As far as Coniferm and Gycadece can help us, we are strongly led to believe that they were primitively, just as they are now, anemophilous and diclinous ; though the subdioecious (?) Welwitschia has points of structure which seem to indicate its being a degraded state of an hermaphrodite pjant. This remarkable monotypic genus is, however, too isolated and unique to afford any safe point of departure on the road to Dicotyledons, so that with regard to the latter we are still driven to specu- lation alone. If, then, we are right in assuming Gymnosperms to have been always diclinous, and Dicotyledons to have arisen from some member of that group, then it is presumable that the first were diclinous, perhaps dioecious, and anemophilous as well. The general opinion seems to be that they were dioecious ; and Mr. Darwin thought that moncecism was the next step, and thence hermaphroditism was ultimately reached. * Origin of Species, 6th ed., p. 31. 31 338 THE STRUCTUfiE OF FLOWERS. Now, we must not forget that when a female flower is pollinated the effect of the impregnation by the pollen-tnbe is not only to create an embryo in the ovule, but to endow it potentially with its own sexuality ; so that the sexless embryo becomes potentially both male and female ; in as much as it may subsequently grow up to be solely a male or solely a female plant ; or else it may combine the sexes, either as a moncecious or hermaphrodite plant. Moreover, we now know that the resulting sex which appears in dioecious plants on maturity is largely, if not entirely, dependent upon conditions of nutrition, possibly aided by other and unknown influences. Consequently, we cannot say for certain whether the first Dicotyledons were not at least moncecious, if not hermaphrodite, since the former of these states prevails abeady in Gymnosperms, as in Pinus ; while the latter is hinted at in not infrequent monstrous conditions when the lowermost scales of the spiral series in cones of Abies excelsa, etc., are antheriferous, instead of being ovnliferons. * Such cases show that one (the male) sex can suddenly appear in the same spiral series as the other. And this is all that is wanted to form an hermaphrodite flower; for continuously spirally-arranged sexual organs are characteristic of many plants, such as of the Ranunculaceae ; and such a monstrous condition may simply be a reversion to a primitive her- maphrodite state. Hence appears the inherent possibility of the production of hermaphroditism without any slow evolutionary process at all ; but simply as a result of the conveyance of the male energy to the female plant, by the very act of pollination itself. Mr. Darwin, when speculating on the origin of herma- phroditism, wrote as follows: "By what graduated steps • Teratology, p. 192. FERTILISATION AND THE ORIGIN OF SPECIES. 339 an hennaplirodite condition -was acquired we do not know. But we can see that if a lowly organised form, in which the two sexes were represented by somewhat different individuals, were to increase by budding either before or after conjugation, the two incipient sexes would be capable of appearing by buds on the same stock, as occasionally occurs with various characters at the present day. The organism would then be in a monoecious condition, and this is probably the first step towards hermaphroditism ; for if very simple male and female flowers on the same stock, each consisting of a single stamen or pistil, were brought close together and surrounded by a common envelope, in nearly the same manner as with the florets of the Composite, we should have a hermaphrodite flower." * It is a singalar fact that Mr. Darwin never seems to have thought of Euphorbia, which tallies 'exactly with his hypo- thetical origin of a hermaphrodite flower ; but, unfortunately, a " blossom " of an Euphorbia is not regarded by botanists as a flower, but an inflorescence. It consists of a " single pistil," on its own pedicel, surrounded by many " siugle stamens," each on their own pedicels ; and are " brought close together and surrounded by a common envelope." Mr. Darwin's mistake resides in his supposition that hermaphroditism must have arisen from dicecism, by passing through monoecism ; so that he is obliged by this order of progress to consider a flower with stamens and a pistil to be made of separate flower-buds, i.e. to be axial structures with their appendages reduced to at least one of each kind. But from phyllotactical reasons, it is clear that the origin and arrangements of the floral members are entirely foliar. Al l that seems necessary for us to assume as the origin of a flower vrith a conspicuous coroUa or perianth, is a leaf-bud • Cross and Self Fertilisation of Plants, p. 410. 340 THE STKUCTUEE OF FLOWERS. of which some of the members have already differentiated into carpellary, others into staminal organs, the outer appendages being simply bracts, like, we will say, those surrounding the stamens or ovule of the Tew. As insects often come for pollen alone — as in honeyless flowers of Laburnum, Poppies, St. John's Wort, and Boses, — and then pierce the juicy tissues for moistening the honey, as they have been seen to do in Anemone, Laburnum, HyacinthSj Orchis, etc., we may, I think, infer with some probability that they did the same with the primitive flowers. Having once attracted insects to come regularly, then a multitudinous series of differentiations would follow. The corolla would in all probability be the first to issue out of the bracts, as being the next whorl to the stamens and as a result of stimulus ; other changes, already described under the Principles of Variation, would follow by degrees and in different combinations ; but in every case they would be due to the responsive action of the protoplasm in consequence of the irritations set np by the weights, pressures, thrusts, tensions, etc., of the insect visitors. Thus, then, do I believe that the whole Floral World has arisen. INDEX, Adelphous filaments, 57 ; imitated, 59 ; and nectaries, 58 Adhesion, analogies in animal king- dom of, 48, 88 ; principle of, 5, 78, seqq. ; rationale of, 80 ; of stamen to perianth, and origin of, 81, and to style (?), Aristolochia, (fig. 21) 83 ^tivations and phyllotazis, (fig. 3) 15 Alpine, dowel's, colours of, 176 ; strawberry, phyllody of, 301 Amaryllis, appendage to perianth, (fig. 41) 134 Androdicedsm, examples, explanation and origin of, 227 Androecium, explained, 4 ; irregu- larity in, origin of, 109 Anemophilons fiowers, 265, seqq. ; characters of, 268 ; cosmopolitan, 283 ; " long-lived " stigmas of, 269 ; pollen of, 266 Anemophily, and Greenland flora, 270 ; and cleistogamy, 264 ; and degeneracy, 266, 272; and hete- rogamy, 269 ; origin of, 266, 270, 272; and protogyny, 200, 269, 272 Anisomerous whorls, explained, 5 causes of disarrangement of, 45 Anthew, on bracts, (fig. 64) 288 connivent, of Violet, 60 ; conta- bescent, 275 ; on glumes, (fig. 65) 288 ; metamorphosed, 293, (fig. 81) 298, (figs. 83, 84) 302 ; stigma- tiferous, (fig. 76) 294; syngene- sious, and interpretation of, (fig. 11) 60; versatile, 266. 268 Ant-plants, hereditary effects of irri- tation in, 115, 142, 157 Appendages, in Amaryllis, (fig. 41) 134 ; and axis, homology between, 309 ; origin of floral, 133 Aguilegia vulgaris, arrangement of fioral whorls of, 22; number of parts in, 22 Arabis albida, leaf-traces of, (fig. 7) 39 Arctic flora, and anemophily, 270 ; and self-fertilisation, 259 Aristolochia, structure of flower, (fig. 21)83 Arrangement, causes of, 47 ; displace- ment of, by anlsomery, and substi- tution, 45 ; illustrations of, in JianuTWulaceiB, 21, seqq. ; principle of, 5, 139 Arrest, of carpels, 4, 8, 278 ; of carpels in Campanulacece, 44; of floral axis, 6 ; in free-central pla- centas, 72, seqq. ; of growth of ovary and seeds in Orchids, 169, 281, and in Willows, 170 Atragene, staminal nectaries of, (fig. 44) 141 Atrophy and hypertrophy in animal kingdom, 88 ; as causes of irregu- larities, 108 ; in compensation, 105 ; in zygomorphism, 116, seqq. 842 INDEX. Autogamy, explained, 198, 311. See Self-feTtilisation. Axis, and appendage, homology be- tween, 309 ; floral, cause of arrest of, 6 B Beta, formation of oTule of, (fig. 16) 73 Boughs, carrature of, due to strain, (fig. 39) 125 Bracts, petaloid, 286, (figs. 62, 63) 287 ; pistiloid (glumes), (fig. 65) 288 ; progressive changes in, 286 ; transitional forms of, in Hellebore, (Sg. 61) 286 Bulbs, origin of, from funicle, 310 ; from leaf-sheath, 310 Cabbages, excrescences on, homologous with ovules, 307 Calyx, arrest of, 8, 184, 194; pro- gressive metamorphosis of, 288 j •tube, 89, seqq. iSee Sepals. Campamila medium, anatomy of flower of, (fig. 8) 43, (fig. 15) 71 Campamiiaceae, arrangement of carpels in geDei*a of, 44 Capparidew, androecinm of, and sym- metry in flower of, 33 Carpels, arrest of, 4, 8, 278 ; in Cam- panulacea, 44 i cohesion of, 62 ; decrease by compensation, 21, 278 j phyllody of, 302 ; superposition of, 44, seqq. ; typical number of whorls of, 4. See Pistil. Carpophore, placental origin of, 72 Cell-division and light, 154 Cell-wall, thickening of, to resist pressure, 127 Centaurea, adaptations for fertilisa- tion, (fig. 11) 60; and sexuality, 240 Change of symmetry, 18, 186 Chorisis, and arrangement, 24, 39, 44, 46 ; multiplication of stamens by, 44, and of carpels by, 44, 308, and of ovules by (in Orchids), 309 Cleistogamy, and anemophily, 264 ; and degeneracy, 251, seqq. ; and en- vironment, 263 ; explained, 198; in flowers, 251 ; illustrations of, 257- 262 ; in Impatiens, (fig. 58) 261 ; in Lamium, (fig. 59) 261 ; origin of, 262-264; in Oxalis, (fig. 57) 260; in Salvia, (fig. 60) 262; in Violets, (figs. 55, 56) 257, 258 Cohesion, of carpels, 62 ; illustrations of, 49, 50 ; origin of, 50 ; of petals, 56, in Fhyteuma, (fig. 9) 50; principle of, 5, 48 ; of sepals, 54 ; of stamens, 57 , to resist strains, 51, 53 ; varieties of, congenital and by contact, 48 Colours, of Alpine flowers, 176 ; changes in, 176 ; and darkness, 177; effect of crossing on, 178 ; effect of salts on, 175; of flowers, 174; and insects, 182; laws of, 174; nutri- tion and, 178 ; origin of, 178 ; as pathfinders, 178, and arrest of, 253 , white and pale tints, and self-fertilisation, 253; whole, and self-fertilisation, 183 Compensation, in adaptations of flowers, 105, 117; atrophy and hypertrophy in, 105; increase of seeds and decrease of carpels by, 21, 278 ; in irregular flowers, 103, seqq. ; in rudimentary organs, 284 Conducting tissue, of Orchids, 165 ; origin of, by irritation of pollen- tube, 165, seqq. ; structure of, (flg. 50) 164 ConifercB, foliage of, adnate and free, 84 ; origin of flowers aud the, 337 Connivent anthers, of Violet, 60 Coutabescence of anthers, 275 Cords, fibro-vascular, alteration in orientation of, 64, 65; as floral units, 300, 308, 309 ; in flower of Campanula, (fig. 8) 43, (fig. 15) 71 ; increase in number of, 55-57 ; orientation of phloSm and trachete INDEX. 343 in, 63 ; in receptacular tubes, (fig. 14) 68, (6g. 28) 95, (fig. 30) 97 ; cepaline, of Salvia, 55; as oHgiu of the staminal and carpellary, in Malvaceae, 43, 44 Corollas, appendages to, origin of, 133, seqq. ; form of, 101, seqq. ; meta- morphoses of, 292, 301 ; movements in, of Genista, (fig. 47) 160; of Zopezia, (fig. 48) 161 ; origin of, irregular, 1 03, seqq. ; petals of, displacement of, by insects, (figs. .33-35) 110, 111; poUiniferous, 292, 293 ; progressive metamor- phoses of, 292; reduction of size of,9, 254, in Geranium, 252; regular and irregular, 101, seqq. ; sensi- tiveness in, Tponuea, 161 ; stameni- ferous. (figs. 72, 73) 292, 293; strains, effect of, on the formation of, 101, seqq., 126; structure of bilateral, 116, seqq. ; virescence of, (figs. 83, 84) 301, seqq. See Petals. Correlation of growth, 112, 113, 117; irregularities by, 108 Cross-fertilisation, advantages of, in evolution of species, 330, and in horticulture, 311 ; colour, effects on, 178 ; disadvantages o^ 314 ; rationale of, 312 ; stimulus pro- duced by, 312 ; views of Mr. Darwin on, 315 Cruciferce, anatomy of floral recep- tacle, (fig. 6) 32; symmetry of, 32 Darkness and colours, 177 Declinate stamens, in Dictamnus, (fig. 33) 110; distribution of forces in, of -Echitm, (fig. 20) 82; of Epilo- bium, (fig. 34) HI ; origin of, due to weight of insects, 110, 111 Degeneracy and degradation, of an- droecinm, 273; and androdioecism, 227 ; and anemophily, 266 ; of flowers, 251, seqq.; in inconspicuous flowers, cause of, 251 ; in Orchids, 172, 281, 319 ; origin of, 282 ; and self-fertilisation, 252, seqq. Development, of floral whorls,191, and continuous during flowering, 122 ; order of, of parts of flowers, relative only, 195 ; rates of, in pistil, 192, 193 Dialysis, explained, 5, 50 ; in Mirmt- las, (fig. 10) 51 Diclinism, and hcterostylism, 228 ; partial, 220 ; in primitive flowers, 337 Dimorphism, and fertilisation in Viola tricolor, 255 ; and heterostylism, 203 ; in stamens, (fig. 37) 121 Di