6 Ss Se yt eee Reb drt) May ete addide mutes eee Ly poe Noereh eae Saher ete RAR > oe anes a 2 ed Sera Wishetee vo on So Ya toma Go en 2 sony tener ser npbnathangeed yy wee 6 LZELCOSO LOZL € | ADATIOO S.1TAVHOIW “LS SO ALISHSAINN ces A Ct Digitized by the Internet Archive in 2007 with funding from Microsoft Corporation http://www.archive.org/details/differentformsof00darwuoft . THE DIFFERENT FORMS OF - FLOWERS ON PLANTS OF THE SAME SPECIES BY CHARLES DARWIN, M.A., F.R.S. WITH ILLUSTRATIONS NEW YORK D. APPLETON AND COMPANY 1897 TO ~ PROFESSOR ASA GRAY _ =x “THIS VOLUME IS DEDICATED BY THE AUTHOR ir 5 —" - “ AS A SMALL TRIBUTE OF RESPECT AND AFFECTION, ae CONTENTS. — Iprropucriox we NSS! ee aw ee eet aot, qe) Pega dels GQHAPTER IL HETEROSTYLED DimorpHic PLANTS: PRIMULACEZ. Primula veris or the Cowslip—Differences in 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—Androsace Vitalliana pare ee NON Maer ced: Ciel. ced: Se” tee: “OE CHAPTER IL ' Hysrip Protas. The Oxlip a hybrid naturally produced between Primula veris and vulgaris—The differences in structure and function. between the two parent-species—Effects of crossing long-styled and short- styled Oxlips with one another and with the two forms of both parent-species—Character of the offspring from Oxlips artificially self-fertilised and cross-fertilised in a state of ».ature—Primuia - elatior shown to be a distinct speciee—Hybrids between other - heterostyled species of Primula—Supplementary note on spon- taneously produced hybrids in the genus Verbaseum ., 655-80 FF. vom athe. vi CONTENTS. CHAPTER IIL HETEROSTYLED DimorPHIo PLANTs—continued. Linum grandiflorum, long-styled form utterly sterile with own-form pollen—Linum perenne, torsion of the pistils in the long-styled form aisne—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 specics, long-styled form ccmpletely self-sterile— Polygonum fagopyrum—Various other heterostyled genera— Rubiaceez—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... se. cs. as! —ieall tow )ale Doone | tig nana CHAPTER IV. HETEROSTYLED TRIMORPHIO 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 Grefferi likewise trimorphic—L. thymifolia dimor- phic—L. hyssopifolia homostyled—Nesaa verticillata trimorphic —Lagerstreemia, nature doubtful—Oxalis, trimorphic species of —0O. Valdiviana—O. Regnelli, the illegitimate unions quite barren—O. speciosa—O, sensitiva—Homostyled species of Oxalis —Pontederia, the one monocotyledonous genus known to include heterustyled species .. «2 «6 of «8 of of . 187-187 CHAPTER V. ILLEGITIMATE OFFSPRING OF HererostyLEep PLANTS. Illegitimate offspring from all three forms of Lythrum salicaria— Their dwarfed stature and sterility, some utterly barren, some CONTENTS. vii 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 MEDCIGIOUR Ge te ces te wees Page 188-248 CHAPTER VI. ConcLtupinc REMARKS ON HETEROSTYLED 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—A ffinities of the genera which include heterostyled species—Nature of the advantages derived from heterostylism—The means by which plants became heterostyled—Transmission of form—Equal- styled varicties of heterostyled plants—Final remarks 244-277 CHAPTER VII. Potyaamous, Diacious, anD GyNno-piccious PLANTS, The conversion in various ways of hermaphrodite into diccious plants—Heterostyled plants rendered dicecious—Rubiacea— Verbenacewx—Polygamous and sub-dicecious plants—Euonymus —Fragaria—The two sub-forms of both sexes of Rhamnus and Epigea—Ilex—Gyno-dicecious plants—Thymus, difference in fertility of the hermaphrodite and female individuals—Satureia —Manner in which the two forms probably originated—Scabiosa and other gyno-diecious plants—Difference in the size of the corolla in the forms of polygamous, dicecious, and gyno-dicecious SORMMO Tos!) eae ie oe ee we ee oe we «= 278-808 vill CONTENTS. ~ CHAPTER VIIL CLEIsTOGAMIC FLowERs. General character of cleistogamic flowers— List of the genera proe 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—Im patiens—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 chief con- clusions which may be drawn from the observations in this volume PT mTerrne mer eo ee THORS Qu bs we ee Se La Re vee THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES. INTRODUCTION. 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 I can lay no claim. As far as the sexual relations of flowers are concerned, Linneus | long ago divided them into hermaphrodite, monecious, dicecious, 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 series of papers read before the Linnean Society,* * “On the Two Forms or Di- — of Primula, and on their remark- 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 stam2ns and in other respects. ‘They were called by me dimorphic and trimorphic, but have since been hetter named by Hildebrand, heterostyled.* As J have many still unpublished observations with respect to these plants, it has seemed to me advisable to re- publish my former papers in & connected and cor- rected form, together with the new matter. It will be , shown that these heterostyled piants 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 Linnean Society,’ vol. vi. 1862, p. 77. “On the Existence of Two Forms, and on their Reciprocal Sexual Relation, in several Species of the Genus Linum.” Ibid. vol vii. 1863, p. 69. “ On the Sexual Relations of the Three Forms of Lythrum salicaria,’ Ibid. vol. viii, 1864, p. 169. “On the Character and Hybrid- like Nature of the Offspring from the Illegitimate Unions of Dimor- hic and Trimorphic Plants,” bid. vol. x. 1868, p. 393. “On the Specific Differences between Primula veris, Brit. Fi. (var. officinalis, Linn.), P. vulgaris, Brit. Fl. (var. acaulis, Liun.), and P. elatior, Jacq.; and on. the Hybrid Nature of the Common Oxlip. With Supplementary Re- marks on Naturally Produced Hy- brids in the Genus Verbascum.” Ibid. vol. x. 1868, p. 437. * The term “ heterostyled ” does not express all the differences be- tween the forms; but this is a failure common in raany cases. As the term has been adopted by writers in various countries, I am unwilling to change it for that of heterogone or heterogonous, though this has been proposed by so high an authority as Prof. Asa Gray: see the ‘American Naturalist, Jan. 1877, p. 42, | f 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 dicecious, 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 when it is 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 papillose 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, whieh bear two kinds of flowers —the one perfect and fully 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 * * Botanische Zeitung,’ 1867, p. 65. Several plants are known occasionally to produce flowers destitute of a corolla; but they belong to a different class of cases from cleistogamic flowers. This deficiency seems to result from the conitiois to which the plants have been subjected, and partakes of the nature of a mon strosity. All the flowers on the same plant are commonly affected in the same manner. Such cases, though they have sometimes been ranked as eleistogamic, do not come within our present scope: see Dr. Maxwell Masters, ‘ Vege tabie Teratology,’ 1509, p. 402 £ INTRODUCTION. will be described in the last chapter of this volume. They are marifestly 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, bury 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. Miller, 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, Rhinanthus erista-galli, 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 Befruchtung der Blumen, 1873 (vol. viii.), p. 433, and Nov. &c., 1873, 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 respecting them. It is familiar to every one that the ray-florets of the Composite often differ remarkably from the others ; and so it is with the outer flowers of many Umbellifera, some Crucifere and a few other families. Several species of Hydrangea and Viburnum offer striking ‘instances of the same fact. The Rubiaceous genus Musseenda 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, coloured bractez, &e., and from what H. Miller has observedf on the frequency of the visits of insects to the flower-heads of the Umbelliferee and Composite 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 Hildebrand statest that the ray-florets of the Composite 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, t See his interesting memoir, pp. 161-164. ‘Ucber die Geschlechtsverhiltniss ¢t ‘Die Befruchtung der Blu- bei den Compositen,’ 1869, p. 92. § INTRODUCTION. however, are of service in another and very different manner, namely, by folding inwards at night and during 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. It is a well-known yet remarkable fact that the cir- cumferential flowers of many of the foregoing plants have both their male and female reproductive organs aborted, as with the Hydrangea, Viburnum and certain Composit; or the male organs alone are aborted, as in many Composite. Between the sexless, female and hermapbrodite states of these latter flowers, the finest gradations may be traced, as Hildebrand has shown. f 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 * Kerner clearly shows that thisis the case : ‘ Die Schutzmittel des Pollens,’ 1873, p. 28. ¢ ‘Gardener’s Chronicle,’ 1861, p- 1067. Lindley, ‘ Vegetable Kingdom,’ on Chrysanthemum, 1853, p. 706. Kerner in his in- teresting essay (‘ Die Schutzmittel der Bliithen gegen unberufene Giiste,” 1875, p. 19) insists that the petals of most plants contain matter which is offensive to in- sects, so that they are seldom gnawed, and thus the organs of fructification are protec’ My grandfather in 1730 (‘Loves of the Plants,’ canto iii. note to lines 184, 188) remarks that “The flowers or peials of plants are perhaps in general more acrid than their leaves; hence they are much seldomer eaten by insects.” t ‘Ueber die Gesehlechtsver- haltnisse bei den Compositen, 1869, pp. 78-91. er =.) CC — 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 dicecious or gyno-dicecious—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-dicecious and dicecious plants being directed (as we shall see in a future chapter) to the for- mation of an increased supply of seeds; whilst in the ease 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 cultivated, the corollas of both the interior _and exterior flowers become largely developed, and their reproductive organs are aborted. * I have discussed this subject xviii. 2nd edit. vol. ii. pp. 152 in my ‘Variation of Animals and = 156, Plauts under Domestication,’ chap. 2 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 respect 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 upper part of the spike— all, no doubt, for the sake of guiding insects to the inconspicuous perfect flowers. From such cases as these we may pass on to certain Labiate, for instance, Salvia Horminum, in which (as I hear from Mr. 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 Umbelliferse, the cen- tral flower has its petals somewhat enlarged, and these are of a dark purplish-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 Vauchert “ cette singuliére dégénération s’étend quelquefois 4 l’ombelle entiére.” 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 | zondition of the species, when one flower alone, the * ‘The English Flora, by Sir d’Europe,’ 1841, tom. ii. p. 614 ; J. E. Smith, 1824, vol. ii. p. 39. On the Echinophora, p. G27. ¢ ‘Hist. Phys. des Plantes : 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 Rue and Adoxa) differ slightly in structure, as in the number of the parts, from the other flowers on the same plant. All 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.} With the Umbelliferze and Composite, 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 moncecious species, or those which have their sexes separated but Lorne on the same plant. The flowers necessarily . differ, but when those of one sex include rudiments * This whole subject, including Domestication,’ chap. xxvi. 2nd pelorism, has been discussed, and edit. vol. ii. p. 338. references given, in my * Variation ¢ ‘Bot. Zeitung,’ 1867, p. 67 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 diccious 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 moncecious 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 fune- tional difference obviously is to favour the cross-fertili- sation of distinct plants. A case of this kind was first al 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. Miller the | individuals of some few hermaphrodite plants differ in a like manner; some being proterandrous and others proterogynous.t On cultivated trees of the Walnut and Mulberry, the male flowers have been observed to abort on certain individualst, which have thus been converted into females; but whether there are any species in a state of nature which co-exist as moncecious and female individuals, I do not know. The third Class consists of dicecious species, and the * Delpino, ‘Studi sopra uno xi. p. 507, and 1875, p. 26. On Lignaggio Anemofilo” Firenze, proterandrous and proterogynous 1871. hermaphrodite individuals of the t Delpino, ‘Ult. Osservazioni same species, see H. Miiller, ‘ Die sulla Dicogamia,’ part ii. fasc. ii, Befruchtung,’ &., pp. 285, 339. p. 337. Mr. Wetterhan and H. ¢ ‘Gardener’s Chron,’ 1847 pp. Miiller on Corylus,‘ Nature,’ vol. 541, 558. INTRODUCTION. Il remarks made under the last class with respect to the amount of difference between the male and female flowers are here applicable. It is at present an in- explicable fact that with some dicecious plants, of which the Restiaceze of Australia and the Cape of Good Hope offer the most striking instance, the dif- ferentiation of the sexes has affected the whole plant to such an extent (as I hear from Mr. Thiselton Dyer) that Mr. Bentham and Professor Oliver have often found it impossible to match the male and female spe- cimens of the same species. In my seventh chapter some observations will be given on the gradual con- version of heterostyled and of ordinary hermaphrodite plants into dicecious or sub-dicecious species. The fourth and last Class consists of the plants which were called polygamous by Linnzus; but it appears to me that it would be convenient to confine this term to the species which co-exist as hermaphrodites, males and females; and to give new names to several other com- binations of the sexes—a plan which I shall here follow. Polygamous plants, in this confined sense of the term, may be divided into two sub-groups, accord- ing as-the three sexual forms are found on the same individual or on distinct individuals. Of this latter or trioicous sub-group, the common Ash (fraainus ex- celsior) offers a good instance: thus, I examined during the spring and autumn fifteen trees growing in the same field; and of these, eight produced male flowers alone, and in the autumn not a single seed ; four pro- duced only female flowers, which set an abundance of seeds; three were hermaphrodites, which had a dif- ferent aspect from the other trees whilst in flower, and two of them produced nearly as many seeds as the female trees, whilst the third produced none, so that it 12 INTRODUCTION. was in function a male. The separation of the sexes, however, is not complete in the Ash; for the female flowers include stamens, which drop off at an early period, and their anthers, which never open or dehisce, generally contain pulpy matter instead of pollen. On some female trees, however, | found a few anthers con- taining pollen-grains apparently sound. On the male trees most of the flowers include pistils, but these like- wise drop off at an early period; and the ovules, which ultimately abort, are very small compared with those in female flowers of the same age. Of the other or monoicous sub-group of polygamous plants, or those which bear hermaphrodite, male and female flowers on the same individual, the common Maple (Acer campestre) offers a good instance; but Lecoq states * that some trees are truly dicecious, and this shows how easily one state passes into another. A considerable number of plants generally ranked as ‘polygamous exist under only two forms, namely, as hermaphrodites and females; and these may be called gyno-dicecious, of which the common Thyme offers a good example. In my seventh chapter I shall give some observations on plants of this nature. Other species, for instance several kinds of Atriplex, ‘bear on the same plant hermaphrodite and female flowers; and these might be called gyno-moneecious, if a name were desirable for them. Again there are plants which produce hermaphrodite and male flowers on the same individual, for in- stance, some species of Galium, Veratrum, &c.; and these might be called andro-monecious. If there exist plants, the individuals of which consist of her- maphrodites and males, these might be distinguished * * Géographie Botanique,’ tom. v. p. 367. INTRODUCTION. 13 as andro-dicecious. But, after making inquiries from several botanists, I can hear of no such cases. Lecoq, however, states,* but without entering into full details, that some plants of Caltha palustris produce only male flowers, and that these live mingled with the here maphrodites. The rarity of such cases as this last one is remarkable, as the presence of hermaphrodite and male flowers on the same individual is not an un- usual occurrence; it would appear as if nature did not think it worth while to devote a distinct indi- vidual to the production of pollen, excepting when this was indispensably necessary, as in the case of dicecious species. I have now finished my brief sketch of the several cases, as far as known to me, in which flowers differing in structure or in function are produced by the same species of plant. Full details will be given in the fol- lowing chapters with respect to many of these plants. I will begin with the heterostyled, then pass on to certain dicecious, sub-dicecious, and polygamous species, and end with the cleistogamic. For the convenience of the reader, and to save space, the less important cases and details have been printed in smaller type. I cannot close this Introduction without expressing my warm thanks to Dr. Hooker for supplying me with specimens and for other aid; and to Mr. Thiselton Dyer and Professor Oliver for giving me much in- formation and other assistance. Professor Asa Gray,- also, has uniformly aided me in many ways. To Fritz Miller of St. Catharina, in Brazil, I am indebted for . many dried flowers of heterostyled plants, often accom- panied with valuable notes. * + Géographie Botanique,’ tom. iv. p. 488, HETEROSTYLED DIMORPHIC PLANTS Cuar. £ 14 CHAPTER I. HETEROSTYLED DiworPHic PLANTS: PRimULACER. Primula veris or the Cowslip—Differences in structure between the two forms—Their degrees of fertility when legitimately and ille- gitimately united—P. elatior, vuigaris, Sinensis, auricula, &.— Summary on the fertility of the heterostyled species of Primula— Homostyled species of Primula—Hottonia palustris—Androsace Vitalliana. It has long been known to botanists that the common Cowslip (Primula veris, Brit. Flora, var. officinalis, Lin.) exists under two forms, about equally numerous, which obviously differ from each other in the length of their pistils and stamens.* This difference has hitherto been looked at as a case of mere varia- bility, but this view, as we shall presently see, is far from the true one. Florists who cultivate the Polyan- thus and Auricula have long been aware of the two kinds of flowers, and they call the plants which dis- play the globular stigma at the mouth of the corolla, “pin-headed ” or “ pin-eyed,” and those which display the anthers, “ thrum-eyed.”t I will designate the two forms as the long-styled and short-styled. The pistil in the long-styled form is almost exactly twice as long as that of the short-styled. The stigma * This fact, according to von Moh] (‘Hot. Zeitung,’ 1863, p. 326) was first observed by Persoon in the year 1794. + In Johnson’s Dictionary, thrum is said to be the ends of weavers’ threads; and I suppose that some weaver who cultivated the polyanthus invented this name, from being struck with some degree of resemblance between the cluster of anthers in the mouth of the corolla and the ends of his threads, - a | Cuap. I PRIMULA VERIS. 15 stands in the mouth of the corolla or projects just above it, and is thus externally visible. It stands high above the anthers, which are situated halfway down the tube and cannot be easily seen. In the short-styled form the anthers are attached near the mouth of the tube, and therefore stand above the stigma, which is seated in about the middle of the tubular corolla. The corolla itself is of a different AWNyiity , \y i My Long-styled form. Short-styled form. PRIMULA VERIS. shape in the two forms; the throat or expanded portion above the attachment of the anthers being much longer in the long-styled than in the short- styled form. Village children notice this difference, as they can best make necklaces by threading and slipping the corollas of the long-styled flowers into one another. But there are much more important differences. The stigma in the long-styled form 16 HETEROSTYLED DIMORPHIC PLANTS. Cuaap. L is globular; in the short-styled it is depressed on the summit, so that the longitudinal axis of the former is sometimes nearly double that of the latter. Although somewhat variable in shape, one difference is persistent, namely, in roughness: in some speci- mens carefully compared, the papille which render the stigma rough were in the long-styled form trom twice to thrice as long as in the short-styled. The anthers do not differ in size in the two forms, which I mention because this is the case with some hetero- styled plants. The most remarkable difference is in the pollen-grains. I measured with the micrometer many specimens, both dry and wet, taken from plants growing in different situations, and always found a palpable difference. The grains distended with water from the short-styled flowers were about +038 mm. (29-11 of an inch) in diameter, whilst those from the long-styled. were about ‘0254 mm. (—*— of an inch), ~ 7000 which is in the ratio of 100 to 67. The pollen-grains therefore from the longer stamens of the short-styled form are plainly larger than those from the shorter stamens of the long-styled. When examined dry, the smaller grains are seen under a low power to be more transparent than the larger grains, and apparently in a greater degree than can be ac- counted for by their less diameter. There is also a difference in shape, the grains from the short-styled plants being nearly spherical, those from the long- styled being cblong with the angles rounded; this difference disappears when the grains are distended with water. The long-styled plants generally tend to flower a little before the short-styled: for instance, I had twelve plants of each form growing in separate pots snd treated in every respect alike; and at the time when only a single short-styled plant was* in ———————— —<—_ Cuar. I. PRIMULA VERIS. 17 flower, seven of the long-styled had expanded their flowers. We shall, also, presently see that the short-styled plants produce more seed than the long-styled. It is remarkable, according to Prof. Oliver,* that the ovules in the unexpanded and unimpregnated flowers of the latter are considerably larger than those of the short- styled flowers; and this I suppose is connected with the long-styled flowers producing fewer seeds, so that the ovules have more space and nourishment for rapid development. To sum up the differences :— The long-styled plants have a much longer pistil, with a globular and much rougher stigma, standing high above the anthers. The stamens are short; the grains of pollen smaller and oblong in shape. The upper half of the tube of the corolla is more expanded. ‘The number of seeds pro- duced is smaller and the ovules larger. The plants tend to flower first. The short-styled plants have a short pistil, half the length of the tube of the corolla, with a smooth de- pressed stigma standing beneath the anthers. The stamens are long; the grains of pollen are spherical and larger. The tube of the corolla is of uniform diameter except close to the upper end. The number of seeds produced is larger. I have examined a large number of flowers; and though the shape of the stigma and the length of the pistil both vary, especially in the short-styled form, I have never met with any transitional states between . the two forms in plants growing in a state of nature. There is never the slightest doubt under which form a plant ought to be classed. The two kinds of flowers are * ‘Nat. Hist. Review,’ July 1862, p. 237. a 18 HWETEROSTYLED DIMORPHIC PLANTS. Cuap. L never found on the same individual plant. I marked many Cowslips and Primroses, and on the following year all retained the same character, as did some in my garden which flowered out of their proper season in the autumn. Mr. W. Wooler, of Darlington, however, in- forms us that he has seen early blossoms on the Polyan- thus,* which were not long-styled, but became so later in the season. Possibly in this case the pistils may not have been fully developed during the early spring. An excellent proof of the permanence of the two forms may be seen in nursery-gardens, where choice varieties of the Polyanthus are propagated by division ; and I found whole beds of several varieties, each consisting exclu- sively of the one or the other form. The two forms exist in the wild state in about equal numbers: I collected 522 umbels from plants growing in several stations, taking a single umbel from each plant; and 241 were long-styled, and 281 short-styled. No difference in tint or size could be perceived in the two great masses of flowers. We shall presently see that most of the species of Primula exist under two analogous forms; and it may be asked what is the meaning of the above-described important differences in their structure? The ques- tion seems well worthy of careful investigation, and I will give my observations on the cowslip in detail. The first idea which naturally occurred to me was, that this species was tending towards a dicecious condition; that the long-styled plants, with their longer pistils, rougher stigmas, and smaller pollen- grains, were more feminine in nature, and would pro- duce more seed ;—that the short-styled plants, with their shorter pistils, longer stamens and larger pol- * I have proved by numerous that the Polyanthus is a variety experiments, hercaiter tobe given, of Primulu ver’s, ee Cuar. IL. PRIMULA VERIS. 19 len-grains, were more masculine in nature. Accord- ingly, in 1860, I marked a few cowslips of both forms growing in my garden, and others growing in an open field, and others in a shady wood, and gathered and weighed the seed. In all the lots the short- styled plants yielded, contrary to my expectation, most seed. Taking the lots together, the following is the result :— TABLE I. Number | Number | Number | Weight —- of ot Umbels of Capsules} of Seed in Plants. | produced. | produced.| grains. Short-styled cowslips . . . 9 33 199 83 Long-styled cowslips . . . 13 51 261 91 If we compare the weight from an equal number of plants, and from an equal number of umbels, and from an equal number of capsules of the two forms, we get the following results :— TABLE 2, Weight | Peas! Weight ae, Shs of Seed | abel pveene | haved Mere d in | Plants, grains. [anole Seed. | sules. reine Short-styled cowslips . 10 92 | 100 | 251 100} 41 Long-styled cowslips . | 10 | 70 | 100] 178 || 100] 34 So that, by all these standards of comparison, the short-styled form is the more fertile; if we take the “number of umbels (which is the fairest standard, for large and small plants are thus equalised), the short- styled plants produce more seed than the long-styled, in the proportion of nearly four to three. In 1861 the (rial was made in a fuller and fairer 20 HETELOSTYLED DIMORPHIC PLANTS. Czar. L manner. A number of wild plants had been trans- planted during the previous autumn into a large bed in my garden, and all were treated alike; the result was— TABLE 3. a Number | Number Weight eee of of of Seed in Plants. Umbels. grains. Short-styled cowslips. . 47 173 745 Long-styled cowslips . . 58 208 692 These figures give us the following proportions :— TABLE 4. Number | Weight or of Seed in Umbels. | grains. Number | Weight of of Seed in Plants. grains. 100 430 100 332 Short-styled cowslips .. 100 1585 Long-styled cowslips . . . 100 1093 The season was much more favourable this year than the last ; the plants also now grew in good soil, instead of in a shady wood or struggling with other plants in the open field; consequently the actual produce of seed was considerably larger. Nevertheless we have the same relative result; for the short-styled plants produced more seed than the long-stvled in nearly the proportion of three to two; but if we take the fairest standard of comparison, namely, the product of seeds from an equal number of umbels, the excess is, as ip the former case, nearly as four to three. Looking to these trials made during two successive years on a large number or plants, we may safely con- elude that the short-styled form is more productive than the long-styled form, and the same result holds Guar. 1. PRIMULA VERIS. ? 21 good with some other species of Primula. Conse- quently my anticipation that the plants with longer pistils, rougher stigmas, shorter stamens and smaller pollen-grains, would prove to be more feminine in nature, is exactly the reverse of the truth. In 1860 a few umbels on some plants of both the long-styled and short-styled form, which had been covered by a net, did not produce any seed, though other umbels on the same plants, artificially fertilised, produced an abundance of seed; and this fact shows that the mere covering in itself was not injurious. | Accordingly, in 1861, several plants were similarly | covered just before they expanded their flowers; these turned out as follows :— TABLE 5, Number Number of of Umbels Product of Seed, Plants. | produced. i | 1°3 grain weight of seed ‘Short-styled . . . . a { or about 50 in number. Long-styled . . . 18 74 Not one seed. Judging from the exposed plants which grew all round in the same bed, and had been treated in the same manner, excepting that they had been exposed to the visits of insects, the above six short-styled plants ought to have produced 92 grains’ weight of seed instead of only 1:3; and the eighteen long-styled plants, which produced not one seed, ought to have . produced above 200 grains’ weight. ‘The production of a few seeds by the short-styled plants was probably due to the action of Thrips or of some other minute insect. It is scarcely necessary to give any additional evidence, but I may add that ten pots of polyanthuses and 22 HETEROSTYLED DIMORPHIC PLANTS. Cuap. 1 cowslips of both forms, protected from insects in my greenhouse, did not set one pod, though artificially fertilised flowers in other pots produced an abundance. We thus see that the visits of insects are absolutely necessary for the fertilisation of Primula veris. If the corolla of the long-styled form had dropped off, in- stead of remaining attached in a withered state to the ovarium, the anthers attached to the lower part of the tube with some pollen still adhering to them would have been dragged over the stigma, and the flowers would have been partially self-fertilised, as is the case with Primula Sinensis through this means. It is a rather curious fact that so trifling a difference as the falling-off of the withered corolla, should make a very great difference in the number of seeds pro- duced by a plant if its flowers are not visited by insects. The flowers of the cowslip and of the other species of the genus secrete plenty of nectar; and I have often seen humble-bees, especially B. hortorum and muscorum, sucking the former in a proper manner,* though they sometimes bite holes through the corolla. No doubt moths likewise visit the flowers, as one of my sons caught Cucullia verbasci in the act. The pollen readily adheres to any thin object which is inserted into a flower. The anthers in the one form stand nearly, but not exactly, on a level with the stigma of the other; for the distance between the anthers and stigma in the short-styled form is greater than that in the long- styled, in the ratio of 100 to 90. This difference is the result of the anthers in the long-styled form standing rather higher in the tube than does the stigma in the short-styled, and this favours their * H. Miiller has also seen An- sucking the flowers. ‘Nature, thophora pilipes and a Bombylius Dec. 10th, 1874, p. 111. i i i i ee. Bee " Cuar. I. _ PRIMULA VERIS. 23. pollen being deposited on it. It follows from the position of the organs that if the proboscis of a dead humble-bee, or a thick bristle or rough needle, be pushed down the corolla, first of one form and then of the other, as an insect would do in visiting the two forms growing mingled together, pollen from the long-stamened form adheres round the base of the object, and is left with certainty on the stigma of the long-styled form; whilst pollen from the short stamens of the long-styled form adheres a little way above the extremity of the object, and some is generally left on the stigma of the other form. In accordance with this observation I found that the two kinds of pollen, which could easily be recog- nised under the microscope, adhered in this manner to the proboscides of the two species of humble- bees and of the moth, which were caught visiting the flowers; but some small grains were mingled with the larger grains round the base of the proboscis, and conversely some large grains with the small grains near the extremity of the proboscis. Thus pollen will be regularly carried from the one form to the other, and they will reciprocally fertilise one another. Nevertheless an insect in withdrawing its proboscis from the corolla of the long-styled form cannot fail occasionally to leave pollen from the same flower on the stigma; and in this case there might be self-fertilisation. But this will be much more likely to occur with the short-styled form; for when I inserted a bristle or other such object into the corolla -of this form, and had, therefore, to pass it down be- tween the anthers seated round the mouth of the corolla, some pollen was almost invariably carried down and left on the stigma. Minute insects, such as Thrips, which sometimes haunt the flowers, would 3 24 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L. likewise be apt to cause the self-fertilisation of both forms. The several foregoing facts led me to try the effects of the two kinds of pollen on the stigmas of the two forms. Four essentially different unions are pos- sible; namely, the fertilisation of the stigma of the long-styled form by its own-form pollen, and by that of the short-styled; and the stigma of the short-styled form by its own-form pollen, and by that of the long- styled. The fertilisation of either form with pollen from the other form may be conveniently called a legitimate union, from reasons hereafter to be made clear; and that of either form with its own-form pollen an ¢dlegitimate union. I formerly applied the term “ heteromorphic ” to the legitimate unions, and “ homomorphic” to the illegitimate unions; but after discovering the exist- ence of trimorphic plants, in which many more unions are possible, these two terms ceased to be applicable. The illegitimate unions of both forms might have been tried in three ways; for a flower of either form may be fertilised with pollen from the same flower, or with that from another flower on the same plant, or with that from a distinct plant of the same form. But to make my experiments perfectly fair, and to avoid any evil result from self-fertilisation or too close interbreeding, I have invariably employed pollen from a distinct plant of the same form for the illegitimate unions of all the species; and therefore it may be observed that * I have used the term “ own-form pollen” in speaking _ of such unions. The several plants in all my experi- — ments were treated in exactly the same manner, and were carefully protected by fine nets from the access of insects, excepting Thrips, which it is impossible to ex- elude. I performed all the manipulations myself, and weighed the seeds in a chemical balance; but during i Oxap. I. PRIMULA VERIS. 25 many subsequent trials I followed the more accurate plan of counting the seeds. Some of the capsules con- tained no seeds, or only two or three, and these are excluded in the column headed “good capsules” in several of the following tables :— TABLE 6. Primula veris. Total Calculated a Namber Number ; Weight Weight of Nature of the Union. owns of of good | of Seed in | Seed from fertilised. acces Capsules. | grains. een Long-styled by pollen of shortestyled. Le- 22 15 14 8°8 62 gitimate union . Long-styled by ate | form pollen. Ille- 20 8 5 2°1 42 gitimate union. Short-styled by age vel of long-styled. Le- 13 12 11 _ 4:9 44 gitimate union . Short-styled by own- form pollen. — Ille- 15 8 6 1°8 30 gitimate union. SUMMARY: The two pene - 492. 2 ahd *} 35 27 25 |-13-7 | 54 The two illegitimate : sa iia *} 35 16 11 3-9 | 35 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. 26 HETEROSTYLED DIMORPHIC PLANTS. Onap. L TABLE 7. | sue Number |Number} Weight |Number Weight ||Number| Weight Nature of the |p < ers} Of | of good| of Seed | of | of Seed || of good | of Secd Union. fers Cap- Cap- in || Cap- in Cap- in sules. | sules. | grains. || sules. | grains. |} sules, | grains, tilised. The two le- | | gitimate 100 77 val 389 || 100] 50 1c0 54 unions | The two il- legitimate 100 45 81 11 100 24 100 357 unions 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 58 capsules: therefore the rate of 77 to 58, or as 100 to 69, is a fairer one than that of 100 to 58. ee e = 1 Cuap, I. PRIMULA VERIS. ZL 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 eapsules, 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. f aS IMegitimate / \\ ‘ Illegitimate union. =| + union. Incomplete { | Incomplete fertility, | i fertility. ‘ ‘ \ \ ee Complete fertility. Long-styled Short-styled form. 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 ean, 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. Cuapr. L 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 1862 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, "- Cuar. L PRIMULA VEBRIS. 29 so here we have two bodies, approximately 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- dividual 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 belongmg 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 be 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 iiber die Bastarderzeugung,’ 1819, p. 216. 30 HETEROSTYLED DIMORPHIC PLANTS. Guar. L 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 caleula- tion of Verbascum lychnitis yielding with its own pollen 100 seeds, it yielded when fertilised by the pollen of V. Pheniceum 90 seeds; by the pollen of V. nigrum, 63 seeds; by that of V. blattaria, 62 seeds. So again, Dianthus barbatus fertilised by the pollen of D. superbus | yielded 81 seeds, and by the pollen of D. Japonicus | 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 between 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, hirsuta, and verticillata), and these hybrid unions yielded a larger average number of seeds than did P. awricula when fertilised illegitimately with its own-form pollen. The benefit which heterostyled dimorphic plants de- rive from the existence of the two forms is sufficiently obvious, namely, the intercrossing of distinct plants being thus ensured.{ 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 * «Journ. Linn. Soe. Bot., vol. _ fertilisation’ how greatly the off- viii. 1864, p. 93. spring from intercrossed plants + I have shown in my work profit in height, vigour, and on the ‘ Effects of Cross and Self- __ fertility. ee ee ee ea _ nn Ouap., I. PRIMULA 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, such 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 pollen should first be placed by insects or fall on the stigma, it by no means follows that cross-fertilisation will be thus pre- vented. It is well known that if pollen 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 effect 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 were 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 belonging 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. Cuar. L all, as judged by the average number of seeds, which the capsules contained. A smaller proportion, 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 ELATIOR, Jacq. Bardfield Oxlip of English Authors. This plant, as well as the last or Cowslip (P. veris, vel officinalis), 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 Befruchtung der Blumen,’ p. 347, _— ; eS Se Cuar. I. PRIMULA 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. | Number Number | Maximum] Minimum| Average Uni of of good | of Seeds | of Seeds | Number of Nature of Union. Flowers Capsules |in any one|in any one , Seeds per fertilised. produced.) Capsule. | Capsule. | Capsule. Long-styled form, by pollen of ee aa 10 6 62 34 46°5 Legitimate union Long-styled form, b own-form pollen. i 20 - 49* 2 27°7 _ legitimate union, Short-styled form, by pollen of long- styled 10 8 61 37 47°7 Legitimate union Short-styled form, own-form pollen. 17 3 19 9 12°1 legitimate sara The two legitimate 20 14 62 37 | 47°1 unions together . The two illegitimate 5 ; unions together , } 87 | us ie : | $028 * These seeds were so poor and small that they could hardly have 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 HETEROSTYLED DIMORPHIC PLANTS. Onap. 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. PRIMULA 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 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 conspicuously more | globose and much more papillose than in the short- styled, in which latter it is depressed on the summit; _ Cuar. I. PRIMULA VULGARIS. 35 ) : Fig. 3. Outlines of pollen-grains of Primula vulgaris, distended with water, mucn magnified and drawn under the camera lucida, The upper and smaller grains from the long-styled form; the lower and larger grains 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 36 HETEROSTYLED DIMORPHIC PLANTS. Cuar. & flowers before they were soaked in water were decidedly broader, in proportion to their length, than those from the long-styled ; after being soaked they were relatively to those from the long-styled as 100 to 71 in diameter, and more transparent. , 20 13 0°45 35 mate union . Short*styled form, by pol- len of 2 ok hela Le- 8 8 0°76 64 gitimate union . Short-styled form, by own- form pollen. thei 7 4 0°23 25 mate union. . The two eerie unions | jepither: vai | 32 24 0-64 | 57 The two illegitimate unions together. ae ee, 17 0°40 | 30 =r - — 40 HETEROSTYLED DIMORPHIC PLANTS. Cuap. 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 68. 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 shown 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 effects of the plant’s own pollen. He counted the seeds. It is remarkable that here all the flowers which 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 1 have observed striking instances with the | Cuap. I. PRIMULA SINENSIS. 41 TABLE 11. Primula Sinensis (from Hildebrand). Number | Number | f f Namboeot d Nature of Union. Pawn Dareales Soeds on fertilised. | produced. | Capsule. Long-styled form, by pollen of short- | 41 styled. Legitimate union . Long-styled form, by own-form pollen, from | 26 26 18 a distinct plant. Illegitimate union . fs Long-styled form, by pollen from same 27 | 21 17 flower. Illegitimate union. Short-styled form, by pollen of eae: 14 | 14 44 styled. Legitimate union . | Short-styled form, by own-form pollen, 16 16 20 from a distinct plant. Illegitimate union Short-styled, by pollen from the same 21 rl 8 flower. Illegitimate union, The two legitimate unions together . . 28 | 28 | 43 The two illegitimate unions together (own-form pollen) . ee Gelert “ =e a | 7 The two illegitimate unions together (pol- 48 32 len from the same flower) . . . . 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 by comparing the right-hand columns in Tables 10 and 11.. The most interesting point in Hildebrand’s experi- ments is the difference in the effects of illegitimate fertilisation with a flower’s own pollen, and with that 42 HETEROSTYLED DIMORPHIC PLANTS. Cuapr. L 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 with 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 which 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 half-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; SS