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UNIVERSITY OF arom URBANA

581. 1502501877 THE DIFFERENT FORMS OF FLOWERS ON PLANTS

MON

THE

DIFFERENT FORMS OF FLOWERS

ON

PLANTS OF THE SAME SPECIES.

By CHARLES DARWIN, M.A., F.RB.S.

WITH ILLUSTRATIONS.

NEW YORK: ‘D. APPLETON AND COMPANY, 549 AND 551 BROADWAY. oT %

5YL.I5 gi yee Bisley re

To PROFESSOR ASA GRAY Chis Volume is Dedicated

BY THE AUTHOR

AS A SMALL TRIBUTE OF RESPECT AND AFFECTION.

438692

¢

Digitized by the Internet Archive in 2010 with funding from University of Illinois Urbana-Champaign

http://www.archive.org/details/differentformsof01darw

CONTENTS.

INTRODUCTION eS esi set teoylste Duet . oa baged=13

CHAPTER L HETEROSTYLED DimorpHic PLANTS: PRIMULACER.

Primula veris or the Cowslip—Differences 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—A ndrosace Vitalliana BE Seca aah ie heed aol dat) pete won PL oee

CHAPTER II. Hysrip PrRIMULAS.

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 nature—Primula elatior shown to be a distinct species—Hybrids between other heterostyled species of Primula—Supplementary note on spon- taneously produced hybrids in the genus Verbascum .. 55-80

vi CONTENTS.

CHAPTER 122 HetTeRostyLeD DimorpHic PLANTS—continued.

Linum grandiflorum, long-styled form utterly sterile with own-form pollen—Linum perenne, torsion of the pistils in the long-styled form alone—Homostyled species of Linum—Pulmonaria oflici- nalis, singular difference in self-fertility between the English and German long-styled plants—Pulmonaria angustifolia shown to be a distinct species, long-styled form completely self-sterile— Polygonum fagopyrum—Various other heterostyled genera— Rubiacex—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 COMMION 65 uy de es, de: ces _ ce, ae

CHAPTER LY. HETEROSTYLED TRIMORPHIC PLANTS.

Lythrum salicaria—Description of the three forms—Their power and complex manner of fertilising one another—Highteen different unions possible—Mid-styled form eminently feminine in nature —Lythrum Grefferi likewise trimorphic—L. thymifolia dimor- phic—L. hyssopifolia homostyled—Nesaa verticillata trimorphic —Lagerstremia, nature doubtful—Oxalis, trimorphic species of —O. Valdiviana—O. Regnelli, the illegitimate unions quite barren—O, speciosa—O, sensitiva—Homostyled species of Oxalis —Pontederia, the one monocotyledonous genus known to include heterostyled species” .. .. o» -. o- ss om) hau cue

OW AP TER NV; ILLEGITIMATE OFFSPRING OF HeTEerosTyLeD 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 mfertile—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 PUM tk Kak ee as vs ve we | ea 189-243

OR APP EHR: VE: ConcLupiInG 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—Affinities 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 varieties of heterostyled plants—Final remarks 244-277

CHAPTER VII.

PotyGamous, Diacious, AND GyNo-piccrous PLANTs,

The conversion in various ways of hermaphrodite into dicecious plants—Heterostyled plants rendered dicecious—Rubiacew— Verbenaceex—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-dicecious plants—Difference in the size of the corolla in the forms of polygamous, dicecious, and gyno-dicecious UP RNs es Saal ek on.) os - ss) at ae LOCUS

vill CONTENTS

CHAPTER OVELL CLEISTOGAMIC FLOWERS.

General character of cleistogamic flowers— List of the 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—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 cleistozamic flowers—The cnief con- clusions which may be drawn from the observations in this volume ca be ae Te Se es, ees ashy Ue

INDEX oe oe ee oe es ee oe ee oe ee oe 346-352

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 can lay no claim. As far as the sexual relations of flowers are concerned, Linnzeus long ago divided them into hermaphrodite, moncecious, 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, ina 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.

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: haye 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

the individuals

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- phic and Trimorphie Plants.” Ibid. vol. x. 1868, p. 393.

“On the Specific Differences between Primula veris, Brit. Fl. (var. officinalis, Linn.), P. vulgaris, Brit. Fl. (var. acaulis, Linn.), and

P. elatior, Jacq.; and on tho 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.

INTRODUCTION. 5

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 igs 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, which bear two kinds of flowers —the one perfect and fully expanded—the other mi- nute, completely closed, with the petals rudimentary, ofteh 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 eases from cleistogamic flowers. This deficiency seems to result from the conditions to which the plants have heen 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 cleistogamic, do not come within our present scope : sce Dr. Maxwell Masters, ‘ Vege- table Teratology,’ 1869, 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, 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. 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, 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. 483, and Nov. &c., 1873, p. 294. 20, 1873 (vol. ix.), p. 44. Also

- a eee eee

—

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 Umbellifere, some Crucifere and a few other families. Several species of Hydrangea and Viburnum offer striking instances of the same fact. The Rubiaceous genus Musszenda 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 bractex, &c., and from what H. Miller has observedt on the frequency of the visits of insects to the flower-heads of the Umbelliferee and Composits 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. ‘Ueber die Geschlechtsverhiiltnisse ¢ ‘Die Befruchtung der Blu- bei den Compositen,’ 1869, p. 92.

6 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 Compositze; or the male organs alone are aborted, as in many Composite. Between the sexless, female and hermaphrodite states of these latter flowers, the finest gradations may be traced, as Hildebrand has shown. tf 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 this is the case : ‘ Die Schatzmittel 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 Giste,’ 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 protected. My grandfather in 1790 (‘Loves of the Plants,’ canto iii. note to lines 184, 188) remarks that “The flowers or petals of plants are perhaps in general more acrid than their leaves; hence they are much seldomer eaten by insects.”

t¢ ‘Ueber die Geschlechtsver- haltnisse bei den Compositen,’ 1869, pp. 78-91.

INTRODUCTION. 7

to insects, it is a natural inference that their corollas haye 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. 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 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 Labiatz, 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 Umbelliferee, 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 Vaucherf “ cette singuliére dégénération s’étend quelquefois 4 ’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 condition of the species, when one flower alone, the

* ‘The English Flora, by Sir d’Europe,’ 1841, tom. ii. p. 614. J. i. Smith, 182+, vol. ii. p. 39. On the Echinophora, p. 627. + ‘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.f With the Umbelliferee 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 borne on the same plant. The flawers 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 dicecious 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 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. 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.

¢ Delpino, ‘Ult. Osservazioni sulla Dicogamia,’ part ii. fase. ii. p. 337. Mr. Wetterhan and H. Miiller on Corylus, ‘ Nature,’ vol.

hermaphrodite individuals of the same species, see H. Miiller, ‘ Die Befruchtung,’ &e., pp. 285, 339.

t ‘Gardener’s Chron.’ 1847, pp. 541, 558.

INTRODUCTION. 1}

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 Linnzeus; 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 (Frawinus ex- célsior) 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, I 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-monececious, if a name were dasieable, for them.

Again there are plants which produce hee and male flowers on the same individual, for in- stance, some species of Galium, Veratrum, &c.; and these might be called andro-moneecious. 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

es 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 her- 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.

14 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L.

CHAPTER I. HETEROSTYLED DiworpHICc 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, &e.— Summary on the fertility of the heterostyled species of Primula— Homostyled species of Primula—Hottonia palustris—Androsace Vitalliana.

lr 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 Mob! (‘Bot. 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,

Cuap. I PRIMULA VERIS. 13

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

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 2

16 HETEROSTYLED DIMORPHIC PLANTS. OCuaapr. 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 papilla which render the stigma rough were in the long-styled form from 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. (49-11 of an inch) in diameter, whilst those from the

7000 long-styled were about *0254 mm. (~7— of an inch),

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 and 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.

18 WETEROSTYLED DIMORPHIC PLANTS. (Cuap. 1.

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-

* T have proved by numerous that the Polyanthus is a variety experiments, hereafter tobe given, of Primula veris.

Cuar. I. 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 1.

Number | Number | Number | Weight

— of of Umbels of Capsules; of Seed in

Plants. | produced. produced. | grains. faa ed ik Et S| ees

: | 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. a2 Number of Seed Samper wet Samper Wh in Plants. grains. | ‘Umbels.| Seed. sules. went : 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 trial was made in a fuller and fairer

20 HETEROSTYLED DIMORPHIC PLANTS. OCuapr. 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—

These figures give us the following proportions :—

TABLE 4. Number | Weight || Number | Weight ——— to) of Seed in of of Seed in Plants. grains. Umbels. | grains. Short-styled cowslips . . . | 100 | 1585 | 100 | 430 Long-styled cowslips . . 100 | 1093 100 | 332 } |

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-styled 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 in the former case, nearly as four to three.

Looking to these trials made during two successive years on a large number of plants, we may safely con- clude that the short-styled form is more productive than the long-styled form, and the same result holds

Cuar. I. PRIMULA VERIS. of

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 coyered just before they expanded their flowers; these turned out as follows :—

TABLE 5,

Number | Number of of Umbels Plants. produced.

Product of Seed.

Pee 4 : Short-styled . . . Git 2A eae grain weight of seed, | 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

pi HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.

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 muscorun, 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 Dee. 10th, 1874, p. 111.

Cuap. I. PRIMULA VERIS. 25

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

24 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.

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- clude. I performed all the manipulations myself, and weighed the seeds in a chemical balance; but during

Cuar. 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.

RAE Total | Calculated f | Number | Number | W eight | Weight of Nature of the Union. eirw ers | G of ; an oe of Seed in | Seed — or apsules | Capsules. ains. {| 100 goo fertilised. “conte i Capsules. Long-styled by pollen ofshort-styled. Le->} 22 |, 15 14 8°8 62 gitimate union . | | | Long-styled by own-] | form pollen. Ille-| 20 | 8 5 2°1 42 gitimate union. . Short-styled by pollen | of long-styled. Le- IB LON iy ga 2 11 4°9 44 Ba oey, gitimate union. .)| Short-styled by own-}| form pollen. Ille- 15) | 8 6 1°8 30 P gitimate union. SUMMARY ‘ The two legitimate)| < ‘ 2 ; mise } a5.) at 25 | 13-7 | 54 The two illegitimate)| e : . EEGUS: tye *} 7 = | = | a8 me

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. Cuar. I.

TABLE 7. ' !Numpber : | of |Number|Number) Weight |Number Weight |Number) Weight Nature of the lr owers of of good | of Seed of | of Seed || of good | of Secd 2

Union. fore Cap- Cap- in Cap- | in Cap- in

| tilisea. sules. | sules. | grains. || sules. Peewee sules. | grains.

—_—nsé——

54

gitimate}/ 100| 77 | 71 39 100 | 50 100

The two le- unions

The two il-

eg 100 | 45 31 11 100 24 | 100 35

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 53 capsules: therefore the rate of 77 to 53, or as 100 to 69, is a fairer one than that of 100 to 58.

Cuap. 1. PRIMULA VERIS. 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.

/ i Illegitimate / \ [legitimate union. | + union. Incomplete |! t Incomplete fertility. | 1 fertility. ‘ 4 4

KW}

Legitimate union. 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 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. Cuap. 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. T. PRIMULA VERIS. 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- selyes, 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 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 bt 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. Giirtner 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,’ 1849, p. 216.

30 HETEROSTYLED DIMORPHIC PLANTS. Cnar. 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 Verbaseum 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 vertiecillata), 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.t 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.

Cuap. I. PRIMULA VERIS. 31

this whole subject I shall reeur. 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 50 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. Cnap. 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.

Cuar. I. PRIMULA ELATIOR. oo

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.

* 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. Guar. 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

——_—

Cuar. 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 conspicuously more globose and much more papillose than in the short- styled, in which latter it is depressed on the summit ;

Fig. 3.

Outlines of pollen-gwains of Primula vulyaris, distended with water, much 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 95. The anthers do not differ in size in the two forms. The pollen-grains from the short-styled

36 HETEROSTYLED DIMORPHIC PLANTS. Cnuap. I.

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. A large number of flowers from the two forms were 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 day visiting the flowers, but I have occasionally observed small kinds of bees at work ; I suppose, therefore, that they are commonly fertilised by nocturnal Lepidoptera. The long-styled plants when protected from insects yield a considerable number of capsules, and they thus differ remarkably from the same form of the cowslip, which is quite sterile under the same circumstances. ‘Twenty-three spontaneously self-fertilised capsules from

Cuar. I. PRIMULA VULGARIS. oF

TABLE 9.

Primula vulgaris.

+ Maximum | Minimum ; ase sine aE Number | Number Holtaee seiee of Puion. Flowers Capsules eee Se cape Seeds per fertilised. produced. Capbaile. Gans Capsule. Long-styled form, by pol- len from short-styled. 12 11 77 47 66°9 Legitimate union, . Long-styled form, by own-form pollen. Il-)) 21 14 66 30 52°2 legitimate union . | ee eal d et S Short-styled form, by}! L pollen from long-style d. 8 i! 75 48 65°0 Legitimate union , Short-styled form, by own-form pollen. II- 18 ii 43 5 18°8* legitimate union . The __ two legitimate), 20 18 a 47 66-0 unions together “Ji | The two illegitimate) 39 1 66 5 35°5* unions together |

* 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 self-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. Cuap. I.

longing to the same form; whilst those which were spontaneously self-fertilised no doubt generally received their own pollen. In a future part of this volume sonie 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- styled 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 transparent 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 appearance of my paper this author published some excellent observations on the present species (‘ Bot. Zeitung,’ Jan. 1, 1864), and he shows

that I erred greatly about the size of the pollen-grains in the two forms. I suppose that by mistake I measured twice over pollen-grains from the same form.

‘Ouar. L PRIMULA SINENSIS. 39

it was longer and had a more elongated and rougher stigma, than in the other; and the pollen-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. veris. 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.

[| 2? |

H P Average Number | Aunler N pole eae of Seeds per : } Co) of goo! eight of | 6 as Nature of Union. | Flowers | Capsules Seeds per eee Be a - fertilised. produced, | Capsule. subsequent | occasion. Long-styled form, by eee siel Ginn, by pollen) | | of short-styled. Saas 24 16 0°58 50 « mate union . Long-styled fxm, by own- form pollen. iy 20 13 0°45 35 mate union , Short- PR iad form, by pol-) form, by pol- | len of agian Le- 8 8 0-76 | 64 lS ae union , (Bhoré-styiea form, by own-] -styled form, by own- form pollen. rice 7 4 O-23. 91 25 mate union. . The two legitimate unions together . sae 32 24 | 0°64 57 The two illegitimate unions ; | | Brae 7) 27 | 17 | 0°40 | 30

40 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L

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 ocea- 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 kere 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 I have observed striking instances with the

Cuap. I. PRIMULA SINENSIS. 41

TABLE 11. Primula Sinensis (from Hildebrand).

Number | Number | Average of of good |Number of

Flowers | Capsules | Seeds per

fertilised. | produced. | Capsule.

Nature of Union.

Long-styled form, by pollen of short- 14 | 14 | 41 styled. Legitimate union. . site | Long-styled form, by own-form pollen, from 2% | 96 | 18 a distinct plant. Illegitimate union .f| ~ Long-styled form, by pollen from same 97 21 17 flower. Illegitimate union. . : ‘i Short-styled form, by pollen of paee styled. Legitimate union . “S| @ | — = ‘Short. styled form, by own-form pollen, 16 16 | 20 from a distinct plant. Illegitimate union Short-styled, by pollen from the same}\| 21 7 8 flower. Illegitimate union. | ra | The two legitimate unions together 28! vad || 228 43 “The two illegitimate unions together)! : | (own-form pollen) =. ee } = = | ue | ee The two illegitimate unions together (pol-)| | len from the same flower) , i) = e _ | '

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. Cuap. 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 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 haying been kept in a room and never having been shaken;

Cuap. I. PRIMULA 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 AURIOCULA.*

This species is heterostyled, 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 in the length of the pistil and stamens in the two forms of the auricula than in the cowslip; the pistil in the long-styled being nearly four times as long as that in the short-styled, in which itis barely longer than the ovarium. The stigma is nearly of the same shape in both forms, but is rougher in the long-styled, though the difference is not so great as between the two forms 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;255 of an inch in diameter, whereas those from the long stamens of the short-styled plants were barely ;255, showing a relative dif- ference of about 71 to 100. The smaller grains of the long- styled plant are also much more transparent, and before disten- tion with water more triangular in outline than those of the other form. Mr. Scott t compared ten plants of both forms grow- ing under similar conditions, and found that, although the long- styled plant produced more umbels and more capsules than the short-styled, yet they yielded fewer seeds, in the ratio of 66 to 100. Three short-styled plants were protected by me from the

* According to Kerner our gar- den auriculas are descended fromP. ubescens, Jacq., which is a hybrid etween the true P. auricula and hirsuta. This hybrid has now been propagated for about 300 years, and produces, when legitimately fertilised, a large number of seeds ; the long-styled forms yielding an average number of 73, and the

short-styled 98 seeds per capsule: see his “ Geschichte der Aurikel,” ‘ Zeitschr. des Deutschen und Oest. Alpen-Vereins, Band vi. p. 52. Also ‘ Die Primulaceen-Bastarten,’ ‘ Oest. Bot. Zeitschrift,’ 1835, Nos. 3, 4, and 5.

+ ‘Journ. Linn. Soc. Bot.’ vol. viii. 1864, p. 86.

44 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.

access of insects, and they did not produce a single seed. Mr. Scott protected six plants of both forms, and found them ex- cessively sterile. The pistil of the long-styled form stands so high above the anthers, that it is scarcely possible that pollen should reach the stigma without some aid; and one of Mr. Scott’s long-styled plants which yielded a few seeds (only 18 in number) was infested by aphides, and he does not doubt that these had imperfectly fertilised it.

I tried a few experiments by reciprocally fertilising the two forms in the same manner as before, but my plants were un- healthy, so I will give, in a condensed form, the results of Mr. Scott’s experiments. For fuller particulars with respect to this and the five following species, the paper lately referred to may be consulted. In each ease the fertility of the two legitimate unions, taken together, is compared with that of the two ille- gitimate unions together, by the same two standards as before, namely, by the proportional number of flowers which pro- duced good capsules, and by the average number of seeds per capsule. The fertility of the legitimate unions is always taken at 100.

By the first standard, the fertility of the two legitimate unions of the auricula is to that of the two illegitimate unions as 100 to 80; and by the second standard as 100 to 15.

PRIMULA SIKKIMENSIS.

According to Mr. Scott, the pistil of the long-styled form is fully four times as long as that of the short-styled, but their stigmas are nearly alike in shape and roughness. The stamens do not differ so much in relative length as the pistils. The pollen- grains differ in a marked manner in the two forms; “those of the long-styled plants are sharply triquetrous, smaller, and more transparent than those of the short-styled, which are of a bluntly triangular form.” ‘The fertility of the two legitimate unions to that of the two illegitimate unions is by the first standard as 100 to 95, and by the second standard as 100 to 31.

PRIMULA CORTUSOIDES.

The pistil of the long-styled form is about thrice as long as that of the short-styled, the stigma being double as long and covered with much longer papillz. The pollen-grains of the short-

Cuar. I. SUMMARY ON PRIMULA. 45

styled form are, as usual, “larger, less transparent, and more bluntly triangular than those from the long-styled plants.” The fertility of the two legitimate unions to that of the two ille- gitimate unions is by the first standard as 100 to 74, and by the second standard as 100 to 66.

PRIMULA INVOLUCRATA.

The pistil of the long-styled form is about thrice as long as that of the short-styled; the stigma of the former is globular and closely beset with papille, whilst that of the short-styled is smooth and depressed on the apex. The pollen-grains of the two forms differ in size and transparency as before, but not in shape. The fertility of the two legitimate to that of the two illegitimate unions is by the first standard as 100 to 72; and by the second standard as 100 to 47.

PRIMULA FARINOSA.

According to Mr. Scott, the pistil of the long-styled form is only about twice as long as that of the short-styled. The stigmas of the two forms differ but little in shape. The pollen- grains differ in the usual manner in size, but not in form. The fertility of the two legitimate to that of the two illegitimate unions is by the first standard as 100 to 71, and by the second standard as 10Q to 44.

Summary on the foregoing heterostyled species of Pri- mula.—The fertility of the long and short-styled plants of the above species of Primula, when the two forms are fertilised legitimately, and illegitimately with pollen of the same form taken from a distinct plant, has now been given. ‘The results are seen in the fol- lowing table; the fertility being judged by two standards, namely, by that of the proportional number of flowers which yielded capsules, and by that of the average number of seeds per capsule. Bunt for full accuracy many more observations, under varied condi- tions, would be requisite.

46 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.

TABLE 12.

Summary on the Fertility of the two Legitimate Unions, compared with that of the two Illegitimate Unions, in the genus Primula. The former taken at 100.

Illegitimate Unions.

Judged of by the Average Number (or Weight in some cases) of Seeds per Capsule,

Name of Species. Judged of by the Proportional Number of Flowers which produced Capsules.

Erimulasveris apace ue ie 69 | 65 oe: - (Probably Pr sClALL OTIS eae aes co. coe de 27 T+ too high.) ‘ (Perhaps P. Wulgaris; 2) Ve) sti ss ee te 60 5a too low.) PP OINENSISs te Ove Risk” homens as 84 35 (second trial) . . ty 53 A: (after Hildebrand) . 100 42 P. auricula (Scott) . . . « 80 15 P. Sikkimensis (Scott) . . . 95 31 P. cortusoides (Scott) . . . V4: 66 P. involucrata (Scott) . . . 72 48 P. farinosa (Scott) . . . - 71 ct Average of the nine species . | 88°4 bese Gk ae

With plants of all kinds some flowers generally fail to produce capsules, from various accidental causes ; but this source of error has been eliminated, as far as possible, in all the previous cases, by the manner in which the calculations have been made. Supposing, for instance, that 20 flowers were fertilised legiti- mately and yielded 18 capsules, and that 30 flowers were fertilised illegitimately and yielded 15 cap- sules, we may assume that on an average an equal proportion of the flowers in both lots would fail to produce capsules from various accidental causes ; and the ratio of 38 to 43, or as 100 to 56 (in whole

_ Cnap. L SUMMARY ON PRIMULA. 47

numbers), would show the proportional number of cap- sules due to the two methods of fertilisation ; and the number 56 would appear in the left-hand column of Table 12, and in my other tables. With respect to the average number of seeds per capsule hardly anything need be said: supposing that the legiti- mately fertilised capsules contained, on an average, 50 seeds, and the illegitimately fertilised capsules 25 seeds; then as 50 is to 25 so is 100 to 50; and the latter number would appear in the right-hand column.

It is impossible to look at the above table and doubt that the legitimate unions between the two forms of the above nine species of Primula are much more fertile than the illegitimate unions; although in the latter ease pollen was always taken from a distinct plant of the same form. There is, however, no close corre- spondence in the two rows of figures, which give, according to the two standards, the difference of fer- tility between the legitimate and illegitimate unions. Thus all the flowers of P. Sinensis which were illegiti- mately fertilised by Hildebrand produced capsules ; but these contained only 42 per cent. of the number of seeds yielded by the legitimately fertilised capsules. So again, 95 per cent. of the illegitimately fertilised flowers of P. Sikkimensis produced capsules ; but these contained only 51 per cent. of the number of seeds in the legitimate capsules. On the other hand, with P. elatior only 27 per cent. of the illegitimately fer- tilised flowers yielded capsules; but these contained nearly 75 per cent. of the legitimate number of seeds. It appears that the setting of the flowers, that is, the production of capsules whether good or bad, is not so much influenced by legitimate and illegitimate fer- tilisation as is the number of seeds which the capsules

48 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IL.

contain. For, as may be seen at the bottom of Table 12, 88:4 per cent. of the illegitimately fertilised flowers yielded capsules; but these contained only 61°8 per cent. of seeds, in comparison, in each case, with the legitimately fertilised flowers and capsules of the same species. There is another point which deserves notice, namely, the relative degree of infertility in the several species of the long-styled and short-styled flowers, when both are illegitimately fertilised. The data may be found in the earlier tables, and in those given by Mr. Scott in the Paper already referred to. If we call the number of seeds per capsule produced by the illegitimately fertilised long-styled flowers 100, the seeds from the illegitimately fertilised short-styled flowers will be represented by the following num- bers :—

Primula veris. 71 Primula auricula. . . 119 : (Probably | P.Sikkimensis . . . 57 LT AN auf too low.) P. cortusoides . . . 93 - (Perhaps BP, ANVOlUCKAta = |e unsieRiee

P. vulgaris. 364 too low.) PB. farinosa | )2)\_.! 1% Bemmape

P. Sinensis . 71

We thus see that, with the exception of P. auricula, the long-styled flowers of all nine species are more fertile than the short-styled flowers, when both forms are illegitimately fertilised. Whether P. auricula really differs from the other species in this respect I can form no opinion, as the result may have been accidental. The degree of self-fertility of a plant depends on two elements, namely, on the stigma receiving its own pollen and on its more or less efficient action when placed there. Now as the anthers of the short-styled flowers of several species of Primula stand directly above the stigma, their pollen is more likely to fall on it, or to be carried down to it by insects, than in the case of

Cuap. I. HOMOSTYLED PRIMULAS. 49

the long-styled form. It appears probable, therefore, at first sight, that the lessened capacity of the short- styled flowers to be fertilised with their own pollen, is a special adaptation for counteracting their greater liability to receive their own pollen, and thus for checking self-fertilisation. But from facts with respect. to other species hereafter to be given, this view can hardly be admitted. In accordance with the above liability, When some of the species of Primula were allowed to fertilise themselves spontaneously under a net, all insects being excluded, except such minute ones as Thrips, the short-styled flowers, notwith- standing their greater mnate self-sterility, yielded more seed than did the long-styled. None of the species, however, when insects were excluded, made a near approach to full fertility. But the long-styled form of P. Sinensis gave, under these circumstances, a considerable number of seeds, as the corolla in falling off drags the anthers, which are seated low down in the tube, over the stigma, and thus leaves plenty of pollen on it.

Homostyled species of Primula—It has now been shown that nine of the species in this genus exist under two forms, which differ not only in structure but in function. Besides these Mr. Scott enumerates 27 other species* which are heterostyled ; and to these probably others will be hereafter added. Nevertheless, some species are homostyled; that is, they exist only under a single form; but much caution is necessary on this head, as several species when cultivated are apt to become equal-styled. Mr. Scott believes that P. Scotica, verticillata, a variety of Stbirica, elata, mollis, and

* H. Miiller has givenin‘Na- viz. the Alpine P. villosa, and ture,’ Dec. 10, 1874, p. 110, a~ shows that it is fertilised exclu drawing of one of these species, sively by Lepidoptera.

50 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I,

longiflora,* are truly homostyled ; and to these may be added, according to Axell, P. stricta. Mz. Scott ex- perimented on P. Scotica, mollis, and verticillata, and found that their flowers yielded an abundance of seeds when fertilised with their own pollen. ‘This shows that they are not heterostyled in function. 2. Scotica is, however, only moderately fertile when insects are excluded, but this depends merely on the coherent pollen not readily falling on the stigma without their aid. Mr. Scott also found that the capsules of P. verticillata contained rather more seed when the flowers were fertilised with pollen from a distinct plant than when with their own pollen; and from this fact he in- fers that they are sub-heterostyled in function, though not in structure. But there is no evidence that two sets of individuals exist, which differ slightly in func- tion and are adapted for reciprocal fertilisation ; and this is the essence of heterostylism. The mere fact of a plant being more fertile with pollen from a distinct individual than with its own pollen, is com- mon to very many species, as I have shown in my work ‘On the Effects of Cross and Self-fertilisation.’

HorroniA PALUSTRIS.

This aquatic member of the Primulacez is con- spicuously heterostyled, as the pistil of the long-styled form projects far out of the flower, the stamens being enclosed within the tube; whilst the stamens of the short-styled flower project far outwards, the pistil being enclosed. This difference between the two forms has attracted the attention of various botanists, and that

* Koch was aware that this . Sprengel und Darwin,” ‘ Bot. Zei« species was homostyled: see“ Tre- tung,’ Jan, 2, 1863, p. 4. yiranus iiber Dichogamie nach

* a

ee Se ae ee

ee

Cuar. I. HOTTONIA PALUSTRIS. 51

of Sprengel,* in 1793, who, with his usual sagacity, adds that he does not believe the existence of the two forms to be accidental, though he cannot explain their purpose. The pistil of the long-styled form is more than twice as long as that of the short-styled, with the stigma rather smaller, though rougher. H. Millert gives figures of the stigmatic papillz of the two forms, and those of the long-styled are seen to be more than double the length, and much thicker than the papille of the short-styled form. The anthers in the one form do not stand exactly on a level with the stigma in the other form; for the distance between the organs is greater in the short-styled than in the long-styled flowers in the proportion of 100 to 71. In dried speci- mens soaked in water the anthers of the short-styled form are larger than those of the long-styled, in the ratio of 100 to 83. The pollen-grains, also, from the short-styled flowers are conspicuously larger than those from the long-styled ; the ratio between the diameters of the moistened grains being as 100 to 64, according to my measurements, but according to the measure- ments of H. Miller as 100 to 61; and his are probably - the more. accurate of the two. The contents of the larger pollen-grains appear more coarsely granular and of a browner tint, than those in the smaller grains. The two forms of Hottonia thus agree closely in most respects with those of the heterostyled species of Primula. The flowers of Hottonia are cross-fertilised, according to Miller, chiefly by Diptera.

Mr. Scott made a few trials on a short-styled plant, and found that the legitimate unions were in all ways more fertile than the illegitimate ; but since the pub-

* ‘Das entdeckte Geheimniss t ‘Journ. Linn. Soc. Bot.’ vol. der Nature,’ p. 103. viil. 1864, p. 79. 7 ‘Die Befruchtung,’ &., p.350.

02

HETEROSTYLED DIMORPHIC PLANTS.

Cuap. I.

lication of his paper H. Miller has made much fuller experiments, and I give his results in the following table, drawn up in accordance with my usual plan :—

TABLE 13. Hottonia palustris (from H. Miller).

Nature of Union.

Long-styled form, by pollen of pias

Legitimate union. . .

distinct plant.

Short-styled form, by aCe of Siete

Legitimate union .

Short-styled form, by own-form pollen, from a)|

distinct plant.

Illegitimate union .

Long-styled form, by own-form pollen, from sack 18

Illegitimate union .

The two legitimate unions together

The two illegitimate unions together .

The most remarkable point in this table is the small average number of seeds from the short-styled flowers when illegitimately fertilised, and the unusually large average number of seeds yielded by the illegiti- © mately fertilised long-styled flowers, relatively in both cases to the product of the legitimately fertilised The two legitimate unions compared with

flowers.*

S Average N umber Number of of Capsules Seeds per examined. rp | 34 91°4 17° | 30 66°2 19 18°7 | | | 64 78°8 . ; 37 48-1

* II. Miiller says (‘Die Be- fruchtung,’ &c., p. 352) that the ‘long-styled flowers, when illegiti- mately fertilised, yield as many seeds as when legitimately fer- tilised; but by adding up the number of seeds from all the cap- sules produced by the two methods of fertilisation, as given by him,

I arrive at the results shown in Table 13. The average number in the long-styled capsules, when , legitimately fertilised, is 91:4,

and when illegitimately fertilised,

77°5; oras 100 to 85. H. Miiller agrees with me that this is the proper manner of viewing the case.

Cuap. I. ANDROSACE. 58

the two illegitimate together yield seeds in the ratio of 100 to 61.

H. Miller also tried the effects of illegitimately fer- tilising the long-styled and short-styled flowers with their own pollen, instead of with that from another plant of the same form; and the results are very striking. For the capsules from the long-styled flowers thus treated contained, on an average, only 15:7 seeds instead of 77:5; and those from the short-styled 6°5, instead of 18-7 seeds per capsule. The number 6°5 agrees closely with Mr. Scott’s result from the same form similarly fertilised.

From some observations by Dr. Torrey, Hottonia inflata, an inhabitant of the United States, does not appear to be heterostyled, but is remarkable from pro- ducing cleistegamic flowers, as will be seen in the last chapter of this volume.

Besides the genera Primula and Hottonia, Androsace (vel Gregoria, vel Aretia) vitalliana is heterostyled. Mr. Scott* fertilised with their own pollen 21 flowers on three short-styled plants in the Edinburgh Botanic Gardens, and not.one yielded a single seed; but eight of them which were fertilised with pollen from one of the other plants of the same form, set two empty capsules. He was able to examine only dried speci- mens of the long-styled forms. But the evidence seems sufficient to leave hardly a doubt that Androsace is heterostyled. Fritz Miller sent me from South Brazil dried flowers of a Statice which he believed to be hete- rostyled. In the one form the pistil was considerably longer and the stamens slightly shorter than the cor- responding organs in the other form. But as in the shorter-styled form the stigmas reached upto the anthers

* See also Treviranus in ‘ Bot. Zeitung,’ 1863, p. 6, on this plant being dimorphic.

54 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L

of the same flower, and as I could not detect in the dried specimens of the two forms any difference in their stigmas, or in the size of their pollen-grains, I dare not rank this plant as heterostyled. From statements made by Vaucher I was led to think that Soldanella alpina was heterostyled, but it is impossible that Kerner, who has closely studied this plant, could have overlooked the fact. So again from other statements it appeared prob- able that Pyrola might be heterostyled, but H. Miller examined for me two species in North Germany, and found this not to be the case.

Cuap. II. HYBRID PRIMULAS. 59

CHAPTER IL.

Hyprip PRIMULAS.

The Oxlip a hybrid naturally produced between Primula veris and yulgaris—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 nature—Primula elatior shown to be a distinct species—Hybrids between other heterostyled species of Primula—Supplementary note on spontaneously produced hybrids in the genus Verbascum.

THE various species of Primula have produced in a state of nature throughout Europe an extraordinary number of hybrid forms. For instance, Proféssor Kerner has found no less than twenty-five such forms in the Alps.* The frequent occurrence of hybrids in this genus no doubt has been favoured by most of the species being heterostyled, and consequently requiring cross-fertilisation by insects; yet in some other genera, species which are not heterostyled and which in some respects appear not well adapted for hybrid-ferti- lisation, have likewise been largely hybridised. In certain districts of England, the common oxlip—a hybrid between the cowslip (P. veris, vel officinalis) and the primrose (P. vulgaris, vel acaulis)—is fre- quently found, and it occurs occasionally almost every-

* “Tie Primulaceen-Bastarten,’ ‘Bull. Soc. Bot. de France,’ tom. x. ‘Oesterr. Bot. Zeitschrift,” Jahr 1853, p. 178. Also in ‘ Revue des 1875, Nos. 3,4, and 5. See also Sciences Nat.’ 1875, p. 331. Godron on hybrid Primulas in

56 HYBRID PRIMULAS. Cuap. II.

where. Owing to the frequency of this intermediate hybrid form, and to the existence of the Bardfield oxlip (P. elatior), which resembles to a certain extent the common oxlip, the claim of the three forms to rank as distinct species has been discussed oftener and at greater length than that of almost any other plant. Linneus considered P. veris, vulgaris and elatior to be varieties of the same species, as do some distinguished botanists at the present day; whilst others who have carefully studied these plants do not doubt that they are distinct species. The following observations prove, I think, that the latter view is correct ; and they further show that the common oxlip is a hybrid between P. veris and vulgaris.

The cowslip differs so conspicuously in general ap- pearance from the primrose, that nothing need here be said with respect to their external characters.* But some less obvious differences deserve notice. As both species are heterostyled, their complete fertili- sation depends on insects. The cowslip is habitually visited during the day by the larger humble-bees (viz. Bombus muscorum and hortorwm), and at night by moths, as I have seen in the case of Cucullia. The primrose is never visited (and I speak after many years’ observation) by the larger humble-bees, and only rarely by the smaller kinds; hence its ferti- lisation must depend almost exclusively on moths. There is nothing in the structure of the flowers of the two plants which can determine the visits of such widely different insects. But they emit a different odour, and perhaps their nectar may have a different taste. Both the long-styled and short-styled forms of

* The Rev. W. A. Leighton seed, in ‘Ann. and Mag. of Nat. has pointed outcertain differences Hist.’ 2nd series, vol. ii. 1848, in the form of the capsules and pp. 164.

Cuar. IL. THE COMMON OXLIP. aT

the primrose, when legitimately and-naturally ferti- lised, yield on an average many more seeds per capsule than the cowslip, n namely) in the proportion of 100 to 55. When illegitimately fertilised they are likewise more fertile than the two forms of the cowslip, as shown by the larger proportion of their flowers which set cap- sules, and by the larger average number of seeds which the capsules contain. The difference also between the number of seeds produced by the long-styled and short- styled flowers of the primrose, when both are illegiti- mately fertilised, is greater than that between the number produced under similar circumstances by the two forms of the cowslip. The long-styled flowers of the primrose when protected from the access of all in- sects, except such minute ones as Thrips, yield a con- siderable number of capsules containing on an average 19-2 seeds per capsule ; whereas 18 plants of the long- styled cowslip similarly treated did not yield a single seed.

The primrose, as every one knows, flowers a little earlier in the spring than the cowslip, and inhabits slightly different stations and districts. The primrose generally grows on banks or in woods, whilst the cow- slip is found in more open places. The geographical range of the two forms is different. Dr. Bromfield re- marks * that “the primrose is absent from all the in- terior region of northern Europe, where the cowslip is indigenous.” In Norway, however, both plants range to the same degree of north latitude.t

The cowslip and primrose, when intercrossed, be-

* *Phytologist,’ vol. iii. p. 694. centre de la France,’ 1840, tom. ii. t H. Lecoq, *Géograph. Bot.de —_p. 376. With respect to the rarity Europe,’ tom. viii. 1858, pp.141, of P. veris in western Scotland, 144. See also ‘Ann. and Mag. of see H.C. Watson, ‘ Cybele Britan- Nat. Hist.’ ix. 1842, pp. 1 56, nica,’ it p. 293: 515. Also Boreau, i Flore du

rn

58 HYBRID PRIMULAS. Cuap. II.

have’ like distinct species, for they are far from being mutually fertile. Gartner* crossed 27 flowers of P. vulgaris with pollen of P. veris, and obtained 16 capsules; but these did not contain any good seed. He also crossed 21 flowers of P. veris with

pollen of P. vulgaris; and now he got only five’

capsules, containing seed in a still less perfect condition. Gartner knew nothing about hetero- stylism; and his complete failure may perhaps be accounted for by his having crossed together the same forms of the cowslip and primrose; for such crosses would have been of an illegitimate as well as of a hybrid nature, and this would have increased their sterility. My trials were rather more fortunate. Twenty-one flowers, consisting of both forms of the cowslip and primrose, were intercrossed legitimately, and yielded seven capsules (¢.e. 83 per cent.), contain- ing on an average 42 seeds; some of these seeds, however, were so poor that they probably would not have germinated. ‘Twenty-one flowers on the same cowslip and primrose plants were also intercrossed illegiti- mately, and they likewise yielded seven capsules (or 33 per cent.), but these contained on an average only 13 good and bad seeds. I should, however, state that some of the above flowers of the primrose were fertilised with pollen from the polyanthus, which is certainly a - variety of the cowslip, as may be inferred from the per- fect fertility inter se of the crossed offspring from these two plants.t ‘To show how sterile these hybrid unions

* ‘ Bastarderzeugung, 1849, p. ciently numerous. ‘The degree of

“721.

+ Mr. Scott has discussed the nature of the polyanthus (‘ Proc. Linn. Soe.’ viii. Bot. 1864, p. 103), and arrives at a different conclusion; but I do not think that his experiments were suffi-

infertility of a cross is liable to much fluctuation. Pollen from the cowslip at first appears rather more efficient on the primrose than that of the polyanthus; for 12 flowers of both forms of the prim- rose, fertilised legitimately and

Cuap. II. THE COMMON OXLIP. 59

were I may remind the reader that 90 per cent. of the flowers of the primrose fertilised legitimately with primrose-pollen yielded capsules, containing on an average 66 seeds; and that 54 per cent. of the flowers fertilised illegitimately yielded capsules containing on an average 30°5 seeds per capsule. The primrose, especially the short-styled form, when fertilised by the cowslip, is less sterile, as Gartner likewise observed,

than is the cowslip when fertilised by the primrose. The above experiments also show that a cross between the. same forms of the primrose and cowslip is much more sterile than that between different forms of these two species. ;

The seeds from the several foregoing crosses were sown, but none germinated except those from the short-styled primrose fertilised with pollen of the polyanthus; and these seeds were the finest of the whole lot. I thus raised six plants, and compared them with a group of wild oxlips which I had trans- planted into my garden. One of these wild oxlips produced slightly larger flowers than the others, and this one was identical in every character (in foliage, flower-peduncle, and flowers) with my six plants, excepting that the flowers of the latter were tinged of a dingy red colour, from being descended from the polyanthus.

We thus see that the cowslip and primrose can- not be crossed either way except with considerable difficulty, that they differ conspicuously in external appearance, that they differ in various physiological

illegitimately with pollen of the cowslip gave five capsules, contain- ing on an average 32:4 seeds,

22°6 seeds. On the other hand, the seeds produced by the poly- anthus- pollen were much the

whilst 18 flowers similarly fertil- ised by polyantlius-pollen yielded only five capsules, containing only

finest of the whole lot, and were the only ones which germinated.

60 HYBRID PRIMULAS. Cuap. IL.

characters, that they inhabit slightly different stations and range differently. Hence those botanists who rank these plants as varieties ought to be able to prove that they are not as well fixed in character as are most species ; and the evidence in favour of such instability of character appears at first sight very strong. It rests, first, on statements made by several competent observers that they have raised cowslips, primroses, and oxlips from seeds of the same plant; and, secondly, on the frequent occurrence in a state of nature of plants presenting every intermediate gradation between the cowslip and primrose.

The first statement, however, is of little value; for, heterostylism not being formerly understood, the seed-bearing plants were in no instance* pro- tected from the visits of insects; and there would be almost as much risk of an isolated cowslip, or of several cowslips if consisting of the same form, being crossed by a neighbouring primrose and producing oxlips, as of one sex of a dicecious plant, under similar circumstances, being crossed by the opposite sex of an allied and neighbouring species. Mr. H. C. Wat- son, a critical and most careful observer, made many experiments by sowing the seeds of cowslips and of

various kinds of oxlips, and arrived at the following

conclusion,t namely, “that seeds of a cowslip can produce cowslips and oxlips, and that seeds of an oxlip can produce cowslips, oxlips, and primroses.” This conclusion harmonises perfectly with the view that in

* One author states in the ¢ Pliy- tologist’ (vol. iii. p. 703) that he coyceredwith bell-glasses some cow- slips, primroses, &e , on which he experimented. He specifies all tiie details of his experiment, but does not say that he artificially fertilised his plants; yet he ob-

tainel an abundance of seed, which is simply impossible. Hence there must have been some strange error in these ex- periments, which may be passed over as valueless,

t ‘Phytologist? ii. pp. 217, 852; ili. p. 43. *

Cuap. II. THE COMMON OXLIP. 61

all eases, when such results have been obtained, the unprotected cowslips have been crossed by primroses, and the unprotected oxlips by either cowslips or primroses ; for in this latter case we might expect, by the aid of reversion, which notoriously comes into powerful action with hybrids, that the two parent-forms in appearance pure, as well as many intermediate gra- dations, would be occasionally produced. Nevertheless the two following statements offer considerable diffi- culty. The Rey. Prof. Henslow* raised from seeds of a cowslip growing in his garden, various kinds of oxlips and one perfect primrose; but a statement in the same paper perhaps throws light on this anomalous result. Prof. Henslow had previously transplanted into his garden a cowslip, which completely changed its ap- pearance during the following year, and now resembled an oxlip. Next year again it changed its character, and produced, in addition to the ordinary umbels, a few single-flowered scapes, bearing flowers somewhat smaller and more deeply coloured than those of the common primrose. From what Ihave myself observed with oxlips, I cannot doubt that this plant was an ox- lip in a highly variable condition, almost like that of the famous Cytisus adami. This presumed oxlip was propagated by offsets, which were planted in different parts of the garden; and if Prof. Henslow took by mistake seeds from one of these plants, especially if it had been crossed by a primrose, the result would be quite intelligible. Another case is still more difficult to understand: Dr. Herbertt raised, from the seeds of a highly cultivated red cowslip, cowslips, oxlips of yarious kinds, and a primrose. ‘This case, if accurately

* Loudon’s ‘ Mag. of Nat. Hist.’ iii. 1830, p. 409. t ‘Transact. Hort. Soc.’ iv. p. 19.

62 HYBRID PRIMULAS. Cuap. II.

recorded, which I much doubt, is explicable only on the improbable assumption that the red cowslip was not of pure parentage. With species and varieties of many kinds, when intercrossed, one is sometimes strongly prepotent over the other; and instances are known* of a variety crossed by another, producing offspring which in certain characters, as in colour, hairiness, &c., haye proved identical with the pollen- bearing parent, and quite dissimilar to the mother- plant; but I do not know of any instance of the off- spring of a cross perfectly resembling, in a consider- able number of important characters, the father alone. It is, therefore, very improbable that a pure cowslip crossed by a primrose should ever produce a primrose in appearance pure. Although the facts given by Dr. Herbert and Prof. Henslow are difficult to explain, yet until it can be shown that a cowslip ora primrose, carefully protected from insects, will give birth to at least oxlips, the cases hitherto recorded have little weight in leading us to admit that the cowslip and primrose are varieties of one and the same species. Negative evidence is of little value; but the follow- ing facts may be worth giving :—Some cowslips which had been transplanted from the fields into a shrubbery were again transplanted into highly manured land. In the following year they were protected from insects, artificially fertilised, and the seed thus procured was sown ina hotbed. The young plants were afterwards planted out, some in very rich soil, some in stiff poor clay, some in old peat, and some in pots in the green- house ; so that these plants, 765 in number, as well as their parents, were subjected to diversified and un-

* T have given instances in my tication,’ chap, xv. 2nd edit. vol. work ‘On the Variation of Ani- ii. p. 69. mals and Plants under Domes-

Cap. II. THE COMMON OXLIP. 63

natural treatment; but not one of them presented the least variation except in size—those in the peat at- taining almost gigantic dimensions, and those in the clay being much dwarfed.

I do not, of course, doubt that cowslips exposed during several successive generations to changed con- ditions would vary, and that this might occasionally occur in a state of nature. Moreover, from the law of analogical variation, the varieties of any one species of Primula would probably in some cases resemble other species of the genus. For instance I raised a red primrose from seed from a protected plant, and the flowers, though still resembling those of the primrose, were borne during one season in umbels on a long foot- stalk like that of a cowslip.

With regard to the second class of facts in support of the cowslip and primrose being ranked as mere varieties, namely, the well-ascertained existence in a state of nature of numerous linking forms* :—If it can be shown that the common wild oxlip, which is inter- mediate in character between the cowslip and prim- rose, resembles in sterility and other essential respects a hybrid plant, and if it can further be shown that the oxlip, though in a high degree sterile, can be fertilised by either parent-species, thus giving rise to still finer gradational links, then the presence of such linking forms in a state of nature ceases to be an argument of any weight in favour of the cowslip and primrose being varieties, and becomes, in fact, an argument on the other side. The hybrid origin of a plant in a state of nature can be recognised by four tests: first, by its occurrence only where both presumed parent-

* See an excellent article on in the ‘ Phytologist, vol. iii. p, this subject by Mr. H. C. Watson 43.

a

64 HYBRID PRIMULAS. Caapr. II.

species exist or have recently existed ; and this holds good, as far as I can discover, with the oxlip; but the P. elatior of Jacq., which, as we shall presently see, constitutes a distinct species, must not be confounded with the common oxlip. Secondly, by the supposed hybrid plant being nearly intermediate in character between the two parent-species, and especially by its resembling hybrids artificially made between the same two species. Now the oxlip is intermediate in cha- racter, and resembles in every respect, except in the colour of the corolla, hybrids artificially produced be- tween the primrose and the polyanthus, which latter is a variety of the cowslip. Thirdly, by the supposed hybrids being more or less sterile when crossed tnter se: but to try this fairly two distinct plants of the same parentage, and not two flowers on the same plant, should be crossed; for many pure species are more or less sterile with pollen from the same individual plant ; and in the case of hybrids from heterostyled species the opposite forms should be crossed. Fourthly and lastly, by the supposed hybrids being much more fertile when crossed with either pure parent-species than when crossed dnter se, but still not as fully fertile as the parent-species.

For the sake of ascertaining the two latter points, I transplanted a group of wild oxlips into my garden. They consisted of one long-styled and three short-styled plants, which, except in the co- rolla of one being slightly larger, resembled each other closely. The trials which were made, and the results obtained, are shown in the five following tables. No less than twenty different crosses are necessary in order to ascertain fully the fertility of hybrid heterostyled plants, both inter se and with their two parent-species. In this instance 256 flowers

_ al

Cuar. II. THE COMMON OXLIP. 65

were crossed in the course of four seasons. I may mention, as a mere curiosity, that if any one were to raise hybrids between two trimorphic heterostyled species, he would have to make 90 distinct unions in order to ascertain their fertility in all ways; and as he would have to try at least 10 flowers in each case, he would be compelled to fertilise 900 flowers and count their seeds. This would probably exhaust the patience of the most patient man.

TABLE 14.

’ Crosses inter se between the two forms of the common Ozlip.

Mlegitimate union. | Legitimate union. Illegitimate union. | Legitimate union.

Short-styled ox-| Short-styled ox- Long-styled ox-| Long-styled ox- lip, by pollen of lip, by pollen of lip, by its own/lip, by pollen of short-styled oxlip:|long-styled oxlip: pollen: 24 flowers | short-styled oxlip: 20 flowers fertilised, |10flowers fertilised, fertilised, produced | 10 flowers fertilised, did not produce one did not produce one five capsules, con- | did not produce one capsule. | capsule. taining 6, 10, 20, ‘capsule.

| 8, and 14 seeds, Average 11°6

TABLE 15.

Both forms of the Oxlip crossed with Pollen of both forms of the Cowslip, P. veris.

Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union.

taining 7, 3, and 3 taining 13 wretched taining 21 and 28 wretched seeds, ap-| seeds, | very tine seeds. parently incapable | of germination.

|

eee

66 HYBRID PRIMULAS. Cuap. 11.

TABLE 16.

Both forms of the Oxlip crossed with Poilen of both forms of the Primrose, P. vulgaris.

Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union.

Short-styled ox-| Short-styled ox-| Long-styled ox-| Long-styled ox- lip, by pollen of}lip, by pollen of lip, by pollen of|lip, by pollen of short-styled prim-}long-styled prim- long-styled prim-|short-styled prim- rose: 34 flowers!rose: 26 flowers|rose: 11 flowers|rose: 5 flowers fertilised, produced | fertilised, produced | fertilised, produced | fertilised, produced two capsules, con-| six capsules, con- ‘four capsules, con-| five capsules, con- taining 5 and 12) taining 16, 20,5, 10,| taining 10, 7,5, and | taining 26, 32, 23, seeds. | 19, and 24 seeds. 6 wretched seeds. | 28, and 34 seeds.

| Average 15°7. Many Average 7°0. Average 28°6. ‘of the seeds very poor, some good.

TABLE 17. Both forms of the Cowslip crossed with Pollen of both forms of the Oxlip.

{ | Illegitimate union. | Legitimate union. | [legitimate union. | Legitimate union.

Short-styled cow-| Long-styled cow- _ Long-styled cow-| Short-styled cow- slip, by pollen ofjslip, by pollen of slip, by pollen of) slip, by pollen of short-styled oxlip:|short-styled oxlip: long-styled oxlip:|long-styled oxlip: 8 flowers fertilised, 8 flowers fertilised, 8 flowers fertilised, | 8 flowers fertilised, produced not one) produced one cap- produced three cap-| produced eight cap-

capsule. sule, containing 26 sules, containing 5, | sules, containing 58, | seeds. 6, and 14 seeds.|38, 31, 44, 23, 26, | Average 8:3. 37, and 66 seeds.

Average 40°4.

TABLE 18. Both forms of the Primrose crossed with Pollen of both forms of the Oxlip.

| Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union.

Short-styledprim-| Long-styled prim- | Long-styled prim- Short-styled prim- rose, by pollen of rose, by pollen of rose, by pollen of rose, by pollen of short-styled oxlip:short-styled oxlip; long-styled oxlip:|long-styled oxlip: 8 flowers fertilised, 8 flowers fertilised, 8 flowers fertilised, | 8 flowers fertilised, produced not one produced two cap- | _ produced eight cap-| produced four cap-

) and 13 seeds. Ave-| seeds,some good and

(Tage 14:0. some bad. Average

| 48°7.

ee a

Cuar. II. THE COMMON OXLIP. 67

We see in these five tables the number of capsules and of seeds produced, by crossing both forms of the oxlip in a legitimate and illegitimate manner with one another, and with the two forms of the primrose and cowslip. I may premise that the pollen of two of the short-styled oxlips consisted of nothing but minute aborted whitish cells; but in the third short-styled plant about one-fifth of the grains appeared in a sound condition. Hence it is not surprising that neither the short-styled nor the long-styled oxlip produced a single seed when fertilised with this pollen. Nor did the pure cowslips or primroses when illegitimately fer- tilised with it; but when thus legitimately fertilised ' they yielded a few good seeds. The female organs of the short-styled oxlips, though greatly deteriorated in power, were in a rather better condition than the male organs; for though the short-styled oxlips yielded no seed when fertilised by the long-styled oxlips, and hardly any when illegitimately fertilised by pure cow- slips or primroses, yet when legitimately fertilised by these latter species, especially by the long-styled primrose, they yielded a moderate supply of good seed.

The long-styled oxlip was more fertile than the three short-styled oxlips, and about half its pollen- grains appeared sound. It bore no seed when legiti- mately fertilised by the short-styled oxlips; but this no doubt was due to the badness of the pollen of the latter; for when illegitimately fertilised (Table 14) by its own pollen it produced some good seeds, though much fewer than self-fertilised cowslips or primroses would have produced. The long-styled ox- lip likewise yielded a very low average of seed, as may be seen in the third compartment of the four latter tables, when illegitimately fertilised by, and when

68 . HYBRID PRIMULAS. Cuar. IL.

illegitimately fertilising, pure cowslips and primroses. The four corresponding legitimate unions, however, were moderately fertile, and one (viz. that between a short- styled cowslip and the long-styled oxlip in Table 17) was nearly as fertile as if both parents had been pure. A short-styled primrose legitimately fertilised by the long-styled oxlip (‘Table 18) also yielded a moderately good average, namely 48°7 seeds; but if this short- styled primrose had been fertilised by a long-styled primrose it would have yielded an average of 65 seeds. If we take the ten legitimate unions together, and the ten illegitimate unidns together, we shall find that 29 per cent. of the flowers fertilised in a legitimate manner yielded capsules, these containing on an average 27°4 good and bad seeds; whilst only 15 per cent. of the flowers fertilised in an illegitimate manner yielded capsules, these containing on an average only 11:°0 good and bad seeds.

In a previous part of this chapter it was shown that illegitimate crosses between the long-styled form of the primrose and the long-styled cowslip, and between the short-styled primrose and short-styled cowslip, are mere sterile than legitimate crosses between these two species; and we now see that the same rule holds good almost invariably with their hybrid offspring, whether — these are crossed inter se, or with either parent-species ; so that in this particular case, but not as we shall pre- sently see in other cases, the same rule prevails with the pure unions between the two forms of the same heterostyled species, with crosses between two distinct heterostyled species, and with their hybrid offspring.

Seeds from the long-styled oxlip fertilised by its own pollen were sown, and three long-styled plants raised. The first of these was identical in every character with its parent. The second bore rather

Cuap. IT. THE COMMON OXLIP. 69

smaller flowers, of a paler colour, almost like those of the primrose; the scapes were at first single-flowered, but later in the season a tall thick scape, bearing many flowers, like that of the parent oxlip, was thrown up. The third plant likewise produced at first only single- flowered scapes, with the flowers rather small and of a darker yellow; but it perished early. The second plant also died in September; and the first plant, though all three grew under very favourable con- ditions, looked very sickly. Hence we may infer that seedlings from self-fertilised oxlips would hardly be able to exist in a state of nature. I was surprised to find that all the pollen-grains in the first of these seed- ling oxlips appeared sound; and in the second only a moderate number were bad. These two plants, however, had not the power of producing a proper number of seeds; for though left uncovered and surrounded by pure primroses and cowslips, the capsules were esti- mated to include an average of only from fifteen to twenty seeds.

From having many experiments in hand, I did not sow the seed obtained by crossing both forms of the primrose and cowslip with both forms of the oxlip, which I now regret; but I ascertained an interest- ing point, namely, the character of the offspring from oxlips growing in a state of nature near both primroses and cowslips. The -oxlips were the same plants which, after their seeds had been collected, were transplanted and experimented on. From the seeds thus obtained eight plants were raised, which, when they flowered, might have been mistaken for pure primroses ; but on close comparison the eye in the centre of the corolla was seen to be of a darker yellow, and the peduncles more elongated.. As the season ad- vanced, one of these plants threw up two naked scapes,

70 HYBRID PRIMULAS. Cuapr. IL

-7 inches in height, which bore umbels of flowers of the same character as before. This fact led me to ex- amine the other plants after they had flowered and were dug ‘up; and I found that the flower-peduncles of all sprung from an extremely short common scape, of which no trace can be found in the pure primrose. Hence these plants are beautifully intermediate be- tween the oxlip and the primrose, inclining rather towards the latter ; and we may safely conclude that the parent oxlips had been fertilised by the surrounding primroses.

From the various facts now given, there can be no doubt that the common oxlip is a hybrid between the cowslip (P. verts, Brit. Fl.) and the primrose (P. vul- garis, Brit. Fl.), as has been surmised by several botanists. It is probable that oxlips may be produced either from the cowslip or the primrose as the seed- bearer, but oftenest from the latter, as I judge from the nature of the stations in which oxlips are generally found,* and from the primrose when crossed by the cowslip being more fertile than, conversely, the cowslip by the primrose. The hybrids themselves.are also rather more fertile when crossed with the primrose than with the cowslip. Whichever may be the seed- bearing plant, the cross is probably between different forms of the two species ; for we have seen that legiti- mate hybrid unions are more fertile than illegitimate hybrid unions. Moreover a friend in Surrey found that 29 oxlips which grew in the neighbourhood of his house consisted of 13 long-styled and 16 short- styled plants; now, if the parent-plants had been illegitimately united, either the long- or short-styled form would have greatly preponderated, as we shall

* See also on this head Hardwicke’s ‘Science Gossip, 1867, pp, 114, 137.

i a _

— ee ee

Cuap. II. THE COMMON OXLIP. ral

hereafter see good reason to believe. The case of the oxlip is interesting; for hardly any other in- stance is known of a hybrid spontaneously arising in such large numbers over so wide an extent of coun- try. The common oxlip (not the P. elatior of Jacq.) is found almost everywhere throughout England, where both cowslips and primroses grow. In some districts, as I have seen near Hartfield in Sussex and in parts of Surrey, specimens may be found on the borders of almost every field and small wood. In other districts the oxlip is comparatively rare: near my own resi- dence I have found, during the last twenty-five years, not more than five or six plants or groups of plants. It is difficult to conjecture what is the cause of this difference in their number. It is almost necessary that a plant, or several plants belonging to the same form, of one parent-species, should grow near the opposite form of the other parent-species; and it is further necessary that both species should be fre- quented by the same kind of insect, no doubt a moth. The cause of the rare appearance of the oxlip in certain districts may be the rarity of some moth, which in other districts habitually visits both the primrose and cowslip.

Finally, as the cowslip and primrose differ in the various characters above specified,—as they are in a high degree sterile when intercrossed,—as there is no trustworthy evidence that either species, when un- crossed, has ever given birth to the other species or to any intermediate form,—and as the intermediate forms which are often found in a state of nature have been shown to be more or less sterile hybrids of the first or second generation,—we must for the future look at the cowslip and primrose as good and true species.

T2 THE BARDFIELD OXLIP. Cuar. IL.

Primula elatior, Jacq., or the Bardfield Oxlip, is found in England only in two or three of the eastern counties. On the Continent it has a somewhat dif- ferent range from that of the cowslip and primrose ; and it inhabits some districts where neither.of these species live.* In general appearance it differs so much from the common oxlip, that no one accustomed to see both forms in the living state could afterwards confound them; but there is scarcely more than a ‘single character by which they can be distinetly de- fined, namely, their linear-oblong capsules equalling the calyx in length.f The capsules when mature differ conspicuously, owing to their length, from those of the cowslip and primrose. With respect to the fertility of the two forms when these are united in the four possible methods, they behave like the other hetero- styled species of the genus, but differ somewhat (see Tables 8 and 12) in the smaller proportion of the il- legitimately fertilised flowers which set capsules. That P. elatior is not a hybrid is certain, for when the two forms were legitimately united they yielded the large average of 47°1 seeds, and when illegitimately united 30°5 per capsule ; whereas, of the four possible unions (Table 14) between the two forms of the common ox- lip which we know to be a hybrid, one alone yielded any seed; and in this case the average number was only 11:6 per capsule. Moreover I could not detect a single bad pollen-grain in the anthers of the short- styled P. elatior ; whilst in two short-styled plants of the common oxlip all the grains were bad, as were a large majority in a third plant. As the common

* For England, see Hewett C. 1858, p, 142. For the Alps, see Watson, ‘Cybele Britannica, vol. ‘Ann. and Mag. Nat. Hist.’ vol. ii, 1849, p. 292. For the Con- ix. 1842, pp. 156 and 515. tinent, see Lecoq, ‘ Géograph. + Babington’s ‘ Manual of Brit- Botanique de ’ Europe, tom. viii. ish Botany,’ 1851, p. 258.

Cuar. I. THE BARDFIELD OXLIP. 13

oxlip is a hybrid between the primrose and cowslip, it is not surprising that eight long-styled flowers of the primrose, fertilised by pollen from the long-styled common oxlip, produced eight capsules (Table 18), containing, however, only a low average of seeds; whilst the same number of flowers of the primrose, similarly fertilised by the long-styled Bardfield oxlip, produced only a single capsule; this latter plant being an altogether distinct species from the primrose. Plants of P. elatior have been propagated by seed in a garden for twenty-five years, and have kept all this time quite constant, excepting that in some cases the flowers varied a little in size and tint.* Nevertheless, according to Mr. H. C. Watson and Dr. Bromfield,t plants may be occasionally found in a state of nature, in which most of the characters by which this species can be distinguished from P. veris and vulgaris fail ; but such intermediate forms are probably due to hybridisation ; for Kerner states, in the paper before referred to, that hybrids sometimes, though rarely, arise in the Alps between P. elatior and veris.

Finally, although we may freely admit that Primula veris, vulgaris, and elatior,as well as all the other species of the genus, are descended from a common

primordial form, yet from the facts above given, we

must conclude that these three forms are now as fixed in character as are many others which are universally ranked as true species. Consequently they have as good a right to receive distinct specific names as have, for instance, the ass, quagga, and zebra.

Mr. Scott has arrived at some interesting results by

* See Mr. H. Doubleday in the __ p. 462. *Gardener’s Chronicle, 1867, p. t ‘ Phytologist,’ vol. i. p. 1001, 435, also Mr. W. Marshall, ibid. and vol. iii. p. 695.

74 HYBRID PRIMULAS. Cuar. IL.

crossing other heterostyled species of Primula.* I have already alluded to his statement, that in four instances (not to mention others) a species when crossed with a distinct one yielded a larger number of seeds than the same species fertilised illegitimately with its own-form pollen, though taken from a distinct plant. It has long been known from the researches of Kélreuter and Gartner, that two species when crossed reciprocally sometimes differ as widely as is possible in their fer- tility : thus A when crossed with the pollen of B will yield a large number of seeds, whilst B may be crossed repeatedly with pollen of A, and will never yield a single seed. Now Mr. Scott shows in several cases that the same law holds good when two heterostyled species of Primula are intercrossed, or when one is crossed with a homostyled species. But the results are much more complicated than with ordinary plants, as two heterostyled dimorphic species can be intercrossed in eight different ways. I will give one instance from Mr. Scott. The long-styled P. hirsuta fertilised legi- timately and illegitimately with pollen from the two forms of P. auricula, and reciprocally the long-styled P. auricula fertilised legitimately and illegitimately with pollen from the two forms of P. hirsuta, did not produce a single seed. Nor did the short- styled P. hirsuta when fertilised legitimately and illegitimately with the pollen of the two forms of P. auricula. On the other hand, the short-styled P. auricula fertilised with pollen from the long-styled P. hirsuta yielded capsules containing on an average no less than 56 seeds; and the short-styled P. auricula by pollen of the short-styled P. hirsuta yielded capsules containing on an average 42 seeds

* ¢ Journ. Linn, Soc. Bot.’ vol. viii. 1864, p. 93 to end.

Ouar. IL. HYBRID VERBASCUMS. 75

per capsule. So that out of the eight possible unions between the two forms of these two species, six were utterly barren, and two fairly fertile. We have seen also the same sort of extraordinary irregularity in the results of my twenty different crosses (Tables 14 to 18), between the two forms of the oxlip, prim- rose, and cowslip. Mr. Scott remarks, with respect to the results of his trials, that they are very surprising, as they show us that “the sexual forms of a species manifest in their respective powers for conjunction with those of another species, physiological peculiari- ties which might well entitle them, by the criterion of fertility, to specifie distinction.”

Finally, although P. veris and vulgaris, when crossed legitimately, and especially when their hybrid offspring are crossed in this manner with both parent-species, were decidedly more fertile, than when crossed in an illegitimate manner, and although the legitimate cross effected by Mr. Scott between P. auricula and hirsuta was more fertile, in the ratio of 56 to 42, than the illegitimate cross, nevertheless it is very doubtful, from the extreme irregularity of the results in the various other hybrid crosses made by Mr. Scott, whether it can be predicted that two heterostyled species are generally more fertile if crossed legitimately (¢.e. when opposite forms are united) than when crossed illegiti- mately.

Supplementary Note on some wild hybrid Verbascums.

In an early part of this chapter I remarked that few other instances could be given of a hybrid spontane- ously arising in such large numbers, and over so wide an extent of country, as that of the common oxlip ; but per- haps the number of well-ascertained cases of naturally

76 UYBRID VERBASCUMS. Crap. IL.

produced hybrid willows is equally great.* Numerous spontaneous hybrids between several species of Cistus, found near Narbonne, have been carefully described by M. Timbal-Lagrave,t and many hybrids between an Aceras and Orchis have been observed by Dr. Weddell. In the genus Verbascum, hybrids are supposed to have often originated§ in a state of nature ; some of these un- doubtedly are hybrids, and several hybrids have origi- nated in gardens; but most of these cases require,|| as Gartner remarks, verification. Hence the following case is worth recording, more especially as the two species in question, V. thapsus and lychnitis, are per- fectly fertile when insects are excluded, showing that the stigma of each flower receives its own pollen. Moreover the flowers offer only pollen to insects, and have not been rendered attractive to them by secret- ing nectar.

I transplanted a young wild plant into my garden for experimental purposes, and when it flowered it plainly differed from the two species just mentioned and from a third which grows in this neighbourhood. I thought that it was a strange variety of V. thapsus. It attained the height (by measurement) of 8 feet! It was covered with a net, and ten flowers were fertilised with pollen from the same -plant; later in the season, ~ when uncovered, the flowers were freely visited by pollen-collecting bees; nevertheless, although many capsules were produced, not one contained a single seed. During the following year this same plant was

* Max Wichura, ‘ Die Bastard- § See, for instance, the *‘ Eng- befruchtung, &c., der Weiden, lish Flora,’ by Sir J. E. Smith, 1865. 1824, vol. i. p. 307.

+ ‘Mém. del Acad. des Sciences || See Gartner, ‘ Bastarderzeu-

de Toulouse,’ 5° série, tom. v. p.28. gung,’ 1849, p. 590. t ‘Annales des Sc. Nat.’ 3° série, Bot. tom. xviii. p. 6.

Cuar. I. HYBRID VERBASCUMS. ie i:

left uncovered near plants of V. thapsus and lychnitis ; but again it did not produce a single seed. Four flowers, however, which were repeatedly fertilised with pollen of V. lychnitis, whilst the plant was tem- porarily kept under a net, produced four capsules, which contained five, one, two, and two seeds; at the same time three flowers were fertilised with pollen of V. thapsus, and these produced two, two, and three seeds. To show how unproductive these seven capsules were, I may state that a fine capsule from a plant of V. thapsus growing close by contained above 700 seeds. These facts led me to search the moderately-sized field whence my plant had been removed, and I found in it many plants of V. thapsus and lychnitis as well as thirty-three plants intermediate in character between these two species. These thirty-three plants differed much from one another. In the branching of the stem they more closely resembled V. lychnitis than V. thapsus, but in height the latter species. In the shape of their leaves they often closely approached V. lychnitis, but “some had leayes extremely woolly on the upper surface and decurrent like those of V. thapsus; yet the degree of woolliness and of decurrency did not always go together. In the petals being flat and remaining open, and in the manner in which the anthers of the longer stamens were attached to the filaments, these plants all took more after V. lychnitis than V. thapsus. In the yellow colour of the corolla they all resembled the latter species. On the whole, these plants appeared to take rather more after V. lychnitis than V. thapsus. On the supposition that they were hybrids, it is not an anomalous circumstance that they should all have pro- duced yellow flowers; for Gartner crossed white and yellow-flowered varieties of Verbascum, and the off- spring thus produced never bore flowers of an inter-

78 HYBRID VERBASCUMS. Cuar. II.

mediate tint, but either pure white or pure yellow flowers, generally of the latter colour.*

My observations were made in the autumn; so that I was able to collect some half-matured capsules from twenty of the thirty-three intermediate plants, and likewise capsules of the pure V. lychnitis and thapsus growing in the same field. All the latter were filled with perfect but immature seeds, whilst the capsules of the twenty intermediate plants did not contain one single perfect seed. These plants, consequently, were absolutely barren. From this fact,—from the one plant which was transplanted into my garden yielding when artificially fertilised with pollen from V. lychnitis and thapsus some seeds, though extremely few in number,— from the circumstance of the two pure species growing in the same field,—and from the intermediate character of the sterile plants, there can be no doubt that they were hybrids. Judging from the position in which they were chiefly found, I am inclined to believe they were descended from V. thapsus as the seed-bearer, and V.lychnitis as the pollen-bearer.

It is known that many species of Verbascum, when the stem is jarred or struck by a stick, cast off their - flowers.| This occurs with V. thapsus, as I have re- peatedly observed. The corolla first separates from its attachment, and then the sepals spontaneously bend inwards so as to clasp the ovarium, pushing off the corolla by their movement, in the course of two or three minutes. Nothing of this kind takes place with young barely expanded flowers. With Verbascum lych- nitis and, as I believe, V. phaeniceum the corolla is not cast

* ‘ Bastarderzeugung, p. 307. Smith, vol. ii. p. 210. I was

+ This was first observed by cuided to these references by the Correa de Serra: see Sir J. E. Rev. W. A. Leighton, who ob- Smith's ‘ English Flora, 1824, vol. _ served this same phenomenon with i. p. 311; also ‘Life of SirJ. E. V. virgatum.

Cuar. IL. HYBRID VERBASCUMS. 79

off, however often and severely the stem may be struck. In this curious property the above-described hybrids took after V. thapsus; 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 V. thapsus 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 pure 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 Effects of Cross and Self-fertilisation,’ 1876, p. 89.

80 HYBRID VERBASCUMS. Cuapr. IT.

cautious in inferring the specific identity of two forms from the presence of intermediate gradations; nor would it be easy in the many cases in which hybrids 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 ease generally produce fairly fertile offspring, yet well- pronounced exceptions to this rule occur; and here we have two species of Verbascuin which evidently cross with the greatest ease, but produce hybrids which are excessively sterile.

Cuar. III. *LINUM GRANDIFLORUM. 81

CHAPTER III. HererostyLeD Diworruic PLANts—continued.

Linum grandiflorum, long-styled form utterly sterile with own-form pollen—Linum perenne, torsion of the pistils in the long-styled form alone—Homostyled species of Linum—Pulmonaria officinalis, singular difference in self-fertility between the English and German long-styled plants—Pulmonaria angustifolia shown to be a distinct species, long-styled form completely self-sterile—Polygonum fago- pyrum—Various other heterostyled genera—Rubiacee—Mitchella repens, fertility of the flowers in pairs—Houstonia—Faramea, remarkable difference in the pollen-grains of the two forms ; tor- sion of the stamens in the short-styled form alone; development not as yet perfect—The heterustyled structure in the several Rubiaceous genera not due to desceut in common.

Ir has long been known* that several species of Linum present two forms, and having observed this fact in L. flavum more than thirty years ago, I was led, after ascertaining the nature of heterostylism in Primula, to examine the first species of Linum which I met with, namely, the beautiful L. grandiflorum. 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

* Treviranus has shown that original paper, ‘Bot. Zeitung,’ this is the case in hisreview of my 1863, p. 189.

* .

82 HETEROSTYLED DIMORPHIC PLANTS. Cuap. II.

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,

Fig. 4.

Long-styled form. Short-styled form. 8s stigmas, LINUM GRANDIFLORUM.

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 the anthers, or reaching up*only to about their middle. Nevertheless, 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 papille 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 papillee are more crowded and darker-coloured than in those with the longer

Cuapr. III. LINUM GRANDIFLORUM. 83

stigmas. Considering the 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 sereen 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 wltimately 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 DIMOKPHIC PLANTS. Cuapr. IIL.

with the short-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 away. 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 sucking 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 1862 [ raised thirty-four plants of this Linum in a hot-bed ; and these consisted of seventeen long-styled and seventeen short-styled forms. Seed sown later in the

i od

Cuap. III. LINUM GRANDIFLORUM. 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 capsule, 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 with pollen from the long-styled form; and they produced seven fine capsules. ‘These included on an average

86 HETEROSTYLED DIMORPHIC PLANTS. Cuar. III.

7°6 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. Irom 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 lett 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 legitimate and two illegitimate unions cannot be compared with certainty; but judging from the number of good seeds per capsule, the difference was at least in the ratio of 100 to 7, and probably much ereater. Hildebrand tested my results, but only on a single

short-styled plant, by fertilismg many flowers with — )

their own-form pollen ; and these did not produce any

Crap. III. LINUM GRANDIFLORUM. 87

seed. This confirms my suspicion that some of the few capsules produced by the foregoing seventeen short-styled plants 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 pots 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 4 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.

Secondly. 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,’ Jan. 1, 1864, p. 2. 5

88 HETEROSTYLED DIMORPHIC PLANTS. Cuap. ITI.

ant this 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.

Thirdly. 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 :—

Siathly. 1 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 were penetrated by innumerable tubes, which were as yet short, 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.

Ninthly. 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 ney short tubes into the tissue.

Tenthly. Repeated the experiment, with the same result after twenty-four hours, excepting that only two own-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 DIMORPHIC PLANTS. Cuap. 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 papillee, 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, apparently 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- jlorum (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 papillae. 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

Cuapr. IIT. LINUM PERENNE. 91

shall presently return. Differently from what occurs in L. grandiflorum, the long-styled flowers have stamens hardly 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 tothe 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 flowers.

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- plant 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 with 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 eyer 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. Cuap. IIL.

the eight good capsules contained on an ayerage 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. grandiflorum, 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

e

Crap. ILL. LINUM PERENNE. 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. grandiflorum, that the pollen-grains of both forms of LD. 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 own 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 grandiflorum 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 which 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 ease, 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 HETEROSTYLED DIMORPHIC PLANTS. Cuape. 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 Coniferee, 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 the stigmas being downy or plumose (as in the Graminew, 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 ease 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 workers. 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 Linwm perenne. 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 ease with the stigmas of the long-styled flowers of J. perenne whilst in bud. But by the time the flowers

Cuar. IIL. 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 not 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. perenne and grandiflorum, and, as I may add, of L. flavum, will not doubt about the meaning of this torsion of the styles in the one form alone of L. perenne, as well as the 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 haye 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. Cuar. IIT.

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 le 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 indifferently the pollen of both forms ; but we know that the pollen algne 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 off by the rough stigmas of the longer pistils ; whilst pollen from the anthers of the shorter stamens will adhere to a different part 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. perenne is more

|

Ounar. III. LINUM PERENNE. 97

expanded than that of L. grandiflorum, 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 proboscides 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

Fig. 5.

4 /

\ i)

N

Long-styled form of L. PERENNE, 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 from published engravings. His made from fresh flowersof thetwo well-known skill ensures accuracy forms. But Mr. Fitch has made in the proportional size of the the above sketch of a long-styled _ parts. flower from dried specimens and

98 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IL

with papillae, 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 grandiflora I have shown* that precocious and partial self-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. J 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,f resting his belief on the usual kind of evidence, states that in Linum Austriacwm (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 Linwm 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 jflavum.—The pistil of the long-styled form

* ‘Fertilisation of Orchids, + ‘Etudes sur la Géogr. Bot., p. 108.—2nd edit. 1877, p. 84. H. Lecoq, 1856, tom. y. p. 325.

Cuar. III. LINUM FLAVUM. 99

of this species is nearly twice as long as that of the short-styled; the stigmas are longer and the papille coarser. In the short-styled form the stigmas diverge and pass out between the filaments, as in the previous species. ‘I'he stamens in the two forms differ 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 HETEROSTYLED DIMORPHIC PLANTS. Cuap. 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. corymbiferum is certainly heterostyled, as is, according to Planchon,* JL. salsoloides. This botanist is the only one who seems to have inferred that heterostylism might have some important fune- tional bearing. Dr. Alefeld, who has made a special study of the genus, says} that about half of the sixty- five species known to him are heterostyled. This is the case with L. trigynum, which differs so much from the other species that it has been formed by him into a distinct genus.{ 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. usitatissimum, angustifolium, and catharti- 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 during the day; but it

* Hooker’s ‘ London Journal of Botany,’ 1848, vol. vii. p. 174. + ‘Bot. Zeitung,’ Sep. 18th,

Journal of Botany,’ 1848, vol. vii. p. 525) to be provided with ‘“‘staminibus exsertis;’ another

1863, p. 281.

t It is not improbable that the allied genus, Hugonia, is hetero- styled, for one species is said by Planchon (Hooker’s ‘ London

with “stylis staminibus longiori- bus,” and another has “stamina 5, majora, stylos longe superantia.”

§ ‘Die Befruchtung der Blu- men,’ &e., p. 168.

ph ol at: i ae

:

a yy

Cuar. III. PULMONARIA 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.*

PuLMONARIA (BORAGINEZ).

Pulmonaria 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.

* Planchon, in Hooker’s‘ Lon- _ of Science,’ vol. xxxvi. Sept. 1863, don Journal of Botany,’ 1848, vol. _p, 284. vii. p. 175. See on this subject + ‘ Bot. Zeitung,’ 1865, Jan. 13, Ase Gray, in ‘American Journal pp. 13

102 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III.

70 per cent.) had set fruit, yielding 1:86 seed per fruit. So that the short-styled plants produced many more flowers, and these set a rather 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 Hildebrand).

Number Average Nature of Union ae of Fruit ri Seeis 2 owers of Seeds fertilised. produced. per Fruit. Long-styled flowers, by pollen of short-)| 14 | styled. Legitimate union . Long-styled flowers, 14 by own-pollen, | and 16 by pollen of other paugd of same | 30 0 0 form. Iilegitimate union | | Sherk-abyled (ye @ pellentp of long a 16 14 | 1°57 styled. Legitimate union . i Short-styled flowers, 11 by own peel | 14 by pollen of other Sm of same 25 | 0 0 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

Cuar. IIL. PULMONARIA 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 half 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 that this difference of treatment may have caused the difference in our results. But this does not appear to me nearly a sufficient 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 heterostyled species of Pri- mula; but it would appear that they had been greatly affected in function, either by long-continued cultiva- tion or by some other cause. We shall see in a future chapter that heterostyled plants illegitimately

104 HETEROSTYLED DIMORPHIC PLANTS. Cuap. TI.

iertilised during several successive generations some- times become more self-fertile; and this may have been the 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, differmg 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 we 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 species 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

a aa*

Cuapr. IIL. PULMONARIA ANGUSTIFOLIA. 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

Long-styled form. Short-styled form.

PULMONARIA ANGUSTIFOLIA.

in the long-styled form, where the anthers are seated, has been overlooked. My 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 than 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 form 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

106 . HETEROSTYLED DIMORPHIC PLANTS. Cuap. 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 the 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 bemg 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-

ee

—_,-" in

Cuap. III. PULMONARIA 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 dicecious.

My son collected in the Isle of Wight on two occa- sions 202 plants, of which 125 were long-styled and 77 short-styled ; so that 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 following table shows the results of my experi- ments :—

TABLE 20.

Pulmonaria angustifolia.

Number | Number | Average Nature of the Union. oe A ij ae of fertilised. | produced, | per Fruit. Long-styled flowers, by pollen pollen of sho short- 211 styled. Legitimate union . Long-styled flowers, by own-form pollen — 0 Illegitimate union | "| " Short-styled flowers, by piety: of 58 2°60 styled. Legitimate union . Short-styled flowers, by own-form meet | 1°86 Illegitimate union na

108 HETEROSTYLED DIMORPHIC PLANTS. Cnap. III.

We see in this table that the fertility of the two legitimate unions to that of the two illegitimate together is as 100 to 35, judged by the proportion of flowers which 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 85. 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. ‘T'wo other long- styled plants were left uncovered (all the short-styled plants having been previously covered up), and humble-bees, which 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 English plants of P. officinalis 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

Cap. III. PULMONARIA ANGUSTIFOLIA. 109

4, and four other fruits contained each 3 seeds. The 12 illegitimately fertilised short-styled flowers yielded 7 fruits, including 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. or 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 haying 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 235 fruits included the highest possible number of seeds, namely 4, and dl 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 half of the

110 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL

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. With 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 ease of the long- styled form of Linwm grandiflorum. On the otliet 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 spectabilis, sent me by Prof. Asa Gray, I formerly thought that this plant, a member of the Boragines, was heterostyled. Tle 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.

Crap. III. POLYGONUM FAGOPYRUM. 111

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 plenty of seeds. Again, from statements made by Vaucher,.and from a hasty inspection, I thought at first that the allied Anchusa arvensis and Echium vulgare were heterostyled, but soon saw my error. From information given me, I examined dried flowers of another member of the Boraginez, Arnebia hispidis- sima, collected from several sites, and though the corolla, to- gether with the included organs, differed much in length, there was no sign of heterostylism.

POLYGONUM FAGOPYRUM (POLYGONACE2).

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 with 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 indiameter. This plant is therefore without doubt heterostyled.

I experimented only in an imperfect manner on the relative fertility of the two forms. Short-styled flowers 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 prodticed 22 seeds, or 11 per flower-head.

Three flower-heads on long-styled plants received

* ‘Die Geschlechter-Vertheilung,’ &c., 1867, p. 34, an

112 HETEROSTYLED DIMORPHIC PLANTS. Cuap. ITI.

pollen in the same manner from other long-styled plants, and were thus illegitimately fertilised. They produced 14 seeds, or only 4°66 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.

Fig. 7.

Upper figure, the long-styled form ; lower figure, the short-styled. - Some of the anthers have dehisced, others have not.

POLYGONUM FAGOPYRUM. (From H. Miiller.)

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 per 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-

i

Cuapr. 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 fertiliséd 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. H. Miller in his interesting description of several

* ‘Dic Befruchtung,’ &., p. 175, and ‘ Nature,’ Jan. 1, 1874, p. 166.

114 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III.

other species shows that P. bistorta is so strongly pro- terandrous (the anthers generally falling off 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- erete 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 Polygonacez are generally fertilised by the wind, instead of by insects as in the present genus.

LevcosmiA BurneETrIANA (THYMELI2).

As Prof, Asa Gray has expressed his belief * that this species and L. acuminata, as well as some species in the allied genus Drymispermum, are dimorphic or heterostyled, I procured from Kew, through the kindness of Dr. Hooker, two dried 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 tubular 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 papillose, 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 throat of the corolla, whilst the anthers of the lower stamens are seated in the throat on a level with the upper stamens of the other 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- ‘Journal of Botany,’ vol. iii. 1865, ence, 1865, p.101,and Seemann’s pp. 305.

Cuap. IIT. MENYANTHES TRIFOLIATA. 115

grains from the short-styled flower was to that of twenty-four

) " }

grains from the long-styled, as 100 to 99. 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 grandiflorum, 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- fertilised 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 dimorphic plant, probably serves to smear the inserted organ thoroughly with pollen.

MENYANTHES TRIFOLIATA (GENTIANEZ).

This plant inhabits marshes: my son William gathered 247 flowers from so many distinct plants, and of these 110 were long-styled, and 187 short-styled. The pistil of the long-styled form is in length to that of the short-styled in the ratio of about 3to2. The stigma of the former, 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 plants, living by themselves in the gardens at Kew, have produced an abundance of capsules, yet the seeds have never germinated; and this looks as if the short-styled form was sterile with its own pollen.

116 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III.

LIMNANTHEMUM INDICUM (GENTIANEX).

This plant 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 thrice as long (i.e. as 14 to 5) as that of the short-styled, and is very much thinner in the ratio of about 8 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. ?] (GENTIANEZ).

Fritz Miller sent me from South Brazil dried flowers of this aquatic plant, which is closely allied to Limnanthemum. In the long-styled form 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 conspicu- 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 informs me that the pollen of the short-styled flowers has a bluish tint, whilst that of the long-styled is yellow. When we treat of Lythrum salicaria we shall find a strongly marked contrast in the colour of the pollen in two of the forms.

The three genera, Menyanthes, Limnanthemum, and Villarsia, now described, constitute a well-marked sub-tribe of the Gen- tianeze. All the species, as far as at present known, are hetero- styled, and all inhabit aquatic or sub-aquatic stations.

CORDIA. 117

FoRSYTHIA SUSPENSA (OLEACEZR).

Professor Asa Gray states that the plants of this species grow- ing in the Botanic Gardens at Cambridge, U-.S., are short-styled,

' put that Siebold and Zuccarini describe the long-styled form,

and give