JBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 581.15 D25d 1877 «M cr> Biology The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. To renew call Telephone Center, 333-8400 UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN WJK^^l'^'^O MAY NOV 6 iW •::?! L161 — O-10O6 UNIVERSITY OF ILLINOIS-URBANA 581 15D25D1877 C001 THE DIFFERENT FORMS OF FLOWERS ON PLANTS 3 0112 010211727 THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES. By CHAKLES DAEWIN, M.A., F.E.S. WITH ILLUSTRATIONS. NEW YORK: D. APPLETON AND COMPANY, 549 AND 551 BROADWAY. 1877. TO PEOFESSOR ASA GRAY £^ts ©'olunu is gtbuatfir BY THE AUTHOR AS A SMALL TRIBUTE OF EESPECT AND AFFECTION. 4:58(H)2 Digitized by the Internet Archive in 2010 with funding from University of Illinois Urbana-Champaign http://www.archive.org/details/differentformsof01darw CONTENTS. Introduction Page 1-13 CHAPTEE I. Heterostyled Dimorphic Plants : Primulace^. Primula veris or the Cowslip — Dift'erences iu structure between the two forms — Their degrees of fertility when legitimately and ille- gitimately united — P. elatior, vulgaris, Sinensis, auricula, &c. — Summary on the fertility of the heterostyled species of Primula — Homostyled species of Primula — Hottonia palustris — Androsacc Vitalliana 14-54 CHAPTER 11. Hybrid Primulas. The Oxlip a hybrid naturally produced between Primula veris and vulgaris — The diflerences in structure and function between the two pareiit-specics — Effects of crossing long-styled and short- styled Oxlijis with one another and with the two forms of both parent-si^jcies — Character of the offspring from Oxiips artificially self-fertilised and cross-fertilised in a state of nature — Primula " elatior shown to be a distinct species — Hybrids between other heterostyled species of Primula — Sui)plementary note on spon- taneously produced hybrids iti the genus Verbascum .. 55-80 VI CONTENTS. CHAPTER III. Hetebostyled Dimorphic Plants — continued. Liuum grandiflorum, long-st}led form utterly sterile with own-form jx)llen — Linura perenne, torsion of the pistils in the long-styled furm alcne — Homostyled species of Linum — Pulmonaria offici- nalis, singular difference in self-fertility between the English and German long-styled plants — Pulmonaria angustifolia shown to be a distinct si^ecies, long-styled form completely self-sterile — Polygonum fagopyrum — Various other heterostyled genera — RubiacefE — Mitchella repens, fertility of the flowers in pairs — Houstonia — Faramea, remarkable difference in the pollen-grains of the two forms; torsion of the stamens in the short-styled form alone; development not as yet perfect — The heterostyled structure in the several Rubiaceous genera not due to descent in common Page 81-136 CHAPTER IV. Heterostyled Trimorphic Plants. Lythrum salicaria — Description of the three forms — Their power and complex manner of fertilising one another — Eighteen different unions possible — Mid-styled form eminently feminine in nature — Lythrum Gra^fteri likewise trimorphic — L. thymifolia dimor- phic — L. hyssopifolia homostyled — Nesaja verticillata trimorphic — Lagerstroemia, nature doubtful — Oxalis, trimorphic species of — 0. Valdiviana — 0. Eegnelli, the illegitimate unions quite barren — 0. speciosa — 0. sensitiva — Homostyled species of Oxalis — Pontederia, the one monocotyledonous genus known to include heterostyled species 137-187 CHAPTER V. Illegitimate Offspring of Heterostyled Plants. Illegitimate ofifspring from all three forms of Lythrum salicaria — Their dwarfed stature and sterility, some utterly barren, some CONTENTS. Vll fertile — Oxalis, transmission of form to the legitimate and il- legitimate seedlings— Primula Sinensis, illegitimate offspring in some degree dwarfed and infertile — Equal-styled varieties of P. Sinensis, auricula, farinosa, and elatior — P. vulgaris, red-flowered variety, illegitimate seedlings sterile — P. veris, illegitimate plants raised during several successive generations, their dwarfed stature and sterility — Equal-styled varieties of P. veris — Trans- mission of form by Pulmonaria and Polygonum — Concluding remarks — Close parallelism between illegitimate fertilisation and hybridism Page 188-243 CHAPTER VI. Concluding Eemarks on Heteeostyled Plants. The essential character of heterostyled plants — Summary of the differences in fertility between legitimately and illegitimately fertilised plants — Diameter of the pollen-grains, size of anthers and structure of stigma in the different forms — Affinities of the genera which include heterostyled sj^ecies — Nature of the advantages derived from heterostylism — Tlie means by which plants became heterostyled — Transmission of form — Equal- styled varieties of heterostyled plants — Final remarks 244-277 CHAPTEE VII. Polygamous, Diojcious, and Gyno-dicecious Plants. Tlie conversion in various ways of hermaphrodite into dioecious plants — Heterostyled plants rendered dioecious — Kubiaceaj — Verbenaceaj — Polygamous and sub-dioecious plants — Euonymus — Fragaria — The two sub-forms of both sexes of Ehamnus and Epigaia — Ilex — Gyno-dioecious plants — Thymus, difference in fertility of the hermaphrodite and female individuals — Satnreia — Manner in which the two forms i)robably originated — Scabiosa and other gyno-dicecious plants — Difference in the size of the corolla in the forms of polygamous, dioecious, and gyno-dioccious plants 278-309 vm CONTENTS CHAPTER VIII. Cleistogamic Floweks. General character of cleistoganiic flowers— List of tlie genera pro- ducing such flowers, and their distribution in the vegetable series — Viola, description of the cleistogamic flowers in the several species ; their fertility compared with that of the perfect flowers — Oxalis acetosella — O. sensitiva, three forms of cleisto- gamic flowers — Vandellia — Ononis — Impatiens — Drosera — Mis- cellaneous observations on various other cleistogamic plants — Anemophilous species producing cleistogamic flowers — Leersia, perfect flowers rarely developed — Summary and concluding remarks on the origin of cleistogamic flowers — The ciiicf con- clusions which may be drawn from the observations in this volume Pao;e 310-345 Index 34C-352 THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES. INTEODUCTION. The subject of the present volume, namely the dif- ferently formed flowers normally produced by certain kinds of plants, either on the same stock or on distinct stocks, ought to have been treated by a professed bota- nist, to which distinction lean lay no claim. As far as the sexual relations of flowers are concerned, Linnseus long ago divided them into hermaphrodite, monoecious, dioecious, and polygamous species. This fundamental distinction, with the aid of several subdivisions in each of the four classes, will serve my purpose ; but the classification is artificial, and the groups often pass into one another. The hermaphrodite class contains two interesting sub-groups, namely, heterostyled and cleistogamic plants; but there are several other less important subdivisions, presently to be given, in which flowers differing in various ways from one another are pro- duced by the same species. Some plants were described by me several years ago, in a scries of papers read before the Linnean Society,* * " Ou the Two Forms or Di- of Primula, and on their reuiark- morphic Condition in the Species able Sexual Relations." ' Journal 2 INTRODUCTION. the individuals of which exist under two or three forms, differing in the length of their pistils and stamens and in other respects. They were called by me dimorphic and trimorphic, but have since been better named by Hildebrand, heterostyled.* As I have many still unpublished observations with respect to these plants, it has seemed to me advisable to re- publish my former papers in a connected and cor- rected form, together with the new matter. It will be shown that these heterostyled plants are adapted for reciprocal fertilisation ; so that the two or three forms, though all are hermaphrodites, are related to one another almost like the males and-females of ordinary unisexual animals. I will also give a full abstract of such observations as have been published since the appearance of my papers ; but only those cases will be noticed, with respect to which the evidence seems fairly satisfactory. Some plants- have been supposed to be heterostyled merely from their pistils and stamens varying greatly in length, and I have been myself more than once thus deceived. With some species the of the Proceedings of the Linaean P. elatior, Jacq. ; and on tlio Society,' vol. vi. 1862, p. 77. Hybrid Nature of the Common " On tlie Existence of Two Oxllp. With Supplementary Ro- Forms, and on tlieir Reciprocal marks on Naturally Produced Hy- Scxual Relation, in several Species brids in the Genus Vorl)abcum." of the Genus Linum." Ibid. vol. Ibid. vol. x. 18G8, p. 437. vii. 18G3, p. 69. * The term "heterostyled "does " On tlic Sexual Relations of the not express all the difterences be- Tliree Forms of 2/ //^/trwjn saZtcar/a.' tween tlie forms; but tliis is a Ibid. vol. viii. 1864, p. 169. failure common in rnany cases. " Oil theCliaracter and Hybriil- As the term has been adopted by like Nature of the Ofl'spring from writers in various countries, I am the Illegitimate Unions of Dinwr- unwilling to change it for that of phic and Trimorphic Plants." heterogone or heterogonmis, though Ibid. vol. X. 1868, p. 393. this has been proposed by so high " On the Specific Differences an authority as Prof. Asa Gray : between Primula veris, Brit. Fl. see the 'American Naturalist,' (var. officinalis, Linn.), P. vulgar!.^, Jan. 1877, p. 42. Brit. Fl. (var. acaulis, Linn.), and INTRODUCTION. 3 pistil continues growing for a long time, so that if old and young flowers are compared they might be thought to be heterostyled. Again, a species tending to become dioecious, with the stamens reduced in some individuals and with the pistils in others, often presents a decep- tive appearance. Unless it be proved that one form is fully fertile only ^^hen it i? fertilised with pollen from another form, we have not complete evidence that the species is heterostyled. But when the pistils and stamens differ in length in two or three sets of individuals, and this is accompanied by a difference in the size of the pollen-grains or in the state of the stigma, we may infer with much safety that the species is heterostyled. I have, however, occasionally trusted to a difference between the two forms in the length of the pistil alone, or in the length of the stigma together with its more or less pajnllose condition ; and in one instance differences of this kind have been proved by trials made on the fertility of the two forms, to be sufficient evidence. The second sub-group above referred to consists of hermaphrodite plants, which bear two kinds of flowers — the one perfect and fidly expanded — the other mi- nute, completely closed, with the petals rudimentary, often with some of the anthers aborted, and the re- maining ones together with the stigmas much reduced in size ; yet these flowers are perfectly fertile. They have been called by Dr. Kuhn* cleistogamic, and they * ' Botaninche Zeitung,' 1867, partakes of the nature of a mon- p. 65. Several plants are known btrosity. All the llowers on tho occasionally to produce flowers same plant are commonly affected destitute of a corolla ; but they in the same manner. Such cases, belong to a diflferent class of though they have sometimes beeu eases from cleistogamic flowers. ranked as cleistogamic, do not This deficiency seems to result come within our present scope : from the conditions to which the see Dr. Maxwell Masters, ' Vege- plants have bet-n subjected, and table Teratology,' 1S69, p. 403. 4 INTRODUCTION. will be described in the last chapter of this volume. They are manifestly adapted for self-fertilisation, which is effected at the cost of a wonderfully small expendi- ture of pollen ; whilst the perfect flowers produced by the same plant are capable of cross-fertilisation. Cer- tain aquatic species, when they flower beneath the water, keep their corollas closed, apparently to protect their pollen ; they might therefore be called cleisto- gamic, but for reasons assigned in the proper place are not included in the present sub-group. Several cleis- togamic species, as we shall hereafter see, bmy their ovaries or young capsules in the ground ; but some few other plants behave in the same manner ; and, as they do not bury all their flowers, they might have formed a small separate subdivision. Another interesting subdivision consists of certain plants, discovered by H. Miiller, some individuals of which bear conspicuous flowers adapted for cross- fertilisation by the aid of insects, and others much smaller and less conspicuous flowers, which have often been slightly modified so as to ensure self-fertilisation. Lysimachia vulgaris, Euphrasia officinalis, Bliinanthus crista-galU, and Viola tricolor come under this head.* The smaller and less conspicuous flowers are not closed, but as far as the purpose which they serve is * con- cerned, namely, the assured propagation of the species, they approach in nature cleistogamic flowers ; but they differ from them by the two kinds being produced on distinct plants. With many plants, the flowers towards the outside of the inflorescence are much larger and more conspicu- ous than the central ones. As I shall not have occa- ♦ H. Miiller, ' Nature,' Sept. 25, ' Die BefnicLtiing der Blumen,' 1873 (vol. viii.), p. 433, and Nov. &c., 1S73, p. 294. 20,1873 (vol. ix.), p. 44. Also INTRODUCTION. 5 sion to refer to plants of this kind in the following chapters, I will here give a few details resj)ecting them. It is familiar to every one that the ray-florets of the Compositoe often differ remarkably from the others ; and so it is Avith the outer flowers of many Umbellifera^, some Cruciferffi and a few other families. Several species of Hydrangea and Viburnum offer striking instances of the same fact. The Rubiaceous genus Mussaenda presents a very curious appearance from some of the flowers having the tip of one of the sepals developed into a large petal-like expansion, coloured either white or purple. The outer flowers in several Acanthaceous genera are large and conspicuous but sterile ; the next in order are smaller, open, moderately fertile and capable of cross-fertilisation; whilst the central ones are cleistogamic, being still smaller, closed and highly fertile ; so that here the inflorescence con- sists of three kinds of flowers.* From what we know in other cases of the use of the corolla, colom-ed bracteae, &c., and from what H. Miiller has observed! on the frequency of the visits of insects to the flower-heads of the Umbelliferoe and Compositce being largely deter- mined by their conspicuousness, there can be no doubt that the increased size of the corolla of the outer flowers, the inner ones being in all the above cases small, serves to attract insects. The result is that cross-fertilisation is thus favoured. Most flowers wither soon after being fertilised, but Hildcbrand states t that the ray-florets of the Compositae last for a long time, until all those on the disc are impregnated ; and this clearly shows the use of the former. The ray-florets, * J. Scott, ' Journal of Botany,' men,' pp. 108, 412. London, new series, vol. i. 1872, J Sec his interesting memoir, pp. 161-1G4. 'UeberdicGeschlechtsverhaltnissB t ' Die Befmchtung dur Blu- bci den Ckjmpositen,' 1869, p. 92. 6 INTRODUCTION. however, are of service in another and very different manner, namely, by folding inwards at night and diu'ing cold rainy weather, so as to protect the florets of the disc* Moreover they often contain matter which is excessively poisonous to insects, as may be seen in the use of flea-powder, and in the case of Pyrethrum, M. Belhomme has shown that the ray- florets are more poisonous than the disc-florets in the ratio of about three to two. We may therefore believe that the ray-florets are useful in protecting the flowers from being gnawed by insects.f It is a well-known yet remarkable fact that the cir- cvmiferential flowers of many of the foregoing plants have both their male and female reproductive organs aborted, as with the Hydrangea, Viburnum and certain Composite ; or the male organs alone are aborted, as in many Compositse. Between the sexless, female and hermaphrodite states of these latter flowers, the finest gradations may be traced, as Hildebrand has sho^vn.| He also shows that there is a close relation between the size of the corolla in the ray-florets and the degree of abortion in their reproductive organs. As we have good reason to believe that these florets are highly serviceable to the plants which possess them, more especially by rendering the flower-heads conspicuous * Kemer clearly shows that gnawed, and thus the organs of thisis the case :' Die Schutzmittel fructlficatioa are protected. My des Pollens,' 1873, p. 28. grandfather in 17a0 (' Loves of *t ' Gardener's Chronicle,' 1861, the Plants,' canto iii. note to lines p. 10(37. Lindley, 'Vegetable 184, 188) remarks that "The Kingdom,' on Chrysantliemum, flowers or petals of plants are 1853, p. 706. Kemer in his in- perhaps in general more acrid teresting essay (' Die Schutzmittel than their leaves ; hence they are der Bliithen gegen unberufene much scldomer eaten by insects." Giiste,' 1875, p. 19) insists that J ' Ueber die Geschlechtsver- the petals of most plants contain haltnisse bei den Compositen,' matter which is offensive to in- 18(.i9, pp. 78-91. sects, so that they are seldom INTRODUCTION. 7 to insects, it is a natural inference that their corollas have been increased in size for this special purpose ; and that their development has subsequently led, through the principle of compensation or balance- ment, to the more or less complete reduction of the reproductive organs. But an opposite view may be maintained, ■ namely, that the reproductive organs first began to fail, as often happens under cultiva- tion,* and, as a consequence, the corolla became, through compensation, more highly developed. This view, however, is not probable, for when hermaphrodite plants become dioecious or gyno-dioecious — that is, are converted into hermaphrodites and females — the corolla of the female seems to be almost invariably reduced in size in consequence of the abortion of the male organs. The difference in the result in these two classes of cases, may perhaps be accounted for by the matter saved through the abortion of the male organs in the females of gyno-dioecious and dioecious plants being directed (as we shall see in a future chapter) to the for- mation of an increased supply of seeds ; whilst in the case of the exterior florets and flowers of the plants which we are here considering, such matter is expended in the development of a conspicuous corolla. Whether in the present class of cases the corolla was first af- fected, as seems to me the more probable view, or the reproductive organs first failed, their states of develop- ment are now firmly correlated. We see this well illus- trated in Hydrangea and Viburnum ; for when these plants are ciiltivated, the corollas of both the interior and exterior flowers become largely developed, and their reproductive organs are aborted. * I have discnesed this subject xviii. 2nd edit. vol. ii. pp. 152, ill my 'Variation of Animals and 15G. Plants under Domestication,' chap. 8 INTRODUCTION. There is a closely analogous subdivision of plants, including the genus Muscari (or Feather Hyacinth) and the allied Bellevalia, which bear* both perfect flowers and closed bud-like bodies that never expand. The latter resemble in this resj)ect cleistogamic flowers, but differ widely from them in being sterile and conspicuous. Not only the aborted flower-buds and their peduncles (which are elongated apparently through the principle of compensation) are brightly coloured, but so is the uj)per part of the spike — all, no doubt, for the sake of guiding insects to the inconspicuous perfect flowers. From such cases as these v,'e may pass on to certain Labiatae, for instance. Salvia Horminursi, in which (as I hear from ]\[r. Thisel- ton Dyer) the upper bracts are enlarged and brightly coloured, no doubt for the same purpose as before, with the flowers suppressed. In the Carrot and some allied Umbelliferae, the cen- tral flower has its petals somewhat enlarged, and these are of a dark pm-plish-red tint ; but it cannot be sup- posed that this one small flower makes the large white umbel at all more conspicuous to insects. The cen- tral flowers are said* to be neuter or sterile, but I obtained by artificial fertilisation a seed (fruit) appa- rently perfect from one such flower. Occasionally two or three of the flowers next to the central one are simi- larly characterised ; and according to Vaucherf " cette singuliere degeneration s'etend quelquefois a rombelle entiere." That the modified central flower is of no functional importance to the plant is almost certain. It may perhaps be a remnant of a former and ancient condition of the species, when one flower alone, the * 'The English Flora,' by Sir d'Europe,' 1811, torn. ii. p. C14. J. E. Smith, l!S24, vol. ii. p. 39. Ou tlie Ecliinophora, p. 627. t ' Hid. riiys. des Plautes INTRODUCTION. 9 central one, was female and yielded seeds, as in the umbelliferous genus Echinophora. There is nothing surprising in the central flower tending to retain its former condition longer than the others ; for when ir- regular flowers become regular or peloric, they are apt to be central ; and such peloric flowers apparently owe their origin either to arrested development — that is, to the preservation of an early stage of development — or to reversion. Central and perfectly developed flowers .in not a few plants in their normal condition (for in- stance, the common Eue and Adoxa) differ slightly in structure, as in the number of the parts, from the other flowers on the same plant. xVU such cases seem con- nected with the fact of the bud which stands at the end of the shoot being better nourished than the others, as it receives the most sap.* The cases hitherto mentioned relate to hermaphro- dite species which bear differently constructed flowers ; but there are some plants that produce differently formed seeds, of which Dr. Kuhn has given a list.f AVith the Umbelliferae and Compositse, the flowers that produce these seeds likewise differ, and the differences in the structure of the seeds are of a very important nature. The causes which have led to differences in the seeds on the same plant are not known ; and it is very doubtful whether they subserve any special end. We now come to our second Class, that of moncccious species, or those which have their sexes separated but lome on the same plant. The flowers necessarily differ, but when those of one sex include rudiments * Thi.s wliolo subject, including Dnmesticp.tion,' chap. xxvi. 2iul pclnrism, has been discussed, and edit. vol. ii. p. 338. references given, in my • Variation t ' liot. Zeituiig,' 18G7, p. G7. of Animals and Plants under 10 INTRODUCTION. of the other sex, the difference between the two kinds is usually not great. When the difference is great, as we see in catkin-bearing plants, this depends largely on many of the species in this, as well as in the next or dioecious class, being fertilised by the aid of the wind ;* for the male flowers have in this case to produce a surprising amount of incoherent pollen. Some few monoecious plants consist of two bodies of individuals, with their flowers differing in function, though not in structure ; for certain indivi- duals mature their pollen before the female flowers on the same plant are ready for fertilisation, and are called proterandrous ; whilst conversely other individuals, called proterogynous, have their stigmas mature before their pollen is ready. The purpose of this curious func- tional difference obviously is to favour the cross-fertili- sation of distinct plants. A case of this kind was first observed by Delpino in the Walnut {Juglans regia), and has since been observed with the common Nut (Corylus avellana). I may add that according to H. Miiller the individuals of some few hermaphrodite plants differ in a like manner ; some being proterandrous and others proterogynous.t On cultivated trees of the W^alnut and Mulberry, the male flowers have been observed to abort on certain individuals!, which have thus been converted into females ; but whether there are any species in a state of nature which co-exist as monoecious and female individuals, I do not know. The third Class consists of dioecious species, and the * Delpino, ' Studi sopra uno xi. p. 507, and 1875, p. 26. Ou Lignaggio Auemofilo.' Firenze, ])roteran gitimate union . . ) oo 15 U 8-8 62 Long-styled by own-jj form pollen. IHe-ll gitimate union . . j 20 8 5 2-1 42 Short-styled by pollen j of long-styled. Le-> gitimate union . . j 13 12 11 4-9 44 Short-styled by own- 1 form pollen. Ille-> gitimate union. . ) . 15 8 6 1-8 30 Summary : The two legitimate"! unions . . . ./ 35 27 25 13-7 54 The two illegitimate unions .... 35 16 11 3-9 The results may be given in another form (Table 7) by comparing, first, the number of capsules, whether good or bad, or of the good alone, produced by 100 flowers of both forms when legitimately and illegiti- mately fertilised ; secondly, by comparing the weight of seed in 100 of these capsules, whether good or bad ; or, thirdly, in 100 of the good capsules. 2G HETEROSTYLED DIMORPHIC PLANTS. Chap. I. Table 7. Nature of the Union. Xumbf-r of Flowers fer- tilised. Xumber of Cap- subes. Xumber of good Cap- sules. Weight of Seed in grains. Xumber of Cap- sules. Weight of Seed in grains. Xumber of good Cap- sules. Wciuht of Seed in grains. The two le-l gitimate unions . ] 1 100 1 77 71 39 100 50 100 54 The two il-j legitimate unions . ] 100 45 31 11 1 100 24 100 35 We here see that the long-styled flowers fertilised with pollen from the short-styled yield more capsules, especially good ones (i.e. containing more than one or two seeds), and that these capsules contain a greater proportional weight of seeds than do the flowers of the long-styled when fertilised with pollen from a distinct plant of the same form. So it is'with the short-styled flowers, if treated in an analogous manner. Therefore I have called the former method of fertilisation a legiti- mate union, and the latter, as it fails to yield the full complement of capsules and seeds, an illegitimate union. These two kinds of union are graphically re- presented in Fig. 2. If we consider the results of the two legitimate unions taken together and the two illegitimate ones, as shown in Table 7, we see that the former com- pared with the latter yielded capsules, whether con- taining many seeds or only a few, in the proportion of 77 to 45, or as 100 to 58. But the inferiority of the illegitimate unions is here perhaps too great, for on a subsequent occasion 100 long-styled and short-styled flowers were illegitimately fertilised, and they together yielded 53 capsules : therefore the rate of 77 to 53, or as 100 to 69, is a fairer one than that of 100 to 58. Chap. I. PRIMULA VERlg. 27 Returning to Table 7, if we consider only the good capsules, those from the two legitimate unions were to those from the two illegitimate in number as 71 to 31, or as 100 to 44. Again, if we take an equal number of capsules, whether good or bad, from the legitimately and illegitimately fertilised flowers, we find that the former contained seeds by weight compared with the latter as 50 to 24, or as 100 to 48 ; but if all the Fig. 2. Legitimate union. Complete fertility. T7 Long-styled form. poor capsules are rejected, of which many were pro- duced by the illegitimately fertilised flowers, the propor- tion is 54 to 35, or as 100 to 65. In this and all other cases, the relative fertility of the two kinds of union can, I think, be judged of more truly by the average number of seeds per capsule than by the proportion of flowers which yield capsules. The two methods might 28 HETEROSTYLED DIMORPHIC PLANTS. Chap. I. have been combined by giving the average number of seeds produced by all the flowers which were fertilised, whether they yielded capsules or not ; but I have thought that it would be more instructive always to show separately the proportion of flowers which pro- duced capsules, and the average number of apparently good seeds which the capsules contained. Flowers legitimately fertilised set seeds under con- ditions which cause the almost complete failure of illegitimately fertilised flowers. Thus in the spring of 18G2 forty flowers were fertilised at the same time in both ways. The plants were accidentally exposed in the greenhouse to too hot a sun, and a large number of umbels perished. Some, however, remained in mo- derately good health, and on these there were twelve flowers which had been fertilised legitimately, and eleven which had been fertilised illegitimately. The twelve legitimate unions yielded seven fine capsules, containing on an average each 57 • 3 good seeds ; whilst the eleven illegitimate unions yielded only two cap- sules, of which one contained 39 seeds, but so poor, that I do not suppose one would have germinated, and the other contained 17 fairly good seeds. From the facts now given the superiority of a legi- timate over an illegitimate union admits of not the least doubt; and we have here a case to which no parallel exists in the vegetable or, indeed, in the animal kingdom. The individual plants of the pre- sent species, and as we shall see of several other species of Primula, are divided into two sets or bodies, which cannot be called distinct sexes, for both are hermaphrodites ; yet they are to a certain extent sexually distinct, for they require reciprocal union for perfect fertility. As quadrupeds are di- vided into two nearly equal bodies of different sexes, CuAi-. I. PRIMULA VERIS. 29 SO here we have two bodies, ajiproximately equal in number, differing in their sexual powers and related to each other like males and females. There are many hermaphrodite animals which cannot fertilise them- selves, but must unite with another hermaphrodite. So it is with numerous plants ; for the pollen is often mature and shed, or is mechanically protruded, before the flower's own stigma is ready ; and such flowers ab- solutely require the presence of another hermaphro- dite for sexual union. But with the cowslip and various other species of Primula there is this wide difference, that one individual, though it can fertilise itself im- perfectly, must unite with another individual for full fertility ; it cannot, however, unite with any other in- di-s-idual in the same manner as an hermaphrodite plant can unite with any other one of the same species ; or as one snail or earth-worm can unite with any other hermaphrodite individual. On the contrary, an indi- vidual belonging to one form of the cowslip in order to be perfectly fertile must unite with one of the other form, just as a male quadruped must and can unite only with the female. I have spoken of the legitimate unions as being fully fertile ; and I am fully justified in doing so, for flowers artificially fertilised in this manner yielded rather more seeds than plants naturally fertilised in a state of nature. The excess may bfe attributed to the plants having been grown separately in good soil. With respect to the illegitimate unions, we shall best appreciate their degree of lessened fertility by the following facts. Gartner estimated the sterility of the unions between distinct species,* in a manner which allows of a strict comparison with the results of the ' Versuche uber die Baetarderzcugung,' 1S19, p. 216. 30 HETEROSTYLED DIMORPHIC PLANTS. Ctiap. I. legitimate and illegitimate unions of Primula. With P. veris, for every 100 seeds yielded by the two le- gitimate unions, only 64 were yielded by an equal number of good capsules from the two illegitimate unions. With P. Sinensis, as we shall hereafter see, the proportion was nearly the same — namely, as 100 to 62. Now Gartner has shown that, on the calcula- tion of Verhasciim hjclmitis yielding with its own pollen 100 seeds, it yielded when fertilised by the pollen of F. Phceniceum 90 seeds ; by the pollen of F. nigrum, 63 seeds ; by that of F. hlattaria, 62 seeds. So again, Dianthus harbatus fertilised by the pollen of D. superbus yielded 81 seeds, and by the pollen of D. Jcqjonicus 66 seeds, relatively to the 100 seeds produced by its own pollen. We thus see — and the fact is highly re- markable — that with Primula the illegitimate unions relatively to the legitimate are more sterile than crosses betw-een distinct species of other genera rela- tively to their pure unions. Mr. Scott has given* a still more striking illustration of the same fact : he crossed Primula auricula with pollen of four other species (P. Palinuri, viscosa, liirsuta, and veriieillata), and these hybrid unions yielded a larger average number of seeds than did P. auricula when fertilised illegitimately with its own-form pollen. The benefit which heterostyled dimorphic plants de- rive from the existence of the two forms is sujSiciently obvious, namely, the intercrossing of distinct plants being thus ensured.f Nothing can be better adapted for this end than the relative positions of the anthers and stigmas in the two forms, as shown in Fig. 2 ; but to * ' Joiirn. Linn. Soc. Bot.,' vol. fertilisation ' how greatly the ofF- viii. ISGi, p. 93. spring from intercrossed plants t I have shown in my work profit in height, vigour, and on the ' Effects of Cross and Self- fertility. Chap. I. PKEMULA VERIS. 31 this whole subject I shall recur. No doubt pollen will occasionally be placed by insects or fall on the stigma of the same flower ; and if cross-fertilisation fails, sucli self-fertilisation will be advantageous to the plant, as it will thus be saved from complete barrenness. But the advantage is not so great as might at first be thought, for the seedlings from illegitimate unions do not generally consist of both forms, but all belong to the parent form ; they are, moreover, in some degree weakly in constitution, as will be shown in a future chapter. If, however, a flower's own jJoUen should first be placed by insects or fall on the stigma, it by no means follows that cross-fertilisation w ill be thus pre- vented. It is well known that if jooUen from a distinct species be placed on the stigma of a plant, and some hours afterwards its own pollen be placed on it, the latter will be prepotent and will quite obliterate any efiiect from the foreign pollen ; and there can hardly be a doubt that with heterostyled dimorphic plants, pollen from the other form will obliterate the effects of pollen from the same form, even when this has been placed on the stigma a considerable time before. To test this belief, I placed on several stigmas of a long- styled cowslip plenty of pollen from the same plant, and after twenty-four hours added some from a short- styled dark-red polyanthus, which is a variety of the cowslip. From the flowers thus treated 30 seedlings Avere raised, and all these, without exception, bore reddish flowers ; so that the effect of pollen from the same form, though placed on the stigmas twenty-four hours previously, was quite destroyed by that of pollen from a plant bcdonging to the other form. Finally, I may remark that of the four kinds of unions, that of the short-styled illegitimately fertilised with its own-form pollen seems to be the most sterile of 32 HETEROSTYLED DIMORPHIC PLANTS. Ciiap. I. all, as judged by the average number of seeds, which the capsules contained. A smaller jjroportion, also, of these seeds than of the others germinated, and they germinated more slowly. The sterility of this union is the more remarkable, as it has already been shown that the short-styled plants yield a larger number of seeds than the long-styled, when both forms are fer- tilised, either naturally or artificially, in a legitimate manner. In a future chapter, when I treat of the offspring from heterostyled dimorphic and trimorphic plants illegitimately fertilised with their own-form pollen, I shall have occasion to show that with the present species and several others, equal-styled varieties some- times appear. Primula elatiou, Jacq. Bardfield Oxlip of Enrjlish Authors. This plant, as well as the last or Cowslip (P. veris, vel oj)icinaUs), and the Primrose (P. vulgaris, vel acaulis) have been considered by some botanists as varieties of the same species. But they are all three undoubtedly distinct, as will be shown in the next chapter. The present species resembles to a certain extent in general appearance the common oxlip, which is a hybrid be- tween the cowslip and primrose. Primula elatior is found in England only in two or three of the eastern counties ; and I was supplied with living plants by Mr. Doubleday, who, as I believe, first called attention to its existence in England. It is common in some parts of the Continent; and H. Miiller* has seen several kinds of humble-bees and other bees, and Bombylius, visiting the flowers in North Germany. * ' Die BefruclituDg der Blumen,' p. 347. Chap. I. PEIMULA ELATIOR. 33 The results of my trials on the relative fertility of the two forms, when legitimately and illegitimately fertilised, are given in the following table : — Table 8. Primula elatior. Nature of Union. Number of Flowers fertilised. Number of good Oipsulos produced. Maximum of Seeds in any one Capsule. Minimum of Seeds in any one Cap.sule. Average Number of Seeds per Capsule. Long-styled form, byl pollen of short-styled. > Legitimate union . J 10 GJ 34- 46-5 Long-styled form, by 1 own-form pollen. ]l-> legitimate union . . ) 20 4 49* 2 27-7 Short-styled form, byl pollen of long-styled. > Legitimate union . ) 10 8 61 37 47-7 Short-styled form, byl own- form pollen. 11- V legitimate union. .) 17 3 19 9 12-1 The two legitimate'! unions together . ./ 20 14 62 37 47-1 The two illegitimate'! unions together . . J 37 7 49* o 35-5 * Tbese seeds were so poor and small that they could hardly bave germinated. If we compare the fertility of the two legitimate unions taken together with that of the two illegitimate unions together, as judged by the proportional number of flowers which when fertilised in the two methods yielded capsules, the ratio is as 100 to 27 ; so that by this standard the present species is much more sterile than P. veris, when both species are illegitimately fer- tilised. If we judge of the relative fertility of the two kinds of unions by the average number of seeds per capsule, the ratio is as 100 to 75. But this latter 34 HETEEOSTYLED DIMORPHIC PLANTS. Chap. I. number is probably much too high, as many of the seeds produced by the illegitimately fertilised long-styled flowers were so small that they probably would not have germinated, and ought not to have been counted. Several long-styled and short-styled plants were pro- tected from the access of insects, and must have been spontaneously self-fertilised. They yielded altogether only six capsules, containing any seeds ; and their average number was only 7 ■ 8 per capsule. Some, moreover, of these seeds were so small that they could hardly have germinated, Herr W. Breitenbach informs me that he examined, in two sites near the Lippe (a tributary of the Rhine), 894 flowers produced by 198 plants of this species ; and he found 467 of these flowers to be long-styled, 411 short-styled, and 16 equal-styled. I have heard of no other instance with heterostyled plants of equal-styled flowers appearing in a state of nature, though far from rare with plants which have been long cultivated. It is still more remarkable that in eighteen cases the same plant produced both long-styled and short-styled, or long-styled and equal-styled flowers ; and in two out of the eighteen cases, long-styled, short-styled, and equal-styled flowers. The long-styled flowers greatly preponderated on these eighteen plants, — 61 consisting of this form, 15 of equal-styled, and 9 of the short- styled form. Peimula vulgaris (var. acaulis, Linn.), The Primrose of English Writers. Mr. J. Scott examined 100 plants growing near Edinburgh, and found 44 to be long-styled, and 56 short-styled ; and I took by chance 79 plants in Kent, of which 39 were long-styled and 40 short-styled ; so Chap. I. PRIMULA VULGARIS. 35 that the two lots together consisted of 83 long-styled and 96 short-styled plants. In the long-styled form the pistil is to that of the short-styled in length, from an average of five measurements, as 100 to 51. The stigma in the long-styled form is conspicnonsly more globose and much more papillose than in the short- styled, in which latter it is depressed on the summit ; Fig. 3. Outlines of poHen-g«-aiiis o{ Primula vuljaris, distended with watei, much magnified and drawn under the camera lucida. The upper and smaller g^-ains from the long-styled form ; the lower and larger gi'ains from the short-styled. it is equally broad in the two forms. In both it stands nearly, but not exactly, on a level with the anthers of the opposite form ; for it was found, from an average of 15 measurements, that the distance between the middle of the stigma and the middle of the anthers in the short-styled form is to that in the long-styled as 100 to 93. The anthers do not differ in size in the two forms. The pollen-grains from the short-styled 3G HETEROSTYLED DIMORPHIC PLANTS. Chap. I. flowers before they wore soaked in water were decidedly broader, in proportion to their length, than those from the long-styled ; after being soaked tliey were relatively to those from the long-styled as 100 to 71 in diameter, and more transparent. A large number of flowers from the two forms w'ere compared, and 12 of the finest flowers from each lot were measured, but there was no sensible difference between them in size. Nine long- styled and eight short-styled plants growing together in a state of nature were marked, and their capsules col- lected after they had been naturally fertilised ; and the seeds from the short-styled weighed exactly twice as much as those from an equal number of long-styled plants. So that the primrose resembles the cowslip in the short-styled plants, being the more productive of the two forms. The results of my trials on the fer- tility of the two forms, when legitimately and illegi- timately fertilised, are given in Table 9. We may infer from this table that the fertility of the two legitimate unions taken together is to that of the two illegitimate unions together, as judged by the pro- portional number of flowers which when fertilised in the two methods yielded capsules, as 100 to 60. If we judge by the average number of seeds per capsule pro- duced by the two kinds of unions, the ratio is as 100 to 54 ; but this latter figure is perhaps rather too low. It is surprising how rarely insects can be seen during the dav visiting the flowers, but I have occasionally observed small kinds of bees at work ; I suppose, therefore, that they are commonly fertilised by noctm-nal Lepidoptera. The long-styled plants when protected from insects yield a considerable number of capsules, and they thus difi'er remarkably from the same form of the cowslip, which is quite sterile under the same circumstances. Twenty-three spontaneously self-fertilised capsules from Chat. I. miMULA VULGARIS. Table 9. Primula vulgaris. 37 Nature of Union. Numbr-r Number of of good Flowers Capsules fertilised, produced. Jlaximum Nunilxrr of Seeds in any one Capsule. Minimum Number of Seeds in any one Capsule. Average Number of Seeds per Capsule. Long-styled form, by pol- j len from short-styled. > Legitimate union . . ) 12 11 77 47 66-9 Long-styled form, byj own-form pollen. 11- > legitimate union . . j 21 14 66 30 52-2 Short-styled form, byj' pollen from long-styled. > 8 7 Legitimate union . . | 75 48 65-0 Short-styled form, byj own-form pollen. 11-) IS 7 legitimate union , . ) 43 5 18-8* The two legitimated ^q jg unions together • •/ 77 47 66-0 The two illegitimate" unions together . 09 21 66 5 35-5* * This average is perhaps rather too low. this form contained, on an average, 19'2 seeds. The short-styled plants produced fewer spontaneously self- fertilised capsules, and fourteen of them contained only 6'2 seeds per capsule. The self-fertilisation of both forms was probably aided by Thrips, which abounded within the flowers ; but these minute insects could not have placed nearly sufficient pollen on the stigmas, as the spontaneously seK-fertilised capsules contained much fewer seeds, on an average, than those (as may be seen in Table 9) which were artificially fertilised with their own-form pollen. But this difference may perhaps be attributed in part to the flowers in the table having been fertilised with pollen from a distinct plant be- 38 HETEROSTYLED DIMORPHIC PLANTS. Chap. I. longing to the same form ; whilst those which were spontaneously self-fertilised no doubt generally received their o\vn pollen. In a future part of this volume some observations will be given on the fertility of a red- coloured variety of the primrose. Primula Sinensis. In the long-styled form the pistil is about twice as long as that of the short-styled, and the stamens differ in a corresponding, but reversed, manner. The stigma is considerably more elongated and rougher than that of the short-styled, which is smooth and almost spherical, being somewhat depressed on the summit ; but the stigma varies much in all its characters, the result, probably, of cultivation. The pollen-grains of the short-styled form, according to Hildebrand,* are 7 divisions of the micrometer in length and 5 in breadth ; whereas those of the long-styled are only 4 in length and 3 in breadth. The grains, there- fore, of the short-styled are to those of the long- styFed in length as 100 to 57. Hildebrand also re- marked, as I had done in the case of P. veris, that the smaller grains from the long-styled are much more trans j)arent than the larger ones from the short-styled form. We shall hereafter see that this cultivated plant varies much in its dimorphic condition and is often equal-styled. Some individuals may be said to be sub-heterostyled ; thus in two white-flowered plants the pistil projected above the stamens, but in one of them * After the appearnnce of my that I erred preatly about the paper this author published some size of the pollL-u-^'rains in the excellent observations on the two forms. I suppose that by present species (' Bot. Zeitung,' mistake I measured twice over Jan. 1, 1864), and he shows pollen-grains from the same form. CuAr. I. PRIMULA SINENSIS. J39 it was longer and had a more elongated and rougher stigma, than in the other ; and the j)olleii-grains from the latter were to those from the plant with a more elongated pistil only as 100 to 88 in diameter, instead of as 100 to 57. The corolla of the long-styled and short-styled form differs in shape, in the same manner as in P. verts. The long-styled plants tend to flower before the short-styled. When both forms were legiti- mately fertilised, the capsules from the short-styled plants contained, on an average, more seeds than those from the long-styled, in the ratio of 12*2 to 9*3 by weight, that is, as 100 to 78. In the following table we have the results of two sets of experiments tried at different periods. Table 10. Primula Sinensis. 1 * 1 Number Nature of Union. j p-,;^^^^ fertilised. Number of good Capsules produced. Average Weight of Seeds per Capsule. Average Number of Seeds per Capsule, as ascertained on a subsequent occasion. Long-styled foi-m, by pollen! of short-styled. Legit i- i mate union . , . . ) 24 16 0-58 50 - Long-styled fornn, by own-j form pollen. lllegiti-> mate union . . . . j 20 13 0-45 1 3.5 Short-styled form, by pol-j len of long-styled. Le-> gitimate union . . . ) 8 8 1 0-76 1 1 64 Short-styled form, by own-1 form pollen. Illegiti-> mate union .... J i 7 ! 4 0-23 25 The two legitimate aiiioiis\' „^ ^ together / ^-^ -* 0-04 i .')7 The two illegitimate unions! ,,_ | together / -' ^' 1 0-40 30 40 HETEROSTYLED DIMORPHIC PLANTS. Chap. I. The fertility, therefore, of the two legitimate unions together to that of the two illegitimate unions, as judged by the proportional number of flowers which yielded capsules, is as 100 to 84. Judging by "the average weight of seeds per capsule produced by the two kinds of unions, the ratio is as 100 to 63. On another occa- sion a large number of flowers of both forms were fertilised in the same manner, but no account of their number was kept. The seeds, however, were carefully counted, and the averages are shown in the right-hand column. The ratio for the number of seeds produced by the two legitimate compared with the two illegiti- mate unions is here 100 to 53, which is probably more accurate than the foregoing one of 100 to 63. Hildebrand in the paper above referred to gives the results of his experiments on the present species ; and these are sho^^^l in a condensed form in the following table (11). Besides using for the illegitimate unions pollen from a distinct plant of the same form, as was always done by me, he tried, in addition, the efi'ects of the plant's own pollen. He counted the seeds. It is remarkable that here all the flowers \\ hich were fertilised legitimately, as well as those fertilised illegitimately with pollen from a distinct plant be- longing to the same form, yielded capsules ; and from this fact it might be inferred that the two forms were reciprocally much more fertile in his case than in mine. But his illegitimately fertilised capsules from both forms contained fewer seeds relatively to the legitimately fertilised capsules than in my experi- ments ; for the ratio in his case is as 42 to 100, instead of, as in mine, as 53 to 100. Fertility is a very variable element with most plants, being deter- mined by the conditions to which they are subjected, of which fact I have observed strikino; instances with the Chap. I. PRIMULA SINENSIS. 41 Table 11. Primula Sinensis (from Eildehrand). Nature of Union. Number of Flowers fertilised. Nimiber of got.d Capsules produced. Average Number of Seeds per Capsule. Long-styled form, by pollen of short-j styled. Legitimate union . . . ./ 14 14 41 Long-styled form, by own-form pollen, from^ a distinct plant. Illegitimate union ./ 26 26 18 Long-styled form, by pollen from samel flower. Illegitimate union. . . ./ 27 21 17 Short-styled form, by pollen of long-j styled. Legitimate union . . . ./ 14 16 14 16 44 Short-styled form, by own-form pollen, 1 from a distinct plant. Illegitimate union/ 20 Short-styled, by pollen from the samel flower. lUescitimate union. . . .) 21 11 8 The two legitimate unions together . 28 28 43 The two illegitimate unions together'! (own-form pollen) / 42 42 18 The two illegitimate unions together (pol-l len from the same flower) . . . .j 48 32 13 present species ; and this may account for the differ- ence between my results and those of Hildebrand. His plants were kept in a room, and perhaps were grown in too small pots or under some other unfavourable condi- tions, for his capsules in almost every case contained a smaller number of seeds than mine, as may be seen liv comparing the right-hand columns in Tables 10 and 11. " The most interesting point in Hildebraud's experi- ments is the difference in the effects of illegitimate fertilisation with a flower's own polhm, and with that 42 IlETEROSTYLED DIMORPHIC PLANTS. Chap. I. from a distinct plant of the same form. In the latter case all the flowers produced capsules, whilst only 67 out of 100 of those fertilised with their own pollen pro- duced capsules. The self-fertilised capsules also con- tained seeds, as compared with capsules from flowers fertilised Avith pollen from a distinct plant of the same form, in the ratio of 72 to 100. In order to ascertain how far the present species was spontaneously self-fertile, five long-styled plants were protected by me from insects ; and they bore up to a given period 147 flowers w^hich set 62 capsules ; but many of these soon fell off, showing that they had not been properly fertilised. At the same time five short- styled plants were similarly treated, and they bore 116 flowers which ultimately produced only seven capsules. On another occasion 13 protected long-styled plants yielded by weight 25 • 9 grains of spontaneously self- fertilised seeds. At the same time seven protected short-styled plants yielded only haK-a-grain weight of seeds. Therefore the long-styled plants yielded nearly 24 times as many spontaneously self-fertilised seeds as did the same number of short-styled plants. The chief cause of this great difference appears to be, that when the corolla of a long-styled plant falls off, the anthers, from being situated near the bottom of the tube are necessarily dragged over the stigma and leave pollen on it, as I saw when I hastened the fall of nearly withered flowers ; whereas in the short-styled flowers, the stamens are seated at the mouth of the corolla, and in falling off do not brush over the lowly-seated stigmas. Hildebrand likewise protected some long- styled and short-styled plants, but neither ever yielded a single capsule. He thinks that the difference in our results may be accounted for by his plants having been kept in a room and never having been shaken ; Chai'. I. TRIMULA AURICULA. 43 but this explanation seems to me doubtful ; bis plants were in a less fertile condition than mine, as shown by the difference in the number of seeds produced, and it is highly probable that their lessened fertility would have interfered with especial force with their capacity for producing self-fertilised seeds. Primula auricula.* Tliis species is hcterostyled, like the preceding ones ; but amongst the varieties distributed by florists the long-styled form is rare, as it is not valued. There is a much greater relative in- equality iu the length of the pistil and stamens in the two forms of the aui'icula than iu the cowslip ; the pistil in the long-styled being nearly four times as long as that in the short-styled, in which it is barely longer than the ovarium. The stigma is nearly of the same shaj^e in both forms, but is rougher iu the long-styled, though the difference is not so great as between the two fonns of the cowslip. In the long-styled plants the stamens are very short, rising but little above the ovarium. The pollen-grains of these short stamens, when distended with water, were barely^^^o of an inch iu diameter, whereas those from the long stamens of the short-styled plants were barely ^Jm,, showing a relative dif- ference of about 71 to 100. The smaller grains of the long- styled plant are also much more trans])arent, and before disten- tion ■with water more triangular in outline than tliose of the other form. Mr. Scott j comi)ared ten plants of both forms grow- ing under sunilar conditions, and found that, although the long- styled plant produced more umbels and more capsules than the shox-t-styled, yet they yielded fewer seeds, in the ratio of 6G to 100. Three short-styled plants were protected by me from tlie * According to Kemer our gar- short-styled 98 seeds per capsule : den auriculas are descemled fromP. see his " Geschichte der Aurikol,"' pubescens, Jacq., vrhich is a hybrid ' Zeitsclir. dcs Deutschen und Ocst. between the true P. auricula and Alpen-Vereins,' Band vi. p. 52. hirmta. This hybrid lias now been Also 'Dierrimulacecn-Bastarten,' propagated for about 300 years, ' Oest. Bot. Zoitschrift,' 1835, Noa. and produces, when legitimately 3, 4, and 5. fertilised, a large number of seeds; t 'Journ. Linn. Soc Bot.' voL the long-8tylehoeniceum the corolla is not cast * ' Bastarderzeugung,' p. 307. Smith,' vol. ii. p. 210. I was t This was first observed by giiided to these references by the Corrua de Serra: see Sir J. E. Eev. W. A. Leighton, who ob- Smith's ' English Flora,' 1824, vol. served this same phenomenon with i. p. 311 ; also 'Life of Sir J. K. V. virgalum. CiiAr. II. IIYBraD VERBASCUMS. 79 off, however often and severely the stem may be struck. In this curious property the above-described hybrids took after V. tliapsus; for I observed, to my surprise, that when I pulled off the flower-buds round the flowers which I wished to mark with a thread, the slight jar invariably caused the corollas to fall off. These hybrids are interesting under several points of view. First, from the number found in various parts of the same moderately-sized field. That they owed their origin to insects flying from flower to flower, whilst col- lecting pollen, there can be no doubt. Although in- sects thus rob the flowers of a most precious substance, yet they do great good ; for, as I have elsewhere shown,* the seedlings of F. tliapsus raised from flowers fertilised with pollen from another plant, are more vigorous than those raised from self-fertilised flowers. But in this particular instance the insects did great harm, as they led to the production of utterly barren plants. Secondly, these hybrids are remarkable from differing much from one another in many of their characters ; for hybrids of the first generation, if raised from uncultivated plants, are generally uni- form in character. That these hybrids belonged to the first generation we may safely conclude, from the absolute sterility of all those observed by me in a state of nature and of the one plant in my garden, excepting when artificially and repeatedly fertilised with jniro pollen, and then the number of seeds produced was extremely small. As these hybrids varied so much, an almost perfectly graduated series of forms, connecting together the two widely distinct parent-species, could easily have been selected. This case, like that of the common oxlip, shows that botanists ought to be ' The Efftcts of Cross and Self-fertilisatiou,' 187G, p. S9. 80 HYBRID VERBASCUMS. Ciiap. II. cautious in inferring the specific identity of two forms from the presence of intermediate gradations ; nor woukl it be easy in the many cases in which liybrids are moderately fertile to detect a slight degree of sterility in such plants growing in a state of nature and liable to be fertilised by either parent-species. Thirdly and lastly, these hybrids offer an excellent illustration of a state- ment made by that admirable observer Gartner, namely, that although plants which can be crossed with case generally produce fairly fertile offspring, yet well- pronounced exceptions to tliis rule occur ; and here we have two species of Verbascum which evidently cross with the greatest ease, but produce hybrids which are excessively sterile. CuAr. III. -LINUM CRANDIFLOEUM. 81 CHAPTEE III. IlETEnosTYLED DiMOUFHic I'lants — Continued. Liniim grandilloium, long-styled form utterly sterile with own-form pollen— Linum perenue, torsion of the pistils in the long-styled form alone — Ilomostyled species of Linum — Pulmonaria olHciiialis, singular difference in self-fertility between the English and Gorman long-styled plants — Pulmonaria a)igUbtifolia shown to be a distinct species, long-styled form completely self-sterile — Polygonum f igo- pyrum — Varioiis other heterostyled genera— Rubiaeeie — Mitehella repens, fertility of the flowers in pairs— Houstonia — Faramea, remarkable diffureuce in the pollen-grains of the two forms ; tor- sion of the stamens in the short-stykd form alone ; development not as yet perfect — The hiter.jstyled structure in the several Rubiaceous genera not due to descent in common. It lias long been known* that several species of Linum present two forms, and having observed this fact in L. jlavum more than thirty years ago, I was led, after ascertaining the nature of heterostylism in Primula, to examine the fii'st species of Linum which I met with, namely, the beautiful L. grandijiorum. This plant exists under two forms, occurring in about equal numbers, which differ little in structure, but greatly in function. The foliage, corolla, stamens, and pollen-grains (the latter examined both distended with water and dry) are alike in the two forms (Fig. 4). The difference is confined to the pistil ; in the short- styled form the styles and the stigmas are only about half the length of those in the long-styled. A more * Troviranus has shown that original paper, ' Cot. Zeitung,' this ia the case iu his review of my IStJo, p. Ibi). 82 HETEEOSTYLED DIMORPHIC PLANTS. Chap. III. important distinction is, that the five stigmas in the short-styled form diverge greatly from one another, and pass out between the filaments of the stamens, Fis. 4. Long-styleJ form. Short-styled form. 8 s stigmas. LiXL'M GU.VXDIFLORUJI. and thus lie within the tube of the corolla. In the long-styled form the elongated stigmas stand nearly: upright, and alternate with the anthers. In this latter form the length of the stigmas varies considerably, their upper extremities projecting even a little above tlie anthers, or reaching up* only to about their middle. Is^evertheless, there is never the slightest difficulty in distinguishing between the two forms ; for, besides the difference in the divergence of the stigmas, those of the short-styled form never reach even to the bases of the anthers. In this form the papilloe on the stig- matic surfaces are shorter, darker-coloured, and more crowded together than in the long-styled form ; but these differences seem due merely to the shortening of the stigma, for in the varieties of the long-styled form with shorter stigmas, the papillae are more crowded and darker-coloured than in those with the longer CiiAP. III. LIXUM GRANDIFLORUM. 83 stigmas, Cousidcring tlio slight and variable differ- ences between the two forms of this Linum, it is not surprising that hitherto they have been overlooked. In 1861 I had eleven plants in my garden, eight of which were long-styled, and three short-styled. Two very fine long-styled plants grew in a bed a hundred yards off all the others, and separated from them by a screen of evergreens. I marked twelve flowers, and placed on their stigmas a little pollen from the short- styled plants. The pollen of the two forms is, as stated, identical in appearance ; the stigmas of the long-styled flowers were already thickly covered with their own pollen — so thickly that I could not find one bare stigma, and it was late in the season, namely, September 15th. Altogether, it seemed almost childish to expect any result. Nevertheless from my experi- ments on Primula, I had faith, and did not hesitate to make the trial, but certainly did not anticipate the full result which was obtained. The germens of these twelve flowers all swelled, and intimately six fine cap- sules (the seed of which germinated on the following year) and two poor capsules were produced ; only four capsules shanking off. These same two long-styled plants produced, in the course of the summer, a vast number of flowers, the stigmas of which were covered with their own pollen ; but they all proved absolutely barren, and their germens did not even swell. The nine other plants, six long-styled and three short-styled, grew not very far apart in my flower- garden. Four of these long-styled plants produced no seed-capsules ; the fifth produced two ; and the remain- ing one grew so close to a short-styled plant that their branches touched, and this produced twelve cap- sules, but they were poor ones. The case was different 84 HETEROSTYLED DIMOrtPHIC PLANTS. Chap. III. with the sliort-styled plants. The one which grew close to the long-styled plant produced ninety-four imperfectly fertilised capsules containing a multitude of bad seeds, with a moderate number of good ones. The two other short-styled plants growing together were small, being partly smothered by other plants ; they did not stand very close to any long-styled plants, yet they yielded together nineteen capsules. These facts seem to show that the short-styled plants are more ' fertile with their own pollen than are the long-styled, and we shall immediately see that this probably is the case. But I suspect that the difference in fertility be- tween the two forms was in this instance in part due to a distinct cause. I repeatedly watched the flowers, and only once saw a humble-bee momentarily alight on one, and then fly aw ay. If bees had visited the several plants, there cannot be a doubt that the four long- styled plants, which did not produce a single capsule, would have borne an abundance. But several times I saw small diptera sacking the flowers ; and these insects, though not visiting the flowers with anything like the regularity of bees, would carry a little pollen from one form to the other, especially when growing near together ; and the stigmas of the short-styled plants, diverging within the tube of the corolla, would be more likely than the upright stigmas of the long- styled plants, to receive a small quantity of pollen if brought to them by small insects. Moreover from the greater number of the long-styled than of the short- styled plants in the garden, the latter would be more likely to receive pollen from the long-styled, than the long-styled from the short-styled. In 18C2 I raised thirty-four plants of this Linum in a hot-bed ; and these consisted of seventeen long-styled and seventeen short-stvled forms. Seed sown later in the Chap. III. LINOI GEANDIFLOEUM. 85 flower-garden yielded seventeen long-styled and twelve short-styled forms. These facts justify the statement that the two forms are produced in about equal num- bers. The thirty-four plants of the first lot were kept under a net which excluded all insects, except such minute ones as Thrips. I fertilised fourteen long-styled flowers legitimately with pollen from the short-styled, and got eleven fine seed-capsules, which contained on an average 8*6 seeds per capsule, but only 5*6 appeared to be good. It may be well to state that ten seeds is the maximum production for a caj)sule, and that our climate cannot be very favourable to this North- African plant. On three occasions the stigmas of nearly a hundred flowers were fertilised illegitimately with their own-form pollen, taken from separate plants, so as to prevent any possible ill effects from close inter-breed- ing. Many other flowers were also produced, which, as before stated, must have received plenty of their own pollen ; yet from all these flowers, borne by the seven- teen long-styled plants, only three capsules were pro- duced. One of these included no seed, and the other two together gave only five good seeds. It is probable that this miserable product of two half-fertile capsules from the seventeen plants, each of which must have produced at least fifty or sixty flowers, resulted from their fertilisation with pollen from the short-styled plants by the aid of Thrips ; for I made a great mistake in keeping the two forms under the same net, with their branches often interlocking ; and it is sur- prising that a greater number of flowers were not accidentally fertilised. Twelve short-styled flowers were in this instance castrated, and afterwards fertilised legitimately ^^■ith pollen from the long-styled form ; and they produced seven fine capsules. These included on an average 8G HETEROSTYLED DIMORPHIC PLANTS. Chap. III. 7 • G seeds, but of apparently good seed only 4 • 3 per capsule. At three separate times nearly a hundred flowers were fertilised illegitimately with their own- form pollen, taken from separate plants ; and nu- merous other flowers were produced, many of which must have received their own pollen. From all these flowers on the seventeen short-styled plants only fifteen capsules were produced, of which only eleven con- tained any good seed, on an average 4 • 2 per capsule. As remarked in the case of the long-styled plants, some even of these capsules were perhaps the product of a little pollen accidentally fallen from the adjoining flowers of the other form on to the stigmas, or trans- ported by Thrips. Nevertheless the short-styled plants seem to be slightly more fertile with their own pollen than the long-styled, in the proportion of fifteen cap- sules to three; nor can this difference be accounted for by the short-styled stigmas being more liable to receive their own pollen than the long-styled, for the reverse is the case. The greater self-fertility of the short-styled flowers was likewise shown in 1861 by the plants in my flower-garden, which were left to themselves, and were but sparingly visited by insects. On account of the probability of some of the flowers on the plants of both forms, which were covered under the same net, having been legitimately fertilised in an accidental manner, the relative fertility of the two lejritimate and two illec:itimate unions cannot be compared with certainty ; but judging from the number of good seeds per capsule, the difl"erence was at least in the ratio of 100 to 7, and probably much greater. Hildcbrand tested my results, but only on a single short-styled plant, by fertilising many flowers with their own-form pollen ; and these did not produce any Chap. III. LINUM GRANDIFLORUM. 87 seed. Tliis confirms my suspicion that some of the few capsuh^s produced by the foregoing seventeen short-styled phints were the product of accidental legitimate fertilisation. Other flowers on the same plant were fertilised by Hildebrand with pollen from the long-styled form, and all produced fruit.* The absolute sterility (judging from the experi- ments of 1861) of the long-styled plants with their own-form pollen led me to examine into its apparent cause ; and the results are so curious that they are worth giving in detail. The experiments were tried on plants grown in jiots and brought successively into the house. First. Pollen from a short-styled plant was placed on the five stigmas of a long-styled flower, and these, after thirty hours, were found deeply penetrated by a multitude of pollen-tubes, far too numerous to be counted ; the stigmas had also become discoloured and twisted. I repeated this experiment on another flower, and in eighteen hours the stigmas were pene- trated by a multitude of long pollen-tubes. This is what might have been expected, as the union is a legitimate one. The converse experiment was likewise tried, and pollen from a long-styled flower was placed on the stigmas of a short-styled flower, and in twenty- four hours the stigmas were discoloured, twisted, and penetrated by numerous pollen-tubes ; and this, again, is what might have been expected, as the union was a legitimate one. Secondhj. Pollen from a long-styled flower was placed on all five stigmas of a long-styled flower on a separate plant : after nineteen hours the stigmas were dissected, and only a single pollen-grain had emitted a tube, * 'Bot. Zeitung,' Jau. 1, 18G4, p. 2. 5 88 HETEROSTYLED DIMOEPHIC PLANTS. Chap. III. and tbis was a very short one. To make sure that the pollen was good, I took in this case, and in most of the other cases, pollen either from the same anther or from the same flower, and proved it to be good by- placing it on the stigma of a short-styled plant, and found numerous pollen-tubes emitted. Tliirdly. Repeated last experiment, and placed own- form pollen on all five stigmas of a long-styled flower ; after nineteen hours and a half, not one single grain had emitted its tube. Fourthly. Repeated the experiment, with the same result after twenty-four hours. Fifthly. Repeated last experiment, and, after leaving pollen on for nineteen hours, put on an additional quantity of own-form pollen on all five stigmas. After an interval of three days, the stigmas were examined, and, instead of being discoloured and twisted, they were straight and fresh-coloured. Only one grain had emitted a quite short tube, which was drawn out of the stigmatic tissue without being ruptured. The following experiments are more striking : — Sixthly. I placed own-form pollen on three of the stigmas of a long-styled flower, and pollen from a short-styled flower on the other two stigmas. After twenty-two hours these two stigmas were discoloured, slightly twisted, and penetrated by the tubes of nu- merous pollen-grains : the other three stigmas, covered with their own-form pollen, were fresh, and all the pollen-grains were loose ; but I did not dissect the whole stigma. Seventhly. Experiment repeated in the same manner, with the same result. Eighthly. Experiment repeated, but the stigmas were carefully examined after an interval of only five hours and a half. The two stigmas with pollen from a CuAP. III. LINUM GRANDIFLORUM. 89 short-styled flower weve penetrated by innumerable tubes, which were as yet sliort, and the stigmas them- selves were not at all discoloured. The three stigmas covered with their own-form pollen were not pene- trated by a single pollen-tube. Ninthhj. Put pollen of a short-styled flower on a single long-styled stigma, and own-form pollen on the other four stigmas ; after twenty-four hours the one stigma was somewhat discoloured and twisted, and penetrated by many long tubes : the other four stigmas were quite straight and fresh ; but on dissecting them I found that three pollen-grains had protruded very short tubes into the tissue. Tenthhj. Repeated the experiment, with the same result after twenty-four hours, excepting that only two ouTi-form grains had penetrated the stigmatic tissue with their tubes to a very short depth. The one stigma, which was deeply penetrated by a multitude of tubes from the short-styled pollen, presented a conspicuous difference in being much curled, half- shrivelled, and discoloured, in comparison with the other four straight and bright pink stigmas. I could add other experiments ; but those now given amply suffice to show that the pollen-grains of a short-styled flower placed on the stigma of a long- styled flower emit a multitude of tubes after an in- terval of from five to six hours, and penetrate the tissue ultimately to a great depth ; and that after twenty-four hours the stigmas thus penetrated change colour, become twisted, and appear half-withered. On the other hand, pollen-grains from a long-styled flower placed on its own stigmas, do not emit their tubes after an interval of a day, or even three days ; or at most only three or four grains out of a multitude emit their tubes, and these apparently never penetrate the 90 HETEROSTYLED DIMOEPHIC PLANTS. Chat. III. stigmatic tissue deeply, and the stigmas themselves do not soon become discoloured and twisted. This seems to me a remarkable physiological fact. The pollen-grains of the two forms are undistinguish- able under the microscope ; the stigmas differ only in length, degree of divergence, and in the size, shade of colour, and approximation of their papilla), these latter differences being variable and apparently due merely to the degree of elongation of the stigma. Yet we plainly see that the two kinds of pollen and the two stigmas are widely dissimilar in their mutual reaction — the stigmas of each form being almost powerless on their own pollen, but causing, through some myste- rious influence, ajDparently by simple contact (for I could detect no viscid secretion), the pollen-grains of the opposite form to protrude their tubes. It may be said that the two pollens and the two stigmas mutually recognise each other by some means. Taking fertility as the criterion of distinctness, it is no exaggeration to say that the pollen of the long-styled Linum grandi- florum (and conversely that of the other form) has been brought to a degree of differentiation, with respect to its action on the stigma of the same form, correspond- ing with that existing between the pollen and stigma of species belonging to distinct genera. Linum perenne. — This species is conspicuously hetero- styled, as has been noticed by several authors. The pistil in the long-styled form is nearly twice as long as that of the short-styled. In the latter the stigmas are smaller and, diverging to a greater degree, pass out low down between the filaments. I could detect no difference in the two forms in the size of the stigmatic papilla3. In the long-styled form alone the stigmatic surfaces of the mature pistils twist round, so as to face the circumference of the flower ; but to this point I Chap. III. LIXUM PERENNE. 91 shall presently return. Differently from what occurs in L. grandijloruin, the long-styled flowers have stamens luirdly more than half the length of those in the short- styled. The size of the pollen-grains is rather variable ; after some doubt, I have come to the conclusion that there is no uniform difference between the grains in the two forms. The long stamens in the short-styled form project to some height above the corolla, and their filaments are coloured blue apparently from ex- posure to the light. The anthers of the longer stamens correspond in height with the lower part of the stigmas of the long-styled flowers; and the anthers of the shorter stamens of the latter correspond in the same manner in height with the stigmas of the short-styled fl owers. I raised from seed twenty-six plants, of which twelve proved to be long-styled and fourteen short-styled. They flowered well, but were not large plants. As I did not expect them to flower so soon, I did not trans- l)lant them, and they unfortunately grew with their branches closely interlocked. All the plants were covered under the same net, excepting one of each form. Of the flowers on the long-styled plants, twelve were illegitimately fertilised ^vith their own-form pol- len, taken in every case from a separate plant ; and not one set a seed-capsule : twelve other flowers were legi- timately fertilised with pollen from short-styled flowers ; and they set nine capsules, each including on an average 7 good seeds, ten being the maximum number ever produced. Of the flowers on the short-styled plants, twelve were illegitimately fertilised with own- form pollen, and they yielded one capsule, including only 3 good seeds ; twelve other flowers were legiti- mately fertilised with pollen from long-styled flowers, and these produced nine capsules, but one was bad ; 92 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. the eight good cap.sules contained on an average 8 good seeds each. Judging from the number of seeds per capsule, the fertility of the two legitimate to that of the two illegitimate unions is as 100 to 20. The numerous flowers on the eleven long-styled plants under the net, which were not fertilised, produced only three capsules, including 8, 4, and 1 good seeds. Whether these three capsules were the product of acci- dental legitimate fertilisation, owing to the branches of the plants of the two forms interlocking, I will not pretend to decide. The single long-styled plant which was left uncovered, and grew close by the uncovered short-styled plant, produced five good pods ; but it was a poor and small plant. The flowers borne on the thirteen short-styled plants under the net, which were not fertilised, produced twelve capsules, containing on an average 5 • 6 seeds. As some of these capsules were very fine, and as five were borne on one twig, I suspect that some minute insect had accidentally got under the net and had brought pollen from the other form to the flowers which produced this little group of capsules. The one uncovered short-styled plant which grew close to the uncovered long-styled plant yielded twelve capsules. From these facts we have some reason to believe, as in the case of L. grandijlorum, that the short-styled plants are in a slight degree more fertile with their own pollen than are the long-styled plants. Anyhow we have the clearest evidence, that the stigmas of each form require for full fertility that pollen from the sta- mens of corresponding height belonging to the opposite form should be brought to them. Hildebrand, in the paper lately referred to, confirms my results. He placed a short-styled plant in his house, and fertilised about 20 flowers with their own Chap. UI. LINUM TEREXNE. 93 pollen, and about 30 with pollen from another plant belonging to the same form, and these 50 flowers did not set a single capsule. On the other hand he ferti- lised about 30 flowers with pollen from the long-styled form, and these, with the exception of two, yielded capsules, containing good seeds. It is a singular fact, in contrast with what occurred in the case ot L. grandijiorum, that the pollen-grains of both forms of L. perenne, when placed on their own- form stigmas, emitted their tubes, though this action did not lead to the production of seeds. After an interval of eighteen hours, the tubes penetrated the stigmatic tissue, but to what depth I did not ascertain. In this case the impotence of the pollen-grains on their o\\u stigmas must have been due either to the tubes not reaching the ovules, or to their not acting pro- perly after reaching them. The plants both of L.perenne and grandijiorum grew, as already stated, with their branches interlocked, and with scores of flowers of the two forms close together ; they were covered by a rather coarse net, through w hich the wind, when high, passed ; and such minute insects as Thrips could not, of course, be excluded ; yet we have seen that the utmost possible amount of accidental fer- tilisation on seventeen long-styled plants in the one case, and on eleven long-styled plants in the other, resulted in the production, in each case, of three poor capsules ; so that when the proper insects are excluded, the wind does hardly anything in the way of carrying pollen from plant to plant. I allude to this fact because botanists, in speaking of the fertilisation of various flowers, often refer to the wind or to insects as if the alternative were indifferent. This view, ac- cording to my experience, is entirely erroneous. When the wind is the agent in carrying pollen, either from 94 IIETEROSTYLED DIMORPHIC PLANTS. Chap. III. one sex to the other, or from hermaphrodite to herma- phrodite, we can recognise structure as manifestly ad- apted to its action as to that of insects when these are the carriers. We see adaptation to the wind in the in- coherence of the pollen, — in the inordinate quantity produced (as in the Cohifera?, Spinage, &c.), — in the dangling anthers well fitted to shake out the pollen, — in the absence or small size of the perianth, — in the protrusion of the stigmas at the period of fertilisation, — in the flowers being produced before they are hidden by the leaves, — and in tlie stigmas being downy or plumose (as in the Graminese, Docks, &c,), so as to secure the chance-blown grains. In plants which are fertilised by the wind, the flowers do not secrete nectar, their pollen is too incoherent to be easily collected by insects, they have not bright-coloured corollas to serve as guides, and they are not, as far as I have seen, visited by insects. When insects are the agents of fer- tilisation (and this is incomparably the more frequent case with hermaphrodite plants), the wind plays no part, but we see an endless number of adaptations to ensure the safe transport of the pollen by the living Avorkers. These adaptations are most easily recognised in irregular flowers ; but they are present in regular flowers, of which those of Linum offer a good instance, as I will now endeavour to show. I have already alluded to the rotation of each sepa- rate stigma in the long-styled form of Linum jperenne. In both forms of the other heterostyled species and in the homostyled species of Linum which I have seen, the stigmatic surfaces face the centre of the flower, with the furrowed backs of the stigmas, to which the styles are attached, facing outwards. This is the case with the stigmas of the long-styled flowers of L. perenne whilst in bud. But by the time the flowers CiiAi'. III. LINUM PERENNE. 95 have expanded, the five stigmas twist round so as to face the circumference, owing to the torsion of that part of the style which lies beneath the stigma.. I should state that the five stigmas do not always turn round completely, two or three sometimes facing only obliquely outwards. My observations were made during October ; and it is nut improbable that earlier in the season the torsion would have been more com- plete ; for after two or three cold and wet days the movement was very imperfectly performed. The flowers should be examined shortly after their ex- pansion, as their duration is brief; as soon as they begin to wither, the styles become spirally twisted all together, the original position of the parts being thus lost. He who will compare the structure of the whole flower in both forms of L. jperenne and r/ranclijiorum, and, as I may add, of L.jiavum, will not doubt about the meaning of this torsion of the styles in the one form alone of L. jperenne, as well as tlie meaning of the divergence of the stigmas in the short-styled form of all three species. It is absolutely necessary as we know, that insects should carry pollen from the flowers of the one form reciprocally to those of the other. Insects are attracted by five drops of nectar, secreted exteriorly at the base of the stamens, so that to reach these drops they must insert their proboscides outside the ring of broad filaments, be- tween them and the petals. In the short-styled form of the above three species, the stigmas face the axis of the flower ; and had the styles retained their original upright and central position, not only would the stig- mas have presented their backs to the insects which sucked the flowers, but their front and fertile surfaces would have been separated from the entering insects 96 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. by the ring of broad filaments, and would never have received any pollen. As it is, the styles diverge and pass out between the filaments. After this move- ment the short stigmas lie within the tube of the corolla ; and their papillous surfaces being now turned upwards are necessarily brushed by every entering insect, and thus receive the required pollen. In the long-styled form of L. grandiflorum, the almost parallel or slightly diverging anthers and stigmas project a little above the tube of the somewhat concave flower ; and they stand directly over the open space leading to the drops of nectar. Consequently when insects visit the flowers of either form (for the stamens in this species occupy the same position in both forms), they will get their foreheads or proboscides well dusted with the coherent pollen. As soon as they visit the flowers of the long-styled form they will necessarily leave pollen on the proper surface of the elongated stigmas ; and when they visit the short- styled flowers, they will leave pollen on the upturned stigmatic surfaces. Thus the stigmas of both forms will receive indifierently the pollen of both forms ; but we know that the pollen alone of the opposite form causes fertilisation. In the case of L. perenne, affairs are arranged more perfectly ; for the stamens in the two forms stand at different heights, so that pollen from the anthers of the longer stamens will adhere to one part of an insect's body, and will afterwards be brushed ofl" by the rough stigmas of the longer pistils ; whilst pollen from the anthers of the shorter stamens will adhere to a different pa.rt of the insect's body, and will afterwards be brushed off by the stigmas of the shorter pistils ; and this is what is required for the legitimate fertilisa- tion of both forms. The corolla of L. loerenne is more Ohap. III. LINmi PERENNE. 97 expanded than that of L. grandijlorum, and the stigmas of the long-styled form do not diverge greatly from one another; nor do the stamens of either form. Hence insects, especially rather small ones, will not insert their proboscidcs between the stigmas of the long-styled form, nor between the anthers of either form (Fig. 5), but will strike against them, at nearly right angles, with the backs of their head or thorax. Now, in the long-styled flowers, if each stigma did Long-styled form of L. perenxe, var. Austriacum in its early condition before the stigmas have rotated. The petals and calyx have been removed on the near side.* not rotate on its axis, insects in visiting them would strike their heads against the backs of the stigmas ; as it is, they strike against that surface which is covered * I neglected to get drawings made from fresh flowers of the two forms. But Mr. Fitch has made the above sketch of a long-styled flower from dried specimens and from published engravings. His well-known skill ensures accuracy in the proportional size of the parts. 98 HETEEOSTYLED DIMORPHIC PLANTS. Cuap. III. with papillfc, with their heads already charged with pollen from the stamens of corresponding height borne by the flowers of the other form, and legitimate fertilisation is thus ensured. Thus we can understand the meaning of the torsion of the styles in the long-styled flowers alone, as well as their divergence in the short-styled flowers. One other point is worth notice. In botanical works many flowers are said to be fertilised in the bud. This statement generally rests, as far as I can discover, on the anthers opening in the bud ; no evidence being adduced that the stigma is at this period mature, or that it is not subsequently acted on by pollen brought from other flowers. In the case of Cephalanthera grandijiora I have shown* that precocious and partial seK-fertilisation, with subsequent full fertilisation, is the regular course of events. The belief that the flowers of many plants are fertilised in the bud, that is, are perpetually self-fertilised, is a most effectual bar to understanding their real structure. I am, however, far from wishing to assert that some flowers, during certain seasons, are not fertilised in the bud ; for I have reason to believe that this is the case. A good observer, t resting his belief on the usual kind of evidence, states that in Linum Austriacum (which is heterostyled, and is considered by Planchon as a variety of L. perenne) the anthers open the evening before the expansion of the flowers, and that the stigmas are then almost always fertilised. Now we know positively that, so far from Linum perenne being fertilised by its own pollen in the bud, its own pollen is as powerless on the stigma as so much inorganic dust. Linum jiavum. — The pistil of the long-styled form * ' Fertilisation of Orchids,' t ' Etudes siir la Ge'ogr. Bot.,* p. 108.— 2ncl edit. 1877, p. 84. H. Lecoq, 1856, torn. v. p. 325. Chap. III. LINUM FLAVUM. 99 of this species is nearly twice as long as that of the short-styled; the stigmas are longer and the papillae coarser. In the short-styled form the stigmas diverge and pass ont between the filaments, as in the previous species. The stamens in the two forms diifer in length; and, what is singular, the anthers of the longer stamens are not so long as those of the other form ; so that in the short-styled form both the stigmas and the anthers are shorter than in the long-styled form. The pollen-grains of the two forms do not differ in size. As this species is propagated by cuttings, generally all the plants in the same garden belong to the same form. I have inquired, but have never heard of its seeding in this country. Certainly my own plants never produced a single seed as long as I possessed only one of the two forms. After considerable search I procured both forms, but from want of time only a few experiments were made. Two plants of the two forms were planted some way apart in my garden, and were not covered by nets. Three flowers on the long-styled plant were legitimately fertilised with pollen from the short-styled plant, and one of them set a fine capsule. No other capsules were produced by this plant. Three flowers on the short-styled plant were legitimately fertilised with pollen from the long-styled, and all three produced capsules, containing respectively no less than 8, 9, and 10 seeds. Three other flowers on this plant, which had not been artificially fertilised, produced capsules containing 5, 1, and 5 seeds ; and it is quite possible that pollen may have been brought to them by insects from the long-styled plant growing in the same garden. Nevertheless, as they did not yield half the number of seeds compared with the other flowers on the same plant which had been artificially and legitimately fertilised, and as the 100 IIETEEOSTYLED DIMORPHIC PLANTS. Chap. III. short-styled plants of the two previous species appa- rently evince some slight capacity for fertilisation with their own-form pollen, these three capsules may have been the product of self-fertilisation. Besides the three species now described, the yellow- flowered L. cori/mhiferum is certainly heterostyled, as is, according to Planchon,* L. salsoloides. This botanist is the only one who seems to have inferred that heterostylism might have some important func- tional bearing. Dr. Alefeld, who has made a special study of the genus, saysf that about half of the sixty- five species known to him are heterostyled. This is the case with L. trigrjnum, which differs so much from the other species that it has been formed by him into a distinct genus, J According to the same author, none of the species which inhabit America and the Cape of Good Hope are heterostyled. I have examined only three homostyled species, namely, L. tisitatissimum, angustifolium, and caiharti- cum. I raised 111 plants of a variety of the first-named species, and these, when protected under a net, all produced plenty of seed. The flowers, according to H. Miiller,§ are frequented by bees and moths. With respect to L. catharticum, the same author shows that the flowers are so constructed that they can freely fertilise themselves ; but if visited by insects they might be cross-fertilised. He has, however, only once seen the flowers thus visited drn-ing the day ; but it * Hooker's ' Loudon Journal of Journal of Botany,' 1848, vol. Botany,' 1848, vol. vii. p. 174. vii. p. 525) to be provided with t 'i3ot. Zeitung,' Sep. 18tb, " staminibus exsertis;'' another 1863, p. 281. with " stylia staminibus longiori- X It is not improbable that the bus," and anotlier has "stamina allied genus, Hugonia, is hetero- 5, majora, stylos longe superantia." styled, for one species is said § ' Die Befruchtung der Blu- by Planchon (Hooker's ' London men,' &c., p. 168. Chap. III. PULMONAEIA OFFICINALIS. 101 may be suspected that they are frequented during the night by small moths for the sake of the five minute drops of nectar secreted. Lastly, L. Lewisii is said by Planchon to bear on the same plant flowers with stamens and pistils of the same height, and others with the pistils either longer or shorter than the stamens. This case formerly appeared to me an extraordinary one ; but I am now inclined to believe that it is one merely of great variability.* PULMOXAEIA (BOEAGIXE.E). Palmonaria officinalis. — Hildebrand has published f a full account of this heterostyled plant. The pistil of the long-styled form is twice as long as that of the short-styled ; and the stamens differ in a corresponding, though converse, manner. There is no marked dif- ference in the shape or state of surface of the stigma in the two forms. The pollen-grains of the short- styled form are to those of the long-styled as 9 to 7, or as 100 to 78, in length, and as 7 to 6 in breadth. They do not differ in the appearance of their contents. The corolla of the one form differs in shape from that of the other in nearly the same manner as in Primula ; but besides this difference the flowers of the short- styled are generally the larger of the two. Hilde- brand collected on the Siebengebirge, ten wild long- styled and ten short-styled plants. The former bore 289 flowers, of which 186 (i.e. 64 per cent.) had set fruit, yielding 1-88 seed per fruit. The ten short- styled plants bore 373 flowers, of which 262 (i.e. * Planclion, in HfKiker's ' Lon- of Science,' vol. xxxvi. Sept. 1863, don Journal of liotany,' 1S18, vol. p. 284. vii. p. 175. See on this subject t ' Bot. Zcitung,' 18G5. Jan. 13, Asa Gray, in ' American Journal p. 13. 102 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. 70 per cent.) Lad set fruit, yielding 1*86 seed per fruit. So that the short-styled plants produced many more flowers, and these set a ratlier larger proportion of fruit, but the fruits themselves yielded a slightly lower average number of seeds than did the long- styled plants. The results of Hildebrand's experiments on the fertility of the two forms are given in the fol- lowing table : — Table 19. Pulmonaria officinalis {from, Eildehrand). Nature of Union. i?i™„™ of Fruits Average Number of Seeds per Fruit. Long-styled flowers, by pollen of short-'l styled. Legitimate union . . . ./ 14 10 1-30 Long-styled flowers, 14 by own-pollen, 1 and 16 by pollen of other plant of same) 30 form. Illegitimate union .... i ' Short-styled flowers, by pollen of long-V ifi 14 1-57 styled. Legitimate union . . . ./| i Short-styled flowers, 11 by own pollen,!' 14 by pollen of other plant of same> 25 form. Illegitimate union . . . .) In the summer of 1864, before I had heard of Hilde- brand's experiments, I noticed some long-styled plants of this species (named for me by Dr. Hooker) growing by themselves in a garden in Surrey ; and to my surprise about half the flowers had set fruit, several of which contained 2, and one contained even 3 seeds. These seeds were sown in my garden and eleven seedlings thus raised, all of which proved long-styled, in accordance with the usual rule in such cases. Two years afterwards the plants were left uncovered, no Chap. III. PULMONAEIA OFFICINALIS. 103 other plant of the same genus growing in my garden, and the flowers were visited by many bees. They set an abundance of seeds : for instance, I gathered from a single plant rather less than lialf of the seeds which it had produced, and they numbered 47. Therefore this illegitimately fertilised plant must have produced about 100 seeds ; that is, thrice as many as one of the wild long-styled plants collected on the Siebengebirge by Hildebrand, and which, no doubt, had been legitimately fertilised. In the following year one of my plants was covered by a net, and even under these un- favourable conditions it produced spontaneously a few seeds. It should be observed that as the flowers stand either almost horizontally or hang considerably downwards, pollen from the short stamens would be likely to fall on the stigma. We thus see that the English long-styled plants when illegitimately ferti- lised were highly fertile, whilst the German plants similarly treated by Hildebrand were completely sterile. How to account for this wide discordance in our results I know not. Hildebrand cultivated his plants in pots and kept them for a time in the house, whilst mine were grown out of doors ; and he thinks tliat this difference of treatment may have caused the diflcrence in our results. But this does not appear to me nearly a sufiicient cause, although his plants were slightly less productive than the wild ones growing on the Siebengebirge. My plants exhibited no ten- dency to become equal-styled, so as to lose their proper long-styled character, as not rarely happens under cultivation with several hcterostyled species of Pri- mula ; but it would appear that they had been greatly aficcted in function, either by long-continued cultiva- tion or by some other cause. We shall see in a future chapter that hcterostyled plants illegitimately 104 HETEEOSTYLED DIMORPHIC PLANTS. CiiAi'. III. iertiliscd during several successive generations some- times become more self-fertile ; and this may have been tlie case with my stock of the present species of Pulmonaria ; but in this case we must assume that the long-styled plants were at first sufficiently fertile to yield some seed, instead of being absolutely self-sterile like the German plants. Pulmonaria angustifolia. — Seedlings of this plant, raised from plants growing wild in the Isle of Wight, were named for me by Dr. Hooker. It is so closely allied to the last species, differing chiefly in the shape and spotting of the leaves, that the two have been con- sidered by several eminent botanists — for instance, Bentham — as mere varieties. But, as w^e shall presently see, good evidence can be assigned for ranking them as distinct. Owing to the doubts on this head, I tried whether the two would mutually fertilise one another. Twelve short-styled flowers of P. angustifolia were legitimately fertilised with pollen from long-styled plants of P. officinalis (which, as we have just seen, are moderately self-fertile), but they did not produce a single fruit. Thirty-six long-styled flowers of P. angustifolia were also illegitimately fertilised during two seasons with pollen from the long-styled P. officinalis, but all these flowers dropped off unim- pregnated. Had the plants been mere varieties of the same sjjecies these illegitimate crosses would probably have yielded some seeds, judging from my success in illegitimately fertilising the long-styled flowers of P. officinalis ; and the twelve legitimate crosses, instead of yielding no fruit, would almost certainly have yielded a considerable number, namely, about nine, judging from the results given in the fol- lowing table (20). Therefore P. officinalis and angusti- folia appear to be good and distinct, species, in Chap. III. PULMONAKIA ANGTISTIFOLIA. 105 conformity with other important functional differences between them, immediately to be described. The long-styled and short-styled flowers of P. angus- tifolia differ from one another in structure in nearly the same manner as those of P. officinalis. But in the accompanying figure a slight bulging of the corolla Fie:. 6. Long-styled form. Shoit-styied form. PrLilOXARIA AKGUSTIFOLIA. in the long-styled form, where the anthers are seated, has been overlooked. IMy son William, who examined a large number of wild plants in the Isle of Wight, observed that the corolla, though variable in size, was generally larger in the long-styled flowers tlian in the short-styled ; and certainly the largest corollas of all were found on the long-styled plants, and the smallest on the short-styled. Exactly the reverse occurs, ac- cording to Hildebrand, with P. officinalis. Both the pistils and stamens of P. angustifolia vary much in length ; so that in the short-styled fonn the distance between the stigma and the anthers varied from 119 to 65 divisions of the micrometer, and in the long- styled from 115 to 112. From an average of seven lOG HETEEOSTYLED DIMORPHIC PLANTS. Chap. III. measurements of each form the distance between these organs in the long-styled is to the same distance in the short-styled form as 100 to 69 ; so that the stigma in the one form does not stand on a level with the anthers in the other. The long-styled pistil is some- times thrice as long as that of tlie short-styled ; but from an average of ten measurements of both, its length to that of the short-styled was as 100 to 56. The stigma varies in being more or less, though slightly, lobed. The anthers also vary much in length in both forms, but in a greater degree in the long-styled than in the short-styled form ; many in the former being from 80 to 63, and in the latter from 80 to 70 divisions of the micrometer in length. From an average of seven measurements, the short- styled anthers were to those from the long-styled as 100 to 91 in length. Lastly, the pollen-grains from the long-styled flowers varied between 13 and 11*5 divisions of the micrometer, and those from the short- styled between 15 and 13. The average diameter of 25 grains from the latter, or short-styled form, was to that of 20 grains from the long-styled as 100 to 91. We see, therefore, that the pollen-grains from the smaller anthers of the shorter stamens in the long- styled form are, as usual, of smaller size than those in the other form. But what is remarkable, a larger proportion of the grains were small, shrivelled, and worthless. This could be seen by merely comparing the contents of the anthers from several distinct plants of each form. But in one instance my son found, by counting, that out of 193 grains from a long-styled flower, 53 were bad, or 27 per cent. ; whilst out of 265 grains from a short-styled flower only 18 were bad, or 7 per cent. From the condition of the pollen in the long-styled form, and from the extreme varia- Chap. III. PULMONAEIA ANGUSTIFOLIA. 107 bility of all the organs in both forms, we may perhaps suspect that the plant is undergoing a change, and tending to become dioecious. My son collected in the Isle of Wight on two occa- sions 202 plants, of which 125 were long-styled and 77 sbort-styled ; so tliat the former were the more numerous. On the other hand, out of 18 plants raised by me from seed, only 4 were long-styled and 14 short-styled. The short-styled plants seemed to my son to produce a greater number of flowers than the long-styled ; and he came to this conclusion before a similar statement had been published by Hildebrand with respect to P. officinalis. My son gathered ten branches from ten different plants of both forms, and found the number of flowers of the two forms to be as 100 to 89, 190 being short-styled and 169 long-styled. With P. officinalis the difference, according to Hilde- brand, is even greater, namely, as 100 flowers for the short-styled to 77 for the long-styled plants. The lol lowing table shows the results of my experi- ments : — Table 20. Pulmonaria anguallfulia. Nature of the Union. Number of Flowers fertilised. Number of Fmits produced. Average Number of Seeds per Fruit. Long-styled flowers, by pollen of short-1 styled. Legitimate union . . . . / 18 9 2-11 Long-styled flowers, by own-form pollen.j Illegitimate union / 18 Short-styled flowers, by pollen of long-"> styled. Legitimate union ... ./ 18 15 2-60 Short-styled flowers, by own-form pollen."> Illegitimate union , 12 7 1-86 108 IIETEROSTYLED DIMORPHIC PLANTS. Ciur. III. We sec in this table that tlie fertility of the two lecfitimate unions to that of tlie two illegitimate together is as 100 to 35, judged by the proportion of flowers w hicli produced fruit ; and as 100 to 32, judged by the average number of seeds per fruit. But the small number of fruit yielded by the 18 long-styled flowers in the first line was probably accidental, and if so, the difference in the proportion of legitimately and illegitimately fertilised flowers which yield fruit is really greater than that represented by the ratio of 100 to 35. The 18 long-styled flowers illegitimately fertilised yielded no seeds, — not even a vestige of one. Two long-styled plants which were placed under a net produced 138 flowers, besides those which were arti- ficially fertilised, and none of these set any fruit ; nor did some plants of the same form which were pro- tected during the next summer. Two other long- styled plants were left uncovered (all the short-styled plants having been previously covered up), and humble-bees, w'hicli had their foreheads white with pollen, incessantly visited the flowers, so that their stigmas must have received an abundance of pollen, yet these flowers did not produce a single fruit. We may therefore conclude that the long-styled plants are absolutely barren with their own-form pollen, though brought from a distinct plant. In this re- spect they differ greatly from the long-styled Englisli plants of P. offieinalis which were found by me to be moderately self-fertile; but they agree in their behaviour with the German plants of P. officinalis experimented on by Hildebrand. Eighteen short-styled flowers legitimately fertilised yielded, as may be seen in Table 20, 15 fruits, each having on an average 2 * 6 seeds. Four of these fruits contained the highest possible number of seeds, namely Chap. III. TULMONAEIA AXGUSTIFOLIA. 109 4, and four other fruits contained each 3 seeds. The 12 illegitimately fertilised short-styled flowers yielded 7 fruits, iucludiug on an average 1 • 86 seed ; and one of these fruits contained the maximum number of 4 seeds. This result is very surprising in contrast with the absolute barrenness of the long-styled flowers when illegitimately fertilised ; and I was thus led to attend carefully to the degree of self-fertility of the short-styled plants. A plant belonging to this form and covered by a net bore 28 flowers besides those which had been artificially fertilised, and of all these only two produced a fruit each including a single seed. This high degree of self-sterility no doubt depended merely on the stigmas not receiving any pollen, or not a sufii- cient quantity. For after carefully covering all the long-styled plants in my garden, several short-styled plants were left exposed to the visits of humble-bees, and their stigmas will thus have received plenty of short-styled pollen ; and now about half the flowers, thus illegitimately fertilised, set fruit. I judge of this proportion partly from estimation and partly from having examined three large branches, which had borne 31 flowers, and these produced 16 fruits. Of the fruits produced 233 were collected (many being left un- gathered), and these included on an average 1*82 seed. No less than 16 out of the 233 fruits included the highest possible number of seeds, namely 4, and 31 included 3 seeds. So we see how highly fertile these short-styled plants were when illegitimately fer- tilised with their own-form pollen by the aid of bees. The great difference in the fertility of the long and short-styled flowers, when both are illegitimately fer- tilised, is a unique case, as far as I have observed with heterostyled plants. The long-styled flowers when thus fertilised are utterly barren, whilst about haK of the 110 HETEEOSTYLED DIMORPHIC PLANTS. Chap. III. short-styled ones produce capsules, and these include a little above two-thirds of the number of seeds yielded by them when legitimately fertilised. The sterility of the illegitimately fertilised long-styled flowers is prob- ably increased by the deteriorated condition of their pollen ; nevertheless this pollen was highly efficient when applied to the stigmas of the short-styled flowers. A\'ith several species of Primula the short-styled flowers are much more sterile than the long-styled, when both are illegitimately fertilised ; and it is a tempting view, as formerly remarked, that this greater sterility of the short-styled flowers is a special adapta- tion to check self-fertilisation, as their stigmas are eminently liable to receive their own pollen. This view is even still more tempting in the case of the long- styled form of Linum grandiflorum. On the other hand, with Pulmonaria angustifolia, it is evident, from the corolla projecting obliquely upwards, that pollen is much more likely to fall on, or to be carried by insects down to the stigma of the short-styled than of the long-styled flowers ; yet the short-styled instead of being more sterile, as a protection against self-ferti- lisation, are far more fertile than the long-styled, when both are illegitimately fertilised. Pulmonaria azurea, according to Hildebrand, is not heterostyled.* From an examination of dried flowers of Amsinckia spedabilis, sent me by Prof. Asa Gray, I formerly thoiight that this plant, a member of the Boragiuese, was heterostyled. The pistil varies to an extraordinary degree in length, being in some specimens twice as long as in others, and the point of insertion of the stamens likewise varies. But on raising many plants from seed, I soon became convinced that the whole case was one of mere variability. The first-formed flowers are apt to Die Geschlechter-Vertheilung bei den Pflanzen,' 1867, p. 37. Chap. III. POLYGONUM FAGOPYRUM. 1 1 1 have stamens somewhat arrested in development, with very little pollen in their anthers ; and in such flowers the stigma projects above the anthers, whilst generally it stands below and sometimes on a level with them. I could detect no difference in the size of the pollen-grain or in the structure of the stigma in the plants which differed most in the above respects ; and all of them, when protected from the access of insects, yielded ]ilenty of seeds. Again, from statements made by Vaucher,.and from a hasty inspection, I thought at first that the allied Anchusa (irvensis and Echium vuJ(/aievrcve heterostyled, but soon saw my error. From information given me, I examined dried flowers of another member of the Boragineae, Amelia hispidis- sima, collected from several sites, and though the corolla, to- gether with tlie included organs, differed much in length, there was no sign of heterostylism. Polygonum fagopyeum (PoLYGONACEiE). Hildebrand has shown that this plant, the common Buck-wheat, is heterostyled,* In the long-styled form (Fig. 7), the three stigmas project considerably above the eight short stamens, and stand on a level with the anthers of the eight long stamens in the short-styled form ; and so it is conversely w ith the stigmas and stamens of this latter form. I could perceive no differ- ence in the structure of the stigmas in the two forms. The pollen-grains of the short-styled form are to those of the long-styled as 100 to 82 in diameter. This plant is therefore without doubt heterostyled. I experimented only in an imperfect manner on the relative fertility of the two forms. Short-styled llowers were dragged several times over two heads of flowers on long-styled plants, protected under a net, which were thus legitimately, though not fully, ferti- lised. They produced 22 seeds, or 11 per flower-head. Three flower-heads on long-styled plants received * 'Die Geschlechter-Vertheilung,' &c., 18G7, p. 34. 6 112 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. pollen ill the same manner from other long-styled plants, and were thus illegitimately fertilised. They produced 14 seeds, or only 4'G6 per flower-head. Two flower-heads on short-styled plants received pollen in like manner from long-styled flowers, and were thus legitimately fertilised. They produced 8 seeds, or 4 per flower-head. Upper figure, the long-styled form ; lower figure, the short-styled. Some of the anthers have dehisced, others have not. Polygonum fagopyrom. (From H. MuUer.) Four heads on short-styled plants similarly received pollen from other short-styled plants, and were thus illegitimately fertilised. They produced 9 seeds, or 2 • 25 ]3er flower-head. The results from fertilising the flower-heads in the above imperfect manner cannot be fully trusted ; but I may state that the four legitimately fertilised flower- Chap. III. POLYGONUM FAGOPYRUM. 113 heads yielded on an average 7 • 50 seeds per head ; whereas the seven illegitimately fertilised heads yielded less than half the number, or on an average only 3 • 28 seeds. The legitimately crossed seeds from the long-styled flowers were finer than those from the illegitimately fertilised flowers on the same plants, in the ratio of 100 to 82, as shown by the weights of an equal number. About a dozen plants, including both forms, were protected under nets, and early in the season they pro- duced spontaneously hardly any seeds, though at this period the artificially fertilised flowers produced an abundance ; but it is a remarkable fact that later in the season, during September, both forms became highly self-fertile. They did not, however, produce so many seeds as some neighbouring uncovered plants which were visited by insects. Therefore the flowers of neither form when left to fertilise themselves late in the season without the aid of insects, are nearly so sterile as most other heterostyled plants. A large number of insects, namely 41 kinds as observed by H. Miiller,* visit the flowers for the sake of the eight drops of nectar. He infers from the structure of the flowers that insects would be apt to fertilise them both illegitimately as well as legitimately ; but he is mis- taken in supposing that the long-styled flowers cannot spontaneously fertilise themselves. Differently to what occurs in the other genera hitherto noticed, Polygonum, though a very large genus, contains, as far as is at present known, only a single heterostyled species, namely the present one. n. jMiiller in his interesting description of several Die Befruchtuug,' &c., p. 175, and * Nature,' Jan. 1, 1874, p. 1G6. 114 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. other species shows that P. historta is so strongly pro- terandrous (the anthers generally falling ofT before the stigmas are mature) that the flowers must be cross- fertilised by the many insects which visit them. Other species bear much less conspicuous flowers which se- crete little or no nectar, and consequently are rarely visited by insects ; these are adapted for self-fertilisa- tion, though still capable of cross-fertilisation. Ac- cording to Delpino, the Polygonacea3 are generally fertilised by the wind, instead of by insects as in the present genus. Leucosmia Buunettiana (Thymeli^). As Prof. Asa Gray has expressed his belief * that this species and L. acuminata, as well as some si)ecies in the allied genus Drymispermum, are dimorphic or heterostyled, I procured from Kew, through the kindness of Dr. Hooker, two diied flowers of the former species, an inhabitant of the Friendly Islands in the Pacific. The pistil of the long-styled form is to that of the short-styled as 100 to 86 in length; the stigma projects just above the throat of the corolla, and is surrounded by five anthers, the tips of which reach up almost to its base ; and lower down, within the tubnJar corolla, five other and rather smaller anthers are seated. In the short-styled form, the stigma stands some way down the tube of the corolla, nearly on a level with the lower anthers of the other form : it differs remarkably from the stigma of the long-styled form, in being more i:)apillose, and in being longer in the ratio of 100 to 60. The anthers of the upper stamens in the short-styled form are supported on free filaments, and project above the tlu-oat of tho corolla, whilst the anthers of the lower stamens are seated in the throat on a level with the upper stamens of the otlier form. The diameters of a considerable number of grains from both sets of anthers in both forms were measured, but they did not differ in any trustworthy degree. The mean diameter of twenty-two * 'American Journal of Sci- ' Jourual of Botany,' vol. ill. 1865, once,' 18G5, p. 101, and Secmann's p. 305. CuAP. III. MENYANTHES TRIFOLIATA. 115 grains from the short-styled flower was to that of twenty-four grains from the long-styled, as 100 to 'J9. The anthers of the upper stamens in the short-styled form appeared to be poorly developed, and contained a considerable number of shrivelled grains which were omitted in striking the above average. Notwithstanding the fact of the pollen-grains from the two forms not differing in diameter in any appreciable degree, there can hardly be a doubt from the great difference in the two forms in the length of the pistil, and especially of the stigma, together with its more papillose condition in the short- styled form, that the present species is truly heterostyled. This case resembles that of Linum yrandiflorum, in which the sole difference between the two forms consists in the length of the pistils and stigmas. From the great length of the tubular corolla of Leucosmia, it is clear that the flowers are cross- fertihsed by large Lepidoptera or by honey-sucking birds, and the position of the stamens in two whorls one beneath the other, which is a character that I have not seen in any other heterostyled dimoriihic plant, probably serves to smear the inserted organ thoroughly with pollen. MeNYAIJTHES TRIFOLIATA (GrENTIANEiE). This plant inhabits marshes : my son William gathered 2i7 flowers from so many distinct plants, and of tbese 110 were long-styled, and 137 short-styled. The pistil of the long-styled form is in length to that of the short-styled in the ratio of about 3 to 2. The stigma of the fonncr, as my son observed, is deci- dedly larger than that of the short-styled ; but in both forms it varies much in size. The stamens of the short-styled are almost double the length of those of the long-styled; so that their anthers stand rather above the level of the stigma of the long- styled form. The anthers also vary much in size, but seem often to be of larger size in the short-styled flowers. My son made with the camera many drawings of the pollen-grains, and those from the short-styled flowers were in diameter in nearly the ratio of 100 to 84 to those from the long-styled flowers. I know nothing about the capacity for fertilisation in the two forms ; but short-styled jilants, living by themselves in the gardens at Kew, have produced an abundance of capsules, yet the seeds have never genninatcd ; and this looks as if tho short-styled form was sterile witli its own pollen. 116 HETEROSTYLED DIMORPHIC PLANTS. Chap. Ill, LiMNANTHEMTJM InDICUM (GeNTIANE^). This ]ilant is mentioned by Mr. Thwaites in his Enumeration of the Plants of Ceylon as presenting two forms; and he was so kind as to send me specimens preserved in spirits. The pistil of the long-styled form is nearly tlu-ice as long (i.e. as 14 to 5) as that of the short-styled, and is very much thinner in the ratio of about 3 to 5. The foliaceous stigma is more expanded, and twice as large as that of the short-styled form. In the latter the stamens are about twice as long as those of the long- styled, and their anthers are larger in the ratio of 100 to 70. The pollen-grains, after having been long kept in spirits, were of the same shape and size in both forms. The ovules, accord- ing to Mr. Thwaites, are equally numerous (viz. from 70 to 80) in the two forms. ViLLARSIA [SP. ?J (GeNTIANE^). Fritz Miiller sent me from South Brazil dried flowers of this aquatic plant, which is closely allied to Limnanthemum. In the long-styled foi-m the stigma stands some way above the anthers, and the whole pistil, together with the ovary, is in length to that of the short-styled form as about 3 to 2. In the latter form the anthers stand above the stigma, and the style is very short and thick ; but the pistil varies a good deal in length, the stigma being either on a level with the tips of the sepals or considerably beneath them. The foliaceous stigma in the long-styled form is larger, with the expansions running farther down the style, than in the other form. One of the most remarkable differences between the two forms is that the anthers of the longer stamens in the short-styled flowers are consjiicu- ously longer than those of the shorter stamens in the long-styled flowers. In the former the sub-triangular pollen-grains are larger ; the ratio between their breadth (measured from one angle to the middle of the opposite side) and that of the grains from the long-styled flowers being about 100 to 75. Fritz Miiller also infoims me that the pollen of the short-styled flowers has a bluish tint, wliilst that of the long-styled is yellow. When we treat of Lythrum sulfcaria we shall find a strongly marked contrast in the colour of the pollen in two of the forms. The tlu'ee genera, Menyanthes, Limnanthemum, and Villarsia, now described, constitute a weU-marked sub-tribe of the Gen- tianese. All the species, as far as at present known, are hetero styled, and all inhabit aquatic or sub-aquatic stations. Chap. IIL CORDIA. 117 FOBSTTHIA 8U8PEKSA (OlEACE^). Professor Asa Gray states that the plants of this species grow- ing in the Botanic Gardens at Cambridge, U.S., are short-styled, but that Siebold and Zuccarini describe the long-styled form, and give figures of two forms ; so that there can be little doubt, as he remarks, about the plant being dimorphic* I therefore applied to Dr. Hooker, who sent me a dried flower from Japan, another from China, and another from the Botanic Gardens at Kew. The first proved to be long-styled, and the other two short-styled. In the long-styled form, the pistil is in length to that of the short-styled as 100 to 38, the lolx-s of the stigma being a little longer (as 10 to 9), but narrower and less diver- gent. This last character, however, may be only a temporary one. There seems to be no difference in the papillose condition of the two stigmas. In the short-styled form, the stamens are in length to tho.se of the long-styled as 100 to 6G, but the anthers are shorter in the ratio of 87 to 100 ; and this is unusual, for when there is any difference in size between the anthers of the two forms, those from the longer stamens of the short-styled are generally the longest. The pollen-grains fi-om the short-styled flowers are certainly larger, but only in a slight degree, than those from the long-styled, namely, as 100 to 94 in diameter. The short-styled form, which grows in the Gardens at Kew, has never there produced fruit. Forsythia viridissinui appears likewise to be heterostyled ; for Professor Asa Gray says that although the long-styled form alone grows in the gardens at Cambridge, U.S., the published figures of this species belong to the short-styled form. CORDIA [SP. ?J (COBDIACE.fi). Fritz Miiller sent me dried specimens of this shrub, which he believes to be heterostyled ; and I have not much doubt that this is the case, though the usual characteristic differences are not well pronounced in the two forms. Linum grandiflorum shows us that a plant may be heterostyled in function in the highest degree, and yet the two forms may have stamens of equal length, and pollen-grains of equal size. In the present species of Cordia, the stamens of both forms are of nearly equal • The American Naturalist,' July 1873, p. 422. 118 HETEKOSTYLED DIMORrillC PLANTS. Chap. III. length, those of the short-styled being rather the longest ; and the anthers of both are seated in the moutli of the corolla. Nor could I detect any difference in the size of the pollen-grains, when dry or after being soaked in water. The. stigmas of the long-stylcd form stand clear above the anthers, and the whole pistil is longer than that of the short-styled, in about the ratio of 3 to 2. The stigmas of the short-styled form are seated beneath the anthers, and they are considerably shorter than those of the long-styled form. Tliis latter difference is the most important one of any between the two forms. GiLIA (IPOMOrSIS) PULCHELLA VEL AGGREGATA (PoLEMONI- ACE^). Professor Asa Gray remarks with respect to this plant : " the tendency to dimorphism, of which there are traces, or perhaps rather incipient manifestations in various j^ortions of the genus, is most marked in O. aggregata."* He sent me some dried flowers, and I procured others from Kew. They differ greatly in size, some being nearly t-uice as long as otliers (viz. as 30 to 17), so that it was not possible to compare, excej^t by calculation, the absolute length of the organs from different plants. More- over, the relative position of the stigmas and anthers is variable : in some long-styled flowers the stigmas and anthers were ex- serted only just beyond the throat of the corolla; whilst in others they were exserted as much as y% of an inch. I suspect also that the pistil goes on growing for some time after the anthers have dehisced. Nevertheless it is possible to class the flowers under two forms. In some of the long-styled, the length of pistil to that of the short-styled was as 100 to 82 ; but this result was gained by reducing the size of the corollas to the same scale. In another pair of flowers the difference in lengtJi between the pistils of the two forms was certainly greater, but they were not actually measured. In the short-styled flowers Avhether large or small, tlie stigma is seated low down within the tube of the corolla. The papilla) on the long-styled stigma are longer than those on the short-styled, in the ratio of 100 to 40. Tlie filaments in some of the short-styled flowers were, to those of the long-styled, as 100 to 25 in length, the free, or * ' Proc. American Acad, of Arts and Seienced,' June 14, 1870, p. 275. CuAr. III. PHLOX SUBULATA. 119 unattached portion being alone measured ; but this ratio can- not be trusted, owing to the great variability of the stamens. The mean diameter of eleven pollen-grains from long-styled flowers, and of twelve from the short-styled, was exactly the same. It follows from those several statements, that the dif- ference in length and state of surface of the stigmas in the flowers is the sole reliable e\ideuce that this species is hetero- styled; for it would be rash to trust to the difference in the length of the pistils, seeing how variable they are. I should have left the case altogether doubtful, had it not been for the observations on the following species; and these leave little doubt on my mind that the present plant is truly heterostyled. Professor Gray informs me that in another species, G. coronopi- foUa, belonging to the same section of the genus, he can see no sign of dimorphism. GiLIA (LErTOSIPnON) micrantha. A few flowers sent me from Kcw had been somewhat injured, SO that I cannot say anything positively with respect to the position and relative length of the organs in the two forms. But their stigmas differed almost exactly in the same manner as in the last si^ecies ; the i^apillse on the long-styled stigma being longer than those on the short-styled, in the ratio of 100 to 42. My son measured nine pollen-grains from the long-styled, and the same number from the short-styled form ; and the mean diameter of the former was to that of the latter as 100 to 81. Considering this difference, as well as that between the stigmas of the two foiTus, there can be no doubt that this sj^ecies is heterostyled. So probably is Gilia nudicaulis, which likewise belongs to the Leptosiphon section of the genus, for I hear from Professor Asa Gray that in some individuals the style is very long, with the stigma more or leSs exscrted, whilst in others it is deeply included within the tube ; the anthers being always seated in the throat of the corolla. Phlox subulata (Polemoniaoe^). Professor Asa Gray informs me that the greater number of the species in this genus have a long pistil, with the stigma more or less exserted ; whilst several other species, especially the annuals, have a short pistil seated low down within the tube of the corolla. In all the species the anthers are arranged one 120 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. below the other, the uppermost just protruding from the throat of the corolla. In Phlox suhulati alone he has " seen both long and short styles ; and here the short-styled plant has (irrespec- tive of this cliaracter) been described as a distinct species (P. nivalis, P. Ilentzii), and is apt to have a pair of ovules in eacli cell, while the long-styled P. subuJata rarely shows more than one."* Some dried flowers of both forms were sent mc by him, and I received others from Kew, but I have failed to make out whether the species is hoterostylcd. In two flowers of nearly equal size, the pistil of the long-styled form was twice as long as that of tlie short-styled ; but in other cases the differ- ence was not nearly so great. The stigma of the long-styled pistil stands nearly in the throat of the corolla ; whilst in the short-styled it is placed low down — sometimes very low down in the tube, for it varies greatly in position. The stigma is more papillose, and of greater length (in one instance in the ratio of 100 to 67), in the short-styled flowers than in the long-styled. My son measured twenty pollen-grains from a short-styled flower, and nine from a long-styled, and the former were in diameter to the latter as 100 to 93; and this difference accords with the belief that the plant is hetcro- styled. But the grains from the short-styled varied much in diameter. He afterwards measured ten grains from a distinct long-styled flower, and ten from another plant of the same form, and these grains diifered in diameter in the ratio of 100 to 90. The mean diameter of these two lots of twenty grains was to that of twelve grains from another short-styled flower as 100 to 75 : here, then, the grains from the short-styled form were con- siderably smaller than those from the long-styled, which is the reverse of what occurred in the former instance, and of what is the general rule with heterostyled plants. The whole case is perplexing in the highest degree, and will not be vmderstood until experiments are tried on living plants. The greater length, and more papillose condition of the stigma in the short-styled than in the long-styled flowers, looks as if the plant was hetero- .styled ; for we know that with some species — for instance, Leu- cosmia and certain Eubiacese — the stigma is longer and more papillose in the short -styled form, though the reverse of this holds good in Gilia, a member of the same family with Phlox. The similar position of • the anthers in the two forms is some- * ' Proc. American Acad, of Arts and Sciences,' June 14, 1870, p. 248. ClIAP. III. ERYTHROXYLUM. 121 what opposed to the present species being lieterostyled ; as is the great difference in the length of the pistil in several short- styled flowers. But the extraordinary variability in diameter of the pollen-grains, and the fact that in one set of flowers the grains from the long-styled flowers were larger than those from the short-styled, is strongly opposed to the l^elief that Fhlox suhulata is lieterostyled. Possibly this sjoecies was once hetero- styled, but is now becoming sub-dioecious; the short-styled plants having been rendered more feminine in nature. Tliis would account for their ovaries iisually containing more ovules, and for the variable condition of their pollen-grains. Whether the long-styled plants are now changing their nature, as would appear to be the case from the variability of their pollen-grains, and are becoming more mascuHne, I will not pretend to con- jectvu'e; they might remain as heimaphrodites, for the co- existence of hermaphrodite and female plants of the same species is by no means a rare event. ErTTHROXTLUM [sp. ?] (ERYTHROXYLtD-a;). Fritz Midler sent me from South Brazil di'ied flowers of tliis tree, together with the accompanying drawings, which show the two forms, magnified about five times, with the petals removed. Fig. 8. Long-styled form. Short-styled form. From a sketch by Fritz Miillcr, magnified five times. Ebtthroxylon [sp. ?j. 122 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. In the long-styled form the stigmas project above the anthers, and the styles arc nearly twice as long as those of the short- styled form, in which the stigmas stand beneath the anthers. The stigmas in many, bnt not in all the short-styled flowers are larger than those in the long-styled. The anthers of the short- styled flowers stand on a level with the stigmas of the other form ; but the stamens are longer by only one-fourth or one-fifth of their own length than those of the long-styled. Consequently the anthers of the latter do not stand on a level with, but ratlier above the stigmas of the other fomi. Differently from what occurs in the following closely allied genus, Sethia, tlie stamens are of nearly equal length in the flowers of the same form. The pollen-grains of the short-styled flowers, measured in their dry state, are a little larger than those from the long-styled flowers in about the ratio of 100 to 93.* Sethia acuminata (EEiTHROXYLrD^). Mr. Thwaites pointed out several years ago t that this plant exists under two forms, which he designated as forma stylosa et stamined ; and the flowers sent to me by him are clearly hetero- styled. In the long-styled fonu the pistil is nearly twice as long, and the stamens half as long as the con-esponding organs in the short-styled form. The stigmas of the long-styled seem rather smaller than those of the short-styled. All the stamens in the short-styled flowers are of nearly equal length, whereas in long-styled they differ in length, being alternately a little longer and shorter; and this difference in the stamens of the two forms is probably related, as we shall hereafter see in the case of the short-styled flowers of Lythrum sallcaria, to the manner in wliich insects can best transport pollen from the long-styled flowers to the stigmas of the short-styled. The pollen-grains from the short-styled flowers, though variable in size, are to those of the long-styled, as far as I could make out, as 100 to 83 in their longer diameter. Sethia obtusifuUa is heterostyled like S. acuminata. * F. Miiller reiuarks in his let- numbers ; but the sepals and petals ter to me that the flowers, of which often vary from 5 to 7 ; the sta- he carefully examined many spe- mens from 10 to 14, and the pistils cimens, are curiously variable from 3 to 4. in the number of their parts : t ' Enumeratio Plantarum Zey- 5 sepals and petals, 10 stamens huiise,' 1864, p. 54. and 3 pistils are the prevailing CuAr. III. ^GIPHILA ELATA. 123 CrATOXYLON rOllMOeUM (IlYPKEICINEiE). ]\Ir. Tliiscltou Dyer remarks that this tree, an inliabitant of Malacca aud Borneo, appears to be hotcrostyled.* lie sent me (.Iried flowers, aud the dilfcrenco between the two forms is con- Rpicuous. In the long-styled form the jjistils are in length to those of the short-styled as 100 to 40, with their globular stigmas about twice as thick. These stand just above the numer- ous anthers and a little beneath the tips of the petals. In the short-styled form the anthers projecit high above the pistils, the stigmas of which diverge between the three bundles of stamens, and stand only a little above the tips of the sepals. The stamens in this form are to those of the long-styled as 100 to 86 in length ; and therefore they do not differ so much in length as do the pistils. Ten pollen-grains from each form were measured, and those from the short-styled were to those from the long-styled as 100 to 86 in diameter. This plant, therefore, is in all respects a well-characterised heterostyled siDecies. iEGIPHILA ELATA (VEEBENACEiE). Mr. Bentham was so kind as to send me dried flowers of this species and of yE. mollis, both inhabitants of South America. The two forms ditfer conspicuously, as the deeply bifid stigma of the one, and the anthers of the other project far above the mouth of the corolla. In the long-styled form of the present species, the style is twice aud a half as long as that of the short- styled. The divergent stigmas of the two forms do not differ much in length, nor as far as I could perceive in their papilke. In the long-styled flowers the filaments adhere to the corolla close up to the anthers, which are enclosed some way down within the tube. In the short-styled flowers the filaments are free above the point where the anthers are seated in the othci- form, aud they project from the corolla to an equal height with that of the stigmas in the long-styled flowers. It is often difficult to measm-e with accuracy pollen-grains, which have long been dried and then soaked in water; but they here manifestly differed greatly in size. Those from the short-styled flowers were to those from the long-styled in diameter in ' Journal of Botany, ' London, 1872, p. 2G. 124 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. about the ratio of 100 to 62. The two forms of ^. mollis present a like difference in the length of their pistils and stamens. .L^GIPHILA OBDtJRATA. Flovrcrs of this' bush were sent me from St. Catharina in Brazil, by Fritz Miiller, and were named for me at Kew. They appeared at first sight grandly heterostyled, as the stigma of the long-styled form projects far out of the corolla, whilst the anthers are seated halfway down within the tube; whereas in the short-styled form the anthers project from the corolla and the stigma is enclosed in the tube at nearly the same level with the anthers of the other form. The pistil of the long-styled is to that of the short-styled as 100 to 60 in length, and the stigmas, taken by themselves, as 100 to 55. Nevertheless, this plant cannot be heterostyled. The anthers in the long-styled fonn are brown, tough, and fleshy, and less than half the length of those in the short-styled form, strictly as 44 to 100 ; and what is much more important, they were in a rudimentary condition in the two flowers examined by me, and did not contain a single grain of pollen. In the short-styled form, the divided stigma, which as we have seen is much shortened, is thicker and more fleshy than the stigma of the long- styled, and is covered with small irregular projections, fonned of rather large cells. It had the appearance of having suf- fered from hypertrophy, and is probably incapable of fertili- sation. If this be so the plant is dioecious, and judging fi-om the two species previously described, it probably was once heterostyled, and has since been rendered dioecious by the pistil in the one form, and the stamens in the other having become functionless and reduced in size. It is, however, possible that the flowers may be in the same state as those of the common thyme and of several other Labiatse, in which females and hermaphrodites regularly co-exist. Fritz Miiller, who thought that the present plant was heterostyled, as I did at first, informs me that he foimd bushes in several places growing quite isolated, and that these were completely sterile ; whilst two plants gi'owing close together were covered with fruit. Tliis fact agrees better with the belief that the species is dioecious than that it consists of hermaphrodites and females; for if any one of the isolated plants had been an hermaplirodite, it would probably have produced some fruit. Chap. III. MITCIIELLA EEPENS. 125 KuBIACEiE. This great natural family contains a muck larger number of heterostylcd genera than any other one, as yet kno\vn. Mitchella repens. — Prof. Asa Gray sent me several living plants collected when out of flower, and nearly half of these proved long-styled, and the other half short-styled. The white flowers, which are fragrant and which secrete plenty of nectar, always grow in pairs with their ovaries united, so that the two together produce "a berry-like double drupe."* In my first series of experiments (1864) I did not suppose that this curious arrangement of the flowers would have any influence on their fertility ; and in several instances only one of the two flowers in a pair was fertilised ; and a large proportion or all of these failed to produce berries. In the ensuing year both flowers of each pair were invariably fertilised in the same manner ; and the latter experiments alone serve to show the proportion of flowers which yield berries, when legiti- mately and illegitimately fertilised ; but for calcu- lating the average number of seeds per berry I have used those produced during both seasons. In the long-styled flowers the stigma projects just above the bearded throat of the corolla, and the anthers are seated some way down the tube. In the short-styled flowers these organs occupy reversed posi- tions. In this latter form the fresh pollen-grains are a little larger and more opaque than those of the long- styled form. The results of my experiments are given in the following table. * A. Gray, 'Manual of the Bot. of the N. United States,' 1856, p. 172. 120 IIETEROSTYLED DIMORPUIC PLANTS. Chat. III. Table 21. MitcheUa repens. Average Number of Number of Number of Pairs of iJrupes pro- good Seeds Nature of Union. Flowers fer- duced during per Drupe in tilised (luring the second all the Drupes the second Season. during the Season. two Seasons. Long-styled flowers, by pollen ofV short-styled. Legitimate union/ 4-G Long-styled flowers, by own-form V „ j „ | n.Q pollen. Illegitimate union . ./ 1 1 " Short-styled flowers, by pollen ofl „ long-styled. Legitimate union. ) | 7 4-1 Short-styled flowers, by own-form r „ pollen. Illegitimate union . ./ 2-0 The two legitimate unions to-V ._ i .^ gether /, | 4-4 The two illegitimate unions to-jl ^^ ^ j g.j gether }\ ! " It follows from this table that 88 per cent, of the paired flowers of both forms, when legitimately fer- tilised, yielded double berries, nineteen of which con- tained on an average 4'4 seeds, with a maximum in one of 8 seeds. Of the illegitimately fertilised paired flowers only 18 per cent, yielded berries, six of which contained on an average only 2*1 seeds, with a maxi- mum in one of 4 seeds. Thus the two legitimate unions are more fertile than the two illegitimate, according to the proportion of flowers which yielded berries, in the ratio of 100 to 20 ; and according to the average number of contained seeds as 100 to 47. Three long-styled and three short-styled plants were protected under separate nets, and they produced alto- gether only 8 berries, containing on an average only Cjur. III. BORRERIA. 127 1'5 seed. Some additional berries were produced which contained no seeds. The plants thus treated were therefore excessively sterile, and their slight degree of fertility may bo attributed in part to the action of the many individuals of Thrips which haunted the flowers. Mr. J. Scott informs me that a single plant (probably a long-styled one), growing in the Botanic Gardens at Edinburgh, which no doubt was freely visited by in- sects, produced plenty of berries, but how many of them contained seeds was not observed. BORRERIA, NOV. SP. NEAR VALERIANOIDES (RuBIACEvE). Fritz Miiller sent me seeds of this plant, which is extremely abundant in St. Catharina, in South Brazil ; and ten plants were raised, consisting of five long- styled and five short-styled. The' pistil of the long- styled flowers projects just beyond the mouth of the corolla, and is thrice as long as that of the short- styled, and the divergent stigmas are likewise rather larger. The anthers in the long-styled form stand low down within the corolla, and are quite hidden. In the short-styled flowers the anthers project just above the mouth of the corolla, and the stigma stands low down within the tube. Considering the great difference in the length of the pistils in the two forms, it is remarkable that the pollen-grains differ very little in size, and Fritz Miiller was struck with the same fact. In a dry state the grains from the short-styled flowers could just be perceived to be larger than those from the long-styled, and when both were swollen by immersion in water, the former were to the latter in diameter in the ratio of 100 to 92. In the long-styled flowers beaded hairs almost fill up the mouth of the corolla and project above it ; they therefore stand above the anthers and beneath the stigma. In the 128 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. short-styled flowers a similar brush of hairs is situated low down within the tubular corolla, above the stigma and beneath the anthers. The presence of these beaded hairs in both forms, though occupying such different positions, shows that they are probably of considerable functional importance. They would serve to guard the stigma of each form from its own pollen; but in accordance with Prof. Kerner's view* their chief use probably is to prevent the copious nectar being stolen by small crawling insects, which could not render any service to the species by carrying pollen from one form to the other. The flowers are so small and so crowded togetlier that I was not willing to expend time in fertilising them separately ; but I dragged repeatedly heads of short-styled flowers over three long-styled flower-heads, which were thus legitimately fertilised ; and they pro- duced many dozen fruits, each containing two good seeds. I fertilised in the same manner three heads on the same long-styled plant with pollen from another long-styled plant, so that these were fertilised illegiti- mately, and they did not yield a single seed. Nor did this plant, which was of course protected by a net, bear spontaneously any seeds. Nevertheless another long-styled plant, which was carefully protected, pro- duced spontaneously a very few seeds; so that the long-styled form is not always quite sterile with its own pollen. FaRAMEA [Sr. ?] (KUBIACEiE). Fritz Miiller has fully described the two forms of this remarkable plant, an inhabitant of South Brazil, f In * 'Die Schutzmittel der Blu- t ' Bot. Zeitung,' Sept. 10, 1869, then gegen unberufene Gasto,' p. 606. 1876, p. 37. CUAP. III. FAEAMEA. 129 the long-styled form the pistil projects above the corolla, and is almost exactly twice as long as that of the short-styled, which is included within the tube. The former is divided into two rather short and broad stigmas, whilst the short-styled pistil is divided into two long, thin, sometimes much curled stigmas. The stamens of each form correspond in height or length with the pistils of the other form. The anthers of the short-styled form are a little larger than those of the long-styled ; and their pollen-grains are to those of the other form as 100 to 67 in diameter. But the pollen-grains of the two forms differ in a much more remarkable manner, of which no other Fig. 9. Short-styled form. Long-styled form. Outlines of flowers from dried specimens. Pollen-grains, magnified 180 times, by Fritz Miiller. Faramea [sp. ?], instance is known ; those from the short-styled flowers being covered with sharp points ; the smaller ones 130 IIETEROSTYLED DIMORPHIC PLANTS. Chap. Ill from the long-styled being quite smooth. Fritz Miiller remarks that this diifercnce between the pollen-grains of the two forms is evidently of service to the plant ; for the grains from the projecting stamens of the short- styled form, if smooth, would have been liable to be blown away by the wind, and would thus have been lost ; but the little points on their surfaces cause them to cohere, and at the same time favour their adhesion to the hairy bodies of insects, which merely brush against the anthers of these stamens whilst visiting the flowers. On the other hand, the smooth grains of the long-styled flowers are safely included witliin the tube of the corolla, so that they cannot be blown away, but are almost sure to adhere to the proboscis of an entering insect, which is necessarily pressed close atrainst the enclosed anthers. It may be remembered that in the long-styled form of Linum perenne each separate stigma rotates on its own axis, when the flower is mature, so as to turn its papillose surface outwards. There can be no doubt that this movement, which is confined to the long- styled form, is effected in order that the proper sur face of the stigma should receive pollen brought by insects from the other form. Now with Faramea, as Fritz Miiller shows, it is the stamens which rotate on their axes in one of the two forms, namely, the short- styled, in order that their pollen should be brushed off by insects and transported to the stigmas of the other form. In the long-styled flowers the anthers of the short enclosed stamens do not rotate on their axes, but dehisce on their inner sides, as is the common rule with the Rubiacere ; and this is the best position for the adherence of the pollen-grains to the proboscis of an entering insect. Fritz Miiller therefore infers that as the plant became heterostyled, and as the CuAr. III. KUBIACE^. 131 stamens of the short-styled form increased in length, they gradually acquired the highly beneficial power uf rotating on their own axes. But he has further shown, by the careful examination of many flowers, that this power has not as yet been perfected ; and, consequently, that a certain proportion of the pollen is rendered useless, namely, that from the anthers which do not rotate properly. It thus appears tliat the development of the plant has not as yet been com- pleted ; the stamens have indeed acquired their proper length, but not their full and perfect power of rotation.* The several points of difference in structure between the two forms of Faramea are highly remarkable. Until within a recent period, if any one had been sh6^vn two plants which differed in a uniform manner in the length of their stamens and pistils, — in the form of their stigmas, — in the manner of dehiscence and slightly in the size of their anthers, — and to an extraordinary degree in the diameter and structure of their pollen-grains, he would have declared it impos- sible that the two could have belonged to one and the same species. SuTEBiA (species unnamed in the herbarium at Kcw) (EUBIACE^). I owe to the kindness of Fritz Miiller dried flowers of this plant from St. Catharina, in Brazil. In the long-styled form the stigma stands in the mouth of the corolla, above the anthers, * Fritz iliiller gives another cordance with the nocturnal liabits instance of the want of absolute of tiiese insects, most of the flowers jicrfcction in the flowers of another open only during the night; but niembcT of the Ilubiacese, namely, some open in the day, and the I'osoqueria fragraiis, which is pollen of such flowers is* robbed, ns adapted in a most wonderful man- Fritz Miiller has often seen, by ner for cross- fertilisation by the humble-bees and other insects. Agency of moths. (See ' Bot. wilhout any benefit being thus Zcitung," ISGO, No. 17.) In ac- conferred on the plant. 132 HETEROSTYLED DIMORrHIC PLANTS. Chap. III. which latter are enclosed within the tube, but only a short way clown. In the short-styled form the anthers are placed in the mouth of the corolla above the stigma, which occupies the same position as the anthers in the other form, being seated only a short way down the tube. Therefore the pistil of the long-styled form does not exceed in length that of the short-styled in nearly so great a degree as in many other Eubiaccse. Never- theless there is a considerable difference in the size of the pollen- grains in the two forms ; for, as Fritz Miiller informs me, those of the short-styled are to those of the long-styled as 100 to 75 in diameter. HOUSTONIA CCEEULBA (EUBIACE^). Prof. Asa Gray has been so kind as to send me an abstract of some observations made by Dr. Eothrock on this plant. The pistil is exserted in the one form and the stamens in the other, as has long been observed. The stigmas of the long- styled form are shorter, stouter, and far more hispid than in the other form. The stigmatic hairs or papillae on the former are • 04 mm., and on the latter only • 023 mm. in length. In the short-styled form the anthers are larger, and the pollen-grains, when distended with water, are to those from the long-styled form as 100 to 72 in diameter. Selected capsules from some long-styled plants growing in the Botanic Gardens at Cambridge, U.S., near where j^lants of the other form gi'ew, contained on an average 13 seeds; but these plants must have been subjected to unfavoui-able conditions, for some long-styled plants in a state of nature yielded an average of 21 • 5 seeds per capsule. Some short-styled plants, which had been planted by themselves in the Botanic Gardens, where it was not Likely that they would have been visited by insects that had previously visited long-styled plants, produced capsules, eleven of which were wholly sterile, but one contained 4, and another 8 seeds. So that the short-styled form seems to be very sterile with its own pollen. Prof. Asa Gray infoi-ms me that the other North American species of this genus are likewise heterostyled. OlDENLANDIA [sP. ?] (EUBIACE.^). Mr. J. Scott sent me from India dried flowers of a hetero- styled species of this genus, which is closely allied to the last. CuAP. III. RUBIACE^. 133 Tlie pistil in the long-styled flowers is longer by about a quarter of its length, and the stamens shorter in about the same pro- ]")ortion, than the corresponding organs in the short-styled flowers. In the latter the anthers are longer, and the divergent stigmas decidedly longer and apparently thinner than in the long-styled form. Owing to the state of the specimens, I could not decide whether the stigmatic papillas were longer in the one form than in the other. The pollen-grains, distended with water, from the short-styled flowers were to those from the long- styled as 100 to 78 in diameter, as deduced from the mean of ten measurements of each kind. IlEDyoTis [sp. ?] (EoBiACE.a:). Fritz Midler sent me from St. Catharina, in Brazil, dried flowers of a small delicate species, which grows on wet sand near the edges of fresh-water pools. In the long-styled form the stigma projects above the corolla, and stands on a level with the pro- jecting anthers of the short-styled form; but in the latter the stigmas stand rather beneath the level of the anthers in the other or long-styled form, these being enclosed witliin the tube of the corolla. The pistil of the long-styled form is nearly thrice as long as that of the short-styled, or, speaking strictly, as 100 to 39 ; and the papillae on the stigma of the former are broader, in the ratio of 4 to 3, but whether longer than those of the short-styled, I could not decide. In the short-styled form, the anthers are rather larger, and the pollen-grains are to those from the long-styled flowers, as 100 to 88 in diameter. Fritz Midler sent me a second, small-sized species, which is likewise heterostyled. CoCCOCTrSELUM [SP. ?] (PiUBIACE^). Fritz Miiller also sent me dried flowers of this plant from St. Catharina, in Brazil. The exserted stigma of the long-styled form stands a Little above the level of the exserted anthers of the short-styled form ; and the enclosed stigma of the latter also stands a little above the level of the enclosed anthers in the long- styled form. The pistil of the long-styled is about twice as long as that of the short-styled, with its two stigmas considerably longer, more divergent, and more curled. Fritz Miiller informs 134 HETEROSTYLED DIMORPHIC PLANTS. Chap. III. me that he could detect no difference in the size of the pollen- grains in the two forms. Nevertheless, there can be no doubt that this plant is heterostyled. LiPOSTOMA [SP. ?] (RUBIAOE.^). Dried flowers of this plant, which grows in small wet ditches in St. Catharina, in Brazil, were likewise sent me by Fritz Miiller. In the long-styled form the exserted stigma stands rather above the level of the exserted anthers of the other form ; whilst in the short-styled form it stands on a level with the anthers of the other form. So that the want of strict corre- spondence in height between the stigmas and anthers in the two forms is reversed, compared with what occurs in Hedyotis. The long-styled pistil is to that of the short-styled as 100 to 36 in length ; and its divergent stigmas are longer by fully one-third of their own length than those of the short-styled form. In the latter the anthers are a little larger, and the pollen-grains arc as 100 to 80 in diameter, compared with those from the long- styled form. Cinchona micrantha (Eubiace^). Dried specimens of both forms of this plant were sent me from Kew.* In the long-styled form the apex of the stigma stands just beneath the bases of the hairy lobes of the corolla; whilst the summits of the anthers are seated about halfway down the tube. The pistil is in length as 100 to 38 to that of the short-styled form. In the latter the anthers occupy the same position as the stigma of the other form, and they are con- sideral^ly longer than those of the long-styled form. As the summit of the stigma in the short-styled form stands beneath the bases of the anthers, which are seated halfway down the corolla, the style has been extremely shortened in this form • its length to that of the long-styled being, in the specimens examined, only as 5*3 to 100! The stigma, also, in the short- styled form is very much shorter than that in the long-styled, in the ratio of 57 to 100. The pollen-grains from the short- * My attention was called to 3, given by Mr. MarkhaTU in his this plant by a drawing copied ' Travels in Peru,' p. 53'J. from Howard's ' Quinologia,' Tab. Chap. III. RUBIACE^. 135 styled flowei-s, after having haen soaked in water, "were rather larger— in aI)Out the ratio of 100 to 91 — than those from tlie long- styled flowers, and they were more triangular, -n-ith the angles more prominent. As all the grains from the short-styled flowers were thus characterised, and as they had been left in water for three days, I am convinced that this difference in shape in the two sets of grains cannot be accounted for by unequal distension ■nith water. Besides the several Paibiaceous genera already mentioned, Fritz Miiller informs me that two or thi-ee species of Psychotria and Eudijea erinnthn, natives of St. Catharina, in Brazil, are hetorostyled, as is Manettia hicohr. I may add that I formerly fertilised with their own pollen several flowers on a plant of tills latter species in my hothouse, but they did not set a single fruit. From Wight and Amott's description, there seems to be Little doubt that Knoxia in India is heterostyled ; and Asa Gray is con\-inced that this is the case with Diodia and Spennacoce in the United States. Lastly, from Mr. W. W. Bailey's descrip- tion,* it appears that the Mexican Bouvardia hiantha is hetero- styled. Altogether wc now know of 17 heterostyled genera in the great family of the Eubiaceae ; though more information is necessary with respect to some of them, more especially those mentioned in the last para- graph, before we can feel absolutely safe. In the * Genera Plantarum,' by Bentham and Hooker, the Rubiacefe are divided into 25 tribes, containing 337 genera ; and it deserves notice that the genera now known to be heterostyled are not grouped in one or two of these tribes, but are distributed in no less than •,'ight of them. From this fact we may infer that most of the genera have acquired their heterostyled structure independently of one another ; that is, they have not inherited this structure from some one or even two or three progenitors in common. It further * ' Bull, of the Torrey Bot Club,' 1870, p. lOG. 7 136 IIETEEOSTYLED DIMOEPHIO PLANTS. Chap. m. deserves notice that in the homostyled genera, as I am informed by Professor Asa Gray, the stamens are either exserted or are included within the tube of the corolla, in a nearly constant manner; so that this cliaractcr, which is not even of specific value in the heterostyled species, is often of generic value in other members of the family. Chap. IV. LYTHRUM SALICARIA. 137 CHAPTER IV. HeTEBOSTYLED TrIJIORPIIIC PLANTa Lytlinmi salicaria — Description of the three forms — Their power and complex manner of fertilising one another — Eighteen different unions possible — Mid-stvled form eminently feminine in nature — Lythrmn GrajftVri likewise trimorphic — L. tliymifolia dimorphic — L. hyssopifolia homostyled — Xesjea verticillata trimorphic — Lager- strcemia, nature doubtful — Oxalis, trimorphic species of — 0. Valdi- viana — O. Regnelli, the illegitimate unions quite barren — O. spe- ciosa — 0. sensitiva — Homostyled species of Oxalis — Ponttderia, the one monocotyledonous genus kno\\Ti to include hetL-rostyled species. In the previous chapters various heterostyled dimor- phic plants have been described, and now we come to heterostyled trimorphic plants, or those which present three forms. These have been observed in three families, and consist of species of Lythrum and of the allied genus Nesaa, of Oxalis and Pontederia. In their manner of fertilisation these plants offer a more remarkable case than can be found in any other plant or animal. Lythrum salicaria. — The pistil in each form differs from that in either of the other forms, and in each there are two sets of stamens different in appearance and function. But one set of stamens in each form corresponds with a set in one of the other two forms. Altogether this one species includes three females or female organs and three sets of male organs, all as distinct from one another as if they belonged to dif- ferent species ; and if smaller functional differences 138 HETEEOSTYLED TRDIORPHIC PLANTS. Chap. IV. are considered, there are five distinct sets of males. Two of the three hermaphrodites mnst coexist, and pollen must be carried by insects reciprocally from one to the other, in order that either of the two should be fully fertile ; but unless all three fonus coexist, two sets of stamens will be wasted, and the organisation of the species, as a whole, will be incomplete. On the other hand, when all throe hermaphrodites coexist, and pollen is carried from one to the other, the scheme is perfect ; there is no waste of pollen and no false co- adaptation. In short, nature has ordained a most com- plex marriage-arrangement, namely a triple union between three hermaphrodites, — each hermaphrodite being in its female organ quite distinct from the other two hermaphrodites and partially distinct in its male organs, and each furnished with two sets of males. The three forms may be conveniently called, from the unequal lengths of their pistils, the long-sfi/Ied, mid- styled, and sliort-styled. The stamens also are of unequal lengths, and these may be called the longest, mid-length, and shortest. Two sets of stamens of different length are found in each form. The existence of the three forms was first observed by Vaucher,* and subsequently more carefully by Wirtgen ; but these botanists, not being guided by any theory or even suspicion of their func- tional differences, did not perceive some of the most curious points of difference in their structure. I will first briefly describe the three forms by the aid of the accompanying diagram, which shows the flowers, six times magnified, in their natural position, with their petals and calyx on the near side removed. " ' Hist. Pliys. des Plantes uiid dessen Formen," ' Verhand. d'Europe,' torn.' ii. 1841, p. 371. dvs naturhist. Vereins fiir preuss. \Virtgeu,"Uober Ly<7i rum sa/Zcana Rheiiil.' 5. Jahrgang, 1848, S. 7. Chat. IV, LYTnRUM SALICARIA. Fig. 10. 139 Diagram of the flowers of the three forms of Lythrum salicaria, in their natural position, with the petals and calyx removed on the near side: enlarged six times. The dotted lines with the arrows show the directions in which polleo must be carried to each stigma to ensure full fertility. 1 10 IIETEROSTYLED TRDIORPHIC PLANTS. Chap. IV. Long-styled form. — This form can be at once recog- nised by the length of the pistil, which is (including the ovarium) fully one-third longer than that of the mid-styled, and more than thrice as long as that of the short-styled form. It is so disproportionately long, that it projects in the bud through the folded petals. It stands out considerably beyond the mid-length sta-" mens ; its terminal portion depends a little, but the stigma itself is slightly upturned. The globular stigma is considerably larger than that of the other t^o forms, with the papilla3 on its surface generally longer. The six mid-length stamens project about two-thirds the length of the pistil, and correspond in length with the pistil of the mid-styled form. Such correspondence in this and the two following forms is generally very close ; the diiference, where there is any, being usually in a slight excess of length in the stamens. The six shortest stamens lie concealed within the calyx ; their ends are turned up, and they are graduated in length, so as to form a double row. The anthers of these sta- mens are smaller than those of the mid-length ones. The pollen is of the same yellow colour in both sets. H. Muller* measured the pollen-grain in all three forms, and his measurements are evidently more trust- worthy than those which I formerly made, so I will give them. The numbers refer to divisions of the micrometer equalling g^^ mm. The grains, distended with water, from the mid-length stamens are 7-7^, and those from the shortest stamens G-6^ in diameter, or as 100 to 86. The capsules of this form contain on an average 93 seeds : how this average was ob- tained will presently be explained. As these seeds, when cleaned, seemed larger than those from the mid- * ' Die Bffruchtuiig der Bluiuoa,' 1873, p. 193. CiiAr. IV. LYTURUM SALIC ARIA. Ill styled or short-styled forms, 100 of them were placed in a good balance, and by the double method of weigh- ing were found to equal 121 seeds of the mid-styled or 142 of the short-styled ; so that five long-styled seeds very nearly equal six mid-styled or seven short-styled seeds. Micl-sUjlecl form. — The pistil occupies the position represented in the diagram, with its extremity consi- derably upturned, but to a variable degree ; the stifrma is seated between the anthers of the lono;est and the shortest stamens. The six longest stamens correspond in length with the pistil of the long-styled form ; their filaments are coloured bright pink ; the anthers are dark-coloured, but from containing bright- green pollen and from their early dehiscence they appear emerald-green. Hence in general appearance these stamens are remarkably dissimilar from the mid-length stamens of the long-styled form. The six shortest sta- mens are enclosed within the calyx, and resemble in all respects the shortest stamens of the long-styled form ; both these sets correspond in length with the short pistil of the short-styled form. The green pol- len-grains of the longest stamens are 9-10 in dia- meter, whilst the yellow grains from the shortest stamens are only 6 ; or as 100 to 63. But the pollen- grains from diiferent plants appeared to me, in this case and others, to be in some degree variable in size. The capsules contain on an average 130 seeds ; but perhaps, as we shall see, this is rather too high an average. The seeds themselves, as before remarked, are smaller than those of the long-styled form. Short-styled form. — The pistil is here very short, not one-third of the length of that of the long-styled form. It is enclosed within the calyx, which, diff'erently from that in the other two forms, does not enclose any an- 142 HETEKOSTYLED TRIMORPHIC PLANTS. Chap. IV. thers. The end of the pistil is generally bent upwards at right angles. The six longest stamens, witli their pink filaments and green jiollen, resemble the corre- sponding stamens of the mid-styled form. But accord- ing to H. Miiller, their pollen-grains are a little larger, viz. 9^10^, instead of 9-10 in diameter. The six mid-length stamens, with their uncoloured filaments and yellow pollen, resemble in the size of their pollen- grains and in all other respects the corresponding stamens of the long-styled form. The diiference in diameter between the grains from the two sets of anthers in the short-styled form is as 100 to 73. The capsules contain fewer seeds on an average than those of either of the preceding forms, namely 83 • 5 ; and the seeds are considerably smaller. In this latter respect, but not in number, there is a gradation parallel to that in the length of the pistil, the long- styled having the largest seeds, the mid-styled the next in size, and the short-styled the smallest. We thus see that this plant exists under three female forms, which diifer in the length and curva- ture of the style, in the size and state of the stigma, and in the number and size of the seed. There are altogether thirty-six males or stamens, and these can be divided into three sets of a dozen each, differing from one another in length, curvature, and colour of the filaments — in the size of the anthers, and especially in the colour and diameter of the pollen-grains. Each form bears half-a-dozen of one kind of stamens and half-a-dozen of another kind, but not all three kinds. The three kinds of stamens correspond in length with the three pistils : the correspondence is always between half of the stamens in two of the forms with the pistil of the third form. Tlie following table of the diameters of the pollen-grains, after immersion in water, from Chap. IV. LYTHRUM SALICAIUA. 143 both sets of stamens in all three forms is cojiied from n. Miiller; thoy arc arranged in the order of their size: — Pollea-gniins from longest st<\uicns of short-stylod form 9^ to loj „ „ „ miJ-styieJ „ 9 „ 10 „ mill-length stamens of long-styled „ 7 „ 7i „ „ „ short-styled „ 7 „ 7| „ shortest st;unens of loug-styled „ „ Gi „ „ „ mid-styled ,, 6 „ 6 We here see that the largest pollen-grains come from the longest stamens, and the least from the shortest ; the extreme difference in diameter between them being as 100 to 60. The average number of seeds in the three forms was ascertained by counting them in eight fine selected capsules taken from plants growing wild, and the result was, as we have seen, for the long-styled (neg- lecting decimals) 93, mid-styled 130, and short-styled 83. I should not have trusted in these ratios had I not possessed a number of plants in my garden which, owing to their youth, did not yield the full comple- ment of seed, but were of the same age and grew under the same conditions, and were freely visited by bees. I took six fine capsules from each, and found the average to be for tlie long-styled 80, for the mid- styled 97, and for the short-styled 61. Lastly, legiti- mate unions effected by me between the three forms gave, as may be seen in the following tables, for the long-styled an average of 90 seeds, for the mid-styled 117, and for the short-styled 71. So that we have good concurrent evidence of a difference in the average production of seed by the three forms. To show that the unions effected by me often produced their full effect and may be trusted, I may state that one mid- styled capsule yielded 151 good seeds, which is the same number as in the finest wild capsule which I 144 HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. examined. Some artificially fertilised short- and long- styled capsules produced a greater number of seeds than was ever observed by me in wild plants of the same forms, but then I did not examine many of the latter. Thisplant, I may add, offers a remarkable instance, how profoundly ignorant we are of the life-conditions of a species. Naturally it grows " in wet ditches, watery places, and especially on the banks of streams," and though it prodvices so many minute seeds, it never spreads on the adjoining land ; yet, when planted in my garden, on clayey soil lying over chalk, and which is so dry that a rush cannot be found, it thrives luxuriantly, grows to above 6 feet in height, produces self-sown seedlings, and (which is a severer test) is as fertile as in a state of nature. Nevertheless it would be almost a miracle to find this plant growing spontaneously on such land as that in my garden. According to Vaucher and Wirtgen, the three forms coexist in all parts of Europe. Some friends gathered for me in North Wales a number of twigs from separate plants growing near one another, and clas- sified them. My son did the same in Hampshire, and here is the result : — Table 22. — Long-stylcd. Mi(i-styled. Sbort-styled. Total. North Wales . . Hampshire 95 53 97 38 72 38 204 129 Total . . 148 135 110 393 If twice or thrice the number had been collected, the three forms would probably have been found nearly equal ; I infer this from considering the above figures, and from my son telling me that if he had CuAT. IV. LYTHRUM SALICARIA. 145 collected in another spot, he felt sure that the niid- styled plants would have been in excess. I several times sowed small parcels of seed, and raised all three forms ; but I neglected to record the parent-form, excepting in one instance, in which I raised from short-styled seed twelve plants, of wliich only one turned out long-styled, four mid-styled, and seven short-styled. Two plants of each form were protected from the access of insects during two successive years, and in the autumn they yielded very few capsules and presented a remarkable contrast with the adjoining uncovered plants, whicli were densely covered with capsules. In 18G3 a protected long-styled plant produced only five poor capsules ; two mid-styled plants produced together the same number ; and two short-styled plants only a single one. These capsules contained very few seeds ; yet the plants were fully productive when artificially fertilised under the net. In a state of nature the flowers are incessantly visited for their nectar by hive- and other bees, various Diptera and Lepidoptera.* The nectar is secreted all round the base of the ovarium ; but a passage is formed along the upper and inner side of the flower by the lateral deflection (not repre- sented in the diagram) of the basal portions of the filaments ; so that insects invariably alight on the pro- jecting stamens and pistil, and insert their proboscides along the upper and inner margin of the corolla. We can now see why the ends of the stamens with their anthers, and the ends of the pistils with their stigmas. * H. Miiller gives a list of the one bee, the Cilissa melanura, specifs, * Die Befruchtung dor almost confines its visits to this Blumen,' p. 11)6, It appears that plant. 146 IIETEROSTYLED TIUMORPHIC I'LANTS. Chap. IV. are a little upturned, so that they may be brushed by the lower hairy surfaces of the insects' bodies. The shortest stamens which lie enclosed within the calyx of the long- and mid-styled forms can be touched only by the proboscis and narrow chin of a bee ; lience they have their ends more upturned, and they are graduated in length, so as to fall into a narrow file, sure to be raked by the tliin intruding proboscis. The anthers of the longer stamens stand laterally farther apart and are more nearly on the same level, for they have to brush against the whole breadth of the insect's body. In very many other flowers the pistil, or the stamens, or both, are rectangularly bent to one side of the flower. This bending may be permanent, as with Lythrum and many others, or may be efl'ected, as in Dictam- nus fraxinella and others, by a temporary movement, which occurs in the case of the stamens when the anthers dehisce, and in the case of the pistil when the stigma is mature ; but these two movements do not always take place simultaneously in the same flower. Now I have found no exception to the rule, that when the stamens and pistil are bent, they bend to that side of the flower which secretes nectar, even though there be a rudimentary nectary of large size on the opposite side, as in some species of Corydalis. When nectar is secreted on all sides, they bend to that side where the structure of the flower allows the easiest access to it, as in Lythrum, various Papilio- naceae, and others. The rule consequently is, that when the pistils and stamens are curved or bent, the stigma and anthers are thus brought into the path- way leading to the nectary. There are a few cases which seem to be exceptions to tliis rule, but tliey are not so in truth ; for instance, in the Gloriosa lily, the stigma of the grotesque and rectangularly bent pistil CiiAi-. IV. LYTHRUM SALICARIA. 147 is brought, not into any pathway from the outside towards the nectar-secreting recesses of the flower, but into the circular route which insects follow in proceed- ing from one nectary to the other. In Scrophularia aquatica the pistil is bent downwards from the mouth of tlie corolla, but it thus strikes the pollen-dusted breast of the wasps which habitually visit these ill- scented flowers. In all these cases we see the supreme dominating power of insects on the structure of flowers, especially of those which have irregular corollas. Flowers which are fertilised by the wind must of course be excepted ; but I do not know of a single instance. of an irregular flower which is thus fertilised. Another point deserves notice. In each of the three forms two sets of stamens correspond in length with the pistils in the other two forms. When bees suck the flowers, the anthers of the longest stamens, bearing the green pollen, are rubbed against the abdomen and the inner sides of the hind legs, as is likewise the stigma of the long-styled form. The anthers of the mid-length stamens and the stigma of the mid-styled form are rubbed against the under side of the thorax and be- twqen the front pair of legs. And, lastly, the anthers of the shortest stamens and the stigma of the short- styled form are rubbed against the proboscis and chin ; for the bees in sucking the flowers insert only the front part of their heads into the flower. On catching bees, I observed much green pollen on the inner sides of the hind legs and on the abdomen, and much yellow pollen on the under side of the thorax. There was also pollen on the chin, and, it may be presumed, on the proboscis, but this was difiicult to observe. I had, however, independent jiroof that pollen is carried on the proboscis ; for a small branch of a protected short- styled plant (which produced spontaneously only two 148 HETEROSTYLED TRIMORPHIC PLANTS. Ciiai'. IV. capsules) was accidentally left during several days pressing against the net, and bees were seen inserting their prohoscides through the meshes, and in conse- quence numerous capsules were formed on this one small branch. From these several facts it follows that insects will generally carry the pollen of each form from the stamens to the pistil of corresponding length ; and we shall presently see the importance of this adapta- tion. It must not, however, be supposed that the bees do not get more or less dusted all over with the several kinds of pollen ; for this could be seen to occur with the green pollen from the longest stamens. Moreover a case will presently be given of a long-styled plant producing an abundance of capsules, though grow- ing quite by itself, and the flowers must have been fertilised by their own two kinds of pollen ; but these capsules contained a very poor average of seed. Hence insects, and chiefly bees, act both as general carriers of pollen, and as special carriers of the right sort. Wirtgen remarks * on the variability of this plant in the branching of the stem, in the length of the bractea?, size of the petals, and in several other characters. Jbe plants which grew in my garden had their leaves, which differed much in shape, arranged oppositely, alternately, or in whorls of three. In this latter case the stems were hexagonal ; those of the other plants being quadrangular. But we are concerned chiefly, with the reproductive organs : the upward bonding of the pistil is variable, and especially in the short-styled form, in which it is sometimes straight, sometimes slightly curved, but generally bent at right angles. The stigma of the long-styled pistil frequently has * ' Verhand. dcs nuturhist. Vcrcins, fiir Pr. Rlieinl.' 5. Jalirgang 1848, pp. 11, 13. OiiAP. IV. LYTHRUM SALICARIA. 149 longer papilla} or is rougher than that of the niid- stylofl, and the latter than that of the short-styled ; but this character, though fixed and uniform in tlie two forms of Primula veris, &c., is here variable, for I liave seen mid-styled stigmas rougher than those of the long-styled.* The degree to which the longest and mid-length stamens are graduated in length and have their ends upturned is variable ; sometimes all are equally long. The colour of the green pollen in the longest stamens is variable, being sometimes pale greenish-yellow ; in one short-styled plant it was almost white. The grains vary a little in size : I examined one short-styled plant with the grains above the average size ; and I have seen a long-styled plant with the grains from the mid-leno^th and shortest anthers of the same size. We here see great variability in many important characters ; and if any of these variations were of service to the plant, or were correlated with useful functional differences, the species is in that state in which natural selection might readily do much for its modification. On the Povjer of Mutual Fertilisation between the three Forms. Nothing shows more clearly the extraordinary com- plexity of the reproductive system of this plant, than the necessity of making eighteen distinct unions in order to ascertain the relative fertilising power of the * Tiie plants which I observed and he appears to have found the grew in iiiy garden, and proliably stigmatic papillte differing con- variid rather more than those stantly in length and structure in growing in a state of nature. H. the three forms, being longest in Miiller has described the stigmas the long-styled form. of all throe forms with great care, 150 HETEROSTYLED TKIMORPHIC PLANTS. Cuap. IV. three forms. Thus the long-styled form has to be fer- tilised with pollen from its own two kinds of anthers, from the two in the mid-styled, and from the two in the short-styled form. The same process has to be repeated ^^ith the mid-styled and short-styled forms. It might have been thought sufficient to have tried on each stigma the green pollen, for instance, from either the mid- or short-styled longest stamens, and not from both ; but the result proves that this would have been insufficient, and that it was necessary to try all six kinds of pollen on each stigma. As in fertilising flowers tliore will always be some failures, it would have been advisable to have repeated each of the eighteen unions a score of times ; but the labour would have l:)een too great ; as it was, 1 made 223 unions, i.e. on an average I fertilised above a dozen flowers in the eighteen different methods. Each flower was castrated ; the adjoining buds had to be removed, so that the flowers might be safely marked with thread, wool, &c. ; and after each fertilisation the stigma was examined with a lens to see that there- was suffi- cient pollen on it. Plants of all three forms were protected during two years by large nets on a frame- work ; two plants were used during one or both years, in order to avoid any individual peculiarity in a par- ticular plant. As soon as the flowers had withered, the nets were removed ; and in the autumn the cap- sules were daily inspected and gathered, the ripe seeds being counted under the microscope. I have given these details that confidence may be placed in the following tables, and as some excuse for two blunders which, I believe, were made. These blunders are referred to, with their probable cause, in two foot-notes to the tables. The erroneous numbers, how- ever, are entered in the tables, that it may not be sup- CuAP. IV. LYTHRUM SALICAIIIA. 151 posed that I have in any one instance tampered with the results. A few words explanatory of the three tables must be given. Each is devoted to one of the three forms, and is divided into six eomixirtments. The two upper ones in each table show the number of good seeds resulting from the application to the stigma of pollen from the two sets of stamens which correspond in length with the pistil of that form, and which are borne by the other two forms. Such unions are of a legitimate nature. The two next lower compartments show the result of the application of pollen fi-om the two sets of stamens, not corresponding in length with the pistil, and which are borne by the other two forms. These unions are illegitimate. The two lowest compartments show the result of the application of each form's own two kinds of pollen from the two sets of stamens be- longing to the same form, and which do not equal the pistil in length. These unions are likewise illegiti- mate. The term own-form pollen here used does not mean pollen from the flower to be fertilised — for this was never used — but from another flower on the same plant, or more commonly from a distinct plant of the same form. The figure (0) means that no capsule was produced, or if a capsule was produced that it contained no good seed. In some part of each row of figures in each compartment, a short horizontal line may be seen ; the unions above this line were made in 1862, and below it in 1863. It is of importance to observe this, as it shows that the same general result was obtained during two successive years ; but more especially be- cause 1863 was a very hot and dry season, and the plants had occasionally to be watered. This did not pre- vent the full complement of seed being produced from the more fertile unions ; but it rendered the less fertile 152 HETEROSTYLED TKIMOEPHIC PLANTS. Cuap. IV ones even more sterile than they otherwise would have been. I have seen striking instances of this fact in makinjr illegitimate and lofritimato unions with Pri- nulla ; and it is well known that the conditions of life must be highly favourable to give any chance of suc- cess in producing hybrids between species which are crossed with difficulty. Table 23. — Long-styled Form. I. II. Legitimate union. 13 flowers fertilised by the longest stamens of the mid-stylod. These stamens equal in length the pistil of the long-styled. Legitimate union. 13 flowers fertilised by the longest stamens of the short-styled. These stamens equal in length the pistil of the long-styled. Product of good seed sule. ;'.6 81 in each cap- 53 Product of good seed in each cap- sule. 159 104 43 119 96 poor seed. 96 103 99 131 116 45 41 114 o8 per cent, of these flowers yielded capsules. Each capsule con- tained, on an average, 51*2 seeds. 84 per cent, of these flowers yielded capsules. Each capsule con- tained, on an average, 107 "3 seeds. III. IV. Illegitimate union. 14 flowers fertilised by the short- est stamens of the mid-styled. Illegitimate union. 12 flowers fertilised by the mid- length stamens of the short-styled. o 20 — ■ Too sterile for an; average. Too sterile for any average. CuAr. IV. LYTHRUM SALICARIA. 153 Table 23. — Long-styled Form — continued. V. VI. TUegitimate union. Illegitimate union. 15 flowers fertilised by own-form 15 flowers fertilised by own-form mid-length stamens. shortest stamens. 2 4 10 8 23 4 Too sterile for any average. Too sterile for any average. Besides the above experiments, I fertilised a coiisi- derable number of long-styled flowers with pollen, taken by a camel's-hair brush, from both the mid- Jength and shortest stamens of their own form : only 5 capsules were produced, and these yielded on an average 14 '5 seeds. In 1863 I tried a much better ex- periment : a long-styled plant was grown by itself, miles away from any other plant, so that the flowers could have received only their own two kinds of pol- len. The flowers wore incessantly visited by bees, and their stigmas must have received successive applica- tions of pollen on the most favourable days and at the most favourable hours : all who have crossed plants know that this highly favoiu's fertilisation. This plant produced an abundant croj) of capsules ; I took by chance 20 capsules, and these contained seeds in number as follows : — 20 20 35 21 19 26 24 12 23 10 7 30 27 29 13 20 12 29 19 35 154 IIETEROSTYLED TRIMORrUIC PLANTS. Chap. IV. This gives an average of 21 • 5 seeds per capsule. As we know that the h^ng-styled form, when standing near plants of the other two forms and fertilised by insects, produces on an average 93 seeds per capsule, we see that this form, fertilised by its own two pollens, yields only between one-fonrtli and one-fifth of the full number of seed. I have spoken as if the plant had re- ceived both its own kinds of pollen, and this is, of course, possible ; but, from the enclosed position of the shortest stamens, it is much more probable that the stigma received exclusively pollen from the mid- length stamens ; and this, as may be seen in com- partment V. in Table 23, is the more fertile of the two self-unions. Table 2L— Mid-styled Form. I. II. Legitimate union. Legitimate union. 12 flowers fertilised by the mid- 12 flowers fertilise! by the mid- length stamens of the long-styled. length stamens of the short -styled. These stamens equal in length the These stamens equal in length the pistil of the mid-styled. pistil of the mid-styled. Product of good seed in each cap- Product of good seed in each cap- sule. sule. 133 122 112 109 149 50 130 143 147 151 143 124 109 1 19 100 145 133 138 33 12 144 — 141 — 104 92 per cent, of the flowers (pro- 100 per cent, of the flowers yielded bably 100 per cent.) yielded cap- .sules. Each capsule contained, on an average, 127 3 seeds. capsules. Each capsule' contained, on an average, 108 '0 seeds; or, ex- cluding capsules with less than 20 seeds, the average is 116*7 seeds. CiiAi-. IV. LYTIIRUM SALICARIA. 155 Table 24. — Mid-sfi/Ied Form — continued. III IV. nieg ■timate union. Illegitimate miion. 13 flowers fertili sed by the short- 15 flowers fertilis ed by the Ion ' est stamens of the 1 ong-styled. est stamens of the short-styled. 83 12 1.30 8«> 19 115 113 o-f seeds small \ and poor. 14 29 6 17 — 2 113 44- 9 79 44 — 128 45 132 54 per cent, of the flowers yielded capsules. Each capsule contained, on an average, 47 '4 seeds; or, ex- cluding capsules with less than 20 seeds, the average is 60*2 seeds. 93 per cent, of the flowers yielded capsules. Each capsule contained, on an average, 69 '5 seeds; or, ex- cluding capsules with less than 20 seeds, the average is 102 • 8. V. VI. Illegitimate union. Illegitimate union. 12 flowers fertilised by own-form 12 flowers fertilised by own-form ngest stamens. shortest stamens. 92 9 G3 — — 1.36 ? * Excluding the capsule with 136 seeds, 25 per cent, of the flowers yielded capsules, and each capsule contained, on an average, 54 • 6 seeds ; or, excluding capsules with less than 20 seeds, the average is 77 "5. Not one flower yielded a capsule. * I have hardly a doubt tliat this result of 136 seeds in compart- ment V. was due to a gross error. The flowers to be fertilised by their own longest stjimens were first marked by " white thread," and those by the mid-lentcth stamens of the lon^-styled form by " white silk ;'' a flower fertilised in the later manmr would have yielded about 136 seeds, and it may be observed that one such po 1 is missing, viz. at the bottom of compartmcntl. Therefore I have hardly any doubt that I fertilised a flower mnrkcd witli "white thread' as if it had been marked with " white silk." With respect to the capsule which yielded 92 seeds, iu the .same column with tliat winch yielded 136, I do not know what to think. I endeavoured to prevent jwllcn drojiping from an upper to a lower 156 HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. Besides the experiments in the above table, I ferti- lised a considerable number of mid-styled flowers with pollen, taken by a camel's-hair brush, from both the longest and shortest stamens of their own form : only 5 capsules were produced, and these yielded on an average 11"0 seeds. Table 25. — Short-styled Form. I. Legitimate union. 12 flowei-s fertilised by the short- est stamens of the long-styled. These stamens equal in length the pistil of the short-styled. 69 56 61 88 88 112 66 111 62 100 83 per cent, of the flowers yielded capsules. Each capsule contained, on an average, 81*3 seeds. III. Illegitimate union. 10 flowers fertilised by the mid- length stamens of the long-styled. 14 — 23 Too sterile for any average. II. Legitimate union. 13 flowers fertilised by the short- est stamens of the mid-styled. These stamens equal in length the pistil of the short-styled. 93 69 77 69 48 53 43 9 — 6 1 per cent, of the flowers yielded capsules. Each capsule contained, on an average, 64*6 seeds. IV. Illegitimate union. 10 flowers fertilised by the long- est stamens of the mid-styled. — Too sterile for any average. flower, and I tried to remember to wipe the pincers carefully after each fertilisation ; but in making eighteen diflferent unions, some- times on windy days, and pestered by bees and flies buzzing about, some few errors could hardly be avoided. One day I had to keep a third man by me all the time to prevent the bees visiting the un- covered plants, for in a few seconds' time they might have done irreparable mischief. It was also extremely difficult to exclude minute Diptera from the net. In 1862 I made the great mistake of placing a mid-styled and long- styled under the same huge net : in 18G3 I avoided this error. Ciur. IV. LYTHKUM SALICARIA. 157 Table 25. — Short-styled Form — continned. V. VI. Illegitimate union. 10 flowers fertilised by own-form longest stamens. Illegitimate union. 10 flowers fertilised by own-form jnid-Iength stamens. 64?* 21 9 Too sterile for any average. Too sterile for any average. Besides the experiments in the table, I fertilised a number of flowers vritliout particular care with tlieir own two kinds of poUefi, but they did not produce a single capsule. Summary of tlie Eesults. Long-stifled form. — Twenty-six flowers fertilised le- gitimately by the stamens of corresponding length, borne by the mid- and short-styled forms, yielded 61*5 per cent, of capsules, which contained on an average 89-7 seeds. Twenty-six long-styled flowers fertilised illegiti- mately by the other stamens of the mid- and short- styled forms yielded only two very poor capsules. Thirty long-styled flowers fertilised illegitimately by their own-form two sets of stamens yielded only eight very poor capsules ; but long-styled flowers fertilised * I suspect that by mistake I to be thus fertilised were marked fertilised this flower iu compart- with black silk ; those with pollen ment VI. with pollen from the from the mid-length stamens of shortest stamens of the long-stjded the short-styled with black thread ; form, and it would then have and thus probably the mistake yielded about CI sceils. Flowers arose. 158 HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. by bees with pollen from their own stamens produced numerous capsules containing on an average 21 '5 seeds. Mid-styled form. — Twenty-four flo\\ers legitimately fertilised by the stamens of corresponding length, borne by the long and short-styled forms, yielded 9G (probably 100) per cent, of capsules, which contained (excluding one capsule with 12 seeds) on an average 117"2 seeds. Fifteen mid-styled flowers fertilised illegitimately by the longest stamens of the short-styled form yielded 93 per cent, of capsules, which (excluding four cap- sules with less than 20 seeds) contained on an average 102-8 seeds. ^ Thirteen mid-styled flowers fertilised illegitimately by the mid-length stamens of the long-styled form yielded 54 per cent, of capsules, which (excluding one with 19 seeds) contained on an average 60*2 seeds. Twelve mid-styled flowers fertilised illegitimately by their own-form longest stamens yielded 25 per cent, of capsules, which (excluding one with 9 seeds) contained on an average 77*5 seeds. Twelve mid-styled flow^ers fertilised illegitimately by their own-form shortest stamens yielded not a single capsule. Short-styled form. — Twenty-five flowers fertilised legitimately by the stamens of corresponding length, borne by the long and mid-styled forms, yielded 72 per cent, of capsules, which (excluding one capsule with only 9 seeds) contained on an average 70"8 seeds. Twenty short-styled flowers fertilised illegitimately by the other stamens of the long and mid-styled forms yielded only two very poor capsules. Twenty short-styled flowers fertilised illegitimately CllAP. IV. LYTHRUM SALICARIA. 159 by their own stamens yielded only two poor (or per- haps three) capsules. If we take all six legitimate unions together, and all twelve illegitimate unions together, we get the fol- lowing results : — Table 26. Number Xumber Kature of Union. of Flowers of Capsules 1 fertilised. | produced. Xumber of o„^,u .^.r Capsule. jmg^ The six lesfitimatel ^_ .„ ° > 7o 56 unions. . . ./ 96-29 71-89 The twelve illegiti-1 ., , , 1 „. mate unions . ./ ^^' -^^ 44-72 11-03 Therefore the fertility of the legitimate unions to that of the illegitimate, as judged by the proportion of the fertilised flowers which yielded capsules, is as 100 to 33 ; and judged by the average number of seeds per capsule, as 100 to 46. From this summary and the several foregoing tables we see that it is only pollen from the longest stamens which can fully fertilise the longest pistil ; only that from the mid-length stamens, the mid-length pistil; and only that from the shortest stamens, the shortest pistil. And now we can comprehend the meaning of the almost exact correspondence in length between the pistil in each form and a set of six stamens in two of the other forms ; for the stigma of each form is thus rubbed against that part of the insect's body which becomes charged with the proper pollen. It is also evident that the stigma of each form, fertilised in three different ways with pollen from the longest, mid-length, and shortest stamens, is acted on very differently, and conversely that tlie pollen from IGO HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. the twelve longest, twelve mid-length, and twelve shortest stamens acts very differently on each of the three stigmas ; so that there are three sets of female and of male organs. Moreover, in most cases the six stamens of each set differ somewhat in their fertilising power from the six corresponding ones in one of tlie other forms. We may further draw the remarkable conclusion that the greater the inequality in length between the pistil and the set of stamens, the pollen of which is em})loyed for its fertilisation, by so much is the sterility of the union increased. There are no exceptions to this rule. To understand what follows the reader should look to Tables 23, 24, and 25, and to the diagram Fig. 10, p. 139. In the long-styled form the shortest stamens obviously differ in length from the pistil to a greater degree than do the mid-length stamens ; and the capsules produced by the use of pollen from the shortest stamens contain fewer seed^ than those produced by the pollen from the mid- length stamens. The same result follows with the long-styled form, from the use of the pollen of the shortest stamens of the mid-styled form and of the mid-length stamens of the short-styled form. The same rule also holds good with the mid-styled and short-styled forms, when illegitimately fertilised with pollen from the stamens more or less unequal in length to their pistils. Certainly the difference in sterility in these several cases is slight ; but, as far as we are enabled to judge, it always increases with the increasing inequality of length between the pistil and the stamens which are used in each case. The correspondence in length between the pistil in each form and a set of stamens in the other two forms, is probably the direct result of adaptation, as it is of high service to the sjiecies by leading to fuU and Chap. IV. LYTHRUM SALICARIA. 161 legitimate fertilisation. But the rule of the increased sterility of the illegitimate unions according to the greater inequality in length between the pistils and stamens employed for the union can be of no service. With some heterostyled dimorphic plants the dif- ference of fertility between the two illegitimate unions appears at first sight to be related to the facility of self-fertilisation ; so that when from the position of the parts the liability in one form to self-fertilisation is greater than in the other, a union of this kind has been checked by having been rendered the more sterile of the two. But this explanation does not apply to Lythrum ; thus the stigma of the long- styled form is more liable to be illegitimately fer- tilised with pollen from its own mid-length stamens, or with pollen from the mid-length stamens of the short-styled form, tlian by its own shortest stamens or those of the mid-styled fonn ; yet the two former unions, which it might have been expected would have been guarded against by increased sterility, are much less sterile than the other two unions which are much less likely to be effected. The same relation holds good even in a more striking manner with the mid-styled form, and with the short- styled form as far as the extreme sterility of all its illegitimate unions allows of any comparison. We are led, therefore, to conclude that the rule of in- creased sterility in accordance with increased in- equality in length between the pistils and stamens, is a purposeless result, incidental on those changes through which the species has passed in acquiring certain characters fitted to ensure the legitimate fertilisation of the three forms. Another conclusion which may be drawn from Tables 2^, 21, and 25, even from a glance at tliem, 1G2 llETEROSTYLED TRIMORPHIC PLANTS. CiiAr. IV. is that the mid-styled form differs from both tlie others in its much higher capacity for fertilisation in various ways. Not only did the twenty-four flowers legitimately fertilised by the stamens of corresponding lengths, all, or all but one, yield capsules rich in seed ; but of the other four illegitimate unions, that by the longest stamens of the short-styled form was highly fertile, though less so than the two legitimate unions, and that by the mid-length stamens of the long-styled form was fertile to a considerable degree ; the remaining two illegitimate unions, namely, with this form's own pollen, were sterile, but in different degrees. So that the mid-styled form, when fertilised in the six different possible methods, evinces five grades of fertility. By comparing compartments III. and VI. in Table 24 we may see that the action of the pollen from the shortest stamens of the long-styled and mid-styled forms is widely different; in the one case above half the fertilised flowers yielded capsules containing a fair number of seeds ; in the other case not one capsule was produced. So, again, the green, large-grained pollen from the longest stamens of the short-styled and mid-styled forms (in compart- ments lY. and V.) is widely different. In both these cases the difference in action is so plain that it cannot be mistaken, but it can be corroborated. If we look to Table 25 to the legitimate action of the shortest stamens of the long- and mid-styled forms on the short-styled form, we again see a similar but slighter difference, the pollen of the shortest stamens of the mid-styled form yielding a smaller average of seed during the two years of 18G2 and 1863 than that from the shortest stamens of the long-styled form. Again, if we look to Table 23, to the legitimate action on the long-styled form of the green pollen of the two Chap. IV. LYTIIEUIM SALICAEIA. 163 sets of longest stamens, we shall find exactly the same result, viz. that the pollen from the longest stamens of the mid-styled form yielded during both years fewer seeds than that from the longest stamens of tlie short-styled form. Hence it is certain that the two kinds of pollen produced by the mid-styled form are less potent than the two similar kinds of pollen pro- duced by the corresponding stamens of the other two forms. In close connection with the lesser potency of the two kinds of pollen of the mid-styled form is the fact that, according to H. Miiller, the grains of both are a little less in diameter than the corresponding grains produced by the other two forms. Thus the graiais from the longest stamens of the mid-styled form are 9 to 10, whilst those from the corresponding stamens of the short-styled form are 9^ to 10 1 in diameter. So, again, the grains from the shortest stamens of the mid-styled are 6, whilst those from the corresponding stamens of the long-styled are 6 to C^ in diameter. It would thus appear as if the male organs of the mid-styled form, though not as yet rudimentary, were tending in this direction. On the other hand, the female organs of this form are in an eminently efficient state, for the naturally fertilised capsules yielded a considerably larger average number of seeds than those of the other two forms — almost every flower which was artificially fertilised in a legitimate manner produced a capsule — and most of the illegitimate unions were highly productive. The mid-styled form thus appears to be highly feminine in nature ; and al- though, as just remarked, it is impossible to consider its two well-developed sets of stamens which produce an abundance of poUen as being in a rudimentary condition, yet we can hardly avoid connecting as 104 HETEROSTYLED TKIMORPHIC PLANTS. Chap. IV. balanced the higher efficiency of the female organs in this form with the lesser efficiency and lesser size of its two kinds of pollen-grains. The whole case appears to me a very curious one. It may be observed in Tables 23' to 25 that some of the illegitimate unions yielded during neither year a single seed ; but, judging from the long-styled plants, it is probable, if such unions were to be effected re- peatedly by the aid of insects under the most favour- able conditions, some few seeds would be produced in every case. Anyhow, it is certain that in all twelve illegitimate unions the pollen-tubes penetrated the stigma in the course of eighteen hours. At first I thought that two kinds of pollen placed together on the same stigma would perhaps yield more seed than one kind by itself ; but we have seen that this is not so with each form's own two kinds of pollen ; nor is it probable in any case, as I occasionally got, by the use of a single kind of pollen, fully as many seeds as a capsule naturally fertilised ever produces. Moreover the pollen from a single • anther is far more than suffi- cient to fertilise fully a stigma ; hence, in this as with so many other plants, more than twelve times as mach of each kind of pollen is produced as is necessary to ensure the full fertilisation of each form. From the dusted condition of the bodies of the bees which I caught on the flowers, it is probable that pollen of various kinds is often deposited on all three stigmas ; but from the facts already given with respect to the two forms of Primula, there can hardly be a doubt that pollen from the stamens of corresponding length placed on a stigma would be prepotent over anv other kind of pollen and obliterate its effects, — even if the latter had been placed on the stigma some hours previously. CiiAr. IV. I^YTHRUM GR^FFERI. 165 Finally, it has now been shown that Ly thrum salicaria presents tlie extraordinary case of the same species beariuc: three females, dift'erent in structure and func- tion, and three or even five sets (if minor differences are considered) of males ; each set consisting of half- a-dozen, which likewise differ from one another in structure and function. Lythtim (JrfcffcrL—l have examined numerous di'icd flowei-s of this species, each from a separate plant, sent me from Kew. Like L. salicaria, it is trimorpliic, and the tlirce forms ap])a- rcntly occvir in about equal numbers. In the long-styled form the pistil projects about one-thii-d of the length of the calyx beyond its mouth, and is therefore relatively much shorter than in L. salicaria ; the globose and hirsute stigma is larger than that of the other two forms ; the six mid-length stamens, -niiich are graduated in length, have their anthers standing close above and close beneath the mouth of the calyx; the six shortest stamens rise rather above the middle of the calj-x. In the mid- styled form the stigma projects just above the mouth of the calyx, and stands almost on a level with the mid-length stjimens of the long and short-styled forais ; its own longest stamens project well above the mouth of the calj'x, and stand a little above the level of the stigma of the long-styled form. In short, without entering on further details, there is a close general correspondence in structure between this species and L. salicaria, but with some differences in the proportional lengths of the parts. The fact of each of the three pistils having two sets of stamens of corrcsi^onding lengths, borne by the two other forms, comes out conspicuously. In the mid-styled fonn the pollen- grains from the longest stamens ai"e nearly double the diameter of those from the shortest stamens ; so that there is a greater difference in tliis resjiect than in L. salicaria. In the long- styled fonn, also, the difference in diameter between the pollen- grains of the mid-length and shortest stamens is greater than in L. salicaria. These comparisons, however, must be received with caution, as they were made on specimens soaked in water after having been long kept dry. l.yihrum thymifolia. — This form, according to Vaucher,* is • ' Ilbt. riiys. tks TLmtcs d'Europe,' torn. ii. (1841), pp. 369, 371. IGG HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. dimorphic, like Primula, and therefore presents only two forms. I received two dried flowers from Kew, which consisted of the two forms; in one the stigma projected far beyond the caljTc, in the other it was included within the calyx; in tliis latter fonn the style was only onc-fourtli of the length of that in the other form. Tlicre are only six stamens ; these are somewhat gradu- ated in length, and their anthers in the short-styled form stand a little above the stigma, but yet by no means equal in length the pistil of the long-styled form. In the latter the stamens are rather shorter than those in the other form. The six stamens alternate with the petals, and therefore correspond homologically with the longest stamens of L. salicaria and L. Grxfferi. Lythrum hyssopifolia. -—Thifi species is said by Vaucher, but I believe eiToneously, to be dimorphic. I have examined dried flowers fi'om twenty-two separate i^lauts from various localities, sent to me by Mr. Hewett C. Watson, Professor Babington, and others. These were all essentially alike, so that the sj^ccies cannot be heterostyled. The pistil varies somewhat in length, but when unusually long, the stamens are likewise generally long; in the bud the stamens are short; and Vaucher was perhaps thus deceived. There are from six to nine stamens, graduated in length. The three stamens, which vary in being either present or absent, correspond with the six shorter stamens of L. salicaria and with the six which are always absent in L. ihymifolia. The stigma is included within the calyx, and stands in the midst of the anthers, and would generally be fertilised by them ; but as the stigma and anthers are uptiu-ned, and as, according to Vaucher, there is a passage left in the upper side of the flower to the nectary, there can hardly be a doubt that the flowers are visited by insects, and would occasionally be cross-fertilised by them, as sixrely as the flowers of the short- styled L. salicaria, the pistil of which and the corresponding stamens in the other two fonns closely resemble those of L. hya- sopifolia. According to Vaucher and Lecoq,* this species, wliich is an annual, generally grows almost solitarily, whereas the three preceding species are social ; and this fact alone would almost have convinced me that L. hyssopifolia was not hetero- styled, as such plants cannot habitually live isolated any better than one sex of a dioecious species. • ' G^ograph. Bot. de I'Europe,' torn. vi. 1857, p. 157. CuAr. IV LAGERSTRCEMIA IXDICA. 167 We thus see that withiu this genus some species arc hetero- styled and trimorphic ; one apparently heterostyled and dimor- pliic, and one homostylcd. Aesaa verticiUata. — I raised a ntmiber of plants from seed sent me by Professor Asa Gray, and they presented three forms. These differed from one another in the proportional lengths of their organs of fructification and in all respects, in very nearly the same way as the three forms of Lijthrum Grxfferi. The gi'eeu pollen-grains from the longest stamens, measured along their longer axis and not distended with water, were ^j^ of an inch in length ; those from the mid-length stamens ^3^, and those from the shortest stamens ^ of an inch. So that the largest pollen-grains are to the smallest in diameter as 100 to 65. This plant inhabits swampy ground in the United States. According to Fritz Miiller,* a si^ecics of this genus in St. Catha- rina, in Southern Brazil, is homostyled. Lagerstroemia Indica. — This jDlant, a member of the Lythraceie, may perhaps be heterostyled, or may formerly have been so. It is remarkable from the extreme variability of its stamens. On a jilant, growing in my hothouse, the flowers included from nineteen to twenty-nine short stamens with yellow pollen, which correspond in position with the shortest stamens of Lythrum; and from one to five (the latter number being the commonest) very long stamens, with tliick flesh-coloured fila- ments and green pollen, corresponding in position with the longest stamens of Lytlu'um. In one flower, two of the long stamens produced green, while a third produced yellow jaollen, although the filaments of all three were tliick and flesh-coloured. In an anther of another flower, one cell contained green and the other yellow pollen. The green and yellow pollen-grains from the stamens of different length are of the same size. The pistil is a little bowed upwards, with the stigma seated between the anthers of the short and long stamens, so that this plant was mid-styled. Eight flowers were fertilised with green pollen, and six with yellow pollen, but not one set fruit. This latter fact by no means proves that the plant is hetero- styled, as it may belong to the class of self-sterile sjjccies. Another plant growing in the Botanic Gardens at Calcutta, as Mr J. Scott informs me, was long-styled, and it was equally * 'Bot. Zcitung,' 18GS, p. 112. 1G8 HETEROSTYLED TEIMOIIPHIC PLANTS. Ciiap. IV. sterile with its own pollen; whilst a long-styled plant of L. reyince, though growing by itself, produced fruit. I examined dried flowers from two plants of L. parviflora, both of which were long-styled, and they differed from L. Jndica in having eight long stamens with thick filaments, and a crowd of shorter stamens. Thus the evidence whether //. Indka is hctero- styled is curiously conflicting : the uneciual number of the short and long stamens, their extreme variability, and especially the fact of their pollen-grains not differing in size, are strongly opposed to this belief; on the other hand, the difference iu length of the pistils in two of the plants, their sterility with their own pollen, and the difference in length and structure of the two sets of stamens in the same flower, and in the colour of their pollen, favour the belief We know that when plants of any kind revert to a former condition, they are apt to be highly variable, and the two halves of the same organ sometimes differ much, as in the case of the above-described anther of the Lagerstroemia ; we may therefore suspect that this species was once heterostyled, and that it still retains traces of its former state, together with a tendency to revert more completely to it. It deserves notice, as bearing on the nature of Lagerstroemia, that in Lythrum hyssopifolia. which is a homostyled species, some of the shorter stamens vary in being either present or absent ; and that these same stamens are altogether absent in L. thymi- folia. In another genus of the Lythracese, namely Cuphea, three species raised by me from seed certainly were homostyled ; nevei*theless their stamens consisted of two sets, differing in length and in the colour and thickness of their filaments, but not in the size or colour of their pollen-grains ; so that they thus far resembled the stamens of Lagerstroemia. I found that Cuphea purpurea was highly fertile with its own pollen when artificially aided, but sterile when insects were excluded.* * Mr. Spence informs mc that phic: but ho did not notice the in several species of the genus length of the pistils. In the Mollia (Tiliacefe) which he col- allied Luhea the outer purplish lected in South America, the starat-ns are destitute of anthers, stumens of the five outer cohorts I procured snme specimens of liave purplish filaments and green MnUia hpidnta and »peci mate union ) 40 2 5-5 Long-styled form, by pollen of own and! own-form shortest stamens. lUegiti-) mate union ) 26 Long-styled form, by pollen of shortest! stamens of short-styled. Illegitimate/ union ) 16 1 1 Long-styled form, by pollen of shortest! stamens of mid-styled. Illegitimate) union J 9 172 HETEROSTYLED TRlMORPniG PLANTS. Chai-. IV Table 27— continued. Oxalis VaUiviana {from Eildebrand). Nature of Union. Mi.l-styled form, by pollen of mid-length sta-| mens of long-styled. Legitimate union . j Mid-styled form, by pollen of mid-length j stamens of .short - styled. Legitimate union ) Mid-styled form, by pollen of own and] own-form longest stamens. Illegitimate, union ] Number of Flciwers fertilised. 38 Number of Capsules produced. 23 52 Mid-styled form, by poHen of own andjl own-form shortest stamens. Illegitimate >| union ) I Mid-styled form, by pollen of shortest jj stamens of long-styled. Illegitimate) union ) i Mid-styled form, by pollen of longest sta-V, ■ ' ' '" ■" sate union/ 16 mens of short-styled. lUegitim;' 16 Short-styled form, by pollen of shortest sta-V mens of long-styled. Legitimate union . j , Short-styled form, by pollen of shortest sta-1 ' mens of mid-styled. Legitimate union . ) j Short-styled form, by pollen of own and! own-form longest atameus. Illegitimate)! union ) Short-styled form, by pollen of own andj own-form mid-length stamens. Illegiti-> mate union j Short-styled form, by pollen of longest sta-j mens of mid-styled. Illegitimate union/ Short-styled form, by pollen of mid-length 1 stamens of long -styled. Illegitimate/ union I 18 Number of Seeds per Capsule. ll- -1" 23 10-4 18 2-5 11-0 10 10 11- 21 22 Chap. IV. OXALIS IlEGNELLI. 173 We here have the remarkable result that every one of 138 legitimately fertilised flowers on the three forms yielded capsules, containing on an average 11 ' 33 seeds. Whilst of the 255 illegitimately fertilised flowers, only 6 yielded capsules, which contained 3 • 83 seeds on an average. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers that yielded capsules, is as 100 to 2, and as judged by the average number of seeds per capsule as 100 to 34. It may be added that some plants which were protected by nets did not spontaneously produce any fi-uit ; nor did one which was left uncovered by itself and was visited by bees. On the other hand, scarcely a single flower on some uncovered plants of the three forms growing near together failed to produce fruit. OxaJis RegneUi. — This species bears white flowers and inhabits Southern Brazil. Hildebrand says that the stigma of the long-styled form is somewhat larger than that of the mid-styled, and this than that of the short-styled. The pistil of the latter is clothed with a few hairs, whilst it is very hairy in the other two forms. The diameter of the pollen-grains from both sets of the longest stamens equals 9 divisions of the micrometer, — that from the mid-length stamens of the long-styled form between 8 and 9, and of the short- styled 8, — and that from the shortest stamens of both sets 7. So that the extreme difference in diameter is as 9 to 7 or as 100 to 78. The experiments made by Hildebrand, which are not so numerous as in the last case, are given in Table 28 in the same manner as before. The results are nearly the same as in the last case, but more striking ; for 41 flowers belonging to the three forms fertilised legitimately all yielded capsules, 174 HETEROSTYLED TKIMORPHIC PLANTS. Chai-. IV. Table 28. Oxalis Piegnelli {from Ilildehrand). Nature of Union. Number Number , Average of of j Number of Flowers Capsules | Seeds per fertiUsed. produced, i Capsule. Long-stjled form, by pollen of longest sta-"^ g 1 q ' 10-1 mens of short-styled. Legitimate unionj 1 | Long-styled form, by pollen of longest sta-V mens of mid-styled. Legitimate union / Long-styled form, by pollen of own mid-) length stamens. Illegitimate union . f 10-G Long-styled form, by pollen of own short-l est stamen. Illegitimate union. . ./ 1 Mid-styled form, by pollen of mid-length sta-'l mens of short-styled. Legitimate union/ 9 9 10-4 Mid-styled form, by pollen of mid-length sta-"! mens of long-styled. Legitimate union./ 10 10 10-1 Mid-styled form, by pollen of own longestV stamens. Illegitimate union . . ./ 9 Mid-styled form, by pollen of own shortest^ | stamens. Illegitimate union . . ./! 2 Mid-styled form, by pollen of longest sta-^ mens of short-styled. Illegitimate union/ 1 Short-styled form, by pollen of shortest sta-"> mens of mid-styled. Legitimate union . / 9 ! 9 i 10-6 Short-styled form,bypollen of shortest sta-"l mens of long-styled. Legitimate union . J 2 2 9-5 Short-styled form, by pollen of own mid-" length stamens. Illegitimate union 12 Short-styled form, by pollen of own long-1 est stamens. Illegitimate union . . / 9 Short-styled form, by pollen of mid-length 1 stamens of long -styled. Illegitimate^ union ) 1 ij Chap. IV. OXALIS SPECIOSA. 175 containing on an average 10 • 31 seeds ; whilst 39 flowers fertilised illegitimately did not yield a single capsule or seed. Therefore the fertility of the six legitimate to that of the several illegitimate unions, as judged both by the proportion of flowers which yielded capsules and by the average number of con- tained seeds, is as 100 to 0. Oxalis speciosa. — This species, which bears pink flowers, was introduced from the Cape of Good Hope. A sketch of the reproductive organs of the three forms (Fig. 11) has already been given. The stigma of the long-styled form (with the papillae on its sur- face included) is twice as large as that of the short- styled, and that of the mid-styled intermediate in size. The pollen-grains from the stamens in the three forms are in their lonjrer diameters as follows : — a the longest stamens of short-styled. Divisions of the Micrometer. . 15 to 16 „ mid-lecgth „ „ . . „ longest stamens of miJ-styled . . 12 „ 13 16 „ shortest „ „ . . . 11 to 12 „ mid-length stamens of long-styled . 14 „ shortest „ „ . . 12 Therefore the extreme difference in diameter is as 16 to 11, or as 100 to 69; but as the measurements were taken at different times, they are probably only approximately accurate. The results of my experiments in fertilising the three forms are given in the following table. 17G HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV Table 29. Oxulis speciosa. Ndture of Union I Kumber I "^ Flowers fiTtllisod. Number of Capsules produced. Average Number of Secd/i per Capsule. Long-styled form, by pollen of longest! stamens of short - styled. Legitimate) 19 15 Long-styled form, by pollen of longest! stamens of mid -styled. Legitimate) 57-4 59-0 Long-styled form, by pollen of own-formV g mid-length stamens. Illegitimate union/ i Long-styled form, by pollen of own-form"! ' .. shortest stamens. Illegitimate union ./i Long-styled form, by pollen of shortest!] stameus of mid -styled. Illegitimate)' 4 union ) 42-5 Long-styled form, by pollen of mid-length 1 stamens of short-styled. Illegitimate)! 12 union ]' 30-0 Jlid-styled form, by pollen of mid-length stamens of long - styled. Legitimate union Jlid-styled form, by pollen of mid-length! stamens of short -styled. Legitimate) union I Mid-styled form, by mixed pollen from! both own -form longest and shortest) stamens. Illegitimate union 63r6 56-3 19 Mid-styled form, by pollen of longest! stamens of short-styled. Illegitimate) OaAP. IV. OXALIS SPECIOSA. m' Table 29 — continued. Oxalis speciosa. Nature of Union. Number of Flowers fertilised. Number ' Average of Number of Capsulos 1 Seeds per produced. 1 Capsule. Short-styled form, by pollen of shortest! stamens of mid - styled. Legitimate > 3 2 1 67 1 Short-styled form, by pollen of shortest) stamens of long -styled. Legitimate) 3 1 3 54 3 Short-styled form, by pollen of own-form "> longest stamens. Illegitimate union . / 5 1 8 Short-styled form, by pollen of own-form' mid-length stamens. Illegitimate union ' 3 Short-styled form, by both pollens mixed! together, of own-form longest and mid-> length stamens. Illegitimate union . ) 13 Short>styled form, by pollen of longest! stamens of mid -styled. Illegitimate) 7 stamens of long -styled. Illegitimate) 10 1 54 We here see that thirty-six flowers on the three forms legitiraately fertilised yiekled 30 capsules, these containing on an average 58 '36 seeds. Ninety-five flowers illegitimately fertilised yielded 12 capsules, containing on an average 28*58 seeds. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers which yielded capsules, is as 100 to 15, and judged by the average number of seeds per capsule as 100 to 49. This plant, in comparison with the two South American species previously described, produces 178 HETEllOSTYLED TRIMOEPHIC PLANTS. Chap IV. many more seeds, and the illegitimately fertilised flowers are not quite so sterile. Oxalis rosea. — Hildebrand possessed in a living state only the long-styled form of this trimorphic Chilian species.* The pollen-grains from the two sets of anthers differ in diameter as 9 to 7*5, or as 100 to 83. He has further shown that there is an analogous difference between the grains from the two sets of anthers of the same flower in five other species of Oxalis, besides those already described. The present species differs remarkably from the long-styled form of the three sj)ecies previously experimented on, in a much larger proportion of the flowers setting capsules when fertilised with their own-form j^oUen. Hildebrand fer- tilised 60 flowers with pollen from the mid-length stamens (of either the same or another flower), and they yielded no less than 55 caj)sules, or 92 per cent. These capsules contained on an average 5 * 62 seeds ; but we have no means of judging how near an approach this average makes to that from flowers legitimately fertilised. He also fertilised 45 flowers with pollen from the shortest stamens, and these yielded only 17 capsules, or 31 per cent., containing on an average only 2*65 seeds. We thus see that about thiice as many flowers, when fertilised with pollen from the mid-length stamens, produced capsules, and these contained twice as many seeds, as did the flowers fertilised with pollen from the shortest stamens. It thus appears (and we find some evidence of the same fact with 0. speciosa), that the same rule holds good with Oxalis as with Lythrum salicaria ; namely, that in any two unions, the greater the in- equality in length between the pistils and stamens, or, ' Monatbber. der Akad. dtr Wise. Berlin,' 1860, p. 372. Chap. IV. OXALIS, OTHER SPECIES OF. 179 which is the same thing, the greater the ilistance of the stigma from the anthers, the pollen of which is used for fertilisation, the less fertile is the union, — whether judged by the proportion of flowers which set capsules, or by the average number of seeds per capsule. The rule cannot be explained in this case any more than in that of Lythrum, by supposing that wherever there is greater liability to self-fertilisa- tion, this is checked by the union being rendered more sterile ; for exactly the reverse occurs, the liability to self-fertilisation being greatest in the unions between the pistils and stamens which ajsproach each other the nearest, and these are the more fertile. I may add that I also possessed some long-styled plants of this species : one was covered by a net, and it set sponta- neously a few capsules, though extremely few com- pared with those produced by a plant growing by itself, but exposed to the visits of bees. With most of the species of Oxalis the short-styled form seems to be the most sterile of the three forms, when these are illegitimately fertilised ; and I will add two other cases to those already given. I fertilised 29 short-styled flowers of 0. compressa with pollen from their own two sets of stamens (the pollen-grains of which differ in diameter as 100 and 83), and not one produced a capsule. I formerly cultivated during several years the short-styled form of a species pur- chased under the name of 0. Bowii (but I have some doubts whether it was rightly named), and fertilised many flowers with their own two kinds of pollen, which differ in diameter in the usual manner, but never got a single seed. On the other hand, Hilde- brand says that the short-styled form of 0. Defpei, growing by itself, yields plenty of seed ; but it is not positively known that this species is heterostyled ; and 180 HETEROSTYLED TRIMORPHIC ri.ANTS. Chap. IV. the pollen-grains from the two sets of anthers do not differ in diameter. Some facts communicated to me by Fritz Miiller afford excellent evidence of the utter sterility of one of the forms of certain trimorphic species of Oxalis, when growing isolated. lie has seen in St. Catharina, in Brazil, a large field of young sugar-cane, many acres in extent, covered with the red blossoms of one form alone, and these did not produce a single seed. His o^Mi land is covered with the short-styled form of a white-flowered trimorphic species, and this is equally sterile ; but when the three forms were planted near together in his garden they seeded freely. AVith two other trimorj)hic species he finds that isolated plants are always sterile. Fritz JMiiller formerly believed that a species of Oxalis, which is so abundant in St. Catharina that it borders the roads for miles, was dimorphic instead of trimorphic. Although the pistils and stamens vary greatly in length, as was evident in some specimens sent to me, yet the plants can be divided into two sets, according to the lengths of these organs. A large proportion of the anthers are of a white colour and quite destitute of pollen ; others which are pale yellow contain many bad with some good grains ; and others again which are bright yellow have apparently sound pollen ; but he has never succeeded in finding any fruit on this species. The stamens in some of the flowers are partially converted into petals. Fritz Miiller after reading my description, hereafter to be given, of the illegitimate offspring of various hetero- styled species, suspects that these plants of Oxalis may be the variable and sterile offspring of a single form of some trimorphic species, perhaps accidentally introduced into tlie district, which lias since been Chap. IV. OXALIS, HOMOSTYLED SPECIES. 181 propagated asexually. It is probable that this kind of propagation wouhl bo mucli aided by there being no expenditnre in the production of seed. Oxalis {Biophytum) sensitiva. — This plant is ranked by many botanists as a distinct genns. Mr. Thwaites sent me a number of flowers preserved in spirits from Ceylon, and they are clearly trimorphic. The style of the long-styled form is clothed with many scattered hairs, both simple and glandular ; such hairs are niucli fewer on the style of the mid-styled, and quite ab- sent from that of the short-styled form ; so that this plant resembles in this respect 0. Vcddiviana and RegneUL Calling the length of the two lobes of the stigma of the long-styled form 100, that of the mid-styled is 141, and that of the short-styled 164. In all other cases, in which the stigma in this genus differs in size in the three forms, the differ- ence is of a reversed nature, the stigma of the long- styled being the largest, and that of the short-styled the smallest. The diameter of the pollen-grains from the longest stamens being represented by 100, those from the mid-length stamens are 91, and those from the shortest stamens 84 in diameter. This plant is remarkable, as we shall see in the last chapter of this volume, by producing long-styled, mid-styled, and short-styled cleistogamic flowers. Homosttjled S_pecies of Oxalis. — Although the majority of tlie species in the large genus Oxalis seem to be trimorphic, some are homostyled, that is, exist under a single form ; for instance the common 0. aceto- sella, and according to Hildebrand two other widely distributed European species, 0. stricta and eornimdata. Fritz Miiller also informs me that a similarly consti- tuted species is found in St. Catharina, and that it is 182 HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV. quite fertile with its own pollen when insects are ex- cluded. The stigmas of 0. strida and of another homo- styled species, viz. 0. tropxoloides, commonly stand on a level with the upper anthers, and both these species are likewise quite fertile when insects are excluded. With respect to 0. acetosella, Hildebrand says that in all the many specimens examined by him the pistil exceeded the longer stamens in length. I procured ] 08 flowers from the same number of plants growing in three distant parts of England ; of these 86 had their stigmas projecting considerably above, whilst 22 had them nearly on a level with the upper anthers. In one lot of 17 flowers from the same wood, the stigmas in every flower projected fully as much above the upper anthers as these stood above the lower anthers. So that these plants might fairly be compared with the long-styled form of a heterostyled species ; and I at first thought that 0. acetosella was trimorphic. But the case is one merely of great variability. The pollen-grains from the two sets of anthers, as observed by Hildebrand and myself, do not differ in diameter. I fertilised twelve flowers on several plants with pol- len from a distinct plant, choosing those with pistils of a different length ; and 10 of these (i.e. 83 per cent.) produced capsules, which contained on an average 7"9 seeds. Fourteen flowers were fertilised with their owa. pollen, and 11 of these (i.e. 79 per cent.) yielded cap- sules, containing a larger average of seed, namely 9*2. These plants, therefore, in function show not the least sign of being heterostyled. I may add that 18 flowers protected by a net were left to fertilise them- selves, and only 10 of these (i.e. 55 per cent.) yielded capsules, which contained on an average only G'3 seeds. So that the access of insects, or artificial aid in placing pollen on the stigma, increases the fertility of the Chap. IV. PONTEDERIA. 183 flowers; aud I found that this applied especially to those having shorter pistils. It should be remem- bered that the flowers hang downwards, so that those with short pistils would be the least likely to receive their own pollen, unless they were aided in some manner. Finally, as Hildebrand has remarked, there is no evidence that any of the heterostyled species of Oxalis are tending towards a dioecious condition, as Zuccarini and Lindley inferred from the differences in the re- productive organs of the three forms, the meaning of which they did not understand. PONTEDEEIA [SP. ?] (PONTEDEEIACEiE.) Fritz Miiller found this aquatic plant, which is al- lied to the Liliaceae, growing in the greatest profusion on the banks of a river in Southern Brazil.* But only two forms were found, the flowers of which include three long and three short stamens. The pistil of the long-styled form, in two dried flowers which were sent me, was in length as 100 to 32, and its stigma as 100 to 80, compared with the same organs in the short- styled form. The long-styled stigma projects conside- rably above the upper anthers of the same flower, and stands on a level with the upper ones of the short-styled form. In the latter the stigma is seated beneath both its own sets of anthers, and is on a level with the anthers of the shorter stamens in the long-styled form. The anthers of the longer stamens of the short-styled form are to those of the shorter stamens of the long-styled form as 100 to 88 in length. The pollen-grains distended '"Ueber den Trimorphismua Zeitsclirift,' (fee, Band 6, 1871, der Poatederien " ; 'Jenaisclio p. 74. 181 HETEEOSTYLED TKIMORrHIC PLANTS. CitAr. IV. with water from the longer stamens of the short-styled form are to those from the shorter stamens of tlie same form as 100 to 87 in diameter, as deduced from ten measurements of each kind. We thus see that the organs in these two forms differ from one another and are arranged in an analogous manner, as in the long and short-styled forms of the trimorphic species of Lythrum and Oxalis. Moreover, the longer stamens of the long-styled form of Pontederia, and the shorter ones of the short-styled form are placed in a proper position for fertilising the stigma of a mid-styled form. But Fritz Miiller, although he examined a vast number of plants, could never find one belonging to the mid- styled form. The older flowers of the long-styled and short-styled plants had set plenty of apparently good fruit ; and this might have been expected, as they could legitimately fertilise one another. Al- though he could not find the mid-styled form of this species, he possessed plants of another species growing in his garden, and all these were mid-styled ; and in this case the pollen-grains from the anthers of the longer stamens were to those from the shorter sta- mens of the same flower as 100 to 86 in diameter, as deduced from ten measurements of each kind. These mid-styled plants growing by themselves never pro- duced a single fruit. Considering these several facts, there can hardly be a doubt that both these species of Pontederia are heterostyled and trimorphic. This case is an interest- ing one, for no other Monocotyledonous plant is known to be heterostyled. Moreover, the flowers are irregular, and all other heterostyled plants have almost sym- metrical flowers. The two forms differ somewhat in the colour of their corollas, that of the short-styled being of a darker blue, whilst that of the long-styled CuAr. IV. PONTEDERIA. 185 tends towards violet, and no other such case is known. Lastly, the three longer stamens alternate with the three shorter ones, whereas in Lythrum and Oxalis the long and short stamens belong to distinct whorls. With respect to the absence of the mid-styled form in the case of the Pontederia which grows wild in Southern Brazil, this would probably follow if only two forms had been originally introduced there ; for, as we shall hereafter see from the observations of Hildebrand, Fritz Miiller and myself, when one form of Oxalis is fertilised exclusively by either of the other two forms, the OjSspring generally belong to the two parent- forms. Fritz Miiller has recently discovered, as he informs me, a third species of Pontederia, with all three forms growing together in pools in the interior of S. Brazil ; so that no shadow of doubt can any longer remain about this genus including trimorphic species. He sent me dried flowers of all three forms. In the lone:- styled form the stigma stands a little above the tips of the petals, and on a level with the anthers of the longest stamens in the other two forms. The pistil is in length to that of the mid-styled as 100 to 56, and to that of the short-styled as 100 to 16. Its summit is rectangularly bent upwards, and the stigma is rather broader than that of the mid-styled, and broader in about the ratio of 7 to 4 than that of the short-styled. In the mid-styled form, the stigma is placed rather above the middle of the corolla, and nearly on a level with the mid-length stamens in the other two forms ; its summit is a little bent upwards. In the short- styled form the pistil is, as we have seen, very short, and differs from that in the other two forms in beinor straight. It stands rather beneath the level of the anthers of the shortest stamens in the long-styled and 186 HETEEOSTYLED TEIMORPHIC PLANTS. CiiAr. IV. mid-styled forms. The three anthers of each set of stamens, more especially those of the shortest stamens, are placed one beneath the other, and the ends of the filaments are bowed a little upwards, so that the pollen from all the anthers would be effectively brushed oif by the proboscis of a visiting insect. The relative diameters of the pollen-grains, after having been long soaked in water, are given in the following list, as measured by my son Francis. Long-styled form, from the mid-length stamens . (Average of 20 measurements.) ., „ from the shortest stamens . (10 measurements.) Mid-styled form, from the longest stamens . (15 measurements.) „ „ from the shortest stamens . (20 measurements.) Short-styled form, from the longest stamens . (20 measurements.) ,, „ from the mid-length stamens . (20 measurements.) Divisions of the Micrometer. 13-2 9-0 16-4 9-1 14-6 12-3 We have here the usual rule of the grains from the longer stamens, the tubes of which have to penetrate the longer pistil, being larger than those from the stamens of less length. The extreme difference in diameter between the grains from the longest stamens of the mid-styled form, and from the shortest stamens of the long-styled, is as 16 '4 to 9*0, or as 100 to 55 ; and this is the greatest difference observed by me in any heterostyled plant. It is a singular fact that the grains from the corresponding longest stamens in the two forms diifer considerably in diameter ; as do those in a lesser degree from the corresponding mid-length stamens in the two forms ; whilst those from the cor- responding shortest stamens in the long- and mid- styled forms are almost exactly equal. Their in- equality in the two first cases depends on the grains CuAP. IV. PONTEDEEIA. 187 in both sets of anthers in the short-styled form being smaller than those from the corresponding anthers in the other two forms ; and here we have a case parallel with that of the mid-styled form of Lythrum salicaria. In this latter plant the pollen-grains of the mid-styled forms are of smaller size and have less fertilising power than the corresponding ones in the other two forms ; whilst the ovarium, however fertilised, yields a greater number of seeds ; so that the mid-styled form is alto- gether more feminine in nature than the other two forms. In the case of Pontederia, the ovarium in- cludes only a single ovule, and what the meaning of the dijQTerence in size between the pollen-grains from the corresponding sets of anthers may be, I will not pretend to conjecture. The clear evidence that the species just described is heterostyled and trimorphic is the more valuable as there is some doubt with respect to P. cordata, an in- habitant of the United States. Mr. Leggett suspects* that it is either dimorphic or trimorphic, for the pollen-grains of the longer stamens are "more than twice the diameter or than eight times the mass of the grains of the shorter stamens. Though minute, these smaller grains seem as perfect as the larger ones." On the other hand, he says that in all the mature flowers, " the style was as long at least as the longer stamens ;" " whilst in the young flowers it was intermediate in length between the two sets of stamens ;" and if this be so, the species can hardly be heterostyled. * 'BuU. of tlie ToiTcy Botanical Club,' 1875, vol. vi. p. 62. 188 ILLEGITIMATE OFFSPRING OF Chap. V. CHAPTER V. Illegitimate Offspring of Heterostyled Plants. llle^timate oflfspring from all three forms of Lythruin salicaria — Their dwarfed skiture and sterility, some utterly Ijarron, some fertile — Oxalis, transmission of form to the legitimate and illegitimate seedlings^ — Primula Sinensis, illegitimate ofispring in some degree dwarfed and infertile — Equal-styled varieties of P. Sinensis, auri- cula, fariuosa, and elatior — P. vulgaris, red-flowered variety, illegi- timate seedlings sterile — P. veris, illegitimate plants raised during several successive generations, tlieir dwarfed stature and sterility — Equal-styled varieties of P. veris — Transmission of form by Pul- monaria and Polygonum — Concluding remarks — Close parallelism between illegitimate fertilisation and iiybridism, We have hitherto treated of the fertility of the flowers of heterostyled plants, when legitimately and illegiti- mately fertilised. The present chapter will be dcyoted to the character of their offspring or seedlings. Those raised from legitimately fertilised seeds will be here called legitimate seedlings or p?a7i#s, and those from illegitimately fertilised seeds, illegitimate seedlings or l^lants. They differ chiefly in their degree of fertility, and in their powers of growth or vigour. I will begin with trimorphic plants, and I mnst remind the reader that each of the three forms can be fertilised in six different ways ; so that all three together can be ferti- lised in eighteen different ways. For instance, a long-styled form can be fertilised legitimately by the longest stamens of the mid-styled and short-styled forms, and illegitimately by its own-form mid-length and shortest stamens, also by the mid-length stamens of the mid-styled and by the shortest stamens of tlio short-styled form ; so that the long-styled can be ferti- CuAi'. V. HETEROSTYLED TRIMOEPHIC PLANTS. 189 Used legitimately in two Mays and illegitimately in four ways. The same holds good with respect to the mid-styled and short-styled forms. Therefore with trimorphic species six of the eighteen unions yield legitimate offspring, and twelve yield illegitimate offspring, I will give the results of my experiments in detail, partly because the observations are extremely trouble- some, and will not probably soon be repeated — thus, I was compelled to count under the microscope above 20,000 seeds of Lythrum salicaria — but chiefly because light is thus indirectly thrown on the important sub- ject of hybridism. Lythrum salicaria. Of the twelve illegitimate unions two were com- pletely barren, so that no seeds were obtained, and of course no seedlings could be raised. Seedlings were, however raised from seven of the ten remaining il- legitimate unions. Such illegitimate seedlings when in flower were generally allowed to be freely and legitimately fertilised, through the agency of bees, by other illegitimate plants belonging to the two other forms growing close by. This is the fairest plan, and was usually followed ; but in several cases (which will always be stated) illegitimate plants were ferti- lised with pollen taken from legitimate plants be- longing to the other two forms ; and this, as might have been expected, increased their fertility. Lythrum salicaria is much afi"ected in its fertility by the nature of the season ; and to avoid error from this source, as far as possible, my observations were continued during several years. Some few experiments were tried in 18G3. The summer of 18G4 was too hot and 190 ILLEGITIMATE OFFSPRING OF Chap. V. dry, aud, though the plants were copiously watered, some few aiDpareutly suffered in their fertility, whilst others were not in the least affected. The years 1865 aud, especially, 18G6, were highly favourable. Only a few observations were made diu'ing 1867. The results are arranged in classes according to the pai-entage of the plants. In each case the average number of seeds per capsule is given, generally taken from ten capsules, which, according to my experience, is a nearly sufficient number. The maximum num- ber of seeds in any one capsule is also given ; and this is a useful point of comparison with the nor- mal standard — that is, with the number of seeds produced by legitimate plants legitimately ferti- lised. I will give likewise in each case the minimum number. When the maximum and minimum differ greatly, if no remark is made on the subject, it may be understood that the extremes are so closely con- nected by intermediate figures that the average is a fair one. Large capsules were always selected for counting, in order to avoid over-estimating the infer- tility of the several illegitimate plants. In order to judge of the degree of inferiority in fertility of the several illegitimate plants, the follow- ing statement of the average and of the maximum number of seeds produced by ordinary or legitimate plants, when legitimately fertilised, some artificially and some naturally, will serve as a standard of com- parison, and may in each case be referred to. But I give under each experiment the percentage of seeds produced by the illegitimate plants, in comparison with the standard legitimate number of the same form. For instance, ten capsules from the illegitimate long-styled plant (No. 10), which was legitimately and naturally fertilised by other illegitimate plants, CiiAi. V. HETEROSTYLED TRIMORPHIC PLANTS. 191 contained on an average 44 '2 seeds; whereas the capsules on legitimate long-styled plants, legitimately and naturally fertilised by other legitimate plants, contained on an average 93 seeds. Therefore this illegitimate j)lant yielded only 47 per cent, of the full and normal complement of seeds. Standard Numher of Seeds jproduced hy Legitimate Plants of the three Forms, ivhen legitimately fertilised. Long-styled form : average number of seeds in each capsule, 93 ; maximum number observed out of twenty- three capsules, 159. Mid-styled form : average number of seeds, 130 ; maximum number observed out of thirty-one capsules, 151. Short-styled form : average number of seeds, 83 • 5 ; but we may, for the sake of brevity, say 83 ; maximum number observed out of twenty-five capsules, 112. Classes I. and II. Illegitimate Plants raised from Long-styled Parents fertilised with pollen from the mid-length or the shortest stamens of other ])la7its of the same form. From this union I raised at different times three lots of illegitimate seedlings, amounting altogether to 56 plants. I must premise that, from not foreseeing the result, I did not keep a memorandum whether the eight plants of the first lot were the product of the mid-length or shortest stamens of the same form ; but I have good reason to believe that they were the pro- duct of the latter. These eight plants were much more dwarfed, and much more sterile than those in the other two lots. The latter were raised from a long-styled 192 ILLEGITIMATE OFFSrRIXG OF Cuap. V. plant growing quite isolated, and fertilised by tho agency of bees with its own pollen ; and it is almost certain, from the relative position of the organs of fructification, that the stigma under these circum- stances would receive pollen from the mid-length stamens. All the fifty-six plants in these three lots proved long- styled ; now, if the parent-plants had been legitimately fertilised by pollen from the longest stamens of the mid-styled and short-styled forms, only about one- third of the seedlings would have been long-styled, the other two-thirds being mid-styled and short-styled. In some other trimorphic and dimorphic genera we shall find the same curious fact, namely, that the long- styled form, fertilised illegitimately by its own-form pollen, produces almost exclusively long-styled seed- lings.* The eight plants of the first lot were of low stature : three which I measured attained, when fully grown, the heights of only 28, 29, and 47 inches ; w'hilst legitimate plants growing close by were double this height, one being 77 inches. They all betrayed in their general appearance a w^eak constitution ; they flowered rather later in the season, and at a later age than ordinary plants. Some did not flower every year ; and one plant, behaving in an unprecedented manner, did not flower until three years old. In the two other lots none of the plants grew quite to their full and proper height, as could at once be seen by comparing them with tho adjoining rows of legitimate plants. In several plants in all three lots, many of the anthers were either slirivelled or contained brown and tough, or pulpy * Hildebrand first called atten- of Primula Sinensis ; but his re- tion (' Bot. Zeitung,' Jan. 1, 1864, suits were not nearly so uniform p. 5) to this fact in the case as mine. CiiAr. V. HETEROSTYLED TRIMORPHIC PLANTS. 193 matter, without any good pollen-grains, and they never shed their contents ; tlioy were in the state designated by Gartner * ;is contabescent, which term I will for the future use. In one flower all the anthers were conta- bescent excepting two which appeared to the naked eye sound ; but under the microscope about two-thirds of the pollen-grains were seen to be small and shrivelled. In another plant, in which all the anthers appeared sound, many of the pollen-grains were shrivelled and of unequal sizes. I counted the seeds produced by seven plants (1 to 7) in the first lot of eight plants, probably the product of parents fertilised by their own-form shortest stamens, and the seeds produced by three plants in the other two lots, almost certainly the product of parents fertilised by their own-form mid- length stamens. Plant 1. This long-styled plant was allowed during 1SG3 to be freely and legitimately fertilised by an adjoining illegitimato mid-styled plant, but it did not yield a single seed-capsule. It was then rcmoyed and planted in a remote place close to a brother long-styled plant No. 2, so that it must have been freely though illegitimately fertilised; under these circumstances it did not yield during 1864 and 1865 a single capsule. I should here state that a legitimate or ordinary long-styled plant, when gi'owing isolated, and freely though illegitimately fertilised by insects with its own pollen, yielded an immense nmuber of capsules, which contained on an average 21 * 5 seeds. Plant 2. Tliis long-styled plant, after flowering during 1863 close to an illegitimate mid-styled plant, j^roduced less than twenty capsules, which contained on an average between four and five seeds, ^^^len subsequently growing in company with Na 1, by which it will have been illegitimately fertilised, it yielded in 18C6 not a single capsule, but in 1865 it yielded twenty-two capsules: the best of these, fifteen in niunber, were examined ; eight contained no seed, and the remaining seven contained on an average only three seeds, and these seeds were * 'Beitrage zur Kenntnisa dur Bcfruchtung,' I8M, p. IIG. 191 ILLEGITIMATE OFFSPRING OF CiiAr. V. so small and shrivelled that I doubt whether they would have germinated. Plants 3 and 4. These two long-styled plants, after being freely and legitimately fertilised dui'ing 18G3 by the same ille- gitimate mid-styled plant as in the last case, were as miserably sterile as No. 2. Plant 5. This long-styled plant, after flowering in 1863 close to an illegitimate mid-styled plant, yielded only four capsules, which altogether included only five seeds. During 1864, 1865, and 1866, it was surrounded either by illegitimate or legitimate plants of the other two forms ; but it did not yield a single capsule. It was a superfluous experiment, but I Likewise arti- ficially fertilised in a legitimate manner twelve flowers ; but not one of these produced a capsule; so that this plant was ahnost absolutely barren. Plant 6. This long-styled plant, after flowering during the favourable year of 1866, surrounded by illegitimate plants of the other two forms, did not produce a single cajisule. Plant 7. This loug-styled plant was the most fertile of the eight i^lants of the first lot. During 186r) it was surrounded by illegitimate plants of various parentage, many of which were highly fertile, and must thus have been legitimately fertilised. It produced a good many capsules, ten of which yielded an average of 36 ■ 1 seeds, with a maximum of 47 and a minimum of 22 ; so that this plant produced 39 per cent, of the full number of seeds. During 1864 it was sui-rounded by legitimate and illegitimate plants of the other two forms; and nine capsules (one poor one being rejected) yielded an average of 41 • 9 seeds, with a maximum of 56 and a minimum of 28 ; so that, under these favourable circimistances, tliis i^lant, the most fertile of the fii'st lot, did not yield, when legitimately fertilised, quite 45 per cent, of the full complement of seeds. In the second lot of plants in the present class, descended from the long-styled form, almost certainly fertilised with pollen from its own mid-length stamens, the plants, as already stated, were not nearly so dwarfed or so sterile as in the first lot. All produced plenty of capsules. I counted the number of seeds in only three plants, viz. Nos. 8, 9, and 10. Chap. V. HETEROSTYLED TRIMORPHIC PLANTS. 195 Plant 8. This jilant was allowed to be freely fertilised in 1864 l)y legitimate and illegitimate plants of the other two forms, and ten capsules yielded on an average 41 '1 seeds, with a maximum of 73 and a minimum of 11. Hence this plant pro- duced only 41 i)er cent, of the full complement of seeds. Plant 9. This loug-stj'led plant was allowed in 1865 to bo freely fertilised by illegitimate plants of the other two forms, most of which were moderately fertile. Fifteen capsules yielded on an average 57 * 1 seeds, with a maximum of 86 and a minimum of 23. Hence the plant yielded 61 per cent, of the full comple- ment of seeds. Plant 10 This long-styled plant was freely fertilised at the same time and in the same manner as the last. Ten capsules yielded an average of 44 ' 2 seeds, with a maximum of 69 and a minimum of 25; hence this plant yielded 47 per cent, of the full complement of seeds. The nineteen long-styled plants of the third lot, of the same parentage as the last lot, were treated dif- ferently ; for they flowered during 1867 by themselves so that they must have been illegitimately fertilised by one another. It has already been stated that a legitimate long-styled plant, growing by itself and visited by insects, yielded an average of 21-5 seeds per capsule, with a maximum of 35 ; but, to judge fairly of its fertility, it ought to have been observed during successive seasons. We may also infer from analogy that, if several legitimate long-styled plants were to fertilise one another, the average number of seeds would be increased; but how much increased I do not know ; hence I have no perfectly fair standard of comparison by which to judge of the fertility of the three following plants of the present lot, the seeds of which I counted. Plant 11. This long-styled plant produced a large crop of capsules, and in this respect was one of the most fertile of the whole lot of nineteen plants. But the average from ten 190 ILLEGITIMATE OFFSPRING OF Chap. V. capsules was only 35 "9 seeds, -n-ith a maximum of GO and a minimum of 8. Plant 12. This long-styled plant produced very few capsules; and ten yielded an average of only 15 '4 seeds, with a maximum of 30 and a minimum of 4. riunt 13. This plant offers an anomalous case; it flowered profusely, yet produced very few capsules ; but these con- tained numerous seeds. Ten capsules yielded an average of 71 • 9 seeds, with a maximum of 95 and a minimum of 29. Con- sidering tliat this plant was illegitimate and illegitimately fer- tilised by its brother long-styled seedlings, the average and the maximum are so remarkalily high that I cannot at all under- stand the case. We should remember that the average for a legitimate plant legitimately fertilised is 93 seeds. Class III. Illegitimate Plants raised from a Short- styled Parent fertilised ivith pollen from own-form mid-length stamen. I raised from tliis union nine plants, of whicli eight were short-styled and one long-styled ; so that there seems to be a strong tendency in this form to repro- duce, when self-fertilised, the parent-form ; but the tendency is not so strong as with the long-styled. These nine plants never attained the full height of legitimate plants growing close to them. The anthers were contabescent in many of the flowers on several plants. Plant 14. This short-styled plant was allowed during 1865 to be freely and legitimately fertilised by illegitimate plants de- scended from self-fertilised mid-, long- and short-styled plants. Fifteen capsules yielded an average of 28 "3 seeds, with a maximum of 51 and a minimum of 11; hence this plant produced only 33 per cent, of the proper number of seeds. The seeds themselves were small and irregular in shape. Although so sterile on the female side, none of the anthers were conta- bescent. Plant 15. This short-styled plant, treated like the last during CiiAP. V. HETEROSTYLED TRIMOKrHIC PLANTS. 197 tho same year, jieldccl an average, from fifteen capsules, of 27 seeds, -mth. a ruaximnm of 49 and a minimum of 7. But two poor capsules may be rejected, and then the average rises to 32 • 6, with the same maximum of 49 and a minimum of 20 ; so that this i)hint attained 88 per cent, of the normal standard of fertility, and was rather more fertile than the last, yet many of the anthers were contabcsccnt. Ffaut 16. This short-styled plant, treated like the two last, yielded from ten capsules an average of 77*8 seeds, with a maximum of 97 and a minimimi of 60; so that this plant produced 94 per cent, of the full numl^er of seeds. ridjit 17. This, the one long -styled plant of the same parent- age as the last thi-ee plants, when freely and legitimately ferti- lised in the same manner as the last, yielded an average from ten capsules of 76 • 3 rather poor seeds, with a maximum of 88 and a minimum of 57. Hence this plant produced S2 per cent, of the proper number of seeds. Twelve flowers enclosed in a net were artificially and legitimately fertilised with poUen from a legitimate short-styled plant ; and nine capsules yielded an average of 82 • 5 seeds, with a maximimi of 98 and a minimum of 51; so that its fertility was increased by the action of pollen from a legitimate plant, but still did not reach the normal standard. Class IV. Illegitimate Plants raised from a Mid-styled Parent fertilised tvith pollen from own-form longest stamens. After two trials, I succeeded in raising only four plants from this illegitimate union. These proved to be three mid-styled and one long-styled ; but from so small a number we can hardly judge of the tendency in mid-styled plants when self-fertilised to reproduce the same form. These four plants never attained their fidl and normal height; the long-styled plant had several of its anthers c(5ntabescent. Plant 18. This mid-styled plant, when freely and legitimately fertilised during 1865 by illegitimate plants descended from self-fertilised long-, short-, and mid-styled plants, jielded an average from ten capsules of 102*6 seeds, with a maximum of 198 ILLEGITIMATE OFFSrHING OF Chap. V. Vol aud a minimum of G3 : licuce this plant did not produce quite 80 per cent, of the normal number of seeds. Twelve flowers were artificially and legitimately fertilised witli pollen from a legitimate long-styled plant, and yielded from nine capsules an average of 116 " 1 seeds, which were finer than in the previous case, with a maximum of 135 and a minimum of 75 ; so that, as with Plant 17, pollen from a legitimate plant increased the fertility, but did not bring it up to the full standard. Flant 19. This mid-styled plant, fertilised in the same manner and at the same period as the last, yielded an average from ten capsrxles of 73 "4 seeds, with a maximum of 87 and a mini- mum of 64 : hence this plant jiroduced only 56 per cent, of the full number of seeds. Thirteen flowers were artificially and legitimately fertilised with pollen from a legitimate long-styled plant, and yielded ten capsules with an average of 95 • 6 seeds ; so that the application of pollen from a legitimate plant added, as in the two jDrevious cases, to the fertility, but did not bring it up to the proper standard. Flant 20. This long-styled plant, of the same parentage with the two last mid-styled i^lants, and freely fertilised in the same manner, yielded an average from ten capsules of 69 ■ 6 seeds, with a maximum of 83 and a minimum of 52 : hence this plant produced 75 per cent, of the full number of seeds. Class V. Illegitimate Plants raised from a Short-styled Parent fertilised ivith pollen from the mid-length stamens of the long-styled form. In the four previous classes, plants raised from the three forms fertilised with pollen from either the longer or shorter stamens of the same form, but generally not from the same plant, have been described. Six other illegitimate unions are possible, namely, between the three forms and the stamens in the other two forms which do not correspond in height with their pistils. But I succeeded in raising plants from only three of these six unions. From one of them, forming the pre- sent Class v., twelve plants were raised ; these con- sisted of eight short-styled, and four long-styled plants. Chap. V. HETEROSTYLED TRBIORPHIC PLANTS. 199 with not one mid-styled. These twelve plants never attained quite their full and proper height, but by no means deserved to be called dwarfs. The anthers in some of the flowers were eontabescent. One plant was remarkable from all the longer stamens in every flower and from many of the shorter ones having their anthers in this condition. The pollen of four other plants, in which none of the anthers were eontabe- scent, was examined ; in one a moderate number of grains were minute and shrivelled, but in the other three they appeared perfectly sound. With respect to the power of producing seed, five plants (Nos. 21 to 25) were observed : one yielded scarcely more than half the normal number ; a second was slightly infer- tile ; but the three others actually produced a larger average number of seeds, with a higher maximum, than the standard. In my concluding remarks I shall recur to this fact, which at first appears inexplicable. Plant 21. This short-styled plant, freely and legitimately fertilised during 1865 by illegitimate plants, descended from self- fertilised long-, mid- and short -styled parents, yielded an average from ten capsules of 4.3 seeds, with a maximum of 63 and a minimum of 26 : hence this plant, which was the one with all its longer and many of its shorter stamens eontabescent, produced only 52 jier cent, of the proper number of seeds. Fkint 22. This short-styled plant produced perfectly sound pollen, as viewed under the microscope. During 1866 it was freely and legitimately fertilised by other illegitimate plants belonging to the present and the following class, both of which include many highly fertile plants. Under these circumstances it yielded from eight capsules an average of 100 • 5 seeds, with a maximiun of 123 and a minimum of 86 ; so that it produced 121 per cent, of seeds in comparison ■with the normal standard. During 1864 it was allowed to be freely and legitimately ferti- lised by legitimate and illegitimate plants, and yielded an average, from eight capsules, of 104 '2 seeds, with a maximimi of 125 and a minimiun of 'JO; consequently it exceeded the normal standard, producing 125 per cent, of seeds. In tliis 200 ILLEGITIMATE OFFSPRING OF Chap. V. case, as iu some previous cases, pollen from legitimate plants added iu a small degree to the fertility of thci^laut; and the fertility would, perhaps, have been still greater had not the summer of 1^64 been very hot and certainly unfavourable to some of the plants of Lythmm. Plant 23. Tliis short-styled plant produced ]3erfcctly sound pollen. During 1866 it was freely and legitimately fertilised by the other illegitimate plants specified under the last experi- ment, and eight capsules yielded an average of 113 '5 seeds, with a maximum of 1'23 and a minimum of 93. Hence this plant exceeded the normal standard, producing no less than 136 per cent, of seeds. riant 24. This long-styled jilant i^roduccd pollen wliicli seemed under the microscope sound; but some of the grains did not swell when placed in water. During 1864 it was legitimately fertilised by legitimate and illegitimate plants in the same manner as Plant 22, but yielded an average, from ten capsules, of only 55 seeds, with a maximum of 88 and a mini- mum of 24, thus attaining 59 per cent, of the normal fertility. This low degree of fertility, I presume, was owing to the im- favourablc season ; for during 1866, when legitimately fertilised by illegitimate plants in the manner described imder No. 22, it yielded an average, from eight capsules, of 82 seeds, with a maximum of 120 and a minimmn of 67, thus producing 88 per cent, of the normal number of seeds. Plant 25. The pollen of this long-styled jjlant contained a moderate nimiber of poor and shrivelled grains ; and this is a surprising circumstance, as it yielded an extraordinary number of seeds. During 1866 it was freely and legitimately fertilised by illegitimate plants, as described under No. 22, and yielded an average, from eight capsules, of 122-5 seeds, with a maximum of 149 aud a minimum of 84. Hence this plant exceeded the normal standard, producing no less than 131 per cent, of seeds. Class VI. Illegitimate Plants raised from Mid-styled Parents fertilised with i)ollen from the shortest stamens of the long-stijledform. I raised from this union twenty-five plants, which proved to be seventeen long-styled and eight mid- CuAi\ V. HETEROSTYLED TRIMORrHIC PLANTS. 201 styled, but not one short-styled. None of these plants were in the least dwarfed. I examined, during the highly favourable season of 186 G, the pollen of four plants : in one mid-styled plant, some of the anthers of the longest stamens were contabescent, but the pollen- grains in the other anthers were mostly sound, as they were in all the anthers of the shortest stamens ; in two other mid-styled and in one long-styled j)lant many of the pollen-grains were small and shrivelled ; and in the latter plant as many as a iifth or sixth part appeared to be in this state. I counted the seeds in five plants (Nos. 26 to 30), of which two were mode- rately sterile and three fully fertile. Plant 26. This mid-styled plant was freely and legitimately fertilised, dui-ing the rather nnfavonrable year 1864, by numer- ous surrounding legitimate and illegitimate jilants. It jielded an average, from ten capsules, of 83 • 5 seeds, with a maximiun of 110 and a minimum of 64, thus attaining 64 per cent, of the normal fertility. During the highly favourable year 1866, it was freely and legitimately fertilised by illegitimate plants belonging to the present Class and to Class V., and yielded an average, fi'om eight capsules, of 86 seeds, with a maximum of 109 and a minimmn of 61, and thus attained 66 per cent, of the normal fertility. This was the jilant with some of the anthers of the longest stamens contabescent as above mentioned. Plant 27. This mid-styled plant, fertilised during 1864 in the same manner as the last, yielded an average, from ten capsules, of 99 "4 seeds, with a maximum of 122 and a minimum of 53, thus attaining to 76 per cent, of the normal fertility. If tho season had been more favoui-able, its fertility would probably have been somewhat greater, but, judging from the last experi- ment, only in a slight degree. Plant 28. This mid-styled plant, when legitimately fertilised during the favourable season of 1866, in the manner described under No. 26, yielded an average, from eight capsules, of 89 seeds, with a maximum of 119 and a minimvun of 69, thus pro- ducing 68 per cent, of the full number of seeds. In the pollen of both sets of anthers, nearly as many grains were small and shrivelled as sound. 202 ILLEGITIMATE OFFSPRING OF Chap. V. I'lant 29. This loug-stylcd plant was legitimately fertilised during the unfavourable season of 1861, in the manner described under No. 26, and yielded an average, from ten capsules, of 84*6 seeds, with a maximum of 132 and a minimimi of 47, thus attaining to 91 per cent, of the normal fertility. During the highly favourable season of 1866, when fertilised in the manner described under No. 26, it yielded an average, from nine cai> sules (one poor capsule having been excluded), of 100 seeds, with a maximum of 121 and a minimmn of 77. This plant thu.s exceeded the normal standard, and produced 107 per cent, of seeds. In both sets of anthers there were a good many bad and shrivelled pollen-grains, but not so many as in the last-described plant. Plant 30. This long-styled plant was legitimately fertilised dui-ing 1866 in the manner described rmder No. 26, and jielded an average, from eight capsules, of 94 seeds, with a maximiun of 106 and a minimum of 66 ; so that it exceeded the normal standard, yielding 101 per cent, of seeds. Fkuit 31. Some flowers on this long-styled plant were arti- ficially and legitimately fertilised by one of its brother illegiti- mate mid-styled plants ; and five ca])sules yielded an average of 90 "6 seeds, with a maximiun of 97 and a minimum of 79. Hence, as far as can be judged from so few capsules, this plant attained, under these favoui'able circumstances, 98 jjer cent, of the normal standard. Class YII. Illegitimate Plants raised from Mid-styled Parents fertilised with pollen from the longest stamens of the short-styled form. It was shown in the last chapter that the union from which these illegitimate plants were raised is far more fertile than any other illegitimate union ; for the mid- styled parent, when thus fertilised, yielded an average (all very poor capsules being excluded) of 102*8 seeds, with a maximum of 130 ; and the seedlings in the present class likewise have their fertility not at all lessened. Forty plants were raised ; and these attained their full height and were covered with seed-capsules. Chap. V. HETEROSTYLED TRIMORrHIC PLANTS. 203 Nor did I observe any contabescent anthers. It de- serves, also, particular notice that these plants, differ- ently from what occurred in any of the previous classes, consisted of all three forms, namely, eighteen short- styled, fourteen long-styled, and eight mid-styled plants. As these plants were so fertile, I counted the seeds only in the two following cases. I'Jant 32. This mid-styled plant was freely and legitimately fertilised dvuing the unfavourable year of 1864, by numerous sirrroimding legitimate and illegitimate plants. Eight cap- sules yielded an average of 127 • 2 seeds, with a maximum of 14.4 and a minimimi of 96 ; so that this plant attained 98 jier cent, of the normal standard. riant 33. Tliis short-styled plant was fertilised in the same manner and at the same time with the last ; and ten capsules yielded an average of 113 "9, with a maximum of 137 and a minimum of 90. Hence this plant produced no less than 137 per cent, of seeds in comparison with the normal standard. Conduding EemarJcs on the Illegitimate Offspring of the three forms of Lythrum salicaria. From the three forms occurring in approximately equal numbers in a state of nature, and from the re- sults of sowing seed naturally produced, there is reason to believe that each form, when legitimately fertilised, reproduces all three forms in about equal numbers. Now, we have seen (and the fact is a very singular one) that the fifty-six plants produced from the long-styled form, illegitimately fertilised with pollen from the same form (Class I. and II.), were all long- styled. The short-styled form, when self-fertilised (Class III.), produced eight short-styled and one long- styled plant; and the mid-styled form, similarly treated (Class IV.), produced three mid-styled and one long- styled offspring ; so that these two forms, when ille- 204 ILLEGITIMATE OFFSrRING OF Chap. V gitimately fertilised with pollen from the same form, evince a strong, but not exclusive, tendency to repro- duce the parent-form. AVhen the short-styled form was illegitimately fertilised by the long-styled form (Class v.), and again when the mid-styled was illegiti- mately fertilised by the long-styled (Class VI.), in each case the two parent-forms alone were reproduced. As thirty-seven plants were raised from these two unions, we may, with much confidence, believe that it is the rule that plants thus derived usually consist of both parent-forms, but not of the third form. When, however, the mid-styled form was illegitimately fer- tilised by the longest stamens of the short-styled (Class VII.), the same rule did not hold good ; for the seedlings consisted of all three forms. The illegiti- mate union from which these latter seedlings were raised is, as previously stated, singularly fertile, and the seedlings themselves exhibited no signs of sterility and grew to their full height. From the consideration of these several facts, and from analogous ones to be given under Oxalis, it seems probable that in a state of nature the pistil of each form usually receives, through the agency of insects, pollen from the stamens of corresponding height from both the other forms. But the case last given shows that the application of two kinds of pollen is not indispensable for the pro- duction of all three forms. Hildebrand has suggested that the cause of all three forms being regularly and naturally reproduced, may be that some of the flowers are fertilised with one kind of pollen, and others on the same plant with the other kind of pollen. Finally, of the three forms, the long-styled evinces somewhat the strongest tendency to reappear amongst the oifspring, whether both, or one, or neither of the parents are long-styled. Chap. V. HETEEOSTYLED TRDIORPHIC PLANTS. 205 Table 30. Tabulated results of the fertility of the foregoing illegitimate plants, wlien legitimately fertilised, generally by illegitimate plants, as described under each experiment. Plants 11, 12 and 13 are excluded, as they were illegitimately fertilised. Normal Standard of Fertility of the three forms, tvhen legitimately and naturally fertilised. Form. Average Number of Seeds per Capsule. Srasimnm 1 Number inl any one Capsule. Minimum Number in any one Capsule. Long-styled .... Mid-styled .... Short-styled . . . 93 130 83-5 159 1 1 151 112 No record was kept, as all very poor capsules were rejected. Class I. and II. — Illegitimate Plants raised from Long- styled Parents fertilised ivitTi polln from oivn-form mid-length or shortest stamens. Number of Plant. Form. Average Num- Average ' Maximum I Minimum ber of Seeds. Number of Number in Number in expressed as Seeds per Cupsule. any one Cai>sule. anyone the percenfcige Capsule. ,of the Normal Standard. Plant 1 2 3 4 5 6 7 8 9 10 Long-styled 4-5 4-5 4-5 Cor 1 36-1 41-1 57-1 44-2 ? ? ? 2 47 22 73 11 8(3 23 69 25 5 5 5 Dor 1 39 44 61 47 Class HI. — Illegitimate Plants raised from Short-styled Parents fertilised with pollen from own-form shortest stamens. Plant 14 . „ 15 . „ 16 . „ 17 . Short-styled 28-3 51 11 32-6 49 20 77-8 97 GO Long-styled 76-3 88 " 1 33 38 94 82 206 ILLEGITIMATE OFFSPRING OF Chap. V. Table 30 — continued. Class IV. — Ilhgitimate Plants raised from Mid-styled Parents fertilised with iiollen from own-form longest stamens. Number of Plant. Form. Average Number of Seeds per Capsule. Maximum Numljer in any one Capsule. Minimum Number in any one Capsule. Average Num- ber of Seeds, expressed as the percentage of i\u'. Normal Standard. Plant 18 . . „ 19 . . „ 20 . . JliJ-styled. Long-styled 102-6 73-4 69-6 131 87 83 63 64 52 80 56 75 Class V. — Illegitimate Plants rained from Short-styled Parents fertilised with pollen from the mid-length stamens of the long- styled form,. Plant 21 » 22 „ 23 „ 24 „ 2& Short-styled Long-styled 43-0 63 26 100-5 123 86 113-5 123 93 82-0 120 67 122-5 149 84 52 121 136 88 131 Class VI. — Illegitimate Plants raised from Mid-styled Parents fertilised with pollen from the shortest stamens of the long- sfyled form. Plant 26 . . Mid-styled . 86-0 109 61 66 „ 27 . . 99-4 122 53 76 „ 28 . . 89-0 119 69 68 „ 29 . . Long-styled 100-0 121 77 107 „ 30 . . 94-0 106 66 101 „ 31 . . » 90-6 97 79 98 Class VII. — Illegitimate Plants raised from Mid-styled Parents fertilised with pollen from the longest stamens of the short- styled form. Plant 32 „ 33 Mid-styled. Short-styled 127-2 113-9 144 137 96 90 98 137 Chap.v. heterostyled trimokphic plants. 207 The lessened fertility of most of these illegitimate plants is in many respects a highly remarkable phe- nomenon. Thirty-three plants in the seven classes were subjected to various trials, and the seeds care- fully counted. Some of them were artificially ferti- lised, but the far greater number were freely fertilised (and this is the better and natural plan) through the agency of insects, by other illegitimate plants. In the rightrhand, or percentage column, in the preceding table, a wide difference in fertility between the plants in the first four and the last three classes may be per- ceived. In the first four classes the plants are de- scended from the three forms illegitimately fertilised with pollen taken from the same form, but only rarely from the same plant. It is necessary to observe this latter circumstance ; for, as I have elsewhere shown,* most plants, when fertilised with their own pollen, 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. None of the nineteen illegitimate plants in the first four classes w'ere completely fertile ; one, however, was nearly so, yielding 96 per cent, of the proper number of seeds. From this high degree of fertility we have many descending gradations, till we reach an absolute zero, when the plants, though bear- ing many flowers, did not produce, during successive years, a single seed or even seed-capsule. Some of the most sterile plants did not even yield a single seed when legitimately fertilised with pollen from legiti- mate plants. There is good reason to believe that the first seven plants in Class I, and II. were the offspring * 'The Effects of Gross and Self-fertilieation in the Vegetable Kingdom,' 187G. 01 208 ILLEGITIMATE OFFSPRING OF " Chap. V. of a long-styled plant fertilised with pollen from its own-form shortest stamens, and these plants were the most sterile of all. The remaining plants in Class I. and II. were almost certainly the product of pollen from the mid-length stamens, and ahhongh very ste- rile, they were less so than the first set. None of the plants in the first four classes attained their full and proper stature ; the first seven, which were the most sterile of all (as already stated), were by far the most dwarfed, several of them never reaching to half their proper height. These same plants did not flower at so early an age, or at so early a period in the season, as they ought to have done. The anthers in many of their flowers, and in the flowers of some other plants in the first six classes, were either contabescent or in- cluded numerous small and shrivelled pollen-grains. As the suspicion at one time occurred to me that the lessened fertility of the illegitimate plants might be due to the pollen alone having been affected, I may remark that this certainly was not the case ; for several of them, when fertilised by sound pollen from legiti- mate plants, did not yield the full complement of seeds ; hence it is certain that both the female and male reproductive organs were affected. In each of the seven classes, the plants, though descended from the same j)arents, sown at the same time and in the same soil, differed much in their average degree of fertility. Turning now to the fifth, sixth, and seventh classes, and looking to the right-hand column of the table, we find nearly as many plants with a percentage of seeds above the normal standard as beneath it. As with most plants the number of seeds produced varies much, it might be thought that the present case was one merely of variability. But this view must be rejected, CuAr. V. IIETEROSTYLED TRIJNIORPHIC PLANTS. 209 as far as the less fertile plants in these three classes are coucerncd : first, because none of the plants in Class V. attained their proper height, which shows that they were in some manner affected ; and, secondly, because many of the plants in Classes V. and VI. pro- duced anthers which were either contabescent or in- cluded small and shrivelled pollen-grains. And as in these cases the male organs were manifestly deterio- rated, it is by far the most probable conclusion that the female organs were in some cases likewise affected, and that this was the cause of the reduced number of seeds. With respect to the six plants in these three classes which yielded a very high percentage of seeds, the thought naturally arises that the normal standard of fertility for the long-styled and short-styled forms (with which alone we are here concerned) may have been fixed too low, and that the six illegitimate plants are merely fully fertile. The standard for the long- styled form was deduced by counting the seeds in twenty-three capsules, and for the short-styled form from twenty-five capsules. I do not pretend that this is a sufficient number of capsules for absolute accu- racy ; but my experience has led me to believe that a very fair result may thus be gained. As, however, the maximum number observed in the twenty-five capsules of the short-styled form was low, the standard in this case may possibly be not quite high enough. But it should be observed, in the case of the illegitimate plants, that in order to avoid over-estimating their in- fertility, ten very fine capsules were always selected ; and the years 1865 and 1866, during which tlie plants in the three latter classes were experimented .on, were highly favourable for seed-production. Now, if this 210 ILLEGITIMATE OFFSPRING OF Chap. V. plan of selecting very fine capsules during favourabla seasons had been followed for obtaining the normal standards, instead of taking, during various seasons, the first capsules which came to hand, the standards would undoubtedly have been considerably higher ; and thus the fact of the six foregoing plants appearing to yield an unnaturally high percentage of seeds may, perhaps, be explained. On this view, these plants are, in fact, merely fully fertile, and not fertile to an ab- normal degree. Nevertheless, as characters of all kinds are liable to variation, especially with organisms unnaturally treated, and as in the four first and more sterile classes, the plants derived from the same pa- rents and treated in the same manner, certainly did vary much in sterility, it is possible that certain plants in the latter and more fertile classes may have varied so as to have acquired an abnormal degree of fertility. But it should be noticed that, if my standards err in being too low, the sterility of all the many sterile plants in the several classes will have to be estimated by so much the higher. Finally, we see that the ille- gitimate plants in the four first classes are all more or less sterile, some being absolutely barren, with one alone almost completely fertile ; in the three latter classes, some of the plants are moderately sterile, whilst others are fully fertile, or possibly fertile in excess. The last point which need here be noticed is that, as far as the means of comparison serve, some degree of relationship generally exists between the infertility of the illegitimate union of the several parent-forms and that of their illegitimate offspring. Thus the two illegitimate unions, from which the plants in Classes VI. and VII. were derived, yielded a fair amount of seed, and only a few of these plants are in Ciur. V. HETEROSTYLED TRIMORPHIC PLANTS. 211 auy degree sterile. On the other hand, the illegiti- mate unions between plants of the same form always yield very few seeds, and their seedlings are very sterile. Long -styled parent-plants when fertilised with pollen from their own-form shortest stamens, ap- pear to be rather more sterile than when fertilised with their o^vn-form mid-length stamens ; and the seedlings from the former union were much more sterile than those from the latter union. In opposition to this re- lationship, short-styled plants illegitimately fertilised with pollen from the mid-length stamens of the long- styled form (Class Y.) are very sterile ; whereas some of the offspring raised from this union were far from being highly sterile. It may be added that there is a tolerably close parallelism in all the classes between the degree of sterility of the plants and their dwarfed stature. As previously stated, an illegitimate plant fertilised with pollen from a legitimate plant has its fertility slightly increased. The importance of the several foregoing conclusions will be apparent at the close of this chapter, when the illegitimate unions be- tween the forms of the same species and their illegiti- mate offspring, are compared with the hybrid unions of distinct species and their hybrid offspring. OXALIS. No one has compared the legitimate and illegiti- mate offspring of any trimorphic species in this genus. Hildebrand sowed illegitimately fertilised seeds of Oxalis Valdiviana* but they did not germinate ; and this fact, as he remarks, supports my view that an illegitimate union resembles a hybrid one between 'Bot. Zeituug,' 1871, p. 433, footnote. 212 ILLEGITiaiATE OFFSPRING OF Ciiaf. V. two distinct species, for the seeds in this latter case are often incapable of germination. The followiDg obsei-vations relate to the nature of the forms which appear among the legitimate seedlings of Oxalis Valdiviana. Hildebrand raised, as described in the paper just referred to, 211 seedlings from all six legitimate unions, and the three forms appeared among the offspring from each union. For instance, long -styled plants were legitimately fertilised with pollen from the longest stamens of the mid-styled form, and the seedUngs consisted of 15 long-styled, 18 mid-styled, and 6 short-styled. We here see that a few short-styled plants were produced, though neither parent was short-stylal ; and so it was with the other legitimate unions. Out of the above 211 seedlings, 173 belonged to the same two forms as their parents, and only 38 belonged to the third form distinct from either parent. In the case of 0. llegneUi, the result, as observed by Hildebrand, was nearly the same, but more striking : all the offspring from four of the legitimate unions consisted of the two parent-forms, whilst amongst the seedlings from the other two legitimate unions the thii-d foiTQ appeared. Thus, of the 43 seedUngs from the six legitimate unions, 35 belonged to the same two forms as their parents, and only 8 to the third form. Fritz Miillcr also raised in Brazil seedlings from long-styled plants of 0. Begnelll legiti- mately fertilised with pollen from the longest stamens of the mid-styled form, and all these belonged to the two parent- forms.* Lastly, seedUngs were raised by me from long-styled plants of 0. speciosa legitimately fertilised by the short-styled form, and from the latter reciprocally fertiUsed by the long- styled; and these consisted of 33 long-styled and 26 short- styled plants, with not one mid-styled form. There can, there- fore, be no doubt that the legitimate offspring from any two forms of Oxalis tend to belong to the same two forms as their parents ; but that a few seedlings belonging to the third form occasionally make their appearance ; and this latter fact, as Hildebrand remarks, may be attributed to atavism, as some of their progenitors will almost certainly have belonged to the third form. When, however, any one form of Oxalis is fertilised illegiti- * * Jenaische Zeitschrift,' &c. Band vi. 1871, p. 75. CiJAr. V. IIETEROSTYLED DIMORPHIC PLANTS. 213 mately with i")ollen from the same form, the seedlings apixiar to belong invariably to this form. Thus Hildebrand states* that long- styled plants of 0. rosea growing by themselves have been propagated in Grcrmany year after year by seed, and have always produced long-styled j^lauts. Again, 17 seedlings were raised from mid-styled plants of 0. hcdymroidcs growing by themselves, and these were all mid-styled. So that the forms of Oxalis, when illegitimately fertilised wth their own pollen, behave like the long-styled form of Lythrum salicaria, which when thus fer- tilised always produced with me long-styled offspring. Peimula. Primula Sinensis. I raised during February 1862, from some long- styled plants illegitimately fertilised with pollen from the same form, twenty-seven seedlings. These were all long-styled. They jiroved fully fertile or even fertile in excess ; for ten flowers, fertilised with pollen from other plants of the same lot, yielded nine cap- sules, containing on an average 39*75 seeds, with a maximum in one capsule of QQ seeds. Four other flowers legitimately crossed with pollen from a legiti- mate plant, and four flowers on the latter crossed with pollen from the illegitimate seedlings, yielded seven capsules with an average of 53 seeds, with a maximum of 72. I mu!?t here state that I have found some difiiculty in estimating the normal standard of fer- tility for the several unions of this species, as the results differ much during successive years, and the seeds vary so greatly in size that it is hard to * 'Ueber den Ti imorpliismus zu Berlin,' 21st June 18GC, p. 373; in dcr Gatturg Oxalis: Monats- and 'Bot. Zcifung,' 1871, p. 435. berichte dcr Akad. dcr Wissen. 214 ILLEGITIMATE OFFSPRING OF Chap. V. decide which ought to be considered good. In order to avoid over-estimating the infertility of the several illegitimate unions.. I have taken the noi*mal standard as low as possible. From the foregoing twenty-seven illegitimate plants, fertilised with their own-form pollen, twenty-five seed- ling grandchildren were raised ; and these were all long-styled ; so that from the two illegitimate gene- rations fifty-two plants were raised, and all without exception proved long-styled. These grandchildren grew vigorously, and soon exceeded in height two other lots of illegitimate seedlings of different parent- age and one lot of equal-styled seedlings presently to be described. Hence I expected that they would have turned out highly ornamental plants ; but when they flowered, they seemed, as my gardener remarked, to have gone back to the wild state ; for the petals were pale-coloured, narrow, sometimes not touching each other, fiat, generally deeply notched in the middle, but not flexuous on the margin, and with the yellow eye or centre conspicuous. Altogether these flowers were strikingly different from those of their pro- genitors; and this, I think, can only be accounted for on the principle of reversion. Most of the anthers on one plant were contabescent. Seventeen flowers on the grandchildren were illegitimately fertilised with pollen taken from other seedlings of the same lot, and produced fourteen capsules, containing on an average 29 • 2 seeds ; but they ought to have con- tained about 35 seeds. Fifteen flowers legitimately fertilised with pollen from an illegitimate short-styled plant (belonging to the lot next to be described) pro- duced fourteen capsules, containing an average of 4G seeds ; they ought to have contained at least 50 seeds. Hence these grandchildren of illegitimate descent ap- Chai'. V. IIETEROSTYLED DIMORPHIC PLANTS. 215 pear to have lost, though only in a very slight degree, their fuU fertility. We will now turn to the short-styled form : from a plant of this kind, fertilised with its own-form pollen, I raised, during February 1862, eight seedlings, seven of w hich were short-styled and one long-styled. They grew slowly, and never attained to the full stature of ordinary plants ; some of them flowered precoeiously, and others late in the season. Four flowers on these short-styled seedlings and four on the one long-styled seedling were illegitimately fertilised with their own- form pollen and produced only three capsules, con- taining on an average 23 • 6 seeds, with a maximum of 29 ; but we cannot judge of their fertility from so few capsules ; and I have greater doubts about the normal standard for this union than about any other ; but I believe that rather above 25 seeds would be a fair estimate. Eight flowers on these same short-styled plants, and the one long-styled illegitimate plant were reciprocally and legitimately crossed ; they pro- duced five capsules, which contained an average of 28*6 seeds, with a maximum of 36. A recij^rocal cross between legitimate plants of the two forms would have yielded an average of at least 57 seeds, with a possible maximum of 74 seeds ; so that these illegitimate plants were sterile when legitimately crossed. I succeeded in raising from the above seven short- styled illegitimate plants, fertilised w ith their own- form pollen, only six plants — grandchildren of the first union. These, like their parents, were of low stature, and had so poor a constitution that four died before flowering. With ordinary plants it has been a rare event with me to have more than a single plant die out of a large lot. The two grandchildren which 21G ILLEGITIMATE OFFSPRING OF Chap. V lived and flowered were short-styled ; and twelve of their flowers were fertilised with their own-form pollen and produced twelve capsules containing an average of 28 • 2 seeds ; so that these two plants, though be- longing to so weakly a set, were rather more fertile than their parents, and perhaps not in any degree sterile. Four flowers on the same two grandchildren were legitimately fertilised by a long-styled illegiti- mate plant, and produced four capsules, containing only 32 "2 seeds instead of about 64 seeds, which is the normal average for legitimate short-styled plants legitimately crossed. By looking back, it will be seen that I raised at first from a short-styled jjlant fertilised with its own- form pollen one long-styled and seven short-styled illegitimate seedlings. These seedlings were legiti- mately intercrossed, and from their seed fifteen plants were raised, grandchildren of the first illegitimate union, and to my surprise all proved short-styled. Twelve short-styled flowers borne by these grand- children were illegitimately fertilised with pollen taken from other plants of the same lot, and produced eight capsules which contained an average of 21*8 seeds, with a maximum of 35. These figures are rather below the normal standard for such a union. Six flowers were also legitimately fertilised with pollen from an illegitimate long-styled plant and produced only three capsules, containing on an average 23 '6 seeds, with a maximum of 35. Such a union in the case of a legitimate plant ought to have yielded an average of 64 seeds, with a possible maximum of 73 seeds. Summary on the Transmission of Form, Constitution, and Fertility of the Illegitimate Offspring of Primula Sinensis. — In regard to the long-styled plants, their CuAP. V. IIETEROSTYLED DIMORrHIC PLANTS. 217 illegitiiuato offspring, of which fifty-two were raised in the course of two generations, were all long-styled.* These plants grew vigorously ; but the flowers in one instance were small, appearing as if they had reverted to the wild state. In the first illegitimate generation they were perfectly fertile, and in the second their fertility was only very slightly impaired. With respect to the short-styled plants, twenty-four out of twenty-five of their illegitimate offspring were short- styled. They were dwarfed in stature, and one lot of grandchildren had so poor a constitution that four out of six plants perished before flowering. The two sur- vivors, when illegitimately fertilised with their own- form pollen, were rather less fertile than they ought to have been ; but their loss of fertility was clearly shown in a special and unexpected manner, namely, when legitimately fertilised by other illegitimate plants : thus altogether eighteen flowers were fertilised in this manner, and yielded twelve capsules, which included on an average only 28 "5 seeds, with a maximum of 45. Now a legitimate short-styled plant w^ould have yielded, when legitimately fertilised, an average of 64 seeds, with a possible maximum of 74. This particular kind of infertility will perhaps be best appreciated by a simile : we may assume that with mankind six children would be born on an average from an ordinary marriage ; but that only three would be born from an incestuous marriage. According to the analogy of Primula Sinensis, the children of such * Dr. Hiltlebrand, wlio first short-s-tyled. From a short-styled called attoution to this subject plant illegitimately fertilised with (' Bot. Zeitung.' 18i)4, p. 5), raised its own pollen he raised fourteen from a similar illegitimnte union plants, of which eleven were short- seventeen plants, of which four- styled and three long-styled. teen were long-btyled and tliree • 218 ILLEGITIMATE OFFSPRING OF Chap. V. incestuous marriages, if tliey continued to marry iu- cestuously, would have their sterility only slightly increased ; but their fertility would not be restored by a proper marriage ; for if two children, both of in- cestuous origin, but in no degree related to each other, were to marry, the marriage would of course be strictly legitimate, nevertheless they would not give birth to more than half the full and proper number of children. E'lual-styhd varittij of Piimida Sinensis. — As any variation in the structure of the reproductive organs, combined with changed function, is a rare event, the following cases are worth giving in detail. My attention was first called to the subject by ob- serving, in 1862, a long-styled plant, descended from a self- fertilised long-styled parent, which had some of its flowers in an anomalous state, namely, with the stamens placed low down in the corolla as in the ordinary long-styled form, but with the pistils so short that the stigmas stood on a level with the anthers. These stigmas were nearly as globular and as smooth as in the short-styled form, instead of being elongated .and rough as iu the long-stjded form. Here, then, we have combined in_ the same flower, the short stamens of the long-styled form with a jiistil closely resembling that of the shoi-t-styled form. But the structure varied much even on the same umbel : for in two flowers the pistil was intermediate in length between that of the long and that of the short-styled form, with the stigma elongated as in the former, and smooth as in the latter; and in three other flowers the structure was in all resi:)ects like that of the long-styled fonn. These niodificatious appeared to me so remarkable that I fertilised eight of the flowers with their own pollen, and obtained five capsules, which contained on an aver- age 43 seeds; and this number shows that the flowers had become abnormally fertile in comparison with those of ordinary long-styled plants when self-fertilised. I was thus led to ex- amine the plants in several small collections, and the result showed that the equal-styled variety was not rare. In a state of nature the long and short-styled forms would no doubt occur in nearly equal numbers, as I infer from tlie analogy of the other heterostiyled species of Primula, and from having 'jHAr. V. IIETEEOSTYLED DIMORPHIC PLANTS. 210 Table 31. rrimula Sinensis. Name of Owner or Place. Long- styled Form. Short-styled Koriii. Eqnal-styli-d Variety. 20 30 12 42 16 1 13 18 9 12 5 7 17 Mr. Duck 9 15 2 llis;h Kims . , My own plants from lurchased seeds Total . . 134 51 43 raised the two forms of the present species in exactly the same nmuber from flowers wliicli had been legitimately crossed. The preponderance in the above table of the long-styled form over the short-styled (in the proportion of 134 to 51) results from gar- deners generally collecting seed from self-fertilised flowers ; and the long-styled flowers produce .spontaneously much more seed (as shown in the first chapter) than the short-styled, owing to the anthers of the long-styled form being placed low down in the corolla, so that, when the flowers fall off, the anthers are dragged over the stigma ; and we now also know that long-styled plants, when self-fertilised, very generally reproduce long-styled off- spring. From the consideration of this table, it occurred to me in the year 1862, that almost all the plants of the Chinese primi-ose cultivated in England would sooner or later become long-styled or equal-styled; and now, at the close of 1876, I have had five small collections of plants examined, and almost all consisted of long-styled, with some more or less well-cha- racterised equal-styled plants, but with not one short-styled. With resjiect to the equal-styled plants in the table, Mr. Hor- wood raised from purchased seeds four plants, which he re- membered were certainly not long-stylctl, but either short or equal-styled, probably the latter. These four plants were kept separate and allowed to fertilise themselves ; from their .seed the seventeen plants in the table were raised, all of wliich ])roved equal-styled. The stamens stood low down in the corolla as in the long-styled fomi ; and the stigmas, which were globular and 220 ILLEGITIMATE OFFSPEING OF Chap. V. smooth, were either completely stUTounded by tlie anthers, or stood close above them. My son William made drawings for me, by the aid of the camera, of the pollen of one of the above equal-styled plants ; and, in accordance with the position of the stamens, the cri'ains resembled in their small size those of the long-styled form. He also examined pollen from two equal-styled plants at Southami^ton ; and in both of them the grains dif- fered extremely in size in the same anthers, a large number being small and shrivelled, wlulst many were fully as large as those of the short-styled form and rather more globular. It is probable that the large size of these grains was due, not to their having assumed the character of the short- styled form, but to monstrosity; for Max Wichura has observed isoUen-grains of monstrous size in certain hybrids. The vast number of the small shrivelled grains in the above two cases explains the fact that, though equal-styled plants are generally fertile in a liigh degree, yet some of them yield few seeds. I may add that my son comjiared, in 1875, the grains from two white-flowered l^lants, in both of which the pistil projected above the anthers, but neither were properly long-styled or equal-styled ; and in the one in which the stigma projected most, the grains were in diameter to those in the other plant, in which the stigma pro- jected less, as 100 to 88; whereas the difference between the grains from perfectly characterised long-styled and short-styled plants is as 100 to 57. So that these two plants were in an intermediate condition. To return to the 17 plants in the first line of Table 31 : from the relative jjosition of their stigmas and anthers, they could hardly fail to fertilise themselves; and ac- cordingly four of them spontaneously yielded no less than ISO capsules ; of these ilr. Horwood selected eight fine capsules for sowing ; and they included on an average 54 • 8 seeds, with a maximum of 72. He gave me thirty other capsules, taken by hazard, of which twenty-seven contained good seeds, aver- aging 35 "5, with a maximum of 70; but if six poor cap- sules, each with less than 13 seeds, be excluded, the average rises to 42 "5. These are higher numbers than could be ex- pected from either well-characterised form if self-fertilised ; and this liigh degree of fertiUty accords with the view that the male organs belonged to one form, and the female organs par- tially to the other form ; so that a self-union in the case of the equal-styled variety is in fact a legitimate union. The seed saved from the above seventeen self-fertilised equal- CiiAi>. V. IIETEROSTYLED DIMORPHIC PLANTS. 22J styled plants produced sixteen j^lants, whieli all proved equal- styled, and resembled tlieir parents in all the above-specified respects. The stamens, jiowever, in one plant were seated higher np the tube of the corolla than in the true long-styled foi'm ; in another plant almost all the anthers were coutabescent. These sixteen plants were the grandchildren of the four original plants, wliich it is believed were equal-styled ; so that this abnormal condition was faithfully transmitted, probably through three, and certainly through two generations. The fertility of one of these graudcliildren was carefully observed: six flowers were fertilised with pollen from the same flower, and produced six capsules, containing on an average 68 seeds, -with a maximum of 82, and a minimum of 40. Thirteen cai:)sules spontaneously self-fertilised yielded an average of 53 ■ 2 seeds, with the astonish- ing maximum in one of 97 seeds. In no legitimate union has so high an average as 68 seeds been observed l>y me, or nearly so high a maximum as 82 and 97. These plants, therefore, not only have lost their proj^er heterostyled structure and peculiar functional powers, but have acquired an abnormal grade of fer- tility — unless, indeed, their high fertility may be accounted for by the stigmas receiving pollen from the circumjacent anthers at exactly the most favourable period. With respect to I\Ir. Duck's lot in Table 31, seed was saved fi-om a single plant, of which the form was not observed, and tills produced nine equal-styled and twenty long-styled plants. The equal-styled resembled in all respects those pre- viously described ; and eight of their cajisules spontaneously self-fertilised contained on an average 44*4 seeds, ■«'ith a maximum of 61 and a minimum of 23. In regard to the twenty long-styled plants, the pistil in some of the flowers did not project quite so high as in ordinary long-styled flowers; and the stigmas, though properly elongated, were smooth ; so that we have here a slight ajiproach in structui-e to the pistil of the short-styled form. Some of these long-.stylcd plants also approached the equal-styled in function ; for one of them pro- duced no less than fifteen spontaneously self-fertilised capsules, and of these eight contained, on an average, 31-7 seeds, with a maximum of 61. This average would be rather low for a long-styled plant artificially fertilised with its own pollen, but is high for one spontaneously sclf-fertili.sed. For instance, tliirty-four capsules produced by the illegitimate grandchildren of a long- styled plant, spontaneously self- fertilised, contained 222 ILLEGITIMATE OFFSPKING OF Chap. V. oa an average only 9 • 1 seeds, with a maximum of 46. Some seeds indiscriminately saved from the foregoing twenty-nine equal-styled and long-styled plants ju-oduccd sixteen seedlings, grandcliildren of the original plant belonging to Mr. Duck ; and these consisted of fourteen equal-styled and two long-styled plants ; and I mention this fact as an additional instance of the transmission of the eqiial-styled variety. The third lot in the table, namely the Bastou plants, are the last which need be mentioned. The long and short-styled plants, and the fifteen equal-styled plants, were descended from two distinct stocks. The latter were derived from a single plant, which the gardener is positive was not long-styled ; hence, pro- bably, it was eqiial-styled. In all these fifteen plants the anthers, occupying the same position as in the long-styled form, closely surrounded the stigma, wliich in one instance alone was slightly elongated. Notwithstanding this position of the stigma, the flowers, as the gardener assured me, did not yield many seeds ; and this difference from the foregoing cases may perhaps have been caused by the pollen being bad, as in some of the South- ampton equal-styled jjlants. Conclusions with respect to the equal-styled variety of P. Sinensis. — That this is a variation, and not a third or distinct form, as in the trimorphic genera Lythriim and Oxalis, is clear ; for we have seen its first appearance in one out of a lot of illegitimate long-styled plants ; and in the case of Mr. Duck's seedlings, long-styled plants, only slightly deviating from the normal state, as well as equal-styled plants were produced from the same self-fertilised parent. The position of the sta- mens in their proper place low down in the tube of the corolla, together with the small size of the pollen- grains, show, firstly, that the equal-styled variety is a modification of the long-styled form, and, secondly, that the pistil is the part which has varied most, as indeed was obvious in many of the plants. This variation is of frequent occurrence, and is strongly inherited when it has once appeared. It would, however, have pos- Chai-. V. IlETEBOSTYLED DlMORnilC PLANTS. 223 scssed little interest if it had consisted of a mere change of structure ; l)ut this is accompanied by modi- fied fertility. Its occm-rence apparently stands in close relation with the illegitimate birth of the parent plant ; but to this whole subject I shall hereafter recur. Primula auricula. Although I made no experiments on the illegitimate offspring of this species, I refer to it for two reasons : — First, because I have observed two equal-styled plants in which the pistil resembled in all respects that of the long-styled form, whilst the stamens had become elongated as in the short-styled form, so that the stigma was almost surrounded by the anthers. The pollcn-gi'ains, however, of the elongated stamens resembled in their small size those of the shorter stamens proper to the long- styled form. Hence these plants have become equal-styled by the increased length of the stamens, instead of, as with F. Sinensis, by the diminished length of the pistil. Mr. J. Scott observed five other plants in the same state, and he shows * that one of them, when self-fertilised, yielded more seed than an ordinary long- or short-styled form would have done when similarly fertilised, but that it was far inferior in fertility to either form when legitimately crossed. Hence it appears that the male and female organs of this equal-styled variety have been modified in some special manner, not only in structure but in functional powers. This, moreover, is shown by the singular fact that both the long-styled and short-styled plants, fertilised with pollen from the equal-styled variety, yield a lower average of seed tlian when these two forms are fertilised with their own pollen. The second point which deserves notice is that florists always throw away the long-styled plants, and save seed exclusively from the short-styled form. Nevertheless, as Mr. Scott was informed by a man who raises this species extensively in Scot- land, about one-fourth of the seedlings appear long-styled ; so tliat the short-styled form of the Auricula, when fertilised l)y its own pollen, docs not reproduce the same form in so large a proportion as in the case of P. Sinensis. We may further infer 'Journal Proc. Linn. Soc' viii. (ISGi) p, 91. 224 ILLEGITIMATE OFFSPKING OF Chap. V. that the short-styled form is not rendered qixite sterile by a long course of fertilisation with pollen of the same form : but as there would ahvays be some liability to an occasional cross with the other form, we cannot tell how long self-fertilisation has been continued. Primula farinosa. • Mr. Scott says * that it is not at all uncommon to find equal- styled plants of this heterostyled species. Judging from the size of the pollen-grains, these plants owe their structui-e, as in the case of P. auricula, to the abnormal elongation of the stamens of the long-styled form. In accordance with this view, they yield less seed when crossed Mith the long-styled form than with the short-styled. But they diflfer in an anomalous manner from the equal-styled plants of P. auricula in being extremely sterile with their own pollen. Primula elatior. It was shown in the first chapter, on the authority of Herr Breitenbach, that equal-styled flowers are occasionally found on tliis sjiecies whilst growing in a state of nature ; and this is the only instance of such an occurrence known to me, with the exception of some wild plants of the Oxlip — a hybrid between P. verts and vulgaris — which were equal-styled. Herr Breitenbach's case is remarkable in another way; for equal- styled flowers were found in two instances on plants which bore both long-styled and short-styled flowers. In every other instance these two forms and the equal-styled variety have been produced by distinct plants. Peimula vulgaris, Brit. Fl. Var. acaulis of Linn, and P. acauUs of Jacq. Var. rubra. — Mr. Scott stalest that this variety, which grew in the Botanic Garden in Edinburgh, was quite sterile when fertilised with pollen from the common primrose, as well as from a A\hite variety of the same * ' Journal Proc. Liun. Soc' viii. (1864), p. 115. t Ibid. p. 98. Chap. V. HETEROSTYLED DIMORPHIC PLANTS. 225 species, but that some of the plants, when artificially fertilised with their own pollen, yielded a moderate supply of seed. He was so kind as to send me some of these self-fertilised seeds, from which I raised the plants immediately to be described. I may premise that the results of my experiments on the seedlings, made on a large scale, do not accord with those by j\lr. Scott on the parent-plant. First, in regard to the transmission of form and colour. The parent-plant was long-styled, and of a rich purple colour. From the self-fertilised seed 23 plants were raised ; of these 18 were purple of dif- ferent shades, with 2 of them a little streaked and freckled with yellow, thus showing a tendency to reversion ; and 5 were yellow, but generally with a brighter orange centre than in the wild flower. All the plants were profuse flowerers. All were long- styled ; but the pistil varied a good deal in length even on the same plant, being rather shorter, or con- siderably longer, than in the normal long-styled form ; and the stigmas likewise varied in shape. It is, therefore, probable that an equal-styled variety of the primrose might be found on careful search ; and I have received two accounts of plants apparently in this condition. The stamens always occupied their proper position low down in the corolla ; and the pollen- grains were of the small size proper to the long-styled form, but were mingled with many minute and shrivelled grains. The yellow-flowered and the purple- flowered plants of this first generation were fertilised under a net with their own pollen, and the seed sepa- rately sown. From the former, 22 plants were raised, and all were yellow and long-styled. From the latter or the purple-flowered plants, 24 long-styled plants were raised, of which 17 were purple and 7 yellow. 226 ILLEGITIMATE OFFSPRING OF Chap. V. In this last case we have an instance of reversion in colour, without the possibility of any cross, to the grand- parents or more distant progenitors of the plants in question. Altogether 23 plants in the first generation and 46 in the second generation were raised ; and the whole of these 69 illegitimate plants were long-styled ! Eight purple-flowered and two yellow-flowered plants of the first illegitimate generation were fertilised in various ways with their own pollen and with that of the common primrose ; and the seeds were separately counted, but as I could detect no difference in fertility between the purple and yellow varieties, the results are run together in the following table. (See next page.) If we compare the figures in this table with those given in the first chapter, showing the normal fertility of the common primrose, we shall see that the illegiti- mate purple- and yellow-flowered varieties are very sterile. For instance, 72 flowers were fertilised with their own pollen and produced only 11 good capsules ; but by the standard they ought to have produced 48 capsules ; and each of these ought to have contained on an average 52*2 seeds, instead of only 11*5 seeds. When these plants were illegitimately and legiti- mately fertilised with pollen from the common prim- rose, the average numbers were increased, but were far from attaining the normal standards. So it was when both forms of the common primrose were fertilised with pollen from these illegitimate plants ; and this shows that their male as well as their female organs were in a deteriorated condition. The sterility of these plants was shown in another way, namely, by their not producing any capsules when the access of all insects (except such minute ones as Thrips) was prevented ; for under these circumstances the common long-styled Chap. V. HETEROSTYLED DIMORPHIC PLANTS. 227 Table 32. Primula vuhjaria. Nature of Plant cxporinipnted on, aud kind uf Uuiou. ^1 z: 1 « o •s e s 6 Average Number of Seeds per Capsule. a = i E— ° B a ^ Purple- and yellow-flowered illegi- timate long-styled plants, illegi- timately fertilised with pollen from the same plant * 72 11 11-5 26 5 Purple- and yellow-flowered illegi- timate long-styled plants, illegi- timately fertilised with pollen • from the common long-stj'led primrose , Or, if the ten poorest capsules, including less than 15 seeds, be rejected, we get 72 72 39 '9 31-4 40*6 62 62 3 18 . Purple- and yellow-flowered illegi- timate long-styled plants, legi- timately fertilised with pollen from the common short-styled primrose Or, if the two poore^t capsules, including less than 1.5 seeds, be rejected, we get 2(3 26 18 i6 36-4 4T-2 60 6o 9 ^5 The long-styled form of the common' primrose, ille git'inately fertilised with pollen from the long-styled illegitimate purple- and yellow- flowered plants Or, if the three poorest capsules' be rejected, we get . . . ,J 20 20 14 II 15-4 i8-9 46 46 1 8 The short-styled form of the common' primrose, legitimately fertilised with pollen from the long-styled illegitimate purple- and yellow- flowered plants . 10 C 30-5 61 6 primrose produces a considerable imniLer of capsules. There can, therefore, be no doubt that the fertility of 228 ILLEGITIMATE OFFSPKING OF Chap. V. these plants was greatly impaired. The loss is not correlated with tlie colour of the flower ; and it was to ascertain this point that I made so many experiments. As the parent-plant growing in Edinburgh was found by Mr. Scott to be in a high degree sterile, it may have transmitted a similar tendency to its oflfspring, independently of their illegitimate birth. I am, how- ever, inclined to attribute some weight to the illegiti- macy of their descent, both from the analogy of other cases, and more especially from the fact that when the plants were legitimatelij fertilised with pollen of the common primrose they yielded an average, as may be seen in the table, of only 5 more seeds than when inegithnatehj fertilised with the same pollen. Now we know that it is eminently characteristic of the illegiti- mate offspring of Primula Sinensis that they yield but few more seeds when legitimately fertilised than when fertilised with their own-form pollen. Peimula veris, JBrit. Fl. Var. officinalis of Linn., P. officinalis of Jacq. Seeds from the short-styled form of the cowslip fertilised witli pollen from the same form germinate so badly that I raised from three successive sowings only fourteen plants, whicli consisted of nine short- styled and five long-styled plants Hence the short- styled form of the cowslip, when self-fertilised, does not transmit the same form nearly so truly as does that of P. Sinensis. From the long-styled form, always fertilised with its own-form pollen, I raised in the first generation three long-styled plants, — from their seed 53 long-styled grandchildren, — from their seed 4 long-styled great-grandchildren, — from their seed 20 long-styled great-great-grandchildren, — and lastly, Chap. V. HETEROSTYLED DlJIOIlPIIiC PLANTS. 229 from their seed 8 long-styled and 2 short-styled great- great-great-grandehihlren. In this last generation short-styled plants appeared for the first time in the course of the six generations, — the parent long-styled plant which was fertilised with pollen from another plant of the same form being counted as tlie first generation. Their appearance may be attributed to atavism. From two other long-styled plants, fertilised with their own-form pollen, 72 plants were raised, which consisted of 68 long-styled and 4 short-styled. So that altogether 162 plants were raised from ille- gitimately fertilised long-styled cowslips, and these consisted of 156 long-styled and 6 short-styled plants. We will now turn to the fertility and powers of growth possessed by the illegitimate plants. From a short-styled plant, fertilised with its own-form pollen, one short-styled and two long-styled plants, and from a long-styled plant similarly fertilised three long-styled plants were at first raised. The fertility of these six illegitimate plants was carefully observed ; but I must premise that I cannot give any satisfactory standard of comparison as far as the number of the seeds is concerned ; for though I counted the seeds of many legitimate plants fertilised legitimately and illegitimately, the number varied so greatly during successive seasons that no one standard will serve well for illegitimate unions made during different seasons. Moreover the seeds in the same capsule frequently differ so much in size that it is scarcely possible to decide which ought to be counted as good seed. There remains as the best standard of comparison the proportional number of fertilised flowers which pro- duce capsules containing any seed. First, for the one illegitimate short-styled plant. In the course of three seasons 27 flowers were illefriti- 230 ILLEGITIMATE OFFSPRING OF Chap. V. mately fertilised with pollen from the same plant, and they, yielded only a single capsnle, which, however, con- tained a ratlier large number of seeds for a union of this nature, namely, 23, As a standard of comparison I may state that during the same tliree seasons 44 flowers borne by legitimate short-styled plants were self-fertilised, and yielded 26 capsules ; so that the fact of the 27 flowers on the illegitimate plant having produced only one capsule proves how sterile it was. To show that the conditions of life were favourable, I will add that numerous plants of this and other species of Primula all produced an abundance of capsules whilst growing close by in the same soil with the present and following plants. The sterility of the above illegitimate short-styled plant depended on both the male and female organs being in a deterio- rated condition. This was manifestly the case with the pollen ; for many of the anthers were shrivelled or contabescent. Nevertheless some of the anthers contained pollen, with which I succeeded in fertilising some flowers on the illegitimate long-styled plants immediately to be described. Four flowers on this same short-styled plant were likewise legitimatehj fer- tilised with pollen from one of the following long- styled plants ; but only one capsule was produced, containing 26 seeds ; and this is a very low number for a legitimate union. With respect to the five illegitimate long-styled plants of the first generation, derived from the above self-fertilised short-styled and long-styled parents, their fertility was observed during the same three years. These five plants, when self-fertilised, differed considerably from one another in their degree of fertility, as was the case with the illegitimate long- styled plants of Lythrum salicaria ; and their fertility Chap. V. HETEROSTYLED DIMORPHIC PLANTS. 231 varied much according to the season. I may premise, as a standard of comparison, that during the same years 56 flowers on legitimate long-styled plants of the same age and grown in the same soil, were fer- tilised with their own pollen, and yielded 27 capsules ; that is, 48 per cent. On one of the five illegitimate long-styled plants 36 flowers were self-fertilised in the course of the three years, but they did not produce a single capsule. Many of the anthers on this plant were contabescent ; but some seemed to contain sound pollen. Nor were the female organs quite impotent; for I obtained from a legitimate cross one capsule with good seed. On a second illegitimate long-styled plant 44 flowei-s were fertilised during the same years with their own pollen, but they produced only a single capsule. The third and fourth plants were in a very slight degree more productive. The fifth and last plant was decidedly more fertile ; for 42 self-fertilised flowers yielded 11 capsules. Alto- gether, in the course of the three years, no less than 160 flowers on these five illegitimate long-styled plants were fertilised with their own pollen, but they yielded only 22 capsules. According to the standard above given, they ought to have yielded 80 capsules. These 22 capsules contained on an average 15*1 seeds. I believe, subject to the doubts before specified, that with legitimate plants the average number from a union of this nature would have been above 20 seeds. Twenty-four flowers on these same five . illegitimate long-styled plants were legitimately fertilised with pollen from the above-described illegitimate short- styled plant, and produced only 9 capsules, which is an extremely small number for a legitimate union. These 9 capsules, however, contained an average of 38 apparently good seeds, which is as large a number as 11 232 ILLEGITIMATE OFFSPRING OF Chap. V. legitimate plants sometimes yield. But this high aver- age was almost certainly false ; and I mention the case for the sake of showing the difficulty of arriving at a fair result ; for this average mainly depended on two capsules containing the extraordinary numbers of 75 and 56 seeds ; these seeds, however, though I felt bound to count them, were so poor that, judging from trials made in other cases, I do not suppose that one would have germinated ; and therefore they ought not to have been included. Lastly, 20 flowers were legiti- mately fertilised with pollen from a legitimate plant, and this increased their fertility ; for they produced 10 capsules. Yet this is but a very small proportion for a legitimate union. There can, therefore, be no doubt that these five long-styled plants and the one short-styled plant of the first illegitimate generation were extremely sterile. Their sterility was shoAvn, as in the case of hybrids, in another way, namely, by their flowering profusely, and especially by the long endurance of the flowers. For instance, I fertilised many flowers on these plants, and fifteen days afterwards (viz. on March 22nd) I fertilised numerous long-styled and short-styled flowers on common cowslips growing close by. These latter flowers, on April 8th, were withered, whilst most of the illegitimate flowers remained quite fresh for several days subsequently ; so that some of these illegitimate plants, after being fertilised, remained in full bloom for above a month. We will now turn to the fertility of the 53 illegiti- mate long-styled grandchildren, descended from the long-styled plant which was first fertilised with its own pollen. The pollen in two of these plants included a multitude of small and shrivelled grains. Never- theless they were not very sterile ; for 25 flowers, fer- Chap. V. HETEROSTYLED DniORPHIC PLANTS. 233 tilised with their own pollen, produced 15 capsules, containing an average of 16 "3 seeds. As already stated, the probable average with legitimate plants for a union of this nature is rather above 20 seeds. These plants were remarkably healthy and vigorous, as long as they were kept under highly favourable conditions in pots in the greenhouse ; and such treat- ment greatly increases the fertility of the cowslip. When these same plants were planted during the next year (which, however, was an unfavourable one), out of doors in good soil, 20 self-fertilised flowers pro- duced only 5 capsules, containing extremely few and wretched seeds. Four long-styled great-grandchildren were raised from the self-fertilised grandchildren, and were kept under the same highly favourable conditions in tlie greenhouse ; 10 of their flowers were fertilised with own-form pollen and yielded the large proportion of 6 capsules, containing on an average 18 "7 seeds. From these seeds 20 long-styled great-great-grandchildren were raised, which were likewise kept in the greenhouse. Thirty of their flowers were fertilised with their own pollen and yielded 17 capsules, containing on an aver- age no less than 32, mostly fine seeds. It appears, therefore, that the fertility of these plants of the fourth illegitimate generation, as long as they were kept under highly favourable conditions, had not decreased, but had rather increased. The result, however, was widely different when they were planted out of doors in good soil, where other cowslips grew vigorously and were completely fertile ; for these illegitimate plants now became much dwarfed in stature and extremely sterile, notwithstanding that they were exposed to the visits of insects, and must have been legitimately fer- tilised by the surrounding legitimate plants. A whole 234 ILLEGITIMATE OFFSPKING OF Chap. V. row of these plants of the fourth illegitimate genera- tion, thus freely exposed and legitimately fertilised, produced only 3 capsules, containing on an average only 17 seeds. During the ensuing winter almost all these plants died, and the few survivors were miserably unhealtliy, whilst the surrounding legitimate plants were not in the least injured. The seeds from the great-great-grandchildren were sown, and 8 long-styled and 2 short-styled plants of the fifth illegitimate generation raised. These whilst still in tlie greenhouse produced smaller leaves and shorter flower-stalks than some legitimate plants with which they grew in competition ; but it should be ob- served that the latter were the product of a cross with a fresh stock, — a circumstance which by itself would have added much to their vigour.* When these ille- gitimate plants were transferred to fairly good soil out of doors, they became during the two following years much more dwarfed in stature and produced very few flower-stems ; and although they must have been legitimately fertilised by insects, they yielded cap- sules, compared with those produced by the surround- ing legitimate plants, in the ratio only of 5 to 100 ! It is therefore certain that illegitimate fertilisation, continued during successive generations, affects the powers of growth and fertility of P. veris to an extra- ordinary degree ; more especially when the plants are exposed to ordinary conditions of life, instead of being protected in a greenhouse. Equal-styled red variety of P. veris. — Mr. Scott has described t a i^laut of this kind growing in the Botanic Garden of Edin- burgh. He states that it was highly self-fertile, although insects * For full details of this ex- t ' Proc. Linn. See' vol. viii. periment, sie mj' ' Effects of Cross (1HG4), p. 105. andSelf-drtilisation,' 1876, p. 220. CuAi'. V. HETEROSTYLED DIMORPHIC PLANTS. 235 were excluded ; and he explains this fact by showing, first, that the anthers and stigma arc in close apposition, and that the stamens in length, position and size of their pollen-grains resemble those of the short-styled form, wliilst the jnstil re- sembles that of the long-styled form lx)th in length and in the structure of the stigma. Hence the self-union of this variety is, in fact, a legitimate union, and consequently is highly fertile. Mr. Scott further states that this variety yielded very few seeds when fertilised by either the long- or short-styled common cowslip, and, again, that both forms of the latter, when fertilised by the equal-styled variety, likewise produced very few seeds. But Ms experiments with the cowslip were few, and my results do not confirm liis in any uniform manner. I raised twenty plants from self-fertilised seed sent me by Mr. Scott ; and they all produced red flowers, varying slightly in tint. Of these, two were strictly long-styled both in structure and in function ; for their reproductive powers were tested by crosses with lx)th forms of the common cowslip. Six plants were equal-styled ; but on the same plant the pistil varied a good deal in length during different seasons. This was likewise the case, according to Mr. Scott, with the parent-plant. Lastly, twelve plants were in appearance short-styled ; but they varied much more in the length of their pistils than ordinary short- styled cowslips, and they differed widely from the latter in their powers of reproduction. Their pistils had become short- styled in structure, whilst remaining long-styled in function. Short-styled cowslips, when insects are excluded, are extremely barren : for instance, on one occasion six fine plants produced only about 50 seeds (that is, less than the product of two good capsule.s), and on another occasion not a single capsule. Now, when the above twelve apparently short-styled seedKngs were similarly treated, nearly all produced a great abimdance of capsules, containing numerous seeds, which germinated re- markably well. Moreover three of these plants, wliich diu-ing the first year were furnished with quite short pistils, on the following year produced pistils of extraordinary length. The greater number, therefore, of these short-styled plants could not be distinguished in fimction from the equal-styled variety. The anthers in the six e(iual-styled and in the ai^parently twelve short-styled plants were seated high up in the corolla, as in the true short-styled cowslip; and the pollen-grains resembled those of the same form in their large size, but were mingled 236 ILLEGITIMATE OFFSPEING OF Chap. V. witli a few shrivelled grains. In function this pollen was identical with that of the short-styled cowslip ; for ten long- styled flowers of the common cowsUp, legitimately fertilised with i)ollen from a true equal-styled variety, produced six cap- sules, containing on an average 34-4 seeds; whilst seven cap- sules on a short-styled cowslip illegitimately fertilised with pollen from the equal-styled variety, yielded an average of only 14 "5 seeds. As the equal-styled plants differ from one another in their powers of reproduction, and as this is an important subject, I will give a few details with respect to five of them. First, an equal-styled plant, protected fi'om insects (as was done in all the following cases, with one stated exception), spontaneously produced numerous capsules, five of which gave an average of 44*8 seeds, with a maximmn in one capsule of 57. But six capsules, the product of fertilisation with pollen from a short- styled cowslip (and this is a legitimate union), gave an average of 28 ■ 5 seeds, with a maximum of 49 ; and this is a much lower average than might have been exijected. Secondly, nine cap- sules from another equal-styled plant, which had not been protected from insects, but probably was self-fertilised, gave an average of 45 • 2 seeds, with a maximum of 58. Thirdly, another plant which had a very short pistil in 1865, produced spon- taneously many capsules, six of which contained an average of 33 ■ 9 seeds, with a maximiun of 38. In 1866 this same i^lant had a pistil of w'onderful length ; for it projected quite above the anthers, and the stigma resembled that of the long-styled form. In this condition it produced spontaneously a vast number of fine capsules, six of which contained almost exactly the same average number as before, viz. 34 '3, with a maximmn of 38. Four flowers on this plant, legitimately fertilised with pollen from a short-styled cowslip, jielded capsules with an average of 30 "2 seeds. Fourthly another short-styled plant si^ontaneously produced in 1865 an abundance of capsules, ten of which contained an average of 35 • 6 seeds, with a maximum of 54. In 1866 this same plant had become in all respects long- styled, and ten capsules gave almost exactly the same average as before, viz. 35 "1 seeds, with a maximum of 47. Eight flowers on this plant, legitimately fertilised with pollen from a short-styled cowslip, produced six capsules, with the high average of 53 seeds, and the high maximum of 67. Eight flowers were also fertilised with pollen from a long-styled cow- Chap. V. HETEROSTYLED DIMORPHIC PLANTS. 237 slip (this being an illegitimate union), and proiluccd seven capsules, containing an average of 24 '4 seeds, ■vs-ith a maximmu of 32. The iifth and last plant remained in the same condition during both years : it had a pistil rather longer than that of the true short-styled form, with the stigma smooth, as it ought to be in tliis form, but abnormal in shape, like a much-elongated inverted cone. It produced spontaneously many capsules, five of which, in 1865, gave an average of only 15 • 6 seeds ; and in 1866 ten capsules still gave an average only a Little higher, viz. of 22-1, with a maximum of 30. Sixteen flowers were fertilised with pollen from a long-styled cowslip, and produced 12 cap- sules, with an average of 24 • 9 seeds, and a maximum of 42. Eight flowers were fertilised with pollen from a short-styled cowsUp, but yielded only two capsules, containing 18 and 23 seeds. Hence this plant, in function and i^artially in structiu-e, was in an almost exactly intermediate state between the long- styled and shoi-t-stylcd fonn, but inclining towards the short- styled ; and this accounts for the low average of seeds which it produced when spontaneously self-fertilised. The foregoing five plants thus differ much from one another in the nature of their fertility. In two individuals a great difference in the length of the pistil diu'ing two siTcceeding years made no difference in the numlier of seeds produced. As all five plants possessed the male organs of the short-styled fonn in a perfect state, and the female organs of the long-styled form in a more or less complete state, they spontaneously produced a surprising numlxjr of capsules, which generally contained a large average of remarkably fine seeds. With ordinary cowslips, legitimately fertilised, I once obtained from plants cultivated in the gi-een- house the high average, fi-om seven capsules, of 58*7 seeds, with a maximum in one capsule of 87 seeds ; but from plants grown out of doors I never obtained a higher average than 41 seeds. Now two of the equal-styled i)lants, gi-own out of doors and spontaneously self-fertilised, gave averages of 44 and 45 seeds ; but this high fertility may perhaps be in part attributed to the stigma receiving pollen from the surrounding anthers at exactly the right period. Two of these plants, fertilised with pollen from a short-styled cowsliji (and tliis in fact is a legitimate union), gave a lower average than when self-fertilised. On the other hand, another ])lant, when similarly fertilised by a cowslip, yielded the imusually liigh average of 53 seeds, with a maximum of 67. Lastly, as we have just seen, one of these plants was in 238 ILLEGITIMATE OFFSPRING OF Chap. V. an almost exactly intermediate condition in its female organs between the long- and sliort-stylcd forms, and consequently, when self-fertilised, yielded a low average of seed. If we add together all the experiments which I made on the equal-styled plants, 41 spontaneously self-fertilised capsules (insects having been excluded) gave an average of 34 seeds, which is exactly the same number as the parent-^jlant yielded in Edinbui-gh. Thirty- four flowers, fertiUsed with pollen from the short-styled cowslip (and this is an analogous union), produced 17 capsules, contain- ing an average of 33 " 8 seeds. It is a rather singular circum- stance, for which I cannot account, that 20 flowers, artificially fer- tilised on one occasion with pollen from the same plants yielded only ten capsules, containing the low average of '26 "7 seeds. As bearing on inheritance, it may be added tliat 72 seed- lings were raised from one of the red-flowered, strictly equal- styled, self-fertilised plants descended from the similarly cha- racterised Edinburgh plant. These 72 plants were there- fore grandchildren of the Edinburgh plant, and they all bore, as in the fij-st generation, red flowers, with the exception of one plant, which reverted in colour to the common cowslip. In regard to structure, nine plants were truly long-styled and had their stamens seated low down in the corolla in the proper position ; the remaining 63 jjlants were equal-styled, though the stigma in about a dozen of them stood a little below the anthers. We thus see that the anomalous combination in the same flower, of the male and female sexual organs which properly exist in the two distinct forms, was inherited with much force. Thirty-six seedlings were also raised from long and short-styled common cowslips, crossed with pollen from the equal-styled variety. Of these plants one alone was equal-styled, 20 were short-styled, but with the pistil in three of them rather too long, and the remaining 15 were long-styled. In this case we have an illustration of the difference between simjile inheritance and prepotency of transmission ; for the equal-styled variety, when self-fertilised, transmits its character, as we have just seen, with much force, but when crossed with the counnon cowslip cannot withstand the greater power of transmission of the latter. PULMONAEIA. I have little to say on this genus. I obtained seeds of P. ojjl- cinalis from a garden where the long-styled form alone grew. Chap. V. HETEROSTYLED PLANTS. 239 and raised 11 §cedlinp;s, which were all long-styled. These plants were named for me by Dr. Hooker. They differed, as has been shown, from the i^Iants belonging to this species which in Germany were experimented on by Ilildebrand;* for he found that the long-styled form was absolutely sterile with its own pollen, whilst my long-styled seedlings and the parent-plants yielded a fair supply of seed when self-fertilised. Plants of the long- styled form of Pulmonaria angiistifolia were, Uke Hildebrand's plants, absolutely sterile with their own pollen, so that I could never procui'e a single seed. On the other hand, the short- styled plants of this species, differently from those of P. offi- cinalis, were fertile with their own pollen in a quite remarkable degree for a heterostyled plant. From seeds carefully self-fer- tilised I raised 18 plants, of which 13 proved short-styled and 5 long-styled. Polygonum fagopykdm. From flowers on long-styled plants fertiUsed illegitimately with pollen from the same plant, 49 seedlings were raised, and these consisted of 45 long-styled and 4 short-styled. From flowers on short-styled plants illegitimately fertilised with jwllen from the same plant 33 seedlings were raised, and these con- sisted of 20 shoi-t-styled and 13 long-styled. So that the usual rule of illegitimately fertilised long-styled plants tending much more strongly than short-styled plants to reproduce their own foi-m here holds good. The illegitimate i)!auts derived from both fonns flowered later than the legitimate, and were to the latter in height as 69 to 1(XJ. But as these illegitimate plants were descended from parents fertilised with their own pollen, whilst the legitimate plants were descended from parents crossed with pollen from a distinct individual, it is impossible to know how much of their difference in height and period of flowering, is due to the illegitimate birth of the one set, and how much to the other set being the product of a cross between distinct plants. Coiiehuling Remarhs on the Illegitimate Offspring of Heterostyled Trimorphic and Dimorphic Plants. It is remarkable how closely and in how many points illegitimate unions between the two or three forms of the * • Bot. Zeitung,' 1865, p. 13, 240 ILLEGITIMATE OFFSPRING OF Chap. V. same heterostyled species, together with* their illegiti- mate offspring, resemble hybrid unions between distinct species together with their hybrid offspring. In both cases wo meet with every degree of sterility, from very slightly lessened fertility to absolute barrenness, when not even a single seed-capsule is produced. In both cases the facility of effecting the first union is much influenced by the conditions to which the plants are exposed.* Both with hybrids and illegitimate plants the innate degree of sterility is highly variable in plants raised from the same mother-plant. In both cases the male organs are more plainly affected than the female ; and we often find contabescent anthers enclosing shrivelled and utterly powerless pollen- grains. The more sterile hybrids, as Max Wichura has well shown,t are sometimes much dwarfed in stature, and have so weak a constitution that they are liable to premature death ; and we have seen exactly parallel cases with the illegitimate seedlings of Lythrum and Primula. Many hybrids are the most persistent and profuse flowerers, as are some illegitimate plants. When a hybrid is crossed by either pure parent-form, it is notoriously much more fertile than when crossed inter se or by another hybrid ; so when an illegitimate plant is fertilised by a legitimate plant, it is more fertile than when fertilised inter se or by another ille- gitimate plant. When two species are crossed and they produce numerous seeds, we expect as a general rule that their hybrid offspring will be moderately fertile ; but if the parent species produce extremely few seeds, we expect that the hybrids will be very * This has been remarked by cliapter a striMnp; illnstration in many experimentalists in effecting the case of Primula veris. crosses between distinct species; t 'Die Bastardbefruchtung im and in regard to illegitimate Pflnnzenrcich,' 18G5. unions I have given in the first Chap. V. HETEROSTYLED PLANTS. 24.1 Sterile. But lliere are marked exceptions, as shown by Gartner, to these rules. So it is with illegitimate unions and illegitimate offspring. Thus the mid- styled form of Lijthrum salicaria, when illegitimately fertilised with pollen from the longest stamens of the short-styled form, produced an unusual number of seeds ; and their illegitimate offspring were not at all, or hardly at all, sterile. On the other hand, the illegitimate offspring from the long-styled form, ferti- lised with pollen from the shortest stamens of the same form, yielded few seeds, and the illegitimate offspring thus produced were very sterile ; but they were more sterile than might have been expected relatively to the difficulty of effecting the union of the parent sexual elements. No point is more remarkable in regard to the crossing of species than their unequal reciprocity. Thus species A will fertilise B with the greatest ease ; but B will not fertilise A after hundreds of trials. We have exactly the same case with illegitimate unions ; for the mid-styled Lijthrum salicaria was easily ferti- lised by pollen from the longest stamens of the short- styled form, and yielded many seeds ; but the latter form did not yield a single seed when fertilised by the longest stamens of the mid-styled form. Another important point is prepotency. Gartner has shown that when a species is fertilised with pollen from another species, if it be afterwards fertilised with its own pollen, or with that of the same species, this is so prepotent over the foreign pollen that the effect of the latter, though placed on the stigma some time previously, is entirely destroyed. Exactly the same thing occurs with the two forms of a heterostyled species. Thus several long-styled flowers of Primula veris were fertilised illegitimately with pollen from another plant of the same form, and twenty-four hours 242 ILLEGITIMATE OFFSPRING OF Cuap. V. afterwards legitimately with pollen from a short-styled dark-red polyanthus which is a variety of P. veris ; and the result was that every one of the thirty seed- lings thus raised bore flowers more or less red, show- ing plainly how prepotent the legitimate pollen from a short-styled plant was over the illegitimate pollen from a long-styled plant. In all the several foregoing points the parallelism is wonderfully close between the effects of illegitimate and hybrid fertilisation. It is hardly an exaggeration to assert that seedlings from an illegitimately fer- tilised heterostyled plant are hybrids formed within the limits of one and the same species. This conclu- sion is important, for we thus learn that the difficulty in sexually uniting two organic forms and the sterility of their offspring, afford no sure criterion of so-called specific distinctness. If any one were to cross two varieties of the same form of Lythrum or Primula for the sake of ascertaining whether they were specifically distinct, and he found that they could be united only with some difficulty, that their offspring were extremely sterile, and that the parents and their offspring re- sembled in a whole series of relations crossed species and their hybrid offspring, he might maintain that his varieties had been proved to be good and true species ; but he would be completely deceived. In the second place, as the forms of the same trimorphic or dimorphic heterostyled species are obviously identical in general structure, with the exception of the reproductive organs, and as they are identical in general constitu- tion (for they live under precisely the same condi- tions), the sterility of their illegitimate unions and that of their illegitimate offspring, must depend ex- clusively on the nature of the sexual elements and on their incompatibility for uniting in a particular CuAr. V HETEROSTYLED PLANTS. 213 manucr. Aud as wc have just seen that distinct species when crossed resemble in a whole series of relations the forms of the same species when illegitimately united, we are led to conclude that the sterility of the former must likewise depend exclusively on the incompatible nature of their sexual elements, and not on any general difierence in constitution or structure. We are, indeed, led to this same conclusion by the impossibility of de- tecting any differences sufficient to account for certain species crossing with the greatest ease, whilst other closely allied species cannot be crossed, or can be crossed only with extreme difficulty. We are led to this con- clusion still more forcibly by considering the great difference which often exists in the facility of crossing reciprocally the same two species ; for it is manifest in this case that the result must depend on the nature of the sexual elements, the male element of the one species acting freely on the female element of the other, but not so in a reversed direction. And now we see that this same conclusion is independently and strongly fortified by the consideration of the illegiti- mate unions of trimorphic and dimorphic hetcrostyled plants. In so complex and obscure a subject as hybrid- ism it is no slight gain to arrive at a definite conclu- sion, namely, that we must look exclusively to func- tional differences in the sexual elements, as the cause of the sterility of species when first crossed and of their hybrid offspring. It was this consideration which led me to make the many observations recorded in this chapter, and which in my opinion make them worthy of publication. 244 CONCLUDING REMARKS Chap. VL CHAPTER VI. Concluding Remarks on IIeteuostyled Plants. The essential character of heteroslylcd plants — Summary of the differences in fertility between legitimately and illegitimately fer- tilised plants — Diameter of the pollen-grains, size of anthers and structure of stigma in the diftcrent forms — Affinities of the genera whic-li include heterostyled species — Nature of the advantages derived from heterostylisra — The means by which plants became heterostyled — Transmission of form — Equal-styled varieties of heterostyled plants — Final remarks. In the foregoing chapters all the heterostyled plants known to me have been more or less fully described. Several other cases have been indicated, especially by Professor Asa Gray and Kuhn,* in which the indi- viduals of the same species diifer in the length of their stamens and pistils ; but as I have been often de- ceived by this character taken alone, it seems to me the more prudent course not to rank any species as heterostyled, unless we have evidence of more impor- tant differences between the forms, as in the diameter of the pollen-grains, or in the structure of the stigma. The individuals of many ordinary hermaphrodite plants habitually fertilise one another, owing to their male and female organs being mature at different periods, or to the structure of the parts, or to self-sterility, &c. ; and so it is with many hermaphrodite animals, for instance, land-snails or earth-worms ; but in all these cases any one individual can fully fertilise or be ferti- * Asa Gray, ' American Joum. elsewhere as already referred to. of Science,' 1865, p. 101 ; and Kuhn, ' Bot. Zeitung,' 1867, p. 67. Chap. VI. ON HETEROSTYLED PLANTS. 245 lised by any other individual of the same species. This is not so with heterostyled plants : a long-styled, mid- styled or short-styled plant cannot fully fertilise or be fertilised by any other individual, but only by one belonging to another form. Thus the essen- tial character of plants belonging to the heterostyled class is that the individuals are divided into two or three bodies, like the males and females of dicecious plants or of the higher animals, which exist in approxi- mately equal numbers and are adapted for reciprocal fertilisation. The existence, therefore, of two or three bodies of individuals, differing from one another in the above more important characteristics, offers by itself good evidence that the species is heterostyled. But absolutely conclusive evidence can be derived only from experiments, and by finding that pollen must be applied from the one form to the other in order to ensure complete fertility. In order to show how much more fertile each form is when legitimately fertilised with pollen from the other form (or in the case of trimorphic species, with the proper pollen from one of the two other forms) than when illegitimately fertilised with its own-form pollen, I will append a Table (33) giving a summary of the results in all the cases hitherto ascertained. The fertility of the unions may be judged by two standards, namely, by the proportion of flowers which, when fertilised in the two methods, yield capsules, and by the average number of seeds per capsule. When there is a dash in the left-hand column opposite to the name of the species, the proportion of the flowers which yielded capsules was not recorded. The two or three forms of the same heterostyled species do not differ from one another in general habit or foliage, as sometimes, though rarely, happens with 24G CONCLUDING REMARKS Table 33. Chap. VI, Fertility of the Legitimate Unions taken together, compared with that of the Illegitimate Unions together. Tlie fertility of the Legitimate Unions, as judged by hoth standards, is taken as 100. Kame of Spt-cies. Primula veris P. elatior P. vulgaris P. Sinensis P. Sinensis (second trial) P. Sinensis (Hildebrand) P. auricula (Scott) P. Sikkimensis „ P. cortusoides „ P.'involucrata „ P. farinosa ,, Average of the nine species of Primula Hottonia palustris (H. Mtiller) Linum grandiflorum (the ditference probably"^ is much greater) / L. jierenne L. jieroune (IlildebranJ) Pulmonaria officinalis (German stock, Hilde-'l brand) / Pulmonaria angustifolia Mitchella repens Borreria, Brazilian sp Polygonum fagopyrum Lythrum salicaria Oxalis Valdiviana (Hildebrand). .... 0. Kegnelli „ O. speciosa Illegitimate Uoiuns. Proportional Number of Flowers which pro- duced Capsules. Average Number of Seeds per Capsule. 65 75 54 63 53 42 15 31 66 48 44 69 61 69 20 32 47 46 46 34 49 the two sexes of dioecious })lants. Nor does the calyx differ, but the corolla sometimes differs slightly in shape, owing to the different position of the anthers. In Bor- reria the hairs within the tube of the corolla are differ- ently situated in the long-styled 'and short-styled forms. In Pulmonaria there is a slight difference in the size of Chap. VI. ON HETEROSTYLED PLANTS. 247 the corolla, and iu Pontederia in its colour. In the re- productive organs the differences arc much greater and more important. In the one form the stamens may be all of the same length, and in the other graduated in length, or alternately longer and shorter. The fila- ments may differ in colour and thickness, and are sometimes nearly thrice as long in the one form as in the other. They adhere also for very different proportional lengths to the corolla. The anthers sometimes differ much in size in the two forms. Owing to the rotation of the filaments, the anthers, when mature, dehisce to- wards the circumference of the flower in one form of Faramea, and towards the centre in the other form. The pollen-grains sometimes differ conspicuously in colour, and often to an extraordinary degree in diameter. They differ also somewhat in shape, and apparently in their contents, as they are unequally opaque. In the short-styled form of Faramea the pollen-grains are covered with sharp points, so as to cohere readily to- gether or to an insect ; whilst the smaller grains of the long-styled form are quite smooth. With respect" to the pistil, the style may be almost thrice as long in the one form as in the other. In Oxalis it sometimes differs in hairiness in the three forms. In Linum the pistils either diverge and pass out between the filaments, or stand nearly upright and parallel to them. The stigmas in the two forms often differ much in size and shape, and more especially in the length and thickness of their papillae ; so that the surface may be rough or quite smooth. Owing to the rotation of the styles, the papillose surface of the stigma is turned outwards in one form of Linum perenne, and inwards in the other form. In flowers of the same age of Primula veris the ovules are larger in the long-styled than in the short-styled form. The 248 CONCLUDING REMARKS Chap. VI. seeds produced by the two or three forms often differ in number, and sometimes in size and weight; thus, five seeds from the hmg-styled form of Lythrum mli- caria equal in weight six from the mid-styled and seven from the short-styled form. Lastly, short-styled plants of Pulmonaria officinalis bear a larger number of flowers, and these set a larger proportional number of fruit, which however yield a lower average number of seed, than the long-styled plants. With hetero- styled plants we thus see in how many and in what important characters the forms of the same undoubted species often differ from one another — characters which with ordinary plants would be amply sufficient to dis- tinguish species of the same genus. As the pollen-grains of ordinary species belonging to the same genus generally resemble one another closely in all respects, it is worth while to show, in tlie following table (34), the difference in diameter be- tween the grains from the two or three forms of the same heterostyled species in the forty-three cases in which this was ascertained. But it should be observed that some of the following measurements are only approximately accurate, as only a few grains were measured. In several cases, also, the grains had been dried and were then soaked in water. Whenever they were of an elongated shape their longer diameters were measured. The grains from the short-styled plants are invariably larger than those from the long- styled, whenever there is any difference between them. The diameter of the former is represented in the table by the number 100. " We here see that, with seven or eight exceptions out of the forty-three cases, the pollen-grains from one form are larger than those from the other form of the same species. The extreme difference is as 100 to 55 ; CUAT. VI. ON HETEROSTYLED PLANTS. 249 Table 34. Belative Diameter of the Pollen-grains from tlte forms of the same Heterostyled Species ; those from the short-slyled form being represented by 100. Dimorphic Species. From the Long- styled form. Primula veris .... 67 „ vulgaris . . . 71 „ Sinensis(HilJebrand) 57 „ auricula . . .71 Hottoniapalustris(H. Jliiller) 61 „ (self) . 64- Linum grandiflorum , . 100 „ perenne(diameter va-l ^ , „ .,. . . 100 riable). 91 99 „ flavum Pulmonaria officinalis . „ angustitblia Polygonum fagopyrum . Leucosmia Burnettiana jEgiphila elata .... 62 Menyanthes tiifoliata . . 84 Limnanthemum ludicum . 100 Vill'arsia (sp. ?) . . . .75 Forsythia suspensa ... 94 From the Long- styled form. . 100 Cordia (sp. ?) Gilia pulchella . ,, micrantha . Sethia acuminata Erythroxylum (sp. ?) Cratosylon formosum Mitchella repens, pollen- grains of the long-styled a little smaller. Borreria (sp. ?).... 92 Faramea (sp. ?) . . . .67 Suteria (sp. ?) (Fritz Muller) 75 Houstonia ccerulea ... 72 Oldenlandia (sp. ?) . . .78 Hedyotis (sp. ?) . . . .88 Coccocvpselum (sp. ?) (F Mulier) .... Lipostoma (sp. ?) ... 80 Cinchona micraatha . . 91 100 81 83 93 86 100 Trimori^hic Species. Ratio expressing the extreme differences in diimieter of the pollen-grains from the two sets of anthers in the three forms. Lythrum salicaria . . . . 60 Nessea verticillata .... 65 Osalis Valdiviana (Hildebrand) 71 „ Regnelli 78 „ speciosa 69 „ sensitiva .... 84 Pontcderia (sp. ?) . . . .55 Ratio between the diameters of the pollen- grains of the two sets of anthers in the same form. Oxalis rosea, long-styled form'l „„ (Hildebrand) . , . / °"* „ compressa, short-styled i „„ form ) Pontederia (sp. ?) short-styled^ „_ form . . . . / „ other sp., mid-styled 'I „p form . , . . / ^ and we should bear in mind that in the case of spheres diifering to this degree in diameter, their contents differ in the ratio of six to one. With all the species in which the grains differ in diameter, there is no exception to the rule that those from the 250 CONCLUDING KEMARKS Chap. VI. anthers of the short-styled form, the tubes of which have to penetrate the longer pistil of the long-styled form, are larger than the grains from the other form. This curious relation led Delpino* (as it formerly did me) to believe that the larger size of the grains in the short-styled flowers is connected with the greater supply of matter needed for the development of their longer tubes. But the case of Linum, in which the grains of the two forms are of equal size, whilst the pistil of the one is about twice as long as that of the other, made me from the first feel very doubtful with respect to this view. My doubts have since been strengthened by the cases of Limnanthe- mum and Coccocypselum, in which the grains are of equal size in the two forms ; whilst in the former genus the pistil is nearly thrice and in the latter twice as long as in the other form. In those species in which the grains are of unequal size in the two forms, there is no close relationship between the de- gree of their inequality and that of their pistils. Thus in Ptdmonaria officinalis and in Erythroxy- lum the pistil in the long-styled form is about twice the length of that in the other form, whilst in the former species the pollen-grains are as 100 to 78, and in the latter as 100 to 93 in diameter. In the two forms of Suteria the pistil differs but little in length, whilst the pollen - grains are as 100 t j 75 in diameter. These cases seem to prove that the difiereuce in size between the grains in the two forms is not determined by the length of the pistil, down which the tubes have to grow. That with plants in general there is no close relationship between * 'Suir Opera, la D.stribiiziono dei Sessi uclle Pi, ntc,' ilc, 1867, p. 17. CuAP. VI. ox HETEROSTYLED TLAXTS. 251 the size of the pollen-grains and the length of the pistil is manifest : for instance, I found that the dis- tended grains of Datura arhorea were "00243 of an inch in diameter, and the pistil no less than 9 '25 inches in length ; now the pistil in the small flowers of Polygonum fagoptjrum is very short, yet the larger pollen-grains from the short styled plants had exactly the same diameter as those from the Datnra, with its enormously elongated pistil. Notwithstanding these several considerations, it is difficult quite to give up the belief that the pollen-grains from the longer stamens of heterostyled plants have become larger in order to allow of the development of longer tubes ; and the foregoing opposing facts may possibly be reconciled in the following manner. The tubes are at first developed from matter contained within the grains, for they are sometimes exserted to a considerable length, before the grains have touched the stigma ; but botanists believe that they afterwards draw nourishment from the conducting tissue of the pistil. It is hardly possible to doubt that this must occur in such cases as that of the Da- tura, in which the tubes have to grow down the whole length of the pistil, and therefore to a length equal- ling 3,806 times the diameter of the grains (namely, •00243 of an inch) from which they are protruded. I may here remark that I have seen the pollen -grains of a willow, immersed in a very weak solution of honey, protrude their tubes, in the course of twelve hours, to a length thirteen times as great as the diameter of the grains. N'ow if we suppose that the tubes in some heterostyled species are developed \\holly or almost wholly from matter contained within the grains, while in other species from matter yielded by the pistil, we can see that in the former case it would be necessary 252 CONCLUDING REMARKS Chap. VI. that the grains of the two forms should differ in size relatively to the length of the pistil which the tubes have to penetrate, but that in the latter case it would not be necessary that the grains should thus differ. Whether this explanation can bo considered satisfac- tory must remain at present doubtful. There is another remarkable difference between the forms of several heterostyled species, namely in the anthers of the short-styled flowers, which contain the larger pollen-grains, being longer than those of the long-styled flowers. This is the case with Hoitonia jMliistris in the ratio of 100 to 83. With Limnan- themum Indicum the ratio is as 100 to 70. With the allied Menyanthes the anthers of the short-styled form are a little and with Villarsia conspicuously larger than those of the long-styled. With Pulmonaria angustifolia they vary much in size, but from an average of seven measurements of each kind the ratio is as 100 to 91. In six genera of the Rubiacese there is a similar difference, either slightly or well marked. Lastly, in the trimorphic Pontederia the ratio is 100 to 88 ; the anthers from the longest stamens in the short-styled form being comjjared with those from the shortest stamens in the long-styled form. On the other hand, there is a similar and well-marked differ- ence in the length of the stamens in the two forms of Forsyihia suspensa and of Linum jlavum ; but in these two cases the anthers of the short-styled flowers are shorter than those of the long-styled. The rela- tive size of the anthers was not particularly attended to in the two forms of the other heterostyled plants, but I believe that they are generally equal, as is certainly the case with those of the common primrose and cowslip. The pistil differs in length in the two forms of every CuAr. VI ON HETEROSTYLED PLANTS. 253 heterostyled plant, and although a similar difference is very general with the stamens, yet in the two forms of Linum grandijloruni and of Cordia they are equal. There can hardly be a doubt that the rela- tive length of these organs is an adaptation for the safe transportal by insects of the pollen from the one ft)rm to the other. The exceptional cases in which these organs do not stand exactly on a level in the two forms may probably be explained by the manner in which the flowers are visited. With most of the species, if there is any difference in the size of the stigma in the two forms, that of the long-styled, what- ever its shape may be, is larger than that of the short- styled. But here again there are some exceptions to the rule, for in the short-styled form of Leucosmia Burnettiana the stigmas are longer and much narrower than those of the long-styled ; the ratio between the lengths of the stigmas in the two forms being 100 to 60. In the three Rubiaceous genera, Faramea, Houstonia and Oldenlandia, the stigmas of the short-styied form are likewise somewhat longer and narrower ; and in the three forms of Oxalis sensitiva the difference is strongly marked, for if the length of the two stigmas of the long-styled pistil be taken as 100, it will be represented in the mid- and short-styled forms by the numbers 141 and 164. As in all these cases the stigmas of the short-styled pistil are seated low down within a more or less tubular corolla, it is probable that they are better fitted by being long and narrow for brushing the pollen off the inserted proboscis of an insect. "With many heterostyled plants the stigma differs in roughness in the two forms, and when this is the case there is no known exception to the rule that the papillai on the stigma of the long-styled form are longer 254 CONCLUDING REMARKS Chap. VI. and often thicker than those on that of the short- styled. For instance, tlie papiUfe on the kmg-styled stif-ma of Hottonia palustris are more than twice the length of those in the other form. This holds good even in the case of Houstonia coeridea, in which the stio-mas are much shorter and stouter in the long- styled than in the short-styled form, for the papillae on the former compared with those on the latter are as 100 to 58 in length. The length of the pistil in the long-styled form of Linum grandiflorum varies much, and the stigmatic papilke vary in a corre- sponding manner. From this fact I inferred at first that in all cases the difference in length between the stigmatic papillaj in the two forms was one merely of correlated growth ; but this can hardly be the true or general explanation, as the shorter stigmas of the long-styled form of Houstonia have the longer papillae. It is a more probable view that the papillae, which render the stigma of the long-styled form of various species rough, serve to entangle effectually the large- sized pollen-grains brought by insects from the short- styled form, thus ensuring its legitimate fertilisation. This view is supported by the fact that the pollen- grains from the two forms of eight species in Table 34 hardly differ in diameter, and the papillae on their stigmas do not differ in length. The species which are at present positively or almost positively knowTi to be heterostyled belong, as shown in the following table, to 38 genera, widely dis- tributed throughout the world. These genera are included in fourteen Families, most of which are very distinct from one another, for they belong to nine of the several great Series, into which phanerogamic plants have been divided by Bentham and Hooker. CUAP. VI. ON HETEROSTYLED PLANTS. 255 Table 35. List of Genera including Ileterostyled Species, DlCOXrLEDONS. Cratoxylon. Hypericineai. Erythroxylura. Sethia. Erythroxylea;. Linum. Geraniacea;. Oxalis. ^j Lythrum. Lythracea;. Nesasa. ij Cinchona. Rubiacea;. Bouvardia. )9 Manettia. )J Hedyotis. Oldealandia. Houstonia. 5) Coccocypselum. Lipostoma. Enosia. ■>■> 5) Faramea. >> ' Psychotria. Rudgea. Suteria. )> Dicotyledons. Mitchella. Rubiaceac. Diodia. >» Borreria. » Spermacoce. 11 I'limula. Primulaceae. Hottouia. 11 Androsace. 11 Forsythia. Oleaceae Menyanthes. Gentianacea;. Limnanthemuin. »> Yillarsia. )) Gilia. Polemoniacete. Cordia. Cordiea;. Pulmonaria. Boragineae. jEgiphila. Verbenacese. Polygonum. Polygoneas. Thymelea. Thymeleae. Monocotyledons. Poutederia. Pontederiaceae In some of these families the heterostyled condition must have been acquired at a very remote period. Thus the three closely allied genera, Menyanthes, Limnanthemum, and Villarsia, inhabit respectively Europe, India, and South America. Heterostyled species of Hedyotis are found in the temperate regions of North and the tropical regions of South America. Trimorphic species of Oxalis live on both sides of the Cordillera in South Ainerica and at the Cape of Good Hope. In these and some other cases it is not probable that each species acquired its heterostyled structure independently of its close allies. If they did not do so, the three closely connected genera of the Menyanthea; and the several trimorphic species of Oxalis must have inherited their structure from a common progenitor. But an immense lapse of time will have been necessary in all such cases for the modified descendants of a common progenitor to have 12 256 CONCLUDING REMARKS Chap. VI. spread from a single centre to such widely remote and separated areas. The family of the Rubiaceai contains not far short of as many heterostyled genera as all the other thirteen families together ; and hereafter nc doubt other Rubiaceous genera will be found to be heterostyled, although a large majority are homo- styled. Several closely allied genera in this family probably owe their heterostyled structure to descent in common ; but as the genera thus characterised are distributed in no less than eight of the tribes into which this family has been divided by Bentham and Hooker, it is almost certain that several of them must have become heterostyled independently of one another. What there is in the constitution or structure of the members of this family which favours their becoming heterostyled, I cannot conjecture. Some families of considerable size, such as the Bo- raginea? and Verbenacese, include, as far as is at present known, only a single heterostyled genus. Polygonum also is the sole heterostyled genus in its family ; and though it is a very large genus, no other species except P. fagopjrum is thus characterised. We may suspect that it has become heterostyled within a comparatively recent period, as it seems to be less strongly so in function than the species in any other genus, for both forms are capable of yielding a con- siderable number of spontaneously self-fertilised seeds. Polygonum in possessing only a single heterostyled species is an extreme case ; but every other genus of considerable size which includes some such species likewise contains homostyled species. Ly thrum in- cludes trimorphic, dimorphic, and homostyled species. Trees, bushes, and herbaceous plants, both large and small, bearing single flowers or flowers in dense spikes or heads, have been rendered heterostyled. Chap. VI. ON IIETEROSTYLED PLANTS. 257 So have plants which iuhabit alpine and lowland sites, dry land, mai"shes and water.* When I first began to experimcntise on hetero- styled plants it was under the impression that they were tending to become dioecious ; but I was soon forced to relinquish this notion, as the long-styled plants of Primula which, from possessing a longer pistil, larger stigma, shorter stamens with smaller pollen-grains, seemed to be the more feminine of the two forms, yielded fewer seeds than the short-styled plants which appeared to be in the above respects the more mascu- line of the two. Moreover, trimorphic plants evidently come under the same category with dimorphic, and the former cannot be looked at as tending to become dioecious. With In/thrum salicaria, however, we have the curious and unique case of the mid-styled form being more feminine or less masculine in nature than the other two forms. This is shown by the large * Out of the 38 genera known which (i.e. 43 per cent.) contain to include heterostylecl species, species inhabiting the just-apeci- about eiijht, or 21 per cent., are fied station3. So that 43 per cent, more or less aquatic in their of those British plants which habits. I was at first struck with have their sexes separated are this fact, for I was not then aware more or less aquatic in their how large a proportion of or- habits, whereas only 21 per cent, dinary plants inhabit such sta- of heterostyled plants have such tions. Heterostyled plants may habits. I may add that the her- be said in one sense to have their maphrodite classes, from Monan- sexes separated, as the forms must dria to Gynandria inclusive, con- mutually fertilise one another. tain 447 genera, of which 113 are Therefore it seemed worthwhile aquatic in the above sense, or only to ascertain what proportion of 25 per cent. It thus appears, as the genera in the Linnean classes, far as cau be judged from such jMoncecia, Dicecia and Poly- imperfect data, that there is some gamia, contained species which connection between the separation live "in water, marshes, bogs or of the sexes in plants and the watery places." In Sir W. J. watery nature of the sites which Hooker's ' British Flora ' (4th they inhabit ; but that tliis does edit. 1838) these three Linnean not hold good with heterostyled classes include 40 genera, 17 of 8pecie^. 258 CONCLUDING REMARKS Ciiap. VI. number of seeds which it yields in whatever manner it may be fertilised, and by its pollen (the grains of which are of smaller size than those from the corre- sponding stamens in the other two forms) when applied to the stigma of any form producing fewer seeds than the normal number. If we suppose the process of deterioration of the male organs in the mid- styled form to continue, the final result would be the production of a female plant ; and Lythrum salicaria would then consist of two heterostyled hermaphrodites and a female. No such case is known to exist, but it is a possible one, as hermaphrodite and female forms of the same species are by no means rare. Although there is no reason to believe that heterostyled plants are regularly becoming dioecious, yet they offer sin- gular facilities, as will hereafter be shown, for such conversion ; and this appears occasionally to have been effected. We may feel sure that plants have been rendered heterostyled to ensure cross-fertilisation, for we now know that a cross between the distinct individuals of the same species is highly important for the vigour and fertility of the offspring. The same end is gained by dichogamy or the maturation of the reproductive ele- ments of the same flower at different periods, — by dioeciousness — self-sterility — the prepotency of pollen fromanother individual over a plant's own pollen, — and lastly, by the structure of the flower in relation to the visits of insects. The wonderful diversity of the means for gaining the same end in this case, and in many others, depends on the nature of all the previous changes through which the species has passed, and on the more or less complete inheritance of the successive adaptations of each part to the surrounding conditions. CiiAi-. Vr. ox HETEKOSTYLED PLANTS. 259 Plants which are already well adapted by the structure of their flowers for cross-fcrtilisanon by the aid of insects often possess an irregular corolla, which has been modelled in relation to their visits ; and it would have been of little or no use to such plants to have become heterostyled. We can thus understand why it is that not a single species is heterostyled in such great families as the Leguminosa}, Labiata:;, Scrophu- lariacese, Orchideaj, &c., all of wliich have irregular flowers. Every known heterostyled plant, however, depends on insects for its fertilisation, and not on the wind ; so that it is a rather surprising fact that only one genus, Pontederia, has a plainly irregular corolla. Why some species are adapted for cross-fertilisation, whilst others within the same genus are not so, or if they once were, have since lost such adaptation and in consequence are now usually self-fertilised, I have endeavoured elsewhere to explain to a certain limited extent.* If it be further asked why some species have been adapted for this end by being made heterostyled, rather than by any of the above specified means, the answer probably lies in the manner in which heterostylism originated, — a subject immedi- ately to be discussed. Heterostyled species, however, have an advantage over dichogamous species, as all the flowers on the same heterostyled plant belong to the same form, so that when fertilised legitimately by insects two distinct individuals are sure to intercross. On the other hand, with dichogamous plants, early or late flowers on the same individual may intercross ; and a cross of this kind does hardly any or no good. Whenever it is profitable to a species to produce a ' The Effects of Cross and Self-fertilisatiou,' 1876, p. 441. 260 CONCLUDING KEMAUKS Ciiai>. VI large number of seeds and this obviously is a very common case, heterostylcd will have an advantage over dioecious plants, as all the individuals of the former, whilst only half of the latter, that is the females, yield seeds. On the other hand, hetero- stylcd plants seem to have no advantage, as far as cross-fertilisation is concerned, over those which are sterile with their own pollen. They lie indeed under a slight disadvantage, for if two self-sterile plants grow near together and far removed from all other plants of the same species, they will mutually and perfectly fertilise one another, whilst this will not be the case with heterostylcd dimorphic plants, unless they chance to belong to opposite forms. It may be added that species which are trimorphic have one slight advantage over the dimorphic ; for if only two individuals of a dimorphic species happen to grow near together in an isolated spot, the chances are even that both will belong to the same form, and in this case they will not produce the full number of vigorous and fertile seedlings ; all these, moreover, will tend strongly to belong to the same form as their parents. On the other hand, if two plants of the same trimorphic species happen to grow in an isolated spot, the chances are two to one in favour of their not be- longing to the same form ; and in this case they will legitimately fertilise one another, and yield the full complement of vigorous offspring. The Means hy which Plants may have leeti rendered Reterostyled. This is a very obscure subject, on which I can throw little light, but which is worthy of discussion. It has Chai\ VI. ON HETEROSTYI.ED PLANTS. 261 been shown that heterostyled plants occur in fourteen natural families, dispersed throui^hout the whole vege- table kingdom, and that even within the family of the Rubiaceae they are dispersed in eight of the tribes. We may therefore conclude that this structure has been acquired by various plants independently of inheritance from a common progenitor, and that it can be acquired without any great difficulty — that is, without any very unusual combination of circumstances. It is probable that the first step towards a species becoming heterostyled is great variability in the length of the pistil and stamens, or of the pistil alone. Such variations are not very rare : with Amsinckia spectahilis and Nolana prostrata these organs differ so much in length in different individuals that, until experiment- ing on them, I thought both species heterostyled. The stigma of Gesjieria pendidina sometimes protrudes far beyond, and is sometimes seated beneath the anthers ; so it is with Oxalis acetosella and various other plants. 1 have also noticed an extraordinary amount of difference in the length of the pistil in cul- tivated varieties of Primula veris and vulgaris. As most plants are at least occasionally cross-fer- tilised by the aid of insects, we may assume that this was the case with our supposed varying plant ; but that it would have been beneficial to it to have been more regularly cross-fertilised. We should bear in mind how important an advantage it has been proved to be to many plants, though in different degrees and ways, to be cross-fertilised. It migh. well happen that our supposed species did not vary in function in the right manner, so as to become either dichogamous or completely self-sterile, or in structure so as to ensure cross-fertilisation. If it had 262 CONCLUDING REMARKS Chat. VI. thus varied, it would never have been rendered hetero- styled, as this state would then have been superfluous. But the parent-species of our several existing hetero- styled plants may have been, and probably were (judg- ing from their present constitution) in some degree self-sterile ; and this would have made regular cross- fertilisation still more desirable. Kow let us take a highly varying species with most (jr all of the anthers exserted in some individuals, and in others seated low down in the corolla ; with the stigma also varying in position in like manner. Insects which visited such flowers would have different parts of their bodies dusted with pollen, and it would be a mere chance whether this were left on the stigma of the next flower which was visited. 1/ all the anthers could have been placed on the same level in all the plants, then abundant pollen would have adhered to the same part of the body of the insects which fre- quented the flowers, and would afterwards have been deposited without loss on the stigma, if it likewise stood on the same unvarying level in all the flowers. But as the stamens and pistils are supposed to have already varied much in length and to be still varying, it might well happen that they could be reduced much more easily through natural selection into two sets of different lengths in different individuals, than all to the same length and level in all the individuals. We know from innumerable instances, in which the two sexes and the young of the same species difi'er, that there is no difficulty in two or more sets of individuals being formed which inherit different characters. In our particular case the law of compensation or balance- ment (which is admitted by many botanists) would tend to cause the pistil to be reduced in tliose indi- CiiAr. VI. ON HETEKOSTYLED PLANTS. 263 viduals in which the stamens were greatly developed, and to be increased in length in those which had their stamens but little developed. Now if in our varying species the longer stamens were to be nearly equalised in length in a considerable body of individuals, with the pistil more or less reduced ; and in another body, the shorter stamens to be simi- larly equalised, with the pistil more or less increased in length, cross-fertilisation would be secured with little loss of pollen ; and this change would be so highly beneficial to the species, that there is no difficulty in be- lieving that it could be effected through natural selec- tion. Our plant would then make a close approach in structure to a heterostyled dimorphic species ; or to a trimorphic species, if the stamens were reduced to two lengths in the same flower in corresj)ondence with that of the pistils in the other two forms. But we have not as yet even touched on the chief difficulty in under- standing how heterostyled species could have origi- nated. A completely self-sterile plant or a dicho- gamous one can fertilise and be fertilised by any other individual of the same species ; whereas the essential character of a heterostyled plant is that an individual of one form cannot fully fertilise or be fer- tilised by an individual of the same form, but only by one belonging to another form. H. Miiller has suggested* that ordinary or homo- styled plants may have been rendered heterostyled merely through the effects of habit. Whenever pollen from one set of anthers is habitually applied to a pistil of particular length in a varying species, he believes that at last the possibility of fertilisation in any other * ' Die Befnichtung der Blumcn,' p. 852. 2(34 CONCLUDING REMARKS Chai'. VI. manner will be nearly or completely lost. He was led to this view by observing that Diptera frequently carried pollen from the long-styled flowers of Hottonia to the stigma of the same form, and that this ille- gitimate union was not nearly so sterile as the corre- sponding union in other heterostyled species. But this conclusion is directly opposed by some other cases, for instance by that of Linum grandijiorum ; for here the long-styled form is utterly barren with its own-form pollen, although from the position of the anthers this pollen is invariably applied to the stigma. It is obvious that with heterostyled dimorphic plants the two female and the two male organs differ in power ; for if the same kind of pollen be placed on the stigmas of the two forms, and again if the two kinds of pollen be placed on the stigmas of the same form, the results are in each case widely dif- ferent. Nor can we see how this differentiation of the two female and two male organs could have been effected merely through each kind of pollen being habitually placed on one of the two stigmas. Another view seems at first sight probable, namely, that an incapacity to be fertilised in certain ways has been specially acquired by heterostyled plants. We may suppose that our varying species was somewhat sterile (as is often the case) with pollen from its own stamens, whether these were long or short ; and that such sterility was transferred to all the individuals with pistils and stamens of the same length, so that these became incapable of intercrossing freely ; but that such sterility was eliminated in the case of the individuals which differed in the length of their pistils and stamens. It is, however, incredible that so peculiar a form of mutual infertility should have been specially Chap. VI. ON HETEROSTYLED PLANTS. 265 acquired unless it were highly beneficial to the species ; and although it may be beneficial to an individual plant to be sterile with its own pollen, cross-fertilisa- tion being thus ensured, how can it be any advan- tage to a plant to be sterile with half its brethren, that is, with all the individuals belonging to the same form ? Moreover, if the sterility of the unions between plants of the same form had been a special acquirement, we might have expected that the long- styled form fertilised by the long-styled would have been sterile iu the same degree as the short-styled fertilised by the short-styled ; but this is hardly ever the case. On the contrary, there is sometimes the widest difference in this respect, as between the two illegitimate unions of Pulmonaria angustifolia and of Hottonia ixilustris. It is a more probable view that the male and female organs in two sets of individuals have been by some means specially adapted for reciprocal action ; and that the sterility between the individuals of the same set or form is an incidental and purposeless result. The meaning of the term " incidental " may be illus- trated by the greater or less difficulty in grafting or budding together two plants belonging to distinct species ; for as this capacity is quite immaterial to the welfare of either, it cannot have been specially ac- quired, and must be the incidental result- of differ- ences in their A'egetative systems. But how the sexual elements of heterostyled plants came to differ from what they were whilst the species was homo- styled, and how they became co-adapted in two sets of individuals, are very obscure points. We know that in the two forms of our existing heterostyled plants the pistil always differs, and the stamens generally differ in length ; so does the stigma in structure, 2(56 CONCLUDING REMARKS Chap. VI. the anthers in size, and the pollen-grains in diameter. It appears, therefore, at first sight probable that organs which differ in such important respects could act on one another only in some manner for which they had been specially adapted. The probability of this view is supported by the curious rule that the greater the difference in length between the pistils and stamens of the trimorphic species of Lythrum and Oxalis, the products of which are united for reproduc- tion, by so much the greater is the infertility of the union. The same rule applies to the two illegitimate unions of some dimorphic species, namely. Primula vulgaris and Pulmonaria angustifolia ; but it entirely fails in other cases, as with Hottonia palustris and Linum grandiflorum. We shall, however, best perceive the difficulty of understanding the nature and origin of the co-adaptation between the reproductive organs of the two forms of hetcrostyled plants, by consider- ing the case of Linum grandijlorum : the two forms of this plant differ exclusively, as far as we can see, in the length of their pistils ; in the long-styled form, the stamens equal the pistil in length, but their pollen has no more effect on it than so much in- organic dust ; whilst this pollen fully fertilises the short pistil of the other form. Now, it is scarcely credible that a mere difference in the length of the pistil can make a wide difference in its capacity for being fertilised. We can believe this the less because with some plants, for instance, Amsinckia spectahilis, the pistil varies greatly in length without affecting the fertility of the individuals which are intercrossed. So again I observed that the same plants of Primula veris and vulgaris differed to an extraordinary degree in the length of their pistils during successive seasons ; nevertheless they yielded during these seasons exactly Chap. VI. ON HETEROSTYLED PLANTS. 267 the same average number of seeds when left to fertilise themselves spontaneously under a net. We must therefore look to the appearance of inner or hidden constitutional diiferences between the indi- viduals of a varying species, of such a nature that the male element of one set is enabled to act efficiently only on the female element of another set. We need not doubt about the possibility of variations in the constitution of the reproductive system of a plant, for we know that some species vary so as to be completely self-sterile or completely self-fertile, either in an appa- rently spontaneous manner or from slightly changed conditions of life. Gartner also has shown* that the in- dividual plants of the same species vary in their sexual powers in such a manner that one will unite with a distinct species much more readily than another. But what the nature of the inner constitutional differences may be between the sets or forms of the same varying species, or between distinct species, is quite unknown. It seems therefore probable that the species which have become heterostyled at first varied so that two or three sets of individuals were formed differing in the length of their pistils and stamens and in other co-adapted characters, and that almost simultaneously their reproductive powers became modified in such a manner that the sexual elements in one set were adapted to act on the sexual elements of another set ; and consequently that these elements in the same set or form incidentally became ill-adapted for mutual interaction, as in the case of distinct species. I have elsewhere shown f that the sterility of species when * Gartner, ' Bastardorzeugung Plants under Domestication,' 2ud im Pflanzenreich,' 1«49, p. 165. edit. vol. ii. p. 169 ; ' The ElJectsof t 'Origin of Species,' 6th edit. Cross and Self-fertilisation,' p. 463. p. 247 ; ' Variation of Animals and It may be well uere to remark 2G8 CONCLUDING REMARKS Chai. VI. first crossed and of their hybrid offspring must also be looked at as merely an incidental result, following from the special co-adaptation of the sexual elements of the same species. We can thus understand the striking parallelism, which has been shown to exist between the effects of illegitimately uniting hetero- styled plants and of crossing distinct species. The great difference in the degree of sterility between the various heterostyled species when illegitimately fer- tilised, and between the two forms of the same species when similarly fertilised, harmonises well with the view that the result is an incidental one which follows from changes gradually effected in their reproductive systems, in order that the sexual elements of the dis- tinct forms should act perfectly on one another. Transmission of tlie Two Forms hy Heterostyled Plants. — The transmission of the two forms by heterostyled plants, wdth respect to which many facts were given in the last chapter, may perhaps be found hereafter to throw some light on their manner of development. Hildebrand observed that seedlings from the long- styled form of Primula Sinensis when fertilised with pollen from the same form were mostly long-styled, and many analogous cases have since been observed by me. All the known cases are given in the two following tables. that, jmlging from the remark- female elements in the two forms of able power with whicli abruptly the same heterostyled species, or changed conditions of life act on in all the individuals of the same the reproductive system of most ordinary species, could be acquired organisms, it is probable that the only under long-continued nearly close adaptation of the male to the uniform conditions of life. CllAl'. VI. ON IIETEllOSTYLED PLANTS. 269 Table 36. Nature of the Offspring from Ulegitimntcly fertilised Dimorphic Plants. I Number j of Long- styled Offspring. Knmb r of Short- styled Offspring. Primula verL« Primula vulgaris Primula auricula Primula Sinensis I Long-styled form, fertilised byu own-form pollen during five 1 1 successive generations, pro-j' duced jj I yShort-styled form, fertilised byl | ■\ own-form pollen, produced ./ Long-styled form, fertilised by j j own-form pollen durinsttwoi successive generations, pro- 1 duced J fSbort-styled form, fertilised by I own-form pollen, is said to .i produce during successive I generations offspring in about ^ the following proportions . I Long-styled form, fertilised by 'J own-form pollen during two I successive generations, pro-j duced ) I Long-styled form, fertilised byj own -form pollen (Hilde-[ brand), produced. yShort-styled form, fertilised by ■\ own-form pollen, produced } ,_ . ,. /Long-styled form, fertilised by 'J olticmalis| own-form pollen, produced ./ r, , c CLong-styled form, fertilised by\ Polygonum fagopyrumj „^.J^,„ p^n^'^^ produced ./ fShort-styled form, fertilised by"! " " \ own-form pollen, produced ./ Pulmonaria 156 69 25 52 14 11 45 13 75 24 20 270 CONCLUDING EEMAKKS CiiAP. VL Table 37. Nature of the Offsprin;j/rom Illegitimately fertilised Trimorphic Plants. Number of Long- styled Number ' Number of Miinn. Soc.' vol. xiii. p. 599. Journal of Science,' Nov. 1862, Dr. Dickie, 'Journal Linn. Soc. p. 419, and 'Prarent pollen-grains. These emitted their tubes in the usual manner. The three other stamens bore very minute rudimentary anthers, one of which was generally larger than the other two, but none of them contained any pollen. In one instance, however, a single cell of the larger rudimentary anther in- cluded a little pollen. The style consists of a short •flattened tube, somewhat expanded at its upper end, and this forms an open channel leading into the ovarium, as described under V. canina. It is slightly bent towards the two fertile anthers. Viola Roxhurghiana. — This species bore in my hot- house during two years a multitude of cleistogamic flowers, which resembled in all respects those of the 320 CLEISTOGAMIC FLOWERS. Chap. VIII. last species ; but no perfect ones were produced. Mr. Scott informs me that in India it bears perfect flowers only during the cold season, and that these are quite fertile. During the hot, and more especially during the rainy season, it bears an abundance of cleisto- gamic flowers. ]\Iany other species, besides the five now described, produce cleistogamic flowers ; this is the case, accord- ing to J). Miiller, Michalet, Von Mohl, and Hermann Miiller, with V. elatior, lancifolia, sylvatica, palustris, mirahilis, hicolor, ionodium, and hijlora. But V. tricolor does not produce them. Michalet asserts that V. palusiris produces near Paris only perfect flowers, which are quite fertile ; but that when the plant grows on mountains cleistogamic flowers are produced ; and so it is with V. hijlora. The same author states that he has seen in the case of V. alba flowers intermediate in structure between the perfect and cleistogamic ones. According to M. Boisduval, an Italian species, V. Bup^ii, never bears in France " des fleurs bien apparentes, ce qui ne I'em- peche pas de fructifier." It is interesting to observe the gradation in the abortion of the parts in the cleistogamic flowers of the several foregoing species. It appears from the statements by D. Miiller and Von Mohl that in V. mi- rahilis the calyx does not remain quite closed ; all five stamens are provided with anthers, and some pollen- grains probably fall out of the cells on the stigma, instead of protruding their tubes whilst still enclosed, as in the other species. In V. hirta all five sta- mens are likewise antheriferous ; the petals are not so much reduced and the pistil not so much modified as in the following species. In V. nana and elatior only two of the stamens properly bear anthers, but Chap. VIII. ' OXALIS. 321 sometimes one or even two of the others arc thns pro- vided. Lastly, in V. eanina never more than two of the stamens, as far as I have seen, bear anthers ; the petals are much more reduced than in V. hirta, and according to D. Miiller are sometimes quite absent. Oxalis acetoseUa. — The existence of cleistogamic llowers on this plant was discovered by Michalet.* They have been fully described by Von Mohl, and I can add hardly anything to his description. In my specimens the anthers of the five longer stamens were nearly on a level with the stigmas ; whilst the smaller and less plainly bilobed anthers of the five shorter stamens stood considerably below the stigmas, so that their tubes had to travel some way upwards. Ac- cording to Michalet these latter anthers are some- times quite aborted. 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 inter- mediate condition between the two kinds. In one of these the pollen-tubes from the lower anthers had reached the stigmas, though the flower was open. The footstalks of the cleistogamic flowers are much shorter than those of the perfect flowers, and are so much bowed downwards that they tend, according to Von ]\[ohl, to bury themselves in the moss and dead leaves on the ground. ]\richalet also says that they are often hypogean. In order to ascertain the num- ber of seeds produced by these flowers, I marked eight of them ; two failed, one cast its seed abroad, and the * 'Bull. Soc. Bot. de France,' torn. vii. 1860, p. 4G5. 322 CLEISTOGAMIC FLOWERS. Cuap. VIII. remaining five contained on an average 10*0 seeds per capsnle. This is rather above the average 9*2, which eleven capsules from perfect flowers fertilised with their own pollen yielded, and considerably, above the average 7*9, from the capsules of perfect flowers fertilised with pollen from another plant; but this latter result must, I think, have been accidental. Hildebrand, whilst searching various Plerbaria, ob- served that many other species of Oxalis besides 0. acetosella produce cleistogamic flowers;* and I hear from him that this is the case with the heterostyled trimorphic 0. incarnata from the Cape of Good Hope. Oxalis {Biopliytum) sensitiva. — This plant is ranked by many botanists as a distinct genus, but as a sub- genus by Bentham and Hooker. Many of the early flowers on a mid-styled plant in my hot-house did not open properly, and were in an intermediate condition between cleistogamic and perfect. Their petals varied from a mere rudiment to about half their proper size ; nevertheless they produced cajisules. I attributed their state to unfavourable conditions, for later in the season fully expanded flowers of the proper size ap- peared. But Mr. Thwaites afterwards sent me from Ceylon a number of long-styled, mid-styled, and short- styled flower-stalks preserved in spirits; and on the same stalks with the perfect flowers, some of which were fully expanded and others still in bud, there were small bud-like bodies containing mature pollen, but with their calyces closed. These cleistogamic flowers do not differ much in structure from the perfect ones of the corresponding form, with the exception that their petals are reduced to extremely minute, barely visible scales, which adhere firmly to the rounded ♦ ' Monatsbericht dcr Akad. dcr Wiss. zu Berlin,' 186(3, p. :]69. Chap. VIII. OXALIS. 323 bases of the shorter stamens. Their stigmas are much less papillose, and smaller iu about the ratio of 13 to 20 divisions of the micrometer, as measured trans- versely from apex to apex, than the stigmas of the perfect flowers. The styles are furrowed longitudinally, and are clotlied with simple as well as glandular hairs, but only in the cleistogamic flowers produced by the long-styled and mid-styled forms. The anthers of the longer stamens are a little smaller than the correspond- ing ones of the perfect flowers, in about the ratio of 11 to 14. They dehisce properly, but do not appear to contain much pollen. Many pollen-grains were attached by short tubes to the stigmas ; but many others, still adhering to the anthers, had emitted their tubes to a considerable length, without having come in contact with the stigmas. Living plants ought to be examined, as the stigmas, at least of the long-styled form, project beyond the calyx, and if visited by insects (which, however, is very improbable) might be fertilised with pollen from a perfect flower. The most singular fact about the present species is that long-styled cleistogamic flowers are produced by the long-styled plants, and mid-styled as well as short-styled cleistogamic flowers by the other Jtwo forms ; so that there are three kinds of cleistosramic and three kinds of perfect flowers produced by this one species ! Most of the heterostyled species of Oxalis are more or less sterile, many absolutely so, if illegitimately fertilised with their own-form pollen. It is therefore probable that the pollen of the cleisto- gamic flowers has been modified in power, so as to act on their own stigmas, for they yield an abundance of seeds. We may perhaps account for the cleistogamic flowers consisting of the three forms, through the prin- ciple of correlated growth, by which the clcistogamio 82-1 CLEISTOGAMIC FLOWERS. Chap. VIII flowers of the double violet have been rendered double. Vandellia nummular if oUa. — Dr. Kulm has collected* all the notices with respect to cleistogamic flowers in this genus, and has described from dried specimens those produced by an Abyssinian species. Mr. Scott sent me from Calcutta seeds of the above common Indian weed, from which many plants were success- ively raised during several years. The cleistogamic flowers are very small, being when fully mature under Jq of an inch (1 • 27 mm.) in length. The calyx does not open, and within it the delicate transparent corolla remains closely folded over the ovarium. There are only two anthers instead of the normal number of four, and their filaments adhere to the corolla. The cells of the anthers diverge much at their lower ends and are only y^Q of an inch ( • 181 mm.) in their longer diameter. They contain but few pollen-grains, and these emit their tubes whilst still within the anther. The pistil is very short, and is surmounted by a bilobed stigma. As the ovary grows the two anthers together with the shrivelled corolla, all attached by the dried pollen- tubes to the stigma, are torn off and carried upwards in the shape of a little cap. The perfect flowers gene- rally appear before the cleistogamic, but sometimes simultaneously with them. During one season a large number of plants produced no perfect flowers. It has been asserted that the latter never yield capsules ; but this is a mistake, as they do so even when insects are excluded. Fifteen capsules from cleistogamic flowers on plants growing under favourable conditions con- tained on an average 64 • 2 seeds, with a maximum of 87; whilst 20 capsules from plants growing much ' Bot. Zeitung,' 1867, p. 65. Chap. YIII. ONONIS. 325 crowded yj jlded an average of only 48. Sixteen cap- sules from perfect flowers artificially crossed with pollen from ar other plant contained on an average 93 seeds, with it maximum of 137. Thirteen capsules from self- fertilised perfect flowers gave an average of 62 seeds, with a maximum of 135. Therefore the capsules from the cleistogamic flowers contained fewer seeds than those from perfect flowers when cross-fertilised, and slightly more than those from perfect flowers self- fertilised. Dr. Kuhn believes that the Abyssinian V. sessifiora does not differ specifically from the foregoing species. But its cleistogamic flowers apparently include four anthers instead of two as above described. The plants, moreover, of F. sessijlora produce subterranean runners which yield capsules ; and I never saw a trace of such runners in V. nummular if olia, although many plants were cidtivated. Linaria sjniria. — Michalet says* that short, thin, twisted branches are developed from the buds in the axils of the lower leaves, and that these bury them- selves in the ground. They there produce flowers not offering any peculiarity in structure, excepting that their corollas, though properly coloured, are de- formed. These flowers may be ranked as cleistogamic, as they are developed, and not merely drawn, beneath the ground. Ononis columnse. — Plants were raised from seeds sent me from Northern Italy. The sepals of the cleisto- gamic flowers are elongated and closely pressed to- gether ; the petals are much reduced in size, colour- ess, and folded over the interior organs. The fila- ments of the ten stamens are united into a tube, and * • Bull. Soc. Bot. de France,' torn, vii. 18G0, p. 4G8. 326 CLEISTOGAMIC FLOWERS. Chap. VIII. this is not the case, according to Von Mol 1, with the cleistogamic flowers of other Leguminosa?. Five of the stamens are destitute of anthers, and alterrnvte with the five thus provided. The two cells of the anthers are minute, rounded and separated from one anotiier by connective tissue ; they contain but few pollen- grains, and these have extremely delicate coats. The pistil is hook-shaped, with a plainly enlarged stigma, which is cuided down, towards the anthers ; it there- fore differs much from that of the perfect flower. During the year 1867 no perfect flowers were pro- duced, but in the following year there were both perfect and cleistogamic ones. Ononis minutissima. — My plants produced both per- fect and cleistogamic flowers ; but 1 did not examine the latter. Some of the former were crossed with pollen from a distinct plant, and six capsules thus ob- tained yielded on an average 3 • 66 seeds, with a maxi- mum of 5 in one. Twelve perfect flowers were marked and allowed to fertilise themselves spontaneously under a net, and they yielded eight caj)sules, containing on an average 2*38 seeds, with a maximum of 3 in one. Fifty-three capsules produced by the cleistogamic flowers contained on an average 4"1 seeds, so that these were the most productive of all ; and the seeds themselves looked finer even than those from the crossed perfect flowers. According to Mr. Bentham 0. 2)arviflora likewise bears cleistogamic flowers ; and he informs me that these flowers are produced by all three species early in the spring ; whilst the perfect ones appear afterwards, and therefore in a reversed order compared with those of Viola and Oxalis. Some of the species, for instance Ononis eolumnas, bear a fresh crop of cleistogamic flowers in the autumn. Lathjrus nissolia apparently offers a case of the first Chai-. VIII. IMPATIENS. 327 stage in the production of cleistogamic flo\^ers, for on plants growing in a state of nature, many of the flowers never expand and yet produce line pods. Some of the buds are so large that they seem on the point of expansion ; others are much smaller, but none so small as the true cleistogamic flowers of the foregoing species. As I marked these buds with thread and examined them daily, there cuidd be no mistake about their producing fruit without having expanded. Several other Leguminous genera produce cleisto- gamic flowers, as may be seen in the previous list ; but much does not appear to be known about them. Yon Mohl says that their petals are commonly rudimentary, that only a few of their anthers are developed, their filaments are not united into a tube and their pistils are hook-shaped. In three of the genera, namely Yicia, Amphicarpaea, and Voandzeia, the cleistogamic flowers are produced on subterranean stems. The perfect flowers of Voandzeia, which is a cultivated plant, are said never to produce fruit ;* but we should remember how often fertility is affected by cultivation. Impatiens fuha. — Mr. A- W. Bennett has published an excellent description, with figures, of this plant.f He shows that the cleistogamic and perfect flowers differ in structure at a very early period of growth, so that the existence of the former cannot be due merely to the arrested development of the latter, — a conclusion which indeed follows from most of the previous de- scriptions. j\Ir. Bennett found on the banks of the Wey that the plants which bore cleistogamic flowers alone were to those bearing perfect flowers as 20 to 1 ; but * Correa de Mello ('Journal African plant, which is sometimes Linn. See. Bot.' vol. xi. 1870, p. cultivated in Brazil. 254) particularly attended to the f ' Journal Linn. See. Bot.' vol liowering and fruiting of this xiii. 1872, p. 147. 15 328 CLEISTOGAMIC FLOWERS. CiiAV. Till. we should remember that this is a naturalised species. The perfect flowers are usually barren in England ; but Prof. ^\sa Gray writes to me that after midsummer in the United States some or many of them ])roduce capsules. Impatiens noli-me-iangere. — I can add nothing of im- portance to Von IMohl's descrijjtion, excepting that one of the rudimentary petals shows a vestige of a nectary, as Mr. Bennett likewise found to be the case with I. fulva. As in this latter species all five stamens produce some jxjllen, though small in amount ; a single anther contains, according to Yon Mohl, not more than 50 grains, and these emit their tubes while still enclosed within it. The pollen-grains of the perfect flowers are tied together by threads, but not, so as far as I could see, those of the cleistogamic flowers ; and a provision of this kind would here have been useless, as the grains can never be transported by insects. The flowers of I. hahamina are visited by himible-bees,* and I am almost sure that this is the case with the perfect flowers of I. noli-me-tangere. From the perfect flowers of this latter species covered with a net eleven spontaneously self-fertilised capsules were produced, and these yielded on an average 3 • 45 seeds. Some perfect flowers with their anthers still containing an abundance of pollen were fertilised with pollen from a distinct plant ; and the three capsules thus produced contained, to my surprise, only 2, 2, and 1 seed. As I. hahamina is proterandrous, so probably is the pre- sent species ; and if so, cross-fertilisation was eifected by me at too early a period, and this may account for the capsules yielding so few seeds. Drosera rotundifolia, — The first flower-stems which * H. Miiller, 'Die BefrucLtung,' &c. p. 170 Chap. VIII. CLEISTOGAMIC FLOWERS. 329 were thrown up by some plants in my green-house bore only cleistogamic flowers. The petals of small size remained permanently closed over the repro- ductive organs, but their white tips could just be seen between the almost completely closed sepals. The pollen, which was scanty in amount, but not so scanty as in Viola or Oxalis, remained enclosed within the anthers, whence the tubes proceeded and penetrated the stigma. As the ovarium swelled the little withered corolla was carried upwards in the form of a cap. These cleistogamic flowers produced an abundance of seed. Later in the season perfect flowers appeared. With plants in a state of nature the flowers open only in the early morning, as I have been informed by Mr. AVallis, who particularly attended to the time of their flowering. In the case of D. Anglica, the still folded petals on some plants in my green- house opened just sufficiently to leave a minute aperture ; the anthers dehisced properly, but the pollen-grains adhered in a mass to them, and thence omitted their tubes, which penetrated the stigmas. These flowers, therefore, were in an intermediate con- dition, and could not be called either perfect or cleistogamic. A few miscellaneous observations may be added with respect to some other species, as throwing liglit on our subject. Mr. Scott states * that Eranthemum amhiguum bears three kinds of flowers, — large, con- spicuous, open ones, which are quite sterile, — others of intermediate size, which are open and moderately fertile — and lastly small closed or cleistogamic ones, which are perfectly fertile. Ruellia tuberosa, likewise one of the Acanthacefe, produces both open and cleis- • 'Journal of Botany,' Loudoii, new scries, vol. i. 1872, pp. lGl-4. 330 CLEISTOGAMIC FLOWERS. Chap. VIII. togamic flowers ; tlic latter yield from 18 to 24, ^vllilst the former only from 8 to 10 seeds ; these two kinds of flowers are produced simultaneonsly, whereas in several other members of the family the cleistogamic ones appear only during the hot season. According to Torrey and Gray, the North American species of He- lianthemum, when growing in poor soil, produce only cleistogamic flowers. The cleistogamic flowers of Speeularia 'perfoliata are highly remarkable, as they are closed by a tympanum formed by the rudi- mentary corolla, and without any trace of an open- ing. The stamens vary from 3 to 5 in number, as do the sepals.* The collecting hairs on the pistil, which play so important a part in the fertilisation of the perfect flowers, are here quite absent. Drs. Hooker and Thomson state f that some of the Indian species of Campanula produce two kinds of flowers ; the smaller ones being borne on longer peduncles with differently formed sepals, and producing a more globose ovary. The flowers are closed by a tym- panum like that in Speeularia. Some of the plants produce both kinds of flowers, others only one kind ; both yield an abundance of seeds. Professor Oliver adds that he has seen flowers on Campanula colorata in an intermediate condition between cleistogamic and perfect ones. The solitary almost sessile cleistogamic flowers pro- duced by Monoclioria vaginalis are differently protected from those in any of the previous cases, namely, within " a short sack formed of the membranous spathe, * Von Mohl, 'Bot. Zeitung,' of the iierfect flower is mostly 1863, pp. 314 and 323. Dr. Brom- 5-cleft. field (' Phytologist,' vol. iii. p. t ' Journal Linn. Soc' vol. ii. 530) also remarks that the calyx 1857, p. 7. See also Professor of the cleistogamic flowers is Oliver in 'Nat. Hist. Review, usually only 3-cleft, while that 1862, p. 210. Chap. VIII. CLEISTOGAMIC FLOWERS. 331 without any opening or fissure." There is only a single fertile stamen ; the style is almost obsolete, with the three stigmatic surfaces directed to one side. Both the perfect and cleistogamic flowers produce seeds.* The cleistogamic flowers on some of the Mal- pighiaceae seem to be more profoundly modified than those in any of the foregoing genera. According to A. de Jussieuf they are difierently situated from the perfect flowers ; they contain only a single stamen, instead of 5 or 6 ; and it is a strange fact that this particular stamen is not developed in the perfect flowers of the same species. The style is absent or rudimentary ; and there are only two ovaries instead of three. Thus these degraded flowers, as Jussieu remarks, " laugh at our classifications, for the greater number of the characters proper to the species, to the genus, to the family, to the class disappear." I may add that their calyces are not glandular, and as, according to Kerner,| the fluid secreted by such glands generally serves to protect the flowers from crawling insects, which steal the nectar without aiding in their cross-fertilisation, the deficiency of the glands in the cleistogamic flowers of these plants may perhaps be accounted for by their not requiring any such protection. As the Asclepiadous genus Stapelia is said to pro- duce cleistogamic flowers, the following case may be worth giving. I have never heard of the perfect flowers of Soya carnosa setting seeds in this country, but some capsules were produced in Mr. Farrer's hot-house ; * Dr. Kirk, ' Journ. Linn. Soc. J 'Die ScliutzmittclflcTBliitheu vol. viii. 18G4, p. 147. gcgen unberufone Gii-ste,' 1876, t ' Archives du Mu.seuni,' torn. p. 25. iii. 1 843, pp. 35-38, 82-8G, 58'J, 5&8. 332 CLEISTOGAMIC FLOWERS. Cum- VIIT. and the gardener detected that they were the product of minute bud-like bodies, three or four of which could sometimes be found on the same umbel with the perfect flowers. They were quite closed and hardly thicker than their peduncles. The sepals presented nothing particular, but internally and alternating with them, there were five small flattened heart-shaped papillae, like rudiments of petals ; but the homological nature of which appeared doubtful to Mr. Bentham and Dr. Hooker. No trace of anthers or of stamens could be detected ; and I knew from ha^dng examined many cleistogamic flowers what to look for. There were two ovaries, full of ovules, quite open at their upper ends, with their edges festooned, but with no trace of a proper stigma. In all these flowers one of the two ovaries withered and blackened long before the other. The one perfect capsule, 3J inches in length, which was sent me, had likewise been de- veloped from a single carpel. This capsule con- tained an abundance of plumose seeds, many of which appeared quite sound, but they did not germinate when soAvn at Kew. Therefore the little bud-like flower which produced this capsule probably was as destitute of pollen as were those which I examined. Juncus hufonius and Hordeum. — All the species hitherto mentioned which produce cleistogamic flowers are entomophilous ; but four genera, Juncus, Hordeum, Cryptostachys, and Leersia are anemophi- lous. Juncus hufonius is remarkable* by bearing in parts of Russia only cleistogamic flowers, which con- tain three instead of the six anthers found in the perfect flowers. In the genus Hordeum it has been * See Dr. Asclierson's interesting paper in ' Lot. Zeituug,' 1871, p. 551. CiiAP. VIII. LEERSIA. 333 shown by Delpino* that the majority of the flowers are cleistogamic, some of the othci's expanding and ap- parently allowing of cross-fertilisation. I hear from Fritz Miiller that there is a grass in Southern Brazil, in which the sheath of the uppermost leaf, half a metre in length, envelopes the whole panicle ; and this sheath never opens until the self-fertilised seeds are ripe. On the roadside some plants had been cut down, whilst the cleistogamic panicles were develop- ing, and these plants afterwards produced free or un- enclosed panicles of small size, bearing perfect flowers. Leersia oryzoides. — It has long been known that this plant produces cleistogamic flowers, but these were first described with care by M. Duval-Jouve.f I pro- cured plants from a stream near Reigato, and cultivated them for several years in my green-house. The cleis- togamic flowers are very small, and usually mature their seeds within the sheaths of the leaves. These flowers are said by Duval-Jouve to be filled by slightly viscid fluid ; but this was not the case with several that I opened ; but there was a thin film of fluid between the coats of the glumes, and when these were pressed the fluid moved about, giving a singularly deceptive appearance of the whole inside of the flower being tlius filled. The stigma is very small and the filaments extremely short ; the anthers are less than ^ of an inch in length or about one-third of the length of those in the perfect flowers. One of the three anthers dehisces before the two others. Can this have any relation with the fact that in some other * ' lioUcttiiu del Coniizio agra- on Honlfeum, in 'Monata^tTic.lit d. rio Parniense.' Marzo e Aprilc, K.Akad. Berlin,' Oct. 1872, p. 7G0, 1871. An abstract of this valuable f 'Bull. Bot. Soc. de Franco, paper ia given in ' Bot. Zeitung,' toin. x. 1863, p. 194. 1871, p. 5:^7. Sec uloo Ilildcbraud 334 CLEISTOGAMIC FLOWERS. Chap. VIII. species of Leersia only two stamens are fully de- veloped?* The anthers shed their pollen on the stigma ; at least in one instance this was clearly the case, and by tearing open the anthers under water the grains were easily detached. Towards the apex of the anther the grains are arranged in a single row and lower down in two or three rows, so that they could be wjunted ; and there were about 35 in each cell, or 70 in the whole anther ; and this is an astonishingly small number for an anemophilous plant. The grains have very delicate coats, are spherical and about yo^oo ^^ an inch ("OlSl mm.), whilst those of the perfect flowers are .about j^^o ^^ ^^ ^^^^ ('0254 mm.) in diameter. M. Duval- Jouve states that the panicles very rarely protrude from their sheaths, but that when this does happen the flowers expand and exhibit well-developed ovaries and stigmas, together with full-sized anthers containing apparently sound pollen ; nevertheless such flowers are invariably quite sterile. Schreiber had pre- viously observed that if a panicle is only half protruded, this half is sterile, whilst the still included half is fertile. Some plants which grew in a large tub of water in my green-house behaved on one occasion in a very different manner. They protruded two- very large much-branched panicles ; but the florets never opened, though these included fully developed stig- mas, and stamens supported on long filaments with large anthers that dehisced properly. If these florets had opened for a short time unperceived by me and had then closed again, the empty anthers would have been left dangling outside. Nevertheless they yielded on August 17th an abundance of fine ripe seeds. Here then we have a near approach to the Afia Gray, ' Manual of Bot. of United States,' 1856, p. 540. CuAP. VIII. LEERSIA. 335 single case as yet known* of this grass producing in a state of nature (in Germany) perfect flowers which yielded a copious supply of fruit. Seeds from the cleis- togamic flowers were sent by me to Mr. Scott in Calcutta, who there cultivated the plants in various ways, but they never produced perfect flowers. In Europe Leersia oryzoides is the sole representa- tive of its genus, and Duval-Jouve, after examining several exotic species, found that it apparently is the sole one which bears cleistogamic flowers. It ranges from Persia to North America, and specimens from Pennsylvania resembled the European ones in their concealed manner of fructification. There can there- fore be little doubt that this plant generally propa- gates itself throughout an immense area by cleisto- gamic seeds, and that it can hardly ever be invigorated by cross-fertilisation. It resembles in this respect those plants which are now widely spread, though they increase solely by asexual generation.! Concluding Remarks on Cleistogamic Flouers. — That these flowers owe their structure primarily to the arrested development of perfect ones, w^e may infer from such cases as that of the lower rudimentary petal in Viola being larger than the others, like the lower lip of the perfect flower, — from a vestige of a spur in the cleistogamic flowers of Impatiens, — from the ten stamens of Ononis being united into a tube, — and other such structures. The same inference may be drawn from the occurrence, in some instances, on the same plant of a series of- gradations between the cleistogamic and perfect flowers. But that the former owe their origin wholly to arrested development is * Dr. Asclierson, ' Bot. Zeitung,* cases in my ' Variation under 18G4, p. 350. Domestication,' ch. xviii. — 2u(l t i have collected several such edit, vol. ii. p. 153. 336 CONCLUDING REMAKKS CiiAr. Vm. by no means the case ; for various parts have been specially modified, so as to aid in the self-fertilisation of the flowers, and as a protection to the pollen ; for instance, the hook-shaped pistil in Viola and in some other genera, by which the stigma is brought close to the fertile anthers, — the rudimentary corolla of Specularia modified into a perfectly closed tympanum, and the sheath of ]Monochoria modified into a closed sack, — the excessively thin coats of the pollen-grains, — the anthers not being all equally aborted, and other such cases. Moreover Mr. Bennett has shown that the buds of the cleistogamic and perfect flowers of fmpatiens differ at a very early period of growth. The degree to Avhich many of the most important organs in these degraded flowers have been reduced or even wholly obliterated, is one of their most re- markable peculiarities, reminding us of many parasitic animals. In some cases only a single anther is left, and this contains but few pollen-grains of diminished size ; in other cases the stigma has disappeared, leaving a simple open passage into the ovarium. It is also interesting to note the complete loss of trifling points in the structure or functions of certain parts, which though of service to the perfect flowers, are of none to the cleistogamic ; for instance the collecting hairs on the pistil of Specularia, the glands on the calyx of the Malpighiaceae, the nectar-secreting ap- pendages to the lower stamens of Viola, the secretion of nectar by other parts, the emission of a sweet odour, and apparently the elasticity of the valves in the buried capsules of Viola odorata. We here see, as throughout nature, that . as soon as any part or character becomes superfluous it tends sooner or later to disappear. Another peculiarity in these flowers is that the CnAi'. VIII. ON CLEISTOGAMIC FLOWERS. 337 pollen-grains generally emit their tubes whilst still enclosed within the anthers ; but this is not so re- markable a fact as was formerly thought, when the case of Asclepias was alone know»n.* It is, however, a wonderful sight to behold the tubes directing them- selves in a straight line to the stigma, when this is at some little distance from the anthers. As soon as they reach the stigma or tlie open passage leading into the ovarium, no doubt they penetrate it, guided by the same means, whatever these may be, as in the case of ordinary flowers. I thought that they might be guided by the avoidance of light : some pollen-grains of a willow were therefore immersed in an extremely weak solution of honey, and the vessel was placed so that the light entered only in one di- rection, laterally or from below or from above, but the long tubes were in each case protruded in every possible direction. As cleistogamic flowers are completely closed tliey are necessarily self-fertilised, not to mention the absence of any attraction to insects; and they thus differ widely from the great majority of ordinary flowers. Delpino believes f that cleistogamic flowers have been developed in order to ensure the production of seeds- under climatic or other conditions which tend * Tlic case of Asclepias was de- pollen-masses whilst still within scribed by R. Brown. Baillon as- the anthers, in three widely distinct serts (' Adansonia,' torn. ii. 1SG2, Orchidean genera namely Aceras, p. 58) that with many plants tlie Malaxis, and Ncottia : see ' The tubes are emitted IVora pollen- Various Contrivances by which grains which have not come into Orchids are Fertilised,' 2nd edit. C(jntact with the stigma ; and that p. 2,58. they may be seen advancing hori- f ' Sull' Opera la Distribuzione zontally through the air towards del Sessi nolle Piante,' 1867, the stigma. I have observed the p. 30. emission of the tubes from tlie 338 CONCLUDING REMARKS Chap. VIIL to prevent the fertilisation of the perfect flowers. I do not doubt that this hokls good to a certain limited extent, but the production of a large supply of seeds with little consumption of nutrient matter or expenditure of vital force is probably a far more efficient motive power. The w hole flower is much reduced in size ; but w^hat is much more important, an extremely small quantity of pollen has to be formed, as none is lost through the action of insects or the weather ; and pollen contains much nitrogen and- phosphorus. Von Mohl estimated that a single cleistogamic anther-cell of Oxalis aceto- sella contained from one to two dozen pollen-grains ; we will say 20, and if so the whole flower can have produced at most 400 grains ; with Impatiens the whole number may be estimated, in the same manner at 250 ; with Leersia at 210 ; and with Viola nana at only 100. These figures are wonderfully low com- pared with the 243,600 pollen-grains produced by a flower of Leontodon, the 4,8G3 by an Hibiscus, or the 3,654,000 by a Pseony.* We thus see that cleisto- gamic flowers produce seeds with a wonderfully small expenditure of pollen ; and they produce as a general rule quite as many seeds as the perfect flowers. That the production of a large number of seeds is necessary or beneficial to many plants needs no evi- dence. So of course is their preservation before they are ready for germination ; and it is one of the many remarkable peculiarities of the plants which bear cleistogamic flowers, that an incomparably larger pro- portion of them than of ordinary plants bury their young ovaries in the ground ; — an action which it may be presumed serves to protect them from being * The authorities for these statements are given in my ' Effects of Cross and Self-Fertilisation,' p. 376. CuAi'. VIII. ON CLEISTOGAMIC FLOWERS. 339 devoured by birds or other enemies. But thi.s advan- tage is accompanied by the loss of the power of wide dissemination. No less than eight of the genera in the list at the beginning of this chapter include species which act in this manner, namely, several kinds of Viola, Oxalis, Yandellia, Linaria, Commelina, and at least tliree genera of Leguminosse. The seeds also of Leersia, though not buried, are concealed in the most perfect manner within the sheaths of the leaves. Cleistogamic flowers possess great facilities for burying their young ovaries or capsules, owing to their small size, pointed shape, closed condition and the absence of a corolla ; and we can thus understand how it is that so many of them have acquired this curious habit. It has already been shown that in about 32 out of the 55 genera in the list just referred to, the perfect flowers are irregular ; and this implies that they have been specially adapted for fertilisation by insects. Moreover three of the genera with regular flowers are adapted by other means for the same end. Flowers thus constructed are liable during certain seasons to be imperfectly fertilised, namely, when the proper insects are scarce ; and it is difiicult to avoid the belief that the production of cleistogamic flowers, which ensures under all circumstances a full supply of seed, has been in part determined by the perfect flowers being liable to fail in their fertilisation. But if this determining cause be a real one, it must be of subordinate importance, as four of the genera in the list are fertilised by the wind ; and there seems no reason why their perfect flowers should fail to be fertilisttd more frequently than those in any other anemophilous genus. In contrast with what we here see with respect to the large proportion of the perfect 340 CONCLUDING REMARKS Chap. VIII. flowers being irregular, one genus alone out of the 38 heterostyled genera described in the previous chapters bears such flo^yers ; yet all these genera are absolutely dependent on insects for their legitimate fertilisation. I know not how to account for this difference in the proportion of the plants bearing regular and irregular flowers in the two classes, unless it be that the hetero- styled flowers are already so well adapted for cross-fer- tilisation, through the position of their stamens and pistils and the difference in power of their two or three kinds of pollen, that any additional adaptation, namely, through the flowers being made irregular, has been rendered superfluous. Although cleistogamic flowers never fail to yield a large number of seeds, yet the plants bearing them usually produce perfect flowers, either simultaneously or more commonly at a different period ; and these are adapted for or admit of cross-fertilisation. From the cases given of the two Indian species of Viola, which produced in this country during several years only cleistogamic flowers, and of the numerous plants of Vandellia and of some plants of Ononis which behaved during one whole season in the same manner, it appears rash to infer from such cases as that of Salvia cleistogama not having produced perfect flowers during five years in Germany,* and of an Aspicarpa not having done so during several years in Paris, that these plants would not bear perfect flowers in their native homes. Von Mohl and several other botanists have repeatedly insisted that as a general rule the perfect flowers produced by cleistogamic plants are sterile ; but it has been shown under the head of the several species that this is not the case. The pe^'fect Dr. Astherson, ' Bot. Zeit.' 1871, p. 555. Chap. VIII. ON CLEISTOGAMIC FLOWERS. 341 flowers of Viola are indeed sterile unless they are visited by bees ; but when thus visited they yield the full number of seeds. As far as I have been able to discover there is only one absolute exception to the rule that the perfect flowers are fertile, namely, that of Voandzeia ; and in this case we should remember that cultivation often affects injuriously the repro- ductive organs. Although the perfect flowers of Leersia sometimes yield seeds, yet this occurs so rarely, as far as hitherto observed, that it practically forms a second exception to the rule. As cleistogamic flowers are invariably fertilised, and as they are produced in large numbers, they yield altogether a much larger supply of seeds than do the perfect flowers on the same plant. But the latter flowers will occasionally be cross-fertilised, and their offspring will thus be invigorated, as we may infer from a wide-spread analogy. But of such invigoration I have only a small amount of direct evidence : two crossed seedlings of Ononis minutissinia were put into competition with two seedlings raised from cleisto- gamic flowers ; they were at first all of equal height ; the crossed were then slightly beaten; but on the fol- lowing year they showed the usual superiority of their class, and were to the self-fertilised plants of cleisto- gamic origin as 100 to 88 in mean height. With Vandellia twenty crossed plants exceeded in height twenty plants raised from cleistogamic seeds only by a little, namely, in the ratio of 100 to 94. It is a natural inquiry how so many plants belong- ing to various very distinct families first came to have the development of their flowers arrested, so as ulti- mately to become cleistogamic. That a passage from the one state to the other is far from difficult is shown by the many recorded cases uf gradations between the 342 CONCLUDING REMARKS Ciiai'. VIII. two states on the same plant, in Viola, Oxalis, Biophy- tum. Campanula, &c. In the several species of Viola the various parts of the flowers have also been modified in very different degrees. Those plants which in their own country produce flowers of full or nearly full size, but never expand (as with Thelymitra), and yet set fruit, might easily be rendered cleistogamic. Lathy rus nissolia seems to be in an incipient transitional state, as does Vrosera Anglica, the flowers of which are not perfectly closed. There is good evidence that flowers sometimes fail to expand and are somewhat reduced in size, owing to exposure to unfavourable conditions, but still retain their fertility unimpaired. Linnaeus observed in 1753 that the flowers on several plants brought from Spain and grown at Upsala did not show any corolla and yet produced seeds. Asa Gray has seen flowers on exotic plants in the North- ern United States .which never expanded and yet fruited. With certain English plants, which bear flowers during nearly the whole year, Mr. Bennett found that those produced during the winter season were fertilised in the bud ; whilst with other species having fixed times for flowering, but " which had been tempted by a mild January to put forth a few wretched flowers," no pollen was discharged from the anthers, and no seed was formed. The flowers of Lysimachia vulgaris if fully exposed to the sun expand properly, while those growing in shady ditches have smaller corollas which open only slightly ; and these two forms graduate into one another in intermediate stations. Herr Bouche's observations are of esjDccial interest, for he shoAvs that both tcmjoerature and the amount of light affect the size of the corolla ; and he gives measurements proving that with some plants the corolla is diminished by the increasing cold and Chap. VIII. ON CLEISTOGAMIC FLOWERS. 343 darkness of the changing season, whilst with others it is diminished by the increasing heat and light.* The belief that the first step towards flowers being rendered cleistogamic was due to the conditions to which they were exposed, is supported by the fact of various plants belonging to this class either not pro- ducing their cleistogamic flowers under certain condi- tions, or, on the other hand, producing them to the complete exclusion of the. perfect ones. Thus some species of Viola do not bear cleistogamic flowers when growing on the lowlands or in certain districts. Other plants when cultivated have failed to produce perfect flowers during several successive years ; and this is the case with Juncus hufonius in its native land of Russia. Cleistogamic flowers are produced by some species late and by others early in the season ; and this agrees with the view that the first step towards their de- velopment was due to climate ; though the periods at which the two sorts of flowers now apj)ear must since have become much more distinctly defined. We do not know whether too low or too high a temperature or the amount of light acts in a direct manner on the size of the corolla, or indirectly through the male organs being first affected. However this may be, if a plant were prevented either early or late in the season from fully expanding its corolla, with some reduction in its size, but with no loss of the power of self-fertilisation, then natural selection might well complete the w^ork and * FortliestatciucntbyLinnicns, p. 543) "that when the autumn .sec Mohl in ' iint. Zcitung,' 18G3, draws en, and huLitiially in winter ]>. ii'J.7. Asa Cray, 'American for buch of our wild llowcrs as Journal of Science,' 2ud si-rics, Idossomatthatsiason," the flowers vol. xxxix. 18G5, p. lO.j. Bennett are self-fertilised. On Lysinia- in 'Nature,' Nov. I8G9, p. 11. chia, II. MiilUr. 'Nature,' Sept. The Ilcv. (r. Henslow also says 187;5, p. 43:5. Bi)uehe', 'Sitzungs- (' Gardener's Ghmnicle,' lS77, p. bcrieht dtr Gciseli. Naturforseh. 271 : also ' Nature,' Oct. VJ, l,s7G, Freundo ' Oct. 1874, p. 'JO. 344 GENERAL CONCLUSIONS. Chap. VIIL render it strictly cleistogamic. The various organs would also, it is probable, be modified by the peculiar conditions to which they are subjected within a com- pletely closed flower ; also by the principle of corre- lated growth, and by the tendency in all reduced organs finally to disappear. The result would be the production of cleistogamic flowers such as we now see them; and these are admirably fitted to yield a copious supply of seed at a wonderfully small cost to the plant. I will now sum up very briefly the chief conclusions which seem to follow from the observations given in this volume. Cleistogamic flowers afford, as just stated, an abundant supply of seeds with little ex- penditure ; and we can hardly doubt that they have had their structure modified and degraded for this special purpose ; perfect flowers being still almost al- ways produced so as to allow of occasional cross-fertilisa- tion. Hermaphrodite plants have often been rendered ■monoBcious, dicecious or polygamous ; but as the sepa- ration of the sexes would have been injurious, had not pollen been already transported habitually by in- sects or by the wind from flower to flower, we may assume that the process of separation did not com- mence and was not completed for the sake of the advantages to be gained from cross-fertilisation. The sole motive for the separation of the sexes which occurs to me, is that the j^roduction of a great number of seeds might become superfluous to a plant under changed conditions of life ; and it might then be highly beneficial to it that tlie same flower or the same indi- vidual should not have its vital powers taxed, under the struggle for life to which all organisms are sub- jected, by producing both polleii and seeds. With CiiAr. VIII. GENERAL CONCLUSIONS. 345 respect to the plants belonging to the gyno-dioecio^is sub-class, or those which co-exist as hermaphrodites and females, it has been proved that they yield a much larger supply of seed than they would have done if they had all remained hermaphrodites ; and we may feel sure from the large number of seeds pro- duced by many plants that such production is often necessary or advantageous. It is therefore probable that the two forms in this sub-class have been sepa- rated or developed for this special end. Various hermaphrodite plants have become hetero- styled, and now exist under two or three forms ; and we may confidently believe that this has been effected in order that cross-fertilisation should be assured. For the full and legitimate fertilisation of these plants pollen from the one form must be applied to the stigma of another. If the sexual elements belonging to the same form are united the union is an illegiti- mate one and more or less sterile. With dimorphic species two illegitimate unions, and with trimorphic species twelve are possible. There is reason to believe that the sterility of these unions has not been specially acquired, but follows as an incidental result from the sexual elements of the two or three forms having been adapted to act on one another in a particular manner, so that any other kind of union is inefficient, like that between distinct species. Another and still more remarkable incidental result is that .the seedlings from an illegitimate union are often dwarfed and more or less or completely barren, like hybrids from tlie union of two widely distinct species. ( 346 ) INDEX. ACANTHACE^. A. Acanthacex, 313 Acer campestre, 12, 308 Acloxa, 9 jJSgiphila elata, 123 mollis, 123 ohdurata, 124, 286 Alefuld, Dr., on Linum, 100 Alisma natans, 311 Amphicarpxa, 327 Amsinckia spectabilis, 110; varia- bility in length of stamens and pistil, 2G1, 266 Anchusa arvensis, 111 Androsace vitalliana, 53 Anthers, size of, in ditierent forms, 252 ; contabescent, 283 Arachis, 312 Arnebia hispidissima, 111 Ascherson, Dr., on Salvia cleisto- gaina, 313, 340 ; Juncus biifonius, 332 ; Leersia orijzoides, 335 Asclepias, 337 Ash, the common, 11 Asperula scoparia, 285 Axell on Primula stricta, 50 B. Biil)ington, Prof., on Primula elalior, 72 ; Stellaria graminea, 313 Baillon, emission of the tubes from l>ollen-graius, 337 I3elhf)mnie, M., on ray-florets, 6 JioniK^tt, A. W., on Impatiens fulva, 327 ; flowers fertilised whilst in tlie bud state, 342 Bentliam, Mr., on the differentiation of the sexes, 11 Bentham, Mr., on tho cleistogamic flowers of Ononis, 326 Boraginew, 101 Boreau on eowslip and primrose, 57 Borreria, 127 Bouche' on Pavonia, 313; effect of temperature and light on corolla, 342 Bouvardia leiantha, 135 Braun on Dracocephalum, 299 Breitenbach, \V., on Primula elatior, 34, 272 Bromfield, Dr., on jirimrose and ct)wslip, 57 ; Primula elatior, 73 ; Specularia perfoliuta, 330 Brown, Eobert, on sexual changes, 282 Buckwheat, the common, 111 Caltha pahistris, 13 Campanula colorata, 330 Cardamine amara, 307 Caspary, Prof., on llhamnus cathar- ticus, 294 Cnttleya, 313 Chamissoa, 292 Cinchona viicrantha, 134 Cleistogamic flowers, 310; list of genera, 312; on tlieir origin, 343 Cnicus acaulis, 307 palustris, 307 Coccocypgclum, 133 ; pulleu-grains of, 250 Coprosma, 285 Cordia, 117 ; pistil of, 253 Corolla, difference in size in the sexes of the same species, 307- 309 INDEX. 347 COBYDALIS. Corijdalis, 146 Corylus avt'Uayia, 10 Cowslip, the common, 14 ; short- nnd long-styled, 19-22, 56-71 Cratojeylon formosum, 123 Crocker, C. W., on Plantago lanceo- lata, 306 Cryptosfachtjs, 313, 332 Cuphea purpurea, 168 Darwin, Charles, on reproductive organs under cultivation, 7; in- tercrossed plants, 30 ; prepotency of pollen, G2 ; insects fertilising flowers, 79 ; Cejihnlanthera gran- diflora, 9S ; Epklendron and Cat- tleya, 313; number of poUcn- gruins, 338 • , W., on Pulmonaria angusti- folia, 105, 107 Datura arhorea, 251 Delpino, plants fertilised by the wind, 10; on the walnut, 10; Fohjgomicex, 114; pollen-grains, 250 ; Thymus serpyllum, 299 ; ch'sed or cleistogamic flowers, 311, 337 ; Viola odurata, 317 Dianthus bitrhatus, 30 Dickie, Dr., on Erioyhoruiii angu»ti- foli'im, 307 Dictamnus fraxinclla, 146 JJiudia, 135 Dioecious and sub-ditecious plants, 287 Discospermum, 286 Duubleday, H., on Frimula elatior, 73 Dracocephalum Moldavicum, 299 Drosera Anglica, 329, 342 rotundifoUa, 328 Duval-Jouve, M., on Cryptonlachys, 313; Leersia oryzoides, 333, 334 Dyer, ThLselton, on Salvia Ilor- minum, 8 ; Cratoxylon formosum, 123 E. Echium vulgare, HI, 305, 307 Epidendron, 313 Epigxa repens, 297 Eranthemum amhigutim, 329 Erioplwrum anguxti/olinm, 307 Erytliroxylum, 121 ; pollen-grains of, 250 Euomjmus Europxus, 287-293 Euphrasia officinalis, 4 Euryale, 311 F. Faramca, 128 ; pollen-grains of, 129 Fitzgerald, Mr., on Thelymitra, 313 Forsythia suspensa, 117; stamens, 252 viridissima, 117 Fragaria Chiloensis, 293 elatior, 293 vesca, 293 Virginiana, 293 Fruxiaus excelsior, 1 1 G. Galium cruciatum, 2S6 Gartner on the sterility of unions between distinct species, 29 ; Pri- mida vulgaris and veris, 58, 59 ; hybrid Verhascums, 76, 77, 80 ; jirepotency of pollen, 241 ; varia- tion in the sexual powers of plants, 267 ; contabesceut anthers, 193, 283 Gentianex, 115 Geraniacae, 169 Geranium sylvaticum., 308 Gesneria penduUna, 261 Gilia aggregata, 118 coronopifolia, 119 • — — micrantha, 119 nudiraulis, 1 1 9 pulchella, 118 Gillibert on Menyanthes, 311 Gloriosa Lilj% tlie, 146 Godron on iiybrid Primulas, 55 Gray, Prof. Asa, proposes the term heterogone or heterogonous, 2 ; on Linum, 101 ; Leucosmia Bur- neitiana and acuminata, 114 ; Forsythia su^penm, 117; Gilia pulchella, 118; G. coronopifolia, 348 INDEX. GYNO-DIOSCIOCS. 119; I'Moz snlmlata, 119; Mit- chella repens, 125 ; lieterostyleil plants, 24-1 ; Coprosma, 285 ; Eu- ottymus, 287 ; Bliamnus lanceo- hiius, 295, 29G ; Epigxa repens, 297 ; Ilex opaca, 298 ; PUintago media, 31 17; Oxybaphus and Nyrta- ginia, 313; Impatlensfulva, 328; Leersia, 334 ; cleistogamic flowers, 342 Gyno-dioecious plants, 298 Hai't, Mr., on Nepeta glechoma, 301 Hautbois Strawberry, the, 293 Hedyotis, 133 Henslow, Rev. Prof., on hybrid Pri- mxdx, 61 Henslow, Kev. G., on flowers self- fertilised during the winter, 343 Herbert, Dr., on hybrid Primulx, 61 Heterostyled plants, illegitimate off- spring of, 188-243; essential cha- racter of, 244 ; sunnnary of the differences of fertility between legrtimately and illegitimately fer- tilised plants, 246; diameter of pollen-grains, 249 ; size of anthers, struetm-e of stigma, 252; list of genera, 255 ; advantages derived from Heterostylism, 258 ; means by which plants became hetero- styled, 260 ; transmission of form, 268 ; equal-styled varieties, 272 ; final remarks, 275 dimorphic i)lanta, 14-54, 81- 136 trimor])luc plants, 137-187 Jlihhcus, pollen-grains, 338 Hildebrand, Prof., introduces the word " heterostyled," 2 ; on the ray-florets of the ComponUe, 5, 6 ; Primula Sinensi.", 38, 40-43, 192, 217 ; Linum grandijlorum, 86, 87 ; L. perenne, 92 ; Pulmonaria offi- cinalis, 101-103, 107, 239; P. azurea, 110; Polygonum fagopij- rum. 111; Oxalis, 169, 171-174, 178, 182, 211-213, 322; henna- l)hrodite plants becoming uni- sexual, 283 ; Uordeum, 333 Homostyled .species of Primula, 49 Hooker, Dr., on Campanula, 330 Hordeum, 332 Hottunia inflata, 53, 313 palustris, 50 ; relative fertility, 52; anthers of, 252; papilla} on stigma, 254 Houstouia ccerulea, 132, 254 Hoy a carnosa, 331 Hybrid Primulas, 55-71 Hydrangea, 6, 7 HypericincK, 123 Hyssojms officinalis, 299 Hex aqnifuUum, 297 opaca, 298 Illegitimate offspring of heterostyled plants, 188; Lythrum salicaria, dwarfed stature and sterility, 192 ; Oxalis, transmission of form to seedlings, 212 ; Primula Sinensis, in some degree dwarfed, 215; equal-styled varieties, 218-223; Primula vulgaris, 224 ; ti'ans- mission of form and colour, 225 ; seedlings, 227; P. veris, 228; dwarfed stature and sterility, 229-234; equal-styled varieties, 234, 238 ; parallelism between illegitimate fertilisation and hy- bridism, 242 Hlecebrum, 311 Impatiens, pollen-grains of, 338 halsamina, 328 fulva, 327 noli-me-tangere, 328 J. Juglans regia, 10 Juncus bujfonius, 332, 343 Jussieu, A. de, on Malpighiacew, 331 E. Kerner, Prof., on ray-florets, 6 ; Atiri- cula, 43 ; hybrid forms of Prtmuia, 55, 73 ; on use of hairs within INDEX. M9 tlie corolla, 128; size of corolla in male flowers, 309 ; use of glauds as a protectiiin to flowers, HlU Kiik. Dr , on Moiwchoria vatjiualis, 331 Kuoxia, 135 Koch on Primula longijlora, 50 Kraschenviihou'ia, 312 Kulm. Dr., on cleistogamic flowers, 3, 310, 311; list of plants pro- duciji^ diftVrently formed seeds, 9 ; heterostyled plants, 244 ; Van- dtllia nummular i Julia, 324; V. sessiflora, 325 Lagerstrcemia Indica, 1G7 ' parvijiora, lUS reninx, 1G8 Lathyrus nissoUa, 326, 342 Leooq, H., on the common maple, 12; cowslips and primroses, 57; Primula elatior, 72 ; Idnum Aus- Iriacum, 98 ; Lythrum hyssopi- folia, 1G6; llhamnus, 2d6 ; gvno- diceeiuus jjlants, 209 ; Scubioaa gticcisa, 305 ; Viola odorata, 317 Leersia oryzoides, 333-335 ; pollen- grains of, 338 Leggett, Mr., Poutederia cordata, 187 Legitimate unions, summary on the fertility of the two, compared with that of the two illegitimate in Pri- mula, 46-49 ; fertility of, com- pared with illegitimate, 246 Lcighton, Kev. W. A., on the cow- slip and primrose, 56; Verhascum virgatum, 78 Leoiitodon, pollen-grains, 338 Li' idosiphon, 119 Lt'ucosmia acuminata, 114 Burnettiana, 1 14 ; stigma, 253 Lily, the Gloriosa, 146 Liiiinaidhemum Indicum, 116; pol- len-grains, 250 ; aiithers, 252 lAnaria spuria, 325 Lindley on Fragaria elatior, 293 Linnajus on Primula veris, vulgaris, and elatior, 56 Linum anguslifolium. 100 MENYANTHE8. Linum Austriacum, 97 catharticum, 100 corymhi/erum, 100 flavum, 81, 98 ; stamens, 252 grand ifliirum, 81 •, various ex- periments, 87-89, 96 ; pistils and stamens, 253, 254 ; sterile with its own-form pollen, 264, 266 Leicisii, 101 perenne, 90 ; torsion of the styles, 95 ; long-styled form, 97 ; stigma, 247 salsoloides, 100 trigynum, 100 usitatisK/inum, 100 Lipostoma, 134 Lysimachia vulgaris, 4, 342 Lythrum Grxfferi, 165 hyssopi/olia, 166 salicaria, 116, 137; power of mutual fertilisation between the three forms, 149-157; summary of results, 157-165; illegitimato offspring from the tliree forms, 191-203 ; concluding remarks on, 203-211; mid-styled form, 241, 257, 258, 280 ; seeds, 248 thym/folia, 165 M. M(dpighiacex, 331 Manettia hiculor, 135 Maple, the common, 12 Marshall, W., on Prirrmla elatior, 73 ; Phmtago lanceolata, 306 blasters. Dr. Maxwell, on cleisto- gamic flowers, 3 Maximowicz on Krascheninihowia, 312 Meehan, Mr., on Mitchella, 285 ; Epigsea repens, 297 Melissa clinipodium, 299 officinalis, 299 Mello, Correa de, on Amrlii>','M'l; Voandzeia. 327 Mentha aquatica, 209 hirsuta, 298 vulgaris, 298 Mcnyauthes, 311 trIfoUuta, 115 350 INDEX. Blichalet on Oxnlis acetosella, 321 ; Linaria spuria, 325 Milchella, 285 re pens, 125 Mohl, H. von, on the common cowslip, 14 ; size of corolla in the eexcd of Ihe same species, 307, 308; TrifoUum and Arachis, 312 ; clcifitoL^amic flowers, 314, 342 ; (Knilin aretoscUa, 321 ; Impatiens noli-me-tangere, 320 ; Specularia ■perfuliata, 330 Mollia Icpidota, 168 speciosa, 168 Monnier, M., on Viola, 318 Monochoria vaginalis, 330 Mulberry, the, 10 Miiller, 1)., on Viola canina, 314 Miiller, Fritz, on pollen of the Vil- larsia, 116; Faramea, 128-130; Fosoqueria fra/jrans, 131 ; Nesxa, 167 ; Oxalis, 180, 181 ; Pontederia, 183-185; Oxalis Fegnelli, 212; Chamis^oa, 292 Jliilier, H., on the frequency of visits by insects to the Umhelli- ferx and Composita', 5 ; on dicho- gamy, 10 ; on Antlmpliora and FomLylius sucking the cowslip, 22 ; Primula elatior, 32 ; P. villosa, 49; Hottonia palustris, 51 ; table of relative fertility of, 52, 53 ; Linuin catlmrticum, 100 ; Poly- gonum fagopyrum, 113; Lythrum mlicaria, 145 ; on the origin of lietero.stylism, 263; on the La- hintx. 299, 304 ; Thymus serpyUum, 300; Scahiosa arvensis, 305 ; Plan- tago laneeolata, 306; size of co- rolla in the two sexes of the same species, 308; Impatiens balsa- mina, 328 ; Lysimachia, 343 3J)/osoP!/rum, 111, 23U; pollen- graius, 251 PoiUfderia, 183 ; pollen-grains, 18G ; size of anthers, 2r)2 cordata, 187 Posoqueria fragrans, 1 3 1 Primrose, the common, 34, 57-71 Pn'iaula, the, lu-terostylcd species of, 14 ; summary on, 45-49 ; homo- styled species 49 auricula, 30, 43, 48, 74. 223 equal-styled varieties, 273 cortugnides, 44 data, 49 elatior, Jacq., 32 ; relative fer- tility of tlie two forms, 33, 47 ; not a hyhrid, 72, 73 ; equal-styled var. of, 224, 273 fariniisa, 45 ; equal-styled var., 224, 273 h'rsnta, 74 iHvolnerata,i5 loiuiijioru, 50 mollis, 49. 50 Scutica, 49, 50 Sihirica, 49 Sihliimensh, 44, 47 Sinemis, 22, 30, 38 : relative fertility. 39-43, 47, 49; long- style. ^\i>jpjoj^TOjsr ^ CO. 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