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diff --git a/3807-h/3807-h.htm b/3807-h/3807-h.htm new file mode 100644 index 0000000..8f5d67a --- /dev/null +++ b/3807-h/3807-h.htm @@ -0,0 +1,13371 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" +"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> +<head> +<meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> +<meta http-equiv="Content-Style-Type" content="text/css" /> +<title>The Project Gutenberg eBook of The Different Forms of Flowers on Plants Of the Same Species, by Charles Darwin</title> + +<style type="text/css" xml:space="preserve"> + + body { margin-left: 20%; margin-right: 20%; text-align: justify;} + p { text-indent: 1em; margin-top: .75em; margin-bottom: .75em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .toc { margin-left: 10%; margin-bottom: .75em;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} +</style> + </head> + <body> + +<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The Different Forms of Flowers on Plants of the Same Species, by Charles Darwin</div> +<div style='display:block; margin:1em 0'> +This eBook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this eBook or online +at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you +are not located in the United States, you will have to check the laws of the +country where you are located before using this eBook. +</div> +<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: The Different Forms of Flowers on Plants of the Same Species</div> +<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Charles Darwin</div> +<div style='display:block; margin:1em 0'>Release Date: September 18, 2001 [eBook #3807]<br /> +[Most recently updated: January 3, 2022]</div> +<div style='display:block; margin:1em 0'>Language: English</div> +<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div> +<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Sue Asscher and David Widger</div> +<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES ***</div> + + <h1> + THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES + </h1> + <h2> + By Charles Darwin + </h2> + <h3> + TO + </h3> + <h3> + PROFESSOR ASA GRAY + </h3> + <h3> + THIS VOLUME IS DEDICATED BY THE AUTHOR + </h3> + <h3> + AS A SMALL TRIBUTE OF RESPECT AND AFFECTION. + </h3> + <hr /> + <p> + <b>CONTENTS</b> + </p> + <p class="toc"> + <a href="#link2H_4_0001"> DETAILED TABLE OF CONTENTS </a> + </p> + <p class="toc"> + <a href="#link2H_4_0003"> THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE + SAME SPECIES. </a> + </p> + <p class="toc"> + <a href="#link2H_INTR"> INTRODUCTION. </a> + </p> + <p class="toc"> + <a href="#link2HCH0001"> CHAPTER I. HETEROSTYLED DIMORPHIC PLANTS: + PRIMULACEÆ. </a> + </p> + <p class="toc"> + <a href="#link2HCH0002"> CHAPTER II. HYBRID PRIMULAS. </a> + </p> + <p class="toc"> + <a href="#link2HCH0003"> CHAPTER III. HETEROSTYLED DIMORPHIC PLANTS—continued. + </a> + </p> + <p class="toc"> + <a href="#link2HCH0004"> CHAPTER IV. HETEROSTYLED TRIMORPHIC PLANTS. </a> + </p> + <p class="toc"> + <a href="#link2HCH0005"> CHAPTER V. ILLEGITIMATE OFFSPRING OF HETEROSTYLED + PLANTS. </a> + </p> + <p class="toc"> + <a href="#link2H_CONC"> CONCLUSIONS WITH RESPECT TO THE EQUAL-STYLED + VARIETY OF P. Sinensis. </a> + </p> + <p class="toc"> + <a href="#link2HCH0006"> CHAPTER VI. CONCLUDING REMARKS ON HETEROSTYLED + PLANTS. </a> + </p> + <p class="toc"> + <a href="#link2HCH0007"> CHAPTER VII. POLYGAMOUS, DIOECIOUS, AND + GYNO-DIOECIOUS PLANTS. </a> + </p> + <p class="toc"> + <a href="#link2HCH0008"> CHAPTER VIII. CLEISTOGAMIC FLOWERS. </a> + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2H_4_0001" id="link2H_4_0001"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + DETAILED TABLE OF CONTENTS + </h2> + <p> + I. HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEÆ. + </p> + <p> + Primula veris or the cowslip.—Differences in structure between the + two forms.— Their degrees of fertility when legitimately and + illegitimately united.—P. elatior, vulgaris, Sinensis, auricula, + etc.—Summary on the fertility of the heterostyled species of + Primula.—Homostyled species of Primula.—Hottonia palustris.—Androsace + vitalliana. + </p> + <p> + II. HYBRID PRIMULAS. + </p> + <p> + 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 + spontaneously produced hybrids in the genus Verbascum. + </p> + <p> + III. HETEROSTYLED DIMORPHIC PLANTS—continued. + </p> + <p> + 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 fagopyrum.—Various other heterostyled + genera.—Rubiaceae.—Mitchella repens, fertility of the flowers + in pairs.—Houstonia.—Faramea, remarkable difference in the + pollen-grains of the two forms; torsion of the stamens in the short-styled + form alone; development not as yet perfect.—The heterostyled + structure in the several Rubiaceous genera not due to descent in common. + </p> + <p> + IV. HETEROSTYLED TRIMORPHIC PLANTS. + </p> + <p> + Lythrum salicaria.—Description of the three forms.—Their power + and complex manner of fertilising one another.—Eighteen different + unions possible.—Mid- styled form eminently feminine in nature.—Lythrum + Graefferi likewise trimorphic.—L. hymifolia dimorphic.—L. + hyssopifolia homostyled.—Nesaea verticillata trimorphic.—Lagerstroemia, + 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. + </p> + <p> + V. ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS. + </p> + <p> + Illegitimate offspring from all three forms of Lythrum salicaria.—Their + dwarfed stature and sterility, some utterly barren, some fertile.—Oxalis, + transmission of form to the legitimate and illegitimate seedlings.—Primula + Sinensis, illegitimate offspring in some degree dwarfed and infertile.—Equal-styled + varieties of P. Sinensis, auricula, farinosa, and elatior.—P. + vulgaris, red- flowered variety, illegitimate seedlings sterile.—P. + veris, illegitimate plants raised during several successive generations, + their dwarfed stature and sterility.—Equal-styled varieties of P. + veris.—Transmission of form by Pulmonaria and Polygonum.—Concluding + remarks.—Close parallelism between illegitimate fertilisation and + hybridism. + </p> + <p> + VI. CONCLUDING REMARKS ON HETEROSTYLED PLANTS. + </p> + <p> + 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. + </p> + <p> + VII. POLYGAMOUS, DIOECIOUS, AND GYNO-DIOECIOUS PLANTS. + </p> + <p> + The conversion in various ways of hermaphrodite into dioecious plants.— + Heterostyled plants rendered dioecious.—Rubiaceae.—Verbenaceae.—Polygamous + and sub-dioecious plants.—Euonymus.—Fragaria.—The two + sub-forms of both sexes of Rhamnus and Epigaea.—Ilex.—Gyno-dioecious + plants.—Thymus, difference in fertility of the hermaphrodite and + female individuals.—Satureia.—Manner in which the two forms + probably originated.—Scabiosa and other gyno-dioecious plants.—Difference + in the size of the corolla in the forms of polygamous, dioecious, and + gyno-dioecious plants. + </p> + <p> + VIII. CLEISTOGAMIC FLOWERS. + </p> + <p> + General character of cleistogamic flowers.—List of the genera + producing 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 cleistogamic flowers.—Vandellia.—Ononis.—Impatiens.—Drosera.—Miscellaneous + observations on various other cleistogamic plants.—Anemophilous + species producing cleistogamic flowers.—Leersia, perfect flowers + rarely developed.— Summary and concluding remarks on the origin of + cleistogamic flowers.—The chief conclusions which may be drawn from + the observations in this volume. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2H_4_0003" id="link2H_4_0003"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES. + </h2> + <p> + <br /><br /> + </p> + <hr /> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2><a name="link2H_INTR" id="link2H_INTR"> </a> + INTRODUCTION. + </h2> + <p> + The subject of the present volume, namely the differently 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 botanist, to + which distinction I can lay no claim. As far as the sexual relations of + flowers are concerned, Linnaeus long ago divided them into hermaphrodite, + monoecious, dioecious, and polygamous species. This fundamental + distinction, with the aid of several subdivisions in each of the four + classes, will serve my purpose; but the classification is artificial, and + the groups often pass into one another. + </p> + <p> + 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 produced by the same species. + </p> + <p> + Some plants were described by me several years ago, in a series of papers + read before the Linnean Society, the individuals of which exist under two + or three forms, differing in the length of their pistils and stamens and + in other respects. (Introduction/1. “On the Two Forms or Dimorphic + Condition in the Species of Primula, and on their remarkable Sexual + Relations” ‘Journal of the Proceedings of the Linnean Society’ volume 6 + 1862 page 77. “On the Existence of Two Forms, and on their Reciprocal + Sexual Relation, in several Species of the Genus Linum” Ibid volume 7 1863 + page 69. “On the Sexual Relations of the Three Forms of Lythrum salicaria” + Ibid volume 8 1864 page 169. “On the Character and Hybrid-like Nature of + the Offspring from the Illegitimate Unions of Dimorphic and Trimorphic + Plants” Ibid volume 10 1868 page 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 the Hybrid Nature of + the Common oxlip. With Supplementary Remarks on Naturally Produced Hybrids + in the Genus Verbascum” Ibid volume 10 1868 page 437.) They were called by + me dimorphic and trimorphic, but have since been better named by + Hildebrand, heterostyled. (Introduction/2. The term “heterostyled” does + not express all the differences between the forms; but this is a failure + common in many 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 + Professor Asa Gray: see the ‘American Naturalist’ January 1877 page 42.) + As I have many still unpublished observations with respect to these + plants, it has seemed to me advisable to republish my former papers in a + connected and corrected form, together with the new matter. It will be + shown that these heterostyled plants are adapted for reciprocal + fertilisation; so that the two or three forms, though all are + hermaphrodites, are related to one another almost like the males and + females of ordinary unisexual animals. I will also give a full abstract of + such observations as have been published since the appearance of my + papers; but only those cases will be noticed, with respect to which the + evidence seems fairly satisfactory. Some plants have been supposed to be + heterostyled merely from their pistils and stamens varying greatly in + length, and I have been myself more than once thus deceived. With some + species the pistil continues growing for a long time, so that if old and + young flowers are compared they might be thought to be heterostyled. + Again, a species tending to become dioecious, with the stamens reduced in + some individuals and with the pistils in others, often presents a + deceptive appearance. Unless it be proved that one form is fully fertile + only when it is fertilised with pollen from another form, we have not + complete evidence that the species is heterostyled. But when the pistils + and stamens differ in length in two or three sets of individuals, and this + is accompanied by a difference in the size of the pollen-grains or in the + state of the stigma, we may infer with much safety that the species is + heterostyled. I have, however, occasionally trusted to a difference + between the two forms in the length of the pistil alone, or in the length + of the stigma together with its more or less papillose condition; and in + one instance differences of this kind have been proved by trials made on + the fertility of the two forms, to be sufficient evidence. + </p> + <p> + 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 minute, completely closed, with the petals rudimentary, often with + some of the anthers aborted, and the remaining 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 will be described + in the last chapter of this volume. (Introduction/3. ‘Botanische Zeitung’ + 1867 page 65. Several plants are known occasionally to produce flowers + destitute of a corolla; but they belong to a different class of cases from + cleistogamic flowers. This deficiency seems to result from the conditions + to which the plants have been subjected, and partakes of the nature of a + monstrosity. 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: see Dr. Maxwell + Masters ‘Vegetable Teratology’ 1869 page 403.) They are manifestly adapted + for self- fertilisation, which is effected at the cost of a wonderfully + small expenditure of pollen; whilst the perfect flowers produced by the + same plant are capable of cross-fertilisation. Certain aquatic species, + when they flower beneath the water, keep their corollas closed, apparently + to protect their pollen; they might therefore be called cleistogamic, but + for reasons assigned in the proper place are not included in the present + sub-group. Several cleistogamic 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. + </p> + <p> + Another interesting subdivision consists of certain plants, discovered by + H. Muller, 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 crista-galli, and Viola tricolor come under this head. + (Introduction/4. H. Muller ‘Nature’ September 25, 1873 volume 8 page 433 + and November 20, 1873 volume 9 page 44. Also ‘Die Befruchtung der Blumen’ + etc. 1873 page 294.) The smaller and less conspicuous flowers are not + closed, but as far as the purpose which they serve is concerned, 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. + </p> + <p> + With many plants, the flowers towards the outside of the inflorescence are + much larger and more conspicuous than the central ones. As I shall not + have occasion 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 Compositae often differ remarkably from the + others; and so it is with the outer flowers of many Umbelliferae, some + Cruciferae and a few other families. Several species of Hydrangea and + Viburnum offer striking instances of the same fact. The Rubiaceous genus + Mussaenda presents a very curious appearance from some of the flowers + having the tip of one of the sepals developed into a large petal-like + expansion, coloured either white or purple. The outer flowers in several + Acanthaceous genera are large and conspicuous but sterile; the next in + order are smaller, open, moderately fertile and capable of + cross-fertilisation; whilst the central ones are cleistogamic, being still + smaller, closed and highly fertile; so that here the inflorescence + consists of three kinds of flowers. (Introduction/5. J. Scott ‘Journal of + Botany’ London new series volume 1 1872 pages 161-164.) From what we know + in other cases of the use of the corolla, coloured bracteae, etc., and + from what H. Muller has observed on the frequency of the visits of insects + to the flower-heads of the Umbelliferae and Compositae being largely + determined 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. (Introduction/6. + ‘Die Befruchtung der Blumen’ pages 108, 412.) The result is that + cross-fertilisation is thus favoured. Most flowers wither soon after being + fertilised, but Hildebrand states that the ray-florets of the Compositae + last for a long time, until all those on the disc are impregnated; and + this clearly shows the use of the former. (Introduction/7. See his + interesting memoir ‘Ueber die Geschlechtsverhaltniss bei den Compositen’ + 1869 page 92.) The ray-florets, 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. (Introduction/8. + Kerner clearly shows that this is the case: ‘Die Schutzmittel des Pollens’ + 1873 page 28.) 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. (Introduction/9. ‘Gardener’s + Chronicle’ 1861 page 1067. Lindley ‘Vegetable Kingdom’ on Chrysanthemum + 1853 page 706. Kerner in his interesting essay ‘Die Schutzmittel der + Bluthen gegen unberufene Gaste’ 1875 page 19, insists that the petals of + most plants contain matter which is offensive to insects, so that they are + seldom gnawed, and thus the organs of fructification are protected. My + grandfather in 1790 ‘Loves of the Plants’ canto 3 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.”) + </p> + <p> + It is a well-known yet remarkable fact that the circumferential flowers of + many of the foregoing plants have both their male and female reproductive + organs aborted, as with the Hydrangea, Viburnum and certain Compositae; or + the male organs alone are aborted, as in many Compositae. Between the + sexless, female and hermaphrodite states of these latter flowers, the + finest gradations may be traced, as Hildebrand has shown. + (Introduction/10. ‘Ueber die Geschlechtsverhaltnisse bei den Compositen’ + 1869 pages 78-91.) 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 to insects, it is a + natural inference that their corollas have been increased in size for this + special purpose; and that their development has subsequently led, through + the principle of compensation or balancement, 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 cultivation, and, as a consequence, the corolla + became, through compensation, more highly developed. (Introduction/11. I + have discussed this subject in my ‘Variation of Animals and Plants under + Domestication’ chapter 18 2nd edition volume 2 pages 152, 156.) This view, + however, is not probable, for when hermaphrodite plants become dioecious + or gyno-dioecious—that is, are converted into hermaphrodites and + females—the corolla of the female seems to be almost invariably + reduced in size in consequence of the abortion of the male organs. The + difference in the result in these two classes of cases, may perhaps be + accounted for by the matter saved through the abortion of the male organs + in the females of gyno-dioecious and dioecious plants being directed (as + we shall see in a future chapter) to the formation of an increased supply + of seeds; whilst in the case of the exterior florets and flowers of the + plants which we are here considering, such matter is expended in the + development of a conspicuous corolla. Whether in the present class of + cases the corolla was first affected, as seems to me the more probable + view, or the reproductive organs first failed, their states of development + are now firmly correlated. We see this well-illustrated 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. + </p> + <p> + 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 Labiatae, for + instance, Salvia Horminum in which (as I hear from Mr. Thiselton Dyer) the + upper bracts are enlarged and brightly coloured, no doubt for the same + purpose as before, with the flowers suppressed. + </p> + <p> + In the Carrot and some allied Umbelliferae, the central flower has its + petals somewhat enlarged, and these are of a dark purplish-red tint; but + it cannot be supposed that this one small flower makes the large white + umbel at all more conspicuous to insects. The central flowers are said to + be neuter or sterile, but I obtained by artificial fertilisation a seed + (fruit) apparently perfect from one such flower. (Introduction/12. ‘The + English Flora’ by Sir J.E. Smith 1824 volume 2 page 39.) Occasionally two + or three of the flowers next to the central one are similarly + characterised; and according to Vaucher “cette singuliere degeneration + s’etend quelquefois a l’ombelle entiere.” (Introduction/13. ‘Hist. Phys. + des Plantes d’Europe’ 1841 tome 2 page 614. On the Echinophora page 627.) + 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 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 irregular 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 instance, 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 connected 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. (Introduction/14. This whole + subject, including pelorism, has been discussed, and references given in + my ‘Variation of Animals and Plants under Domestication’ chapter 26 2nd + edition volume 2 page 338.) + </p> + <p> + The cases hitherto mentioned relate to hermaphrodite species which bear + differently constructed flowers; but there are some plants that produce + differently formed seeds, of which Dr. Kuhn has given a list. + (Introduction/15. ‘Botanische Zeitung’ 1867 page 67.) With the + Umbelliferae and Compositae, 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. + </p> + <p> + We now come to our second Class, that of monoecious species, or those + which have their sexes separated but borne on the same plant. The flowers + necessarily differ, but when those of one sex include rudiments of the + other sex, the difference between the two kinds is usually not great. When + the difference is great, as we see in catkin-bearing plants, this depends + largely on many of the species in this, as well as in the next or + dioecious class, being fertilised by the aid of the wind; for the male + flowers have in this case to produce a surprising amount of incoherent + pollen. (Introduction/16. Delpino ‘Studi sopra uno Lignaggio Anemofilo’ + Firenze 1871.) Some few monoecious plants consist of two bodies of + individuals, with their flowers differing in function, though not in + structure; for certain individuals 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 functional difference obviously is to favour the + cross-fertilisation 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. Muller the individuals of some few hermaphrodite plants differ in a + like manner; some being proterandrous and others proterogynous. + (Introduction/17. Delpino ‘Ult. Osservazioni sulla Dicogamia’ part 2 fasc + 2 page 337. Mr. Wetterhan and H. Muller on Corylus ‘Nature’ volume 11 page + 507 and 1875 page 26. On proterandrous and proterogynous hermaphrodite + individuals of the same species, see H. Muller ‘Die Befruchtung’ etc. + pages 285, 339.) On cultivated trees of the Walnut and Mulberry, the male + flowers have been observed to abort on certain individuals, which have + thus been converted into females; but whether there are any species in a + state of nature which co-exist as monoecious and female individuals, I do + not know. (Introduction/18. ‘Gardener’s Chronicle’ 1847 pages 541, 558.) + </p> + <p> + The third Class consists of dioecious species, and the 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 inexplicable + fact that with some dioecious plants, of which the Restiaceae of Australia + and the Cape of Good Hope offer the most striking instance, the + differentiation 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 + specimens of the same species. In my seventh chapter some observations + will be given on the gradual conversion of heterostyled and of ordinary + hermaphrodite plants into dioecious or sub-dioecious species. + </p> + <p> + The fourth and last Class consists of the plants which were called + polygamous by Linnaeus; but it appears to me that it would be convenient + to confine this term to the species which coexist as hermaphrodites, males + and females; and to give new names to several other combinations 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, according + 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 + (Fraxinus excelsior) 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 produced only female flowers, which set an abundance of seeds; three + were hermaphrodites, which had a different 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 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 containing pollen grains apparently sound. On the male trees most + of the flowers include pistils, but these likewise drop off at an early + period; and the ovules, which ultimately abort, are very small compared + with those in female flowers of the same age. + </p> + <p> + 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 dioecious, and this shows how easily one state + passes into another. (Introduction/19. ‘Geographie Botanique’ tome 5 page + 367.) + </p> + <p> + 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- dioecious, 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-monoecious, if a name were desirable for them. + </p> + <p> + Again there are plants which produce hermaphrodite and male flowers on the + same individual, for instance, some species of Galium, Veratrum, etc.; and + these might be called andro-monoecious. If there exist plants, the + individuals of which consist of hermaphrodites and males, these might be + distinguished as andro-dioecious. 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 + hermaphrodites. (Introduction/20. ‘Geographie Botanique’ tome 4 page 488.) + 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 unusual + occurrence; it would appear as if nature did not think it worth while to + devote a distinct individual to the production of pollen, excepting when + this was indispensably necessary, as in the case of dioecious species. + </p> + <p> + 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 following + chapters with respect to many of these plants. I will begin with the + heterostyled, then pass on to certain dioecious, sub-dioecious, 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. + </p> + <p> + 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 information and + other assistance. Professor Asa Gray, also, has uniformly aided me in many + ways. To Fritz Muller of St. Catharina, in Brazil, I am indebted for many + dried flowers of heterostyled plants, often accompanied with valuable + notes. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0001" id="link2HCH0001"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER I. HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEÆ. + </h2> +<pre xml:space="preserve"> + Primula veris or the cowslip. + Differences in structure between the two forms. + Their degrees of fertility when legitimately and illegitimately united. + P. elatior, vulgaris, Sinensis, auricula, etc. + Summary on the fertility of the heterostyled species of Primula. + Homostyled species of Primula. + Hottonia palustris. + Androsace vitalliana. + + (FIGURE 1.1. Primula veris. + Left: Long-styled form. + Right: Short-styled form.) +</pre> + <p> + It has long been known to botanists that the common cowslip (Primula + veris, Brit. Flora, var. officinalis, Lin.) exists under two forms, about + equally numerous, which obviously differ from each other in the length of + their pistils and stamens. (1/1. This fact, according to Von Mohl + ‘Botanische Zeitung’ 1863 page 326, was first observed by Persoon in the + year 1794.) This difference has hitherto been looked at as a case of mere + variability, but this view, as we shall presently see, is far from the + true one. Florists who cultivate the Polyanthus and Auricula have long + been aware of the two kinds of flowers, and they call the plants which + display the globular stigma at the mouth of the corolla, “pin-headed” or + “pin-eyed,” and those which display the anthers, “thrum-eyed.” (1/2. 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.) I will designate the two forms as the long-styled and + short-styled. + </p> + <p> + The pistil in the long-styled form is almost exactly twice as long as that + of the short-styled. The stigma 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 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 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 specimens carefully compared, the papillae 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 heterostyled + 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 millimetres (10 to 11/7000 of an inch) in diameter, whilst + those from the long-styled were about .0254 millimetres (7/7000 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 accounted + 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 oblong 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 flower, seven of the long-styled had expanded + their flowers. + </p> + <p> + We shall, also, presently see that the short-styled plants produce more + seed than the long-styled. It is remarkable, according to Professor + Oliver, that the ovules in the unexpanded and unimpregnated flowers of the + latter are considerably larger than those of the short-styled flowers + (1/3. ‘Natural History Review’ July 1862 page 237.); 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. + </p> + <p> + 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 produced is smaller and the ovules larger. The plants tend + to flower first. + </p> + <p> + The short-styled plants have a short pistil, half the length of the tube + of the corolla, with a smooth depressed 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. + </p> + <p> + 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 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, + informs us that he has seen early blossoms on the Polyanthus, which were + not long-styled, but became so later in the season. (1/4. I have proved by + numerous experiments, hereafter to be given, that the Polyanthus is a + variety of Primula veris.) 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 exclusively 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. + </p> + <p> + 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 question + 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 dioecious + condition; that the long-styled plants, with their longer pistils, rougher + stigmas, and smaller pollen-grains, were more feminine in nature, and + would produce more seed;—that the short-styled plants, with their + shorter pistils, longer stamens and larger pollen-grains, were more + masculine in nature. Accordingly, 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:— + </p> + <h3> + TABLE 1.1. + </h3> + <p> + Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels + Produced. Column 4: Number of Capsules Produced. Column 5: Weight of Seed + In Grains. + </p> + <p> + Short-styled cowslips : 9 : 33 : 199 : 83. Long-styled cowslips : 13 : 51 + : 261 : 91. + </p> + <p> + 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:— + </p> + <h3> + TABLE 1.2. + </h3> + <p> + Column 1: Plant. Column 2: Number of Plants. Column 3: Weight of Seed in + grains. ... Column 4: Number of Umbels. Column 5: Weight of Seed. ... + Column 6: Number of Capsules. Column 7: Weight of Seed in grains. + </p> + <p> + Short-styled cowslips : 10 : 92 :: 100 : 251 :: 100 : 41. Long-styled + cowslips : 10 : 70 :: 100 : 178 :: 100 : 34. + </p> + <p> + 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. + </p> + <p> + In 1861 the trial was made in a fuller and fairer manner. A number of wild + plants had been transplanted during the previous autumn into a large bed + in my garden, and all were treated alike; the result was:— + </p> + <h3> + TABLE 1.3. + </h3> + <p> + Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels. + Column 4: Weight of Seed in grains. + </p> + <p> + Short-styled cowslips : 47 : 173 : 745. Long-styled cowslips : 58 : 208 : + 692. + </p> + <p> + These figures give us the following proportions:— + </p> + <h3> + TABLE 1.4. + </h3> + <p> + Column 1: Plant. Column 2: Number of Plants. Column 3: Weight of Seed in + grains. ... Column 4: Number of Umbels. Column 5: Weight of Seed in + grains. + </p> + <p> + Short-styled cowslips : 100 : 1585 :: 100 : 430. Long-styled cowslips : + 100 : 1093 :: 100 : 332. + </p> + <p> + 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. + </p> + <p> + Looking to these trials made during two successive years on a large number + of plants, we may safely conclude that the short-styled form is more + productive than the long-styled form, and the same result holds good with + some other species of Primula. Consequently 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. + </p> + <p> + In 1860 a few umbels on some plants of both the long-styled and + short-styled form, which had been covered by a net, did not produce any + seed, though other umbels on the same plants, artificially fertilised, + produced an abundance of seed; and this fact shows that the mere covering + in itself was not injurious. Accordingly, in 1861, several plants were + similarly covered just before they expanded their flowers; these turned + out as follows:— + </p> + <h3> + TABLE 1.5. + </h3> + <p> + Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels + produced. Column 4: Product of Seed. + </p> + <p> + Short-styled : 6 : 24 : 1.3 grain weight of seed, or about 50 in number. + Long-styled : 18 : 74 : Not one seed. + </p> + <p> + 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 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, instead 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 produced by a plant if + its flowers are not visited by insects. + </p> + <p> + The flowers of the cowslip and of the other species of the genus secrete + plenty of nectar; and I have often seen humble bees, especially B. + hortorum and muscorum, sucking the former in a proper manner, though they + sometimes bite holes through the corolla. (1/5. H. Muller has also seen + Anthophora pilipes and a Bombylius sucking the flowers. ‘Nature’ December + 10, 1874 page 111.) 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 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 recognised 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 between 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 likewise be apt to cause the self-fertilisation of both + forms. + </p> + <p> + 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 possible; 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 + ILLEGITIMATE UNION. I formerly applied the term “heteromorphic” to the + legitimate unions, and “homomorphic” to the illegitimate unions; but after + discovering the existence 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 a 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 experiments 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 exclude. I + performed all the manipulations myself, and weighed the seeds in a + chemical balance; but during many subsequent trials I followed the more + accurate plan of counting the seeds. Some of the capsules contained no + seeds, or only two or three, and these are excluded in the column headed + “good capsules” in several of the following tables:— + </p> + <p> + TABLE 1.6. Primula veris. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Capsules produced. Column 4: Number of good Capsules. + Column 5: Weight of Seed in grains. Column 6: Calculated Weight of Seed + from 100 good Capsules. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 22 : 15 : 14 : + 8.8 : 62. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 20 : 8 : 5 : 2.1 : + 42. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union : 13 : 12 : 11 : + 4.9 : 44. + </p> + <p> + Short-styled by own-form pollen. Illegitimate union : 15 : 8 : 6 : 1.8 : + 30. + </p> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions : 35 : 27 : 25 : 13.7 : 54. + </p> + <p> + The two illegitimate unions : 35 : 16 : 11 : 3.9 : 35. + </p> + <p> + The results may be given in another form (Table 1.7) 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 illegitimately + 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. + </p> + <p> + TABLE 1.7. Primula veris. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Capsules. Column 4: Number of good Capsules. Column 5: + Weight of Seed in grains. ... Column 6: Number of Capsules. Column 7: + Weight of Seed in grains. ... Column 8: Number of good Capsules. Column 9: + Weight of Seed in grains. + </p> + <p> + The two legitimate unions : 100 : 77 : 71 : 39 :: 100 : 50 :: 100 : 54. + </p> + <p> + The two illegitimate unions : 100 : 45 : 31 : 11 :: 100 : 24 :: 100 : 35. + </p> + <p> + 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 legitimate + 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 represented in Figure 1.2. + </p> + <p> + (FIGURE 1.2. Primula veris. Graphic representation of two kinds of union + between: Left: Long-styled form. Right: Short-styled form.) + </p> + <p> + If we consider the results of the two legitimate unions taken together and + the two illegitimate ones, as shown in Table 1.7, we see that the former + compared with the latter yielded capsules, whether containing 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. Returning to Table 1.7, 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 poor capsules are rejected, of which many were produced by the + illegitimately fertilised flowers, the proportion 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 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 + produced capsules, and the average number of apparently good seeds which + the capsules contained. + </p> + <p> + Flowers legitimately fertilised set seeds under conditions 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 + moderately 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 capsules, 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. + </p> + <p> + From the facts now given the superiority of a legitimate 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 present 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 divided into two + nearly equal bodies of different sexes, 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 themselves, but most 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 absolutely require the presence of + another hermaphrodite 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 imperfectly, must unite with + another individual for full fertility; it cannot, however, unite with any + other individual 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 + individual 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. + </p> + <p> + I have spoken of the legitimate unions as being fully fertile; and I am + fully justified in doing so, for flowers artificially fertilised in this + manner yielded rather more seeds than plants naturally fertilised in a + state of nature. The excess may be attributed to the plants having been + grown separately in good soil. With respect to the illegitimate unions, we + shall best appreciate their degree of lessened fertility by the following + facts. Gartner estimated the sterility of the unions between distinct + species, in a manner which allows of a strict comparison with the results + of the legitimate and illegitimate unions of Primula. (1/6. ‘Versuche uber + die Bastarderzeugung’ 1849 page 216.) With P. veris, for every 100 seeds + yielded by the two legitimate 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 calculation of + Verbascum lychnitis yielding with its own pollen 100 seeds, it yielded + when fertilised by the pollen of Verbascum Phoeniceum 90 seeds; by the + pollen of Verbascum nigrum, 63 seeds; by that of Verbascum 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 remarkable—that with Primula the illegitimate unions + relatively to the legitimate are more sterile than crosses between + distinct species of other genera relatively to their pure unions. Mr. + Scott has given a still more striking illustration of the same fact: he + crossed Primula auricula with pollen of four other species (P. palinuri, + viscosa, hirsuta, and verticillata), and these hybrid unions yielded a + larger average number of seeds than did P. auricula when fertilised + illegitimately with its own-form pollen. (1/7. ‘Journal of the Linnean + Society Botany’ volume 8 1864 page 93.) + </p> + <p> + The benefit which heterostyled dimorphic plants derive from the existence + of the two forms is sufficiently obvious, namely, the intercrossing of + distinct plants being thus ensured. (1/8. I have shown in my work on the + ‘Effects of Cross and Self-fertilisation’ how greatly the offspring from + intercrossed plants profit in height, vigour, and fertility.) Nothing can + be better adapted for this end than the relative positions of the anthers + and stigmas in the two forms, as shown in Figure 1.2; but to this whole + subject I shall recur. No doubt pollen will occasionally be placed by + insects or fall on the stigma of the same flower; and if + cross-fertilisation fails, such self-fertilisation will be advantageous to + the plant, as it will thus be saved from complete barrenness. But the + advantage is not so great as might at first be thought, for the seedlings + from illegitimate unions do not generally consist of both forms, but all + belong to the parent form; they are, moreover, in some degree weakly in + constitution, as will be shown in a future chapter. If, however, a + flower’s own pollen should first be placed by insects or fall on the + stigma, it by no means follows that cross-fertilisation will be thus + prevented. It is well known that if pollen from a distinct species be + placed on the stigma of a plant, and some hours afterwards its own pollen + be placed on it, the latter will be prepotent and will quite obliterate + any effect from the foreign pollen; and there can hardly be a doubt that + with heterostyled dimorphic plants, pollen from the other form will + obliterate the effects of pollen from the same form, even when this has + been placed on the stigma a considerable time before. To test this belief, + I placed on several stigmas of a long-styled cowslip plenty of pollen from + the same plant, and after twenty-four hours added some from a short-styled + dark-red Polyanthus, which is a variety of the cowslip. From the flowers + thus treated 30 seedlings were raised, and all these, without exception, + bore reddish flowers; so that the effect of pollen from the same form, + though placed on the stigmas twenty-four hours previously, was quite + destroyed by that of pollen from a plant belonging to the other form. + </p> + <p> + 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 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 fertilised, either naturally or + artificially, in a legitimate manner. + </p> + <p> + 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 sometimes appear. + </p> + <p> + Primula elatior, Jacq. Bardfield oxlip of English authors. + </p> + <p> + 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 between 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. Muller has seen several kinds of humble-bees and + other bees, and Bombylius, visiting the flowers in North Germany. (1/9. + ‘Die Befruchtung der Blumen’ page 347.) + </p> + <p> + The results of my trials on the relative fertility of the two forms, when + legitimately and illegitimately fertilised, are given in Table 1.8. + </p> + <p> + TABLE 1.8. Primula elatior. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of good Capsules produced. Column 4: Maximum Number of + Seeds in any one Capsule. Column 5: Minimum Number of Seeds in any one + Capsule. Column 6: Average Number of Seeds per Capsule. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 10 : 6 : 62 : 34 + : 46.5. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 20 : 4 : 49* : 2 : + 27.7. (*These seeds were so poor and small that they could hardly have + germinated.) + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 10 : 8 : 61 : 37 + : 47.7. + </p> + <p> + Short-styled by own-form pollen. Illegitimate union : 17 : 3 : 19 : 9 : + 12.1. + </p> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions together : 20 : 14 : 62 : 37 : 47.1. + </p> + <p> + The two illegitimate unions together : 37 : 7 : 49* : 2 : 35.5. (*These + seeds were so poor and small that they could hardly have germinated.) + </p> + <p> + 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 fertilised. 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 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 + protected 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. + </p> + <p> + 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. + </p> + <p> + Primula vulgaris (var. acaulis, Linn.) The primrose of English Writers. + </p> + <p> + (FIGURE 1.3. Outlines of pollen-grains of Primula vulgaris, 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.) + </p> + <p> + Mr. J. Scott examined 100 plants growing near Edinburgh, and found 44 to + be long-styled, and 56 short-styled; and I took by chance 79 plants in + Kent, of which 39 were long-styled and 40 short-styled; so that the two + lots together consisted of 83 long-styled and 96 short-styled plants. In + the long-styled form the pistil is to that of the short-styled in length, + from an average of five measurements, as 100 to 51. The stigma in the + long-styled form is conspicuously more globose and much more papillose + than in the short-styled, in which latter it is depressed on the summit; + it is equally broad in the two forms. In both it stands nearly, but not + exactly, on a level with the anthers of the opposite form; for it was + found, from an average of 15 measurements, that the distance between the + middle of the stigma and the middle of the anthers in the short- styled + form is to that in the long-styled as 100 to 93. The anthers do not differ + in size in the two forms. The pollen-grains from the short-styled 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 collected 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 fertility of + the two forms, when legitimately and illegitimately fertilised, are given + in Table 1.9. + </p> + <p> + TABLE 1.9. Primula vulgaris. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of good Capsules produced. Column 4: Maximum Number of + Seeds in any one Capsule. Column 5: Minimum Number of Seeds in any one + Capsule. Column 6: Average Number of Seeds per Capsule. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 12 : 11 : 77 : + 47 : 66.9. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 21 : 14 : 66 : 30 : + 52.2. + </p> +<pre xml:space="preserve"> +Short-styled by pollen of long-styled. Legitimate union: + 8 : 7 : 75 : 48 : 65.0. +</pre> + <p> + Short-styled by own-form pollen. Illegitimate union : 18 : 7 : 43 : 5 : + 18.8 (This average is perhaps rather too low). + </p> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions together : 20 : 18 : 77 : 47 : 66.0. + </p> + <p> + The two illegitimate unions together : 39 : 21 : 66 : 5 : 35.5 (This + average is perhaps rather too low). + </p> + <p> + 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 proportional 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 produced 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 + 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 1.9.) + 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 belonging 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 some + observations will be given on the fertility of a red-coloured variety of + the primrose. + </p> + <p> + Primula Sinensis. + </p> + <p> + 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. (1/10. After the appearance of my + paper this author published some excellent observations on the present + species ‘Botanische Zeitung’ January 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.) + The grains, therefore, of the short-styled are to those of the long- + styled in length as 100 to 57. Hildebrand also remarked, 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 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 legitimately 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 Table 1.10 we have the results of two sets of + experiments tried at different periods. + </p> + <p> + TABLE 1.10. Primula Sinensis. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of good Capsules produced. Column 4: Average Weight of + Seeds per Capsule. ... Column 5: Average Number of Seeds per Capsule as + ascertained on a subsequent occasion. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 24 : 16 : 0.58 + :: 50. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 20 : 13 : 0.45 :: 35. + </p> +<pre xml:space="preserve"> +Short-styled by pollen of long-styled. Legitimate union: + 8 : 8 : 0.76 :: 64. +</pre> +<pre xml:space="preserve"> +Short-styled by own-form pollen. Illegitimate union : + 7 : 4 : 0.23 :: 25. +</pre> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions together : 32 : 24 : 0.64 :: 57. + </p> + <p> + The two illegitimate unions together : 27 : 17 : 0.40 :: 30. + </p> + <p> + 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 occasion 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 illegitimate unions is here + 100 to 53, which is probably more accurate than the foregoing one of 100 + to 63. + </p> + <p> + TABLE 1.11. Primula Sinensis (from Hildebrand). + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of good Capsules produced. Column 4: Average Number of + Seeds per Capsule. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 14 : 14 : 41. + </p> + <p> + Long-styled by own-form pollen, from a distinct plant. Illegitimate union + : 26 : 26 : 18. + </p> + <p> + Long-styled by pollen from same flower. Illegitimate union : 27 : 21 : 17. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 14 : 14 : 44. + </p> + <p> + Short-styled by own-form pollen, from a distinct plant. Illegitimate union + : 16 : 16 : 20. + </p> + <p> + Short-styled by pollen from the same flower. Illegitimate union : 21 : 11 + : 8. + </p> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions together : 28 : 28 : 43. + </p> + <p> + The two illegitimate unions together (own-form pollen): 42 : 42 : 18. + </p> + <p> + The two illegitimate unions together (pollen from the same flower ): 48 : + 32 : 13. + </p> + <p> + 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 Table 1.11. 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. + </p> + <p> + It is remarkable that here all the flowers which were fertilised + legitimately, as well as those fertilised illegitimately with pollen from + a distinct plant belonging 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 experiments; 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 determined by the + conditions to which they are subjected, of which fact I have observed + striking instances with the present species; and this may account for the + difference 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 conditions, 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 1.10 and 1.11. + </p> + <p> + The most interesting point in Hildebrand’s experiments is the difference + in the effects of illegitimate fertilisation with a flower’s own pollen, + and with that 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 produced capsules. The self-fertilised + capsules also contained 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. + </p> + <p> + In order to ascertain how far the present species was spontaneously self- + fertile, five long-styled plants were protected by me from insects; and + they bore up to a given period 147 flowers which set 62 capsules; but many + of these soon fell off, showing that they had not been properly + fertilised. At the same time five short-styled plants were similarly + treated, and they bore 116 flowers which ultimately produced only seven + capsules. On another occasion 13 protected long-styled plants yielded by + weight 25.9 grains of spontaneously self- fertilised seeds. At the same + time seven protected short-styled plants yielded only half-a-grain weight + of seeds. Therefore the long-styled plants yielded nearly 24 times as many + spontaneously self-fertilised seeds as did the same number of short-styled + plants. The chief cause of this great difference appears to be, that when + the corolla of a long-styled plant falls off, the anthers, from being + situated near the bottom of the tube are necessarily dragged over the + stigma and leave pollen on it, as I saw when I hastened the fall of nearly + withered flowers; whereas in the short-styled flowers, the stamens are + seated at the mouth of the corolla, and in falling off do not brush over + the lowly-seated stigmas. Hildebrand likewise protected some long-styled + and short-styled plants, but neither ever yielded a single capsule. He + thinks that the difference in our results may be accounted for by his + plants having been kept in a room and never having been shaken; but this + explanation seems to me doubtful; his 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. + </p> + <p> + [Primula auricula. (1/11. According to Kerner our garden auriculas are + descended from P. pubescens, Jacq., which is a hybrid between 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 6 page 52. Also + ‘Die Primulaceen-Bastarten’ ‘Oest. Botanische Zeitschrift’ 1835 Numbers 3, + 4 and 5.) + </p> + <p> + 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 inequality 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 it is 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 5/6000 of an inch in + diameter, whereas those from the long stamens of the short-styled plants + were barely 7/6000, showing a relative difference of about 71 to 100. The + smaller grains of the long-styled plant are also much more transparent, + and before distention with water more triangular in outline than those of + the other form. Mr. Scott compared ten plants of both forms growing 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. (1/12. ‘Journal of the + Linnean Society Botany’ volume 8 1864 page 86.) Three short-styled plants + were protected by me from the access of insects, and they did not produce + a single seed. Mr. Scott protected six plants of both forms, and found + them excessively 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. + </p> + <p> + I tried a few experiments by reciprocally fertilising the two forms in the + same manner as before, but my plants were unhealthy, 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 case the fertility of the two + legitimate unions, taken together, is compared with that of the two + illegitimate unions together, by the same two standards as before, namely, + by the proportional number of flowers which produced good capsules, and by + the average number of seeds per capsule. The fertility of the legitimate + unions is always taken at 100. + </p> + <p> + 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. + </p> + <p> + Primula Sikkimensis. + </p> + <p> + 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. + </p> + <p> + Primula cortusoides. + </p> + <p> + 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 papillae. The pollen-grains of the short-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 illegitimate unions is by the first standard as 100 to 74, and by + the second standard as 100 to 66. + </p> + <p> + Primula involucrata. + </p> + <p> + 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 + papillae, 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. + </p> + <p> + Primula farinosa. + </p> + <p> + 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 100 to 44.] + </p> + <h3> + A SUMMARY ON THE FOREGOING HETEROSTYLED SPECIES OF PRIMULA. + </h3> + <p> + TABLE 1.12. 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. + </p> + <p> + Column 1: Name of Species. Column 2: Illegitimate Unions, Judged of by the + Proportional Number of Flowers which produced Capsules. Column 3: + Illegitimate Unions, Judged of by the Average Number (or Weight in some + cases) of Seeds per Capsule. + </p> + <p> + Primula veris : 69 : 65. + </p> + <p> + Primula elatior : 27 : 75 (Probably too high). + </p> + <p> + Primula vulgaris : 60 : 54 (Perhaps too low). + </p> + <p> + Primula Sinensis : 84 : 63. + </p> + <p> + Primula Sinensis (second trial) : ? : 53. Primula Sinensis (after + Hildebrand) : 100 : 42. + </p> + <p> + Primula auricula (Scott) : 80 : 15. + </p> + <p> + Primula Sikkimensis (Scott): 95 : 31. + </p> + <p> + Primula cortusoides (Scott): 74 : 66. + </p> + <p> + Primula involucrata (Scott): 72 : 48. + </p> + <p> + Primula farinosa (Scott): 71 : 44. + </p> + <p> + Average of the nine species : 88.4 : 61.8. + </p> + <p> + 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 Table 1.12; 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. But for full accuracy many more observations, under + varied conditions, would be requisite. + </p> + <p> + 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 legitimately and yielded 18 capsules, and that 30 + flowers were fertilised illegitimately and yielded 15 capsules, 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 18/20 to 15/30, or as 100 to 56 (in whole numbers), would show + the proportional number of capsules due to the two methods of + fertilisation; and the number 56 would appear in the left-hand column of + Table 1.12, and in my other tables. With respect to the average number of + seeds per capsule hardly anything need be said: supposing that the + legitimately 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. + </p> + <p> + 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 case + pollen was always taken from a distinct plant of the same form. There is, + however, no close correspondence in the two rows of figures, which give, + according to the two standards, the difference of fertility between the + legitimate and illegitimate unions. Thus all the flowers of P. Sinensis + which were illegitimately 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 31 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 fertilised 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 + fertilisation as is the number of seeds which the capsules contain. For, + as may be seen at the bottom of Table 1.12, 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 numbers (Table 1.a.):— + </p> + <p> + TABLE 1.a. + </p> + <p> + Primula veris : 71. + </p> + <p> + Primula elatior : 44 (Probably too low). + </p> + <p> + Primula vulgaris : 36 (Perhaps too low). + </p> + <p> + Primula Sinensis : 71. + </p> + <p> + Primula auricula : 119. + </p> + <p> + Primula Sikkimensis : 57. + </p> + <p> + Primula cortusoides : 93. + </p> + <p> + Primula involucrata : 74. + </p> + <p> + Primula farinosa : 63. + </p> + <p> + 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 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, notwithstanding their greater innate 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. + </p> + <h3> + HOMOSTYLED SPECIES OF PRIMULA. + </h3> + <p> + 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 (1/13. + H. Muller has given in ‘Nature’ December 10, 1874 page 110, a drawing of + one of these species, viz. The alpine P. villosa, and shows that it is + fertilised exclusively by Lepidoptera.); 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 Sibirica, + elata, mollis, and longiflora, are truly homostyled; and to these may be + added, according to Axell, P. stricta. (1/14. Koch was aware that this + species was homostyled: see “Treviranus uber Dichogamie nach Sprengel und + Darwin” ‘Botanische Zeitung’ January 2, 1863 page 4.) Mr. Scott + experimented 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. P. 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 infers 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 function 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 common to very many species, as I + have shown in my work ‘On the Effects of Cross and Self-fertilisation.’ + </p> + <p> + Hottonia palustris. + </p> + <p> + This aquatic member of the Primulaceae is conspicuously 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 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. (1/15. ‘Das entdeckte + Geheimniss der Nature’ page 103.) 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. Muller gives figures of the stigmatic + papillae of the two forms, and those of the long-styled are seen to be + more than double the length, and much thicker than the papillae of the + short-styled form. (1/16. ‘Die Befruchtung’ etc. page 350.) 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 + specimens 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 measurements of H. Muller 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 Muller, chiefly by + Diptera. + </p> + <p> + 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 + (1/17. ‘Journal of the Linnean Society Botany’ volume 8 1864 page 79.); + but since the publication of his paper H. Muller has made much fuller + experiments, and I give his results in Table 1.13, drawn up in accordance + with my usual plan:— + </p> + <p> + TABLE 1.13. Hottonia palustris (from H. Muller). + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Capsules examined. + Column 3: Average Number of Seeds per Capsule. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union: 34 : 91.4. + </p> + <p> + Long-styled by own-form pollen, from a distinct plant. Illegitimate union: + 18 : 77.5. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 30 : 66.2. + </p> + <p> + Short-styled by own-form pollen, from a distinct plant. Illegitimate + union: 19 : 18.7. + </p> + <h3> + A SUMMARY: + </h3> + <p> + The two legitimate unions together: 64 : 78.8. + </p> + <p> + The two illegitimate unions together: 37 : 48.1. + </p> + <p> + 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 illegitimately + fertilised long- styled flowers, relatively in both cases to the product + of the legitimately fertilised flowers. (1/18. H. Muller says ‘Die + Befruchtung’ etc. page 352, that the long-styled flowers, when + illegitimately fertilised, yield as many seeds as when legitimately + fertilised; but by adding up the number of seeds from all the capsules + produced by the two methods of fertilisation, as given by him, I arrive at + the results shown in Table 1.13. The average number in the long-styled + capsules, when legitimately fertilised, is 91.4, and when illegitimately + fertilised, 77.5; or as 100 to 85. H. Muller agrees with me that this is + the proper manner of viewing the case.) The two legitimate unions compared + with the two illegitimate together yield seeds in the ratio of 100 to 61. + </p> + <p> + H. Muller also tried the effects of illegitimately fertilising 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. + </p> + <p> + From some observations by Dr. Torrey, Hottonia inflata, an inhabitant of + the United States, does not appear to be heterostyled, but is remarkable + from producing cleistogamic flowers, as will be seen in the last chapter + of this volume. + </p> + <p> + 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. (1/19. See also Treviranus in ‘Botanische Zeitung’ + 1863 page 6 on this plant being dimorphic.) He was able to examine only + dried specimens of the long-styled forms. But the evidence seems + sufficient to leave hardly a doubt that Androsace is heterostyled. Fritz + Muller sent me from South Brazil dried flowers of a Statice which he + believed to be heterostyled. In the one form the pistil was considerably + longer and the stamens slightly shorter than the corresponding organs in + the other form. But as in the shorter-styled form the stigmas reached up + to the anthers 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 probable that Pyrola might be heterostyled, but H. Muller + examined for me two species in North Germany, and found this not to be the + case. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0002" id="link2HCH0002"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER II. HYBRID PRIMULAS. + </h2> +<pre xml:space="preserve"> + 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 spontaneously produced hybrids in the genus Verbascum. +</pre> + <p> + The various species of Primula have produced in a state of nature + throughout Europe an extraordinary number of hybrid forms. For instance, + Professor Kerner has found no less than twenty-five such forms in the + Alps. (2/1. “Die Primulaceen-Bastarten” ‘Oesterr. Botanische Zeitschrift’ + Jahr 1875 Numbers 3, 4 and 5. See also Godron on hybrid Primulas in ‘Bull. + Soc. Bot. de France’ tome 10 1853 page 178. Also in ‘Revue des Sciences + Nat.’ 1875 page 331.) 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-fertilisation, 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 frequently found, and it occurs + occasionally almost everywhere. 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. Linnaeus + 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. + </p> + <p> + The cowslip differs so conspicuously in general appearance from the + primrose, that nothing need here be said with respect to their external + characters. (2/2. The Reverend W.A. Leighton has pointed out certain + differences in the form of the capsules and seed in ‘Annals and Magazine + of Natural History’ 2nd series volume 2 1848 page 164.) But some less + obvious differences deserve notice. As both species are heterostyled, + their complete fertilisation depends on insects. The cowslip is habitually + visited during the day by the larger humble-bees (namely Bombus muscorum + and hortorum), 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 fertilisation 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 primrose, when legitimately + and naturally fertilised, yield on an average many more seeds per capsule + than the cowslip, 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 capsules, 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 + illegitimately 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 + insects, except such minute ones as Thrips, yield a considerable 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. + </p> + <p> + 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 cowslip is + found in more open places. The geographical range of the two forms is + different. Dr. Bromfield remarks that “the primrose is absent from all the + interior region of northern Europe, where the cowslip is indigenous.” + (2/3. ‘Phytologist’ volume 3 page 694.) In Norway, however, both plants + range to the same degree of north latitude. (2/4. H. Lecoq ‘Geograph. Bot. + de l’Europe’ tome 8 1858 pages 141, 144. See also ‘Annals and Magazine of + Natural History’ 9 1842 pages 156, 515. Also Boreau ‘Flore du centre de la + France’ 1840 tome 2 page 376. With respect to the rarity of P. veris in + western Scotland, see H.C. Watson ‘Cybele Britannica’ 2 page 293.) + </p> + <p> + The cowslip and primrose, when intercrossed, behave 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. (2/5. ‘Bastarderzeugung’ 1849 page + 721.) 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 heterostylism; 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 (i.e. 33 per + cent), containing 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 + illegitimately, 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 perfect fertility inter se of + the crossed offspring from these two plants. (2/6. Mr. Scott has discussed + the nature of the polyanthus (‘Proceedings of the Linnean Society’ 8 + Botany 1864 page 103), and arrives at a different conclusion; but I do not + think that his experiments were sufficiently numerous. The degree of + 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 primrose, + fertilised legitimately and illegitimately with pollen of the cowslip gave + five capsules, containing on an average 32.4 seeds; whilst 18 flowers + similarly fertilised by polyanthus-pollen yielded only five capsules, + containing only 22.6 seeds. On the other hand, the seeds produced by the + polyanthus-pollen were much the finest of the whole lot, and were the only + ones which germinated.) To show how sterile these hybrid unions 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 35.5 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. + </p> + <p> + 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 transplanted 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. + </p> + <p> + We thus see that the cowslip and primrose cannot be crossed either way + except with considerable difficulty, that they differ conspicuously in + external appearance, that they differ in various physiological 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. + </p> + <p> + The first statement, however, is of little value; for, heterostylism not + being formerly understood, the seed-bearing plants were in no instance + protected from the visits of insects (2/7. One author states in the + ‘Phytologist’ volume 3 page 703 that he covered with bell-glasses some + cowslips, primroses, etc., on which he experimented. He specifies all the + details of his experiment, but does not say that he artificially + fertilised his plants; yet he obtained an abundance of seed, which is + simply impossible. Hence there must have been some strange error in these + experiments, which may be passed over as valueless.); 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 dioecious plant, under similar + circumstances, being crossed by the opposite sex of an allied and + neighbouring species. Mr. H.C. Watson, 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, namely, + “that seeds of a cowslip can produce cowslips and oxlips, and that seeds + of an oxlip can produce cowslips, oxlips, and primroses.” (2/8. + ‘Phytologist’ 2 pages 217, 852; 3 page 43.) This conclusion harmonises + perfectly with the view that in all cases, 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 gradations, would be occasionally + produced. Nevertheless the two following statements offer considerable + difficulty. The Reverend Professor 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. (2/9. Loudon’s ‘Magazine of Natural History’ 3 1830 page 409.) + Professor Henslow had previously transplanted into his garden a cowslip, + which completely changed its appearance 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 I have myself observed with + oxlips, I cannot doubt that this plant was an oxlip 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 Professor 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. Herbert raised, from the seeds of a highly cultivated red + cowslip, cowslips, oxlips of various kinds, and a primrose. (2/10. + ‘Transactions of the Horticultural Society’ 4 page 19.) This case, if + accurately 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, etc., have proved identical with the pollen-bearing + parent, and quite dissimilar to the mother-plant (2/11. I have given + instances in my work ‘On the Variation of Animals and Plants under + Domestication’ chapter 15 2nd edition volume 2 page 69.); but I do not + know of any instance of the offspring of a cross perfectly resembling, in + a considerable 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 Professor Henslow are difficult to explain, yet + until it can be shown that a cowslip or a 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. + </p> + <p> + Negative evidence is of little value; but the following 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 in a 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 greenhouse; so that these + plants, 765 in number, as well as their parents, were subjected to + diversified and unnatural treatment; but not one of them presented the + least variation except in size—those in the peat attaining almost + gigantic dimensions, and those in the clay being much dwarfed. + </p> + <p> + I do not, of course, doubt that cowslips exposed during SEVERAL successive + generations to changed conditions 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. + </p> + <p> + 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 (2/12. See an + excellent article on this subject by Mr. H.C. Watson in the ‘Phytologist’ + volume 3 page 43.):—If it can be shown that the common wild oxlip, + which is intermediate in character between the cowslip and primrose, + 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-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 character, + and resembles in every respect, except in the colour of the corolla, + hybrids artificially produced between 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 inter 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 inter se, but still not + as fully fertile as the parent-species. + </p> + <p> + 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 corolla of one being slightly + larger, resembled each other closely. The trials which were made, and the + results obtained, are shown in tables 2.14, 2.15, 2.16, 2.17 and 2.18. 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 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. + </p> + <p> + TABLE 2.14. Crosses inter se between the two forms of the common Oxlip. + </p> + <p> + Column 1: Illegitimate union. Short-styled oxlip, by pollen of + short-styled oxlip: 20 flowers fertilised, did not produce one capsule. + </p> + <p> + Column 2: Legitimate union. Short-styled oxlip, by pollen of long-styled + oxlip: 10 flowers fertilised, did not produce one capsule. + </p> + <p> + Column 3: Illegitimate union. Long-styled oxlip, by its own pollen: 24 + flowers fertilised, produced five capsules, containing 6, 10, 20, 8, and + 14 seeds. Average 11.6. + </p> + <p> + Column 4: Legitimate union. Long-styled oxlip, by pollen of short-styled + oxlip: 10 flowers fertilised, did not produce one capsule. + </p> + <p> + TABLE 2.15. Both forms of the Oxlip crossed with Pollen of both forms of + the Cowslip, P. veris. + </p> + <p> + Column 1: Illegitimate union. Short-styled oxlip, by pollen of + short-styled cowslip: 18 flowers fertilised, did not produce one capsule. + </p> + <p> + Column 2: Legitimate union. Short-styled oxlip, by pollen of long-styled + cowslip: 18 flowers fertilised, produced three capsules, containing 7, 3, + and 3 wretched seeds, apparently incapable of germination. + </p> + <p> + Column 3: Illegitimate union. Long-styled oxlip, by pollen of long-styled + cowslip: 11 flowers fertilised, produced one capsule, containing 13 + wretched seeds. + </p> + <p> + Column 4: Legitimate union. Long-styled oxlip, by pollen of short-styled + cowslip: 5 flowers fertilised, produced two capsules, containing 21 and 28 + very fine seeds. + </p> + <p> + TABLE 2.16. Both forms of the Oxlip crossed with Pollen of both forms of + the Primrose, P. vulgaris. + </p> + <p> + Column 1: Illegitimate union. Short-styled oxlip, by pollen of + short-styled primrose: 34 flowers fertilised, produced two capsules, + containing 5 and 12 seeds. + </p> + <p> + Column 2: Legitimate union. Short-styled oxlip, by pollen of long-styled + primrose: 26 flowers fertilised, produced six capsules, containing 16, 20, + 5, 10, 19, and 24 seeds. Average 15.7. Many of the seeds very poor, some + good. + </p> + <p> + Column 3: Illegitimate union. Long-styled oxlip, by pollen of long-styled + primrose: 11 flowers fertilised, produced four capsules, containing 10, 7, + 5, and 6 wretched seeds. Average 7.0. + </p> + <p> + Column 4: Legitimate union. Long-styled oxlip, by pollen of short-styled + primrose: 5 flowers fertilised, produced five capsules, containing 26, 32, + 23, 28, and 34 seeds. Average 28.6. + </p> + <p> + TABLE 2.17. Both forms of the Cowslip crossed with Pollen of both forms of + the Oxlip. + </p> + <p> + Column 1: Illegitimate union. Short-styled cowslip, by pollen of + short-styled oxlip: 8 flowers fertilised, did not produce one capsule. + </p> + <p> + Column 2: Legitimate union. Long-styled cowslip, by pollen of short-styled + oxlip: 8 flowers fertilised, produced one capsule, containing 26 seeds. + </p> + <p> + Column 3: Illegitimate union. Long-styled cowslip, by pollen of + long-styled oxlip: 8 flowers fertilised, produced three capsules, + containing 5, 6 and 14 seeds. Average 8.3. + </p> + <p> + Column 4: Legitimate union. Short-styled cowslip, by pollen of long-styled + oxlip: 8 flowers fertilised, produced 8 capsules, containing 58, 38, 31, + 44, 23, 26, 37, and 66 seeds. Average 40.4. + </p> + <p> + TABLE 2.18. Both forms of the Primrose crossed with Pollen of both forms + of the Oxlip. + </p> + <p> + Column 1: Illegitimate union. Short-styled primrose, by pollen of + short-styled oxlip: 8 flowers fertilised, did not produce one capsule. + </p> + <p> + Column 2: Legitimate union. Long-styled primrose, by pollen of + short-styled oxlip: 8 flowers fertilised, produced two capsules, + containing 5 and 2 seeds. + </p> + <p> + Column 3: Illegitimate union. Long-styled primrose, by pollen of + long-styled oxlip: 8 flowers fertilised, produced 8 capsules, containing + 15, 7, 12, 20, 22, 7, 16, and 13 seeds. Average 14.0. + </p> + <p> + Column 4: Legitimate union. Short-styled primrose, by pollen of + long-styled oxlip: 8 flowers fertilised, produced 4 capsules, containing + 52, 52, 42, and 49 seeds, some good and some bad. Average 48.7. + </p> + <p> + We see in Tables 2/14 to 2/18 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 fertilised 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 cowslips or primroses, yet when + legitimately fertilised by these latter species, especially by the + long-styled primrose, they yielded a moderate supply of good seed. + </p> + <p> + 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 + legitimately 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 2.14) by its own pollen it produced some good seeds, + though much fewer than self- fertilised cowslips or primroses would have + produced. The long-styled oxlip likewise yielded a very low average of + seed, as may be seen in the third compartment of Tables 2.15 to 2.18, when + illegitimately fertilised by, and when illegitimately fertilising, pure + cowslips and primroses. The four corresponding legitimate unions, however, + were moderately fertile, and one (namely that between a short-styled + cowslip and the long-styled oxlip in Table 2.17) was nearly as fertile as + if both parents had been pure. A short-styled primrose legitimately + fertilised by the long-styled oxlip (Table 2.18) 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 unions 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. + </p> + <p> + 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 more + 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 + presently 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. + </p> + <p> + 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 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 conditions, 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 seedling 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 + estimated to include an average of only from fifteen to twenty seeds. + </p> + <p> + 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 interesting 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 advanced, one of + these plants threw up two naked scapes, 7 inches in height, which bore + umbels of flowers of the same character as before. This fact led me to + examine 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 between 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. + </p> + <p> + From the various facts now given, there can be no doubt that the common + oxlip is a hybrid between the cowslip (P. veris, Brit. Fl.) and the + primrose (P. vulgaris, 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 (2/13. See also on this head Hardwicke’s ‘Science Gossip’ 1867 pages + 114, 137.), 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 legitimate 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 hereafter see good reason to believe. The case of the oxlip is + interesting; for hardly any other instance is known of a hybrid + spontaneously arising in such large numbers over so wide an extent of + country. 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 residence 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 + frequented 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. + </p> + <p> + 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 uncrossed, 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. + </p> + <p> + 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 different range from that of the cowslip and primrose; and it + inhabits some districts where neither of these species live. (2/14. For + England, see Hewett C. Watson ‘Cybele Britannica’ volume 2 1849 page 292. + For the Continent, see Lecoq ‘Geograph. Botanique de l’Europe’ tome 8 1858 + page 142. For the Alps see ‘Annals and Magazine of Natural History’ volume + 9 1842 pages 156 and 515.) 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 distinctly defined, namely, their + linear-oblong capsules equalling the calyx in length. (2/15. Babington + ‘Manual of British Botany’ 1851 page 258.) 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 + heterostyled species of the genus, but differ somewhat (see Tables 1.8 and + 1.12.) in the smaller proportion of the illegitimately 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 35.5 per capsule; whereas, of + the four possible unions (Table 2.14) between the two forms of the common + oxlip 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 + 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 1.18), + 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. (2/16. See Mr. H. Doubleday in + the ‘Gardener’s Chronicle’ 1867 page 435, also Mr. W. Marshall ibid. page + 462.) Nevertheless, according to Mr. H.C. Watson and Dr. Bromfield (2/17. + ‘Phytologist’ volume 1 page 1001 and volume 3 page 695.), 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. + </p> + <p> + 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. + </p> + <p> + Mr. Scott has arrived at some interesting results by crossing other + heterostyled species of Primula. (2/18. ‘Journal of the Linnean Society + Botany’ volume 8 1864 page 93 to end.) 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 + Kolreuter and Gartner, that two species when crossed reciprocally + sometimes differ as widely as is possible in their fertility: 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 + legitimately 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 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 2.14 to 2.18), between the two forms of the oxlip, primrose, 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 peculiarities which might well entitle + them, by the criterion of fertility, to specific distinction.” + </p> + <p> + 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 + (i.e. when opposite forms are united) than when crossed illegitimately. + </p> + <h3> + SUPPLEMENTARY NOTE ON SOME WILD HYBRID VERBASCUMS. + </h3> + <p> + In an early part of this chapter I remarked that few other instances could + be given of a hybrid spontaneously arising in such large numbers, and over + so wide an extent of country, as that of the common oxlip; but perhaps the + number of well-ascertained cases of naturally produced hybrid willows is + equally great. (2/19. Max Wichura ‘Die Bastardbefruchtung etc. der Weiden’ + 1865.) Numerous spontaneous hybrids between several species of Cistus, + found near Narbonne, have been carefully described by M. Timbal-Lagrave + (2/20. ‘Mem. de l’Acad. des Sciences de Toulouse’ 5e serie tome 5 page + 28.), and many hybrids between an Aceras and Orchis have been observed by + Dr. Weddell. (2/21. ‘Annales des Sc. Nat.’ 3e serie Bot. tome 18 page 6.) + In the genus Verbascum, hybrids are supposed to have often originated in a + state of nature (2/22. See for instance the ‘English Flora’ by Sir J.E. + Smith 1824 volume 1 page 307.); some of these undoubtedly are hybrids, and + several hybrids have originated in gardens; but most of these cases + require, as Gartner remarks, verification. (2/23. See Gartner + ‘Bastarderzeugung’ 1849 page 590.) Hence the following case is worth + recording, more especially as the two species in question, V. thapsus and + lychnitis, are perfectly 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 secreting nectar. + </p> + <p> + 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 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 + temporarily 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 leaves 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 produced yellow flowers; for Gartner crossed white and + yellow-flowered varieties of Verbascum, and the offspring thus produced + never bore flowers of an intermediate tint, but either pure white or pure + yellow flowers, generally of the latter colour. (2/24. ‘Bastardzeugung’ + page 307.) + </p> + <p> + 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. + </p> + <p> + It is known that many species of Verbascum, when the stem is jarred or + struck by a stick, cast off their flowers. (2/25. This was first observed + by Correa de Serra: see Sir J.E. Smith’s ‘English Flora’ 1824 volume 1 + page 311; also ‘Life of Sir J.E. Smith’ volume 2 page 210. I was guided to + these references by the Reverend W.A. Leighton, who observed this same + phenomenon with V. virgatum.) This occurs with V. thapsus, as I have + repeatedly 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 lychnitis and, as I believe, V. phoeniceum the + corolla is not cast 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. + </p> + <p> + 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 + collecting pollen, there can be no doubt. Although insects 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. (2/26. ‘The Effects of Cross and + Self-fertilisation’ 1876 page 89.) 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 uniform 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 + 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 statement 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 Verbascum + which evidently cross with the greatest ease, but produce hybrids which + are excessively sterile. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0003" id="link2HCH0003"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER III. HETEROSTYLED DIMORPHIC PLANTS—continued. + </h2> +<pre xml:space="preserve"> + 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 fagopyrum. + Various other heterostyled genera. + Rubiaceae. + Mitchella repens, fertility of the flowers in pairs. + Houstonia. + Faramea, remarkable difference in the pollen-grains of the two forms; torsion of + the stamens in the short-styled form alone; development not as yet perfect. + The heterostyled structure in the several Rubiaceous genera not due to descent + in common. + + (FIGURE 3.4. Linum grandiflorum. + Left: Long-styled form. + Right: Short-styled form. + s, s: stigmas.) +</pre> + <p> + It has long been known that several species of Linum present two forms + (3/1. Treviranus has shown that this is the case in his review of my + original paper ‘Botanische Zeitung’ 1863 page 189.), 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 (Figure 3.4). 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 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, 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 papillae on the stigmatic surfaces are shorter, darker-coloured, + and more crowded together than in the long-styled form; but these + differences seem due merely to the shortening of the stigma, for in the + varieties of the long-styled form with shorter stigmas, the papillae are + more crowded and darker-coloured than in those with the longer stigmas. + Considering the slight and variable differences between the two forms of + this Linum, it is not surprising that hitherto they have been overlooked. + </p> + <p> + In 1861 I had eleven plants in my garden, eight of which were long-styled, + and three short-styled. Two very fine long-styled plants grew in a bed a + hundred yards off all the others, and separated from them by a screen of + evergreens. I marked twelve flowers, and placed on their stigmas a little + pollen from the short-styled plants. The pollen of the two forms is, as + stated, identical in appearance; the stigmas of the long-styled flowers + were already thickly covered with their own pollen—so thickly that I + could not find one bare stigma, and it was late in the season, namely, + September 15th. Altogether, it seemed almost childish to expect any + result. Nevertheless from my experiments 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 ultimately six fine capsules (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. + </p> + <p> + 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 remaining one + grew so close to a short-styled plant that their branches touched, and + this produced twelve capsules, but they were poor ones. The case was + different 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 between 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. + </p> + <p> + In 1862 I 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 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 numbers. 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-breeding. 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 seventeen long-styled plants, only three + capsules were produced. 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 surprising that a + greater number of flowers were not accidentally fertilised. + </p> + <p> + 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 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 numerous other flowers + were produced, many of which must have received their own pollen. From all + these flowers on the seventeen short-styled plants only fifteen capsules + were produced, of which only eleven contained 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 transported 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 capsules to three; nor can this + difference be accounted for by the short-styled stigmas being more liable + to receive their own pollen than the long-styled, for the reverse is the + case. The greater self-fertility of the short-styled flowers was likewise + shown in 1861 by the plants in my flower- garden, which were left to + themselves, and were but sparingly visited by insects. + </p> + <p> + 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 greater. + </p> + <p> + Hildebrand tested my results, but only on a single short-styled plant, by + fertilising many flowers with their own-form pollen; and these did not + produce any 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. (3/2. ‘Botanische Zeitung’ January 1, 1864 page 2.) + </p> + <p> + The absolute sterility (judging from the experiments 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. + </p> + <h3> + FIRST. + </h3> + <p> + 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 + penetrated by a multitude of long pollen- tubes. This is what might have + been expected, as the union is a legitimate one. The converse experiment + was likewise tried, and pollen from a long-styled flower was placed on the + stigmas of a short-styled flower, and in twenty-four hours the stigmas + were discoloured, twisted, and penetrated by numerous pollen-tubes; and + this, again, is what might have been expected, as the union was a + legitimate one. + </p> + <h3> + SECONDLY. + </h3> + <p> + 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, and + 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. + </p> + <h3> + THIRDLY. + </h3> + <p> + 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. + </p> + <h3> + FOURTHLY. + </h3> + <p> + Repeated the experiment, with the same result after twenty-four hours. + </p> + <h3> + FIFTHLY. + </h3> + <p> + 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. + </p> + <p> + The following experiments are more striking:— + </p> + <h3> + SIXTHLY. + </h3> + <p> + I placed own-form pollen on three of the stigmas of a long-styled flower, + and pollen from a short-styled flower on the other two stigmas. After + twenty-two hours these two stigmas were discoloured, slightly twisted, and + penetrated by the tubes of numerous 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. + </p> + <h3> + SEVENTHLY. + </h3> + <p> + Experiment repeated in the same manner, with the same result. + </p> + <h3> + EIGHTHLY. + </h3> + <p> + 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 + short-styled flower were penetrated by innumerable tubes, which were as + yet short, and the stigmas themselves were not at all discoloured. The + three stigmas covered with their own-form pollen were not penetrated by a + single pollen-tube. + </p> + <h3> + NINTHLY. + </h3> + <p> + Put pollen of a short-styled flower on a single long-styled stigma, and + own-form pollen on the other four stigmas; after twenty-four hours the one + stigma was somewhat discoloured and twisted, and penetrated by many long + tubes: the other four stigmas were quite straight and fresh; but on + dissecting them I found that three pollen-grains had protruded very short + tubes into the tissue. + </p> + <h3> + TENTHLY. + </h3> + <p> + 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. + </p> + <p> + 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 interval 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 stigmatic tissue deeply, and the + stigmas themselves do not soon become discoloured and twisted. + </p> + <p> + This seems to me a remarkable physiological fact. The pollen-grains of the + two forms are undistinguishable under the microscope; the stigmas differ + only in length, degree of divergence, and in the size, shade of colour, + and approximation of their papillae, 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 mysterious 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 grandiflorum (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, corresponding with that + existing between the pollen and stigma of species belonging to distinct + genera. + </p> + <p> + Linum perenne. + </p> + <p> + This species is conspicuously heterostyled, 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 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 exposure to the light. The anthers of the longer stamens correspond + in height with the lower part of the stigmas of the long-styled flowers; + and the anthers of the shorter stamens of the latter correspond in the + same manner in height with the stigmas of the short-styled flowers. + </p> + <p> + 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 + transplant 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 pollen, taken in every case + from a separate plant; and not one set a seed- capsule: twelve other + flowers were legitimately fertilised with pollen from short-styled + flowers; and they set nine capsules, each including on an average 7 good + seeds, ten being the maximum number ever produced. Of the flowers on the + short-styled plants, twelve were illegitimately fertilised with own-form + pollen, and they yielded one capsule, including only 3 good seeds; twelve + other flowers were legitimately fertilised with pollen from long-styled + flowers, and these produced nine capsules, but one was bad; the eight good + capsules contained on an average 8 good seeds each. Judging from the + number of seeds per capsule, the fertility of the two legitimate to that + of the two illegitimate unions is as 100 to 20. + </p> + <p> + 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 accidental + 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. + </p> + <p> + 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. + </p> + <p> + 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 stamens of corresponding height belonging + to the opposite form should be brought to them. + </p> + <p> + 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 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 fertilised about 30 flowers with pollen from + the long-styled form, and these, with the exception of two, yielded + capsules, containing good seeds. + </p> + <p> + It is a singular fact, in contrast with what occurred in the case of L. + grandiflorum, that the pollen-grains of both forms of L. perenne, when + placed on their own-form stigmas, emitted their tubes, though this action + did not lead to the production of seeds. After an interval of eighteen + hours, the tubes penetrated the stigmatic tissue, but to what depth I did + not ascertain. In this case the impotence of the pollen-grains on their + own stigmas must have been due either to the tubes not reaching the + ovules, or to their not acting properly after reaching them. + </p> + <p> + 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 fertilisation on seventeen long-styled plants in the + one case, and on eleven long-styled plants in the other, resulted in the + production, in each case, of three poor capsules; so that when the proper + insects are excluded, the wind does hardly anything in the way of carrying + pollen from plant to plant. I allude to this fact because botanists in + speaking of the fertilisation of various flowers, often refer to the wind + or to insects as if the alternative were indifferent. This view, according + to my experience, is entirely erroneous. When the wind is the agent in + carrying pollen, either from one sex to the other, or from hermaphrodite + to hermaphrodite, we can recognise structure as manifestly adapted to its + action as to that of insects when these are the carriers. We see + adaptation to the wind in the incoherence of the pollen,—in the + inordinate quantity produced (as in the Coniferae, Spinage, etc.),—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 Gramineae, Docks, etc), 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 fertilisation (and this is incomparably the more + frequent case with hermaphrodite plants), the wind plays no part, but we + see an endless number of adaptations to ensure the safe transport of the + pollen by the living 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. + </p> + <p> + I have already alluded to the rotation of each separate stigma in the + long- styled form of Linum 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 case with the stigmas of the long-styled flowers of + L. perenne whilst in bud. But by the time the flowers 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 complete; for after two or three cold and wet + days the movement was very imperfectly performed. The flowers should be + examined shortly after their expansion, 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. + </p> + <p> + 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, between 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 stigmas have presented their backs to the insects which sucked + the flowers, but their front and fertile surfaces would have been + separated from the entering insects 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 movement the short stigmas lie + within the tube of the corolla; and their papillous surfaces being now + turned upwards are necessarily brushed by every entering insect, and thus + receive the required pollen. + </p> + <p> + 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 alone of the opposite form causes + fertilisation. + </p> + <p> + (Figure 3.5. 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. (3/3. I neglected to get drawings made from + fresh flowers of the two forms. But Mr. Fitch has made the above sketch of + a long- styled flower from dried specimens and from published engravings. + His well-known skill ensures accuracy in the proportional size of the + parts.) + </p> + <p> + 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 fertilisation of both forms. The corolla of L. + perenne is more 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 (Figure 3.5), 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 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 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. + </p> + <p> + 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. + </p> + <p> + 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. (3/4. ‘Fertilisation of Orchids’ page 108; 2nd edition + 1877 page 84.) The belief that the flowers of many plants are fertilised + in the bud, that is, are perpetually self-fertilised, is a most effectual + bar to understanding their real structure. I am, however, far from wishing + to assert that some flowers, during certain seasons, are not fertilised in + the bud; for I have reason to believe that this is the case. A good + observer, resting his belief on the usual kind of evidence, states that in + Linum Austriacum (which is heterostyled, and is considered by Planchon as + a variety of L. perenne) the anthers open the evening before the expansion + of the flowers, and that the stigmas are then almost always fertilised. + (3/5. H. Lecoq ‘Etudes sur la Geogr. Bot.’ 1856 tome 5 page 325.) Now we + know positively that, so far from Linum perenne being fertilised by its + own pollen in the bud, its own pollen is as powerless on the stigma as so + much inorganic dust. + </p> + <p> + Linum flavum. + </p> + <p> + The pistil of the long-styled form of this species is nearly twice as long + as that of the short-styled; the stigmas are longer and the papillae + coarser. In the short-styled form the stigmas diverge and pass out between + the filaments, as in the previous species. The 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 short-styled plants of the two previous species apparently + evince some slight capacity for fertilisation with their own-form pollen, + these three capsules may have been the product of self-fertilisation. + </p> + <p> + Besides the three species now described, the yellow-flowered L. + corymbiferum is certainly heterostyled, as is, according to Planchon, L. + salsoloides. (3/6. Hooker’s ‘London Journal of Botany’ 1848 volume 7 page + 174.) This botanist is the only one who seems to have inferred that + heterostylism might have some important functional 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. (3/7. ‘Botanische + Zeitung’ September 18, 1863 page 281.) 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. (3/8. It is not improbable that the allied + genus, Hugonia, is heterostyled, for one species is said by Planchon + (Hooker’s ‘London Journal of Botany’ 1848 volume 7 page 525) to be + provided with “staminibus exsertis;” another with “stylis staminibus + longioribus,” and another has “stamina 5, majora, stylos longe + superantia.”) According to the same author, none of the species which + inhabit America and the Cape of Good Hope are heterostyled. + </p> + <p> + I have examined only three homostyled species, namely, L. usitatissimum, + angustifolium, and catharticum. 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. Muller, are frequented by + bees and moths. (3/9. ‘Die Befruchtung der Blumen’ etc. page 168.) 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 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. (3/10. + Planchon in Hooker’s ‘London Journal of Botany’ 1848 volume 7 page 175. + See on this subject Asa Gray in ‘American Journal of Science’ volume 36 + September 1863 page 284.) + </p> + <h3> + PULMONARIA (BORAGINEAE). + </h3> + <p> + Pulmonaria officinalis. + </p> + <p> + Hildebrand has published a full account of this heterostyled plant. (3/11. + ‘Botanische Zeitung’ 1865 January 13 page 13.) 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 difference 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. Hildebrand 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. 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 Table 3.19. + </p> + <p> + TABLE 3.19. Pulmonaria officinalis (from Hildebrand). + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Fruits produced. Column 4: Average Number of Seeds per + Fruit. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 14 : 10 : 1.30. + </p> + <p> + Long-styled 14 by own-pollen, and 16 by pollen of other plant of same + form. Illegitimate union : 30 : 0 : 0. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 16 : 14 : 1.57. + </p> + <p> + Short-styled 11 by own-pollen, 14 by pollen of other plant of same form. + Illegitimate union : 25 : 0 : 0. + </p> + <p> + In the summer of 1864, before I had heard of Hildebrand’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 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 unfavourable 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 fertilised 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 + Siebengbirge. My plants exhibited no tendency to become equal-styled, so + as to lose their proper long-styled character, as not rarely happens under + cultivation with several heterostyled species of Primula; but it would + appear that they had been greatly affected in function, either by + long-continued cultivation or by some other cause. We shall see in a + future chapter that heterostyled plants illegitimately fertilised during + several successive generations sometimes 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. + </p> + <p> + Pulmonaria angustifolia. + </p> + <p> + (FIGURE 3.6. Pulmonaria angustifolia. Left: Long-styled form. Right: + Short-styled form.) + </p> + <p> + Seedlings of this plant, raised from plants growing wild in the Isle of + Wight, were named for me by Dr. Hooker. It is so closely allied to the + last species, differing chiefly in the shape and spotting of the leaves, + that the two have been considered 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 + unimpregnated. 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 Table 3.20. Therefore P. + officinalis and angustifolia appear to be good and distinct species, in + conformity with other important functional differences between them, + immediately to be described. + </p> + <p> + TABLE 3.20. Pulmonaria angustifolia. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Fruits produced. Column 4: Average Number of Seeds per + Fruit. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 18 : 9 : 2.11. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 18 : 0 : 0. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 18 : 15 : 2.60. + </p> + <p> + Short-styled by own-form pollen. Illegitimate union : 12 : 7 : 1.86. + </p> + <p> + The long-styled and short-styled flowers of P. angustifolia differ from + one another in structure in nearly the same manner as those of P. + officinalis. But in Figure 3.6 a slight bulging of the corolla 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, according 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 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 sometimes 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 being + from 80 to 63, and in the latter from 80 to 70 divisions of the micrometer + in length. From an average of seven measurements, the short-styled anthers + were to those from the long-styled as 100 to 91 in length. Lastly, the + pollen-grains from the long-styled flowers varied between 13 and 11.5 + divisions of the micrometer, and those from the short-styled between 15 + and 13. The average diameter of 25 grains from the latter, or short-styled + form, was to that of 20 grains from the long-styled as 100 to 91. We see, + therefore, that the pollen-grains from the smaller anthers of the shorter + stamens in the long-styled form are, as usual, of smaller size than those + in the other form. But what is remarkable, a larger proportion of the + grains were small, shrivelled, and worthless. This could be seen by merely + comparing the contents of the anthers from several distinct plants of each + form. But in one instance my son found, by counting, that out of 193 + grains from a long-styled flower, 53 were bad, or 27 per cent; whilst out + of 265 grains from a short-styled flower only 18 were bad, or 7 per cent. + From the condition of the pollen in the long-styled form, and from the + extreme variability of all the organs in both forms, we may perhaps + suspect that the plant is undergoing a change, and tending to become + dioecious. + </p> + <p> + My son collected in the Isle of Wight on two occasions 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 Hildebrand, is even greater, namely, as 100 flowers for the + short- styled to 77 for the long-styled plants. Table 3.20 shows the + results of my experiments. + </p> + <p> + We see in Table 3.20 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 35. The 18 long-styled + flowers illegitimately fertilised yielded no seeds,—not even a + vestige of one. Two long-styled plants which were placed under a net + produced 138 flowers, besides those which were artificially fertilised, + and none of these set any fruit; nor did some plants of the same form + which were protected during the next summer. Two other long-styled plants + were left uncovered (all the short-styled plants having been previously + covered up), and humble-bees, 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 respect 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. + </p> + <p> + Eighteen short-styled flowers legitimately fertilised yielded, as may be + seen in Table 3.20, 15 fruits, each having on an average 2.6 seeds. Four + of these fruits contained the highest possible number of seeds, namely 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 sufficient quantity. For after carefully + covering all the long-styled plants in my garden, several short-styled + plants were left exposed to the visits of humble-bees, and their stigmas + will thus have received plenty of short-styled pollen; and now about half + the flowers, thus illegitimately fertilised, set fruit. I judge of this + proportion partly from estimation and partly from having examined three + large branches, which had borne 31 flowers, and these produced 16 fruits. + Of the fruits produced 233 were collected (many being left ungathered), + and these included on an average 1.82 seed. No less than 16 out of the 233 + fruits included the highest possible number of seeds, namely 4, and 31 + included 3 seeds. So we see how highly fertile these short-styled plants + were when illegitimately fertilised with their own-form pollen by the aid + of bees. + </p> + <p> + The great difference in the fertility of the long and short-styled + flowers, when both are illegitimately fertilised, 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 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 probably + 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 adaptation to check self-fertilisation, as their stigmas are + eminently liable to receive their own pollen. This view is even still more + tempting in the case of the long-styled form of Linum grandiflorum. On the + other hand, with Pulmonaria angustifolia, it is evident, from the corolla + projecting obliquely upwards, that pollen is much more likely to fall on, + or to be carried by insects down to the stigma of the short-styled than of + the long-styled flowers; yet the short-styled instead of being more + sterile, as a protection against self-fertilisation, are far more fertile + than the long-styled, when both are illegitimately fertilised. + </p> + <p> + Pulmonaria azurea, according to Hildebrand, is not heterostyled. (3/12. + ‘Die Geschlechter-Vertheilung bei den Pflanzen’ 1867 page 37.) + </p> + <p> + [From an examination of dried flowers of Amsinckia spectabilis, sent me by + Professor Asa Gray, I formerly thought that this plant, a member of the + Boragineae, was heterostyled. The pistil varies to an extraordinary degree + in length, being in some specimens twice as long as in others, and the + point of insertion of the stamens likewise varies. But on raising many + plants from seed, I soon became convinced that the whole case was one of + mere variability. The first-formed flowers are apt to 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 Boragineae, Arnebia + hispidissima, collected from several sites, and though the corolla, + together with the included organs, differed much in length, there was no + sign of heterostylism.] + </p> + <p> + Polygonum fagopyrum (Polygonaceae). + </p> + <p> + (FIGURE 3.7. Polygonum fagopyrum. (From H. Muller.) Upper figure, the + long-styled form; lower figure, the short-styled. Some of the anthers have + dehisced, others have not.) + </p> + <p> + Hildebrand has shown that this plant, the common Buck-wheat, is + heterostyled. (3/13. ‘Die Geschlechter-Vertheilung’ etc. 1867 page 34.) In + the long-styled form (Figure 3.7), 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 + difference in the structure of the stigmas in the two forms. The + pollen-grains of the short-styled form are to those of the long-styled as + 100 to 82 in diameter. This plant is therefore without doubt heterostyled. + </p> + <p> + 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, fertilised. They produced 22 seeds, + or 11 per flower-head. + </p> + <p> + Three flower-heads on long-styled plants received 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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-heads yielded on an average 7.50 seeds per head; whereas + the seven illegitimately fertilised heads yielded less than half the + number, or on an average only 3.28 seeds. The legitimately crossed seeds + from the long-styled flowers were finer than those from the illegitimately + fertilised flowers on the same plants, in the ratio of 100 to 82, as shown + by the weights of an equal number. + </p> + <p> + About a dozen plants, including both forms, were protected under nets, and + early in the season they produced 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. Muller, visit the flowers for the sake + of the eight drops of nectar. (3/14. ‘Die Befruchtung’ etc. page 175 and + ‘Nature’ January 1, 1874 page 166.) 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 mistaken in supposing that the long-styled + flowers cannot spontaneously fertilise themselves. + </p> + <p> + 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. + Muller in his interesting description of several other species shows that + P. bistorta is so strongly proterandrous (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 secrete little or no nectar, and + consequently are rarely visited by insects; these are adapted for + self-fertilisation, though still capable of cross-fertilisation. According + to Delpino, the Polygonaceae are generally fertilised by the wind, instead + of by insects as in the present genus. + </p> + <p> + [Leucosmia Burnettiana (Thymeliae). + </p> + <p> + As Professor 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 (3/15. ‘American Journal of Science’ 1865 page + 101 and Seemann’s ‘Journal of Botany’ volume 3 1865 page 305.), 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 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. + </p> + <p> + Menyanthes trifoliata (Gentianeae). + </p> + <p> + This plant inhabits marshes: my son William gathered 247 flowers from so + many distinct plants, and of these 110 were long-styled, and 137 + short-styled. The pistil of the long-styled form is in length to that of + the short-styled in the ratio of about 3 to 2. The stigma of the former, + as my son observed, is decidedly 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. + </p> + <p> + Limnanthemum Indicum (Gentianeae). + </p> + <p> + 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 3 to 5. The foliaceous stigma + is more expanded, and twice as large as that of the short-styled form. In + the latter the stamens are about twice as long as those of the + long-styled, and their anthers are larger in the ratio of 100 to 70. The + pollen-grains, after having been long kept in spirits, were of the same + shape and size in both forms. The ovules, according to Mr. Thwaites, are + equally numerous (namely from 70 to 80) in the two forms. + </p> + <p> + Villarsia [sp.?] (Gentianeae). + </p> + <p> + Fritz Muller 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 + conspicuously 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 Muller 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. + </p> + <p> + The three genera, Menyanthes, Limnanthemum, and Villarsia, now described, + constitute a well-marked sub-tribe of the Gentianeae. All the species, as + far as at present known, are heterostyled, and all inhabit aquatic or + sub-aquatic stations. + </p> + <p> + Forsythia suspensa (Oleaceae). + </p> + <p> + Professor Asa Gray states that the plants of this species growing in the + Botanic Gardens at Cambridge, U.S., are short-styled, but that Siebold and + Zuccarini describe the long-styled form, and give figures of two forms; so + that there can be little doubt, as he remarks, about the plant being + dimorphic. (3/16. ‘The American Naturalist’ July 1873 page 422.) I + therefore applied to Dr. Hooker, who sent me a dried flower from Japan, + another from China, and another from the Botanic Gardens at Kew. The first + proved to be long-styled, and the other two short-styled. In the + long-styled form, the pistil is in length to that of the short-styled as + 100 to 38, the lobes of the stigma being a little longer (as 10 to 9), but + narrower and less divergent. This last character, however, may be only a + temporary one. There seems to be no difference in the papillose condition + of the two stigmas. In the short-styled form, the stamens are in length to + those of the long-styled as 100 to 66, but the anthers are shorter in the + ratio of 87 to 100; and this is unusual, for when there is any difference + in size between the anthers of the two forms, those from the longer + stamens of the short-styled are generally the longest. The pollen-grains + from the short-styled flowers are certainly larger, but only in a slight + degree, than those from the long-styled, namely, as 100 to 94 in diameter. + The short-styled form, which grows in the Gardens at Kew, has never there + produced fruit. + </p> + <p> + Forsythia viridissima appears likewise to be heterostyled; for Professor + Asa Gray says that although the long-styled form alone grows in the + gardens at Cambridge, U.S., the published figures of this species belong + to the short- styled form. + </p> + <p> + Cordia [sp.?] (Cordiaceae). + </p> + <p> + Fritz Muller sent me dried specimens of this shrub, which he believes to + be heterostyled; and I have not much doubt that this is the case, though + the usual characteristic differences are not well pronounced in the two + forms. Linum grandiflorum shows us that a plant may be heterostyled in + function in the highest degree, and yet the two forms may have stamens of + equal length, and pollen-grains of equal size. In the present species of + Cordia, the stamens of both forms are of nearly equal length, those of the + short-styled being rather the longest; and the anthers of both are seated + in the mouth of the corolla. Nor could I detect any difference in the size + of the pollen-grains, when dry or after being soaked in water. The stigmas + of the long-styled form stand clear above the anthers, and the whole + pistil is longer than that of the short-styled, in about the ratio of 3 to + 2. + </p> + <p> + The stigmas of the short-styled form are seated beneath the anthers, and + they are considerably shorter than those of the long-styled form. This + latter difference is the most important one of any between the two forms. + </p> + <p> + Gilia (Ipomopsis) pulchella vel aggregata (Polemoniaceae). + </p> + <p> + Professor Asa Gray remarks with respect to this plant: “the tendency to + dimorphism, of which there are traces, or perhaps rather incipient + manifestations in various portions of the genus, is most marked in G. + aggregata.” (3/17. ‘Proceedings of the American Academy of Arts and + Sciences.’ June 14, 1870 page 275.) He sent me some dried flowers, and I + procured others from Kew. They differ greatly in size, some being nearly + twice as long as others (namely as 30 to 17), so that it was not possible + to compare, except by calculation, the absolute length of the organs from + different plants. Moreover, the relative position of the stigmas and + anthers is variable: in some long- styled flowers the stigmas and anthers + were exserted only just beyond the throat of the corolla; whilst in others + they were exserted as much as 4/10 of an inch. I suspect also that the + pistil goes on growing for some time after the anthers have dehisced. + Nevertheless it is possible to class the flowers under two forms. In some + of the long-styled, the length of pistil to that of the short-styled was + as 100 to 82; but this result was gained by reducing the size of the + corollas to the same scale. In another pair of flowers the difference in + length between the pistils of the two forms was certainly greater, but + they were not actually measured. In the short-styled flowers whether large + or small, the stigma is seated low down within the tube of the corolla. + The papillae on the long-styled stigma are longer than those on the + short-styled, in the ratio of 100 to 40. The filaments in some of the + short-styled flowers were, to those of the long-styled, as 100 to 25 in + length, the free, or unattached portion being alone measured; but this + ratio cannot be trusted, owing to the great variability of the stamens. + The mean diameter of eleven pollen-grains from long-styled flowers, and of + twelve from the short-styled, was exactly the same. It follows from these + several statements, that the difference in length and state of surface of + the stigmas in the flowers is the sole reliable evidence that this species + is heterostyled; for it would be rash to trust to the difference in the + length of the pistils, seeing how variable they are. I should have left + the case altogether doubtful, had it not been for the observations on the + following species; and these leave little doubt on my mind that the + present plant is truly heterostyled. Professor Gray informs me that in + another species, G. coronopifolia, belonging to the same section of the + genus, he can see no sign of dimorphism. + </p> + <p> + Gilia (Leptosiphon) micrantha. + </p> + <p> + A few flowers sent me from Kew had been somewhat injured, so that I cannot + say anything positively with respect to the position and relative length + of the organs in the two forms. But their stigmas differed almost exactly + in the same manner as in the last species; the papillae on the long-styled + stigma being longer than those on the short-styled, in the ratio of 100 to + 42. My son measured nine pollen-grains from the long-styled, and the same + number from the short-styled form; and the mean diameter of the former was + to that of the latter as 100 to 81. Considering this difference, as well + as that between the stigmas of the two forms, there can be no doubt that + this species is heterostyled. So probably is Gilia nudicaulis, which + likewise belongs to the Leptosiphon section of the genus, for I hear from + Professor Asa Gray that in some individuals the style is very long, with + the stigma more or less exserted, whilst in others it is deeply included + within the tube; the anthers being always seated in the throat of the + corolla. + </p> + <p> + Phlox subulata (Polemoniaceae). + </p> + <p> + Professor Asa Gray informs me that the greater number of the species in + this genus have a long pistil, with the stigma more or less exserted; + whilst several other species, especially the annuals, have a short pistil + seated low down within the tube of the corolla. In all the species the + anthers are arranged one below the other, the uppermost just protruding + from the throat of the corolla. In Phlox subulata alone he has “seen both + long and short styles; and here the short-styled plant has (irrespective + of this character) been described as a distinct species (P. nivalis, P. + Hentzii), and is apt to have a pair of ovules in each cell, while the + long-styled P. subulata rarely shows more than one.” (3/18. ‘Proceedings + of the American Academy of Arts and Sciences’ June 14, 1870 page 248.) + Some dried flowers of both forms were sent me by him, and I received + others from Kew, but I have failed to make out whether the species is + heterostyled. In two flowers of nearly equal size, the pistil of the + long-styled form was twice as long as that of the short-styled; but in + other cases the difference was not nearly so great. The stigma of the + long-styled pistil stands nearly in the throat of the corolla; whilst in + the short-styled it is placed low down—sometimes very low down in + the tube, for it varies greatly in position. The stigma is more papillose, + and of greater length (in one instance in the ratio of 100 to 67), in the + short-styled flowers than in the long-styled. My son measured twenty + pollen-grains from a short-styled flower, and nine from a long- styled, + and the former were in diameter to the latter as 100 to 93; and this + difference accords with the belief that the plant is heterostyled. But the + grains from the short-styled varied much in diameter. He afterwards + measured ten grains from a distinct long-styled flower, and ten from + another plant of the same form, and these grains differed in diameter in + the ratio of 100 to 90. The mean diameter of these two lots of twenty + grains was to that of twelve grains from another short-styled flower as + 100 to 75: here, then, the grains from the short-styled form were + considerably smaller than those from the long-styled, which is the reverse + of what occurred in the former instance, and of what is the general rule + with heterostyled plants. The whole case is perplexing in the highest + degree, and will not be understood until experiments are tried on living + plants. The greater length, and more papillose condition of the stigma in + the short-styled than in the long-styled flowers, looks as if the plant + was heterostyled; for we know that with some species—for instance, + Leucosmia and certain Rubiaceae—the stigma is longer and more + papillose in the short-styled form, though the reverse of this holds good + in Gilia, a member of the same family with Phlox. The similar position of + the anthers in the two forms is somewhat opposed to the present species + being heterostyled; as is the great difference in the length of the pistil + in several short-styled flowers. But the extraordinary variability in + diameter of the pollen-grains, and the fact that in one set of flowers the + grains from the long-styled flowers were larger than those from the + short-styled, is strongly opposed to the belief that Phlox subulata is + heterostyled. Possibly this species was once heterostyled, but is now + becoming sub-dioecious; the short-styled plants having been rendered more + feminine in nature. This would account for their ovaries usually + containing more ovules, and for the variable condition of their + pollen-grains. Whether the long- styled plants are now changing their + nature, as would appear to be the case from the variability of their + pollen-grains, and are becoming more masculine, I will not pretend to + conjecture; they might remain as hermaphrodites, for the coexistence of + hermaphrodite and female plants of the same species is by no means a rare + event. + </p> + <p> + Erythroxylum [sp.?] (Erythroxylidae). + </p> + <p> + (FIGURE 3.8. Erythroxylon [sp.?] Left: Long-styled form. Right: + Short-styled form. From a sketch by Fritz Muller, magnified five times.) + </p> + <p> + Fritz Muller sent me from South Brazil dried flowers of this tree, + together with the drawings (Figure 3.8.), which show the two forms, + magnified about five times, with the petals removed. In the long-styled + form the stigmas project above the anthers, and the styles are nearly + twice as long as those of the short-styled form, in which the stigmas + stand beneath the anthers. The stigmas in many, but not in all the + short-styled flowers are larger than those in the long-styled. The anthers + of the short-styled flowers stand on a level with the stigmas of the other + form; but the stamens are longer by only one-fourth or one- fifth of their + own length than those of the long-styled. Consequently the anthers of the + latter do not stand on a level with, but rather above the stigmas of the + other form. Differently from what occurs in the following closely allied + genus, Sethia, the stamens are of nearly equal length in the flowers of + the same form. The pollen-grains of the short-styled flowers, measured in + their dry state, are a little larger than those from the long-styled + flowers in about the ratio of 100 to 93. (3/19. F. Muller remarks in his + letter to me that the flowers, of which he carefully examined many + specimens, are curiously variable in the number of their parts: 5 sepals + and petals, 10 stamens and 3 pistils are the prevailing numbers; but the + sepals and petals often vary from 5 to 7; the stamens from 10 to 14, and + the pistils from 3 to 4.) + </p> + <p> + Sethia acuminata (Erythroxylidae). + </p> + <p> + Mr. Thwaites pointed out several years ago that this plant exists under + two forms, which he designated as forma stylosa et staminea; and the + flowers sent to me by him are clearly heterostyled. (3/20. ‘Enumeratio + Plantarum Zeylaniae’ 1864 page 54.) In the long-styled form the pistil is + nearly twice as long, and the stamens half as long as the corresponding + organs in the short-styled form. The stigmas of the long-styled seem + rather smaller than those of the short-styled. All the stamens in the + short-styled flowers are of nearly equal length, whereas in long-styled + they differ in length, being alternately a little longer and shorter; and + this difference in the stamens of the two forms is probably related, as we + shall hereafter see in the case of the short-styled flowers of Lythrum + salicaria, to the manner in which insects can best transport pollen from + the long-styled flowers to the stigmas of the short-styled. The + pollen-grains from the short-styled flowers, though variable in size, are + to those of the long-styled, as far as I could make out, as 100 to 83 in + their longer diameter. Sethia obtusifolia is heterostyled like S. + acuminata. + </p> + <p> + Cratoxylon formosum (Hypericineae). + </p> + <p> + Mr. Thiselton Dyer remarks that this tree, an inhabitant of Malacca and + Borneo, appears to be heterostyled. (3/21. ‘Journal of Botany’ London 1872 + page 26.) He sent me dried flowers, and the difference between the two + forms is conspicuous. In the short-styled form the pistils are in length + to those of the short-styled as 100 to 40, with their globular stigmas + about twice as thick. These stand just above the numerous anthers and a + little beneath the tips of the petals. In the short-styled form the + anthers project high above the pistils, the stigmas of which diverge + between the three bundles of stamens, and stand only a little above the + tips of the sepals. The stamens in this form are to those of the long- + styled as 100 to 86 in length; and therefore they do not differ so much in + length as do the pistils. Ten pollen-grains from each form were measured, + and those from the short-styled were to those from the long-styled as 100 + to 86 in diameter. This plant, therefore, is in all respects a + well-characterised heterostyled species. + </p> + <p> + Aegiphila elata (Verbenaceae). + </p> + <p> + Mr. Bentham was so kind as to send me dried flowers of this species and of + Ae. mollis, both inhabitants of South America. The two forms differ + conspicuously, as the deeply bifid stigma of the one, and the anthers of + the other project far above the mouth of the corolla. In the long-styled + form of the present species, the style is twice and a half as long as that + of the short-styled. The divergent stigmas of the two forms do not differ + much in length, nor as far as I could perceive in their papillae. In the + long-styled flowers the filaments adhere to the corolla close up to the + anthers, which are enclosed some way down within the tube. In the + short-styled flowers the filaments are free above the point where the + anthers are seated in the other form, and they project from the corolla to + an equal height with that of the stigmas in the long-styled flowers. It is + often difficult to measure with accuracy pollen-grains, which have long + been dried and then soaked in water; but they here manifestly differed + greatly in size. Those from the short-styled flowers were to those from + the long-styled in diameter in about the ratio of 100 to 62. The two forms + of Ae. mollis present a like difference in the length of their pistils and + stamens. + </p> + <p> + Aegiphila obdurata. + </p> + <p> + Flowers of this bush were sent me from St. Catharina in Brazil, by Fritz + Muller, and were named for me at Kew. They appeared at first sight grandly + heterostyled, as the stigma of the long-styled form projects far out of + the corolla, whilst the anthers are seated halfway down within the tube; + whereas in the short-styled form the anthers project from the corolla and + the stigma is enclosed in the tube at nearly the same level with the + anthers of the other form. The pistil of the long-styled is to that of the + short-styled as 100 to 60 in length, and the stigmas, taken by themselves, + as 100 to 55. Nevertheless, this plant cannot be heterostyled. The anthers + in the long-styled form are brown, tough, and fleshy, and less than half + the length of those in the short-styled form, strictly as 44 to 100; and + what is much more important, they were in a rudimentary condition in the + two flowers examined by me, and did not contain a single grain of pollen. + In the short-styled form, the divided stigma, which as we have seen is + much shortened, is thicker and more fleshy than the stigma of the + long-styled, and is covered with small irregular projections, formed of + rather large cells. It had the appearance of having suffered from + hyperthrophy, and is probably incapable of fertilisation. If this be so + the plant is dioecious, and judging from the two species previously + described, it probably was once heterostyled, and has since been rendered + dioecious by the pistil in the one form, and the stamens in the other + having become functionless and reduced in size. It is, however, possible + that the flowers may be in the same state as those of the common thyme and + of several other Labiatae, in which females and hermaphrodites regularly + co-exist. Fritz Muller, who thought that the present plant was + heterostyled, as I did at first, informs me that he found bushes in + several places growing quite isolated, and that these were completely + sterile; whilst two plants growing close together were covered with fruit. + This fact agrees better with the belief that the species is dioecious than + that it consists of hermaphrodites and females; for if any one of the + isolated plants had been an hermaphrodite, it would probably have produced + some fruit.] + </p> + <h3> + RUBIACEAE. + </h3> + <p> + This great natural family contains a much larger number of heterostyled + genera than any other one, as yet known. + </p> + <p> + Mitchella repens. + </p> + <p> + Professor Asa Gray sent me several living plants collected when out of + flower, and nearly half of these proved long-styled, and the other half + short-styled. The white flowers, which are fragrant and which secrete + plenty of nectar, always grow in pairs with their ovaries united, so that + the two together produce “a berry-like double drupe.” (3/22. A. Gray + ‘Manual of the Botany of the United States’ 1856 page 172.) In my first + series of experiments (1864) I did not suppose that this curious + arrangement of the flowers would have any influence on their fertility; + and in several instances only one of the two flowers in a pair was + fertilised; and a large proportion or all of these failed to produce + berries. In the ensuing year both flowers of each pair were invariably + fertilised in the same manner; and the latter experiments alone serve to + show the proportion of flowers which yield berries, when legitimately and + illegitimately fertilised; but for calculating the average number of seeds + per berry I have used those produced during both seasons. + </p> + <p> + In the long-styled flowers the stigma projects just above the bearded + throat of the corolla, and the anthers are seated some way down the tube. + In the short- styled flowers those organs occupy reversed positions. In + this latter form the fresh pollen-grains are a little larger and more + opaque than those of the long- styled form. The results of my experiments + are given in Table 3.21. + </p> + <p> + TABLE 3.21. Mitchella repens. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Pairs of Flowers + fertilised during the second season. Column 3: Number of Drupes produced + during the second season. Column 4: Average Number of good Seeds per Drupe + in all the Drupes during the two Seasons. + </p> + <p> + Long-styled by pollen of short-styled. Legitimate union : 9 : 8 : 4.6. + </p> + <p> + Long-styled by own-form pollen. Illegitimate union : 8 : 3 : 2.2. + </p> + <p> + Short-styled by pollen of long-styled. Legitimate union: 8 : 7 : 4.1. + </p> + <p> + Short-styled by own-form pollen. Illegitimate union : 9 : 0 : 2.0. + </p> + <p> + The two legitimate unions together : 17 : 15 : 4.4. + </p> + <p> + The two illegitimate unions together : 17 : 3 : 2.1. + </p> + <p> + It follows from this table that 88 per cent of the paired flowers of both + forms, when legitimately fertilised, yielded double berries, nineteen of + which contained on an average 4.4 seeds, with a maximum in one of 8 seeds. + Of the illegitimately fertilised paired flowers only 18 per cent yielded + berries, six of which contained on an average only 2.1 seeds, with a + maximum in one of 4 seeds. Thus the two legitimate unions are more fertile + than the two illegitimate, according to the proportion of flowers which + yielded berries, in the ratio of 100 to 20; and according to the average + number of contained seeds as 100 to 47. + </p> + <p> + Three long-styled and three short-styled plants were protected under + separate nets, and they produced altogether only 8 berries, containing on + an average only 1.5 seed. Some additional berries were produced which + contained no seeds. The plants thus treated were therefore excessively + sterile, and their slight degree of fertility may be attributed in part to + the action of the many individuals of Thrips which haunted the flowers. + Mr. J. Scott informs me that a single plant (probably a long-styled one), + growing in the Botanic Gardens at Edinburgh, which no doubt was freely + visited by insects, produced plenty of berries, but how many of them + contained seeds was not observed. + </p> + <p> + Borreria, nov. sp. near valerianoides (Rubiaceae). + </p> + <p> + Fritz Muller sent me seeds of this plant, which is extremely abundant in + St. Catharina, in South Brazil; and ten plants were raised, consisting of + five long- styled and five short-styled. The pistil of the long-styled + flowers projects just beyond the mouth of the corolla, and is thrice as + long as that of the short-styled, and the divergent stigmas are likewise + rather larger. The anthers in the long-styled form stand low down within + the corolla, and are quite hidden. In the short-styled flowers the anthers + project just above the mouth of the corolla, and the stigma stands low + down within the tube. Considering the great difference in the length of + the pistils in the two forms, it is remarkable that the pollen-grains + differ very little in size, and Fritz Muller was struck with the same + fact. In a dry state the grains from the short-styled flowers could just + be perceived to be larger than those from the long-styled, and when both + were swollen by immersion in water, the former were to the latter in + diameter in the ratio of 100 to 92. In the long-styled flowers beaded + hairs almost fill up the mouth of the corolla and project above it; they + therefore stand above the anthers and beneath the stigma. In the + short-styled flowers a similar brush of hairs is situated low down within + the tubular corolla, above the stigma and beneath the anthers. The + presence of these beaded hairs in both forms, though occupying such + different positions, shows that they are probably of considerable + functional importance. They would serve to guard the stigma of each form + from its own pollen; but in accordance with Professor Kerner’s view their + chief use probably is to prevent the copious nectar being stolen by small + crawling insects, which could not render any service to the species by + carrying pollen from one form to the other. (3/23. ‘Die Schutzmittel der + Bluthen gegen unberufene Gaste’ 1876 page 37.) + </p> + <p> + The flowers are so small and so crowded together that I was not willing to + expend time in fertilising them separately; but I dragged repeatedly heads + of short-styled flowers over three long-styled flower-heads, which were + thus legitimately fertilised; and they produced many dozen fruits, each + containing two good seeds. I fertilised in the same manner three heads on + the same long- styled plant with pollen from another long-styled plant, so + that these were fertilised illegitimately, and they did not yield a single + seed. Nor did this plant, which was of course protected by a net, bear + spontaneously any seeds. Nevertheless another long-styled plant, which was + carefully protected, produced spontaneously a very few seeds; so that the + long-styled form is not always quite sterile with its own pollen. + </p> + <p> + Faramea [sp.?] (Rubiaceae). + </p> + <p> + (FIGURE 3.9. Faramea [sp.?] Left: Short-styled form. Right: Long-styled + form. Outlines of flowers from dried specimens. Pollen-grains magnified + 180 times, by Fritz Muller.) + </p> + <p> + Fritz Muller has fully described the two forms of this remarkable plant, + an inhabitant of South Brazil. (3/24. ‘Botanische Zeitung’ September 10, + 1869 page 606.) In the long-styled form the pistil projects above the + corolla, and is almost exactly twice as long as that of the short-styled, + which is included within the tube. The former is divided into two rather + short and broad stigmas, whilst the short-styled pistil is divided into + two long, thin, sometimes much curled stigmas. The stamens of each form + correspond in height or length with the pistils of the other form. The + anthers of the short-styled form are a little larger than those of the + long-styled; and their pollen-grains are to those of the other form as 100 + to 67 in diameter. But the pollen-grains of the two forms differ in a much + more remarkable manner, of which no other instance is known; those from + the short-styled flowers being covered with sharp points; the smaller ones + from the long-styled being quite smooth. Fritz Muller remarks that this + difference between the pollen-grains of the two forms is evidently of + service to the plant; for the grains from the projecting stamens of the + short-styled form, if smooth, would have been liable to be blown away by + the wind, and would thus have been lost; but the little points on their + surfaces cause them to cohere, and at the same time favour their adhesion + to the hairy bodies of insects, which merely brush against the anthers of + these stamens whilst visiting the flowers. On the other hand, the smooth + grains of the long-styled flowers are safely included within the tube of + the corolla, so that they cannot be blown away, but are almost sure to + adhere to the proboscis of an entering insect, which is necessarily + pressed close against the enclosed anthers. + </p> + <p> + It may be remembered that in the long-styled form of Linum perenne each + separate stigma rotates on its own axis, when the flower is mature, so as + to turn its papillose surface outwards. There can be no doubt that this + movement, which is confined to the long-styled form, is effected in order + that the proper surface of the stigma should receive pollen brought by + insects from the other form. Now with Faramea, as Fritz Muller shows, it + is the stamens which rotate on their axes in one of the two forms, namely, + the short-styled, in order that their pollen should be brushed off by + insects and transported to the stigmas of the other form. In the + long-styled flowers the anthers of the short enclosed stamens do not + rotate on their axes, but dehisce on their inner sides, as is the common + rule with the Rubiaceae; and this is the best position for the adherence + of the pollen-grains to the proboscis of an entering insect. Fritz Muller + therefore infers that as the plant became heterostyled, and as the stamens + of the short- styled form increased in length, they gradually acquired the + highly beneficial power of rotating on their own axes. But he has further + shown, by the careful examination of many flowers, that this power has not + as yet been perfected; and, consequently, that a certain proportion of the + pollen is rendered useless, namely, that from the anthers which do not + rotate properly. It thus appears that the development of the plant has not + as yet been completed; the stamens have indeed acquired their proper + length, but not their full and perfect power of rotation. (3/25. Fritz + Muller gives another instance of the want of absolute perfection in the + flowers of another member of the Rubiaceae, namely, Posoqueria fragrans, + which is adapted in a most wonderful manner for cross-fertilisation by the + agency of moths. (See ‘Botanische Zeitung’ 1866 Number 17.) In accordance + with the nocturnal habits of these insects, most of the flowers open only + during the night; but some open in the day, and the pollen of such flowers + is robbed, as Fritz Muller has often seen, by humble-bees and other + insects, without any benefit being thus conferred on the plant.) + </p> + <p> + The several points of difference in structure between the two forms of + Faramea are highly remarkable. Until within a recent period, if any one + had been shown two plants which differed in a uniform manner in the length + of their stamens and pistils,—in the form of their stigmas,—in + the manner of dehiscence and slightly in the size of their anthers,—and + to an extraordinary degree in the diameter and structure of their + pollen-grains, he would have declared it impossible that the two could + have belonged to one and the same species. + </p> + <p> + [Suteria (species unnamed in the herbarium at Kew.) (Rubiaceae). + </p> + <p> + I owe to the kindness of Fritz Muller dried flowers of this plant from St. + Catharina, in Brazil. In the long-styled form the stigma stands in the + mouth of the corolla, above the anthers, which latter are enclosed within + the tube, but only a short way down. In the short-styled form the anthers + are placed in the mouth of the corolla above the stigma, which occupies + the same position as the anthers in the other form, being seated only a + short way down the tube. Therefore the pistil of the long-styled form does + not exceed in length that of the short-styled in nearly so great a degree + as in many other Rubiaceae. Nevertheless there is a considerable + difference in the size of the pollen-grains in the two forms; for, as + Fritz Muller informs me, those of the short-styled are to those of the + long-styled as 100 to 75 in diameter. + </p> + <p> + Houstonia coerulea (Rubiaceae). + </p> + <p> + Professor Asa Gray has been so kind as to send me an abstract of some + observations made by Dr. Rothrock on this plant. The pistil is exserted in + the one form and the stamens in the other, as has long been observed. The + stigmas of the long-styled form are shorter, stouter, and far more hispid + than in the other form. The stigmatic hairs or papillae on the former are + .04 millimetres, and on the latter only .023 millimetres in length. In the + short-styled form the anthers are larger, and the pollen-grains, when + distended with water, are to those from the long-styled form as 100 to 72 + in diameter. + </p> + <p> + Selected capsules from some long-styled plants growing in the Botanic + Gardens at Cambridge, U.S., near where plants of the other form grew, + contained on an average 13 seeds; but these plants must have been + subjected to unfavourable conditions, for some long-styled plants in a + state of nature yielded an average of 21.5 seeds per capsule. Some + short-styled plants, which had been planted by themselves in the Botanic + Gardens, where it was not likely that they would have been visited by + insects that had previously visited long-styled plants, produced capsules, + eleven of which were wholly sterile, but one contained 4, and another 8 + seeds. So that the short-styled form seems to be very sterile with its own + pollen. Professor Asa Gray informs me that the other North American + species of this genus are likewise heterostyled. + </p> + <p> + Oldenlandia [sp.?] (Rubiaceae). + </p> + <p> + Mr. J. Scott sent me from India dried flowers of a heterostyled species of + this genus, which is closely allied to the last. The pistil in the + long-styled flowers is longer by about a quarter of its length, and the + stamens shorter in about the same proportion, than the corresponding + organs in the short-styled flowers. In the latter the anthers are longer, + and the divergent stigmas decidedly longer and apparently thinner than in + the long-styled form. Owing to the state of the specimens, I could not + decide whether the stigmatic papillae were longer in the one form than in + the other. The pollen-grains, distended with water, from the short-styled + flowers were to those from the long-styled as 100 to 78 in diameter, as + deduced from the mean of ten measurements of each kind. + </p> + <p> + Hedyotis [sp.?] (Rubiaceae). + </p> + <p> + Fritz Muller sent me from St. Catharina, in Brazil, dried flowers of a + small delicate species, which grows on wet sand near the edges of + fresh-water pools. In the long-styled form the stigma projects above the + corolla, and stands on a level with the projecting anthers of the + short-styled form; but in the latter the stigmas stand rather beneath the + level of the anthers in the other or long- styled form, these being + enclosed within the tube of the corolla. The pistil of the long-styled + form is nearly thrice as long as that of the short-styled, or, speaking + strictly, as 100 to 39; and the papillae on the stigma of the former are + broader, in the ratio of 4 to 3, but whether longer than those of the + short- styled, I could not decide. In the short-styled form, the anthers + are rather larger, and the pollen-grains are to those from the long-styled + flowers, as 100 to 88 in diameter. Fritz Muller sent me a second, + small-sized species, which is likewise heterostyled. + </p> + <p> + Coccocypselum [sp.?] (Rubiaceae). + </p> + <p> + Fritz Muller also sent me dried flowers of this plant from St. Catharina, + in Brazil. The exserted stigma of the long-styled form stands a little + above the level of the exserted anthers of the short-styled form; and the + enclosed stigma of the latter also stands a little above the level of the + enclosed anthers in the long-styled form. The pistil of the long-styled is + about twice as long as that of the short-styled, with its two stigmas + considerably longer, more divergent, and more curled. Fritz Muller informs + me that he could detect no difference in the size of the pollen-grains in + the two forms. Nevertheless, there can be no doubt that this plant is + heterostyled. + </p> + <p> + Lipostoma [sp.?] (Rubiaceae). + </p> + <p> + Dried flowers of this plant, which grows in small wet ditches in St. + Catharina, in Brazil, were likewise sent me by Fritz Muller. In the + long-styled form the exserted stigma stands rather above the level of the + exserted anthers of the other form; whilst in the short-styled form it + stands on a level with the anthers of the other form. So that the want of + strict correspondence in height between the stigmas and anthers in the two + forms is reversed, compared with what occurs in Hedyotis. The long-styled + pistil is to that of the short-styled as 100 to 36 in length; and its + divergent stigmas are longer by fully one-third of their own length than + those of the short-styled form. In the latter the anthers are a little + larger, and the pollen-grains are as 100 to 80 in diameter, compared with + those from the long-styled form. + </p> + <p> + Cinchona micrantha (Rubiaceae). + </p> + <p> + Dried specimens of both forms of this plant were sent me from Kew. (3/26. + My attention was called to this plant by a drawing copied from Howard’s + ‘Quinologia’ Table 3 given by Mr. Markham in his ‘Travels in Peru’ page + 539.) In the long-styled form the apex of the stigma stands just beneath + the bases of the hairy lobes of the corolla; whilst the summits of the + anthers are seated about halfway down the tube. The pistil is in length as + 100 to 38 to that of the short-styled form. In the latter the anthers + occupy the same position as the stigma of the other form, and they are + considerably longer than those of the long-styled form. As the summit of + the stigma in the short-styled form stands beneath the bases of the + anthers, which are seated halfway down the corolla, the style has been + extremely shortened in this form, its length to that of the long- styled + being, in the specimens examined, only as 5.3 to 100! The stigma, also, in + the short-styled form is very much shorter than that in the long-styled, + in the ratio of 57 to 100. The pollen grains from the short-styled + flowers, after having been soaked in water, were rather larger—in + about the ratio of 100 to 91—than those from the long-styled + flowers, and they were more triangular, with the angles more prominent. As + all the grains from the short-styled flowers were thus characterised, and + as they had been left in water for three days, I am convinced that this + difference in shape in the two sets of grains cannot be accounted for by + unequal distension with water. + </p> + <p> + Besides the several Rubiaceous genera already mentioned, Fritz Muller + informs me that two or three species of Psychotria and Rudgea eriantha, + natives of St. Catharina, in Brazil, are heterostyled, as is Manettia + bicolor. I may add that I formerly fertilised with their own pollen + several flowers on a plant of this latter species in my hothouse, but they + did not set a single fruit. From Wight and Arnott’s description, there + seems to be little doubt that Knoxia in India is heterostyled; and Asa + Gray is convinced that this is the case with Diodia and Spermacoce in the + United States. Lastly, from Mr. W.W. Bailey’s description, it appears that + the Mexican Bouvardia leiantha is heterostyled. (3/27. ‘Bulletin of the + Torrey Bot. Club’ 1876 page 106.)] + </p> + <p> + Altogether we now know of 17 heterostyled genera in the great family of + the Rubiaceae; though more information is necessary with respect to some + of them, more especially those mentioned in the last paragraph, before we + can feel absolutely safe. In the ‘Genera Plantarum,’ by Bentham and + Hooker, the Rubiaceae are divided into 25 tribes, containing 337 genera; + and it deserves notice that the genera now known to be heterostyled are + not grouped in one or two of these tribes, but are distributed in no less + than eight of them. From this fact we may infer that most of the genera + have acquired their heterostyled structure independently of one another; + that is, they have not inherited this structure from some one or even two + or three progenitors in common. It further deserves notice that in the + homostyled genera, as I am informed by Professor Asa Gray, the stamens are + either exserted or are included within the tube of the corolla, in a + nearly constant manner; so that this character, which is not even of + specific value in the heterostyled species, is often of generic value in + other members of the family. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0004" id="link2HCH0004"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER IV. HETEROSTYLED TRIMORPHIC PLANTS. + </h2> +<pre xml:space="preserve"> + Lythrum salicaria. + Description of the three forms. + Their power and complex manner of fertilising one another. + Eighteen different unions possible. + Mid-styled form eminently feminine in nature. + Lythrum Graefferi likewise trimorphic. + L. thymifolia dimorphic. + L. Hyssopifolia homostyled. + Nesaea verticillata trimorphic. + Lagerstroemia, 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. +</pre> + <p> + In the previous chapters various heterostyled dimorphic plants have been + described, and now we come to heterostyled trimorphic plants, or those + which present three forms. These have been observed in three families, and + consist of species of Lythrum and of the allied genus Nesaea, of Oxalis + and Pontederia. In their manner of fertilisation these plants offer a more + remarkable case than can be found in any other plant or animal. + </p> + <p> + Lythrum salicaria. + </p> + <p> + (FIGURE 4.10. Diagram of the flowers of the three forms of Lythrum + salicaria, in their natural position, with the petals and calyx removed on + the near side: enlarged six times. Top: Long-styled. Middle: Mid-styled. + Bottom: Short-styled. The dotted lines with the arrows show the directions + in which pollen must be carried to each stigma to ensure full fertility.) + </p> + <p> + The pistil in each form differs from that in either of the other forms, + and in each there are two sets of stamens different in appearance and + function. But one set of stamens in each form corresponds with a set in + one of the other two forms. Altogether this one species includes three + females or female organs and three sets of male organs, all as distinct + from one another as if they belonged to different species; and if smaller + functional differences are considered, there are five distinct sets of + males. Two of the three hermaphrodites must coexist, and pollen must be + carried by insects reciprocally from one to the other, in order that + either of the two should be fully fertile; but unless all three forms + coexist, two sets of stamens will be wasted, and the organisation of the + species, as a whole, will be incomplete. On the other hand, when all three + hermaphrodites coexist, and pollen is carried from one to the other, the + scheme is perfect; there is no waste of pollen and no false co-adaptation. + In short, nature has ordained a most complex marriage-arrangement, namely + a triple union between three hermaphrodites,—each hermaphrodite + being in its female organ quite distinct from the other two hermaphrodites + and partially distinct in its male organs, and each furnished with two + sets of males. + </p> + <p> + The three forms may be conveniently called, from the unequal lengths of + their pistils, the LONG-STYLED, MID-STYLED, and SHORT-STYLED. The stamens + also are of unequal lengths, and these may be called the LONGEST, + MID-LENGTH, and SHORTEST. Two sets of stamens of different length are + found in each form. The existence of the three forms was first observed by + Vaucher, and subsequently more carefully by Wirtgen ; but these botanists, + not being guided by any theory or even suspicion of their functional + differences, did not perceive some of the most curious points of + difference in their structure. (4/1. Vaucher ‘Hist. Phys. des Plantes + d’Europe’ tome 2 1841 page 371. Wirtgen “Ueber Lythrum salicaria und + dessen Formen” ‘Verhand. des naturhist. Vereins fur preuss. Rheinl.’ 5 + Jahrgang 1848 S. 7.) I will first briefly describe the three forms by the + aid of Figure 4.10, which shows the flowers, six times magnified, in their + natural position, with their petals and calyx on the near side removed. + </p> + <h3> + LONG-STYLED FORM. + </h3> + <p> + This form can be at once recognised by the length of the pistil, which is + (including the ovarium) fully one-third longer than that of the + mid-styled, and more than thrice as long as that of the short-styled form. + It is so disproportionately long, that it projects in the bud through the + folded petals. It stands out considerably beyond the mid-length stamens; + its terminal portion depends a little, but the stigma itself is slightly + upturned. The globular stigma is considerably larger than that of the + other two forms, with the papillae on its surface generally longer. The + six mid-length stamens project about two-thirds the length of the pistil, + and correspond in length with the pistil of the mid-styled form. Such + correspondence in this and the two following forms is generally very + close; the difference, where there is any, being usually in a slight + excess of length in the stamens. The six shortest stamens lie concealed + within the calyx; their ends are turned up, and they are graduated in + length, so as to form a double row. The anthers of these stamens are + smaller than those of the mid-length ones. The pollen is of the same + yellow colour in both sets. H. Muller measured the pollen-grain in all + three forms, and his measurements are evidently more trustworthy than + those which I formerly made, so I will give them. (4/2. ‘Die Befruchtung + der Blumen’ 1873 page 193.) The numbers refer to divisions of the + micrometer equalling 1/300 millimetres. The grains, distended with water, + from the mid-length stamens are 7 to 7 1/2, and those from the shortest + stamens 6 to 6 1/2 in diameter, or as 100 to 86. The capsules of this form + contain on an average 93 seeds: how this average was obtained will + presently be explained. As these seeds, when cleaned, seemed larger than + those from the mid-styled or short-styled forms, 100 of them were placed + in a good balance, and by the double method of weighing were found to + equal 121 seeds of the mid-styled or 142 of the short-styled; so that five + long-styled seeds very nearly equal six mid-styled or seven short-styled + seeds. + </p> + <h3> + MID-STYLED FORM. + </h3> + <p> + The pistil occupies the position represented in Figure 4.10, with its + extremity considerably upturned, but to a variable degree; the stigma is + seated between the anthers of the longest and the shortest stamens. The + six longest stamens correspond in length with the pistil of the + long-styled form; their filaments are coloured bright pink; the anthers + are dark-coloured, but from containing bright-green pollen and from their + early dehiscence they appear emerald-green. Hence in general appearance + these stamens are remarkably dissimilar from the mid-length stamens of the + long-styled form. The six shortest stamens are enclosed within the calyx, + and resemble in all respects the shortest stamens of the long-styled form; + both these sets correspond in length with the short pistil of the + short-styled form. The green pollen-grains of the longest stamens are 9 to + 10 in diameter, whilst the yellow grains from the shortest stamens are + only 6; or as 100 to 63. But the pollen-grains from different plants + appeared to me, in this case and others, to be in some degree variable in + size. The capsules contain on an average 130 seeds; but perhaps, as we + shall see, this is rather too high an average. The seeds themselves, as + before remarked, are smaller than those of the long-styled form. + </p> + <h3> + SHORT-STYLED FORM. + </h3> + <p> + The pistil is here very short, not one-third of the length of that of the + long- styled form. It is enclosed within the calyx, which, differently + from that in the other two forms, does not enclose any anthers. The end of + the pistil is generally bent upwards at right angles. The six longest + stamens, with their pink filaments and green pollen, resemble the + corresponding stamens of the mid-styled form. But according to H. Muller, + their pollen-grains are a little larger, namely 9 1/2 to 10 1/2, instead + of 9 to 10 in diameter. The six mid-length stamens, with their uncoloured + filaments and yellow pollen, resemble in the size of their pollen-grains + and in all other respects the corresponding stamens of the long-styled + form. The difference in diameter between the grains from the two sets of + anthers in the short-styled form is as 100 to 73. The capsules contain + fewer seeds on an average than those of either of the preceding forms, + namely 83.5; and the seeds are considerably smaller. In this latter + respect, but not in number, there is a gradation parallel to that in the + length of the pistil, the long-styled having the largest seeds, the + mid-styled the next in size, and the short-styled the smallest. + </p> + <p> + We thus see that this plant exists under three female forms, which differ + in the length and curvature of the style, in the size and state of the + stigma, and in the number and size of the seed. There are altogether + thirty-six males or stamens, and these can be divided into three sets of a + dozen each, differing from one another in length, curvature, and colour of + the filaments—in the size of the anthers, and especially in the + colour and diameter of the pollen-grains. Each form bears half-a-dozen of + one kind of stamens and half-a-dozen of another kind, but not all three + kinds. The three kinds of stamens correspond in length with the three + pistils: the correspondence is always between half of the stamens in two + of the forms with the pistil of the third form. Table 4.a of the diameters + of the pollen-grains, after immersion in water, from both sets of stamens + in all three forms is copied from H. Muller; they are arranged in the + order of their size:— + </p> + <p> + TABLE 4.a. Lythrum salicaria. Diameters of pollen-grains after immersion + in water. + </p> + <p> + Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: + Maximum diameter. + </p> + <p> + Longest stamens of short-styled form : 9 1/2 : 10 1/2. Longest stamens of + mid-styled form : 9 : 10. Mid-length stamens of long-styled form : 7 : 7 + 1/2. Mid-length stamens of short-styled form : 7 : 7 1/2. Shortest stamens + of long-styled form : 6 : 6 1/2. Shortest stamens of mid-styled form : 6 : + 6. + </p> + <p> + We here see that the largest pollen-grains come from the longest stamens, + and the least (smallest) from the shortest; the extreme difference in + diameter between them being as 100 to 60. + </p> + <p> + The average number of seeds in the three forms was ascertained by counting + them in eight fine selected capsules taken from plants growing wild, and + the result was, as we have seen, for the long-styled (neglecting decimals) + 93, mid-styled 130, and short-styled 83. I should not have trusted in + these ratios had I not possessed a number of plants in my garden which, + owing to their youth, did not yield the full complement of seed, but were + of the same age and grew under the same conditions, and were freely + visited by bees. I took six fine capsules from each, and found the average + to be for the long-styled 80, for the mid-styled 97, and for the + short-styled 61. Lastly, legitimate unions effected by me between the + three forms gave, as may be seen in the following tables, for the long- + styled an average of 90 seeds, for the mid-styled 117, and for the + short-styled 71. So that we have good concurrent evidence of a difference + in the average production of seed by the three forms. To show that the + unions effected by me often produced their full effect and may be trusted, + I may state that one mid- styled capsule yielded 151 good seeds, which is + the same number as in the finest wild capsule which I examined. Some + artificially fertilised short- and long- styled capsules produced a + greater number of seeds than was ever observed by me in wild plants of the + same forms, but then I did not examine many of the latter. This plant, I + may add, offers a remarkable instance, how profoundly ignorant we are of + the life-conditions of a species. Naturally it grows “in wet ditches, + watery places, and especially on the banks of streams,” and though it + produces so many minute seeds, it never spreads on the adjoining land; + yet, when planted in my garden, on clayey soil lying over chalk, and which + is so dry that a rush cannot be found, it thrives luxuriantly, grows to + above 6 feet in height, produces self-sown seedlings, and (which is a + severer test) is as fertile as in a state of nature. Nevertheless it would + be almost a miracle to find this plant growing spontaneously on such land + as that in my garden. + </p> + <p> + According to Vaucher and Wirtgen, the three forms coexist in all parts of + Europe. Some friends gathered for me in North Wales a number of twigs from + separate plants growing near one another, and classified them. My son did + the same in Hampshire, and here is the result:— + </p> + <p> + TABLE 4.22. Lythrum salicaria. Classification according to form of flower. + </p> + <p> + Column 1: Place of origin. Column 2: Long-styled. Column 3: Mid-styled. + Column 4: Short-styled. Column 5: Total. + </p> + <p> + North Wales : 95 : 97 : 72 : 264. Hampshire : 53 : 38 : 38 : 129. Total : + 148 : 135 : 110 : 393. + </p> + <p> + If twice or thrice the number had been collected, the three forms would + probably have been found nearly equal; I infer this from considering the + above figures, and from my son telling me that if he had collected in + another spot, he felt sure that the mid-styled plants would have been in + excess. I several times sowed small parcels of seed, and raised all three + forms; but I neglected to record the parent-form, excepting in one + instance, in which I raised from short-styled seed twelve plants, of which + only one turned out long-styled, four mid-styled, and seven short-styled. + </p> + <p> + Two plants of each form were protected from the access of insects during + two successive years, and in the autumn they yielded very few capsules and + presented a remarkable contrast with the adjoining uncovered plants, which + were densely covered with capsules. In 1863 a protected long-styled plant + produced only five poor capsules; two mid-styled plants produced together + the same number; and two short-styled plants only a single one. These + capsules contained very few seeds; yet the plants were fully productive + when artificially fertilised under the net. In a state of nature the + flowers are incessantly visited for their nectar by hive- and other bees, + various Diptera and Lepidoptera. (4/3. H. Muller gives a list of the + species ‘Die Befruchtung der Blumen’ page 196. It appears that one bee, + the Cilissa melanura, almost confines its visits to this plant.) The + nectar is secreted all round the base of the ovarium; but a passage is + formed along the upper and inner side of the flower by the lateral + deflection (not represented in the diagram) of the basal portions of the + filaments; so that insects invariably alight on the projecting stamens and + pistil, and insert their proboscides along the upper and inner margin of + the corolla. We can now see why the ends of the stamens with their + anthers, and the ends of the pistils with their stigmas, are a little + upturned, so that they may be brushed by the lower hairy surfaces of the + insects’ bodies. The shortest stamens which lie enclosed within the calyx + of the long- and mid-styled forms can be touched only by the proboscis and + narrow chin of a bee; hence they have their ends more upturned, and they + are graduated in length, so as to fall into a narrow file, sure to be + raked by the thin intruding proboscis. The anthers of the longer stamens + stand laterally farther apart and are more nearly on the same level, for + they have to brush against the whole breadth of the insect’s body. In very + many other flowers the pistil, or the stamens, or both, are rectangularly + bent to one side of the flower. This bending may be permanent, as with + Lythrum and many others, or may be effected, as in Dictamnus fraxinella + and others, by a temporary movement, which occurs in the case of the + stamens when the anthers dehisce, and in the case of the pistil when the + stigma is mature; but these two movements do not always take place + simultaneously in the same flower. Now I have found no exception to the + rule, that when the stamens and pistil are bent, they bend to that side of + the flower which secretes nectar, even though there be a rudimentary + nectary of large size on the opposite side, as in some species of + Corydalis. When nectar is secreted on all sides, they bend to that side + where the structure of the flower allows the easiest access to it, as in + Lythrum, various Papilionaceae, and others. The rule consequently is, that + when the pistils and stamens are curved or bent, the stigma and anthers + are thus brought into the pathway leading to the nectary. There are a few + cases which seem to be exceptions to this rule, but they are not so in + truth; for instance, in the Gloriosa lily, the stigma of the grotesque and + rectangularly bent pistil is brought, not into any pathway from the + outside towards the nectar-secreting recesses of the flower, but into the + circular route which insects follow in proceeding from one nectary to the + other. In Scrophularia aquatica the pistil is bent downwards from the + mouth of the corolla, but it thus strikes the pollen-dusted breast of the + wasps which habitually visit these ill-scented flowers. In all these cases + we see the supreme dominating power of insects on the structure of + flowers, especially of those which have irregular corollas. Flowers which + are fertilised by the wind must of course be excepted; but I do not know + of a single instance of an irregular flower which is thus fertilised. + </p> + <p> + Another point deserves notice. In each of the three forms two sets of + stamens correspond in length with the pistils in the other two forms. When + bees suck the flowers, the anthers of the longest stamens, bearing the + green pollen, are rubbed against the abdomen and the inner sides of the + hind legs, as is likewise the stigma of the long-styled form. The anthers + of the mid-length stamens and the stigma of the mid-styled form are rubbed + against the under side of the thorax and between the front pair of legs. + And, lastly, the anthers of the shortest stamens and the stigma of the + short-styled form are rubbed against the proboscis and chin: for the bees + in sucking the flowers insert only the front part of their heads into the + flower. On catching bees, I observed much green pollen on the inner sides + of the hind legs and on the abdomen, and much yellow pollen on the under + side of the thorax. There was also pollen on the chin, and, it may be + presumed, on the proboscis, but this was difficult to observe. I had, + however, independent proof that pollen is carried on the proboscis; for a + small branch of a protected short-styled plant (which produced + spontaneously only two capsules) was accidentally left during several days + pressing against the net, and bees were seen inserting their proboscides + through the meshes, and in consequence numerous capsules were formed on + this one small branch. From these several facts it follows that insects + will generally carry the pollen of each form from the stamens to the + pistil of corresponding length; and we shall presently see the importance + of this adaptation. It must not, however, be supposed that the bees do not + get more or less dusted all over with the several kinds of pollen; for + this could be seen to occur with the green pollen from the longest + stamens. Moreover a case will presently be given of a long-styled plant + producing an abundance of capsules, though growing quite by itself, and + the flowers must have been fertilised by their own kinds of pollen; but + these capsules contained a very poor average of seed. Hence insects, and + chiefly bees, act both as general carriers of pollen, and as special + carriers of the right sort. + </p> + <p> + Wirtgen remarks on the variability of this plant in the branching of the + stem, in the length of the bracteae, size of the petals, and in several + other characters. (4/4. ‘Verhand. des naturhist. Vereins fur Pr. Rheinl.’ + 5 Jahrgang 1848 pages 11, 13.) The plants which grew in my garden had + their leaves, which differed much in shape, arranged oppositely, + alternately, or in whorls of three. In this latter case the stems were + hexagonal; those of the other plants being quadrangular. But we are + concerned chiefly, with the reproductive organs: the upward bending of the + pistil is variable, and especially in the short-styled form, in which it + is sometimes straight, sometimes slightly curved, but generally bent at + right angles. The stigma of the long-styled pistil frequently has longer + papillae or is rougher than that of the mid-styled, and the latter than + that of the short-styled; but this character, though fixed and uniform in + the two forms of Primula veris, etc., is here variable, for I have seen + mid- styled stigmas rougher than those of the long-styled. (4/5. The + plants which I observed grew in my garden, and probably varied rather more + than those growing in a state of nature. H. Muller has described the + stigmas of all three forms with great care, and he appears to have found + the stigmatic papillae differing constantly in length and structure in the + three forms, being longest in the long-styled form.) The degree to which + the longest and mid-length stamens are graduated in length and have their + ends upturned is variable; sometimes all are equally long. The colour of + the green pollen in the longest stamens is variable, being sometimes pale + greenish-yellow; in one short-styled plant it was almost white. The grains + vary a little in size: I examined one short-styled plant with the grains + from the mid-length and shortest anthers of the same size. We here see + great variability in many important characters; and if any of these + variations were of service to the plant, or were correlated with useful + functional differences, the species is in that state in which natural + selection might readily do much for its modification. + </p> + <h3> + ON THE POWER OF MUTUAL FERTILISATION BETWEEN THE THREE FORMS. + </h3> + <p> + Nothing shows more clearly the extraordinary complexity of the + reproductive system of this plant, than the necessity of making eighteen + distinct unions in order to ascertain the relative fertilising power of + the three forms. Thus the long-styled form has to be fertilised with + pollen from its own two kinds of anthers, from the two in the mid-styled, + and from the two in the short-styled form. The same process has to be + repeated with the mid-styled and short-styled forms. It might have been + thought sufficient to have tried on each stigma the green pollen, for + instance, from either the mid- or short-styled longest stamens, and not + from both; but the result proves that this would have been insufficient, + and that it was necessary to try all six kinds of pollen on each stigma. + As in fertilising flowers there will always be some failures, it would + have been advisable to have repeated each of the eighteen unions a score + of times; but the labour would have been too great; as it was, I made 223 + unions, i.e. on an average I fertilised above a dozen flowers in the + eighteen different methods. Each flower was castrated; the adjoining buds + had to be removed, so that the flowers might be safely marked with thread, + wool, etc.; and after each fertilisation the stigma was examined with a + lens to see that there was sufficient pollen on it. Plants of all three + forms were protected during two years by large nets on a framework; two + plants were used during one or both years, in order to avoid any + individual peculiarity in a particular plant. As soon as the flowers had + withered, the nets were removed; and in the autumn the capsules were daily + inspected and gathered, the ripe seeds being counted under the microscope. + I have given these details that confidence may be placed in the following + tables, and as some excuse for two blunders which, I believe, were made. + These blunders are referred to, with their probable cause, in two + footnotes to the tables. The erroneous numbers, however, are entered in + the tables, that it may not be supposed that I have in any one instance + tampered with the results. + </p> + <p> + A few words explanatory of the three tables must be given. Each is devoted + to one of the three forms, and is divided into six compartments. The two + upper ones in each table show the number of good seeds resulting from the + application to the stigma of pollen from the two sets of stamens which + correspond in length with the pistil of that form, and which are borne by + the other two forms. Such unions are of a legitimate nature. The two next + lower compartments show the result of the application of pollen from the + two sets of stamens, not corresponding in length with the pistil, and + which are borne by the other two forms. These unions are illegitimate. The + two lowest compartments show the result of the application of each form’s + own two kinds of pollen from the two sets of stamens belonging to the same + form, and which do not equal the pistil in length. These unions are + likewise illegitimate. The term own-form pollen here used does not mean + pollen from the flower to be fertilised—for this was never used—but + from another flower on the same plant, or more commonly from a distinct + plant of the same form. The figure “0” means that no capsule was produced, + or if a capsule was produced that it contained no good seed. In some part + of each row of figures in each compartment, a short horizontal line may be + seen; the unions above this line were made in 1862, and below it in 1863. + It is of importance to observe this, as it shows that the same general + result was obtained during two successive years; but more especially + because 1863 was a very hot and dry season, and the plants had + occasionally to be watered. This did not prevent the full complement of + seed being produced from the more fertile unions; but it rendered the less + fertile ones even more sterile than they otherwise would have been. I have + seen striking instances of this fact in making illegitimate and legitimate + unions with Primula; and it is well known that the conditions of life must + be highly favourable to give any chance of success in producing hybrids + between species which are crossed with difficulty. + </p> + <p> + TABLE 4.23. Lythrum salicaria, long-styled form. + </p> + <p> + TABLE 4.23.1. Legitimate union. + </p> + <p> + 13 flowers fertilised by the longest stamens of the mid-styled. These + stamens equal in length the pistil of the long-styled. + </p> + <p> + Product of good seed in each capsule. + </p> +<pre xml:space="preserve"> + 36 53 + 81 0 + 0 0 + 0 0 + 0 0 + - 0 + 45 + 41 +</pre> + <p> + 38 percent of these flowers yielded capsules. Each capsule contained, on + an average, 51.2 seeds. + </p> + <p> + TABLE 4.23.2. Legitimate union. + </p> + <p> + 13 flowers fertilised by the longest stamens of the short-styled. These + stamens equal in length the pistil of the long-styled. + </p> + <p> + Product of good seed in each capsule. + </p> +<pre xml:space="preserve"> + 159 104 + 43 119 + 96 poor seed. 96 + 103 99 + 0 131 + 0 116 + - + 114 +</pre> + <p> + 84 percent of these flowers yielded capsules. Each capsule contained, on + an average, 107.3 seeds. + </p> + <p> + TABLE 4.23.3. Illegitimate union. + </p> + <p> + 14 flowers fertilised by the shortest stamens of the mid-styled. + </p> +<pre xml:space="preserve"> + 3 0 + 0 0 + 0 0 + 0 0 + 0 0 + - 0 + 0 0 + 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.23.4. Illegitimate union. + </p> + <p> + 12 flowers fertilised by the mid-length stamens of the short-styled. + </p> +<pre xml:space="preserve"> + 20 0 + 0 0 + 0 0 + 0 0 + - 0 + 0 0 + 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.23.5. Illegitimate union. + </p> + <p> + 15 flowers fertilised by own-form mid-length stamens. + </p> +<pre xml:space="preserve"> + 2 - + 10 0 + 23 0 + 0 0 + 0 0 + 0 0 + 0 0 + 0 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.23.6. Illegitimate union. + </p> + <p> + 15 flowers fertilised by own-form shortest stamens. + </p> +<pre xml:space="preserve"> + 4 - + 8 0 + 4 0 + 0 0 + 0 0 + 0 0 + 0 0 + 0 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + Besides the above experiments, I fertilised a considerable number of + long-styled flowers with pollen, taken by a camel’s-hair brush, from both + the mid-length and shortest stamens of their own form: only 5 capsules + were produced, and these yielded on an average 14.5 seeds. In 1863 I tried + a much better experiment: a long-styled plant was grown by itself, miles + away from any other plant, so that the flowers could have received only + their own two kinds of pollen. The flowers were incessantly visited by + bees, and their stigmas must have received successive applications of + pollen on the most favourable days and at the most favourable hours: all + who have crossed plants know that this highly favours fertilisation. This + plant produced an abundant crop of capsules; I took by chance 20 capsules, + and these contained seeds in number as follows:— + </p> +<pre xml:space="preserve"> + 20 20 35 21 19 + 26 24 12 23 10 + 7 30 27 29 13 + 20 12 29 19 35 +</pre> + <p> + This gives an average of 21.5 seeds per capsule. As we know that the + long-styled form, when standing near plants of the other two forms and + fertilised by insects, produces on an average 93 seeds per capsule, we see + that this form, fertilised by its own two pollens, yields only between + one-fourth and one-fifth of the full number of seed. I have spoken as if + the plant had received both its own kinds of pollen, and this is, of + course, possible; but, from the enclosed position of the shortest stamens, + it is much more probable that the stigma received exclusively pollen from + the mid-length stamens; and this, as may be seen in Table 4.23.5, is the + more fertile of the two self-unions. + </p> + <p> + TABLE 4.24. Lythrum salicaria, mid-styled form. + </p> + <p> + TABLE 4.24.1. Legitimate union. + </p> + <p> + 12 flowers fertilised by the mid-length stamens of the long-styled. These + stamens equal in length the pistil of the mid-styled. + </p> + <p> + Product of good seed in each capsule. + </p> +<pre xml:space="preserve"> + 138 122 + 149 50 + 147 151 + 109 119 + 133 138 + 144 0 + - +</pre> + <p> + 92 percent of these flowers (probably 100 per cent) yielded capsules. Each + capsule contained, on an average, 127.3 seeds. + </p> + <p> + TABLE 4.24.2. Legitimate union. + </p> + <p> + 12 flowers fertilised by the mid-length stamens of the short-styled. These + stamens equal in length the pistil of the mid-styled. + </p> + <p> + Product of good seed in each capsule. + </p> +<pre xml:space="preserve"> + 112 109 + 130 143 + 143 124 + 100 145 + 33 12 + - 141 + 104 +</pre> + <p> + 100 percent of these flowers yielded capsules. Each capsule contained, on + an average, 108.0 seeds; or, excluding capsules with less than 20 seeds, + the average is 116.7 seeds. + </p> + <p> + TABLE 4.24.3. Illegitimate union. + </p> + <p> + 13 flowers fertilised by the shortest stamens of the long-styled. + </p> +<pre xml:space="preserve"> + 83 12 + 0 19 + 0 85 seeds small and poor. + - 0 + 44 0 + 44 0 + 45 0 +</pre> + <p> + 54 percent of these flowers yielded capsules. Each capsule contained, on + an average, 47.4 seeds; or, excluding capsules with less than 20 seeds, + the average is 60.2 seeds. + </p> + <p> + TABLE 4.24.4. Illegitimate union. + </p> + <p> + 15 flowers fertilised by the longest stamens of the short-styled. + </p> +<pre xml:space="preserve"> + 130 86 + 115 113 + 14 29 + 6 17 + 2 113 + 9 79 + - 128 + 132 0 +</pre> + <p> + 93 percent of these flowers yielded capsules. Each capsule contained, on + an average, 69.5 seeds; or, excluding capsules with less than 20 seeds, + the average is 102.8 seeds. + </p> + <p> + TABLE 4.24.5. Illegitimate union. + </p> + <p> + 12 flowers fertilised by own-form longest stamens. + </p> +<pre xml:space="preserve"> + 92 0 + 9 0 + 63 0 + - 0 + 136?* 0 + 0 0 + 0 +</pre> + <p> + (4/6. * I have hardly a doubt that this result of 136 seeds in Table + 4.24.5 was due to a gross error. The flowers to be fertilised by their own + longest stamens were first marked by “white thread,” and those by the + mid-length stamens of the long-styled form by “white silk;” a flower + fertilised in the later manner would have yielded about 136 seeds, and it + may be observed that one such pod is missing, namely at the bottom of + Table 4.24.1. Therefore I have hardly any doubt that I fertilised a flower + marked with “white thread” as if it had been marked with “white silk.” + With respect to the capsule which yielded 92 seeds, in the same column + with that which yielded 136, I do not know what to think. I endeavoured to + prevent pollen dropping from an upper to a lower flower, and I tried to + remember to wipe the pincers carefully after each fertilisation; but in + making eighteen different unions, sometimes on windy days, and pestered by + bees and flies buzzing about, some few errors could hardly be avoided. One + day I had to keep a third man by me all the time to prevent the bees + visiting the uncovered plants, for in a few seconds’ time they might have + done irreparable mischief. It was also extremely difficult to exclude + minute Diptera from the net. In 1862 I made the great mistake of placing a + mid-styled and long-styled under the same huge net: in 1863 I avoided this + error.) + </p> + <p> + Excluding the capsule with 136 seeds, 25 percent of the flowers yielded + capsules, and each capsule contained, on an average, 54.6 seeds; or, + excluding capsules with less than 20 seeds, the average is 77.5. + </p> + <p> + TABLE 4.24.6. Illegitimate union. + </p> + <p> + 12 flowers fertilised by own-form shortest stamens. + </p> +<pre xml:space="preserve"> + 0 0 + 0 0 + 0 0 + - 0 + 0 0 + 0 0 + 0 +</pre> + <p> + Not one flower yielded a capsule. + </p> + <p> + Besides the experiments in Table 4.24, I fertilised a considerable number + of mid-styled flowers with pollen, taken by a camel’s-hair brush, from + both the longest and shortest stamens of their own form: only 5 capsules + were produced, and these yielded on an average 11.0 seeds. + </p> + <p> + TABLE 4.25. Lythrum salicaria, short-styled form. + </p> + <p> + TABLE 4.25.1. Legitimate union. + </p> + <p> + 12 flowers fertilised by the shortest stamens of the long-styled. These + stamens equal in length the pistil of the short-styled. + </p> +<pre xml:space="preserve"> + 69 56 + 61 88 + 88 112 + 66 111 + 0 62 + 0 100 + - +</pre> + <p> + 83 percent of the flowers yielded capsules. Each capsule contained, on an + average, 81.3 seeds. + </p> + <p> + TABLE 4.25.2. Legitimate union. + </p> + <p> + 13 flowers fertilised by the shortest stamens of the mid-styled. These + stamens equal in length the pistil of the short-styled. + </p> +<pre xml:space="preserve"> + 93 69 + 77 69 + 48 53 + 43 9 + 0 0 + 0 0 + - 0 +</pre> + <p> + 61 percent of the flowers yielded capsules. Each capsule contained, on an + average, 64.6 seeds. + </p> + <p> + TABLE 4.25.3. Illegitimate union. + </p> + <p> + 10 flowers fertilised by the mid-length stamens of the long-styled. + </p> +<pre xml:space="preserve"> + 0 14 + 0 0 + 0 0 + 0 0 + - 0 + 23 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.25.4. Illegitimate union. 10 flowers fertilised by the longest + stamens of the mid-styled. + </p> +<pre xml:space="preserve"> + 0 0 + 0 0 + 0 0 + 0 0 + - 0 + 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.25.5. Illegitimate union. + </p> + <p> + 10 flowers fertilised by own-form longest stamens. + </p> +<pre xml:space="preserve"> + 0 0 + 0 0 + 0 0 + - 0 + 0 0 + 0 +</pre> + <p> + Too sterile for any average. + </p> + <p> + TABLE 4.25.6. Illegitimate union. + </p> + <p> + 10 flowers fertilised by own-form mid-length stamens. + </p> +<pre xml:space="preserve"> + 64?* 0 + 0 0 + 0 0 + - 0 + 21 0 + 9 +</pre> + <p> + (4/7. *I suspect that by mistake I fertilised this flower in Table 4.25.6 + with pollen from the shortest stamens of the long-styled form, and it + would then have yielded about 64 seeds. Flowers to be thus fertilised were + marked with black silk; those with pollen from the mid-length stamens of + the short-styled with black thread; and thus probably the mistake arose.) + </p> + <p> + Too sterile for any average. + </p> + <p> + Besides the experiments in the table, I fertilised a number of flowers + without particular care with their own two kinds of pollen, but they did + not produce a single capsule. + </p> + <h3> + A SUMMARY OF THE RESULTS. + </h3> + <h3> + LONG-STYLED FORM. + </h3> + <p> + Twenty-six flowers fertilised legitimately by the stamens of corresponding + length, borne by the mid-and short-styled forms, yielded 61.5 per cent of + capsules, which contained on an average 89.7 seeds. + </p> + <p> + Twenty-six long-styled flowers fertilised illegitimately by the other + stamens of the mid-and short-styled forms yielded only two very poor + capsules. + </p> + <p> + Thirty long-styled flowers fertilised illegitimately by their own-form two + sets of stamens yielded only eight very poor capsules; but long-styled + flowers fertilised by bees with pollen from their own stamens produced + numerous capsules containing on an average 21.5 seeds. + </p> + <h3> + MID-STYLED FORM. + </h3> + <p> + Twenty-four flowers legitimately fertilised by the stamens of + corresponding length, borne by the long and short-styled forms, yielded 96 + (probably 100) per cent of capsules, which contained (excluding one + capsule with 12 seeds) on an average 117.2 seeds. + </p> + <p> + Fifteen mid-styled flowers fertilised illegitimately by the longest + stamens of the short-styled form yielded 93 per cent of capsules, which + (excluding four capsules with less than 20 seeds) contained on an average + 102.8 seeds. + </p> + <p> + Thirteen mid-styled flowers fertilised illegitimately by the mid-length + stamens of the long-styled form yielded 54 per cent of capsules, which + (excluding one with 19 seeds) contained on an average 60.2 seeds. + </p> + <p> + Twelve mid-styled flowers fertilised illegitimately by their own-form + longest stamens yielded 25 per cent of capsules, which (excluding one with + 9 seeds) contained on an average 77.5 seeds. + </p> + <p> + Twelve mid-styled flowers fertilised illegitimately by their own-form + shortest stamens yielded not a single capsule. + </p> + <h3> + SHORT-STYLED FORM. + </h3> + <p> + Twenty-five flowers fertilised legitimately by the stamens of + corresponding length, borne by the long and mid-styled forms, yielded 72 + per cent of capsules, which (excluding one capsule with only 9 seeds) + contained on an average 70.8 seeds. + </p> + <p> + Twenty short-styled flowers fertilised illegitimately by the other stamens + of the long and mid-styled forms yielded only two very poor capsules. + </p> + <p> + Twenty short-styled flowers fertilised illegitimately by their own stamens + yielded only two poor (or perhaps three) capsules. + </p> + <p> + If we take all six legitimate unions together, and all twelve illegitimate + unions together, we get the following results: + </p> + <h3> + TABLE 4.26. + </h3> + <p> + Column 1: Nature of union. Column 2: Number of Flowers fertilised. Column + 3: Number of Capsules produced. Column 4: Average Number of Seeds per + Capsule. Column 5: Average Number of Seeds per Flower fertilised. + </p> + <p> + The six legitimate unions : 75 : 56 : 96.29 : 71.89. The twelve + illegitimate unions : 146 : 36 : 44.72 : 11.03. + </p> + <p> + Therefore the fertility of the legitimate unions to that of the + illegitimate, as judged by the proportion of the fertilised flowers which + yielded capsules, is as 100 to 33; and judged by the average number of + seeds per capsule, as 100 to 46. + </p> + <p> + From this summary and the several foregoing tables we see that it is only + pollen from the longest stamens which can fully fertilise the longest + pistil; only that from the mid-length stamens, the mid-length pistil; and + only that from the shortest stamens, the shortest pistil. And now we can + comprehend the meaning of the almost exact correspondence in length + between the pistil in each form and a set of six stamens in two of the + other forms; for the stigma of each form is thus rubbed against that part + of the insect’s body which becomes charged with the proper pollen. It is + also evident that the stigma of each form, fertilised in three different + ways with pollen from the longest, mid-length, and shortest stamens, is + acted on very differently, and conversely that the pollen from the twelve + longest, twelve mid-length, and twelve shortest stamens acts very + differently on each of the three stigmas; so that there are three sets of + female and of male organs. Moreover, in most cases the six stamens of each + set differ somewhat in their fertilising power from the six corresponding + ones in one of the other forms. We may further draw the remarkable + conclusion that the greater the inequality in length between the pistil + and the set of stamens, the pollen of which is employed for its + fertilisation, by so much is the sterility of the union increased. There + are no exceptions to this rule. To understand what follows the reader + should look to Tables 4.23, 4.24 and 4.25, and to the diagram Figure 4.10. + In the long-styled form the short stamens obviously differ in length from + the pistil to a greater degree than do the mid-length stamens; and the + capsules produced by the use of pollen from the shortest stamens contain + fewer seeds than those produced by the pollen from the mid-length stamens. + The same result follows with the long-styled form, from the use of the + pollen of shortest stamens of the mid-styled form and of the mid-length + stamens of the short-styled form. The same rule also holds good with the + mid-styled and short- styled forms, when illegitimately fertilised with + pollen from the stamens more or less unequal in length to their pistils. + Certainly the difference in sterility in these several cases is slight; + but, as far as we are enabled to judge, it always increases with the + increasing inequality of length between the pistil and the stamens which + are used in each case. + </p> + <p> + The correspondence in length between the pistil in each form and a set of + stamens in the other two forms, is probably the direct result of + adaptation, as it is of high service to the species by leading to full and + legitimate fertilisation. But the rule of the increased sterility of the + illegitimate unions according to the greater inequality in length between + the pistils and stamens employed for the union can be of no service. With + some heterostyled dimorphic plants the difference of fertility between the + two illegitimate unions appears at first sight to be related to the + facility of self-fertilisation; so that when from the position of the + parts the liability in one form to self- fertilisation is greater than in + the other, a union of this kind has been checked by having been rendered + the more sterile of the two. But this explanation does not apply to + Lythrum; thus the stigma of the long-styled form is more liable to be + illegitimately fertilised with pollen from its own mid- length stamens, or + with pollen from the mid-length stamens of the short-styled form, than by + its own shortest stamens or those of the mid-styled form; yet the two + former unions, which it might have been expected would have been guarded + against by increased sterility, are much less likely to be effected. The + same relation holds good even in a more striking manner with the + mid-styled form, and with the short-styled form as far as the extreme + sterility of all its illegitimate unions allows of any comparison. We are + led, therefore, to conclude that the rule of increased sterility in + accordance with increased inequality in length between the pistils and + stamens, is a purposeless result, incidental on those changes through + which the species has passed in acquiring certain characters fitted to + ensure the legitimate fertilisation of the three forms. + </p> + <p> + Another conclusion which may be drawn from Tables 4.23, 4.24, and 4.25, + even from a glance at them, is that the mid-styled form differs from both + the others in its much higher capacity for fertilisation in various ways. + Not only did the twenty-four flowers legitimately fertilised by the + stamens of corresponding lengths, all, or all but one, yield capsules rich + in seed; but of the other four illegitimate unions, that by the longest + stamens of the short-styled form was highly fertile, though less so than + the two legitimate unions, and that by the mid-length stamens of the + long-styled form was fertile to a considerable degree; the remaining two + illegitimate unions, namely, with this form’s own pollen, were sterile, + but in different degrees. So that the mid-styled form, when fertilised in + the six different possible methods, evinces five grades of fertility. By + comparing Tables 4.24.3 and 4.24.6 we may see that the action of the + pollen from the shortest stamens of the long-styled and mid-styled forms + is widely different; in the one case above half the fertilised flowers + yielded capsules containing a fair number of seeds; in the other case not + one capsule was produced. So, again, the green, large-grained pollen from + the longest stamens of the short-styled and mid-styled forms (in Tables + 4.24.4 and 4.24.5) is widely different. In both these cases the difference + in action is so plain that it cannot be mistaken, but it can be + corroborated. If we look to Table 4.25 to the legitimate action of the + shortest stamens of the long- and mid-styled forms on the short-styled + form, we again see a similar but slighter difference, the pollen of the + shortest stamens of the mid-styled form yielding a smaller average of seed + during the two years of 1862 and 1863 than that from the shortest stamens + of the long-styled form. Again, if we look to Table 4.23, to the + legitimate action on the long-styled form of the green pollen of the two + sets of longest stamens, we shall find exactly the same result, namely, + that the pollen from the longest stamens of the mid-styled form yielded + during both years fewer seeds than that from the longest stamens of the + short-styled form. Hence it is certain that the two kinds of pollen + produced by the mid-styled form are less potent than the two similar kinds + of pollen produced by the corresponding stamens of the other two forms. + </p> + <p> + In close connection with the lesser potency of the two kinds of pollen of + the mid-styled form is the fact that, according to H. Muller, the grains + of both are a little less in diameter than the corresponding grains + produced by the other two forms. Thus the grains from the longest stamens + of the mid-styled form are 9 to 10, whilst those from the corresponding + stamens of the short-styled form are 9 1/2 to 10 1/2 in diameter. So, + again, the grains from the shortest stamens of the mid-styled are 6, + whilst those from the corresponding stamens of the long- styled are 6 to 6 + 1/2 in diameter. It would thus appear as if the male organs of the + mid-styled form, though not as yet rudimentary, were tending in this + direction. On the other hand, the female organs of this form are in an + eminently efficient state, for the naturally fertilised capsules yielded a + considerably larger average number of seeds than those of the other two + forms—almost every flower which was artificially fertilised in a + legitimate manner produced a capsule—and most of the illegitimate + unions were highly productive. The mid- styled form thus appears to be + highly feminine in nature; and although, as just remarked, it is + impossible to consider its two well-developed sets of stamens which + produce an abundance of pollen as being in a rudimentary condition, yet we + can hardly avoid connecting as balanced the higher efficiency of the + female organs in this form with the lesser efficiency and lesser size of + its two kinds of pollen-grains. The whole case appears to me a very + curious one. + </p> + <p> + It may be observed in Tables 4.23 to 4.25 that some of the illegitimate + unions yielded during neither year a single seed; but, judging from the + long-styled plants, it is probable, if such unions were to be effected + repeatedly by the aid of insects under the most favourable conditions, + some few seeds would be produced in every case. Anyhow, it is certain that + in all twelve illegitimate unions the pollen-tubes penetrated the stigma + in the course of eighteen hours. At first I thought that two kinds of + pollen placed together on the same stigma would perhaps yield more seed + than one kind by itself; but we have seen that this is not so with each + form’s own two kinds of pollen; nor is it probable in any case, as I + occasionally got, by the use of a single kind of pollen, fully as many + seeds as a capsule naturally fertilised ever produces. Moreover the pollen + from a single anther is far more than sufficient to fertilise fully a + stigma; hence, in this as with so many other plants, more than twelve + times as much of each kind of pollen is produced as is necessary to ensure + the full fertilisation of each form. From the dusted condition of the + bodies of the bees which I caught on the flowers, it is probable that + pollen of various kinds is often deposited on all three stigmas; but from + the facts already given with respect to the two forms of Primula, there + can hardly be a doubt that pollen from the stamens of corresponding length + placed on a stigma would be prepotent over any other kind of pollen and + obliterate its effects,—even if the latter had been placed on the + stigma some hours previously. + </p> + <p> + Finally, it has now been shown that Lythrum salicaria presents the + extraordinary case of the same species bearing three females, different in + structure and function, and three or even five sets (if minor differences + are considered) of males; each set consisting of half-a-dozen, which + likewise differ from one another in structure and function. + </p> + <p> + [Lythrum Graefferi. + </p> + <p> + I have examined numerous dried flowers of this species, each from a + separate plant, sent me from Kew. Like L. salicaria, it is trimorphic, and + the three forms apparently occur in about equal numbers. In the + long-styled form the pistil projects about one-third of the length of the + calyx beyond its mouth, and is therefore relatively much shorter than in + L. salicaria; the globose and hirsute stigma is larger than that of the + other two forms; the six mid-length stamens, which are graduated in + length, have their anthers standing close above and close beneath the + mouth of the calyx; the six shortest stamens rise rather above the middle + of the calyx. In the mid-styled form the stigma projects just above the + mouth of the calyx, and stands almost on a level with the mid-length + stamens of the long and short-styled forms; its own longest stamens + project well above the mouth of the calyx, and stand a little above the + level of the stigma of the long-styled form. In short, without entering on + further details, there is a close general correspondence in structure + between this species and L. salicaria, but with some differences in the + proportional lengths of the parts. The fact of each of the three pistils + having two sets of stamens of corresponding lengths, borne by the two + other forms, comes out conspicuously. In the mid-styled form the + pollen-grains from the longest stamens are nearly double the diameter of + those from the shortest stamens; so that there is a greater difference in + this respect than in L. salicaria. In the long-styled form, also, the + difference in diameter between the pollen-grains of the mid-length and + shortest stamens is greater than in L. salicaria. These comparisons, + however, must be received with caution, as they were made on specimens + soaked in water after having been long kept dry. + </p> + <p> + Lythrum thymifolia. + </p> + <p> + This form, according to Vaucher, is dimorphic, like Primula, and therefore + presents only two forms. (4/8. ‘Hist. Phys. des Plantes d’Europe’ tome 2 + 1841 pages 369, 371.) I received two dried flowers from Kew, which + consisted of the two forms; in one the stigma projected far beyond the + calyx, in the other it was included within the calyx; in this latter form + the style was only one-fourth of the length of that in the other form. + There are only six stamens; these are somewhat graduated in length, and + their anthers in the short-styled form stand a little above the stigma, + but yet by no means equal in length the pistil of the long-styled form. In + the latter the stamens are rather shorter than those in the other form. + The six stamens alternate with the petals, and therefore correspond + homologically with the longest stamens of L. salicaria and L. Graefferi. + </p> + <p> + Lythrum hyssopifolia. + </p> + <p> + This species is said by Vaucher, but I believe erroneously, to be + dimorphic. I have examined dried flowers from twenty-two separate plants + from various localities, sent to me by Mr. Hewett C. Watson, Professor + Babington, and others. These were all essentially alike, so that the + species cannot be heterostyled. The pistil varies somewhat in length, but + when unusually long, the stamens are likewise generally long; in the bud + the stamens are short; and Vaucher was perhaps thus deceived. There are + from six to nine stamens, graduated in length. The three stamens, which + vary in being either present or absent, correspond with the six shorter + stamens of L. salicaria and with the six which are always absent in L. + thymifolia. The stigma is included within the calyx, and stands in the + midst of the anthers, and would generally be fertilised by them; but as + the stigma and anthers are upturned, and as, according to Vaucher, there + is a passage left in the upper side of the flower to the nectary, there + can hardly be a doubt that the flowers are visited by insects, and would + occasionally be cross-fertilised by them, as surely as the flowers of the + short-styled L. salicaria, the pistil of which and the corresponding + stamens in the other two forms closely resemble those of L. hyssopifolia. + According to Vaucher and Lecoq, this species, which is an annual, + generally grows almost solitarily (4/9. ‘Geograph. Bot. de l’Europe’ tome + 6 1857 page 157.), whereas the three preceding species are social; and + this fact alone would almost have convinced me that L. hyssopifolia was + not heterostyled, as such plants cannot habitually live isolated any + better than one sex of a dioecious species. + </p> + <p> + We thus see that within this genus some species are heterostyled and + trimorphic; one apparently heterostyled and dimorphic, and one homostyled. + </p> + <p> + Nesaea verticillata. + </p> + <p> + I raised a number of plants from seed sent me by Professor Asa Gray, and + they presented three forms. These differed from one another in the + proportional lengths of their organs of fructification and in all + respects, in very nearly the same way as the three forms of Lythrum + Graefferi. The green pollen-grains from the longest stamens, measured + along their longer axis and not distended with water, were 13/7000 of an + inch in length; those from the mid-length stamens 9 to 10/7000, and those + from the shortest stamens 8 to 9/7000 of an inch. So that the largest + pollen-grains are to the smallest in diameter as 100 to 65. This plant + inhabits swampy ground in the United States. According to Fritz Muller, a + species of this genus in St. Catharina, in Southern Brazil, is homostyled. + (4/10. ‘Botanische Zeitung’ 1868 page 112.) + </p> + <p> + Lagerstroemia Indica. + </p> + <p> + This plant, a member of the Lythraceae, may perhaps be heterostyled, or + may formerly have been so. It is remarkable from the extreme variability + of its stamens. On a plant, growing in my hothouse, the flowers included + from nineteen to twenty-nine short stamens with yellow pollen, which + correspond in position with the shortest stamens of Lythrum; and from one + to five (the latter number being the commonest) very long stamens, with + thick flesh-coloured filaments and green pollen, corresponding in position + with the longest stamens of Lythrum. In one flower, two of the long + stamens produced green, while a third produced yellow pollen, although the + filaments of all three were thick and flesh- coloured. In an anther of + another flower, one cell contained green and the other yellow pollen. The + green and yellow pollen-grains from the stamens of different length are of + the same size. The pistil is a little bowed upwards, with the stigma + seated between the anthers of the short and long stamens, so that this + plant was mid-styled. Eight flowers were fertilised with green pollen, and + six with yellow pollen, but not one set fruit. This latter fact by no + means proves that the plant is heterostyled, as it may belong to the class + of self-sterile species. Another plant growing in the Botanic Gardens at + Calcutta, as Mr. J. Scott informs me, was long-styled, and it was equally + sterile with its own pollen; whilst a long-styled plant of L. reginae, + though growing by itself, produced fruit. I examined dried flowers from + two plants of L. parviflora, both of which were long-styled, and they + differed from L. Indica in having eight long stamens with thick filaments, + and a crowd of shorter stamens. Thus the evidence whether L. Indica is + heterostyled is curiously conflicting: the unequal number of the short and + long stamens, their extreme variability, and especially the fact of their + pollen-grains not differing in size, are strongly opposed to this belief; + on the other hand, the difference in length of the pistils in two of the + plants, their sterility with their own pollen, and the difference in + length and structure of the two sets of stamens in the same flower, and in + the colour of their pollen, favour the belief. We know that when plants of + any kind revert to a former condition, they are apt to be highly variable, + and the two halves of the same organ sometimes differ much, as in the case + of the above-described anther of the Lagerstroemia; we may therefore + suspect that this species was once heterostyled, and that it still retains + traces of its former state, together with a tendency to revert more + completely to it. It deserves notice, as bearing on the nature of + Lagerstroemia, that in Lythrum hyssopifolia, which is a homostyled + species, some of the shorter stamens vary in being either present or + absent; and that these same stamens are altogether absent in L. + thymifolia. In another genus of the Lythraceae, namely Cuphea, three + species raised by me from seed certainly were homostyled; nevertheless + their stamens consisted of two sets, differing in length and in the colour + and thickness of their filaments, but not in the size or colour of their + pollen-grains; so that they thus far resembled the stamens of + Lagerstroemia. I found that Cuphea purpurea was highly fertile with its + own pollen when artificially aided, but sterile when insects were + excluded. (4/11. Mr. Spence informs me that in several species of the + genus Mollia (Tiliaceae) which he collected in South America, the stamens + of the five outer cohorts have purplish filaments and green pollen, whilst + the stamens of the five inner cohorts have yellow pollen. He therefore + suspected that these species might prove to be heterostyled and + trimorphic: but he did not notice the length of the pistils. In the allied + Luhea the outer purplish stamens are destitute of anthers. I procured some + specimens of Mollia lepidota and speciosa from Kew, but could not make out + that their pistils differed in length in different plants; and in all + those which I examined the stigma stood close beneath the uppermost + anthers. The numerous stamens are graduated in length, and the + pollen-grains from the longest and shortest ones did not present any + marked difference in diameter. Therefore these species do not appear to be + heterostyled.)] + </p> + <p> + Oxalis (Geraniaceae). + </p> + <p> + (Figure 4.11. Oxalis speciosa (with the petals removed). Left: + Long-styled. Centre: Mid-styled. Right: Short-styled. S, S, S, stigmas. + The dotted lines with arrows show which pollen must be carried to the + stigmas for legitimate fertilisation.) + </p> + <p> + In 1863 Mr. Roland Trimen wrote to me from the Cape of Good Hope that he + had there found species of Oxalis which presented three forms; and of + these he enclosed drawings and dried specimens. Of one species he + collected 43 flowers from distinct plants, and they consisted of 10 + long-styled, 12 mid-styled, and 21 short-styled. Of another species he + collected 13 flowers, consisting of 3 long-styled, 7 mid-styled, and 3 + short-styled. In 1866 Professor Hildebrand proved by an examination of the + specimens in several herbaria that 20 species are certainly heterostyled + and trimorphic, and 51 others almost certainly so. (4/12. ‘Monatsber. der + Akad. der Wiss. Berlin’ 1866 pages 352, 372. He gives drawings of the + three forms at page 42 of his ‘Geschlechter-Vertheilung’ etc. 1867.) He + also made some interesting observations on living plants belonging to one + form alone; for at that time he did not possess the three forms of any + living species. During the years 1864 to 1868 I occasionally experimented + on Oxalis speciosa, but until now have never found time to publish the + results. In 1871 Hildebrand published an admirable paper in which he shows + in the case of two species of Oxalis, that the sexual relations of the + three forms are nearly the same as in Lythrum salicaria. (4/13. + ‘Botanische Zeitung’ 1871 pages 416 and 432.) I will now give an abstract + of his observations, and afterwards of my own less complete ones. I may + premise that in all the species seen by me, the stigmas of the five + straight pistils of the long-styled form stand on a level with the anthers + of the longest stamens in the two other forms. In the mid- styled form, + the stigmas pass out between the filaments of the longest stamens (as in + the short-styled form of Linum); and they stand rather nearer to the upper + anthers than to the lower ones. In the short-styled form, the stigmas also + pass out between the filaments nearly on a level with the tips of the + sepals. The anthers in this latter form and in the mid-styled rise to the + same height as the corresponding stigmas in the other two forms. + </p> + <p> + Oxalis Valdiviana. + </p> + <p> + This species, an inhabitant of the west coast of South America, bears + yellow flowers. Hildebrand states that the stigmas of the three forms do + not differ in any marked manner, but that the pistil of the short-styled + form alone is destitute of hairs. The diameters of the pollen-grains are + as follows:— + </p> + <p> + Table 4.b. Oxalis Valdiviana. Diameters of pollen-grains in divisions of + the micrometer. + </p> + <p> + Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: + Maximum diameter. + </p> + <p> + From the: Longest stamens of short-styled form : 8 to 9. Mid-length + stamens of short-styled form : 7 to 8. Longest stamens of mid-styled form + : 8. Shortest stamens of mid-styled form : 8. Mid-length stamens of + long-styled form : 7. Shortest stamens of long-styled form : 6. + </p> + <p> + Therefore the extreme difference in diameter is as 8.5 to 6, or as 100 to + 71. The results of Hildebrand’s experiments are given in Table 4.27, drawn + up in accordance with my usual plan. + </p> + <p> + Table 4.27. Oxalis Valdiviana (from Hildebrand). + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Capsules produced. Column 4: Number of Seeds per + Capsule. + </p> + <p> + Long-styled by pollen of longest stamens of short-styled. Legitimate union + : 28 : 28 : 11.9. + </p> + <p> + Long-styled by pollen of longest stamens of mid-styled. Legitimate union : + 21 : 21 : 12.0. + </p> + <p> + Long-styled by pollen of own and own-form mid-length stamens. Illegitimate + union : 40 : 2 : 5.5. + </p> + <p> + Long-styled by pollen of own and own-form shortest stamens. Illegitimate + union : 26 : 0 : 0. + </p> + <p> + Long-styled by pollen of shortest stamens of short-styled. Illegitimate + union : 16 : 1 : 1. + </p> + <p> + Long-styled by pollen of shortest stamens of mid-styled. Illegitimate + union : 9 : 0 : 0. + </p> + <p> + Mid-styled by pollen of mid-length stamens of long-styled. Legitimate + union : 38 : 38 : 11.3. + </p> + <p> + Mid-styled by pollen of mid-length stamens of short-styled. Legitimate + union : 23 : 23 : 10.4. + </p> + <p> + Mid-styled by pollen of own and own-form longest stamens. Illegitimate + union : 52 : 0 : 0. + </p> + <p> + Mid-styled by pollen of own and own-form shortest stamens. Illegitimate + union : 30 : 1 : 6. + </p> + <p> + Mid-styled by pollen of shortest stamens of long-styled. Illegitimate + union : 16 : 0 : 0. + </p> + <p> + Mid-styled by pollen of longest stamens of short-styled. Illegitimate + union : 16 : 2 : 2.5. + </p> + <p> + Short-styled by pollen of shortest stamens of long-styled. Legitimate + union: 18 : 18 : 11.0. + </p> + <p> + Short-styled by pollen of shortest stamens of mid-styled. Legitimate + union: 10 : 10 : 11.3. + </p> + <p> + Short-styled by pollen of own and own-form longest stamens. Illegitimate + union : 21 : 0 : 0. + </p> + <p> + Short-styled by pollen of own and own-form mid-length stamens. + Illegitimate union : 22 : 0 : 0. + </p> + <p> + Short-styled by pollen of longest stamens of mid-styled. Illegitimate + union: 4 : 0 : 0. + </p> + <p> + Short-styled by pollen of mid-length stamens of long-styled. Illegitimate + union: 3 : 0 : 0. + </p> + <p> + We here have the remarkable result that every one of 138 legitimately + fertilised flowers on the three forms yielded capsules, containing on an + average 11.33 seeds. Whilst of the 255 illegitimately fertilised flowers, + only 6 yielded capsules, which contained 3.83 seeds on an average. + Therefore the fertility of the six legitimate to that of the twelve + illegitimate unions, as judged by the proportion of flowers that yielded + capsules, is as 100 to 2, and as judged by the average number of seeds per + capsule as 100 to 34. It may be added that some plants which were + protected by nets did not spontaneously produce any fruit; nor did one + which was left uncovered by itself and was visited by bees. On the other + hand, scarcely a single flower on some uncovered plants of the three forms + growing near together failed to produce fruit. + </p> + <p> + Oxalis Regnelli. + </p> + <p> + This species bears white flowers and inhabits Southern Brazil. Hildebrand + says that the stigma of the long-styled form is somewhat larger than that + of the mid- styled, and this than that of the short-styled. The pistil of + the latter is clothed with a few hairs, whilst it is very hairy in the + other two forms. The diameter of the pollen-grains from both sets of the + longest stamens equals 9 divisions of the micrometer,—that from the + mid-length stamens of the long- styled form between 8 and 9, and of the + short-styled 8,—and that from the shortest stamens of both sets 7. + So that the extreme difference in diameter is as 9 to 7 or as 100 to 78. + The experiments made by Hildebrand, which are not so numerous as in the + last case, are given in Table 4.28 in the same manner as before. + </p> + <p> + TABLE 4.28. Oxalis Regnelli (from Hildebrand). + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Capsules produced. Column 4: Average Number of Seeds + per Capsule. + </p> + <p> + Long-styled by pollen of longest stamens of short-styled. Legitimate union + : 6 : 6 : 10.1. + </p> + <p> + Long-styled by pollen of longest stamens of mid-styled. Legitimate union : + 5 : 5 : 10.6. + </p> + <p> + Long-styled by pollen of own mid-length stamens. Illegitimate union : 4 : + 0 : 0. + </p> + <p> + Long-styled by pollen of own shortest stamens. Illegitimate union : 1 : 0 + : 0. + </p> + <p> + Mid-styled by pollen of mid-length stamens of short-styled. Legitimate + union : 9 : 9 : 10.4. + </p> + <p> + Mid-styled by pollen of mid-length stamens of long-styled. Legitimate + union : 10 : 10 : 10.1. + </p> + <p> + Mid-styled by pollen of own longest stamens. Illegitimate union : 9 : 0 : + 0. + </p> + <p> + Mid-styled by pollen of own shortest stamens. Illegitimate union : 2 : 0 : + 0. + </p> + <p> + Mid-styled by pollen of longest stamens of short-styled. Illegitimate + union : 1 : 0 : 0. + </p> + <p> + Short-styled by pollen of shortest stamens of mid-styled. Legitimate + union: 9 : 9 : 10.6. + </p> + <p> + Short-styled by pollen of shortest stamens of long-styled. Legitimate + union: 2 : 2 : 9.5. + </p> + <p> + Short-styled by pollen of own mid-length stamens. Illegitimate union : 12 + : 0 : 0. + </p> + <p> + Short-styled by pollen of own longest stamens. Illegitimate union : 9 : 0 + : 0. + </p> + <p> + Short-styled by pollen of mid-length stamens of long-styled. Illegitimate + union: 1 : 0 : 0. + </p> + <p> + The results are nearly the same as in the last case, but more striking; + for 41 flowers belonging to the three forms fertilised legitimately all + yielded capsules, containing on an average 10.31 seeds; whilst 39 flowers + fertilised illegitimately did not yield a single capsule or seed. + Therefore the fertility of the six legitimate to that of the several + illegitimate unions, as judged both by the proportion of flowers which + yielded capsules and by the average number of contained seeds, is as 100 + to 0. + </p> + <p> + Oxalis speciosa. + </p> + <p> + This species, which bears pink flowers, was introduced from the Cape of + Good Hope. A sketch of the reproductive organs of the three forms (Figure + 4.11) has already been given. The stigma of the long-styled form (with the + papillae on its surface included) is twice as large as that of the + short-styled, and that of the mid-styled intermediate in size. The + pollen-grains from the stamens in the three forms are in their longer + diameters as follows:— + </p> + <p> + Table 4.c. Oxalis speciosa. Diameters of pollen-grains in divisions of the + micrometer. + </p> + <p> + Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: + Maximum diameter. + </p> + <p> + From the: Longest stamens of short-styled form : 15 to 16. Mid-length + stamens of short-styled form : 12 to 13. Longest stamens of mid-styled + form : 16. Shortest stamens of mid-styled form : 11 to 12. Mid-length + stamens of long-styled form : 14. Shortest stamens of long-styled form : + 12. + </p> + <p> + Therefore the extreme difference in diameter is as 16 to 11, or as 100 to + 69; but as the measurements were taken at different times, they are + probably only approximately accurate. The results of my experiments in + fertilising the three forms are given in Table 4.29. + </p> + <p> + Table 4.29. Oxalis speciosa. + </p> + <p> + Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. + Column 3: Number of Capsules produced. Column 4: Average Number of Seeds + per Capsule. + </p> + <p> + Long-styled by pollen of longest stamens of short-styled. Legitimate union + : 19 : 15 : 57.4. + </p> + <p> + Long-styled by pollen of longest stamens of mid-styled. Legitimate union : + 4 : 3 : 59.0. + </p> + <p> + Long-styled by pollen of own-form mid-length stamens. Illegitimate union : + 9 : 2 : 42.5. + </p> + <p> + Long-styled by pollen of own-form shortest stamens. Illegitimate union : + 11 : 0 : 0. + </p> + <p> + Long-styled by pollen of shortest stamens of mid-styled. Illegitimate + union : 4 : 0 : 0. + </p> + <p> + Long-styled by pollen of mid-length stamens of short-styled. Illegitimate + union : 12 : 5 : 30.0. + </p> + <p> + Mid-styled by pollen of mid-length stamens of long-styled. Legitimate + union : 3 : 3 : 63.6. + </p> + <p> + Mid-styled by pollen of mid-length stamens of short-styled. Legitimate + union : 4 : 4 : 56.3. + </p> + <p> + Mid-styled by mixed pollen from both own-form longest and shortest + stamens. Illegitimate union : 9 : 2 : 19. + </p> + <p> + Mid-styled by pollen of longest stamens of short-styled. Illegitimate + union : 12 : 1 : 8. + </p> + <p> + Short-styled by pollen of shortest stamens of mid-styled. Legitimate + union: 3 : 2 : 67. + </p> + <p> + Short-styled by pollen of shortest stamens of long-styled. Legitimate + union: 3 : 3 : 54.3. + </p> + <p> + Short-styled by pollen of own-form longest stamens. Illegitimate union: 5 + : 1 : 8. + </p> + <p> + Short-styled by pollen of own-form mid-length stamens. Illegitimate union + : 3 : 0 : 0. + </p> + <p> + Short-styled by both pollens mixed together, of own-form longest and + mid-length stamens. Illegitimate union: 13 : 0 : 0. + </p> + <p> + Short-styled by pollen of longest stamens of mid-styled. Illegitimate + union : 7 : 0 : 0. + </p> + <p> + Short-styled by pollen of mid-length stamens of long-styled. Illegitimate + union: 10 : 1 : 54. + </p> + <p> + We here see that thirty-six flowers on the three forms legitimately + fertilised yielded 30 capsules, these containing on an average 58.36 + seeds. Ninety-five flowers illegitimately fertilised yielded 12 capsules, + containing on an average 28.58 seeds. Therefore the fertility of the six + legitimate to that of the twelve illegitimate unions, as judged by the + proportion of flowers which yielded capsules, is as 100 to 15, and judged + by the average number of seeds per capsule as 100 to 49. This plant, in + comparison with the two South American species previously described, + produces many more seeds, and the illegitimately fertilised flowers are + not quite so sterile. + </p> + <p> + Oxalis rosea. + </p> + <p> + Hildebrand possessed in a living state only the long-styled form of this + trimorphic Chilian species. (4/14. ‘Monatsber. der Akad. der Wiss. Berlin’ + 1866 page 372.) The pollen-grains from the two sets of anthers differ in + diameter as 9 to 7.5, or as 100 to 83. He has further shown that there is + an analogous difference between the grains from the two sets of anthers of + the same flower in five other species of Oxalis, besides those already + described. The present species differs remarkably from the long-styled + form of the three species previously experimented on, in a much larger + proportion of the flowers setting capsules when fertilised with their + own-form pollen. Hildebrand fertilised 60 flowers with pollen from the + mid-length stamens (of either the same or another flower), and they + yielded no less than 55 capsules, or 92 per cent. These capsules contained + on an average 5.62 seeds; but we have no means of judging how near an + approach this average makes to that from flowers legitimately fertilised. + He also fertilised 45 flowers with pollen from the shortest stamens, and + these yielded only 17 capsules, or 31 per cent, containing on an average + only 2.65 seeds. We thus see that about thrice as many flowers, when + fertilised with pollen from the mid-length stamens, produced capsules, and + these contained twice as many seeds, as did the flowers fertilised with + pollen from the shortest stamens. It thus appears (and we find some + evidence of the same fact with O. speciosa), that the same rule holds good + with Oxalis as with Lythrum salicaria; namely, that in any two unions, the + greater the inequality in length between the pistils and stamens, or, + which is the same thing, the greater the distance of the stigma from the + anthers, the pollen of which is used for fertilisation, the less fertile + is the union,—whether judged by the proportion of flowers which set + capsules, or by the average number of seeds per capsule. The rule cannot + be explained in this case any more than in that of Lythrum, by supposing + that wherever there is greater liability to self-fertilisation, this is + checked by the union being rendered more sterile; for exactly the reverse + occurs, the liability to self-fertilisation being greatest in the unions + between the pistils and stamens which approach each other the nearest, and + these are the more fertile. I may add that I also possessed some + long-styled plants of this species: one was covered by a net, and it set + spontaneously a few capsules, though extremely few compared with those + produced by a plant growing by itself, but exposed to the visits of bees. + </p> + <p> + With most of the species of Oxalis the short-styled form seems to be the + most sterile of the three forms, when these are illegitimately fertilised; + and I will add two other cases to those already given. I fertilised 29 + short-styled flowers of O. compressa with pollen from their own two sets + of stamens (the pollen- grains of which differ in diameter as 100 and 83), + and not one produced a capsule. I formerly cultivated during several years + the short-styled form of a species purchased under the name of O. Bowii + (but I have some doubts whether it was rightly named), and fertilised many + flowers with their own two kinds of pollen, which differ in diameter in + the usual manner, but never got a single seed. On the other hand, + Hildebrand says that the short-styled form of O. Deppei, growing by + itself, yields plenty of seed; but it is not positively known that this + species is heterostyled; and the pollen-grains from the two sets of + anthers do not differ in diameter. + </p> + <p> + Some facts communicated to me by Fritz Muller afford excellent evidence of + the utter sterility of one of the forms of certain trimorphic species of + Oxalis, when growing isolated. He has seen in St. Catharina, in Brazil, a + large field of young sugar-cane, many acres in extent, covered with the + red blossoms of one form alone, and these did not produce a single seed. + His own land is covered with the short-styled form of a white-flowered + trimorphic species, and this is equally sterile; but when the three forms + were planted near together in his garden they seeded freely. With two + other trimorphic species he finds that isolated plants are always sterile. + </p> + <p> + Fritz Muller formerly believed that a species of Oxalis, which is so + abundant in St. Catharina that it borders the roads for miles, was + dimorphic instead of trimorphic. Although the pistils and stamens vary + greatly in length, as was evident in some specimens sent to me, yet the + plants can be divided into two sets, according to the lengths of these + organs. A large proportion of the anthers are of a white colour and quite + destitute of pollen; others which are pale yellow contain many bad with + some good grains; and others again which are bright yellow have apparently + sound pollen; but he has never succeeded in finding any fruit on this + species. The stamens in some of the flowers are partially converted into + petals. Fritz Muller after reading my description, hereafter to be given, + of the illegitimate offspring of various heterostyled species, suspects + that these plants of Oxalis may be the variable and sterile offspring of a + single form of some trimorphic species, perhaps accidentally introduced + into the district, which has since been propagated asexually. It is + probable that this kind of propagation would be much aided by there being + no expenditure in the production of seed. + </p> + <p> + Oxalis (Biophytum) sensitiva. + </p> + <p> + This plant is ranked by many botanists as a distinct genus. Mr. Thwaites + sent me a number of flowers preserved in spirits from Ceylon, and they are + clearly trimorphic. The style of the long-styled form is clothed with many + scattered hairs, both simple and glandular; such hairs are much fewer on + the style of the mid-styled, and quite absent from that of the + short-styled form; so that this plant resembles in this respect O. + Valdiviana and Regnelli. Calling the length of the two lobes of the stigma + of the long-styled form 100, that of the mid- styled is 141, and that of + the short-styled 164. In all other cases, in which the stigma in this + genus differs in size in the three forms, the difference is of a reversed + nature, the stigma of the long-styled being the largest, and that of the + short-styled the smallest. The diameter of the pollen-grains from the + longest stamens being represented by 100, those from the mid-length + stamens are 91, and those from the shortest stamens 84 in diameter. This + plant is remarkable, as we shall see in the last chapter of this volume, + by producing long-styled, mid-styled, and short-styled cleistogamic + flowers. + </p> + <h3> + HOMOSTYLED SPECIES OF OXALIS. + </h3> + <p> + Although the majority of the species in the large genus Oxalis seem to be + trimorphic, some are homostyled, that is, exist under a single form; for + instance the common O. acetosella, and according to Hildebrand two other + widely distributed European species, O. stricta and corniculata. Fritz + Muller also informs me that a similarly constituted species is found in + St. Catharina, and that it is quite fertile with its own pollen when + insects are excluded. The stigmas of O. stricta and of another homostyled + species, namely O. tropaeoloides, commonly stand on a level with the upper + anthers, and both these species are likewise quite fertile when insects + are excluded. + </p> + <p> + With respect to O. acetosella, Hildebrand says that in all the many + specimens examined by him the pistil exceeded the longer stamens in + length. I procured 108 flowers from the same number of plants growing in + three distant parts of England; of these 86 had their stigmas projecting + considerably above, whilst 22 had them nearly on a level with the upper + anthers. In one lot of 17 flowers from the same wood, the stigmas in every + flower projected fully as much above the upper anthers as these stood + above the lower anthers. So that these plants might fairly be compared + with the long-styled form of a heterostyled species; and I at first + thought that O. acetosella was trimorphic. But the case is one merely of + great variability. The pollen-grains from the two sets of anthers, as + observed by Hildebrand and myself, do not differ in diameter. I fertilised + twelve flowers on several plants with pollen from a distinct plant, + choosing those with pistils of a different length; and 10 of these (i.e. + 83 per cent) produced capsules, which contained on an average 7.9 seeds. + Fourteen flowers were fertilised with their own pollen, and 11 of these + (i.e. 79 per cent) yielded capsules, containing a larger average of seed, + namely 9.2. These plants, therefore, in function show not the least sign + of being heterostyled. I may add that 18 flowers protected by a net were + left to fertilise themselves, and only 10 of these (i.e. 55 per cent) + yielded capsules, which contained on an average only 6.3 seeds. So that + the access of insects, or artificial aid in placing pollen on the stigma, + increases the fertility of the flowers; and I found that this applied + especially to those having shorter pistils. It should be remembered that + the flowers hang downwards, so that those with short pistils would be the + least likely to receive their own pollen, unless they were aided in some + manner. + </p> + <p> + Finally, as Hildebrand has remarked, there is no evidence that any of the + heterostyled species of Oxalis are tending towards a dioecious condition, + as Zuccarini and Lindley inferred from the differences in the reproductive + organs of the three forms, the meaning of which they did not understand. + </p> + <h3> + PONTEDERIA [SP.?] (PONTEDERIACEAE). + </h3> + <p> + Fritz Muller found this aquatic plant, which is allied to the Liliaceae, + growing in the greatest profusion on the banks of a river in Southern + Brazil. (4/15. “Ueber den Trimorphismus der Pontederien” ‘Jenaische + Zeitschrift’ etc. Band 6 1871 page 74.) But only two forms were found, the + flowers of which include three long and three short stamens. The pistil of + the long-styled form, in two dried flowers which were sent me, was in + length as 100 to 32, and its stigma as 100 to 80, compared with the same + organs in the short-styled form. The long-styled stigma projects + considerably above the upper anthers of the same flower, and stands on a + level with the upper ones of the short-styled form. In the latter the + stigma is seated beneath both its own sets of anthers, and is on a level + with the anthers of the shorter stamens in the long-styled form. The + anthers of the longer stamens of the short-styled form are to those of the + shorter stamens of the long-styled form as 100 to 88 in length. The + pollen-grains distended with water from the longer stamens of the + short-styled form are to those from the shorter stamens of the same form + as 100 to 87 in diameter, as deduced from ten measurements of each kind. + We thus see that the organs in these two forms differ from one another and + are arranged in an analogous manner, as in the long and short-styled forms + of the trimorphic species of Lythrum and Oxalis. Moreover, the longer + stamens of the long-styled form of Pontederia, and the shorter ones of the + short-styled form are placed in a proper position for fertilising the + stigma of a mid-styled form. But Fritz Muller, although he examined a vast + number of plants, could never find one belonging to the mid-styled form. + The older flowers of the long-styled and short-styled plants had set + plenty of apparently good fruit; and this might have been expected, as + they could legitimately fertilise one another. Although he could not find + the mid-styled form of this species, he possessed plants of another + species growing in his garden, and all these were mid-styled; and in this + case the pollen-grains from the anthers of the longer stamens were to + those from the shorter stamens of the same flower as 100 to 86 in + diameter, as deduced from ten measurements of each kind. These mid-styled + plants growing by themselves never produced a single fruit. + </p> + <p> + Considering these several facts, there can hardly be a doubt that both + these species of Pontederia are heterostyled and trimorphic. This case is + an interesting one, for no other Monocotyledonous plant is known to be + heterostyled. Moreover, the flowers are irregular, and all other + heterostyled plants have almost symmetrical flowers. The two forms differ + somewhat in the colour of their corollas, that of the short-styled being + of a darker blue, whilst that of the long-styled tends towards violet, and + no other such case is known. Lastly, the three longer stamens alternate + with the three shorter ones, whereas in Lythrum and Oxalis the long and + short stamens belong to distinct whorls. With respect to the absence of + the mid-styled form in the case of the Pontederia which grows wild in + Southern Brazil, this would probably follow if only two forms had been + originally introduced there; for, as we shall hereafter see from the + observations of Hildebrand, Fritz Muller and myself, when one form of + Oxalis is fertilised exclusively by either of the other two forms, the + offspring generally belong to the two parent-forms. + </p> + <p> + Fritz Muller has recently discovered, as he informs me, a third species of + Pontederia, with all three forms growing together in pools in the interior + of S. Brazil; so that no shadow of doubt can any longer remain about this + genus including trimorphic species. He sent me dried flowers of all three + forms. In the long-styled form the stigma stands a little above the tips + of the petals, and on a level with the anthers of the longest stamens in + the other two forms. The pistil is in length to that of the mid-styled as + 100 to 56, and to that of the short-styled as 100 to 16. Its summit is + rectangularly bent upwards, and the stigma is rather broader than that of + the mid-styled, and broader in about the ratio of 7 to 4 than that of the + short-styled. In the mid-styled form, the stigma is placed rather above + the middle of the corolla, and nearly on a level with the mid-length + stamens in the other two forms; its summit is a little bent upwards. In + the short-styled form the pistil is, as we have seen, very short, and + differs from that in the other two forms in being straight. It stands + rather beneath the level of the anthers of the shortest stamens in the + long-styled and mid-styled forms. The three anthers of each set of + stamens, more especially those of the shortest stamens, are placed one + beneath the other, and the ends of the filaments are bowed a little + upwards, so that the pollen from all the anthers would be effectively + brushed off by the proboscis of a visiting insect. The relative diameters + of the pollen-grains, after having been long soaked in water, are given in + Table 4.d, as measured by my son Francis. + </p> + <p> + TABLE 4.d. Pontederia. Diameters of pollen-grains, after having been long + soaked in water, in divisions of the micrometer. + </p> + <p> + Column 1: Source of Pollen-grains. Column 2: diameter. + </p> + <p> + Long-styled form, mid-length stamens (Average of 20 measurements): 13.2. + Long-styled form, shortest stamens (10 measurements): 9.0. + </p> + <p> + Mid-styled form, longest stamens (15 measurements) : 16.4. Mid-styled + form, shortest stamens (20 measurements): 9.1. + </p> + <p> + Short-styled form, longest stamens (20 measurements): 14.6. Short-styled + form, mid-length stamens (20 measurements): 12.3. + </p> + <p> + We have here the usual rule of the grains from the longer stamens, the + tubes of which have to penetrate the longer pistil, being larger than + those from the stamens of less length. The extreme difference in diameter + between the grains from the longest stamens of the mid-styled form, and + from the shortest stamens of the long-styled, is as 16.4 to 9.0, or as 100 + to 55; and this is the greatest difference observed by me in any + heterostyled plant. It is a singular fact that the grains from the + corresponding longest stamens in the two forms differ considerably in + diameter; as do those in a lesser degree from the corresponding mid-length + stamens in the two forms; whilst those from the corresponding shortest + stamens in the long- and mid-styled forms are almost exactly equal. Their + inequality in the two first cases depends on the grains in both sets of + anthers in the short-styled form being smaller than those from the + corresponding anthers in the other two forms; and here we have a case + parallel with that of the mid-styled form of Lythrum salicaria. In this + latter plant the pollen-grains of the mid-styled forms are of smaller size + and have less fertilising power than the corresponding ones in the other + two forms; whilst the ovarium, however fertilised, yields a greater number + of seeds; so that the mid-styled form is altogether more feminine in + nature than the other two forms. In the case of Pontederia, the ovarium + includes only a single ovule, and what the meaning of the difference in + size between the pollen-grains from the corresponding sets of anthers may + be, I will not pretend to conjecture. + </p> + <p> + The clear evidence that the species just described is heterostyled and + trimorphic is the more valuable as there is some doubt with respect to P. + cordata, an inhabitant of the United States. Mr. Leggett suspects that it + is either dimorphic or trimorphic, for the pollen-grains of the longer + stamens are “more than twice the diameter or than eight times the mass of + the grains of the shorter stamens. Though minute, these smaller grains + seem as perfect as the larger ones.” (4/16. ‘Bulletin of the Torrey + Botanical Club’ 1875 volume 6 page 62.) On the other hand, he says that in + all the mature flowers, “the style was as long at least as the longer + stamens;” “whilst in the young flowers it was intermediate in length + between the two sets of stamens;” and if this be so, the species can + hardly be heterostyled. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0005" id="link2HCH0005"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER V. ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS. + </h2> +<pre xml:space="preserve"> + Illegitimate offspring from all three forms of Lythrum salicaria. + Their dwarfed stature and sterility, some utterly barren, some fertile. + Oxalis, transmission of form to the legitimate and illegitimate seedlings. + Primula Sinensis, Illegitimate offspring in some degree dwarfed and infertile. + Equal-styled varieties of P. Sinensis, auricula, farinosa, and elatior. + P. vulgaris, red-flowered variety, Illegitimate seedlings sterile. + P. veris, Illegitimate plants raised during several successive generations, + their dwarfed stature and sterility. + Equal-styled varieties of P. veris. + Transmission of form by Pulmonaria and Polygonum. + Concluding remarks. + Close parallelism between illegitimate fertilisation and hybridism. +</pre> + <p> + We have hitherto treated of the fertility of the flowers of heterostyled + plants, when legitimately and illegitimately fertilised. The present + chapter will be devoted to the character of their offspring or seedlings. + Those raised from legitimately fertilised seeds will be here called + LEGITIMATE SEEDLINGS or PLANTS, and those from illegitimately fertilised + seeds, ILLEGITIMATE SEEDLINGS or PLANTS. They differ chiefly in their + degree of fertility, and in their powers of growth or vigour. I will begin + with trimorphic plants, and I must remind the reader that each of the + three forms can be fertilised in six different ways; so that all three + together can be fertilised in eighteen different ways. For instance, a + long-styled form can be fertilised legitimately by the longest stamens of + the mid-styled and short-styled forms, and illegitimately by its own- form + and mid-length and shortest stamens, also by the mid-length stamens of the + mid-styled and by the shortest stamens of the short-styled form; so that + the long-styled can be fertilised legitimately in two ways and + illegitimately in four ways. The same holds good with respect to the + mid-styled and short-styled forms. Therefore with trimorphic species six + of the eighteen unions yield legitimate offspring, and twelve yield + illegitimate offspring. + </p> + <p> + I will give the results of my experiments in detail, partly because the + observations are extremely troublesome, and will not probably soon be + repeated— thus, I was compelled to count under the microscope above + 20,000 seeds of Lythrum salicaria—but chiefly because light is thus + indirectly thrown on the important subject of hybridism. + </p> + <p> + Lythrum salicaria. + </p> + <p> + Of the twelve illegitimate unions two were completely barren, so that no + seeds were obtained, and of course no seedlings could be raised. Seedlings + were, however, raised from seven of the ten remaining illegitimate unions. + Such illegitimate seedlings when in flower were generally allowed to be + freely and legitimately fertilised, through the agency of bees, by other + illegitimate plants belonging to the two other forms growing close by. + This is the fairest plan, and was usually followed; but in several cases + (which will always be stated) illegitimate plants were fertilised with + pollen taken from legitimate plants belonging to the other two forms; and + this, as might have been expected, increased their fertility. Lythrum + salicaria is much affected in its fertility by the nature of the season; + and to avoid error from this source, as far as possible, my observations + were continued during several years. Some few experiments were tried in + 1863. The summer of 1864 was too hot and dry, and, though the plants were + copiously watered, some few apparently suffered in their fertility, whilst + others were not in the least affected. The years 1865 and, especially, + 1866, were highly favourable. Only a few observations were made during + 1867. The results are arranged in classes according to the parentage of + the plants. In each case the average number of seeds per capsule is given, + generally taken from ten capsules, which, according to my experience, is a + nearly sufficient number. The maximum number of seeds in any one capsule + is also given; and this is a useful point of comparison with the normal + standard—that is, with the number of seeds produced by legitimate + plants legitimately fertilised. I will give likewise in each case the + minimum number. When the maximum and minimum differ greatly, if no remark + is made on the subject, it may be understood that the extremes are so + closely connected by intermediate figures that the average is a fair one. + Large capsules were always selected for counting, in order to avoid + over-estimating the infertility of the several illegitimate plants. + </p> + <p> + In order to judge of the degree of inferiority in fertility of the several + illegitimate plants, the following statement of the average and of the + maximum number of seeds produced by ordinary or legitimate plants, when + legitimately fertilised, some artificially and some naturally, will serve + as a standard of comparison, and may in each case be referred to. But I + give under each experiment the percentage of seeds produced by the + illegitimate plants, in comparison with the standard legitimate number of + the same form. For instance, ten capsules from the illegitimate + long-styled plant (Number 10), which was legitimately and naturally + fertilised by other illegitimate plants, contained on an average 44.2 + seeds; whereas the capsules on legitimate long-styled plants, legitimately + and naturally fertilised by other legitimate plants, contained on an + average 93 seeds. Therefore this illegitimate plant yielded only 47 per + cent of the full and normal complement of seeds. + </p> + <p> + STANDARD NUMBER OF SEEDS PRODUCED BY LEGITIMATE PLANTS OF THE THREE FORMS, + WHEN LEGITIMATELY FERTILISED. + </p> + <p> + Long-styled form: Average number of seeds in each capsule, 93; Maximum + number observed out of twenty-three capsules, 159. + </p> + <p> + Mid-styled form: Average number of seeds, 130; Maximum number observed out + of thirty-one capsules, 151. + </p> + <p> + Short-styled form: Average number of seeds, 83.5; but we may, for the sake + of brevity, say 83; Maximum number observed out of twenty-five capsules, + 112. + </p> + <p> + CLASSES 1 AND 2. ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS + FERTILISED WITH POLLEN FROM THE MID-LENGTH OR THE SHORTEST STAMENS OF + OTHER PLANTS OF THE SAME FORM. + </p> + <p> + From this union I raised at different times three lots of illegitimate + seedlings, amounting altogether to 56 plants. I must premise that, from + not foreseeing the result, I did not keep a memorandum whether the eight + plants of the first lot were the product of the mid-length or shortest + stamens of the same form; but I have good reason to believe that they were + the product of the latter. These eight plants were much more dwarfed, and + much more sterile than those in the other two lots. The latter were raised + from a long-styled plant growing quite isolated, and fertilised by the + agency of bees with its own pollen; and it is almost certain, from the + relative position of the organs of fructification, that the stigma under + these circumstances would receive pollen from the mid-length stamens. + </p> + <p> + All the fifty-six plants in these three lots proved long-styled; now, if + the parent-plants had been legitimately fertilised by pollen from the + longest stamens of the mid-styled and short-styled forms, only about + one-third of the seedlings would have been long-styled, the other + two-thirds being mid-styled and short-styled. In some other trimorphic and + dimorphic genera we shall find the same curious fact, namely, that the + long-styled form, fertilised illegitimately by its own-form pollen, + produces almost exclusively long-styled seedlings. (5/1. Hildebrand first + called attention to this fact in the case of Primula Sinensis (‘Botanische + Zeitung’ January 1, 1864 page 5); but his results were not nearly so + uniform as mine.) + </p> + <p> + The eight plants of the first lot were of low stature: three which I + measured attained, when fully grown, the heights of only 28, 29, and 47 + inches; whilst legitimate plants growing close by were double this height, + one being 77 inches. They all betrayed in their general appearance a weak + constitution; they flowered rather later in the season, and at a later age + than ordinary plants. Some did not flower every year; and one plant, + behaving in an unprecedented manner, did not flower until three years old. + In the two other lots none of the plants grew quite to their full and + proper height, as could at once be seen by comparing them with the + adjoining rows of legitimate plants. In several plants in all three lots, + many of the anthers were either shrivelled or contained brown and tough, + or pulpy matter, without any good pollen-grains, and they never shed their + contents; they were in the state designated by Gartner as contabescent, + which term I will for the future use. (5/2. ‘Beitrage zur Kenntniss der + Befruchtung’ 1844 page 116.) In one flower all the anthers were + contabescent excepting two which appeared to the naked eye sound; but + under the microscope about two-thirds of the pollen-grains were seen to be + small and shrivelled. In another plant, in which all the anthers appeared + sound, many of the pollen- grains were shrivelled and of unequal sizes. I + counted the seeds produced by seven plants (1 to 7) in the first lot of + eight plants, probably the product of parents fertilised by their own-form + shortest stamens, and the seeds produced by three plants in the other two + lots, almost certainly the product of parents fertilised by their own-form + mid-length stamens. + </p> + <h3> + [PLANT 1. + </h3> + <p> + This long-styled plant was allowed during 1863 to be freely and + legitimately fertilised by an adjoining illegitimate mid-styled plant, but + it did not yield a single seed-capsule. It was then removed and planted in + a remote place close to a brother long-styled plant Number 2, so that it + must have been freely though illegitimately fertilised; under these + circumstances it did not yield during 1864 and 1865 a single capsule. I + should here state that a legitimate or ordinary long-styled plant, when + growing isolated, and freely though illegitimately fertilised by insects + with its own pollen, yielded an immense number of capsules, which + contained on an average 21.5 seeds. + </p> + <h3> + PLANT 2. + </h3> + <p> + This long-styled plant, after flowering during 1863 close to an + illegitimate mid-styled plant, produced less than twenty capsules, which + contained on an average between four and five seeds. When subsequently + growing in company with Number 1, by which it will have been + illegitimately fertilised, it yielded in 1866 not a single capsule, but in + 1865 it yielded twenty-two capsules: the best of these, fifteen in number, + were examined; eight contained no seed, and the remaining seven contained + on an average only three seeds, and these seeds were so small and + shrivelled that I doubt whether they would have germinated. + </p> + <h3> + PLANTS 3 AND 4. + </h3> + <p> + These two long-styled plants, after being freely and legitimately + fertilised during 1863 by the same illegitimate mid-styled plant as in the + last case, were as miserably sterile as Number 2. + </p> + <h3> + PLANT 5. + </h3> + <p> + This long-styled plant, after flowering in 1863 close to an illegitimate + mid- styled plant, yielded only four capsules, which altogether included + only five seeds. During 1864, 1865, and 1866, it was surrounded either by + illegitimate or legitimate plants of the other two forms; but it did not + yield a single capsule. It was a superfluous experiment, but I likewise + artificially fertilised in a legitimate manner twelve flowers; but not one + of these produced a capsule; so that this plant was almost absolutely + barren. + </p> + <h3> + PLANT 6. + </h3> + <p> + This long-styled plant, after flowering during the favourable year of + 1866, surrounded by illegitimate plants of the other two forms, did not + produce a single capsule. + </p> + <h3> + PLANT 7. + </h3> + <p> + This long-styled plant was the most fertile of the eight plants of the + first lot. During 1865 it was surrounded by illegitimate plants of various + parentage, many of which were highly fertile, and must thus have been + legitimately fertilised. It produced a good many capsules, ten of which + yielded an average of 36.1 seeds, with a maximum of 47 and a minimum of + 22; so that this plant produced 39 per cent of the full number of seeds. + During 1864 it was surrounded by legitimate and illegitimate plants of the + other two forms; and nine capsules (one poor one being rejected) yielded + an average of 41.9 seeds, with a maximum of 56 and a minimum of 28; so + that, under these favourable circumstances, this plant, the most fertile + of the first lot, did not yield, when legitimately fertilised, quite 45 + per cent of the full complement of seeds.] + </p> + <p> + In the second lot of plants in the present class, descended from the + long-styled form, almost certainly fertilised with pollen from its own + mid-length stamens, the plants, as already stated, were not nearly so + dwarfed or so sterile as in the first lot. All produced plenty of + capsules. I counted the number of seeds in only three plants, namely + Numbers 8, 9, and 10. + </p> + <h3> + [PLANT 8. + </h3> + <p> + This plant was allowed to be freely fertilised in 1864 by legitimate and + illegitimate plants of the other two forms, and ten capsules yielded on an + average 41.1 seeds, with a maximum of 73 and a minimum of 11. Hence this + plant produced only 44 per cent of the full complement of seeds. + </p> + <h3> + PLANT 9. + </h3> + <p> + This long-styled plant was allowed in 1865 to be freely fertilised by + illegitimate plants of the other two forms, most of which were moderately + fertile. Fifteen capsules yielded on an average 57.1 seeds, with a maximum + of 86 and a minimum of 23. Hence the plant yielded 61 per cent of the full + complement of seeds. + </p> + <h3> + PLANT 10. + </h3> + <p> + This long-styled plant was freely fertilised at the same time and in the + same manner as the last. Ten capsules yielded an average of 44.2 seeds, + with a maximum of 69 and a minimum of 25; hence this plant yielded 47 per + cent of the full complement of seeds.] + </p> + <p> + The nineteen long-styled plants of the third lot, of the same parentage as + the last lot, were treated differently; for they flowered during 1867 by + themselves so that they must have been illegitimately fertilised by one + another. It has already been stated that a legitimate long-styled plant, + growing by itself and visited by insects, yielded an average of 21.5 seeds + per capsule, with a maximum of 35; but, to judge fairly of its fertility, + it ought to have been observed during successive seasons. We may also + infer from analogy that, if several legitimate long-styled plants were to + fertilise one another, the average number of seeds would be increased; but + how much increased I do not know; hence I have no perfectly fair standard + of comparison by which to judge of the fertility of the three following + plants of the present lot, the seeds of which I counted. + </p> + <h3> + [PLANT 11. + </h3> + <p> + This long-styled plant produced a large crop of capsules, and in this + respect was one of the most fertile of the whole lot of nineteen plants. + But the average from ten capsules was only 35.9 seeds, with a maximum of + 60 and a minimum of 8. + </p> + <h3> + PLANT 12. + </h3> + <p> + This long-styled plant produced very few capsules; and ten yielded an + average of only 15.4 seeds, with a maximum of 30 and a minimum of 4. + </p> + <h3> + PLANT 13. + </h3> + <p> + This plant offers an anomalous case; it flowered profusely, yet produced + very few capsules; but these contained numerous seeds. Ten capsules + yielded an average of 71.9 seeds, with a maximum of 95 and a minimum of + 29. Considering that this plant was illegitimate and illegitimately + fertilised by its brother long-styled seedlings, the average and the + maximum are so remarkably high that I cannot at all understand the case. + We should remember that the average for a legitimate plant legitimately + fertilised is 93 seeds.] + </p> + <p> + CLASS 3. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED + WITH POLLEN FROM OWN-FORM MID-LENGTH STAMENS. + </p> + <p> + I raised from this union nine plants, of which eight were short-styled and + one long-styled; so that there seems to be a strong tendency in this form + to reproduce, when self-fertilised, the parent-form; but the tendency is + not so strong as with the long-styled. These nine plants never attained + the full height of legitimate plants growing close to them. The anthers + were contabescent in many of the flowers on several plants. + </p> + <h3> + [PLANT 14. + </h3> + <p> + This short-styled plant was allowed during 1865 to be freely and + legitimately fertilised by illegitimate plants descended from + self-fertilised mid-, long- and short-styled plants. Fifteen capsules + yielded an average of 28.3 seeds, with a maximum of 51 and a minimum of + 11; hence this plant produced only 33 per cent of the proper number of + seeds. The seeds themselves were small and irregular in shape. Although so + sterile on the female side, none of the anthers were contabescent. + </p> + <h3> + PLANT 15. + </h3> + <p> + This short-styled plant, treated like the last during the same year, + yielded an average, from fifteen capsules, of 27 seeds, with a maximum of + 49 and a minimum of 7. But two poor capsules may be rejected, and then the + average rises to 32.6, with the same maximum of 49 and a minimum of 20; so + that this plant attained 38 per cent of the normal standard of fertility, + and was rather more fertile than the last, yet many of the anthers were + contabescent. + </p> + <h3> + PLANT 16. + </h3> + <p> + This short-styled plant, treated like the two last, yielded from ten + capsules an average of 77.8 seeds, with a maximum of 97 and a minimum of + 60; so that this plant produced 94 per cent of the full number of seeds. + </p> + <h3> + PLANT 17. + </h3> + <p> + This, the one long-styled plant of the same parentage as the last three + plants, when freely and legitimately fertilised in the same manner as the + last, yielded an average from ten capsules of 76.3 rather poor seeds, with + a maximum of 88 and a minimum of 57. Hence this plant produced 82 per cent + of the proper number of seeds. Twelve flowers enclosed in a net were + artificially and legitimately fertilised with pollen from a legitimate + short-styled plant; and nine capsules yielded an average of 82.5 seeds, + with a maximum of 98 and a minimum of 51; so that its fertility was + increased by the action of pollen from a legitimate plant, but still did + not reach the normal standard.] + </p> + <p> + CLASS 4. ILLEGITIMATE PLANTS RAISED FROM A MID-STYLED PARENT FERTILISED + WITH POLLEN FROM OWN-FORM LONGEST STAMENS. + </p> + <p> + After two trials, I succeeded in raising only four plants from this + illegitimate union. These proved to be three mid-styled and one + long-styled; but from so small a number we can hardly judge of the + tendency in mid-styled plants when self-fertilised to reproduce the same + form. These four plants never attained their full and normal height; the + long-styled plant had several of its anthers contabescent. + </p> + <h3> + [PLANT 18. + </h3> + <p> + This mid-styled plant, when freely and legitimately fertilised during 1865 + by illegitimate plants descended from self-fertilised long-, short-, and + mid-styled plants, yielded an average from ten capsules of 102.6 seeds, + with a maximum of 131 and a minimum of 63: hence this plant did not + produce quite 80 per cent of the normal number of seeds. Twelve flowers + were artificially and legitimately fertilised with pollen from a + legitimate long-styled plant, and yielded from nine capsules an average of + 116.1 seeds, which were finer than in the previous case, with a maximum of + 135 and a minimum of 75; so that, as with Plant 17, pollen from a + legitimate plant increased the fertility, but did not bring it up to the + full standard. + </p> + <h3> + PLANT 19. + </h3> + <p> + This mid-styled plant, fertilised in the same manner and at the same + period as the last, yielded an average from ten capsules of 73.4 seeds, + with a maximum of 87 and a minimum of 64: hence this plant produced only + 56 per cent of the full number of seeds. Thirteen flowers were + artificially and legitimately fertilised with pollen from a legitimate + long-styled plant, and yielded ten capsules with an average of 95.6 seeds; + so that the application of pollen from a legitimate plant added, as in the + two previous cases, to the fertility, but did not bring it up to the + proper standard. + </p> + <h3> + PLANT 20. + </h3> + <p> + This long-styled plant, of the same parentage with the two last mid-styled + plants, and freely fertilised in the same manner, yielded an average from + ten capsules of 69.6 seeds, with a maximum of 83 and a minimum of 52: + hence this plant produced 75 per cent of the full number of seeds.] + </p> + <p> + CLASS 5. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED + WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM. + </p> + <p> + In the four previous classes, plants raised from the three forms + fertilised with pollen from either the longer or shorter stamens of the + same form, but generally not from the same plant, have been described. Six + other illegitimate unions are possible, namely, between the three forms + and the stamens in the other two forms which do not correspond in height + with their pistils. But I succeeded in raising plants from only three of + these six unions. From one of them, forming the present Class 5, twelve + plants were raised; these consisted of eight short- styled, and four + long-styled plants, with not one mid-styled. These twelve plants never + attained quite their full and proper height, but by no means deserved to + be called dwarfs. The anthers in some of the flowers were contabescent. + One plant was remarkable from all the longer stamens in every flower and + from many of the shorter ones having their anthers in this condition. The + pollen of four other plants, in which none of the anthers were + contabescent, was examined; in one a moderate number of grains were minute + and shrivelled, but in the other three they appeared perfectly sound. With + respect to the power of producing seed, five plants (Numbers 21 to 25) + were observed: one yielded scarcely more than half the normal number; a + second was slightly infertile; but the three others actually produced a + larger average number of seeds, with a higher maximum, than the standard. + In my concluding remarks I shall recur to this fact, which at first + appears inexplicable. + </p> + <h3> + [PLANT 21. + </h3> + <p> + This short-styled plant, freely and legitimately fertilised during 1865 by + illegitimate plants, descended from self-fertilised long-, mid- and + short-styled parents, yielded an average from ten capsules of 43 seeds, + with a maximum of 63 and a minimum of 26: hence this plant, which was the + one with all its longer and many of its shorter stamens contabescent, + produced only 52 per cent of the proper number of seeds. + </p> + <h3> + PLANT 22. + </h3> + <p> + This short-styled plant produced perfectly sound pollen, as viewed under + the microscope. During 1866 it was freely and legitimately fertilised by + other illegitimate plants belonging to the present and the following + class, both of which include many highly fertile plants. Under these + circumstances it yielded from eight capsules an average of 100.5 seeds, + with a maximum of 123 and a minimum of 86; so that it produced 121 per + cent of seeds in comparison with the normal standard. During 1864 it was + allowed to be freely and legitimately fertilised by legitimate and + illegitimate plants, and yielded an average, from eight capsules, of 104.2 + seeds, with a maximum of 125 and a minimum of 90; consequently it exceeded + the normal standard, producing 125 per cent of seeds. In this case, as in + some previous cases, pollen from legitimate plants added in a small degree + to the fertility of the plant; and the fertility would, perhaps, have been + still greater had not the summer of 1864 been very hot and certainly + unfavourable to some of the plants of Lythrum. + </p> + <h3> + PLANT 23. + </h3> + <p> + This short-styled plant produced perfectly sound pollen. During 1866 it + was freely and legitimately fertilised by the other illegitimate plants + specified under the last experiment, and eight capsules yielded an average + of 113.5 seeds, with a maximum of 123 and a minimum of 93. Hence this + plant exceeded the normal standard, producing no less than 136 per cent of + seeds. + </p> + <h3> + PLANT 24. + </h3> + <p> + This long-styled plant produced pollen which seemed under the microscope + sound; but some of the grains did not swell when placed in water. During + 1864 it was legitimately fertilised by legitimate and illegitimate plants + in the same manner as Plant 22, but yielded an average, from ten capsules, + of only 55 seeds, with a maximum of 88 and a minimum of 24, thus attaining + 59 per cent of the normal fertility. This low degree of fertility, I + presume, was owing to the unfavourable season; for during 1866, when + legitimately fertilised by illegitimate plants in the manner described + under Number 22, it yielded an average, from eight capsules, of 82 seeds, + with a maximum of 120 and a minimum of 67, thus producing 88 per cent of + the normal number of seeds. + </p> + <h3> + PLANT 25. + </h3> + <p> + The pollen of this long-styled plant contained a moderate number of poor + and shrivelled grains; and this is a surprising circumstance, as it + yielded an extraordinary number of seeds. During 1866 it was freely and + legitimately fertilised by illegitimate plants, as described under Number + 22, and yielded an average, from eight capsules, of 122.5 seeds, with a + maximum of 149 and a minimum of 84. Hence this plant exceeded the normal + standard, producing no less than 131 per cent of seeds.] + </p> + <p> + CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED + WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM. + </p> + <p> + I raised from this union twenty-five plants, which proved to be seventeen + long- styled and eight mid-styled, but not one short-styled. None of these + plants were in the least dwarfed. I examined, during the highly favourable + season of 1866, the pollen of four plants: in one mid-styled plant, some + of the anthers of the longest stamens were contabescent, but the + pollen-grains in the other anthers were mostly sound, as they were in all + the anthers of the shortest stamens; in two other mid-styled and in one + long-styled plant many of the pollen-grains were small and shrivelled; and + in the latter plant as many as a fifth or sixth part appeared to be in + this state. I counted the seeds in five plants (Numbers 26 to 30), of + which two were moderately sterile and three fully fertile. + </p> + <h3> + [PLANT 26. + </h3> + <p> + This mid-styled plant was freely and legitimately fertilised, during the + rather unfavourable year 1864, by numerous surrounding legitimate and + illegitimate plants. It yielded an average, from ten capsules, of 83.5 + seeds, with a maximum of 110 and a minimum of 64, thus attaining 64 per + cent of the normal fertility. During the highly favourable year 1866, it + was freely and legitimately fertilised by illegitimate plants belonging to + the present Class and to Class 5, and yielded an average, from eight + capsules, of 86 seeds, with a maximum of 109 and a minimum of 61, and thus + attained 66 per cent of the normal fertility. This was the plant with some + of the anthers of the longest stamens contabescent as above mentioned. + </p> + <h3> + PLANT 27. + </h3> + <p> + This mid-styled plant, fertilised during 1864 in the same manner as the + last, yielded an average, from ten capsules, of 99.4 seeds, with a maximum + of 122 and a minimum of 53, thus attaining to 76 per cent of the normal + fertility. If the season had been more favourable, its fertility would + probably have been somewhat greater, but, judging from the last + experiment, only in a slight degree. + </p> + <h3> + PLANT 28. + </h3> + <p> + This mid-styled plant, when legitimately fertilised during the favourable + season of 1866, in the manner described under Number 26, yielded an + average, from eight capsules, of 89 seeds, with a maximum of 119 and a + minimum of 69, thus producing 68 per cent of the full number of seeds. In + the pollen of both sets of anthers, nearly as many grains were small and + shrivelled as sound. + </p> + <h3> + PLANT 29. + </h3> + <p> + This long-styled plant was legitimately fertilised during the unfavourable + season of 1864, in the manner described under Number 26, and yielded an + average, from ten capsules, of 84.6 seeds, with a maximum of 132 and a + minimum of 47, thus attaining to 91 per cent of the normal fertility. + During the highly favourable season of 1866, when fertilised in the manner + described under Number 26, it yielded an average, from nine capsules (one + poor capsule having been excluded), of 100 seeds, with a maximum of 121 + and a minimum of 77. This plant thus exceeded the normal standard, and + produced 107 per cent of seeds. In both sets of anthers there were a good + many bad and shrivelled pollen-grains, but not so many as in the + last-described plant. + </p> + <p> + Plant 30. + </p> + <p> + This long-styled plant was legitimately fertilised during 1866 in the + manner described under Number 26, and yielded an average, from eight + capsules, of 94 seeds, with a maximum of 106 and a minimum of 66; so that + it exceeded the normal standard, yielding 101 per cent of seeds. + </p> + <p> + Plant 31. + </p> + <p> + Some flowers on this long-styled plant were artificially and legitimately + fertilised by one of its brother illegitimate mid-styled plants; and five + capsules yielded an average of 90.6 seeds, with a maximum of 97 and a + minimum of 79. Hence, as far as can be judged from so few capsules, this + plant attained, under these favourable circumstances, 98 per cent of the + normal standard.] + </p> + <p> + CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED + WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM. + </p> + <p> + It was shown in the last chapter that the union from which these + illegitimate plants were raised is far more fertile than any other + illegitimate union; for the mid-styled parent, when thus fertilised, + yielded an average (all very poor capsules being excluded) of 102.8 seeds, + with a maximum of 130; and the seedlings in the present class likewise + have their fertility not at all lessened. Forty plants were raised; and + these attained their full height and were covered with seed-capsules. Nor + did I observe any contabescent anthers. It deserves, also, particular + notice that these plants, differently from what occurred in any of the + previous classes, consisted of all three forms, namely, eighteen + short-styled, fourteen long-styled, and eight mid-styled plants. As these + plants were so fertile, I counted the seeds only in the two following + cases. + </p> + <h3> + [PLANT 32. + </h3> + <p> + This mid-styled plant was freely and legitimately fertilised during the + unfavourable year of 1864, by numerous surrounding legitimate and + illegitimate plants. Eight capsules yielded an average of 127.2 seeds, + with a maximum of 144 and a minimum of 96; so that this plant attained 98 + per cent of the normal standard. + </p> + <h3> + PLANT 33. + </h3> + <p> + This short-styled plant was fertilised in the same manner and at the same + time with the last; and ten capsules yielded an average of 113.9, with a + maximum of 137 and a minimum of 90. Hence this plant produced no less than + 137 per cent of seeds in comparison with the normal standard.] + </p> + <p> + CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF THE THREE FORMS OF + Lythrum salicaria. + </p> + <p> + From the three forms occurring in approximately equal numbers in a state + of nature, and from the results of sowing seed naturally produced, there + is reason to believe that each form, when legitimately fertilised, + reproduces all three forms in about equal numbers. Now, we have seen (and + the fact is a very singular one) that the fifty-six plants produced from + the long-styled form, illegitimately fertilised with pollen from the same + form (Class 1 and 2), were all long-styled. The short-styled form, when + self-fertilised (Class 3), produced eight short-styled and one long-styled + plant; and the mid-styled form, similarly treated (Class 4), produced + three mid-styled and one long-styled offspring; so that these two forms, + when illegitimately fertilised with pollen from the same form, evince a + strong, but not exclusive, tendency to reproduce the parent-form. When the + short-styled form was illegitimately fertilised by the long-styled form + (Class 5), and again when the mid-styled was illegitimately fertilised by + the long-styled (Class 6), in each case the two parent-forms alone were + reproduced. As thirty-seven plants were raised from these two unions, we + may, with much confidence, believe that it is the rule that plants thus + derived usually consist of both parent-forms, but not of the third form. + When, however, the mid-styled form was illegitimately fertilised by the + longest stamens of the short-styled (Class 7), the same rule did not hold + good; for the seedlings consisted of all three forms. The illegitimate + union from which these latter seedlings were raised is, as previously + stated, singularly fertile, and the seedlings themselves exhibited no + signs of sterility and grew to their full height. From the consideration + of these several facts, and from analogous ones to be given under Oxalis, + it seems probable that in a state of nature the pistil of each form + usually receives, through the agency of insects, pollen from the stamens + of corresponding height from both the other forms. But the case last given + shows that the application of two kinds of pollen is not indispensable for + the production of all three forms. Hildebrand has suggested that the cause + of all three forms being regularly and naturally reproduced, may be that + some of the flowers are fertilised with one kind of pollen, and others on + the same plant with the other kind of pollen. Finally, of the three forms, + the long-styled evinces somewhat the strongest tendency to reappear + amongst the offspring, whether both, or one, or neither of the parents are + long-styled. + </p> + <p> + [TABLE 5.30. Tabulated results of the fertility of the foregoing + illegitimate plants, when legitimately fertilised, generally by + illegitimate plants, as described under each experiment. Plants 11, 12 and + 13 are excluded, as they were illegitimately fertilised. + </p> + <p> + NORMAL STANDARD OF FERTILITY OF THE THREE FORMS, WHEN LEGITIMATELY AND + NATURALLY FERTILISED. + </p> + <p> + Column 1: Form. Column 2: Average number of seeds per capsule. Column 3: + Maximum number in any one capsule. Column 4: Minimum number in any one + capsule. + </p> + <p> + Long-styled : 93 : 159 : No record was kept as all very poor capsules were + rejected. Mid-styled : 130 : 151 : No record was kept as all very poor + capsules were rejected. Short-styled : 83.5 : 112 : No record was kept as + all very poor capsules were rejected. + </p> + <p> + TABLE 5.30. Continued. + </p> + <p> + CLASS 1 AND CLASS 2.—ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED + PARENTS FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH OR SHORTEST + STAMENS. + </p> + <p> + Column 1: Number (name) of plant. Column 2: Form. Column 3: Average number + of seeds per capsule. Column 4: Maximum number of seeds in any one + capsule. Column 5: Minimum number of seeds in any one capsule. Column 6: + Average number of seeds, expressed as the percentage of the normal + standard. + </p> +<pre xml:space="preserve"> + 1 : Long-styled : 0 : 0 : 0 : 0. + 2 : Long-styled : 4.5 : ? : 0 : 5. + 3 : Long-styled : 4.5 : ? : 0 : 5. + 4 : Long-styled : 4.5 : ? : 0 : 5. + 5 : Long-styled : 0 or 1 : 2 : 0 : 0 or 1. + 6 : Long-styled : 0 : 0 : 0 : 0. + 7 : Long-styled : 36.1 : 47 : 22 : 39. + 8 : Long-styled : 41.1 : 73 : 11 : 44. + 9 : Long-styled : 57.1 : 86 : 23 : 61. +10 : Long-styled : 44.2 : 69 : 25 : 47. +</pre> + <p> + CLASS 3. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED + WITH POLLEN FROM OWN-FORM SHORTEST STAMENS. + </p> + <p> + 14 : Short-styled : 28.3 : 51 : 11 : 33. 15 : Short-styled : 32.6 : 49 : + 20 : 38. 16 : Short-styled : 77.8 : 97 : 60 : 94. 17 : Long-styled : 76.3 + : 88 : 57 : 82. + </p> + <p> + CLASS 4. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED + WITH POLLEN FROM OWN-FORM LONGEST STAMENS. + </p> + <p> + 18 : Mid-styled : 102.6 : 131 : 63 : 80. 19 : Mid-styled : 73.4 : 87 : 64 + : 56. 20 : Long-styled : 69.6 : 83 : 52 : 75. + </p> + <p> + CLASS 5. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED + WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM. + </p> + <p> + 21 : Short-styled : 43.0 : 63 : 26 : 52. 22 : Short-styled : 100.5 : 123 : + 86 : 121. 23 : Short-styled : 113.5 : 123 : 93 : 136. 24 : Long-styled : + 82.0 : 120 : 67 : 88. 25 : Long-styled : 122.5 : 149 : 84 : 131. + </p> + <p> + CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED + WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM. + </p> + <p> + 26 : Mid-styled : 86.0 : 109 : 61 : 66. 27 : Mid-styled : 99.4 : 122 : 53 + : 76. 28 : Mid-styled : 89.0 : 119 : 69 : 68. 29 : Long-styled : 100.0 : + 121 : 77 : 107. 30 : Long-styled : 94.0 : 106 : 66 : 101. 31 : Long-styled + : 90.6 : 97 : 79 : 98. + </p> + <p> + CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED + WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM. + </p> + <p> + 32 : Mid-styled : 127.2 : 144 : 96 : 98. 33 : Short-styled : 113.9 : 137 : + 90 : 137. + </p> + <p> + The lessened fertility of most of these illegitimate plants is in many + respects a highly remarkable phenomenon. Thirty-three plants in the seven + classes were subjected to various trials, and the seeds carefully counted. + Some of them were artificially fertilised, but the far greater number were + freely fertilised (and this is the better and natural plan) through the + agency of insects, by other illegitimate plants. In the right hand, or + percentage column, in Table 5.30, a wide difference in fertility between + the plants in the first four and the last three classes may be perceived. + In the first four classes the plants are descended from the three forms + illegitimately fertilised with pollen taken from the same form, but only + rarely from the same plant. It is necessary to observe this latter + circumstance; for, as I have elsewhere shown, most plants, when fertilised + with their own pollen, or that from the same plant, are in some degree + sterile, and the seedlings raised from such unions are likewise in some + degree sterile, dwarfed, and feeble. (5/3. ‘The Effects of Cross and Self- + fertilisation in the Vegetable Kingdom’ 1876.) None of the nineteen + illegitimate plants in the first four classes were completely fertile; + one, however, was nearly so, yielding 96 per cent of the proper number of + seeds. From this high degree of fertility we have many descending + gradations, till we reach an absolute zero, when the plants, though + bearing many flowers, did not produce, during successive years, a single + seed or even seed-capsule. Some of the most sterile plants did not even + yield a single seed when legitimately fertilised with pollen from + legitimate plants. There is good reason to believe that the first seven + plants in Class 1 and 2 were the offspring of a long-styled plant + fertilised with pollen from its own-form shortest stamens, and these + plants were the most sterile of all. The remaining plants in Class 1 and 2 + were almost certainly the product of pollen from the mid-length stamens, + and although very sterile, they were less so than the first set. None of + the plants in the first four classes attained their full and proper + stature; the first seven, which were the most sterile of all (as already + stated), were by far the most dwarfed, several of them never reaching to + half their proper height. These same plants did not flower at so early an + age, or at so early a period in the season, as they ought to have done. + The anthers in many of their flowers, and in the flowers of some other + plants in the first six classes, were either contabescent or included + numerous small and shrivelled pollen-grains. As the suspicion at one time + occurred to me that the lessened fertility of the illegitimate plants + might be due to the pollen alone having been affected, I may remark that + this certainly was not the case; for several of them, when fertilised by + sound pollen from legitimate plants, did not yield the full complement of + seeds; hence it is certain that both the female and male reproductive + organs were affected. In each of the seven classes, the plants, though + descended from the same parents, sown at the same time and in the same + soil, differed much in their average degree of fertility. + </p> + <p> + Turning now to the fifth, sixth, and seventh classes, and looking to the + right hand column of Table 5.30, we find nearly as many plants with a + percentage of seeds above the normal standard as beneath it. As with most + plants the number of seeds produced varies much, it might be thought that + the present case was one merely of variability. But this view must be + rejected, as far as the less fertile plants in these three classes are + concerned: first, because none of the plants in Class 5 attained their + proper height, which shows that they were in some manner affected; and, + secondly, because many of the plants in Classes 5 and 6 produced anthers + which were either contabescent or included small and shrivelled + pollen-grains. And as in these cases the male organs were manifestly + deteriorated, it is by far the most probable conclusion that the female + organs were in some cases likewise affected, and that this was the cause + of the reduced number of seeds. + </p> + <p> + With respect to the six plants in these three classes which yielded a very + high percentage of seeds, the thought naturally arises that the normal + standard of fertility for the long-styled and short-styled forms (with + which alone we are here concerned) may have been fixed too low, and that + the six legitimate plants are merely fully fertile. The standard for the + long-styled form was deduced by counting the seeds in twenty-three + capsules, and for the short-styled form from twenty-five capsules. I do + not pretend that this is a sufficient number of capsules for absolute + accuracy; but my experience has led me to believe that a very fair result + may thus be gained. As, however, the maximum number observed in the + twenty-five capsules of the short-styled form was low, the standard in + this case may possibly be not quite high enough. But it should be + observed, in the case of the illegitimate plants, that in order to avoid + over-estimating their infertility, ten very fine capsules were always + selected; and the years 1865 and 1866, during which the plants in the + three latter classes were experimented on, were highly favourable for + seed-production. Now, if this plan of selecting very fine capsules during + favourable seasons had been followed for obtaining the normal standards, + instead of taking, during various seasons, the first capsules which came + to hand, the standards would undoubtedly have been considerably higher; + and thus the fact of the six foregoing plants appearing to yield an + unnaturally high percentage of seeds may, perhaps, be explained. On this + view, these plants are, in fact, merely fully fertile, and not fertile to + an abnormal degree. Nevertheless, as characters of all kinds are liable to + variation, especially with organisms unnaturally treated, and as in the + four first and more sterile classes, the plants derived from the same + parents and treated in the same manner, certainly did vary much in + sterility, it is possible that certain plants in the latter and more + fertile classes may have varied so as to have acquired an abnormal degree + of fertility. But it should be noticed that, if my standards err in being + too low, the sterility of all the many sterile plants in the several + classes will have to be estimated by so much the higher. Finally, we see + that the illegitimate plants in the four first classes are all more or + less sterile, some being absolutely barren, with one alone almost + completely fertile; in the three latter classes, some of the plants are + moderately sterile, whilst others are fully fertile, or possibly fertile + in excess. + </p> + <p> + The last point which need here be noticed is that, as far as the means of + comparison serve, some degree of relationship generally exists between the + infertility of the illegitimate union of the several parent-forms and that + of their illegitimate offspring. Thus the two illegitimate unions, from + which the plants in Classes 6 and 7 were derived, yielded a fair amount of + seed, and only a few of these plants are in any degree sterile. On the + other hand, the illegitimate unions between plants of the same form always + yield very few seeds, and their seedlings are very sterile. Long-styled + parent-plants when fertilised with pollen from their own-form shortest + stamens, appear to be rather more sterile than when fertilised with their + own-form mid-length stamens; and the seedlings from the former union were + much more sterile than those from the latter union. In opposition to this + relationship, short-styled plants illegitimately fertilised with pollen + from the mid-length stamens of the long- styled form (Class 5) are very + sterile; whereas some of the offspring raised from this union were far + from being highly sterile. It may be added that there is a tolerably close + parallelism in all the classes between the degree of sterility of the + plants and their dwarfed stature. As previously stated, an illegitimate + plant fertilised with pollen from a legitimate plant has its fertility + slightly increased. The importance of the several foregoing conclusions + will be apparent at the close of this chapter, when the illegitimate + unions between the forms of the same species and their illegitimate + offspring, are compared with the hybrid unions of distinct species and + their hybrid offspring. + </p> + <h3> + OXALIS. + </h3> + <p> + No one has compared the legitimate and illegitimate offspring of any + trimorphic species in this genus. Hildebrand sowed illegitimately + fertilised seeds of Oxalis Valdiviana, but they did not germinate (5/4. + ‘Botanische Zeitung’ 1871 page 433 footnote.); and this fact, as he + remarks, supports my view that an illegitimate union resembles a hybrid + one between two distinct species, for the seeds in this latter case are + often incapable of germination. + </p> + <p> + [The following observations relate to the nature of the forms which appear + among the legitimate seedlings of Oxalis Valdiviana. Hildebrand raised, as + described in the paper just referred to, 211 seedlings from all six + legitimate unions, and the three forms appeared among the offspring from + each union. For instance, long-styled plants were legitimately fertilised + with pollen from the longest stamens of the mid-styled form, and the + seedlings consisted of 15 long-styled, 18 mid-styled, and 6 short-styled. + We here see that a few short-styled plants were produced, though neither + parent was short-styled; and so it was with the other legitimate unions. + Out of the above 211 seedlings, 173 belonged to the same two forms as + their parents, and only 38 belonged to the third form distinct from either + parent. In the case of O. Regnelli, the result, as observed by Hildebrand, + was nearly the same, but more striking: all the offspring from four of the + legitimate unions consisted of the two parent-forms, whilst amongst the + seedlings from the other two legitimate unions the third form appeared. + Thus, of the 43 seedlings from the six legitimate unions, 35 belonged to + the same two forms as their parents, and only 8 to the third form. Fritz + Muller also raised in Brazil seedlings from long-styled plants of O. + Regnelli legitimately fertilised with pollen from the longest stamens of + the mid-styled form, and all these belonged to the two parent-forms. (5/5. + ‘Jenaische Zeitschrift’ etc. Band 6 1871 page 75.) Lastly, seedlings were + raised by me from long-styled plants of O. speciosa legitimately + fertilised by the short-styled form, and from the latter reciprocally + fertilised by the long-styled; and these consisted of 33 long-styled and + 26 short-styled plants, with not one mid-styled form. There can, + therefore, be no doubt that the legitimate offspring from any two forms of + Oxalis tend to belong to the same two forms as their parents; but that a + few seedlings belonging to the third form occasionally make their + appearance; and this latter fact, as Hildebrand remarks, may be attributed + to atavism, as some of their progenitors will almost certainly have + belonged to the third form. + </p> + <p> + When, however, any one form of Oxalis is fertilised illegitimately with + pollen from the same form, the seedlings appear to belong invariably to + this form. Thus Hildebrand states that long-styled plants of O. rosea + growing by themselves have been propagated in Germany year after year by + seed, and have always produced long-styled plants. (5/6. ‘Ueber den + Trimorphismus in der Gattung Oxalis: Monatsberichte der Akad. der Wissen. + zu Berlin’ 21 June 1866 page 373 and ‘Botanische Zeitung’ 1871 page 435.) + Again, 17 seedlings were raised from mid- styled plants of O. hedysaroides + growing by themselves, and these were all mid- styled. So that the forms + of Oxalis, when illegitimately fertilised with their own pollen, behave + like the long-styled form of Lythrum salicaria, which when thus fertilised + always produced with me long-styled offspring.] + </p> + <h3> + PRIMULA. + </h3> + <p> + Primula Sinensis. + </p> + <p> + I raised during February 1862, from some long-styled plants illegitimately + fertilised with pollen from the same form, twenty-seven seedlings. These + were all long-styled. They proved fully fertile or even fertile in excess; + for ten flowers, fertilised with pollen from other plants of the same lot, + yielded nine capsules, containing on an average 39.75 seeds, with a + maximum in one capsule of 66 seeds. Four other flowers legitimately + crossed with pollen from a legitimate plant, and four flowers on the + latter crossed with pollen from the illegitimate seedlings, yielded seven + capsules with an average of 53 seeds, with a maximum of 72. I must here + state that I have found some difficulty in estimating the normal standard + of fertility for the several unions of this species, as the results differ + much during successive years, and the seeds vary so greatly in size that + it is hard to decide which ought to be considered good. In order to avoid + over- estimating the infertility of the several illegitimate unions, I + have taken the normal standard as low as possible. + </p> + <p> + From the foregoing twenty-seven illegitimate plants, fertilised with their + own- form pollen, twenty-five seedling grandchildren were raised; and + these were all long-styled; so that from the two illegitimate generations + fifty-two plants were raised, and all without exception proved + long-styled. These grandchildren grew vigorously, and soon exceeded in + height two other lots of illegitimate seedlings of different parentage and + one lot of equal-styled seedlings presently to be described. Hence I + expected that they would have turned out highly ornamental plants; but + when they flowered, they seemed, as my gardener remarked, to have gone + back to the wild state; for the petals were pale-coloured, narrow, + sometimes not touching each other, flat, generally deeply notched in the + middle, but not flexuous on the margin, and with the yellow eye or centre + conspicuous. Altogether these flowers were strikingly different from those + of their progenitors; and this I think, can only be accounted for on the + principle of reversion. Most of the anthers on one plant were + contabescent. Seventeen flowers on the grandchildren were illegitimately + fertilised with pollen taken from other seedlings of the same lot, and + produced fourteen capsules, containing on an average 29.2 seeds; but they + ought to have contained about 35 seeds. Fifteen flowers legitimately + fertilised with pollen from an illegitimate short-styled plant (belonging + to the lot next to be described) produced fourteen capsules, containing an + average of 46 seeds; they ought to have contained at least 50 seeds. Hence + these grandchildren of illegitimate descent appear to have lost, though + only in a very slight degree, their full fertility. + </p> + <p> + We will now turn to the short-styled form: from a plant of this kind, + fertilised with its own-form pollen, I raised, during February 1862, eight + seedlings, seven of which were short-styled and one long-styled. They grew + slowly, and never attained to the full stature of ordinary plants; some of + them flowered precociously, and others late in the season. Four flowers on + these short-styled seedlings and four on the one long-styled seedling were + illegitimately fertilised with their own-form pollen and produced only + three capsules, containing on an average 23.6 seeds, with a maximum of 29; + but we cannot judge of their fertility from so few capsules; and I have + greater doubts about the normal standard for this union than about any + other; but I believe that rather above 25 seeds would be a fair estimate. + Eight flowers on these same short- styled plants, and the one long-styled + illegitimate plant were reciprocally and legitimately crossed; they + produced five capsules, which contained an average of 28.6 seeds, with a + maximum of 36. A reciprocal cross between legitimate plants of the two + forms would have yielded an average of at least 57 seeds, with a possible + maximum of 74 seeds; so that these illegitimate plants were sterile when + legitimately crossed. + </p> + <p> + I succeeded in raising from the above seven short-styled illegitimate + plants, fertilised with their own-form pollen, only six plants—grandchildren + of the first union. These, like their parents, were of low stature, and + had so poor a constitution that four died before flowering. With ordinary + plants it has been a rare event with me to have more than a single plant + die out of a large lot. The two grandchildren which lived and flowered + were short-styled; and twelve of their flowers were fertilised with their + own-form pollen and produced twelve capsules containing an average of 28.2 + seeds; so that these two plants, though belonging to so weakly a set, were + rather more fertile than their parents, and perhaps not in any degree + sterile. Four flowers on the same two grandchildren were legitimately + fertilised by a long-styled illegitimate plant, and produced four + capsules, containing only 32.2 seeds instead of about 64 seeds, which is + the normal average for legitimate short-styled plants legitimately + crossed. + </p> + <p> + By looking back, it will be seen that I raised at first from a + short-styled plant fertilised with its own-form pollen one long-styled and + seven short-styled illegitimate seedlings. These seedlings were + legitimately intercrossed, and from their seed fifteen plants were raised, + grandchildren of the first illegitimate union, and to my surprise all + proved short-styled. Twelve short-styled flowers borne by these + grandchildren were illegitimately fertilised with pollen taken from other + plants of the same lot, and produced eight capsules which contained an + average of 21.8 seeds, with a maximum of 35. These figures are rather + below the normal standard for such a union. Six flowers were also + legitimately fertilised with pollen from an illegitimate long-styled plant + and produced only three capsules, containing on an average 23.6 seeds, + with a maximum of 35. Such a union in the case of a legitimate plant ought + to have yielded an average of 64 seeds, with a possible maximum of 73 + seeds. + </p> + <p> + A SUMMARY ON THE TRANSMISSION OF FORM, CONSTITUTION, AND FERTILITY OF THE + ILLEGITIMATE OFFSPRING OF Primula Sinensis. + </p> + <p> + In regard to the long-styled plants, their illegitimate offspring, of + which fifty-two were raised in the course of two generations, were all + long-styled. (5/7. Dr. Hildebrand, who first called attention to this + subject ‘Botanische Zeitung’ 1864 page 5, raised from a similar + illegitimate union seventeen plants, of which fourteen were long-styled + and three short-styled. From a short-styled plant illegitimately + fertilised with its own pollen he raised fourteen plants, of which eleven + were short-styled and three long-styled.) These plants grew vigorously; + but the flowers in one instance were small, appearing as if they had + reverted to the wild state. In the first illegitimate generation they were + perfectly fertile, and in the second their fertility was only very + slightly impaired. With respect to the short-styled plants, twenty-four + out of twenty- five of their illegitimate offspring were short-styled. + They were dwarfed in stature, and one lot of grandchildren had so poor a + constitution that four out of six plants perished before flowering. The + two survivors, when illegitimately fertilised with their own-form pollen, + were rather less fertile than they ought to have been; but their loss of + fertility was clearly shown in a special and unexpected manner, namely, + when legitimately fertilised by other illegitimate plants: thus altogether + eighteen flowers were fertilised in this manner, and yielded twelve + capsules, which included on an average only 28.5 seeds, with a maximum of + 45. Now a legitimate short-styled plant would have yielded, when + legitimately fertilised, an average of 64 seeds, with a possible maximum + of 74. This particular kind of infertility will perhaps be best + appreciated by a simile: we may assume that with mankind six children + would be born on an average from an ordinary marriage; but that only three + would be born from an incestuous marriage. According to the analogy of + Primula Sinensis, the children of such incestuous marriages, if they + continued to marry incestuously, would have their sterility only slightly + increased; but their fertility would not be restored by a proper marriage; + for if two children, both of incestuous origin, but in no degree related + to each other, were to marry, the marriage would of course be strictly + legitimate, nevertheless they would not give birth to more than half the + full and proper number of children. + </p> + <p> + [EQUAL-STYLED VARIETY OF Primula Sinensis. + </p> + <p> + As any variation in the structure of the reproductive organs, combined + with changed function, is a rare event, the following cases are worth + giving in detail. My attention was first called to the subject by + observing, in 1862, a long-styled plant, descended from a self-fertilised + long-styled parent, which had some of its flowers in an anomalous state, + namely, with the stamens placed low down in the corolla as in the ordinary + long-styled form, but with the pistils so short that the stigmas stood on + a level with the anthers. These stigmas were nearly as globular and as + smooth as in the short-styled form, instead of being elongated and rough + as in the long-styled form. Here, then, we have combined in the same + flower, the short stamens of the long-styled form with a pistil closely + resembling that of the short-styled form. But the structure varied much + even on the same umbel: for in two flowers the pistil was intermediate in + length between that of the long and that of the short-styled form, with + the stigma elongated as in the former, and smooth as in the latter; and in + three other flowers the structure was in all respects like that of the + long-styled form. These modifications appeared to me so remarkable that I + fertilised eight of the flowers with their own pollen, and obtained five + capsules, which contained on an average 43 seeds; and this number shows + that the flowers had become abnormally fertile in comparison with those of + ordinary long- styled plants when self-fertilised. I was thus led to + examine the plants in several small collections, and the result showed + that the equal-styled variety was not rare. + </p> + <p> + TABLE 5.31. Primula Sinensis. Preponderance of long-styled over the + short-styled form. + </p> + <p> + Column 1: Name of owner or place. Column 2: Long-styled form. Column 3: + Short-styled form. Column 4: equal-styled variety. + </p> + <p> + Mr. Horwood : 0 : 0 : 17. Mr. Duck : 20 : 0 : 9. Baston : 30 : 18 : 15. + Chichester : 12 : 9 : 2. Holwood : 42 : 12 : 0. High Elms : 16 : 0 : 0. + Westerham : 1 : 5 : 0. My own plants from purchased seeds : 13 : 7 : 0. + Total : 134 : 51 : 43. + </p> + <p> + In a state of nature the long and short-styled forms would no doubt occur + in nearly equal numbers, as I infer from the analogy of the other + heterostyled species of Primula, and from having raised the two forms of + the present species in exactly the same number from flowers which had been + LEGITIMATELY crossed. The preponderance in Table 5.31 of the long-styled + form over the short-styled (in the proportion of 134 to 51) results from + gardeners generally collecting seed from self-fertilised flowers; and the + long-styled flowers produce spontaneously much more seed (as shown in the + first chapter) than the short-styled, owing to the anthers of the + long-styled form being placed low down in the corolla, so that, when the + flowers fall off, the anthers are dragged over the stigma; and we now also + know that long-styled plants, when self-fertilised, very generally + reproduce long-styled offspring. From the consideration of this table, it + occurred to me in the year 1862, that almost all the plants of the Chinese + primrose cultivated in England would sooner or later become long-styled or + equal-styled; and now, at the close of 1876, I have had five small + collections of plants examined, and almost all consisted of long-styled, + with some more or less well-characterised equal-styled plants, but with + not one short-styled. + </p> + <p> + With respect to the equal-styled plants in the table, Mr. Horwood raised + from purchased seeds four plants, which he remembered were certainly not + long-styled, but either short or equal-styled, probably the latter. These + four plants were kept separate and allowed to fertilise themselves; from + their seed the seventeen plants in the table were raised, all of which + proved equal-styled. The stamens stood low down in the corolla as in the + long-styled form; and the stigmas, which were globular and smooth, were + either completely surrounded by the anthers, or stood close above them. My + son William made drawings for me, by the aid of the camera, of the pollen + of one of the above equal-styled plants; and, in accordance with the + position of the stamens, the grains resembled in their small size those of + the long-styled form. He also examined pollen from two equal- styled + plants at Southampton; and in both of them the grains differed extremely + in size in the same anthers, a large number being small and shrivelled, + whilst many were fully as large as those of the short-styled form and + rather more globular. It is probable that the large size of these grains + was due, not to their having assumed the character of the short-styled + form, but to monstrosity; for Max Wichura has observed pollen-grains of + monstrous size in certain hybrids. The vast number of the small shrivelled + grains in the above two cases explains the fact that, though equal-styled + plants are generally fertile in a high degree, yet some of them yield few + seeds. I may add that my son compared, in 1875, the grains from two + white-flowered plants, in both of which the pistil projected above the + anthers, but neither were properly long-styled or equal- styled; and in + the one in which the stigma projected most, the grains were in diameter to + those in the other plant, in which the stigma projected less, as 100 to + 88; whereas the difference between the grains from perfectly characterised + long-styled and short-styled plants is as 100 to 57. So that these two + plants were in an intermediate condition. To return to the 17 plants in + the first line of Table 5.31: from the relative position of their stigmas + and anthers, they could hardly fail to fertilise themselves; and + accordingly four of them spontaneously yielded no less than 180 capsules; + of these Mr. Horwood selected eight fine capsules for sowing; and they + included on an average 54.8 seeds, with a maximum of 72. He gave me thirty + other capsules, taken by hazard, of which twenty-seven contained good + seeds, averaging 35.5, with a maximum of 70; but if six poor capsules, + each with less than 13 seeds, be excluded, the average rises to 42.5. + These are higher numbers than could be expected from either well- + characterised form if self-fertilised; and this high degree of fertility + accords with the view that the male organs belonged to one form, and the + female organs partially to the other form; so that a self-union in the + case of the equal- styled variety is in fact a legitimate union. + </p> + <p> + The seed saved from the above seventeen self-fertilised equal-styled + plants produced sixteen plants, which all proved equal-styled, and + resembled their parents in all the above-specified respects. The stamens, + however, in one plant were seated higher up the tube of the corolla than + in the true long-styled form; in another plant almost all the anthers were + contabescent. These sixteen plants were the grandchildren of the four + original plants, which it is believed were equal-styled; so that this + abnormal condition was faithfully transmitted, probably through three, and + certainly through two generations. The fertility of one of these + grandchildren was carefully observed: six flowers were fertilised with + pollen from the same flower, and produced six capsules, containing on an + average 68 seeds, with a maximum of 82, and a minimum of 40. Thirteen + capsules spontaneously self-fertilised yielded an average of 53.2 seeds, + with the astonishing maximum in one of 97 seeds. In no legitimate union + has so high an average as 68 seeds been observed by me, or nearly so high + a maximum as 82 and 97. These plants, therefore, not only have lost their + proper heterostyled structure and peculiar functional powers, but have + acquired an abnormal grade of fertility—unless, indeed, their high + fertility may be accounted for by the stigmas receiving pollen from the + circumjacent anthers at exactly the most favourable period. + </p> + <p> + With respect to Mr. Duck’s lot in Table 5.31, seed was saved from a single + plant, of which the form was not observed, and this produced nine + equal-styled and twenty long-styled plants. The equal-styled resembled in + all respects those previously described; and eight of their capsules + spontaneously self-fertilised contained on an average 44.4 seeds, with a + maximum of 61 and a minimum of 23. In regard to the twenty long-styled + plants, the pistil in some of the flowers did not project quite so high as + in ordinary long-styled flowers; and the stigmas, though properly + elongated, were smooth; so that we have here a slight approach in + structure to the pistil of the short-styled form. Some of these + long-styled plants also approached the equal-styled in function; for one + of them produced no less than fifteen spontaneously self-fertilised + capsules, and of these eight contained, on an average, 31.7 seeds, with a + maximum of 61. This average would be rather low for a long-styled plant + artificially fertilised with its own pollen, but is high for one + spontaneously self-fertilised. For instance, thirty- four capsules + produced by the illegitimate grandchildren of a long-styled plant, + spontaneously self-fertilised, contained on an average only 9.1 seeds, + with a maximum of 46. Some seeds indiscriminately saved from the foregoing + twenty-nine equal-styled and long-styled plants produced sixteen + seedlings, grandchildren of the original plant belonging to Mr. Duck; and + these consisted of fourteen equal- styled and two long-styled plants; and + I mention this fact as an additional instance of the transmission of the + equal-styled variety. + </p> + <p> + The third lot in Table 5.31, namely the Baston plants, are the last which + need be mentioned. The long and short-styled plants, and the fifteen + equal-styled plants, were descended from two distinct stocks. The latter + were derived from a single plant, which the gardener is positive was not + long-styled; hence, probably, it was equal-styled. In all these fifteen + plants the anthers, occupying the same position as in the long-styled + form, closely surrounded the stigma, which in one instance alone was + slightly elongated. Notwithstanding this position of the stigma, the + flowers, as the gardener assured me, did not yield many seeds; and this + difference from the foregoing cases may perhaps have been caused by the + pollen being bad, as in some of the Southampton equal-styled plants.] + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2H_CONC" id="link2H_CONC"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CONCLUSIONS WITH RESPECT TO THE EQUAL-STYLED VARIETY OF P. Sinensis. + </h2> + <p> + That this is a variation, and not a third or distinct form, as in the + trimorphic genera Lythrum and Oxalis, is clear; for we have seen its first + appearance in one out of a lot of illegitimate long-styled plants; and in + the case of Mr. Duck’s seedlings, long-styled plants, only slightly + deviating from the normal state, as well as equal-styled plants were + produced from the same self- fertilised parent. The position of the + stamens in their proper place low down in the tube of the corolla, + together with the small size of the pollen-grains, show, firstly, that the + equal-styled variety is a modification of the long- styled form, and, + secondly, that the pistil is the part which has varied most, as indeed was + obvious in many of the plants. This variation is of frequent occurrence, + and is strongly inherited when it has once appeared. It would, however, + have possessed little interest if it had consisted of a mere change of + structure; but this is accompanied by modified fertility. Its occurrence + apparently stands in close relation with the illegitimate birth of the + parent plant; but to this whole subject I shall hereafter recur. + </p> + <p> + [Primula auricula. + </p> + <p> + Although I made no experiments on the illegitimate offspring of this + species, I refer to it for two reasons:—First, because I have + observed two equal-styled plants in which the pistil resembled in all + respects that of the long-styled form, whilst the stamens had become + elongated as in the short-styled form, so that the stigma was almost + surrounded by the anthers. The pollen-grains, however, of the elongated + stamens resembled in their small size those of the shorter stamens proper + to the long-styled form. Hence these plants have become equal-styled by + the increased length of the stamens, instead of, as with P. Sinensis, by + the diminished length of the pistil. Mr. J. Scott observed five other + plants in the same state, and he shows that one of them, when self- + fertilised, yielded more seed than an ordinary long- or short-styled form + would have done when similarly fertilised, but that it was far inferior in + fertility to either form when legitimately crossed. (5/8. ‘Journal of the + Proceedings of the Linnean Society’ 8 1864 page 91.) Hence it appears that + the male and female organs of this equal-styled variety have been modified + in some special manner, not only in structure but in functional powers. + This, moreover, is shown by the singular fact that both the long-styled + and short-styled plants, fertilised with pollen from the equal-styled + variety, yield a lower average of seed than when these two forms are + fertilised with their own pollen. + </p> + <p> + The second point which deserves notice is that florists always throw away + the long-styled plants, and save seed exclusively from the short-styled + form. Nevertheless, as Mr. Scott was informed by a man who raises this + species extensively in Scotland, about one-fourth of the seedlings appear + long-styled; so that the short-styled form of the Auricula, when + fertilised by its own pollen, does not reproduce the same form in so large + a proportion as in the case of P. Sinensis. We may further infer that the + short-styled form is not rendered quite sterile by a long course of + fertilisation with pollen of the same form: but as there would always be + some liability to an occasional cross with the other form, we cannot tell + how long self-fertilisation has been continued. + </p> + <p> + Primula farinosa. + </p> + <p> + Mr. Scott says that it is not at all uncommon to find equal-styled plants + of this heterostyled species. (5/9. ‘Journal of the Proceedings of the + Linnean Society’ 8 1864 page 115.) Judging from the size of the + pollen-grains, these plants owe their structure, as in the case of P. + auricula, to the abnormal elongation of the stamens of the long-styled + form. In accordance with this view, they yield less seed when crossed with + the long-styled form than with the short- styled. But they differ in an + anomalous manner from the equal-styled plants of P. auricula in being + extremely sterile with their own pollen. + </p> + <p> + Primula elatior. + </p> + <p> + It was shown in the first chapter, on the authority of Herr Breitenbach, + that equal-styled flowers are occasionally found on this species whilst + growing in a state of nature; and this is the only instance of such an + occurrence known to me, with the exception of some wild plants of the + Oxlip—a hybrid between P. veris and vulgaris—which were + equal-styled. Herr Breitenbach’s case is remarkable in another way; for + equal-styled flowers were found in two instances on plants which bore both + long-styled and short-styled flowers. In every other instance these two + forms and the equal-styled variety have been produced by distinct plants.] + </p> + <p> + Primula vulgaris, BRIT. FL. + </p> + <p> + VAR. acaulis OF LINN. AND P. acaulis OF JACQ. + </p> + <h3> + VAR. RUBRA. + </h3> + <p> + Mr. Scott states that this variety, which grew in the Botanic Garden in + Edinburgh, was quite sterile when fertilised with pollen from the common + primrose, as well as from a white variety of the same species, but that + some of the plants, when artificially fertilised with their own pollen, + yielded a moderate supply of seed. (5/10. ‘Journal of the Proceedings of + the Linnean Society’ 8 1864 page 98.) He was so kind as to send me some of + these self- fertilised seeds, from which I raised the plants immediately + to be described. I may premise that the results of my experiments on the + seedlings, made on a large scale, do not accord with those by Mr. Scott on + the parent-plant. + </p> + <p> + First, in regard to the transmission of form and colour. The parent-plant + was long-styled, and of a rich purple colour. From the self-fertilised + seed 23 plants were raised; of these 18 were purple of different shades, + with two of them a little streaked and freckled with yellow, thus showing + a tendency to reversion; and 5 were yellow, but generally with a brighter + orange centre than in the wild flower. All the plants were profuse + flowerers. All were long-styled; but the pistil varied a good deal in + length even on the same plant, being rather shorter, or considerably + longer, than in the normal long-styled form; and the stigmas likewise + varied in shape. It is, therefore, probable that an equal- styled variety + of the primrose might be found on careful search; and I have received two + accounts of plants apparently in this condition. The stamens always + occupied their proper position low down in the corolla; and the + pollen-grains were of the small size proper to the long-styled form, but + were mingled with many minute and shrivelled grains. The yellow-flowered + and the purple-flowered plants of this first generation were fertilised + under a net with their own pollen, and the seed separately sown. From the + former, 22 plants were raised, and all were yellow and long-styled. From + the latter or the purple-flowered plants, 24 long-styled plants were + raised, of which 17 were purple and 7 yellow. In this last case we have an + instance of reversion in colour, without the possibility of any cross, to + the grandparents or more distant progenitors of the plants in question. + Altogether 23 plants in the first generation and 46 in the second + generation were raised; and the whole of these 69 illegitimate plants were + long-styled! + </p> + <p> + Eight purple-flowered and two yellow-flowered plants of the first + illegitimate generation were fertilised in various ways with their own + pollen and with that of the common primrose; and the seeds were separately + counted, but as I could detect no difference in fertility between the + purple and yellow varieties, the results are run together in Table 5.32. + </p> + <p> + TABLE 5.32. Primula vulgaris. + </p> + <p> + Column 1: Nature of plant experimented on, and kind of union. Column 2: + Number of flowers fertilised. Column 3: Number of capsules produced. + Column 4: Average Number of seeds per capsule. Column 5: Maximum Number of + seeds in any one capsule. Column 6: Minimum Number of seeds in any one + capsule. + </p> + <p> + Purple- and yellow-flowered illegitimate long-styled plants, + ILLEGITIMATELY fertilised with pollen from the same plant : 72 : 11 : 11.5 + : 26 : 5. + </p> + <p> + Purple- and yellow-flowered illegitimate long-styled plants, + ILLEGITIMATELY fertilised with pollen from the common long-styled primrose + : 72 : 39 : 31.4 : 62 : 3. + </p> + <p> + Or, if the ten poorest capsules, including less than 15 seeds, be + rejected, we get: 72 : 29 : 40.6 : 62 : 18. + </p> + <p> + Purple- and yellow-flowered illegitimate long-styled plants, LEGITIMATELY + fertilised with pollen from the common short-styled primrose : 26 : 18 : + 36.4 : 60 : 9. + </p> + <p> + Or, if the two poorest capsules, including less than 15 seeds, be + rejected, we get: 26 : 16 : 41.2 : 60 : 15. + </p> + <p> + The long-styled form of the common primrose ILLEGITIMATELY fertilised with + pollen from the long-styled illegitimate purple- and yellow-flowered + plants: 20 : 14 : 15.4 : 46 : 1. + </p> + <p> + Or, if the three poorest capsules be rejected, we get: 20 : 11 : 18.9 : 46 + : 8. + </p> + <p> + The short-styled form of the common primrose LEGITIMATELY fertilised with + pollen from the long-styled illegitimate purple- and yellow-flowered + plants: 10 : 6 : 30.5 : 61 : 6. + </p> + <p> + If we compare the figures in this table with those given in the first + chapter, showing the normal fertility of the common primrose, we shall see + that the illegitimate purple- and yellow-flowered varieties are very + sterile. For instance, 72 flowers were fertilised with their own pollen + and produced only 11 good capsules; but by the standard they ought to have + produced 48 capsules; and each of these ought to have contained on an + average 52.2 seeds, instead of only 11.5 seeds. When these plants were + illegitimately and legitimately fertilised with pollen from the common + primrose, the average numbers were increased, but were far from attaining + the normal standards. So it was when both forms of the common primrose + were fertilised with pollen from these illegitimate plants; and this shows + that their male as well as their female organs were in a deteriorated + condition. The sterility of these plants was shown in another way, namely, + by their not producing any capsules when the access of all insects (except + such minute ones as Thrips) was prevented; for under these circumstances + the common long-styled primrose produces a considerable number of + capsules. There can, therefore, be no doubt that the fertility of these + plants was greatly impaired. The loss is not correlated with the colour of + the flower; and it was to ascertain this point that I made so many + experiments. As the parent-plant growing in Edinburgh was found by Mr. + Scott to be in a high degree sterile, it may have transmitted a similar + tendency to its offspring, independently of their illegitimate birth. I + am, however, inclined to attribute some weight to the illegitimacy of + their descent, both from the analogy of other cases, and more especially + from the fact that when the plants were LEGITIMATELY fertilised with + pollen of the common primrose they yielded an average, as may be seen in + the table, of only 5 more seeds than when ILLEGITIMATELY fertilised with + the same pollen. Now we know that it is eminently characteristic of the + illegitimate offspring of Primula Sinensis that they yield but few more + seeds when legitimately fertilised than when fertilised with their + own-form pollen. + </p> + <p> + Primula veris, Brit. Fl. + </p> + <p> + Var. officinalis of Linn., P. officinalis OF Jacq. + </p> + <p> + Seeds from the short-styled form of the cowslip fertilised with pollen + from the same form germinate so badly that I raised from three successive + sowings only fourteen plants, which consisted of nine short-styled and + five long-styled plants. Hence the short-styled form of the cowslip, when + self-fertilised, does not transmit the same form nearly so truly as does + that of P. Sinensis. From the long-styled form, always fertilised with its + own-form pollen, I raised in the first generation three long-styled + plants,—from their seed 53 long-styled grandchildren,—from + their seed 4 long-styled great-grandchildren,—from their seed 20 + long-styled great-great-grandchildren,—and lastly, from their seed 8 + long-styled and 2 short-styled great-great-great-grandchildren. In this + last generation short-styled plants appeared for the first time in the + course of the six generations,—the parent long-styled plant which + was fertilised with pollen from another plant of the same form being + counted as the first generation. Their appearance may be attributed to + atavism. From two other long-styled plants, fertilised with their own-form + pollen, 72 plants were raised, which consisted of 68 long-styled and 4 + short-styled. So that altogether 162 plants were raised from + illegitimately fertilised long-styled cowslips, and these consisted of 156 + long-styled and 6 short-styled plants. + </p> + <p> + We will now turn to the fertility and powers of growth possessed by the + illegitimate plants. From a short-styled plant, fertilised with its + own-form pollen, one short-styled and two long-styled plants, and from a + long-styled plant similarly fertilised three long-styled plants were at + first raised. The fertility of these six illegitimate plants was carefully + observed; but I must premise that I cannot give any satisfactory standard + of comparison as far as the number of the seeds is concerned; for though I + counted the seeds of many legitimate plants fertilised legitimately and + illegitimately, the number varied so greatly during successive seasons + that no one standard will serve well for illegitimate unions made during + different seasons. Moreover the seeds in the same capsule frequently + differ so much in size that it is scarcely possible to decide which ought + to be counted as good seed. There remains as the best standard of + comparison the proportional number of fertilised flowers which produce + capsules containing any seed. + </p> + <p> + First, for the one illegitimate short-styled plant. In the course of three + seasons 27 flowers were illegitimately fertilised with pollen from the + same plant, and they yielded only a single capsule, which, however, + contained a rather large number of seeds for a union of this nature, + namely, 23. As a standard of comparison I may state that during the same + three seasons 44 flowers borne by legitimate short-styled plants were + self-fertilised, and yielded 26 capsules; so that the fact of the 27 + flowers on the illegitimate plant having produced only one capsule proves + how sterile it was. To show that the conditions of life were favourable, I + will add that numerous plants of this and other species of Primula all + produced an abundance of capsules whilst growing close by in the same soil + with the present and following plants. The sterility of the above + illegitimate short-styled plant depended on both the male and female + organs being in a deteriorated condition. This was manifestly the case + with the pollen; for many of the anthers were shrivelled or contabescent. + Nevertheless some of the anthers contained pollen, with which I succeeded + in fertilising some flowers on the illegitimate long-styled plants + immediately to be described. Four flowers on this same short-styled plant + were likewise LEGITIMATELY fertilised with pollen from one of the + following long-styled plants; but only one capsule was produced, + containing 26 seeds; and this is a very low number for a legitimate union. + </p> + <p> + With respect to the five illegitimate long-styled plants of the first + generation, derived from the above self-fertilised short-styled and + long-styled parents, their fertility was observed during the same three + years. These five plants, when self-fertilised, differed considerably from + one another in their degree of fertility, as was the case with the + illegitimate long-styled plants of Lythrum salicaria; and their fertility + varied much according to the season. I may premise, as a standard of + comparison, that during the same years 56 flowers on legitimate + long-styled plants of the same age and grown in the same soil, were + fertilised with their own pollen, and yielded 27 capsules; that is, 48 per + cent. On one of the five illegitimate long-styled plants 36 flowers were + self- fertilised in the course of the three years, but they did not + produce a single capsule. Many of the anthers on this plant were + contabescent; but some seemed to contain sound pollen. Nor were the female + organs quite impotent; for I obtained from a LEGITIMATE cross one capsule + with good seed. On a second illegitimate long-styled plant 44 flowers were + fertilised during the same years with their own pollen, but they produced + only a single capsule. The third and fourth plants were in a very slight + degree more productive. The fifth and last plant was decidedly more + fertile; for 42 self-fertilised flowers yielded 11 capsules. Altogether, + in the course of the three years, no less than 160 flowers on these five + illegitimate long-styled plants were fertilised with their own pollen, but + they yielded only 22 capsules. According to the standard above given, they + ought to have yielded 80 capsules. These 22 capsules contained on an + average 15.1 seeds. I believe, subject to the doubts before specified, + that with legitimate plants the average number from a union of this nature + would have been above 20 seeds. Twenty-four flowers on these same five + illegitimate long-styled plants were legitimately fertilised with pollen + from the above-described illegitimate short-styled plant, and produced + only 9 capsules, which is an extremely small number for a legitimate + union. These 9 capsules, however, contained an average of 38 apparently + good seeds, which is as large a number as legitimate plants sometimes + yield. But this high average was almost certainly false; and I mention the + case for the sake of showing the difficulty of arriving at a fair result; + for this average mainly depended on two capsules containing the + extraordinary numbers of 75 and 56 seeds; these seeds, however, though I + felt bound to count them, were so poor that, judging from trials made in + other cases, I do not suppose that one would have germinated; and + therefore they ought not to have been included. Lastly, 20 flowers were + legitimately fertilised with pollen from a legitimate plant, and this + increased their fertility; for they produced 10 capsules. Yet this is but + a very small proportion for a legitimate union. + </p> + <p> + There can, therefore, be no doubt that these five long-styled plants and + the one short-styled plant of the first illegitimate generation were + extremely sterile. Their sterility was shown, as in the case of hybrids, + in another way, namely, by their flowering profusely, and especially by + the long endurance of the flowers. For instance, I fertilised many flowers + on these plants, and fifteen days afterwards (namely on March 22nd) I + fertilised numerous long-styled and short- styled flowers on common + cowslips growing close by. These latter flowers, on April 8th, were + withered, whilst most of the illegitimate flowers remained quite fresh for + several days subsequently; so that some of these illegitimate plants, + after being fertilised, remained in full bloom for above a month. + </p> + <p> + We will now turn to the fertility of the 53 illegitimate long-styled + grandchildren, descended from the long-styled plant which was first + fertilised with its own pollen. The pollen in two of these plants included + a multitude of small and shrivelled grains. Nevertheless they were not + very sterile; for 25 flowers, fertilised with their own pollen, produced + 15 capsules, containing an average of 16.3 seeds. As already stated, the + probable average with legitimate plants for a union of this nature is + rather above 20 seeds. These plants were remarkably healthy and vigorous, + as long as they were kept under highly favourable conditions in pots in + the greenhouse; and such treatment greatly increases the fertility of the + cowslip. When these same plants were planted during the next year (which, + however, was an unfavourable one), out of doors in good soil, 20 + self-fertilised flowers produced only 5 capsules, containing extremely few + and wretched seeds. + </p> + <p> + Four long-styled great-grandchildren were raised from the self-fertilised + grandchildren, and were kept under the same highly favourable conditions + in the greenhouse; 10 of their flowers were fertilised with own-form + pollen and yielded the large proportion of 6 capsules, containing on an + average 18.7 seeds. From these seeds 20 long-styled + great-great-grandchildren were raised, which were likewise kept in the + greenhouse. Thirty of their flowers were fertilised with their own pollen + and yielded 17 capsules, containing on an average no less than 32, mostly + fine seeds. It appears, therefore, that the fertility of these plants of + the fourth illegitimate generation, as long as they were kept under highly + favourable conditions, had not decreased, but had rather increased. The + result, however, was widely different when they were planted out of doors + in good soil, where other cowslips grew vigorously and were completely + fertile; for these illegitimate plants now became much dwarfed in stature + and extremely sterile, notwithstanding that they were exposed to the + visits of insects, and must have been legitimately fertilised by the + surrounding legitimate plants. A whole row of these plants of the fourth + illegitimate generation, thus freely exposed and legitimately fertilised, + produced only 3 capsules, containing on an average only 17 seeds. During + the ensuing winter almost all these plants died, and the few survivors + were miserably unhealthy, whilst the surrounding legitimate plants were + not in the least injured. + </p> + <p> + The seeds from the great-great-grandchildren were sown, and 8 long-styled + and 2 short-styled plants of the fifth illegitimate generation raised. + These whilst still in the greenhouse produced smaller leaves and shorter + flower-stalks than some legitimate plants with which they grew in + competition; but it should be observed that the latter were the product of + a cross with a fresh stock,—a circumstance which by itself would + have added much to their vigour. (5/11. For full details of this + experiment, see my ‘Effects of Cross and Self- fertilisation’ 1876 page + 220.) When these illegitimate plants were transferred to fairly good soil + out of doors, they became during the two following years much more dwarfed + in stature and produced very few flower-stems; and although they must have + been legitimately fertilised by insects, they yielded capsules, compared + with those produced by the surrounding legitimate plants, in the ratio + only of 5 to 100! It is therefore certain that illegitimate fertilisation, + continued during successive generations, affects the powers of growth and + fertility of P. veris to an extraordinary degree; more especially when the + plants are exposed to ordinary conditions of life, instead of being + protected in a greenhouse. + </p> + <p> + [EQUAL-STYLED RED VARIETY OF Primula veris. + </p> + <p> + Mr. Scott has described a plant of this kind growing in the Botanic Garden + of Edinburgh. (5/12. ‘Proceedings of the Linnean Society’ volume 8 1864 + page 105.) He states that it was highly self-fertile, although insects + were excluded; and he explains this fact by showing, first, that the + anthers and stigma are in close apposition, and that the stamens in + length, position and size of their pollen-grains resemble those of the + short-styled form, whilst the pistil resembles that of the long-styled + form both in length and in the structure of the stigma. Hence the + self-union of this variety is, in fact, a legitimate union, and + consequently is highly fertile. Mr. Scott further states that this variety + yielded very few seeds when fertilised by either the long- or short- + styled common cowslip, and, again, that both forms of the latter, when + fertilised by the equal-styled variety, likewise produced very few seeds. + But his experiments with the cowslip were few, and my results do not + confirm his in any uniform manner. + </p> + <p> + I raised twenty plants from self-fertilised seed sent me by Mr. Scott; and + they all produced red flowers, varying slightly in tint. Of these, two + were strictly long-styled both in structure and in function; for their + reproductive powers were tested by crosses with both forms of the common + cowslip. Six plants were equal-styled; but on the same plant the pistil + varied a good deal in length during different seasons. This was likewise + the case, according to Mr. Scott, with the parent-plant. Lastly, twelve + plants were in appearance short-styled; but they varied much more in the + length of their pistils than ordinary short- styled cowslips, and they + differed widely from the latter in their powers of reproduction. Their + pistils had become short-styled in structure, whilst remaining long-styled + in function. Short-styled cowslips, when insects are excluded, are + extremely barren: for instance, on one occasion six fine plants produced + only about 50 seeds (that is, less than the product of two good capsules), + and on another occasion not a single capsule. Now, when the above twelve + apparently short-styled seedlings were similarly treated, nearly all + produced a great abundance of capsules, containing numerous seeds, which + germinated remarkably well. Moreover three of these plants, which during + the first year were furnished with quite short pistils, on the following + year produced pistils of extraordinary length. The greater number, + therefore, of these short-styled plants could not be distinguished in + function from the equal- styled variety. The anthers in the six + equal-styled and in the apparently twelve short-styled plants were seated + high up in the corolla, as in the true short- styled cowslip; and the + pollen-grains resembled those of the same form in their large size, but + were mingled with a few shrivelled grains. In function this pollen was + identical with that of the short-styled cowslip; for ten long-styled + flowers of the common cowslip, legitimately fertilised with pollen from a + true equal-styled variety, produced six capsules, containing on an average + 34.4 seeds; whilst seven capsules on a short-styled cowslip illegitimately + fertilised with pollen from the equal-styled variety, yielded an average + of only 14.5 seeds. + </p> + <p> + As the equal-styled plants differ from one another in their powers of + reproduction, and as this is an important subject, I will give a few + details with respect to five of them. First, an equal-styled plant, + protected from insects (as was done in all the following cases, with one + stated exception), spontaneously produced numerous capsules, five of which + gave an average of 44.8 seeds, with a maximum in one capsule of 57. But + six capsules, the product of fertilisation with pollen from a short-styled + cowslip (and this is a legitimate union), gave an average of 28.5 seeds, + with a maximum of 49; and this is a much lower average than might have + been expected. Secondly, nine capsules from another equal-styled plant, + which had not been protected from insects, but probably was + self-fertilised, gave an average of 45.2 seeds, with a maximum of 58. + Thirdly, another plant which had a very short pistil in 1865, produced + spontaneously many capsules, six of which contained an average of 33.9 + seeds, with a maximum of 38. In 1866 this same plant had a pistil of + wonderful length; for it projected quite above the anthers, and the stigma + resembled that of the long-styled form. In this condition it produced + spontaneously a vast number of fine capsules, six of which contained + almost exactly the same average number as before, namely 34.3, with a + maximum of 38. Four flowers on this plant, legitimately fertilised with + pollen from a short-styled cowslip, yielded capsules with an average of + 30.2 seeds. Fourthly another short-styled plant spontaneously produced in + 1865 an abundance of capsules, ten of which contained an average of 35.6 + seeds, with a maximum of 54. In 1866 this same plant had become in all + respects long-styled, and ten capsules gave almost exactly the same + average as before, namely 35.1 seeds, with a maximum of 47. Eight flowers + on this plant, legitimately fertilised with pollen from a short-styled + cowslip, produced six capsules, with the high average of 53 seeds, and the + high maximum of 67. Eight flowers were also fertilised with pollen from a + long-styled cowslip (this being an illegitimate union), and produced seven + capsules, containing an average of 24.4 seeds, with a maximum of 32. The + fifth and last plant remained in the same condition during both years: it + had a pistil rather longer than that of the true short-styled form, with + the stigma smooth, as it ought to be in this form, but abnormal in shape, + like a much-elongated inverted cone. It produced spontaneously many + capsules, five of which, in 1865, gave an average of only 15.6 seeds; and + in 1866 ten capsules still gave an average only a little higher, namely of + 22.1, with a maximum of 30. Sixteen flowers were fertilised with pollen + from a long-styled cowslip, and produced 12 capsules, with an average of + 24.9 seeds, and a maximum of 42. Eight flowers were fertilised with pollen + from a short-styled cowslip, but yielded only two capsules, containing 18 + and 23 seeds. Hence this plant, in function and partially in structure, + was in an almost exactly intermediate state between the long-styled and + short-styled form, but inclining towards the short-styled; and this + accounts for the low average of seeds which it produced when spontaneously + self-fertilised. + </p> + <p> + The foregoing five plants thus differ much from one another in the nature + of their fertility. In two individuals a great difference in the length of + the pistil during two succeeding years made no difference in the number of + seeds produced. As all five plants possessed the male organs of the + short-styled form in a perfect state, and the female organs of the + long-styled form in a more or less complete state, they spontaneously + produced a surprising number of capsules, which generally contained a + large average of remarkably fine seeds. With ordinary cowslips + LEGITIMATELY FERTILISED, I once obtained from plants cultivated in the + greenhouse the high average, from seven capsules, of 58.7 seeds, with a + maximum in one capsule of 87 seeds; but from plants grown out of doors I + never obtained a higher average than 41 seeds. Now two of the equal- + styled plants, grown out of doors and spontaneously SELF-FERTILISED, gave + averages of 44 and 45 seeds; but this high fertility may perhaps be in + part attributed to the stigma receiving pollen from the surrounding + anthers at exactly the right period. Two of these plants, fertilised with + pollen from a short-styled cowslip (and this in fact is a legitimate + union), gave a lower average than when self-fertilised. On the other hand, + another plant, when similarly fertilised by a cowslip, yielded the + unusually high average of 53 seeds, with a maximum of 67. Lastly, as we + have just seen, one of these plants was in an almost exactly intermediate + condition in its female organs between the long- and short-styled forms, + and consequently, when self-fertilised, yielded a low average of seed. If + we add together all the experiments which I made on the equal-styled + plants, 41 spontaneously self-fertilised capsules (insects having been + excluded) gave an average of 34 seeds, which is exactly the same number as + the parent-plant yielded in Edinburgh. Thirty-four flowers, fertilised + with pollen from the short-styled cowslip (and this is an analogous + union), produced 17 capsules, containing an average of 33.8 seeds. It is a + rather singular circumstance, for which I cannot account, that 20 flowers, + artificially fertilised on one occasion with pollen from the same plants + yielded only ten capsules, containing the low average of 26.7 seeds. + </p> + <p> + As bearing on inheritance, it may be added that 72 seedlings were raised + from one of the red-flowered, strictly equal-styled, self-fertilised + plants descended from the similarly characterised Edinburgh plant. These + 72 plants were therefore grandchildren of the Edinburgh plant, and they + all bore, as in the first generation, red flowers, with the exception of + one plant, which reverted in colour to the common cowslip. In regard to + structure, nine plants were truly long-styled and had their stamens seated + low down in the corolla in the proper position; the remaining 63 plants + were equal-styled, though the stigma in about a dozen of them stood a + little below the anthers. We thus see that the anomalous combination in + the same flower, of the male and female sexual organs which properly exist + in the two distinct forms, was inherited with much force. Thirty- six + seedlings were also raised from long and short-styled common cowslips, + crossed with pollen from the equal-styled variety. Of these plants one + alone was equal-styled, 20 were short-styled, but with the pistil in three + of them rather too long, and the remaining 15 were long-styled. In this + case we have an illustration of the difference between simple inheritance + and prepotency of transmission; for the equal-styled variety, when + self-fertilised, transmits its character, as we have just seen, with much + force, but when crossed with the common cowslip cannot withstand the + greater power of transmission of the latter. + </p> + <h3> + PULMONARIA. + </h3> + <p> + I have little to say on this genus. I obtained seeds of P. officinalis + from a garden where the long-styled form alone grew, and raised 11 + seedlings, which were all long-styled. These plants were named for me by + Dr. Hooker. They differed, as has been shown, from the plants belonging to + this species which in Germany were experimented on by Hildebrand (5/13. + ‘Botanische Zeitung’ 1865 page 13.); for he found that the long-styled + form was absolutely sterile with its own pollen, whilst my long-styled + seedlings and the parent-plants yielded a fair supply of seed when + self-fertilised. Plants of the long-styled form of Pulmonaria angustifolia + were, like Hildebrand’s plants, absolutely sterile with their own pollen, + so that I could never procure a single seed. On the other hand, the + short-styled plants of this species, differently from those of P. + officinalis, were fertile with their own pollen in a quite remarkable + degree for a heterostyled plant. From seeds carefully self-fertilised I + raised 18 plants, of which 13 proved short-styled and 5 long-styled. + </p> + <p> + Polygonum fagopyrum. + </p> + <p> + From flowers on long-styled plants fertilised illegitimately with pollen + from the same plant, 49 seedlings were raised, and these consisted of 45 + long-styled and 4 short-styled. From flowers on short-styled plants + illegitimately fertilised with pollen from the same plant 33 seedlings + were raised, and these consisted of 20 short-styled and 13 long-styled. So + that the usual rule of illegitimately fertilised long-styled plants + tending much more strongly than short-styled plants to reproduce their own + form here holds good. The illegitimate plants derived from both forms + flowered later than the legitimate, and were to the latter in height as 69 + to 100. But as these illegitimate plants were descended from parents + fertilised with their own pollen, whilst the legitimate plants were + descended from parents crossed with pollen from a distinct individual, it + is impossible to know how much of their difference in height and period of + flowering, is due to the illegitimate birth of the one set, and how much + to the other set being the product of a cross between distinct plants.] + </p> + <p> + CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF HETEROSTYLED + TRIMORPHIC AND DIMORPHIC PLANTS. + </p> + <p> + It is remarkable how closely and in how many points illegitimate unions + between the two or three forms of the same heterostyled species, together + with their illegitimate offspring, resemble hybrid unions between distinct + species together with their hybrid offspring. In both cases we meet with + every degree of sterility, from very slightly lessened fertility to + absolute barrenness, when not even a single seed-capsule is produced. In + both cases the facility of effecting the first union is much influenced by + the conditions to which the plants are exposed. (5/14. This has been + remarked by many experimentalists in effecting crosses between distinct + species; and in regard to illegitimate unions I have given in the first + chapter a striking illustration in the case of Primula veris.) Both with + hybrids and illegitimate plants the innate degree of sterility is highly + variable in plants raised from the same mother-plant. In both cases the + male organs are more plainly affected than the female; and we often find + contabescent anthers enclosing shrivelled and utterly powerless + pollen-grains. The more sterile hybrids, as Max Wichura has well shown, + are sometimes much dwarfed in stature, and have so weak a constitution + that they are liable to premature death (5/15. ‘Die Bastardbefruchtung im + Pflanzenreich’ 1865.); and we have seen exactly parallel cases with the + illegitimate seedlings of Lythrum and Primula. Many hybrids are the most + persistent and profuse flowerers, as are some illegitimate plants. When a + hybrid is crossed by either pure parent-form, it is notoriously much more + fertile than when crossed inter se or by another hybrid; so when an + illegitimate plant is fertilised by a legitimate plant, it is more fertile + than when fertilised inter se or by another illegitimate plant. When two + species are crossed and they produce numerous seeds, we expect as a + general rule that their hybrid offspring will be moderately fertile; but + if the parent species produce extremely few seeds, we expect that the + hybrids will be very sterile. But there are marked exceptions, as shown by + Gartner, to these rules. So it is with illegitimate unions and + illegitimate offspring. Thus the mid- styled form of Lythrum salicaria, + when illegitimately fertilised with pollen from the longest stamens of the + short-styled form, produced an unusual number of seeds; and their + illegitimate offspring were not at all, or hardly at all, sterile. On the + other hand, the illegitimate offspring from the long-styled form, + fertilised with pollen from the shortest stamens of the same form, yielded + few seeds, and the illegitimate offspring thus produced were very sterile; + but they were more sterile than might have been expected relatively to the + difficulty of effecting the union of the parent sexual elements. No point + is more remarkable in regard to the crossing of species than their unequal + reciprocity. Thus species A will fertilise B with the greatest ease; but B + will not fertilise A after hundreds of trials. We have exactly the same + case with illegitimate unions; for the mid-styled Lythrum salicaria was + easily fertilised by pollen from the longest stamens of the short-styled + form, and yielded many seeds; but the latter form did not yield a single + seed when fertilised by the longest stamens of the mid-styled form. + </p> + <p> + Another important point is prepotency. Gartner has shown that when a + species is fertilised with pollen from another species, if it be + afterwards fertilised with its own pollen, or with that of the same + species, this is so prepotent over the foreign pollen that the effect of + the latter, though placed on the stigma some time previously, is entirely + destroyed. Exactly the same thing occurs with the two forms of a + heterostyled species. Thus several long-styled flowers of Primula veris + were fertilised illegitimately with pollen from another plant of the same + form, and twenty-four hours afterwards legitimately with pollen from a + short- styled dark-red polyanthus which is a variety of P. veris; and the + result was that every one of the thirty seedlings thus raised bore flowers + more or less red, showing plainly how prepotent the legitimate pollen from + a short-styled plant was over the illegitimate pollen from a long-styled + plant. + </p> + <p> + In all the several foregoing points the parallelism is wonderfully close + between the effects of illegitimate and hybrid fertilisation. It is hardly + an exaggeration to assert that seedlings from an illegitimately fertilised + heterostyled plant are hybrids formed within the limits of one and the + same species. This conclusion is important, for we thus learn that the + difficulty in sexually uniting two organic forms and the sterility of + their offspring, afford no sure criterion of so-called specific + distinctness. If any one were to cross two varieties of the same form of + Lythrum or Primula for the sake of ascertaining whether they were + specifically distinct, and he found that they could be united only with + some difficulty, that their offspring were extremely sterile, and that the + parents and their offspring resembled in a whole series of relations + crossed species and their hybrid offspring, he might maintain that his + varieties had been proved to be good and true species; but he would be + completely deceived. In the second place, as the forms of the same + trimorphic or dimorphic heterostyled species are obviously identical in + general structure, with the exception of the reproductive organs, and as + they are identical in general constitution (for they live under precisely + the same conditions), the sterility of their illegitimate unions and that + of their illegitimate offspring, must depend exclusively on the nature of + the sexual elements and on their incompatibility for uniting in a + particular manner. And as we have just seen that distinct species when + crossed resemble in a whole series of relations the forms of the same + species when illegitimately united, we are led to conclude that the + sterility of the former must likewise depend exclusively on the + incompatible nature of their sexual elements, and not on any general + difference in constitution or structure. We are, indeed, led to this same + conclusion by the impossibility of detecting any differences sufficient to + account for certain species crossing with the greatest ease, whilst other + closely allied species cannot be crossed, or can be crossed only with + extreme difficulty. We are led to this conclusion still more forcibly by + considering the great difference which often exists in the facility of + crossing reciprocally the same two species; for it is manifest in this + case that the result must depend on the nature of the sexual elements, the + male element of the one species acting freely on the female element of the + other, but not so in a reversed direction. And now we see that this same + conclusion is independently and strongly fortified by the consideration of + the illegitimate unions of trimorphic and dimorphic heterostyled plants. + In so complex and obscure a subject as hybridism it is no slight gain to + arrive at a definite conclusion, namely, that we must look exclusively to + functional differences in the sexual elements, as the cause of the + sterility of species when first crossed and of their hybrid offspring. It + was this consideration which led me to make the many observations recorded + in this chapter, and which in my opinion make them worthy of publication. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0006" id="link2HCH0006"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VI. CONCLUDING REMARKS ON HETEROSTYLED PLANTS. + </h2> +<pre xml:space="preserve"> + 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. +</pre> + <p> + In the foregoing chapters all the heterostyled plants known to me have + been more or less fully described. Several other cases have been + indicated, especially by Professor Asa Gray and Kuhn, in which the + individuals of the same species differ in the length of their stamens and + pistils (6/1. Asa Gray ‘American Journal of Science’ 1865 page 101 and + elsewhere as already referred to. Kuhn ‘Botanische Zeitung’ 1867 page + 67.); but as I have been often deceived by this character taken alone, it + seems to me the more prudent course not to rank any species as + heterostyled, unless we have evidence of more important differences + between the forms, as in the diameter of the pollen-grains, or in the + structure of the stigma. The individuals of many ordinary hermaphrodite + plants habitually fertilise one another, owing to their male and female + organs being mature at different periods, or to the structure of the + parts, or to self-sterility, etc.; and so it is with many hermaphrodite + animals, for instance, land-snails or earth-worms; but in all these cases + any one individual can fully fertilise or be fertilised by any other + individual of the same species. This is not so with heterostyled plants: a + long-styled, mid-styled or short-styled plant cannot fully fertilise or be + fertilised by any other individual, but only by one belonging to another + form. Thus the essential character of plants belonging to the heterostyled + class is that the individuals are divided into two or three bodies, like + the males and females of dioecious plants or of the higher animals, which + exist in approximately equal numbers and are adapted for reciprocal + fertilisation. The existence, therefore, of two or three bodies of + individuals, differing from one another in the above more important + characteristics, offers by itself good evidence that the species is + heterostyled. But absolutely conclusive evidence can be derived only from + experiments, and by finding that pollen must be applied from the one form + to the other in order to ensure complete fertility. + </p> + <p> + In order to show how much more fertile each form is when legitimately + fertilised with pollen from the other form (or in the case of trimorphic + species, with the proper pollen from one of the two other forms) than when + illegitimately fertilised with its own-form pollen, I will append Table + 6.33 giving a summary of the results in all the cases hitherto + ascertained. The fertility of the unions may be judged by two standards, + namely, by the proportion of flowers which, when fertilised in the two + methods, yield capsules, and by the average number of seeds per capsule. + When there is a dash in the left hand column opposite to the name of the + species, the proportion of the flowers which yielded capsules was not + recorded. + </p> + <p> + TABLE 6.33. Fertility of the legitimate unions taken together, compared + with that of the illegitimate unions together. The fertility of the + legitimate unions, as judged by both standards, is taken as 100. + </p> + <p> + Column 1: Name of species. Column 2: Illegitimate unions : proportional + number of flowers which produced capsules. Column 3: Illegitimate unions : + average number of seeds per capsule. + </p> + <p> + Primula veris : 69 : 65. + </p> + <p> + Primula elatior : 27 : 75. + </p> + <p> + Primula vulgaris : 60 : 54. + </p> + <p> + Primula Sinensis : 84 : 63. + </p> + <p> + Primula Sinensis (second trial) : 0 : 53. + </p> + <p> + Primula Sinensis (Hildebrand) : 100 : 42. + </p> + <p> + Primula auricula (Scott) : 80 : 15. + </p> + <p> + Primula Sikkimensis (Scott) : 95 : 31. + </p> + <p> + Primula cortusoides (Scott) : 74 : 66. + </p> + <p> + Primula involucrata (Scott) : 72 : 48. + </p> + <p> + Primula farinosa (Scott) : 71 : 44. + </p> + <p> + Average of the nine species of Primula : 88.4 : 69. + </p> + <p> + Hottonia palustris (H. Muller) : - : 61. + </p> + <p> + Linum grandiflorum (the difference probably is much greater) : - : 69. + </p> + <p> + Linum perenne : - : 20. + </p> + <p> + Linum perenne (Hildebrand) : 0 : 0. + </p> + <p> + Pulmonaria officinalis (German stock, Hildebrand) : 0 : 0. + </p> + <p> + Pulmonaria angustifolia : 35 : 32. + </p> + <p> + Mitchella repens : 20 : 47. + </p> + <p> + Borreria, Brazilian sp. : - : 0. + </p> + <p> + Polygonum fagopyrum : - : 46. + </p> + <p> + Lythrum salicaria : 33 : 46. + </p> + <p> + Oxalis Valdiviana (Hildebrand) : 2 : 34. + </p> + <p> + Oxalis Regnelli : 0 : 0. + </p> + <p> + Oxalis speciosa : 15 : 49. + </p> + <p> + The two or three forms of the same heterostyled species do not differ from + one another in general habit or foliage, as sometimes, though rarely, + happens with the two sexes of dioecious plants. Nor does the calyx differ, + but the corolla sometimes differs slightly in shape, owing to the + different position of the anthers. In Borreria the hairs within the tube + of the corolla are differently situated in the long-styled and + short-styled forms. In Pulmonaria there is a slight difference in the size + of the corolla, and in Pontederia in its colour. In the reproductive + organs the differences are much greater and more important. In the one + form the stamens may be all of the same length, and in the other graduated + in length, or alternately longer and shorter. The filaments may differ in + colour and thickness, and are sometimes nearly thrice as long in the one + form as in the other. They adhere also for very different proportional + lengths to the corolla. The anthers sometimes differ much in size in the + two forms. Owing to the rotation of the filaments, the anthers, when + mature, dehisce towards the circumference of the flower in one form of + Faramea, and towards the centre in the other form. The pollen-grains + sometimes differ conspicuously in colour, and often to an extraordinary + degree in diameter. They differ also somewhat in shape, and apparently in + their contents, as they are unequally opaque. In the short-styled form of + Faramea the pollen-grains are covered with sharp points, so as to cohere + readily together or to an insect; whilst the smaller grains of the + long-styled form are quite smooth. + </p> + <p> + With respect to the pistil, the style may be almost thrice as long in the + one form as in the other. In Oxalis it sometimes differs in hairiness in + the three forms. In Linum the pistils either diverge and pass out between + the filaments, or stand nearly upright and parallel to them. The stigmas + in the two forms often differ much in size and shape, and more especially + in the length and thickness of their papillae; so that the surface may be + rough or quite smooth. Owing to the rotation of the styles, the papillose + surface of the stigma is turned outwards in one form of Linum perenne, and + inwards in the other form. In flowers of the same age of Primula veris the + ovules are larger in the long-styled than in the short-styled form. The + seeds produced by the two or three forms often differ in number, and + sometimes in size and weight; thus, five seeds from the long-styled form + of Lythrum salicaria equal in weight six from the mid-styled and seven + from the short-styled form. Lastly, short-styled plants of Pulmonaria + officinalis bear a larger number of flowers, and these set a larger + proportional number of fruit, which however yield a lower average number + of seed, than the long-styled plants. With heterostyled plants we thus see + in how many and in what important characters the forms of the same + undoubted species often differ from one another—characters which + with ordinary plants would be amply sufficient to distinguish species of + the same genus. + </p> + <p> + As the pollen-grains of ordinary species belonging to the same genus + generally resemble one another closely in all respects, it is worth while + to show, in Table 6.34, the difference in diameter between the grains from + the two or three forms of the same heterostyled species in the forty-three + cases in which this was ascertained. But it should be observed that some + of the following measurements are only approximately accurate, as only a + few grains were measured. In several cases, also, the grains had been + dried and were then soaked in water. Whenever they were of an elongated + shape their longer diameters were measured. The grains from the + short-styled plants are invariably larger than those from the long-styled, + whenever there is any difference between them. The diameter of the former + is represented in the table by the number 100. + </p> + <p> + TABLE 6.34. Relative diameter of the pollen-grains from the forms of the + same heterostyled species; those from the short-styled form being + represented by 100. + </p> + <h3> + DIMORPHIC SPECIES. + </h3> + <p> + Column 1: Name of species. Column 2: From the long-styled form : relative + diameter. + </p> + <p> + Primula veris : 67. + </p> + <p> + Primula vulgaris : 71. + </p> + <p> + Primula Sinensis (Hildebrand) : 57. + </p> + <p> + Primula auricula : 71. + </p> + <p> + Hottonia palustris (H. Muller) : 61. + </p> + <p> + Hottonia palustris (self) : 64. + </p> + <p> + Linum grandiflorum : 100. + </p> + <p> + Linum perenne (diameter variable) : 100 (?). + </p> + <p> + Linum flavum : 100. + </p> + <p> + Pulmonaria officinalis : 78. + </p> + <p> + Pulmonaria angustifolia : 91. + </p> + <p> + Polygonum fagopyrum : 82. + </p> + <p> + Leucosmia Burnettiana : 99. + </p> + <p> + Aegiphila elata : 62. + </p> + <p> + Menyanthes trifoliata : 84. + </p> + <p> + Limnanthemum Indicum : 100. + </p> + <p> + Villarsia (sp.?) : 75. + </p> + <p> + Forsythia suspensa : 94. + </p> + <p> + Cordia (sp.?) : 100. + </p> + <p> + Gilia pulchella : 100. + </p> + <p> + Gilia micrantha : 81. + </p> + <p> + Sethia acuminata : 83. + </p> + <p> + Erythroxylum (sp.?) : 93. + </p> + <p> + Cratoxylon formosum : 86. + </p> + <p> + Mitchella repens, pollen-grains of the long-styled a little smaller. + </p> + <p> + Borreria (sp.?) : 92. + </p> + <p> + Faramea (sp.?) : 67. + </p> + <p> + Suteria (sp.?) (Fritz Muller) : 75. + </p> + <p> + Houstonia coerulea : 72. + </p> + <p> + Oldenlandia (sp.?) : 78. + </p> + <p> + Hedyotis (sp.?) : 88. + </p> + <p> + Coccocypselum (sp.?) (Fritz Muller) : 100. + </p> + <p> + Lipostoma (sp.?) : 80. + </p> + <p> + Cinchona micrantha : 91. + </p> + <h3> + TRIMORPHIC SPECIES. + </h3> + <p> + Column 1: Name of species. Column 2: Ratio expressing the extreme + differences in diameter of the pollen- grains from the two sets of anthers + in the three forms. + </p> + <p> + Lythrum salicaria : 60. + </p> + <p> + Nesaea verticillata : 65. + </p> + <p> + Oxalis Valdiviana (Hildebrand) : 71. + </p> + <p> + Oxalis Regnelli : 78. + </p> + <p> + Oxalis speciosa : 69. + </p> + <p> + Oxalis sensitiva : 84. + </p> + <p> + Pontederia (sp.?) : 55. + </p> + <p> + Column 1: Name of species. Column 2: Ratio between the diameters of the + pollen-grains of the two sets of anthers in the same form. + </p> + <p> + Oxalis rosea, long-styled form (Hildebrand) : 83. + </p> + <p> + Oxalis compressa, short-styled form : 83. + </p> + <p> + Pontederia (sp.?) short-styled form : 87. + </p> + <p> + Pontederia other sp. mid-styled form : 86. + </p> + <p> + We here see that, with seven or eight exceptions out of the forty-three + cases, the pollen-grains from one form are larger than those from the + other form of the same species. The extreme difference is as 100 to 55; + and we should bear in mind that in the case of spheres differing to this + degree in diameter, their contents differ in the ratio of six to one. With + all the species in which the grains differ in diameter, there is no + exception to the rule that those from the anthers of the short-styled + form, the tubes of which have to penetrate the longer pistil of the + long-styled form, are larger than the grains from the other form. This + curious relation led Delpino (as it formerly did me) to believe that the + larger size of the grains in the short-styled flowers is connected with + the greater supply of matter needed for the development of their longer + tubes. (6/2. ‘Sull’ Opera, la Distribuzione dei Sessi nelle Piante’ etc + 1867 page 17.) But the case of Linum, in which the grains of the two forms + are of equal size, whilst the pistil of the one is about twice as long as + that of the other, made me from the first feel very doubtful with respect + to this view. My doubts have since been strengthened by the cases of + Limnanthemum and Coccocypselum, in which the grains are of equal size in + the two forms; whilst in the former genus the pistil is nearly thrice and + in the latter twice as long as in the other form. In those species in + which the grains are of unequal size in the two forms, there is no close + relationship between the degree of their inequality and that of their + pistils. Thus in Pulmonaria officinalis and in Erythroxylum the pistil in + the long-styled form is about twice the length of that in the other form, + whilst in the former species the pollen-grains are as 100 to 78, and in + the latter as 100 to 93 in diameter. In the two forms of Suteria the + pistil differs but little in length, whilst the pollen-grains are as 100 + to 75 in diameter. These cases seem to prove that the difference in size + between the grains in the two forms is not determined by the length of the + pistil, down which the tubes have to grow. That with plants in general + there is no close relationship between the size of the pollen-grains and + the length of the pistil is manifest: for instance, I found that the + distended grains of Datura arborea were .00243 of an inch in diameter, and + the pistil no less than 9.25 inches in length; now the pistil in the small + flowers of Polygonum fagopyrum is very short, yet the larger pollen-grains + from the short-styled plants had exactly the same diameter as those from + the Datura, with its enormously elongated pistil. + </p> + <p> + Notwithstanding these several considerations, it is difficult quite to + give up the belief that the pollen-grains from the longer stamens of + heterostyled plants have become larger in order to allow of the + development of longer tubes; and the foregoing opposing facts may possibly + be reconciled in the following manner. The tubes are at first developed + from matter contained within the grains, for they are sometimes exserted + to a considerable length, before the grains have touched the stigma; but + botanists believe that they afterwards draw nourishment from the + conducting tissue of the pistil. It is hardly possible to doubt that this + must occur in such cases as that of the Datura, in which the tubes have to + grow down the whole length of the pistil, and therefore to a length + equalling 3,806 times the diameter of the grains (namely, .00243 of an + inch) from which they are protruded. I may here remark that I have seen + the pollen-grains of a willow, immersed in a very weak solution of honey, + protrude their tubes, in the course of twelve hours, to a length thirteen + times as great as the diameter of the grains. Now if we suppose that the + tubes in some heterostyled species are developed wholly or almost wholly + from matter contained within the grains, while in other species from + matter yielded by the pistil, we can see that in the former case it would + be necessary that the grains of the two forms should differ in size + relatively to the length of the pistil which the tubes have to penetrate, + but that in the latter case it would not be necessary that the grains + should thus differ. Whether this explanation can be considered + satisfactory must remain at present doubtful. + </p> + <p> + There is another remarkable difference between the forms of several + heterostyled species, namely in the anthers of the short-styled flowers, + which contain the larger pollen-grains, being longer than those of the + long-styled flowers. This is the case with Hottonia palustris in the ratio + of 100 to 83. With Limnanthemum Indicum the ratio is as 100 to 70. With + the allied Menyanthes the anthers of the short-styled form are a little + and with Villarsia conspicuously larger than those of the long-styled. + With Pulmonaria angustifolia they vary much in size, but from an average + of seven measurements of each kind the ratio is as 100 to 91. In six + genera of the Rubiaceae there is a similar difference, either slightly or + well marked. Lastly, in the trimorphic Pontederia the ratio is 100 to 88; + the anthers from the longest stamens in the short-styled form being + compared with those from the shortest stamens in the long-styled form. On + the other hand, there is a similar and well-marked difference in the + length of the stamens in the two forms of Forsythia suspensa and of Linum + flavum; but in these two cases the anthers of the short-styled flowers are + shorter than those of the long-styled. The relative size of the anthers + was not particularly attended to in the two forms of the other + heterostyled plants, but I believe that they are generally equal, as is + certainly the case with those of the common primrose and cowslip. + </p> + <p> + The pistil differs in length in the two forms of every heterostyled plant, + and although a similar difference is very general with the stamens, yet in + the two forms of Linum grandiflorum and of Cordia they are equal. There + can hardly be a doubt that the relative length of these organs is an + adaptation for the safe transportal by insects of the pollen from the one + form to the other. The exceptional cases in which these organs do not + stand exactly on a level in the two forms may probably be explained by the + manner in which the flowers are visited. With most of the species, if + there is any difference in the size of the stigma of the two forms, that + of the long-styled, whatever its shape may be, is larger than that of the + short-styled. But here again there are some exceptions to the rule, for in + the short-styled form of Leucosmia Burnettiana the stigmas are longer and + much narrower than those of the long-styled; the ratio between the lengths + of the stigmas in the two forms being 100 to 60. In the three Rubiaceous + genera, Faramea, Houstonia and Oldenlandia, the stigmas of the short- + styled form are likewise somewhat longer and narrower; and in the three + forms of Oxalis sensitiva the difference is strongly marked, for if the + length of the two stigmas of the long-styled pistil be taken as 100, it + will be represented in the mid- and short-styled forms by the numbers 141 + and 164. As in all these cases the stigmas of the short-styled pistil are + seated low down within a more or less tubular corolla, it is probable that + they are better fitted by being long and narrow for brushing the pollen + off the inserted proboscis of an insect. + </p> + <p> + With many heterostyled plants the stigma differs in roughness in the two + forms, and when this is the case there is no known exception to the rule + that the papillae on the stigma of the long-styled form are longer and + often thicker than those on that of the short-styled. For instance, the + papillae on the long-styled stigma of Hottonia palustris are more than + twice the length of those in the other form. This holds good even in the + case of Houstonia coerulea, in which the stigmas are much shorter and + stouter in the long-styled than in the short-styled form, for the papillae + on the former compared with those on the latter are as 100 to 58 in + length. The length of the pistil in the long-styled form of Linum + grandiflorum varies much, and the stigmatic papillae vary in a + corresponding manner. From this fact I inferred at first that in all cases + the difference in length between the stigmatic papillae in the two forms + was one merely of correlated growth; but this can hardly be the true or + general explanation, as the shorter stigmas of the long-styled form of + Houstonia have the longer papillae. It is a more probable view that the + papillae, which render the stigma of the long-styled form of various + species rough, serve to entangle effectually the large-sized pollen-grains + brought by insects from the short-styled form, thus ensuring its + legitimate fertilisation. This view is supported by the fact that the + pollen-grains from the two forms of eight species in Table 6.34 hardly + differ in diameter, and the papillae on their stigmas do not differ in + length. + </p> + <p> + The species which are at present positively or almost positively known to + be heterostyled belong, as shown in Table 6.35, to 38 genera, widely + distributed throughout the world. These genera are included in fourteen + Families, most of which are very distinct from one another, for they + belong to nine of the several great Series, into which phanerogamic plants + have been divided by Bentham and Hooker. + </p> + <p> + TABLE 6.35. List of genera including heterostyled species. + </p> + <h3> + DICOTYLEDONS. + </h3> + <p> + HYPERICINEAE: Cratoxylon. + </p> + <p> + ERYTHROXYLEAE: Erythroxylum. Sethia. + </p> + <p> + GERANIACEAE: Linum. Oxalis. + </p> + <p> + LYTHRACEAE: Lythrum. Neseae. + </p> + <p> + RUBIACEAE: Cinchona. Bouvardia. Manettia. Hedyotis. Oldenlandia. + Houstonia. Coccocypselum. Lipostoma. Knoxia. Faramea. Psychotria. Rudgea. + Suteria. Mitchella. Diodia. Borreria. Spermacoce. + </p> + <p> + PRIMULACEAE: Primula. Hottonia. Androsace. + </p> + <p> + OLEACEAE: Forsythia. + </p> + <p> + GENTIANACEAE: Menyanthes. Limnanthemum. Villarsia. + </p> + <p> + POLEMONIACEAE: Gilia. + </p> + <p> + CORDIEAE: Cordia. + </p> + <p> + BORAGINEAE: Pulmonaria. + </p> + <p> + VERBENACEAE: Aegiphila. + </p> + <p> + POLYGONEAE: Polygonum. + </p> + <p> + THYMELEAE: Thymelea. + </p> + <h3> + MONOCOTYLEDONS. + </h3> + <p> + PONTEDERIACEAE: Pontederia. + </p> + <p> + In some of these families the heterostyled condition must have been + acquired at a very remote period. Thus the three closely allied genera, + Menyanthes, Limnanthemum, and Villarsia, inhabit respectively Europe, + India, and South America. Heterostyled species of Hedyotis are found in + the temperate regions of North and the tropical regions of South America. + Trimorphic species of Oxalis live on both sides of the Cordillera in South + America and at the Cape of Good Hope. In these and some other cases it is + not probable that each species acquired its heterostyled structure + independently of its close allies. If they did not do so, the three + closely connected genera of the Menyantheae and the several trimorphic + species of Oxalis must have inherited their structure from a common + progenitor. But an immense lapse of time will have been necessary in all + such cases for the modified descendants of a common progenitor to have + spread from a single centre to such widely remote and separated areas. The + family of the Rubiaceae contains not far short of as many heterostyled + genera as all the other thirteen families together; and hereafter no doubt + other Rubiaceous genera will be found to be heterostyled, although a large + majority are homostyled. Several closely allied genera in this family + probably owe their heterostyled structure to descent in common; but as the + genera thus characterised are distributed in no less than eight of the + tribes into which this family has been divided by Bentham and Hooker, it + is almost certain that several of them must have become heterostyled + independently of one another. What there is in the constitution or + structure of the members of this family which favours their becoming + heterostyled, I cannot conjecture. Some families of considerable size, + such as the Boragineae and Verbenaceae, include, as far as is at present + known, only a single heterostyled genus. Polygonum also is the sole + heterostyled genus in its family; and though it is a very large genus, no + other species except P. fagopyrum is thus characterised. We may suspect + that it has become heterostyled within a comparatively recent period, as + it seems to be less strongly so in function than the species in any other + genus, for both forms are capable of yielding a considerable number of + spontaneously self-fertilised seeds. Polygonum in possessing only a single + heterostyled species is an extreme case; but every other genus of + considerable size which includes some such species likewise contains + homostyled species. Lythrum includes trimorphic, dimorphic, and homostyled + species. + </p> + <p> + Trees, bushes, and herbaceous plants, both large and small, bearing single + flowers or flowers in dense spikes or heads, have been rendered + heterostyled. So have plants which inhabit alpine and lowland sites, dry + land, marshes and water. (6/3. Out of the 38 genera known to include + heterostyled species, about eight, or 21 per cent, are more or less + aquatic in their habits. I was at first struck with this fact, for I was + not then aware how large a proportion of ordinary plants inhabit such + stations. Heterostyled plants may be said in one sense to have their sexes + separated, as the forms must mutually fertilise one another. Therefore it + seemed worth while to ascertain what proportion of the genera in the + Linnean classes, Monoecia, Dioecia and Polygamia, contained species which + live “in water, marshes, bogs or watery places.” In Sir W.J. Hooker’s + ‘British Flora’ 4th edition 1838, these three Linnean classes include 40 + genera, 17 of which (i.e. 43 per cent) contain species inhabiting the + just-specified stations. So that 43 per cent of those British plants which + have their sexes separated are more or less aquatic in their habits, + whereas only 21 per cent of heterostyled plants have such habits. I may + add that the hermaphrodite classes, from Monandria to Gynandria inclusive, + contain 447 genera, of which 113 are aquatic in the above sense, or only + 25 per cent. It thus appears, as far as can be judged from such imperfect + data, that there is some connection between the separation of the sexes in + plants and the watery nature of the sites which they inhabit; but that + this does not hold good with heterostyled species.) + </p> + <p> + When I first began to experimentise on heterostyled plants it was under + the impression that they were tending to become dioecious; but I was soon + forced to relinquish this notion, as the long-styled plants of Primula + which, from possessing a longer pistil, larger stigma, shorter stamens + with smaller pollen- grains, seemed to be the more feminine of the two + forms, yielded fewer seeds than the short-styled plants which appeared to + be in the above respects the more masculine of the two. Moreover, + trimorphic plants evidently come under the same category with dimorphic, + and the former cannot be looked at as tending to become dioecious. With + Lythrum salicaria, however, we have the curious and unique case of the + mid-styled form being more feminine or less masculine in nature than the + other two forms. This is shown by the large number of seeds which it + yields in whatever manner it may be fertilised, and by its pollen (the + grains of which are of smaller size than those from the corresponding + stamens in the other two forms) when applied to the stigma of any form + producing fewer seeds than the normal number. If we suppose the process of + deterioration of the male organs in the mid-styled form to continue, the + final result would be the production of a female plant; and Lythrum + salicaria would then consist of two heterostyled hermaphrodites and a + female. No such case is known to exist, but it is a possible one, as + hermaphrodite and female forms of the same species are by no means rare. + Although there is no reason to believe that heterostyled plants are + regularly becoming dioecious, yet they offer singular facilities, as will + hereafter be shown, for such conversion; and this appears occasionally to + have been effected. + </p> + <p> + We may feel sure that plants have been rendered heterostyled to ensure + cross- fertilisation, for we now know that a cross between the distinct + individuals of the same species is highly important for the vigour and + fertility of the offspring. The same end is gained by dichogamy or the + maturation of the reproductive elements of the same flower at different + periods,—by dioeciousness—self-sterility—the prepotency + of pollen from another individual over a plant’s own pollen,—and + lastly, by the structure of the flower in relation to the visits of + insects. The wonderful diversity of the means for gaining the same end in + this case, and in many others, depends on the nature of all the previous + changes through which the species has passed, and on the more or less + complete inheritance of the successive adaptations of each part to the + surrounding conditions. Plants which are already well adapted by the + structure of their flowers for cross-fertilisation by the aid of insects + often possess an irregular corolla, which has been modelled in relation to + their visits; and it would have been of little or no use to such plants to + have become heterostyled. We can thus understand why it is that not a + single species is heterostyled in such great families as the Leguminosae, + Labiatae, Scrophulariaceae, Orchideae, etc., all of which have irregular + flowers. Every known heterostyled plant, however, depends on insects for + its fertilisation, and not on the wind; so that it is a rather surprising + fact that only one genus, Pontederia, has a plainly irregular corolla. + </p> + <p> + Why some species are adapted for cross-fertilisation, whilst others within + the same genus are not so, or if they once were, have since lost such + adaptation and in consequence are now usually self-fertilised, I have + endeavoured elsewhere to explain to a certain limited extent. (6/4. ‘The + Effects of Cross and Self- fertilisation’ 1876 page 441.) If it be further + asked why some species have been adapted for this end by being made + heterostyled, rather than by any of the above specified means, the answer + probably lies in the manner in which heterostylism originated,—a + subject immediately to be discussed. Heterostyled species, however, have + an advantage over dichogamous species, as all the flowers on the same + heterostyled plant belong to the same form, so that when fertilised + legitimately by insects two distinct individuals are sure to intercross. + On the other hand, with dichogamous plants, early or late flowers on the + same individual may intercross; and a cross of this kind does hardly any + or no good. Whenever it is profitable to a species to produce a large + number of seeds and this obviously is a very common case, heterostyled + will have an advantage over dioecious plants, as all the individuals of + the former, whilst only half of the latter, that is the females, yield + seeds. On the other hand, heterostyled plants seem to have no advantage, + as far as cross-fertilisation is concerned, over those which are sterile + with their own pollen. They lie indeed under a slight disadvantage, for if + two self-sterile plants grow near together and far removed from all other + plants of the same species, they will mutually and perfectly fertilise one + another, whilst this will not be the case with heterostyled dimorphic + plants, unless they chance to belong to opposite forms. + </p> + <p> + It may be added that species which are trimorphic have one slight + advantage over the dimorphic; for if only two individuals of a dimorphic + species happen to grow near together in an isolated spot, the chances are + even that both will belong to the same form, and in this case they will + not produce the full number of vigorous and fertile seedlings; all these, + moreover, will tend strongly to belong to the same form as their parents. + On the other hand, if two plants of the same trimorphic species happen to + grow in an isolated spot, the chances are two to one in favour of their + not belonging to the same form; and in this case they will legitimately + fertilise one another, and yield the full complement of vigorous + offspring. + </p> + <h3> + THE MEANS BY WHICH PLANTS MAY HAVE BEEN RENDERED HETEROSTYLED. + </h3> + <p> + This is a very obscure subject, on which I can throw little light, but + which is worthy of discussion. It has been shown that heterostyled plants + occur in fourteen natural families, dispersed throughout the whole + vegetable kingdom, and that even within the family of the Rubiaceae they + are dispersed in eight of the tribes. We may therefore conclude that this + structure has been acquired by various plants independently of inheritance + from a common progenitor, and that it can be acquired without any great + difficulty—that is, without any very unusual combination of + circumstances. + </p> + <p> + It is probable that the first step towards a species becoming heterostyled + is great variability in the length of the pistil and stamens, or of the + pistil alone. Such variations are not very rare: with Amsinckia + spectabilis and Nolana prostrata these organs differ so much in length in + different individuals that, until experimenting on them, I thought both + species heterostyled. The stigma of Gesneria pendulina sometimes protrudes + far beyond, and is sometimes seated beneath the anthers; so it is with + Oxalis acetosella and various other plants. I have also noticed an + extraordinary amount of difference in the length of the pistil in + cultivated varieties of Primula veris and vulgaris. + </p> + <p> + As most plants are at least occasionally cross-fertilised by the aid of + insects, we may assume that this was the case with our supposed varying + plant; but that it would have been beneficial to it to have been more + regularly cross- fertilised. We should bear in mind how important an + advantage it has been proved to be to many plants, though in different + degrees and ways, to be cross- fertilised. It might well happen that our + supposed species did not vary in function in the right manner, so as to + become either dichogamous or completely self-sterile, or in structure so + as to ensure cross-fertilisation. If it had thus varied, it would never + have been rendered heterostyled, as this state would then have been + superfluous. But the parent-species of our several existing heterostyled + plants may have been, and probably were (judging from their present + constitution) in some degree self-sterile; and this would have made + regular cross-fertilisation still more desirable. + </p> + <p> + Now let us take a highly varying species with most or all of the anthers + exserted in some individuals, and in others seated low down in the + corolla; with the stigma also varying in position in like manner. Insects + which visited such flowers would have different parts of their bodies + dusted with pollen, and it would be a mere chance whether this were left + on the stigma of the next flower which was visited. If all the anthers + could have been placed on the same level in all the plants, then abundant + pollen would have adhered to the same part of the body of the insects + which frequented the flowers, and would afterwards have been deposited + without loss on the stigma, if it likewise stood on the same unvarying + level in all the flowers. But as the stamens and pistils are supposed to + have already varied much in length and to be still varying, it might well + happen that they could be reduced much more easily through natural + selection into two sets of different lengths in different individuals, + than all to the same length and level in all the individuals. We know from + innumerable instances, in which the two sexes and the young of the same + species differ, that there is no difficulty in two or more sets of + individuals being formed which inherit different characters. In our + particular case the law of compensation or balancement (which is admitted + by many botanists) would tend to cause the pistil to be reduced in those + individuals in which the stamens were greatly developed, and to be + increased in length in those which had their stamens but little developed. + </p> + <p> + Now if in our varying species the longer stamens were to be nearly + equalised in length in a considerable body of individuals, with the pistil + more or less reduced; and in another body, the shorter stamens to be + similarly equalised, with the pistil more or less increased in length, + cross-fertilisation would be secured with little loss of pollen; and this + change would be so highly beneficial to the species, that there is no + difficulty in believing that it could be effected through natural + selection. Our plant would then make a close approach in structure to a + heterostyled dimorphic species; or to a trimorphic species, if the stamens + were reduced to two lengths in the same flower in correspondence with that + of the pistils in the other two forms. But we have not as yet even touched + on the chief difficulty in understanding how heterostyled species could + have originated. A completely self-sterile plant or a dichogamous one can + fertilise and be fertilised by any other individual of the same species; + whereas the essential character of a heterostyled plant is that an + individual of one form cannot fully fertilise or be fertilised by an + individual of the same form, but only by one belonging to another form. + </p> + <p> + H. Muller has suggested that ordinary or homostyled plants may have been + rendered heterostyled merely through the effects of habit. (6/5. ‘Die + Befruchtung der Blumen’ page 352.) Whenever pollen from one set of anthers + is habitually applied to a pistil of particular length in a varying + species, he believes that at last the possibility of fertilisation in any + other manner will be nearly or completely lost. He was led to this view by + observing that Diptera frequently carried pollen from the long-styled + flowers of Hottonia to the stigma of the same form, and that this + illegitimate union was not nearly so sterile as the corresponding union in + other heterostyled species. But this conclusion is directly opposed by + some other cases, for instance by that of Linum grandiflorum; for here the + long-styled form is utterly barren with its own-form pollen, although from + the position of the anthers this pollen is invariably applied to the + stigma. It is obvious that with heterostyled dimorphic plants the two + female and the two male organs differ in power; for if the same kind of + pollen be placed on the stigmas of the two forms, and again if the two + kinds of pollen be placed on the stigmas of the same form, the results are + in each case widely different. Nor can we see how this differentiation of + the two female and two male organs could have been effected merely through + each kind of pollen being habitually placed on one of the two stigmas. + </p> + <p> + Another view seems at first sight probable, namely, that an incapacity to + be fertilised in certain ways has been specially acquired by heterostyled + plants. We may suppose that our varying species was somewhat sterile (as + is often the case) with pollen from its own stamens, whether these were + long or short; and that such sterility was transferred to all the + individuals with pistils and stamens of the same length, so that these + became incapable of intercrossing freely; but that such sterility was + eliminated in the case of the individuals which differed in the length of + their pistils and stamens. It is, however, incredible that so peculiar a + form of mutual infertility should have been specially acquired unless it + were highly beneficial to the species; and although it may be beneficial + to an individual plant to be sterile with its own pollen, + cross-fertilisation being thus ensured, how can it be any advantage to a + plant to be sterile with half its brethren, that is, with all the + individuals belonging to the same form? Moreover, if the sterility of the + unions between plants of the same form had been a special acquirement, we + might have expected that the long-styled form fertilised by the + long-styled would have been sterile in the same degree as the short-styled + fertilised by the short-styled; but this is hardly ever the case. On the + contrary, there is sometimes the widest difference in this respect, as + between the two illegitimate unions of Pulmonaria angustifolia and of + Hottonia palustris. + </p> + <p> + It is a more probable view that the male and female organs in two sets of + individuals have been by some means specially adapted for reciprocal + action; and that the sterility between the individuals of the same set or + form is an incidental and purposeless result. The meaning of the term + “incidental” may be illustrated by the greater or less difficulty in + grafting or budding together two plants belonging to distinct species; for + as this capacity is quite immaterial to the welfare of either, it cannot + have been specially acquired, and must be the incidental result of + differences in their vegetative systems. But how the sexual elements of + heterostyled plants came to differ from what they were whilst the species + was homostyled, and how they became co-adapted in two sets of individuals, + are very obscure points. We know that in the two forms of our existing + heterostyled plants the pistil always differs, and the stamens generally + differ in length; so does the stigma in structure, the anthers in size, + and the pollen-grains in diameter. It appears, therefore, at first sight + probable that organs which differ in such important respects could act on + one another only in some manner for which they had been specially adapted. + The probability of this view is supported by the curious rule that the + greater the difference in length between the pistils and stamens of the + trimorphic species of Lythrum and Oxalis, the products of which are united + for reproduction, by so much the greater is the infertility of the union. + The same rule applies to the two illegitimate unions of some dimorphic + species, namely, Primula vulgaris and Pulmonaria angustifolia; but it + entirely fails in other cases, as with Hottonia palustris and Linum + grandiflorum. We shall, however, best perceive the difficulty of + understanding the nature and origin of the co-adaptation between the + reproductive organs of the two forms of heterostyled plants, by + considering the case of Linum grandiflorum: the two forms of this plant + differ exclusively, as far as we can see, in the length of their pistils; + in the long-styled form, the stamens equal the pistil in length, but their + pollen has no more effect on it than so much inorganic dust; whilst this + pollen fully fertilises the short pistil of the other form. Now, it is + scarcely credible that a mere difference in the length of the pistil can + make a wide difference in its capacity for being fertilised. We can + believe this the less because with some plants, for instance, Amsinckia + spectabilis, the pistil varies greatly in length without affecting the + fertility of the individuals which are intercrossed. So again I observed + that the same plants of Primula veris and vulgaris differed to an + extraordinary degree in the length of their pistils during successive + seasons; nevertheless they yielded during these seasons exactly the same + average number of seeds when left to fertilise themselves spontaneously + under a net. + </p> + <p> + We must therefore look to the appearance of inner or hidden constitutional + differences between the individuals of a varying species, of such a nature + that the male element of one set is enabled to act efficiently only on the + female element of another set. We need not doubt about the possibility of + variations in the constitution of the reproductive system of a plant, for + we know that some species vary so as to be completely self-sterile or + completely self-fertile, either in an apparently spontaneous manner or + from slightly changed conditions of life. Gartner also has shown that the + individual plants of the same species vary in their sexual powers in such + a manner that one will unite with a distinct species much more readily + than another. (6/6. Gartner ‘Bastarderzeugung im Pflanzenreich’ 1849 page + 165.) But what the nature of the inner constitutional differences may be + between the sets or forms of the same varying species, or between distinct + species, is quite unknown. It seems therefore probable that the species + which have become heterostyled at first varied so that two or three sets + of individuals were formed differing in the length of their pistils and + stamens and in other co-adapted characters, and that almost simultaneously + their reproductive powers became modified in such a manner that the sexual + elements in one set were adapted to act on the sexual elements of another + set; and consequently that these elements in the same set or form + incidentally became ill-adapted for mutual interaction, as in the case of + distinct species. I have elsewhere shown that the sterility of species + when first crossed and of their hybrid offspring must also be looked at as + merely an incidental result, following from the special co-adaptation of + the sexual elements of the same species. (6/7. ‘Origin of Species’ 6th + edition page 247; ‘Variation of Animals and Plants under Domestication’ + 2nd edition volume 2 page 169; ‘The Effects of Cross and + Self-fertilisation’ page 463. It may be well here to remark that, judging + from the remarkable power with which abruptly changed conditions of life + act on the reproductive system of most organisms, it is probable that the + close adaptation of the male to the female elements in the two forms of + the same heterostyled species, or in all the individuals of the same + ordinary species, could be acquired only under long-continued nearly + uniform conditions of life.) We can thus understand the striking + parallelism, which has been shown to exist between the effects of + illegitimately uniting heterostyled plants and of crossing distinct + species. The great difference in the degree of sterility between the + various heterostyled species when illegitimately fertilised, and between + the two forms of the same species when similarly fertilised, harmonises + well with the view that the result is an incidental one which follows from + changes gradually effected in their reproductive systems, in order that + the sexual elements of the distinct forms should act perfectly on one + another. + </p> + <h3> + TRANSMISSION OF THE TWO FORMS BY HETEROSTYLED PLANTS. + </h3> + <p> + The transmission of the two forms by heterostyled plants, with respect to + which many facts were given in the last chapter, may perhaps be found + hereafter to throw some light on their manner of development. Hildebrand + observed that seedlings from the long-styled form of Primula Sinensis when + fertilised with pollen from the same form were mostly long-styled, and + many analogous cases have since been observed by me. All the known cases + are given in Tables 6.36 and 6.37. + </p> + <p> + TABLE 6.36. Nature of the offspring from illegitimately fertilised + dimorphic plants. + </p> + <p> + Column 1: Species and form. Column 2: Number of long-styled offspring. + Column 3: Number of short-styled offspring. + </p> + <p> + Primula veris. Long-styled form, fertilised by own-form pollen during five + successive generations : 156 : 6. + </p> + <p> + Primula veris. Short-styled form, fertilised by own-form pollen : 5 : 9. + </p> + <p> + Primula vulgaris. Long-styled form, fertilised by own-form pollen during + two successive generations : 69 : 0. + </p> + <p> + Primula auricula. Short-styled form, fertilised by own-form pollen, is + said to produce during successive generations offspring in about the + following proportions : 25 : 75. + </p> + <p> + Primula Sinensis. Long-styled form, fertilised by own-form pollen during + two successive generations : 52 : 0. + </p> + <p> + Primula Sinensis. Long-styled form, fertilised by own-form pollen + (Hildebrand) : 14 : 3. + </p> + <p> + Primula Sinensis. Short-styled form, fertilised by own-form pollen: 1 : + 24. + </p> + <p> + Pulmonaria officinalis. Long-styled form, fertilised by own-form pollen : + 11 : 0. + </p> + <p> + Polygonum fagopyrum. Long-styled form, fertilised by own-form pollen : 45 + : 4. + </p> + <p> + Polygonum fagopyrum. Short-styled form, fertilised by own-form pollen : 13 + : 20. + </p> + <p> + TABLE 6.37. Nature of the offspring from illegitimately fertilised + trimorphic plants. + </p> + <p> + Column 1: Species and form. Column 2: Number of long-styled offspring. + Column 3: Number of mid-styled offspring. Column 4: Number of short-styled + offspring. + </p> + <p> + Lythrum salicaria. Long-styled form, fertilised by own-form pollen : 56 : + 0 : 0. + </p> + <p> + Lythrum salicaria. Short-styled form, fertilised by own-form pollen : 1 : + 0 : 8. + </p> + <p> + Lythrum salicaria. Short-styled form, fertilised by pollen from mid-length + stamens of long-styled form : 4 : 0 : 8. + </p> + <p> + Lythrum salicaria. Mid-styled form, fertilised by own-form pollen : 1 : 3 + : 0. + </p> + <p> + Lythrum salicaria. Mid-styled form, fertilised by pollen from shortest + stamens of long-styled form : 17 : 8 : 0. + </p> + <p> + Lythrum salicaria. Mid-styled form, fertilised by pollen from longest + stamens of short-styled form : 14 : 8 : 18. + </p> + <p> + Oxalis rosea. Long-styled form, fertilised during several generations by + own- form pollen, produced offspring in the ratio of : 100 : 0 : 0. + </p> + <p> + Oxalis hedysaroides. Mid-styled form, fertilised by own-form pollen : 0 : + 17 : 0. + </p> + <p> + We see in these two tables that the offspring from a form illegitimately + fertilised with pollen from another plant of the same form belong, with a + few exceptions, to the same form as their parents. For instance, out of + 162 seedlings from long-styled plants of Primula veris fertilised during + five generations in this manner, 156 were long-styled and only 6 + short-styled. Of 69 seedlings from P. vulgaris similarly raised all were + long-styled. So it was with 56 seedlings from the long-styled form of the + trimorphic Lythrum salicaria, and with numerous seedlings from the + long-styled form of Oxalis rosea. The offspring from the short-styled + forms of dimorphic plants, and from both the mid-styled and short-styled + forms of trimorphic plants, fertilised with their own-form pollen, + likewise tend to belong to the same form as their parents, but not in so + marked a manner as in the case of the long-styled form. There are three + cases in Table 6.37, in which a form of Lythrum was fertilised + illegitimately with pollen from another form; and in two of these cases + all the offspring belonged to the same two forms as their parents, whilst + in the third case they belonged to all three forms. + </p> + <p> + The cases hitherto given relate to illegitimate unions, but Hildebrand, + Fritz Muller, and myself found that a very large proportion, or all of the + offspring, from a legitimate union between any two forms of the trimorphic + species of Oxalis belonged to the same two forms. A similar rule therefore + holds good with unions which are fully fertile, as with those of an + illegitimate nature which are more or less sterile. When some of the + seedlings from a heterostyled plant belong to a different form from that + of its parents, Hildebrand accounts for the fact by reversion. For + instance, the long-styled parent-plant of Primula veris, from which the + 162 illegitimate seedlings in Table 6.36 were derived in the course of + five generations, was itself no doubt derived from the union of a + long-styled and a short-styled parent; and the 6 short-styled seedlings + may be attributed to reversion to their short-styled progenitor. But it is + a surprising fact in this case, and in other similar ones, that the number + of the offspring which thus reverted was not larger. The fact is rendered + still more strange in the particular instance of P. veris, for there was + no reversion until four or five generations of long-styled plants had been + raised. It may be seen in both tables that the long-styled form transmits + its form much more faithfully than does the short-styled, when both are + fertilised with their own-form pollen; and why this should be so it is + difficult to conjecture, unless it be that the aboriginal parent-form of + most heterostyled species possessed a pistil which exceeded its own + stamens considerably in length. (6/8. It may be suspected that this was + the case with Primula, judging from the length of the pistil in several + allied genera (see Mr. J. Scott ‘Journal of the Linnean Society Botany’ + volume 8 1864 page 85). Herr Breitenbach found many specimens of Primula + elatior growing in a state of nature with some flowers on the same plant + long-styled, others short-styled and others equal-styled; and the + long-styled form greatly preponderated in number; there being 61 of this + form to 9 of the short-styled and 15 of the equal-styled.) I will only add + that in a state of nature any single plant of a trimorphic species no + doubt produces all three forms; and this may be accounted for either by + its several flowers being separately fertilised by both the other forms, + as Hildebrand supposes; or by pollen from both the other forms being + deposited by insects on the stigma of the same flower. + </p> + <h3> + EQUAL-STYLED VARIETIES. + </h3> + <p> + The tendency of the dimorphic species of Primula to produce equal-styled + varieties deserves notice. Cases of this kind have been observed, as shown + in the last chapter, in no less than six species, namely, P. veris, + vulgaris, Sinensis, auricula, farinosa, and elatior. In the case of P. + veris, the stamens resemble in length, position and size of their + pollen-grains the stamens of the short-styled form; whilst the pistil + closely resembles that of the long-styled, but as it varies much in + length, one proper to the short-styled form appears to have been elongated + and to have assumed at the same time the functions of a long-styled + pistil. Consequently the flowers are capable of spontaneous self- + fertilisation of a legitimate nature and yield a full complement of seed, + or even more than the number produced by ordinary flowers legitimately + fertilised. With P. Sinensis, on the other hand, the stamens resemble in + all respects the shorter ones proper to the long-styled form, whilst the + pistil makes a near approach to that of the short-styled, but as it varies + in length, it would appear as if a long-styled pistil had been reduced in + length and modified in function. The flowers in this case as in the last + are capable of spontaneous legitimate fertilisation, and are rather more + productive than ordinary flowers legitimately fertilised. With P. auricula + and farinosa the stamens resemble those of the short-styled form in + length, but those of the long-styled in the size of their pollen-grains; + the pistil also resembles that of the long-styled, so that although the + stamens and pistil are of nearly equal length, and consequently pollen is + spontaneously deposited on the stigma, yet the flowers are not + legitimately fertilised and yield only a very moderate supply of seed. We + thus see, firstly, that equal-styled varieties have originated in various + ways, and, secondly, that the combination of the two forms in the same + flower differs in completeness. With P. elatior some of the flowers on the + same plant have become equal-styled, instead of all of them as in the + other species. + </p> + <p> + Mr. Scott has suggested that the equal-styled varieties arise through + reversion to the former homostyled condition of the genus. This view is + supported by the remarkable fidelity with which the equal-styled variation + is transmitted after it has once appeared. I have shown in Chapter 13 of + my ‘Variation of Animals and Plants under Domestication,’ that any cause + which disturbs the constitution tends to induce reversion, and it is + chiefly the cultivated species of Primula which become equal-styled. + Illegitimate fertilisation, which is an abnormal process, is likewise an + exciting cause; and with illegitimately descended long- styled plants of + P. Sinensis, I have observed the first appearance and subsequent stages of + this variation. With some other plants of P. Sinensis of similar parentage + the flowers appeared to have reverted to their original wild condition. + Again, some hybrids between P. veris and vulgaris were strictly + equal-styled, and others made a near approach to this structure. All these + facts support the view that this variation results, at least in part, from + reversion to the original state of the genus, before the species had + become heterostyled. On the other hand, some considerations indicate, as + previously remarked, that the aboriginal parent-form of Primula had a + pistil which exceeded the stamens in length. The fertility of the + equal-styled varieties has been somewhat modified, being sometimes greater + and sometimes less than that of a legitimate union. Another view, however, + may be taken with respect to the origin of the equal- styled varieties, + and their appearance may be compared with that of hermaphrodites amongst + animals which properly have their sexes separated; for the two sexes are + combined in a monstrous hermaphrodite in a somewhat similar manner as the + two sexual forms are combined in the same flower of an equal- styled + variety of a heterostyled species. + </p> + <h3> + FINAL REMARKS. + </h3> + <p> + The existence of plants which have been rendered heterostyled is a highly + remarkable phenomenon, as the two or three forms of the same undoubted + species differ not only in important points of structure, but in the + nature of their reproductive powers. As far as structure is concerned, the + two sexes of many animals and of some plants differ to an extreme degree; + and in both kingdoms the same species may consist of males, females, and + hermaphrodites. Certain hermaphrodite cirripedes are aided in their + reproduction by a whole cluster of what I have called complemental males, + which differ wonderfully from the ordinary hermaphrodite form. With ants + we have males and females, and two or three castes of sterile females or + workers. With Termites there are, as Fritz Muller has shown, both winged + and wingless males and females, besides the workers. But in none of these + cases is there any reason to believe that the several males or several + females of the same species differ in their sexual powers, except in the + atrophied condition of the reproductive organs in the workers of social + insects. Many hermaphrodite animals must unite for reproduction, but the + necessity of such union apparently depends solely on their structure. On + the other hand, with heterostyled dimorphic species there are two females + and two sets of males, and with trimorphic species three females and three + sets of males, which differ essentially in their sexual powers. We shall, + perhaps, best perceive the complex and extraordinary nature of the + marriage arrangements of a trimorphic plant by the following illustration. + Let us suppose that the individuals of the same species of ant always + lived in triple communities; and that in one of these, a large-sized + female (differing also in other characters) lived with six middle-sized + and six small-sized males; in the second community a middle-sized female + lived with six large- and six small-sized males; and in the third, a + small-sized female lived with six large- and six middle-sized males. Each + of these three females, though enabled to unite with any male, would be + nearly sterile with her own two sets of males, and likewise with two other + sets of males of the same size with her own which lived in the other two + communities; but she would be fully fertile when paired with a male of her + own size. Hence the thirty-six males, distributed by half-dozens in the + three communities, would be divided into three sets of a dozen each; and + these sets, as well as the three females, would differ from one another in + their reproductive powers in exactly the same manner as do the distinct + species of the same genus. But it is a still more remarkable fact that + young ants raised from any one of the three female ants, illegitimately + fertilised by a male of a different size would resemble in a whole series + of relations the hybrid offspring from a cross between two distinct + species of ants. They would be dwarfed in stature, and more or less, or + even utterly barren. Naturalists are so much accustomed to behold great + diversities of structure associated with the two sexes, that they feel no + surprise at almost any amount of difference; but differences in sexual + nature have been thought to be the very touchstone of specific + distinction. We now see that such sexual differences—the greater or + less power of fertilising and being fertilised—may characterise the + co-existing individuals of the same species, in the same manner as they + characterise and have kept separate those groups of individuals, produced + during the lapse of ages, which we rank and denominate as distinct + species. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0007" id="link2HCH0007"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VII. POLYGAMOUS, DIOECIOUS, AND GYNO-DIOECIOUS PLANTS. + </h2> +<pre xml:space="preserve"> + The conversion in various ways of hermaphrodite into dioecious plants. + Heterostyled plants rendered dioecious. + Rubiaceae. + Verbenaceae. + Polygamous and sub-dioecious plants. + Euonymus. + Fragaria. + The two sub-forms of both sexes of Rhamnus and Epigaea. + Ilex. + Gyno-dioecious plants. + Thymus, difference in fertility of the hermaphrodite and female individuals. + Satureia. + Manner in which the two forms probably originated. + Scabiosa and other gyno-dioecious plants. + Difference in the size of the corolla in the forms of polygamous, dioecious, and + gyno-dioecious plants. +</pre> + <p> + There are several groups of plants in which all the species are dioecious, + and these exhibit no rudiments in the one sex of the organs proper to the + other. About the origin of such plants nothing is known. It is possible + that they may be descended from ancient lowly organised forms, which had + from the first their sexes separated; so that they have never existed as + hermaphrodites. There are, however, many other groups of species and + single ones, which from being allied on all sides to hermaphrodites, and + from exhibiting in the female flowers plain rudiments of male organs, and + conversely in the male flowers rudiments of female organs, we may feel + sure are descended from plants which formerly had the two sexes combined + in the same flower. It is a curious and obscure problem how and why such + hermaphrodites have been rendered bisexual. + </p> + <p> + If in some individuals of a species the stamens alone were to abort, + females and hermaphrodites would be left existing, of which many instances + occur; and if the female organs of the hermaphrodite were afterwards to + abort, the result would be a dioecious plant. Conversely, if we imagine + the female organs alone to abort in some individuals, males and + hermaphrodites would be left; and the hermaphrodites might afterwards be + converted into females. + </p> + <p> + In other cases, as in that of the common Ash-tree mentioned in the + Introduction, the stamens are rudimentary in some individuals, the pistils + in others, others again remaining as hermaphrodites. Here the modification + of the two sets of organs appears to have occurred simultaneously, as far + as we can judge from their equal state of abortion. If the hermaphrodites + were supplanted by the individuals having separated sexes, and if these + latter were equalised in number, a strictly dioecious species would be + formed. + </p> + <p> + There is much difficulty in understanding why hermaphrodite plants should + ever have been rendered dioecious. There would be no such conversion, + unless pollen was already carried regularly by insects or by the wind from + one individual to the other; for otherwise every step towards + dioeciousness would lead towards sterility. As we must assume that + cross-fertilisation was assured before an hermaphrodite could be changed + into a dioecious plant, we may conclude that the conversion has not been + effected for the sake of gaining the great benefits which follow from + cross-fertilisation. We can, however, see that if a species were subjected + to unfavourable conditions from severe competition with other plants, or + from any other cause, the production of the male and female elements and + the maturation of the ovules by the same individual, might prove too great + a strain on its powers, and the separation of the sexes would then be + highly beneficial. This, however, would be effected only under the + contingency of a reduced number of seeds, produced by the females alone, + being sufficient to keep up the stock. + </p> + <p> + There is another way of looking at the subject which partially removes a + difficulty that appears at first sight insuperable, namely, that during + the conversion of an hermaphrodite into a dioecious plant, the male organs + must abort in some individuals and the female organs in others. Yet as all + are exposed to the same conditions, it might have been expected that those + which varied would tend to vary in the same manner. As a general rule only + a few individuals of a species vary simultaneously in the same manner; and + there is no improbability in the assumption that some few individuals + might produce larger seeds than the average, better stocked with + nourishment. If the production of such seeds were highly beneficial to a + species, and on this head there can be little doubt, the variety with the + large seeds would tend to increase. (7/1. See the facts given in ‘The + Effects of Cross and Self-fertilisation’ page 353.) But in accordance with + the law of compensation we might expect that the individuals which + produced such seeds would, if living under severe conditions, tend to + produce less and less pollen, so that their anthers would be reduced in + size and might ultimately become rudimentary. This view occurred to me + owing to a statement by Sir J.E. Smith that there are female and + hermaphrodite plants of Serratula tinctoria, and that the seeds of the + former are larger than those of the hermaphrodite form. (7/2. + ‘Transactions of the Linnean Society’ volume 8 page 600.) It may also be + worth while to recall the case of the mid-styled form of Lythrum + salicaria, which produces a larger number of seeds than the other forms, + and has somewhat smaller pollen-grains which have less fertilising power + than those of the corresponding stamens in the other two forms; but + whether the larger number of seeds is the indirect cause of the diminished + power of the pollen, or vice versa, I know not. As soon as the anthers in + a certain number of individuals became reduced in size in the manner just + suggested or from any other cause, the other individuals would have to + produce a larger supply of pollen; and such increased development would + tend to reduce the female organs through the law of compensation, so as + ultimately to leave them in a rudimentary condition; and the species would + then become dioecious. + </p> + <p> + Instead of the first change occurring in the female organs we may suppose + that the male ones first varied, so that some individuals produced a + larger supply of pollen. This would be beneficial under certain + circumstances, such as a change in the nature of the insects which visited + the flowers, or in their becoming more anemophilous, for such plants + require an enormous quantity of pollen. The increased action of the male + organs would tend to affect through compensation the female organs of the + same flower; and the final result would be that the species would consist + of males and hermaphrodites. But it is of no use considering this case and + other analogous ones, for, as stated in the Introduction, the coexistence + of male and hermaphrodite plants is excessively rare. + </p> + <p> + It is no valid objection to the foregoing views that changes of such a + nature would be effected with extreme slowness, for we shall presently see + good reason to believe that various hermaphrodite plants have become or + are becoming dioecious by many and excessively small steps. In the case of + polygamous species, which exist as males, females and hermaphrodites, the + latter would have to be supplanted before the species could become + strictly dioecious; but the extinction of the hermaphrodite form would + probably not be difficult, as a complete separation of the sexes appears + often to be in some way beneficial. The males and females would also have + to be equalised in number, or produced in some fitting proportion for the + effectual fertilisation of the females. + </p> + <p> + There are, no doubt, many unknown laws which govern the suppression of the + male or female organs in hermaphrodite plants, quite independently of any + tendency in them to become monoecious, dioecious, or polygamous. We see + this in those hermaphrodites which from the rudiments still present + manifestly once possessed more stamens or pistils than they now do,—even + twice as many, as a whole verticil has often been suppressed. Robert Brown + remarks that “the order of reduction or abortion of the stamina in any + natural family may with some confidence be predicted,” by observing in + other members of the family, in which their number is complete, the order + of the dehiscence of the anthers (7/3. ‘Transactions of the Linnean + Society’ volume 12 page 98 or ‘Miscellaneous Works’ volume 2 pages + 278-81.); for the lesser permanence of an organ is generally connected + with its lesser perfection, and he judges of perfection by priority of + development. He also states that whenever there is a separation of the + sexes in an hermaphrodite plant, which bears flowers on a simple spike, it + is the females which expand first; and this he likewise attributes to the + female sex being the more perfect of the two, but why the female should be + thus valued he does not explain. + </p> + <p> + Plants under cultivation or changed conditions of life frequently become + sterile; and the male organs are much oftener affected than the female, + though the latter alone are sometimes affected. The sterility of the + stamens is generally accompanied by a reduction in their size; and we may + feel sure, from a wide-spread analogy, that both the male and female + organs would become rudimentary in the course of many generations if they + failed altogether to perform their proper functions. According to Gartner, + if the anthers on a plant are contabescent (and when this occurs it is + always at a very early period of growth) the female organs are sometimes + precociously developed. (7/4. ‘Beitrage zur Kenntniss’ etc. page 117 et + seq. The whole subject of the sterility of plants from various causes has + been discussed in my ‘Variation of Animals and Plants under Domestication’ + chapter 18 2nd edition volume 2 pages 146-56.) I mention this case as it + appears to be one of compensation. So again is the well- known fact, that + plants which increase largely by stolons or other such means are often + utterly barren, with a large proportion of their pollen-grains in a + worthless condition. + </p> + <p> + Hildebrand has shown that with hermaphrodite plants which are strongly + proterandrous, the stamens in the flowers which open first sometimes + abort; and this seems to follow from their being useless, as no pistils + are then ready to be fertilised. Conversely the pistils in the flowers + which open last sometimes abort; as when they are ready for fertilisation + all the pollen has been shed. He further shows by means of a series of + gradations amongst the Compositae, that a tendency from the causes just + specified to produce either male or female florets, sometimes spreads to + all the florets on the same head, and sometimes even to the whole plant + (7/5. ‘Ueber die Geschlechtsverhaltnisse bei den Compositen’ 1869 page + 89.); and in this latter case the species becomes dioecious. In those rare + instances mentioned in the Introduction, in which some of the individuals + of both monoecious and hermaphrodite plants are proterandrous, others + being proterogynous, their conversion into a dioecious condition would + probably be much facilitated, as they already consist of two bodies of + individuals, differing to a certain extent in their reproductive + functions. + </p> + <p> + Dimorphic heterostyled plants offer still more strongly marked facilities + for becoming dioecious; for they likewise consist of two bodies of + individuals in approximately equal numbers, and what probably is more + important, both the male and female organs differ in the two forms, not + only in structure but in function, in nearly the same manner as do the + reproductive organs of two distinct species belonging to the same genus. + Now if two species are subjected to changed conditions, though of the same + nature, it is notorious that they are often affected very differently; + therefore the male organs, for instance, in one form of a heterostyled + plant might be affected by those unknown causes which induce abortion, + differently from the homologous but functionally different organs in the + other form; and so conversely with the female organs. Thus the great + difficulty before alluded to is much lessened in understanding how any + cause whatever could lead to the simultaneous reduction and ultimate + suppression of the male organs in half the individuals of a species, and + of the female organs in the other half, whilst all were subjected to + exactly the same conditions of life. + </p> + <p> + That such reduction or suppression has occurred in some heterostyled + plants is almost certain. The Rubiaceae contain more heterostyled genera + than any other family, and from their wide distribution we may infer that + many of them became heterostyled at a remote period, so that there will + have been ample time for some of the species to have been since rendered + dioecious. Asa Gray informs me that Coprosma is dioecious, and that it is + closely allied through Nertera to Mitchella, which as we know is a + heterostyled dimorphic species. In the male flowers of Coprosma the + stamens are exserted, and in the female flowers the stigmas; so that, + judging from the affinities of the above three genera, it seems probable + that an ancient short-styled form bearing long stamens with large anthers + and large pollen-grains (as in the case of several Rubiaceous genera) has + been converted into the male Coprosma; and that an ancient long-styled + form with short stamens, small anthers and small pollen-grains has been + converted into the female form. But according to Mr. Meehan, Mitchella + itself is dioecious in some districts; for he says that one form has small + sessile anthers without a trace of pollen, the pistil being perfect; while + in another form the stamens are perfect and the pistil rudimentary. (7/6. + ‘Proceedings of the Academy of Sciences of Philadelphia’ July 28, 1868 + page 183.) He adds that plants may be observed in the autumn bearing an + abundant crop of berries, and others without a single one. Should these + statements be confirmed, Mitchella will be proved to be heterostyled in + one district and dioecious in another. + </p> + <p> + Asperula is likewise a Rubiaceous genus, and from the published + description of the two forms of A. scoparia, an inhabitant of Tasmania, I + did not doubt that it was heterostyled; but on examining some flowers sent + me by Dr. Hooker they proved to be dioecious. The male flowers have large + anthers and a very small ovarium, surmounted by a mere vestige of a stigma + without any style; whilst the female flowers possess a large ovarium, the + anthers being rudimentary and apparently quite destitute of pollen. + Considering how many Rubiaceous genera are heterostyled, it is a + reasonable suspicion that this Asperula is descended from a heterostyled + progenitor; but we should be cautious on this head, for there is no + improbability in a homostyled Rubiaceous plant becoming dioecious. + Moreover, in an allied plant, Galium cruciatum, the female organs have + been suppressed in most of the lower flowers, whilst the upper ones remain + hermaphrodite; and here we have a modification of the sexual organs + without any connection with heterostylism. + </p> + <p> + Mr. Thwaites informs me that in Ceylon various Rubiaceous plants are + heterostyled; but in the case of Discospermum one of the two forms is + always barren, the ovary containing about two aborted ovules in each + loculus; whilst in the other form each loculus contains several perfect + ovules; so that the species appears to be strictly dioecious. + </p> + <p> + Most of the species of the South American genus Aegiphila, a member of the + Verbenaceae, apparently are heterostyled; and both Fritz Muller and myself + thought that this was the case with Ae. obdurata, so closely did its + flowers resemble those of the heterostyled species. But on examining the + flowers, the anthers of the long-styled form were found to be entirely + destitute of pollen and less than half the size of those in the other + form, the pistil being perfectly developed. On the other hand, in the + short-styled form the stigmas are reduced to half their proper length, + having also an abnormal appearance; whilst the stamens are perfect. This + plant therefore is dioecious; and we may, I think, conclude that a + short-styled progenitor, bearing long stamens exserted beyond the corolla, + has been converted into the male; and a long-styled progenitor with fully + developed stigmas into the female. + </p> + <p> + From the number of bad pollen-grains in the small anthers of the short + stamens of the long-styled form of Pulmonaria angustifolia, we may suspect + that this form is tending to become female; but it does not appear that + the other or short-styled form is becoming more masculine. Certain + appearances countenance the belief that the reproductive system of Phlox + subulata is likewise undergoing a change of some kind. + </p> + <p> + I have now given the few cases known to me in which heterostyled plants + appear with some considerable degree of probability to have been rendered + dioecious. Nor ought we to expect to find many such cases, for the number + of heterostyled species is by no means large, at least in Europe, where + they could hardly have escaped notice. Therefore the number of dioecious + species which owe their origin to the transformation of heterostyled + plants is probably not so large as might have been anticipated from the + facilities which they offer for such conversion. + </p> + <p> + In searching for cases like the foregoing ones, I have been led to examine + some dioecious or sub-dioecious plants, which are worth describing, + chiefly as they show by what fine gradations hermaphrodites may pass into + polygamous or dioecious species. + </p> + <h3> + POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS. + </h3> + <p> + Euonymus Europaeus (CELASTRINEAE). + </p> + <p> + (Figure 7.12. Euonymus Europaeus Left: Hermaphrodite or male. Right: + Female.) + </p> + <p> + The spindle-tree is described in all the botanical works which I have + consulted as an hermaphrodite. Asa Gray speaks of the flowers of the + American species as perfect, whilst those in the allied genus Celastrus + are said to be “polygamo- dioecious.” If a number of bushes of our + spindle-tree be examined, about half will be found to have stamens equal + in length to the pistil, with well-developed anthers; the pistil being + likewise to all appearance well developed. The other half have a perfect + pistil, with the stamens short, bearing rudimentary anthers destitute of + pollen; so that these bushes are females. All the flowers on the same + plant present the same structure. The female corolla is smaller than that + on the polleniferous bushes. The two forms are shown in Figure 7.12. + </p> + <p> + I did not at first doubt that this species existed under an hermaphrodite + and female form; but we shall presently see that some of the bushes which + appear to be hermaphrodites never produce fruit, and these are in fact + males. The species, therefore, is polygamous in the sense in which I use + the term, and trioecious. The flowers are frequented by many Diptera and + some small Hymenoptera for the sake of the nectar secreted by the disc, + but I did not see a single bee at work; nevertheless the other insects + sufficed to fertilise effectually female bushes growing at a distance of + even 30 yards from any polleniferous bush. + </p> + <p> + The small anthers borne by the short stamens of the female flowers are + well formed and dehisce properly, but I could never find in them a single + grain of pollen. It is somewhat difficult to compare the length of the + pistils in the two forms, as they vary somewhat in this respect and + continue to grow after the anthers are mature. The pistils, therefore, in + old flowers on a polleniferous plant are often of considerably greater + length than in young flowers on a female plant. On this account the + pistils from five flowers from so many hermaphrodite or male bushes were + compared with those from five female bushes, before the anthers had + dehisced and whilst the rudimentary ones were of a pink colour and not at + all shrivelled. These two sets of pistils did not differ in length, or if + there was any difference those of the polleniferous flowers were rather + the longest. In one hermaphrodite plant, which produced during three years + very few and poor fruit, the pistil much exceeded in length the stamens + bearing perfect and as yet closed anthers; and I never saw such a case on + any female plant. It is a surprising fact that the pistil in the male and + in the semi-sterile hermaphrodite flowers has not been reduced in length, + seeing that it performs very poorly or not at all its proper function. The + stigmas in the two forms are exactly alike; and in some of the + polleniferous plants which never produced any fruit I found that the + surface of the stigma was viscid, so that pollen-grains adhered to it and + had exserted their tubes. The ovules are of equal size in the two forms. + Therefore the most acute botanist, judging only by structure, would never + have suspected that some of the bushes were in function exclusively males. + </p> + <p> + Thirteen bushes growing near one another in a hedge consisted of eight + females quite destitute of pollen and of five hermaphrodites with + well-developed anthers. In the autumn the eight females were well covered + with fruit, excepting one, which bore only a moderate number. Of the five + hermaphrodites, one bore a dozen or two fruits, and the remaining four + bushes several dozen; but their number was as nothing compared with those + on the female bushes, for a single branch, between two and three feet in + length, from one of the latter, yielded more than any one of the + hermaphrodite bushes. The difference in the amount of fruit produced by + the two sets of bushes is all the more striking, as from the sketches + above given it is obvious that the stigmas of the polleniferous flowers + can hardly fail to receive their own pollen; whilst the fertilisation of + the female flowers depends on pollen being brought to them by flies and + the smaller Hymenoptera, which are far from being such efficient carriers + as bees. + </p> + <p> + I now determined to observe more carefully during successive seasons some + bushes growing in another place about a mile distant. As the female bushes + were so highly productive, I marked only two of them with the letters A + and B, and five polleniferous bushes with the letters C to G. I may + premise that the year 1865 was highly favourable for the fruiting of all + the bushes, especially for the polleniferous ones, some of which were + quite barren except under such favourable conditions. The season of 1864 + was unfavourable. In 1863 the female A produced “some fruit;” in 1864 only + 9; and in 1865, 97 fruit. The female B in 1863 was “covered with fruit;” + in 1864 it bore 28; and in 1865 “innumerable very fine fruits.” I may add, + that three other female trees growing close by were observed, but only + during 1863, and they then bore abundantly. With respect to the + polleniferous bushes, the one marked C did not bear a single fruit during + the years 1863 and 1864, but during 1865 it produced no less than 92 + fruit, which, however, were very poor. I selected one of the finest + branches with 15 fruit, and these contained 20 seeds, or on an average + 1.33 per fruit. I then took by hazard 15 fruit from an adjoining female + bush, and these contained 43 seeds; that is, more than twice as many, or + on an average 2.86 per fruit. Many of the fruits from the female bushes + included four seeds, and only one had a single seed; whereas not one fruit + from the polleniferous bushes contained four seeds. Moreover when the two + lots of seeds were compared, it was manifest that those from the female + bushes were the larger. The second polleniferous bush, D, bore in 1863 + about two dozen fruit,—in 1864 only 3 very poor fruit, each + containing a single seed,—and in 1865, 20 equally poor fruit. + Lastly, the three polleniferous bushes, E, F, and G, did not produce a + single fruit during the three years 1863, 1864, and 1865. + </p> + <p> + We thus see that the female bushes differ somewhat in their degree of + fertility, and the polleniferous ones in the most marked manner. We have a + perfect gradation from the female bush, B, which in 1865 was covered with + “innumerable fruits,”—through the female A, which produced during + the same year 97,—through the polleniferous bush C, which produced + this year 92 fruits, these, however, containing a very low average number + of seeds of small size,—through the bush D, which produced only 20 + poor fruit,—to the three bushes, E, F, and G, which did not this + year, or during the two previous years, produce a single fruit. If these + latter bushes and the more fertile female ones were to supplant the + others, the spindle-tree would be as strictly dioecious in function as any + plant in the world. This case appears to me very interesting, as showing + how gradually an hermaphrodite plant may be converted into a dioecious + one. (7/7. According to Fritz Muller ‘Botanische Zeitung’ 1870 page 151, a + Chamissoa (Amaranthaceae) in Southern Brazil is in nearly the same state + as our Euonymus. The ovules are equally developed in the two forms. In the + female the pistil is perfect, whilst the anthers are entirely destitute of + pollen. In the polleniferous form, the pistil is short and the stigmas + never separate from one another, so that, although their surfaces are + covered with fairly well-developed papillae, they cannot be fertilised, + these latter plants do not commonly yield any fruit, and are therefore in + function males. Nevertheless, on one occasion Fritz Muller found flowers + of this kind in which the stigmas had separated, and they produced some + fruit.) + </p> + <p> + Seeing how general it is for organs which are almost or quite functionless + to be reduced in size, it is remarkable that the pistils of the + polleniferous plants should equal or even exceed in length those of the + highly fertile female plants. This fact formerly led me to suppose that + the spindle-tree had once been heterostyled; the hermaphrodite and male + plants having been originally long- styled, with the pistils since reduced + in length, but with the stamens retaining their former dimensions; whilst + the female plant had been originally short- styled, with the pistil in its + present state, but with the stamens since greatly reduced and rendered + rudimentary. A conversion of this kind is at least possible, although it + is the reverse of that which appears actually to have occurred with some + Rubiaceous genera and Aegiphila; for with these plants the short-styled + form has become the male, and the long-styled the female. It is, however, + a more simple view that sufficient time has not elapsed for the reduction + of the pistil in the male and hermaphrodite flowers of our Euonymus; + though this view does not account for the pistils in the polleniferous + flowers being sometimes longer than those in the female flowers. + </p> + <p> + Fragaria vesca, Virginiana, chiloensis, etc. (ROSACEAE). + </p> + <p> + A tendency to the separation of the sexes in the cultivated strawberry + seems to be much more strongly marked in the United States than in Europe; + and this appears to be the result of the direct action of climate on the + reproductive organs. In the best account which I have seen, it is stated + that many of the varieties in the United States consist of three forms, + namely, females, which produce a heavy crop of fruit,—of + hermaphrodites, which “seldom produce other than a very scanty crop of + inferior and imperfect berries,”—and of males, which produce none. + (7/8. Mr. Leonard Wray ‘Gardener’s Chronicle’ 1861 page 716.) The most + skilful cultivators plant “seven rows of female plants, then one row of + hermaphrodites, and so on throughout the field.” The males bear large, the + hermaphrodites mid-sized, and the females small flowers. The latter plants + produce few runners, whilst the two other forms produce many; + consequently, as has been observed both in England and in the United + States, the polleniferous forms increase rapidly and tend to supplant the + females. We may therefore infer that much more vital force is expended in + the production of ovules and fruit than in the production of pollen. + Another species, the Hautbois strawberry (F. elatior), is more strictly + dioecious; but Lindley made by selection an hermaphrodite stock. (7/9. For + references and further information on this subject, see ‘Variation under + Domestication’ chapter 10 2nd edition volume 1 page 375.) + </p> + <p> + Rhamnus catharticus (RHAMNEAE). + </p> + <p> + (FIGURE 7.13. Rhamnus catharticus (from Caspary.) Left: Long-styled male. + Right: Short-styled male.) + </p> + <p> + (FIGURE 7.14. Rhamnus catharticus. Left: Long-styled female. Right: + Short-styled female.) + </p> + <p> + This plant is well known to be dioecious. My son William found the two + sexes growing in about equal numbers in the Isle of Wight, and sent me + specimens, together with observations on them. Each sex consists of two + sub-forms. The two forms of the male differ in their pistils: in some + plants it is quite small, without any distinct stigma; in others the + pistil is much more developed, with the papillae on the stigmatic surfaces + moderately large. The ovules in both kinds of males are in an aborted + condition. On my mentioning this case to Professor Caspary, he examined + several male plants in the botanic gardens at Konigsberg, where there were + no females, and sent me the drawings in Figure 7.13. + </p> + <p> + In the English plants the petals are not so greatly reduced as represented + in this drawing. My son observed that those males which had their pistils + moderately well-developed bore slightly larger flowers, and, what is very + remarkable, their pollen-grains exceeded by a little in diameter those of + the males with greatly reduced pistils. This fact is opposed to the belief + that the present species was once heterostyled; for in this case it might + have been expected that the shorter-styled plants would have had larger + pollen-grains. + </p> + <p> + In the female plants the stamens are in an extremely rudimentary + condition, much more so than the pistils in the males. The pistil varies + considerably in length in the female plants, so that they may be divided + into two sub-forms according to the length of this organ. Both the petals + and sepals are decidedly smaller in the females than in the males; and the + sepals do not turn downwards, as do those of the male flowers when mature. + All the flowers on the same male or same female bush, though subject to + some variability, belong to the same sub-form; and as my son never + experienced any difficulty in deciding under which class a plant ought to + be included, he believes that the two sub-forms of the same sex do not + graduate into one another. I can form no satisfactory theory how the four + forms of this plant originated. + </p> + <p> + Rhamnus lanceolatus. + </p> + <p> + This plant exists in the United States, as I am informed by Professor Asa + Gray, under two hermaphrodite forms. In the one, which may be called the + short-styled, the flowers are sub-solitary, and include a pistil about + two-thirds or only half as long as that in the other form; it has also + shorter stigmas. The stamens are of equal length in the two forms; but the + anthers of the short-styled contain rather less pollen, as far as I could + judge from a few dried flowers. My son compared the pollen-grains from the + two forms, and those from the long-styled flowers were to those from the + short-styled, on an average from ten measurements, as 10 to 9 in diameter; + so that the two hermaphrodite forms of this species resemble in this + respect the two male forms of R. catharticus. The long-styled form is not + so common as the short-styled. The latter is said by Asa Gray to be the + more fruitful of the two, as might have been expected from its appearing + to produce less pollen, and from the grains being of smaller size; it is + therefore the more highly feminine of the two. The long-styled form + produces a greater number of flowers, which are clustered together instead + of being sub- solitary; they yield some fruit, but as just stated are less + fruitful than the other form, so that this form appears to be the more + masculine of the two. On the supposition that we have here an + hermaphrodite plant becoming dioecious, there are two points deserving + notice; firstly, the greater length of the pistil in the incipient male + form; and we have met with a nearly similar case in the male and + hermaphrodite forms of Euonymus compared with the females. Secondly, the + larger size of the pollen-grains in the more masculine flowers, which + perhaps may be attributed to their having retained their normal size; + whilst those in the incipient female flowers have been reduced. The + long-styled form of R. lanceolatus seems to correspond with the males of + R. catharticus which have a longer pistil and larger pollen-grains. Light + will perhaps be thrown on the nature of the forms in this genus, as soon + as the power of both kinds of pollen on both stigmas is ascertained. + Several other species of Rhamnus are said to be dioecious or + sub-dioecious. (7/10. Lecoq ‘Geogr. Bot.’ tome 5 1856 pages 420- 26.) On + the other hand, R. frangula is an ordinary hermaphrodite, for my son found + a large number of bushes all bearing an equal profusion of fruit. + </p> + <p> + Epigaea repens (ERICACEAE). + </p> + <p> + This plant appears to be in nearly the same state as Rhamnus catharticus. + It is described by Asa Gray as existing under four forms. (7/11. ‘American + Journal of Science’ July 1876. Also ‘The American Naturalist’ 1876 page + 490.) (1.) With long style, perfect stigma, and short abortive stamens. + (2.) Shorter style, but with stigma equally perfect, short abortive + stamens. These two female forms amounted to 20 per cent of the specimens + received from one locality in Maine; but all the fruiting specimens + belonged to the first form. (3.) Style long, as in Number 1, but with + stigma imperfect, stamens perfect. (4.) Style shorter than in the last, + stigma imperfect, stamens perfect. These two latter forms are evidently + males. Therefore, as Asa Gray remarks, “the flowers may be classified into + two kinds, each with two modifications; the two main kinds characterised + by the nature and perfection of the stigma, along with more or less + abortion of the stamens; their modifications, by the length of the style.” + Mr. Meehan has described the extreme variability of the corolla and calyx + in this plant, and shows that it is dioecious. (7/12. “Variations in + Epigaea repens” ‘Proc. Acad. Nat. Soc. of Philadelphia’ May 1868 page + 153.) It is much to be wished that the pollen-grains in the two male forms + should be compared, and their fertilising power tried on the two female + forms. + </p> + <p> + Ilex aquifolium (AQUIFOLIACEAE). + </p> + <p> + In the several works which I have consulted, one author alone says that + the holly is dioecious. (7/13. Vaucher ‘Hist. Phys. des Plantes d’Europe’ + 1841 tome 2 page 11.) During several years I have examined many plants, + but have never found one that was really hermaphrodite. I mention this + genus because the stamens in the female flowers, although quite destitute + of pollen, are but slightly and sometimes not at all shorter than the + perfect stamens in the male flowers. In the latter the ovary is small and + the pistil is almost aborted. The filaments of the perfect stamens adhere + for a greater length to the petals than in the female flowers. The corolla + of the latter is rather smaller than that of the male. The male trees + produce a greater number of flowers than the females. Asa Gray informs me + that I. opaca, which represents in the United States our common holly, + appears (judging from dried flowers) to be in a similar state; and so it + is, according to Vaucher, with several other but not with all the species + of the genus. + </p> + <h3> + GYNO-DIOECIOUS PLANTS. + </h3> + <p> + The plants hitherto described either show a tendency to become dioecious, + or apparently have become so within a recent period. But the species now + to be considered consist of hermaphrodites and females without males, and + rarely show any tendency to be dioecious, as far as can be judged from + their present condition and from the absence of species having separated + sexes within the same groups. Species belonging to the present class, + which I have called gyno- dioecious, are found in various widely distinct + families; but are much more common in the Labiatae (as has long been + noticed by botanists) than in any other group. Such cases have been + noticed by myself in Thymus serpyllum and vulgaris, Satureia hortensis, + Origanum vulgare, and Mentha hirsuta; and by others in Nepeta glechoma, + Mentha vulgaris and aquatica, and Prunella vulgaris. In these two latter + species the female form, according to H. Muller, is infrequent. To these + must be added Dracocephalum Moldavicum, Melissa officinalis and + clinopodium, and Hyssopus officinalis. (7/14. H. Muller ‘Die Befruchtung + der Blumen’ 1873 and ‘Nature’ 1873 page 161. Vaucher ‘Plantes d’Europe’ + tome 3 page 611. For Dracocephalum Schimper as quoted by Braun ‘Annals and + Magazine of Natural History’ 2nd series volume 18 1856 page 380. Lecoq + ‘Geographie Bot. de l’Europe’ tome 8 pages 33, 38, 44, etc. Both Vaucher + and Lecoq were mistaken in thinking that several of the plants named in + the text are dioecious. They appear to have assumed that the hermaphrodite + form was a male; perhaps they were deceived by the pistil not becoming + fully developed and of proper length until some time after the anthers + have dehisced.) In the two last-named plants the female form likewise + appears to be rare, for I raised many seedlings of both, and all were + hermaphrodites. It has already been remarked in the Introduction that + andro-dioecious species, as they may be called, or those which consist of + hermaphrodites and males, are extremely rare, or hardly exist. + </p> + <p> + Thymus serpyllum. + </p> + <p> + The hermaphrodite plants present nothing particular in the state of their + reproductive organs; and so it is in all the following cases. The females + of the present species produce rather fewer flowers and have somewhat + smaller corollas than the hermaphrodites; so that near Torquay, where this + plant abounds, I could, after a little practice, distinguish the two forms + whilst walking quickly past them. According to Vaucher, the smaller size + of the corolla is common to the females of most or all of the + above-mentioned Labiatae. The pistil of the female, though somewhat + variable in length, is generally shorter, with the margins of the stigma + broader and formed of more lax tissue, than that of the hermaphrodite. The + stamens in the female vary excessively in length; they are generally + enclosed within the tube of the corolla, and their anthers do not contain + any sound pollen; but after long search I found a single plant with the + stamens moderately exserted, and their anthers contained a very few + full-sized grains, together with a multitude of minute empty ones. In some + females the stamens are extremely short, and their minute anthers, though + divided into the two normal cells or loculi, contained not a trace of + pollen: in others again the anthers did not exceed in diameter the + filaments which supported them, and were not divided into two loculi. + Judging from what I have myself seen and from the descriptions of others, + all the plants in Britain, Germany, and near Mentone, are in the state + just described; and I have never found a single flower with an aborted + pistil. It is, therefore, remarkable that, according to Delpino, this + plant near Florence is generally trimorphic, consisting of males with + aborted pistils, females with aborted stamens, and hermaphrodites. (7/15. + ‘Sull’ Opera, la Distribuzione dei Sessi nelle Piante, etc’ 1867 page 7. + With respect to Germany H. Muller ‘Die Befruchtung etc.’ page 327.) + </p> + <p> + I found it very difficult to judge of the proportional number of the two + forms at Torquay. They often grow mingled together, but with large patches + consisting of one form alone. At first I thought that the two were nearly + equal in number; but on examining every plant which grew close to the edge + of a little overhanging dry cliff, about 200 yards in length, I found only + 12 females; all the rest, some hundreds in number, being hermaphrodites. + Again, on an extensive gently sloping bank, which was so thickly covered + with this plant that, viewed from the distance of half a mile it appeared + of a pink colour, I could not discover a single female. Therefore the + hermaphrodites must greatly exceed in number the females, at least in the + localities examined by me. A very dry station apparently favours the + presence of the female form. With some of the other above-named Labiatae + the nature of the soil or climate likewise seems to determine the presence + of one or both forms; thus with Nepeta glechoma, Mr. Hart found in 1873 + that all the plants which he examined near Kilkenny in Ireland were + females; whilst all near Bath were hermaphrodites, and near Hertford both + forms were present, but with a preponderance of hermaphrodites. (7/16. + ‘Nature’ June 1873 page 162.) It would, however, be a mistake to suppose + that the nature of the conditions determines the form independently of + inheritance; for I sowed in the same small bed seeds of T. serpyllum, + gathered at Torquay from the female alone, and these produced an abundance + of both forms. There is every reason to believe, from large patches + consisting of the same form, that the same individual plant, however much + it may spread, always retains the same form. In two distant gardens I + found masses of the lemon-thyme (T. citriodorus, a var. of T. serpyllum, + which I was informed had grown there during many years, and every flower + was female. + </p> + <p> + With respect to the fertility of the two forms, I marked at Torquay a + large hermaphrodite and a large female plant of nearly equal sizes, and + when the seeds were ripe I gathered all the heads. The two heaps were of + very nearly equal bulk; but the heads from the female plant numbered 160, + and their seeds weighed 8.7 grains; whilst those from the hermaphrodite + plant numbered 200, and their seeds weighed only 4.9 grains; so that the + seeds from the female plant were to those from the hermaphrodite as 100 to + 56 in weight. If the relative weight of the seeds from an equal number of + flower-heads from the two forms be compared, the ratio is as 100 for the + female to 45 for the hermaphrodite form. + </p> + <p> + Thymus vulgaris. + </p> + <p> + (FIGURE 7.15. Thymus vulgaris (magnified). Left: Hermaphrodite. Right: Two + females.) + </p> + <p> + The common garden thyme resembles in almost every respect T. serpyllum. + The same slight differences between the stigmas of the two forms could be + perceived. In the females the stamens are not generally quite so much + reduced as in the same form of T. serpyllum. In some specimens sent me + from Mentone by Mr. Moggridge, together with the sketches in Figure 7.15, + the anthers of the female, though small, were well formed, but they + contained very little pollen, and not a single sound grain could be + detected. Eighteen seedlings were raised from purchased seed, sown in the + same small bed; and these consisted of seven hermaphrodites and eleven + females. They were left freely exposed to the visits of bees, and no doubt + every female flower was fertilised; for on placing under the microscope a + large number of stigmas from female plants, not one could be found to + which pollen-grains of thyme did not adhere. The seeds were carefully + collected from the eleven female plants, and they weighed 98.7 grains; and + those from the seven hermaphrodites 36.5 grains. This gives for an equal + number of plants the ratio of 100 to 58; and we here see, as in the last + case, how much more fertile the females are than the hermaphrodites. These + two lots of seeds were sown separately in two adjoining beds, and the + seedlings from both the hermaphrodite and female parent-plants consisted + of both forms. + </p> + <p> + Satureia hortensis. + </p> + <p> + Eleven seedlings were raised in separate pots in a hotbed and afterwards + kept in the greenhouse. They consisted of ten females and of a single + hermaphrodite. Whether or not the conditions to which they had been + subjected caused the great excess of females I do not know. In the females + the pistil is rather longer than that of the hermaphrodite, and the + stamens are mere rudiments, with minute colourless anthers destitute of + pollen. The windows of the greenhouse were left open, and the flowers were + incessantly visited by humble and hive bees. Although the ten females did + not produce a single grain of pollen, yet they were all thoroughly well + fertilised by the one hermaphrodite plant, and this is an interesting + fact. It should be added that no other plant of this species grew in my + garden. The seeds were collected from the finest female plant, and they + weighed 78 grains; whilst those from the hermaphrodite, which was a rather + larger plant than the female, weighed only 33.2 grains; that is, in the + ratio of 100 to 43. The female form, therefore, is very much more fertile + than the hermaphrodite, as in the two last cases; but the hermaphrodite + was necessarily self-fertilised, and this probably diminished its + fertility. + </p> + <p> + We may now consider the probable means by which so many of the Labiatae + have been separated into two forms, and the advantages thus gained. H. + Muller supposes that originally some individuals varied so as to produce + more conspicuous flowers; and that insects habitually visited these first, + and then dusted with their pollen visited and fertilised the less + conspicuous flowers. (7/17. ‘Die Befruchtung der Blumen’ pages 319, 326.) + The production of pollen by the latter plants would thus be rendered + superfluous, and it would be advantageous to the species that their + stamens should abort, so as to save useless expenditure. They would thus + be converted into females. But another view may be suggested: as the + production of a large supply of seeds evidently is of high importance to + many plants, and as we have seen in the three foregoing cases that the + females produce many more seeds than the hermaphrodites, increased + fertility seems to me the more probable cause of the formation and + separation of the two forms. From the data above given it follows that ten + plants of Thymus serpyllum, if half consisted of hermaphrodites and half + of females, would yield seeds compared with ten hermaphrodite plants in + the ratio of 100 to 72. Under similar circumstances the ratio with + Satureia hortensis (subject to the doubt from the self-fertilisation of + the hermaphrodite) would be as 100 to 60. Whether the two forms originated + in certain individuals varying and producing more seed than usual, and + consequently producing less pollen; or in the stamens of certain + individuals tending from some unknown cause to abort, and consequently + producing more seed, it is impossible to decide; but in either case, if + the tendency to the increased production of seed were steadily favoured, + the result would be the complete abortion of the male organs. I shall + presently discuss the cause of the smaller size of the female corolla. + </p> + <p> + [Scabiosa arvensis (DIPSACEAE). + </p> + <p> + It has been shown by H. Muller that this species exists in Germany under + an hermaphrodite and female form. (7/18. ‘Die Befruchtung der Blumen’ page + 368. The two forms occur not only in Germany, but in England and France. + Lecoq ‘Geographie Bot.’ 1857 tome 6 pages 473, 477, says that male plants + as well as hermaphrodites and females coexist; it is, however, possible + that he may have been deceived by the flowers being so strongly + proterandrous. From what Lecoq says, S. succisa likewise appears to occur + under two forms in France.) In my neighbourhood (Kent) the female plants + do not nearly equal in number the hermaphrodites. The stamens of the + females vary much in their degree of abortion; in some plants they are + quite short and produce no pollen; in others they reach to the mouth of + the corolla, but their anthers are not half the proper size, never + dehisce, and contain but few pollen-grains, these being colourless and of + small diameter. The hermaphrodite flowers are strongly proterandrous, and + H. Muller shows that, whilst all the stigmas on the same flower-head are + mature at nearly the same time, the stamens dehisce one after the other; + so that there is a great excess of pollen, which serves to fertilise the + female plants. As the production of pollen by one set of plants is thus + rendered superfluous, their male organs have become more or less + completely aborted. Should it be hereafter proved that the female plants + yield, as is probable, more seeds than the hermaphrodites, I should be + inclined to extend the same view to this plant as to the Labiatae. I have + also observed the existence of two forms in our endemic S. succisa, and in + the exotic S. atro-purpurea. In the latter plant, differently to what + occurs in S. arvensis, the female flowers, especially the larger + circumferential ones, are smaller than those of the hermaphrodite form. + According to Lecoq, the female flower-heads of S. succisa are likewise + smaller than those of what he calls the male plants, but which are + probably hermaphrodites. + </p> + <p> + Echium vulgare (BORAGINEAE). + </p> + <p> + The ordinary hermaphrodite form appears to be proterandrous, and nothing + more need be said about it. The female differs in having a much smaller + corolla and shorter pistil, but a well-developed stigma. The stamens are + short; the anthers do not contain any sound pollen-grains, but in their + place yellow incoherent cells which do not swell in water. Some plants + were in an intermediate condition; that is, had one or two or three + stamens of proper length with perfect anthers, the other stamens being + rudimentary. In one such plant half of one anther contained green perfect + pollen-grains, and the other half yellowish- green imperfect grains. Both + forms produced seed, but I neglected to observe whether in equal numbers. + As I thought that the state of the anthers might be due to some fungoid + growth, I examined them both in the bud and mature state, but could find + no trace of mycelium. In 1862 many female plants were found; and in 1864, + 32 plants were collected in two localities, exactly half of which were + hermaphrodites, fourteen were females, and two in an intermediate + condition. In 1866, 15 plants were collected in another locality, and + these consisted of four hermaphrodites and eleven females. I may add that + this season was a wet one, which shows that the abortion of the stamens + can hardly be due to the dryness of the sites where the plants grew, as I + at one time thought probable. Seeds from an hermaphrodite were sown in my + garden, and of the 23 seedlings raised, one belonged to the intermediate + form, all the others being hermaphrodites, though two or three of them had + unusually short stamens. I have consulted several botanical works, but + have found no record of this plant varying in the manner here described. + </p> + <p> + Plantago lanceolata (PLANTAGINEAE). + </p> + <p> + Delpino states that this plant presents in Italy three forms, which + graduate from an anemophilous into an entomophilous condition. According + to H. Muller, there are only two forms in Germany, neither of which show + any special adaptation for insect fertilisation, and both appear to be + hermaphrodites. (7/19. ‘Die Befruchtung’ etc. page 342.) But I have found + in two localities in England female and hermaphrodite forms existing + together; and the same fact has been noticed by others. (7/20. Mr. C.W. + Crocker ‘The Gardener’s Chronicle’ 1864 page 294. Mr. W. Marshall writes + to me to the same effect from Ely.) The females are less frequent than the + hermaphrodites; their stamens are short, and their anthers, which are of a + brighter green whilst young than those of the other form, dehisce + properly, yet contain either no pollen, or a small amount of imperfect + grains of variable size. All the flower-heads on a plant belong to the + same form. It is well known that this species is strongly proterogynous, + and I found that the protruding stigmas of both the hermaphrodite and + female flowers were penetrated by pollen-tubes, whilst their own anthers + were immature and had not escaped out of the bud. Plantago media does not + present two forms; but it appears from Asa Gray’s description, that such + is the case with four of the North American species. (7/21. ‘Manual of the + Botany of the Northern United States’ 2nd edition 1856 page 269. See also + ‘American Journal of Science’ November 1862 page 419 and ‘Proceedings of + the American Academy of Science’ October 14, 1862 page 53.) The corolla + does not properly expand in the short- stamened form of these plants. + </p> + <p> + Cnicus, Serratula, Eriophorum. + </p> + <p> + In the Compositae, Cnicus palustris and acaulis are said by Sir J.E. Smith + to exist as hermaphrodites and females, the former being the more + frequent. With Serratula tinctoria a regular gradation may be followed + from the hermaphrodite to the female form; in one of the latter plants the + stamens were so tall that the anthers embraced the style as in the + hermaphrodites, but they contained only a few grains of pollen, and these + in an aborted condition; in another female, on the other hand, the anthers + were much more reduced in size than is usual. Lastly, Dr. Dickie has shown + that with Eriophorum angustifolium (Cyperaceae) hermaphrodite and female + forms exist in Scotland and the Arctic regions, both of which yield seed. + (7/22. Sir J.E. Smith ‘Transactions of the Linnean Society’ volume 13 page + 599. Dr. Dickie ‘Journal of the Linnean Society Botany’ volume 9 1865 page + 161.)] + </p> + <p> + It is a curious fact that in all the foregoing polygamous, dioecious, and + gyno- dioecious plants in which any difference has been observed in the + size of the corolla in the two or three forms, it is rather larger in the + females, which have their stamens more or less or quite rudimentary, than + in the hermaphrodites or males. This holds good with Euonymus, Rhamnus + catharticus, Ilex, Fragaria, all or at least most of the before-named + Labiatae, Scabiosa atro-purpurea, and Echium vulgare. So it is, according + to Von Mohl, with Cardamine amara, Geranium sylvaticum, Myosotis, and + Salvia. On the other hand, as Von Mohl remarks, when a plant produces + hermaphrodite flowers and others which are males owing to the more or less + complete abortion of the female organs, the corollas of the males are not + at all increased in size, or only exceptionally and in a slight degree, as + in Acer. (7/23. ‘Botanische Zeitung’ 1863 page 326.) It seems therefore + probable that the decreased size of the female corollas in the foregoing + cases is due to a tendency to abortion spreading from the stamens to the + petals. We see how intimately these organs are related in double flowers, + in which the stamens are readily converted into petals. Indeed some + botanists believe that petals do not consist of leaves directly + metamorphosed, but of metamorphosed stamens. That the lessened size of the + corolla in the above case is in some manner an indirect result of the + modification of the reproductive organs is supported by the fact that in + Rhamnus catharticus not only the petals but the green and inconspicuous + sepals of the female have been reduced in size; and in the strawberry the + flowers are largest in the males, mid-sized in the hermaphrodites, and + smallest in the females. These latter cases,—the variability in the + size of the corolla in some of the above species, for instance in the + common thyme,—together with the fact that it never differs greatly + in size in the two forms—make me doubt much whether natural + selection has come into play;—that is whether, in accordance with H. + Muller’s belief, the advantage derived from the polleniferous flowers + being visited first by insects has been sufficient to lead to a gradual + reduction of the corolla of the female. We should bear in mind that as the + hermaphrodite is the normal form, its corolla has probably retained its + original size. (7/24. It does not appear to me that Kerner’s view ‘Die + Schutzmittel des Pollens’ 1873 page 56, can be accepted in the present + cases, namely that the larger corolla in the hermaphrodites and males + serves to protect their pollen from rain. In the genus Thymus, for + instance, the aborted anthers of the female are much better protected than + the perfect ones of the hermaphrodite.) An objection to the above view + should not be passed over; namely, that the abortion of the stamens in the + females ought to have added through the law of compensation to the size of + the corolla; and this perhaps would have occurred, had not the expenditure + saved by the abortion of the stamens been directed to the female + reproductive organs, so as to give to this form increased fertility. + </p> + <p> + <br /><br /> + </p> + <hr /> + <p> + <a name="link2HCH0008" id="link2HCH0008"> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER VIII. CLEISTOGAMIC FLOWERS. + </h2> +<pre xml:space="preserve"> + General character of cleistogamic flowers. + List of the genera producing 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 cleistogamic flowers. + Vandellia. + Ononis. + Impatiens. + Drosera. + Miscellaneous observations on various other cleistogamic plants. + Anemophilous species producing cleistogamic flowers. + Leersia, perfect flowers rarely developed. + Summary and concluding remarks on the origin of cleistogamic flowers. + The chief conclusions which may be drawn from the observations in this volume. +</pre> + <p> + It was known even before the time of Linnaeus that certain plants produced + two kinds of flowers, ordinary open, and minute closed ones; and this fact + formerly gave rise to warm controversies about the sexuality of plants. + These closed flowers have been appropriately named cleistogamic by Dr. + Kuhn. (8/1. ‘Botanische Zeitung’ 1867 page 65.) They are remarkable from + their small size and from never opening, so that they resemble buds; their + petals are rudimentary or quite aborted; their stamens are often reduced + in number, with the anthers of very small size, containing few + pollen-grains, which have remarkably thin transparent coats, and generally + emit their tubes whilst still enclosed within the anther-cells; and, + lastly, the pistil is much reduced in size, with the stigma in some cases + hardly at all developed. These flowers do not secrete nectar or emit any + odour; from their small size, as well as from the corolla being + rudimentary, they are singularly inconspicuous. Consequently insects do + not visit them; nor if they did, could they find an entrance. Such flowers + are therefore invariably self-fertilised; yet they produce an abundance of + seed. In several cases the young capsules bury themselves beneath the + ground, and the seeds are there matured. These flowers are developed + before, or after, or simultaneously with the perfect ones. Their + development seems to be largely governed by the conditions to which the + plants are exposed, for during certain seasons or in certain localities + only cleistogamic or only perfect flowers are produced. + </p> + <p> + Dr. Kuhn, in the article above referred to, gives a list of 44 genera + including species which bear flowers of this kind. To this list I have + added some genera, and the authorities are appended in a footnote. I have + omitted three names, from reasons likewise given in the footnote. But it + is by no means easy to decide in all cases whether certain flowers ought + to be ranked as cleistogamic. For instance, Mr. Bentham informs me that in + the South of France some of the flowers on the vine do not fully open and + yet set fruit; and I hear from two experienced gardeners that this is the + case with the vine in our hothouses; but as the flowers do not appear to + be completely closed it would be imprudent to consider them as + cleistogamic. The flowers of some aquatic and marsh plants, for instance + of Ranunculus aquatalis, Alisma natans, Subularia, Illecebrum, Menyanthes, + and Euryale, remain closely shut as long as they are submerged, and in + this condition fertilise themselves. (8/2. Delpino ‘Sull’ Opera, la + Distribuzione dei Sessi nelle Piante’ etc. 1867 page 30. Subularia, + however, sometimes has its flowers fully expanded beneath the water, see + Sir J.E. Smith ‘English Flora’ volume 3 1825 page 157. For the behaviour + of Menyanthes in Russia see Gillibert in ‘Act. Acad. St. Petersb.’ 1777 + part 2 page 45.—On Euryale ‘Gardener’s Chronicle’ 1877 page 280.) + They behave in this manner, apparently as a protection to their pollen, + and produce open flowers when exposed to the air; so that these cases seem + rather different from those of true cleistogamic flowers, and have not + been included in the list. Again, the flowers of some plants which are + produced very early or very late in the season do not properly expand; and + these might perhaps be considered as incipiently cleistogamic; but as they + do not present any of the remarkable peculiarities proper to the class, + and as I have not found any full record of such cases, they are not + entered in the list. When, however, it is believed on fairly good evidence + that the flowers on a plant in its native country do not open at any hour + of the day or night, and yet set seeds capable of germination, these may + fairly be considered as cleistogamic, notwithstanding that they present no + peculiarities of structure. I will now give as complete a list of the + genera containing cleistogamic species as I have been able to collect. + </p> + <p> + TABLE 8.38. List of genera including cleistogamic species (chiefly after + Kuhn). (8/3. I have omitted Trifolium and Arachis from the list, because + Von Mohl says ‘Botanische Zeitung’ 1863 page 312, that the flower-stems + merely draw the flowers beneath the ground, and that these do not appear + to be properly cleistogamic. Correa de Mello ‘Journal of the Linnean + Society Botany’ volume 11 1870 page 254, observed plants of Arachis in + Brazil, and could never find such flowers. Plantago has been omitted + because as far as I can discover it produces hermaphrodite and female + flower-heads, but not cleistogamic flowers. Krascheninikowia (vel + Stellaria) has been omitted because it seems very doubtful from + Maximowicz’ description whether the lower flowers which have no petals or + very small ones, and barren stamens or none, are cleistogamic; the upper + hermaphrodite flowers are said never to produce fruit, and therefore + probably act as males. Moreover in Stellaria graminea, as Babington + remarks ‘British Botany’ 1851 page 51, “shorter and longer petals + accompany an imperfection of the stamens or germen.” + </p> + <p> + I have added to the list the following cases: Several Acanthaceae, for + which see J. Scott in ‘Journal of Botany’ London new series volume 1 1872 + page 161. With respect to salvia see Dr. Ascherson in ‘Botanische Zeitung’ + 1871 page 555. For Oxybaphus and Nyctaginia see Asa Gray in ‘American + Naturalist’ November 1873 page 692. From Dr. Torrey’s account of Hottonia + inflata ‘Bulletin of the Torrey Botanical Club’ volume 2 June 1871, it is + manifest that this plant produces true cleistogamic flowers. For Pavonia + see Bouche in ‘Sitzungsberichte d. Gesellsch. Natur. Freunde’ October 20, + 1874 page 90. I have added Thelymitra, as from the account given by Mr. + Fitzgerald in his magnificent work on ‘Australian Orchids’ it appears that + the flowers of this plant in its native home never open, but they do not + appear to be reduced in size. Nor is this the case with the flowers of + certain species of Epidendron, Cattleya, etc. see second edition of my + ‘Fertilisation of Orchids’ page 147, which without expanding produce + capsules. It is therefore doubtful whether these Orchideae ought to have + been included in the list. From what Duval-Jouve says about Cryptostachys + in ‘Bulletin of the Soc. Bot. de France’ tome 10 1863 page 195, this plant + appears to produce cleistogamic flowers. the other additions to the list + are noticed in my text.) + </p> + <h3> + DICOTYLEDONS. + </h3> + <p> + BORAGINEAE: Eritrichium. + </p> + <p> + CONVOLVULACEAE: Cuscuta. + </p> + <p> + SCROPHULARINEAE: Scrophularia. Linaria. Vandellia. + </p> + <p> + ACANTHACEAE: Cryphiacanthus. Eranthemum. Daedalacanthus. Dipteracanthus. + Aechmanthera. Ruellia. + </p> + <p> + LABIATAE: Lamium. Salvia. + </p> + <p> + NYCTAGINEAE: Oxybaphus. Nyctaginia. + </p> + <p> + ASCLEPIADAE: Stapelia. + </p> + <p> + CAMPANULACEAE: Specularia. Campanula. + </p> + <p> + PRIMULACEAE: Hottonia. + </p> + <p> + COMPOSITAE: Anandria. + </p> + <p> + CRUCIFERAE: Heterocarpaea. + </p> + <p> + VIOLACEAE: Viola. + </p> + <p> + CISTINEAE: Helianthemum. Lechea. + </p> + <p> + MALVEACEAE: Pavonia. + </p> + <p> + MALPIGHIACEAE: Gaudichaudia. Aspicarpa. Camarea. Janusia. + </p> + <p> + POLYGALEAE: Polygala. + </p> + <p> + BALSAMINEAE: Impatiens. + </p> + <p> + GERANIACAEA: Oxalis. + </p> + <p> + LEGUMINOSAE: Ononis. Parochaetus. Chapmannia. Stylosanthus. Lespedeza. + Vicia. Lathyrus. Martinsia vel Neurocarpum. Amphicarpaea. Glycine. + Galactia. Voandzeia. + </p> + <p> + DROSERACEAE: Drosera. + </p> + <h3> + MONOCOTYLEDONS. + </h3> + <p> + JUNCEAE: Juncus. + </p> + <p> + GRAMINEAE: Leersia. Hordeum. Cryptostachys. + </p> + <p> + COMMELINEAE: Commelina. + </p> + <p> + PONTEDERACEAE: Monochoria. + </p> + <p> + ORCHIDEAE: Schomburgkia. Cattleya. Epidendron. Thelymitra. + </p> + <p> + The first point that strikes us in considering this list of 55 genera, is + that they are very widely distributed in the vegetable series. They are + more common in the family of the Leguminosae than in any other, and next + in order in that of the Acanthaceae and Malpighiaceae. A large number, but + not all the species, of certain genera, as of Oxalis and Viola, bear + cleistogamic as well as ordinary flowers. A second point which deserves + notice is that a considerable proportion of the genera produce more or + less irregular flowers; this is the case with about 32 out of the 55 + genera, but to this subject I shall recur. + </p> + <p> + I formerly made many observations on cleistogamic flowers, but only a few + of them are worth giving, since the appearance of an admirable paper by + Hugo Von Mohl, whose examination was in some respects much more complete + than mine. (8/4. ‘Botanische Zeitung’ 1863 page 309-28.) His paper + includes also an interesting history of our knowledge on the subject. + </p> + <p> + Viola canina. + </p> + <p> + The calyx of the cleistogamic flowers differs in no respect from that of + the perfect ones. The petals are reduced to five minute scales; the lower + one, which represents the lower lip, is considerably larger than the + others, but with no trace of the spur-like nectary; its margins are + smooth, whilst those of the other four scale-like petals are papillose. D. + Muller of Upsala says that in the specimens which he observed the petals + were completely aborted. (8/5. Ibid. 1857 page 730. This paper contains + the first full and satisfactory account of any cleistogamic flower.) The + stamens are very small, and only the two lower ones are provided with + anthers, which do not cohere together as in the perfect flowers. The + anthers are minute, with the two cells or loculi remarkably distinct; they + contain very little pollen in comparison with those of the perfect + flowers. The connective expands into a membranous hood-like shield which + projects above the anther-cells. These two lower stamens have no vestige + of the curious appendages which secrete nectar in the perfect flowers. The + three other stamens are destitute of anthers and have broader filaments, + with their terminal membranous expansions flatter or not so hood-like as + those of the two antheriferous stamens. The pollen-grains have remarkably + thin transparent coats; when exposed to the air they shrivel up quickly; + when placed in water they swell, and are then 8-10/7000 of an inch in + diameter, and therefore of smaller size than the ordinary pollen-grains + similarly treated, which have a diameter of 13-14/7000 of an inch. In the + cleistogamic flowers, the pollen-grains, as far as I could see, never + naturally fall out of the anther-cells, but emit their tubes through a + pore at the upper end. I was able to trace the tubes from the grains some + way down the stigma. The pistil is very short, with the style hooked, so + that its extremity, which is a little enlarged or funnel-shaped and + represents the stigma, is directed downwards, being covered by the two + membranous expansions of the antheriferous stamens. It is remarkable that + there is an open passage from the enlarged funnel-shaped extremity to + within the ovarium; this was evident, as slight pressure caused a bubble + of air, which had been drawn in by some accident, to travel freely from + one end to the other: a similar passage was observed by Michalet in V. + alba. The pistil therefore differs considerably from that of the perfect + flower; for in the latter it is much longer, and straight with the + exception of the rectangularly bent stigma; nor is it perforated by an + open passage. + </p> + <p> + The ordinary or perfect flowers have been said by some authors never to + produce capsules; but this is an error, though only a small proportion of + them do so. This appears to depend in some cases on their anthers not + containing even a trace of pollen, but more generally on bees not visiting + the flowers. I twice covered with a net a group of flowers, and marked + with threads twelve of them which had not as yet expanded. This precaution + is necessary, for though as a general rule the perfect flowers appear + considerably before the cleistogamic ones, yet occasionally some of the + latter are produced early in the season, and their capsules might readily + be mistaken for those produced by the perfect flowers. Not one of the + twelve marked perfect flowers yielded a capsule, whilst others under the + net which had been artificially fertilised produced five capsules; and + these contained exactly the same average number of seeds as some capsules + from flowers outside the net which had been fertilised by bees. I have + repeatedly seen Bombus hortorum, lapidarius, and a third species, as well + as hive-bees, sucking the flowers of this violet: I marked six which were + thus visited, and four of them produced fine capsules; the two others were + gnawed off by some animal. I watched Bombus hortorum for some time, and + whenever it came to a flower which did not stand in a convenient position + to be sucked, it bit a hole through the spur-like nectary. Such ill-placed + flowers would not yield any seed or leave descendants; and the plants + bearing them would thus tend to be eliminated through natural selection. + </p> + <p> + The seeds produced by the cleistogamic and perfect flowers do not differ + in appearance or number. On two occasions I fertilised several perfect + flowers with pollen from other individuals, and afterwards marked some + cleistogamic flowers on the same plants; and the result was that 14 + capsules produced by the perfect flowers contained on an average 9.85 + seeds; and 17 capsules from the cleistogamic ones contained 9.64 seeds,—an + amount of difference of no significance. It is remarkable how much more + quickly the capsules from the cleistogamic flowers are developed than + those from the perfect ones; for instance, several perfect flowers were + cross-fertilised on April 14th, 1863, and a month afterwards (May 15th) + eight young cleistogamic flowers were marked with threads; and when the + two sets of capsules thus produced were compared on June 3rd, there was + scarcely any difference between them in size. + </p> + <p> + Viola odorata (WHITE-FLOWERED, SINGLE, CULTIVATED VARIETY). + </p> + <p> + The petals are represented by mere scales as in the last species; but + differently from in the last, all five stamens are provided with + diminutive anthers. Small bundles of pollen-tubes were traced from the + five anthers into the somewhat distant stigma. The capsules produced by + these flowers bury themselves in the soil, if it be loose enough, and + there mature themselves. (8/6. Vaucher says ‘Hist. Phys. des Plantes + d’Europe’ tome 3 1844 page 309, that V. hirta and collina likewise bury + their capsules. See also Lecoq ‘Geograph. Bot.’ tome 5 1856 page 180.) + Lecoq says that it is only these latter capsules which possess elastic + valves; but I think this must be a misprint, as such valves would + obviously be of no use to the buried capsules, but would serve to scatter + the seeds of the sub-aerial ones, as in the other species of Viola. It is + remarkable that this plant, according to Delpino, does not produce + cleistogamic flowers in one part of Liguria, whilst the perfect flowers + are there abundantly fertile (8/7. ‘Sull’ Opera, la Distribuzione dei + Sessi nelle Piante’ etc. 1867 page 30.); on the other hand, cleistogamic + flowers are produced by it near Turin. Another fact is worth giving as an + instance of correlated development: I found on a purple variety, after it + had produced its perfect double flowers, and whilst the white single + variety was bearing its cleistogamic flowers, many bud-like bodies which + from their position on the plant were certainly of a cleistogamic nature. + They consisted, as could be seen on bisecting them, of a dense mass of + minute scales closely folded over one another, exactly like a cabbage-head + in miniature. I could not detect any stamens, and in the place of the + ovarium there was a little central column. The doubleness of the perfect + flowers had thus spread to the cleistogamic ones, which therefore were + rendered quite sterile. + </p> + <p> + Viola hirta. + </p> + <p> + The five stamens of the cleistogamic flowers are provided, as in the last + case, with small anthers, from all of which pollen-tubes proceed to the + stigma. The petals are not quite so much reduced as in V. canina, and the + short pistil instead of being hooked is merely bent into a rectangle. Of + several perfect flowers which I saw visited by hive-and humble-bees, six + were marked, but they produced only two capsules, some of the others + having been accidentally injured. M. Monnier was therefore mistaken in + this case as in that of V. odorata, in supposing that the perfect flowers + always withered away and aborted. He states that the peduncles of the + cleistogamic flowers curve downwards and bury the ovaries beneath the + soil. (8/8. These statements are taken from Professor Oliver’s excellent + article in the ‘Natural History Review’ July 1862 page 238. With respect + to the supposed sterility of the perfect flowers in this genus see also + Timbal-Lagrave ‘Botanische Zeitung’ 1854 page 772.) I may here add that + Fritz Muller, as I hear from his brother, has found in the highlands of + Southern Brazil a white-flowered species of violet which bears + subterranean cleistogamic flowers. + </p> + <p> + Viola nana. + </p> + <p> + Mr. Scott sent me seeds of this Indian species from the Sikkim Terai, from + which I raised many plants, and from these other seedlings during several + successive generations. They produced an abundance of cleistogamic flowers + during the whole of each summer, but never a perfect one. When Mr. Scott + wrote to me his plants in Calcutta were behaving similarly, though his + collector saw the species in flower in its native site. This case is + valuable as showing that we ought not to infer, as has sometimes been + done, that a species does not bear perfect flowers when growing naturally, + because it produces only cleistogamic flowers under culture. The calyx of + these flowers is sometimes formed of only three sepals; two being actually + suppressed and not merely coherent with the others; this occurred with + five out of thirty flowers which were examined for this purpose. The + petals are represented by extremely minute scales. Of the stamens, two + bear anthers which are in the same state as in the previous species, but, + as far as I could judge, each of the two cells contained only from 20 to + 25 delicate transparent pollen-grains. These emitted their tubes in the + usual manner. The three other stamens bore very minute rudimentary + anthers, one of which was generally larger than the other two, but none of + them contained any pollen. In one instance, however, a single cell of the + larger rudimentary anther included a little pollen. The style consists of + a short flattened tube, somewhat expanded at its upper end, and this forms + an open channel leading into the ovarium, as described under V. canina. It + is slightly bent towards the two fertile anthers. + </p> + <p> + Viola Roxburghiana. + </p> + <p> + This species bore in my hothouse during two years a multitude of + cleistogamic flowers, which resembled in all respects those of the last + species; but no perfect ones were produced. Mr. Scott informs me that in + India it bears perfect flowers only during the cold season, and that these + are quite fertile. During the hot, and more especially during the rainy + season, it bears an abundance of cleistogamic flowers. + </p> + <p> + Many other species, besides the five now described, produce cleistogamic + flowers; this is the case, according to D. Muller, Michalet, Von Mohl, and + Hermann Muller, with V. elatior, lancifolia, sylvatica, palustris, + mirabilis, bicolor, ionodium, and biflora. But V. tricolor does not + produce them. + </p> + <p> + Michalet asserts that V. palustris produces near Paris only perfect + flowers, which are quite fertile; but that when the plant grows on + mountains cleistogamic flowers are produced; and so it is with V. biflora. + The same author states that he has seen in the case of V. alba flowers + intermediate in structure between the perfect and cleistogamic ones. + According to M. Boisduval, an Italian species, V. Ruppii, never bears in + France “des fleurs bien apparentes, ce qui ne l’empeche pas de + fructifier.” + </p> + <p> + It is interesting to observe the gradation in the abortion of the parts in + the cleistogamic flowers of the several foregoing species. It appears from + the statements by D. Muller and Von Mohl that in V. mirabilis the calyx + does not remain quite closed; all five stamens are provided with anthers, + and some pollen-grains probably fall out of the cells on the stigma, + instead of protruding their tubes whilst still enclosed, as in the other + species. In V. hirta all five stamens are likewise antheriferous; the + petals are not so much reduced and the pistil not so much modified as in + the following species. In V. nana and elatior only two of the stamens + properly bear anthers, but sometimes one or even two of the others are + thus provided. Lastly, in V. canina never more than two of the stamens, as + far as I have seen, bear anthers; the petals are much more reduced than in + V. hirta, and according to D. Muller are sometimes quite absent. + </p> + <p> + Oxalis acetosella. + </p> + <p> + The existence of cleistogamic flowers on this plant was discovered by + Michalet. (8/9. ‘Bulletin Soc. Bot. de France’ tome 7 1860 page 465.) They + have been fully described by Von Mohl, and I can add hardly anything to + his description. In my specimens the anthers of the five longer stamens + were nearly on a level with the stigmas; whilst the smaller and less + plainly bilobed anthers of the five shorter stamens stood considerably + below the stigmas, so that their tubes had to travel some way upwards. + According to Michalet these latter anthers are sometimes quite aborted. In + one case the tubes, which ended in excessively fine points, were seen by + me stretching upwards from the lower anthers towards the stigmas, which + they had not as yet reached. My plants grew in pots, and long after the + perfect flowers had withered they produced not only cleistogamic but a few + minute open flowers, which were in an intermediate condition between the + two kinds. In one of these the pollen-tubes from the lower anthers had + reached the stigmas, though the flower was open. The footstalks of the + cleistogamic flowers are much shorter than those of the perfect flowers, + and are so much bowed downwards that they tend, according to Von Mohl, to + bury themselves in the moss and dead leaves on the ground. Michalet also + says that they are often hypogean. In order to ascertain the number of + seeds produced by these flowers, I marked eight of them; two failed, one + cast its seed abroad, and the remaining five contained on an average 10.0 + seeds per capsule. This is rather above the average 9.2, which eleven + capsules from perfect flowers fertilised with their own pollen yielded, + and considerably above the average 7.9, from the capsules of perfect + flowers fertilised with pollen from another plant; but this latter result + must, I think, have been accidental. + </p> + <p> + Hildebrand, whilst searching various Herbaria, observed that many other + species of Oxalis besides O. acetosella produce cleistogamic flowers + (8/10. ‘Monatsbericht der Akad. der Wiss. zu Berlin’ 1866 page 369.); and + I hear from him that this is the case with the heterostyled trimorphic O. + incarnata from the Cape of Good Hope. + </p> + <p> + Oxalis (Biophytum) sensitiva. + </p> + <p> + This plant is ranked by many botanists as a distinct genus, but as a + sub-genus by Bentham and Hooker. Many of the early flowers on a mid-styled + plant in my hothouse did not open properly, and were in an intermediate + condition between cleistogamic and perfect. Their petals varied from a + rudiment to about half their proper size; nevertheless they produced + capsules. I attributed their state to unfavourable conditions, for later + in the season fully expanded flowers of the proper size appeared. But Mr. + Thwaites afterwards sent me from Ceylon a number of long-styled, + mid-styled, and short-styled flower-stalks preserved in spirits; and on + the same stalks with the perfect flowers, some of which were fully + expanded and others still in bud, there were small bud-like bodies + containing mature pollen, but with their calyces closed. These + cleistogamic flowers do not differ much in structure from the perfect ones + of the corresponding form, with the exception that their petals are + reduced to extremely minute, barely visible scales, which adhere firmly to + the rounded bases of the shorter stamens. Their stigmas are much less + papillose, and smaller in about the ratio of 13 to 20 divisions of the + micrometer, as measured transversely from apex to apex, than the stigmas + of the perfect flowers. The styles are furrowed longitudinally, and are + clothed with simple as well as glandular hairs, but only in the + cleistogamic flowers produced by the long- styled and mid-styled forms. + The anthers of the longer stamens are a little smaller than the + corresponding ones of the perfect flowers, in about the ratio of 11 to 14. + They dehisce properly, but do not appear to contain much pollen. Many + pollen-grains were attached by short tubes to the stigmas; but many + others, still adhering to the anthers, had emitted their tubes to a + considerable length, without having come in contact with the stigmas. + Living plants ought to be examined, as the stigmas, at least of the + long-styled form, project beyond the calyx, and if visited by insects + (which, however, is very improbable) might be fertilised with pollen from + a perfect flower. The most singular fact about the present species is that + long-styled cleistogamic flowers are produced by the long-styled plants, + and mid-styled as well as short-styled cleistogamic flowers by the other + two forms; so that there are three kinds of cleistogamic and three kinds + of perfect flowers produced by this one species! Most of the heterostyled + species of Oxalis are more or less sterile, many absolutely so, if + illegitimately fertilised with their own-form pollen. It is therefore + probable that the pollen of the cleistogamic flowers has been modified in + power, so as to act on their own stigmas, for they yield an abundance of + seeds. We may perhaps account for the cleistogamic flowers consisting of + the three forms, through the principle of correlated growth, by which the + cleistogamic flowers of the double violet have been rendered double. + </p> + <p> + Vandellia nummularifolia. + </p> + <p> + Dr. Kuhn has collected all the notices with respect to cleistogamic + flowers in this genus, and has described from dried specimens those + produced by an Abyssinian species. (8/11. ‘Botanische Zeitung’ 1867 page + 65.) Mr. Scott sent me from Calcutta seeds of the above common Indian + weed, from which many plants were successively raised during several + years. The cleistogamic flowers are very small, being when fully mature + under 1/20 of an inch (1.27 millimetres) in length. The calyx does not + open, and within it the delicate transparent corolla remains closely + folded over the ovarium. There are only two anthers instead of the normal + number of four, and their filaments adhere to the corolla. The cells of + the anthers diverge much at their lower ends and are only 5/700 of an inch + (.181 millimetres) in their longer diameter. They contain but few + pollen-grains, and these emit their tubes whilst still within the anther. + The pistil is very short, and is surmounted by a bilobed stigma. As the + ovary grows the two anthers together with the shrivelled corolla, all + attached by the dried pollen-tubes to the stigma, are torn off and carried + upwards in the shape of a little cap. The perfect flowers generally appear + before the cleistogamic, but sometimes simultaneously with them. During + one season a large number of plants produced no perfect flowers. It has + been asserted that the latter never yield capsules; but this is a mistake, + as they do so even when insects are excluded. Fifteen capsules from + cleistogamic flowers on plants growing under favourable conditions + contained on an average 64.2 seeds, with a maximum of 87; whilst 20 + capsules from plants growing much crowded yielded an average of only 48. + Sixteen capsules from perfect flowers artificially crossed with pollen + from another plant contained on an average 93 seeds, with a maximum of + 137. Thirteen capsules from self-fertilised perfect flowers gave an + average of 62 seeds, with a maximum of 135. Therefore the capsules from + the cleistogamic flowers contained fewer seeds than those from perfect + flowers when cross-fertilised, and slightly more than those from perfect + flowers self-fertilised. + </p> + <p> + Dr. Kuhn believes that the Abyssinian V. sessiflora does not differ + specifically from the foregoing species. But its cleistogamic flowers + apparently include four anthers instead of two as above described. The + plants, moreover, of V. sessiflora produce subterranean runners which + yield capsules; and I never saw a trace of such runners in V. + nummularifolia, although many plants were cultivated. + </p> + <p> + Linaria spuria. + </p> + <p> + Michalet says that short, thin, twisted branches are developed from the + buds in the axils of the lower leaves, and that these bury themselves in + the ground. (8/12. ‘Bulletin Soc. Bot. de France’ tome 7 1860 page 468.) + They there produce flowers not offering any peculiarity in structure, + excepting that their corollas, though properly coloured, are deformed. + These flowers may be ranked as cleistogamic, as they are developed, and + not merely drawn, beneath the ground. + </p> + <p> + Ononis columnae. + </p> + <p> + Plants were raised from seeds sent me from Northern Italy. The sepals of + the cleistogamic flowers are elongated and closely pressed together; the + petals are much reduced in size, colourless, and folded over the interior + organs. The filaments of the ten stamens are united into a tube, and this + is not the case, according to Von Mohl, with the cleistogamic flowers of + other Leguminosae. Five of the stamens are destitute of anthers, and + alternate with the five thus provided. The two cells of the anthers are + minute, rounded and separated from one another by connective tissue; they + contain but few pollen-grains, and these have extremely delicate coats. + The pistil is hook-shaped, with a plainly enlarged stigma, which is curled + down, towards the anthers; it therefore differs much from that of the + perfect flower. During the year 1867 no perfect flowers were produced, but + in the following year there were both perfect and cleistogamic ones. + </p> + <p> + Ononis minutissima. + </p> + <p> + My plants produced both perfect and cleistogamic flowers; but I did not + examine the latter. Some of the former were crossed with pollen from a + distinct plant, and six capsules thus obtained yielded on an average 3.66 + seeds, with a maximum of 5 in one. Twelve perfect flowers were marked and + allowed to fertilise themselves spontaneously under a net, and they + yielded eight capsules, containing on an average 2.38 seeds, with a + maximum of 3 in one. Fifty-three capsules produced by the cleistogamic + flowers contained on an average 4.1 seeds, so that these were the most + productive of all; and the seeds themselves looked finer even than those + from the crossed perfect flowers. According to Mr. Bentham O. parviflora + likewise bears cleistogamic flowers; and he informs me that these flowers + are produced by all three species early in the spring; whilst the perfect + ones appear afterwards, and therefore in a reversed order compared with + those of Viola and Oxalis. Some of the species, for instance Ononis + columnae, bear a fresh crop of cleistogamic flowers in the autumn. + </p> + <p> + Lathyrus nissolia. + </p> + <p> + This plant apparently offers a case of the first stage in the production + of cleistogamic flowers, for on plants growing in a state of nature, many + of the flowers never expand and yet produce fine pods. Some of the buds + are so large that they seem on the point of expansion; others are much + smaller, but none so small as the true cleistogamic flowers of the + foregoing species. As I marked these buds with thread and examined them + daily, there could be no mistake about their producing fruit without + having expanded. + </p> + <p> + Several other Leguminous genera produce cleistogamic flowers, as may be + seen in Table 8.38; but much does not appear to be known about them. Von + Mohl says that their petals are commonly rudimentary, that only a few of + their anthers are developed, their filaments are not united into a tube + and their pistils are hook-shaped. In three of the genera, namely Vicia, + Amphicarpaea, and Voandzeia, the cleistogamic flowers are produced on + subterranean stems. The perfect flowers of Voandzeia, which is a + cultivated plant, are said never to produce fruit (8/13. Correa de Mello + ‘Journal of the Linnean Society Botany’ volume 11 1870 page 254, + particularly attended to the flowering and fruiting of this African plant, + which is sometimes cultivated in Brazil.); but we should remember how + often fertility is affected by cultivation. + </p> + <p> + Impatiens fulva. + </p> + <p> + Mr. A.W. Bennett has published an excellent description, with figures, of + this plant. (8/14. ‘Journal of the Linnean Society Botany’ volume 13 1872 + page 147.) He shows that the cleistogamic and perfect flowers differ in + structure at a very early period of growth, so that the existence of the + former cannot be due merely to the arrested development of the latter,—a + conclusion which indeed follows from most of the previous descriptions. + Mr. Bennett found on the banks of the Wey that the plants which bore + cleistogamic flowers alone were to those bearing perfect flowers as 20 to + 1; but we should remember that this is a naturalised species. The perfect + flowers are usually barren in England; but Professor Asa Gray writes to me + that after midsummer in the United States some or many of them produce + capsules. + </p> + <p> + Impatiens noli-me-tangere. + </p> + <p> + I can add nothing of importance to Von Mohl’s description, excepting that + one of the rudimentary petals shows a vestige of a nectary, as Mr. Bennett + likewise found to be the case with I. fulva. As in this latter species all + five stamens produce some pollen, though small in amount; a single anther + contains, according to Von Mohl, not more than 50 grains, and these emit + their tubes while still enclosed within it. The pollen-grains of the + perfect flowers are tied together by threads, but not, so far as I could + see, those of the cleistogamic flowers; and a provision of this kind would + here have been useless, as the grains can never be transported by insects. + The flowers of I. balsamina are visited by humble-bees (8/15. H. Muller + ‘Die Befruchtung’ etc. page 170.), and I am almost sure that this is the + case with the perfect flowers of I. noli-me-tangere. From the perfect + flowers of this latter species covered with a net eleven spontaneously + self-fertilised capsules were produced, and these yielded on an average + 3.45 seeds. Some perfect flowers with their anthers still containing an + abundance of pollen were fertilised with pollen from a distinct plant; and + the three capsules thus produced contained, to my surprise, only 2, 2, and + 1 seed. As I. balsamina is proterandrous, so probably is the present + species; and if so, cross-fertilisation was effected by me at too early a + period, and this may account for the capsules yielding so few seeds. + </p> + <p> + Drosera rotundifolia. + </p> + <p> + The first flower-stems which were thrown up by some plants in my + greenhouse bore only cleistogamic flowers. The petals of small size + remained permanently closed over the reproductive organs, but their white + tips could just be seen between the almost completely closed sepals. The + pollen, which was scanty in amount, but not so scanty as in Viola or + Oxalis, remained enclosed within the anthers, whence the tubes proceeded + and penetrated the stigma. As the ovarium swelled the little withered + corolla was carried upwards in the form of a cap. These cleistogamic + flowers produced an abundance of seed. Later in the season perfect flowers + appeared. With plants in a state of nature the flowers open only in the + early morning, as I have been informed by Mr. Wallis, who particularly + attended to the time of their flowering. In the case of D. Anglica, the + still folded petals on some plants in my greenhouse opened just + sufficiently to leave a minute aperture; the anthers dehisced properly, + but the pollen-grains adhered in a mass to them, and thence emitted their + tubes, which penetrated the stigmas. These flowers, therefore, were in an + intermediate condition, and could not be called either perfect or + cleistogamic. + </p> + <p> + A few miscellaneous observations may be added with respect to some other + species, as throwing light on our subject. Mr. Scott states that + Eranthemum ambiguum bears three kinds of flowers,—large, + conspicuous, open ones, which are quite sterile,—others of + intermediate size, which are open and moderately fertile—and lastly + small closed or cleistogamic ones, which are perfectly fertile. (8/16. + ‘Journal of Botany’ London new series volume 1 1872 pages 161- 4.) Ruellia + tuberosa, likewise one of the Acanthaceae, produces both open and + cleistogamic flowers; the latter yield from 18 to 24, whilst the former + only from 8 to 10 seeds; these two kinds of flowers are produced + simultaneously, whereas in several other members of the family the + cleistogamic ones appear only during the hot season. According to Torrey + and Gray, the North American species of Helianthemum, when growing in poor + soil, produce only cleistogamic flowers. The cleistogamic flowers of + Specularia perfoliata are highly remarkable, as they are closed by a + tympanum formed by the rudimentary corolla, and without any trace of an + opening. The stamens vary from 3 to 5 in number, as do the sepals. (8/17. + Von Mohl ‘Botanische Zeitung’ 1863 pages 314 and 323. Dr. Bromfield + ‘Phytologist’ volume 3 page 530, also remarks that the calyx of the + cleistogamic flowers is usually only 3-cleft, while that of the perfect + flower is mostly 5- cleft.) The collecting hairs on the pistil, which play + so important a part in the fertilisation of the perfect flowers, are here + quite absent. Drs. Hooker and Thomson state that some of the Indian + species of Campanula produce two kinds of flowers; the smaller ones being + borne on longer peduncles with differently formed sepals, and producing a + more globose ovary. (8/18. ‘Journal of the Linnean Society’ volume 2 1857 + page 7. See also Professor Oliver in ‘Natural History Review’ 1862 page + 240.) The flowers are closed by a tympanum like that in Specularia. Some + of the plants produce both kinds of flowers, others only one kind; both + yield an abundance of seeds. Professor Oliver adds that he has seen + flowers on Campanula colorata in an intermediate condition between + cleistogamic and perfect ones. + </p> + <p> + The solitary almost sessile cleistogamic flowers produced by Monochoria + vaginalis are differently protected from those in any of the previous + cases, namely, within “a short sack formed of the membranous spathe, + without any opening or fissure.” There is only a single fertile stamen; + the style is almost obsolete, with the three stigmatic surfaces directed + to one side. Both the perfect and cleistogamic flowers produce seeds. + (8/19. Dr. Kirk ‘Journal of the Linnean Society’ volume 8 1864 page 147.) + </p> + <p> + The cleistogamic flowers on some of the Malpighiaceae seem to be more + profoundly modified than those in any of the foregoing genera. According + to A. de Jussieu they are differently situated from the perfect flowers; + they contain only a single stamen, instead of 5 or 6; and it is a strange + fact that this particular stamen is not developed in the perfect flowers + of the same species. (8/20. ‘Archives du Museum’ tome 3 1843 pages 35-38, + 82-86, 589, 598.) The style is absent or rudimentary; and there are only + two ovaries instead of three. Thus these degraded flowers, as Jussieu + remarks, “laugh at our classifications, for the greater number of the + characters proper to the species, to the genus, to the family, to the + class disappear.” I may add that their calyces are not glandular, and as, + according to Kerner, the fluid secreted by such glands generally serves to + protect the flowers from crawling insects, which steal the nectar without + aiding in their cross-fertilisation (8/21. ‘Die Schutzmittel der Bluthen + gegen unberufene Gaste’ 1876 page 25.), the deficiency of the glands in + the cleistogamic flowers of these plants may perhaps be accounted for by + their not requiring any such protection. + </p> + <p> + As the Asclepiadous genus Stapelia is said to produce cleistogamic + flowers, the following case may be worth giving. I have never heard of the + perfect flowers of Hoya carnosa setting seeds in this country, but some + capsules were produced in Mr. Farrer’s hothouse; and the gardener detected + that they were the product of minute bud-like bodies, three or four of + which could sometimes be found on the same umbel with the perfect flowers. + They were quite closed and hardly thicker than their peduncles. The sepals + presented nothing particular, but internally and alternating with them, + there were five small flattened heart-shaped papillae, like rudiments of + petals; but the homological nature of which appeared doubtful to Mr. + Bentham and Dr. Hooker. No trace of anthers or of stamens could be + detected; and I knew from having examined many cleistogamic flowers what + to look for. There were two ovaries, full of ovules, quite open at their + upper ends, with their edges festooned, but with no trace of a proper + stigma. In all these flowers one of the two ovaries withered and blackened + long before the other. The one perfect capsule, 3 1/2 inches in length, + which was sent me, had likewise been developed from a single carpel. This + capsule contained an abundance of plumose seeds, many of which appeared + quite sound, but they did not germinate when sown at Kew. Therefore the + little bud-like flower which produced this capsule probably was as + destitute of pollen as were those which I examined. + </p> + <p> + Juncus bufonius and Hordeum. + </p> + <p> + All the species hitherto mentioned which produce cleistogamic flowers are + entomophilous; but four genera, Juncus, Hordeum, Cryptostachys, and + Leersia are anemophilous. Juncus bufonius is remarkable by bearing in + parts of Russia only cleistogamic flowers, which contain three instead of + the six anthers found in the perfect flowers. (8/22. See Dr. Ascherson’s + interesting paper in ‘Botanische Zeitung’ 1871 page 551.) In the genus + Hordeum it has been shown by Delpino that the majority of the flowers are + cleistogamic, some of the others expanding and apparently allowing of + cross-fertilisation. (8/23. ‘Bollettini del Comizio agrario Parmense.’ + Marzo e Aprile 1871. An abstract of this valuable paper is given in + ‘Botanische Zeitung’ 1871 page 537. See also Hildebrand on Hordeum in + ‘Monatsbericht d. K. Akad Berlin’ October 1872 page 760.) I hear from + Fritz Muller that there is a grass in Southern Brazil, in which the sheath + of the uppermost leaf, half a metre in length, envelopes the whole + panicle; and this sheath never opens until the self-fertilised seeds are + ripe. On the roadside some plants had been cut down, whilst the + cleistogamic panicles were developing, and these plants afterwards + produced free or unenclosed panicles of small size, bearing perfect + flowers. + </p> + <p> + Leersia oryzoides. + </p> + <p> + It has long been known that this plant produces cleistogamic flowers, but + these were first described with care by M. Duval-Jouve. (8/24. ‘Bulletin + Bot. Soc. de France’ tome 10 1863 page 194.) I procured plants from a + stream near Reigate, and cultivated them for several years in my + greenhouse. The cleistogamic flowers are very small, and usually mature + their seeds within the sheaths of the leaves. These flowers are said by + Duval-Jouve to be filled by slightly viscid fluid; but this was not the + case with several that I opened; but there was a thin film of fluid + between the coats of the glumes, and when these were pressed the fluid + moved about, giving a similarly deceptive appearance of the whole inside + of the flower being thus filled. The stigma is very small and the + filaments extremely short; the anthers are less than 1/50 of an inch in + length or about one-third of the length of those in the perfect flowers. + One of the three anthers dehisces before the two others. Can this have any + relation with the fact that in some other species of Leersia only two + stamens are fully developed? (8/25. Asa Gray ‘Manual of Botany of the + United States’ 1856 page 540.) The anthers shed their pollen on the + stigma; at least in one instance this was clearly the case, and by tearing + open the anthers under water the grains were easily detached. Towards the + apex of the anther the grains are arranged in a single row and lower down + in two or three rows, so that they could be counted; and there were about + 35 in each cell, or 70 in the whole anther; and this is an astonishingly + small number for an anemophilous plant. The grains have very delicate + coats, are spherical and about 5/7000 of an inch (.0181 millimetres), + whilst those of the perfect flowers are about 7/7000 of an inch (.0254 + millimetres) in diameter. + </p> + <p> + M. Duval-Jouve states that the panicles very rarely protrude from their + sheaths, but that when this does happen the flowers expand and exhibit + well-developed ovaries and stigmas, together with full-sized anthers + containing apparently sound pollen; nevertheless such flowers are + invariably quite sterile. Schreiber had previously observed that if a + panicle is only half protruded, this half is sterile, whilst the still + included half is fertile. Some plants which grew in a large tub of water + in my greenhouse behaved on one occasion in a very different manner. They + protruded two very large much-branched panicles; but the florets never + opened, though these included fully developed stigmas, and stamens + supported on long filaments with large anthers that dehisced properly. If + these florets had opened for a short time unperceived by me and had then + closed again, the empty anthers would have been left dangling outside. + Nevertheless they yielded on August 17th an abundance of fine ripe seeds. + Here then we have a near approach to the single case as yet known of this + grass producing in a state of nature (in Germany) perfect flowers which + yielded a copious supply of fruit. (8/26. Dr. Ascherson ‘Botanische + Zeitung’ 1864 page 350.) Seeds from the cleistogamic flowers were sent by + me to Mr. Scott in Calcutta, who there cultivated the plants in various + ways, but they never produced perfect flowers. + </p> + <p> + In Europe Leersia oryzoides is the sole representative of its genus, and + Duval- Jouve, after examining several exotic species, found that it + apparently is the sole one which bears cleistogamic flowers. It ranges + from Persia to North America, and specimens from Pennsylvania resembled + the European ones in their concealed manner of fructification. There can + therefore be little doubt that this plant generally propagates itself + throughout an immense area by cleistogamic seeds, and that it can hardly + ever be invigorated by cross- fertilisation. It resembles in this respect + those plants which are now widely spread, though they increase solely by + asexual generation. (8/27. I have collected several such cases in my + ‘Variation under Domestication’ chapter 18 2nd edition volume 2 page 153.) + </p> + <h3> + CONCLUDING REMARKS ON CLEISTOGAMIC FLOWERS. + </h3> + <p> + That these flowers owe their structure primarily to the arrested + development of perfect ones, we may infer from such cases as that of the + lower rudimentary petal in Viola being larger than the others, like the + lower lip of the perfect flower,—from a vestige of a spur in the + cleistogamic flowers of Impatiens,— from the ten stamens of Ononis + being united into a tube,—and other such structures. The same + inference may be drawn from the occurrence, in some instances, on the same + plant of a series of gradations between the cleistogamic and perfect + flowers. But that the former owe their origin wholly to arrested + development is by no means the case; for various parts have been specially + modified, so as to aid in the self-fertilisation of the flowers, and as a + protection to the pollen; for instance, the hook-shaped pistil in Viola + and in some other genera, by which the stigma is brought close to the + fertile anthers,- -the rudimentary corolla of Specularia modified into a + perfectly closed tympanum, and the sheath of Monochoria modified into a + closed sack,—the excessively thin coats of the pollen-grains,—the + anthers not being all equally aborted, and other such cases. Moreover Mr. + Bennett has shown that the buds of the cleistogamic and perfect flowers of + Impatiens differ at a very early period of growth. + </p> + <p> + The degree to which many of the most important organs in these degraded + flowers have been reduced or even wholly obliterated, is one of their most + remarkable peculiarities, reminding us of many parasitic animals. In some + cases only a single anther is left, and this contains but few + pollen-grains of diminished size; in other cases the stigma has + disappeared, leaving a simple open passage into the ovarium. It is also + interesting to note the complete loss of trifling points in the structure + or functions of certain parts, which though of service to the perfect + flowers, are of none to the cleistogamic; for instance the collecting + hairs on the pistil of Specularia, the glands on the calyx of the + Malpighiaceae, the nectar-secreting appendages to the lower stamens of + Viola, the secretion of nectar by other parts, the emission of a sweet + odour, and apparently the elasticity of the valves in the buried capsules + of Viola odorata. We here see, as throughout nature, that as soon as any + part or character becomes superfluous it tends sooner or later to + disappear. + </p> + <p> + Another peculiarity in these flowers is that the pollen-grains generally + emit their tubes whilst still enclosed within the anthers; but this is not + so remarkable a fact as was formerly thought, when the case of Asclepias + was alone known. (8/28. The case of Asclepias was described by R. Brown. + Baillon asserts ‘Adansonia’ tome 2 1862 page 58, that with many plants the + tubes are emitted from pollen-grains which have not come into contact with + the stigma; and that they may be seen advancing horizontally through the + air towards the stigma. I have observed the emission of the tubes from the + pollen-masses whilst still within the anthers, in three widely distinct + Orchidean genera namely Aceras, Malaxis, and Neottia: see ‘The Various + Contrivances by which Orchids are Fertilised’ 2nd edition page 258.) It + is, however, a wonderful sight to behold the tubes directing themselves in + a straight line to the stigma, when this is at some little distance from + the anthers. As soon as they reach the stigma or the open passage leading + into the ovarium, no doubt they penetrate it, guided by the same means, + whatever these may be, as in the case of ordinary flowers. I thought that + they might be guided by the avoidance of light: some pollen-grains of a + willow were therefore immersed in an extremely weak solution of honey, and + the vessel was placed so that the light entered only in one direction, + laterally or from below or from above, but the long tubes were in each + case protruded in every possible direction. + </p> + <p> + As cleistogamic flowers are completely closed they are necessarily self- + fertilised, not to mention the absence of any attraction to insects; and + they thus differ widely from the great majority of ordinary flowers. + Delpino believes that cleistogamic flowers have been developed in order to + ensure the production of seeds under climatic or other conditions which + tend to prevent the fertilisation of the perfect flowers. (8/29. ‘Sull’ + Opera la Distribuzione dei Sessi nelle Piante’ 1867 page 30.) I do not + doubt that this holds good to a certain limited extent, but the production + of a large supply of seeds with little consumption of nutrient matter or + expenditure of vital force is probably a far more efficient motive power. + The whole flower is much reduced in size; but what is much more important, + an extremely small quantity of pollen has to be formed, as none is lost + through the action of insects or the weather; and pollen contains much + nitrogen and phosphorus. Von Mohl estimated that a single cleistogamic + anther-cell of Oxalis acetosella contained from one to two dozen + pollen-grains; we will say 20, and if so the whole flower can have + produced at most 400 grains; with Impatiens the whole number may be + estimated in the same manner at 250; with Leersia at 210; and with Viola + nana at only 100. These figures are wonderfully low compared with the + 243,600 pollen-grains produced by a flower of Leontodon, the 4,863 by an + Hibiscus, or the 3,654,000 by a Paeony. (8/30. The authorities for these + statements are given in my ‘Effects of Cross and Self-Fertilisation’ page + 376.) We thus see that cleistogamic flowers produce seeds with a + wonderfully small expenditure of pollen; and they produce as a general + rule quite as many seeds as the perfect flowers. + </p> + <p> + That the production of a large number of seeds is necessary or beneficial + to many plants needs no evidence. So of course is their preservation + before they are ready for germination; and it is one of the many + remarkable peculiarities of the plants which bear cleistogamic flowers, + that an incomparably larger proportion of them than of ordinary plants + bury their young ovaries in the ground;—an action which it may be + presumed serves to protect them from being devoured by birds or other + enemies. But this advantage is accompanied by the loss of the power of + wide dissemination. No less than eight of the genera in the list at the + beginning of this chapter include species which act in this manner, + namely, several kinds of Viola, Oxalis, Vandellia, Linaria, Commelina, and + at least three genera of Leguminosae. The seeds also of Leersia, though + not buried, are concealed in the most perfect manner within the sheaths of + the leaves. Cleistogamic flowers possess great facilities for burying + their young ovaries or capsules, owing to their small size, pointed shape, + closed condition and the absence of a corolla; and we can thus understand + how it is that so many of them have acquired this curious habit. + </p> + <p> + It has already been shown that in about 32 out of the 55 genera in the + list just referred to, the perfect flowers are irregular; and this implies + that they have been specially adapted for fertilisation by insects. + Moreover three of the genera with regular flowers are adapted by other + means for the same end. Flowers thus constructed are liable during certain + seasons to be imperfectly fertilised, namely, when the proper insects are + scarce; and it is difficult to avoid the belief that the production of + cleistogamic flowers, which ensures under all circumstances a full supply + of seed, has been in part determined by the perfect flowers being liable + to fail in their fertilisation. But if this determining cause be a real + one, it must be of subordinate importance, as four of the genera in the + list are fertilised by the wind; and there seems no reason why their + perfect flowers should fail to be fertilised more frequently than those in + any other anemophilous genus. In contrast with what we here see with + respect to the large proportion of the perfect flowers being irregular, + one genus alone out of the 38 heterostyled genera described in the + previous chapters bears such flowers; yet all these genera are absolutely + dependent on insects for their legitimate fertilisation. I know not how to + account for this difference in the proportion of the plants bearing + regular and irregular flowers in the two classes, unless it be that the + heterostyled flowers are already so well adapted for cross-fertilisation, + through the position of their stamens and pistils and the difference in + power of their two or three kinds of pollen, that any additional + adaptation, namely, through the flowers being made irregular, has been + rendered superfluous. + </p> + <p> + Although cleistogamic flowers never fail to yield a large number of seeds, + yet the plants bearing them usually produce perfect flowers, either + simultaneously or more commonly at a different period; and these are + adapted for or admit of cross-fertilisation. From the cases given of the + two Indian species of Viola, which produced in this country during several + years only cleistogamic flowers, and of the numerous plants of Vandellia + and of some plants of Ononis which behaved during one whole season in the + same manner, it appears rash to infer from such cases as that of Salvia + cleistogama not having produced perfect flowers during five years in + Germany (8/31. Dr. Ascherson ‘Botanische Zeitung’ 1871 page 555.), and of + an Aspicarpa not having done so during several years in Paris, that these + plants would not bear perfect flowers in their native homes. Von Mohl and + several other botanists have repeatedly insisted that as a general rule + the perfect flowers produced by cleistogamic plants are sterile; but it + has been shown under the head of the several species that this is not the + case. The perfect flowers Viola are indeed sterile unless they are visited + by bees; but when thus visited they yield the full number of seeds. As far + as I have been able to discover there is only one absolute exception to + the rule that the perfect flowers are fertile, namely, that of Voandzeia; + and in this case we should remember that cultivation often affects + injuriously the reproductive organs. Although the perfect flowers of + Leersia sometimes yield seeds, yet this occurs so rarely, as far as + hitherto observed, that it practically forms a second exception to the + rule. + </p> + <p> + As cleistogamic flowers are invariably fertilised, and as they are + produced in large numbers, they yield altogether a much larger supply of + seeds than do the perfect flowers on the same plant. But the latter + flowers will occasionally be cross-fertilised, and their offspring will + thus be invigorated, as we may infer from a wide-spread analogy. But of + such invigoration I have only a small amount of direct evidence: two + crossed seedlings of Ononis minutissima were put into competition with two + seedlings raised from cleistogamic flowers; they were at first all of + equal height; the crossed were then slightly beaten; but on the following + year they showed the usual superiority of their class, and were to the + self-fertilised plants of cleistogamic origin as 100 to 88 in mean height. + With Vandellia twenty crossed plants exceeded in height twenty plants + raised from cleistogamic seeds only by a little, namely, in the ratio of + 100 to 94. + </p> + <p> + It is a natural inquiry how so many plants belonging to various very + distinct families first came to have the development of their flowers + arrested, so as ultimately to become cleistogamic. That a passage from the + one state to the other is far from difficult is shown by the many recorded + cases of gradations between the two states on the same plant, in Viola, + Oxalis, Biophytum, Campanula, etc. In the several species of Viola the + various parts of the flowers have also been modified in very different + degrees. Those plants which in their own country produce flowers of full + or nearly full size, but never expand (as with Thelymitra), and yet set + fruit, might easily be rendered cleistogamic. Lathyrus nissolia seems to + be in an incipient transitional state, as does Drosera Anglica, the + flowers of which are not perfectly closed. There is good evidence that + flowers sometimes fail to expand and are somewhat reduced in size, owing + to exposure to unfavourable conditions, but still retain their fertility + unimpaired. Linnaeus observed in 1753 that the flowers on several plants + brought from Spain and grown at Upsala did not show any corolla and yet + produced seeds. Asa Gray has seen flowers on exotic plants in the Northern + United States which never expanded and yet fruited. With certain English + plants, which bear flowers during nearly the whole year, Mr. Bennett found + that those produced during the winter season were fertilised in the bud; + whilst with other species having fixed times for flowering, but “which had + been tempted by a mild January to put forth a few wretched flowers,” no + pollen was discharged from the anthers, and no seed was formed. The + flowers of Lysimachia vulgaris if fully exposed to the sun expand + properly, while those growing in shady ditches have smaller corollas which + open only slightly; and these two forms graduate into one another in + intermediate stations. Herr Bouche’s observations are of especial + interest, for he shows that both temperature and the amount of light + affect the size of the corolla; and he gives measurements proving that + with some plants the corolla is diminished by the increasing cold and + darkness of the changing season, whilst with others it is diminished by + the increasing heat and light. (8/32. For the statement by Linnaeus see + Mohl in ‘Botanische Zeitung’ 1863 page 327. Asa Gray ‘American Journal of + Science’ 2nd series volume 39 1865 page 105. Bennett in ‘Nature’ November + 1869 page 11. The Reverend G. Henslow also says ‘Gardener’s Chronicle’ + 1877 page 271, also ‘Nature’ October 19, 1876 page 543, “that when the + autumn draws on, and habitually in winter for such of our wild flowers as + blossom at that season” the flowers are self-fertilised. On Lysimachia H. + Muller ‘Nature’ September 1873 page 433. Bouche ‘Sitzungsbericht der + Gesell. Naturforsch. Freunde’ October 1874 page 90.) + </p> + <p> + The belief that the first step towards flowers being rendered cleistogamic + was due to the conditions to which they were exposed, is supported by the + fact of various plants belonging to this class either not producing their + cleistogamic flowers under certain conditions, or, on the other hand, + producing them to the complete exclusion of the perfect ones. Thus some + species of Viola do not bear cleistogamic flowers when growing on the + lowlands or in certain districts. Other plants when cultivated have failed + to produce perfect flowers during several successive years; and this is + the case with Juncus bufonius in its native land of Russia. Cleistogamic + flowers are produced by some species late and by others early in the + season; and this agrees with the view that the first step towards their + development was due to climate; though the periods at which the two sorts + of flowers now appear must since have become much more distinctly defined. + We do not know whether too low are too high a temperature or the amount of + light acts in a direct manner on the size of the corolla, or indirectly + through the male organs being first affected. However this may be, if a + plant were prevented either early or late in the season from fully + expanding its corolla, with some reduction in its size, but with no loss + of the power of self-fertilisation, then natural selection might well + complete the work and render it strictly cleistogamic. The various organs + would also, it is probable, be modified by the peculiar conditions to + which they are subjected within a completely closed flower; also by the + principle of correlated growth, and by the tendency in all reduced organs + finally to disappear. The result would be the production of cleistogamic + flowers such as we now see them; and these are admirably fitted to yield a + copious supply of seed at a wonderfully small cost to the plant. + </p> + <p> + I will now sum up very briefly the chief conclusions which seem to follow + from the observations given in this volume. Cleistogamic flowers afford, + as just stated, an abundant supply of seeds with little expenditure; and + we can hardly doubt that they have had their structure modified and + degraded for this special purpose; perfect flowers being still almost + always produced so as to allow of occasional cross-fertilisation. + Hermaphrodite plants have often been rendered monoecious, dioecious or + polygamous; but as the separation of the sexes would have been injurious, + had not pollen been already transported habitually by insects or by the + wind from flower to flower, we may assume that the process of separation + did not commence and was not completed for the sake of the advantages to + be gained from cross-fertilisation. The sole motive for the separation of + the sexes which occurs to me, is that the production of a great number of + seeds might become superfluous to a plant under changed conditions of + life; and it might then be highly beneficial to it that the same flower or + the same individual should not have its vital powers taxed, under the + struggle for life to which all organisms are subjected, by producing both + pollen and seeds. With respect to the plants belonging to the + gyno-dioecious sub-class, or those which co-exist as hermaphrodites and + females, it has been proved that they yield a much larger supply of seed + than they would have done if they had all remained hermaphrodites; and we + may feel sure from the large number of seeds produced by many plants that + such production is often necessary or advantageous. It is therefore + probable that the two forms in this sub-class have been separated or + developed for this special end. + </p> + <p> + Various hermaphrodite plants have become heterostyled, and now exist under + two or three forms; and we may confidently believe that this has been + effected in order that cross-fertilisation should be assured. For the full + and legitimate fertilisation of these plants pollen from the one form must + be applied to the stigma of another. If the sexual elements belonging to + the same form are united the union is an illegitimate one and more or less + sterile. With dimorphic species two illegitimate unions, and with + trimorphic species twelve are possible. There is reason to believe that + the sterility of these unions has not been specially acquired, but follows + as an incidental result from the sexual elements of the two or three forms + having been adapted to act on one another in a particular manner, so that + any other kind of union is inefficient, like that between distinct + species. Another and still more remarkable incidental result is that the + seedlings from an illegitimate union are often dwarfed and more or less or + completely barren, like hybrids from the union of two widely distinct + species. + </p> + <h3> + INDEX. + </h3> + <p> + Acanthaceae. + </p> + <p> + Acer campestre. + </p> + <p> + Adoxa. + </p> + <p> + Aegiphila elata. —mollis. —obdurata. + </p> + <p> + Alefeld, Dr., on Linum. + </p> + <p> + Alisma natans. + </p> + <p> + Amphicarpaea. + </p> + <p> + Amsinckia spectabilis. Variability in length of stamens and pistil. + </p> + <p> + Anchusa arvensis. + </p> + <p> + Androsace vitalliana. + </p> + <p> + Anthers, size of, in different forms. contabescent. + </p> + <p> + Arachis. + </p> + <p> + Arnebia hispidissima. + </p> + <p> + Ascherson, Dr., on Salvia cleistogama. Juncus bufonius. Leersia oryzoides. + </p> + <p> + Asclepias. + </p> + <p> + Ash, the common. + </p> + <p> + Asperula scoparia. + </p> + <p> + Axell on Primula stricta. + </p> + <p> + Babington, Professor, on Primula elatior. Stellaria graminea. + </p> + <p> + Baillon, emission of the tubes from pollen-grains. + </p> + <p> + Belhomme, M., on ray-florets. + </p> + <p> + Bennett, A.W., on Impatiens fulva. flowers fertilised whilst in the bud + state. + </p> + <p> + Bentham, Mr., on the differentiation of the sexes. on the cleistogamic + flowers of Ononis. + </p> + <p> + Boragineae. + </p> + <p> + Boreau on cowslip and primrose. + </p> + <p> + Borreria. + </p> + <p> + Bouche on Pavonia. effect of temperature and light on corolla. + </p> + <p> + Bouvardia leiantha. + </p> + <p> + Braun on Dracocephalum. + </p> + <p> + Breitenbach, W., on Primula elatior. + </p> + <p> + Bromfield, Dr., on primrose and cowslip. Primula elatior. Specularia + perfoliata. + </p> + <p> + Brown, Robert, on sexual changes. + </p> + <p> + Buckwheat, the common. + </p> + <p> + Caltha palustris. + </p> + <p> + Campanula colorata. + </p> + <p> + Cardamine amara. + </p> + <p> + Caspary, Professor, on Rhamnus catharticus. + </p> + <p> + Cattleya. + </p> + <p> + Chamissoa. + </p> + <p> + Cinchona micrantha. + </p> + <p> + Cleistogamic flowers. list of genera. on their origin. + </p> + <p> + Cnicus acaulis. — palustris. + </p> + <p> + Coccocypselum. pollen-grains of. + </p> + <p> + Coprosma. + </p> + <p> + Cordia. pistil of. + </p> + <p> + Corolla, difference in size in the sexes of the same species. + </p> + <p> + Corydalis. + </p> + <p> + Corylus avellana. + </p> + <p> + Cowslip, the common. short- and long-styled. + </p> + <p> + Cratoxylon formosum. + </p> + <p> + Crocker, C.W., on Plantago lanceolata. + </p> + <p> + Cryptostachys. + </p> + <p> + Cuphea purpurea. + </p> + <p> + Darwin, Charles, on reproductive organs under cultivation. intercrossed + plants. prepotency of pollen. insects fertilising flowers. Cephalanthera + grandiflora. Epidendron and Cattleya. number of pollen-grains. + </p> + <p> + Darwin, W., on Pulmonaria angustifolia. + </p> + <p> + Datura arborea. + </p> + <p> + Delpino, plants fertilised by the wind. on the walnut. Polygonaceae. + pollen-grains. Thymus serpyllum. closed or cleistogamic flowers. Viola + odorata. + </p> + <p> + Dianthus barbatus. + </p> + <p> + Dickie, Dr., on Eriophorum angustifolium. + </p> + <p> + Dictamnus fraxinella. + </p> + <p> + Diodia. + </p> + <p> + Dioecious and sub-dioecious plants. + </p> + <p> + Discospermum. + </p> + <p> + Doubleday, H., on Primula elatior. + </p> + <p> + Dracocephalum Moldavicum. + </p> + <p> + Drosera Anglica. — rotundifolia. + </p> + <p> + Duval-Jouve, M., on Cryptostachys. Leersia oryzoides. + </p> + <p> + Dyer, Thiselton, on Salvia Horminum. Cratoxylon formosum. + </p> + <p> + Echium vulgare. + </p> + <p> + Epidendron. + </p> + <p> + Epigaea repens. + </p> + <p> + Eranthemum ambiguum. + </p> + <p> + Eriophorum angustifolium. + </p> + <p> + Erythroxylum. pollen-grains of. + </p> + <p> + Euonymus Europaeus. + </p> + <p> + Euphrasia officinalis. + </p> + <p> + Euryale. + </p> + <p> + Faramea. pollen-grains of. + </p> + <p> + Fitzgerald, Mr., on Thelymitra. + </p> + <p> + Forsythia suspensa. stamens. — viridissima. + </p> + <p> + Fragaria Chiloensis. — elatior. — vesca. — Virginiana. + </p> + <p> + Fraxinus excelsior. + </p> + <p> + Galium cruciatum. + </p> + <p> + Gartner on the sterility of unions between distinct species. Primula + vulgaris and veris. hybrid Verbascums. prepotency of pollen. variation in + the sexual powers of plants. contabescent anthers. + </p> + <p> + Gentianeae. + </p> + <p> + Geraniaceae. + </p> + <p> + Geranium sylvaticum. + </p> + <p> + Gesneria pendulina. + </p> + <p> + Gilia aggregata. — coronopifolia. — micrantha. — + nudicaulis. — pulchella. + </p> + <p> + Gillibert on Menyanthes. + </p> + <p> + Gloriosa Lily, the. + </p> + <p> + Godron on hybrid Primulas. + </p> + <p> + Gray, Professor Asa, proposes the term heterogone or heterogonous. on + Linum. Leucosmia Burnettiana and acuminata. Forsythia suspensa. Gilia + pulchella. G. coronopifolia. Phlox subulata. Mitchella repens. + heterostyled plants. Coprosma. Euonymus. Rhamnus lanceolatus. Epigaea + repens. Ilex opaca. Plantago media. Oxybaphus and Nyctaginia. Impatiens + fulva. Leersia. cleistogamic flowers. + </p> + <p> + Gyno-dioecious plants. + </p> + <p> + Hart, Mr., on Nepeta glechoma. + </p> + <p> + Hautbois Strawberry, the. + </p> + <p> + Hedyotis. + </p> + <p> + Henslow, Reverend Professor, on hybrid Primulae. + </p> + <p> + Henslow, Reverend G., on flowers self-fertilised during the winter. + </p> + <p> + Herbert, Dr., on hybrid Primulae. + </p> + <p> + Heterostyled plants, illegitimate offspring of. essential character of. + summary of the differences of fertility between legitimately and + illegitimately fertilised plants. diameter of pollen-grains. size of + anthers, structure of stigma. list of genera. advantages derived from + Heterostylism. means by which plants became heterostyled. transmission of + form. equal-styled varieties. final remarks. — dimorphic plants. + — trimorphic plants. + </p> + <p> + Hibiscus, pollen-grains. + </p> + <p> + Hildebrand, Professor, introduces the word “heterostyled.” on the + ray-florets of the Compositae. Primula Sinensis. Linum grandiflorum. L. + perenne. Pulmonaria officinalis. P. azurea. Polygonum fagopyrum. Oxalis. + hermaphrodite plants becoming uni-sexual. Hordeum. + </p> + <p> + Homostyled species of Primula. + </p> + <p> + Hooker Dr., on Campanula. + </p> + <p> + Hordeum. + </p> + <p> + Hottonia inflata. — palustris. relative fertility. anthers of. + papillae on stigma. + </p> + <p> + Houstonia coerulea. + </p> + <p> + Hoya carnosa. + </p> + <p> + Hybrid Primulas. + </p> + <p> + Hydrangea. + </p> + <p> + Hypericineae. Hyssopus officinalis. + </p> + <p> + Ilex aquifolium — opaca. + </p> + <p> + Illegitimate offspring of heterostyled plants. Lythrum salicaria, dwarfed + stature and sterility. Oxalis, transmission of form to seedlings. Primula + Sinensis, in some degree dwarfed. equal-styled varieties. Primula + vulgaris. transmission of form and colour. seedlings. P. veris. dwarfed + stature and sterility. equal-styled varieties. parallelism between + illegitimate fertilisation and hybridism. + </p> + <p> + Illecebrum. + </p> + <p> + Impatiens, pollen-grains of. — balsamina. — fulva. — + noli-me-tangere. + </p> + <p> + Juglans regia. + </p> + <p> + Juncus bufonius. + </p> + <p> + Jussieu, A. de, on Malpighiaceae. + </p> + <p> + Kerner, Professor, on ray-florets. Auricula. hybrid forms of Primula. on + use of hairs within the corolla. size of corolla in male flowers. use of + glands as a protection to flowers. + </p> + <p> + Kirk, Dr., on Monochoria vaginalis. + </p> + <p> + Knoxia. + </p> + <p> + Koch on Primula longiflora. + </p> + <p> + Krascheninikowia. + </p> + <p> + Kuhn, Dr., on cleistogamic flowers. list of plants producing differently + formed seeds. heterostyled plants. Vandellia nummularifolia. V. + sessiflora. + </p> + <p> + Lagerstroemia Indica. — parviflora. — reginae. + </p> + <p> + Lathyrus nissolia. + </p> + <p> + Lecoq, H., on the common maple. cowslips and primroses. Primula elatior. + Linum Austriacum. Lythrum hyssopifolia. Rhamnus. gyno-dioecious plants. + Scabiosa succisa. Viola odorata. + </p> + <p> + Leersia oryzoides. pollen-grains of. + </p> + <p> + Leggett, Mr., Pontederia cordata. + </p> + <p> + Legitimate unions, summary on the fertility of the two, compared with that + of the two illegitimate in Primula. fertility of, compared with + illegitimate. + </p> + <p> + Leighton, Reverend W.A., on the cowslip and primrose. Verbascum virgatum. + </p> + <p> + Leontodon, pollen-grains. + </p> + <p> + Leptosiphon. + </p> + <p> + Leucosmia acuminata. — Burnettiana. stigma. + </p> + <p> + Lily, the Gloriosa. + </p> + <p> + Limnanthemum Indicum. pollen-grains. anthers. + </p> + <p> + Linaria spuria. + </p> + <p> + Lindley on Fragaria elatior. + </p> + <p> + Linnaeus on Primula veris, vulgaris, and elatior. + </p> +<pre xml:space="preserve"> +Linum angustifolium. +— Austriacum. +— catharticum +— corymbiferum. +— flavum. + stamens. +— grandiflorum. + various experiments. + pistils and stamens. + sterile with its own-form pollen. +— Lewisii. +— perenne. + torsion of the styles. + long-styled form. + stigma. +— salsoloides. +— trigynum. +— usitatissimum. +</pre> + <p> + Lipostoma. + </p> + <p> + Lysimachia vulgaris. + </p> +<pre xml:space="preserve"> +Lythrum Graefferi. +— hyssopifolia. +— salicaria. + power of mutual fertilisation between the three forms. + summary of results. + illegitimate offspring from the three forms. + concluding remarks on. + mid-styled form. + seeds. +— thymifolia. +</pre> + <p> + Malpighiaceae. + </p> + <p> + Manettia bicolor. + </p> + <p> + Maple, the common. + </p> + <p> + Marshall, W., on Primula elatior. Plantago lanceolata. + </p> + <p> + Masters, Dr. Maxwell, on cleistogamic flowers. + </p> + <p> + Maximowicz on Krascheninikowia. + </p> + <p> + Meehan, Mr., on Mitchella. Epigaea repens. + </p> + <p> + Melissa clinopodium — officinalis. + </p> + <p> + Mello, Correa de, on Arachis. Voandzeia. + </p> + <p> + Mentha aquatica. — hirsuta. — vulgaris. + </p> + <p> + Menyanthes. — trifoliata. + </p> + <p> + Michalet on Oxalis acetosella. Linaria spuria. + </p> + <p> + Mitchella. — repens. + </p> + <p> + Mohl, H. Von, on the common cowslip. size of corolla in the sexes of the + same species. Trifolium and Arachis. cleistogamic flowers. Oxalis + acetosella. Impatiens noli-me-tangere. Specularia perfoliata. + </p> + <p> + Mollia lepidota. — speciosa. + </p> + <p> + Monnier, M., on Viola. + </p> + <p> + Monochoria vaginalis. + </p> + <p> + Mulberry, the. + </p> + <p> + Muller, D., on Viola canina. + </p> + <p> + Muller, Fritz, on pollen of the Villarsia. Faramea. Posoqueria fragrans. + Nesaea. Oxalis. Pontederia. Oxalis Regnelli. Chamissoa. + </p> + <p> + Muller, H., on the frequency of visits by insects to the Umbelliferae and + Compositae. on dichogamy. on Anthophora and Bombylius sucking the cowslip. + Primula elatior. — villosa. Hottonia palustris. table of relative + fertility of. Linum catharticum. Polygonum fagopyrum. Lythrum salicaria. + on the origin of heterostylism. on the Labiatae. Thymus serpyllum. + Scabiosa arvensis. Plantago lanceolata. size of corolla in the two sexes + of the same species. Impatiens balsamina. Lysimachia. + </p> + <p> + Myosotis. + </p> + <p> + Nepeta glechoma. + </p> + <p> + Nertera. + </p> + <p> + Nesaea verticillata. + </p> + <p> + Nolana prostrata, variability in length of stamens and pistil. + </p> + <p> + Nyctaginia. + </p> + <p> + Oldenlandia. + </p> + <p> + Oleaceae. + </p> + <p> + Oliver, Professor, on ovules of Primula veris. Viola. Campanula colorata. + </p> + <p> + Ononis columnae. — minutissima. — parviflora. + </p> + <p> + Origanum vulgare. + </p> +<pre xml:space="preserve"> +Oxalis acetosella. +pisil of. +cleistogamic flowers. +pollen-grains. +— Bowii. +— compressa. +— corniculata. +— Deppei. +— hedysaroides. +— homostyled species. +— incarnata. +— Regnelli. +— rosea. +— (Biophytum) sensitiva. + stigma. +— speciosa. +— stricta. +— tropaeoloides. +— Valdiviana. +</pre> +<pre xml:space="preserve"> +Oxlip, the Bardfield. +—, the common. + differences in structure and function between the two parent-species. + effects of crossing. + a hybrid between the cowslip and primrose. +</pre> + <p> + Oxybaphus. + </p> + <p> + Paeony, pollen-grains of. + </p> + <p> + Parallelism between illegitimate and hybrid fertilisation. + </p> + <p> + Pavonia. + </p> + <p> + Phlox Hentzii. — nivalis. — subulata. + </p> + <p> + Planchon on Linum salsoloides. L. Lewisii. on Hugonia. + </p> + <p> + Plantago lanceolata. — media. + </p> + <p> + Polemoniaceae. + </p> + <p> + Pollen-grains, relative diameter of. + </p> + <p> + Polyanthus. + </p> + <p> + Polygonaceae. + </p> + <p> + Polygonum bistorta. — fagopyrum. pollen-grains. + </p> + <p> + Pontederia. pollen-grains. size of anthers. — cordata. + </p> + <p> + Posoqueria fragrans. + </p> + <p> + Primrose, the common. + </p> +<pre xml:space="preserve"> +Primula, the, heterostyled species of. +summary on. +homostyled species. +— auricula. +— equal-styled varieties. +— cortusoides. +— elata. +— elatior, Jacq. + relative fertility of the two forms. + not a hybrid. + equal-styled var. of. +— farinosa. + equal-styled var. +— hirsuta. +— involucrata. +— longiflora. +— mollis. +— Scotica. +— Sibirica. +— Sikkimensis. +— Sinensis. + relative fertility. + long-styled. + short-styled. + transmission of form, constitution and fertility. + equal-styled variety. +— stricta. +— veris. + difference in structure between the two forms. + degrees of fertility when legitimately or illegitimately united. + fertility possessed by illegitimate plants. + equal-styled red variety. + long-styled. + length of pistil. +— verticillata. +— villosa. +— vulgaris (var. acaulis Linn.). + pollen-grains. + relative fertility of the two forms. + length of pistil +</pre> + <p> + Primula vulgaris, var. rubra. + </p> + <p> + Prunella vulgaris. + </p> + <p> + Psychotria. + </p> +<pre xml:space="preserve"> +Pulmonaria angustifolia. +anthers. +— azurea. +— officinalis. + number of flowers. + pistil. +</pre> + <p> + Ranunculus aquatilis. + </p> + <p> + Ray-florets, their use. + </p> + <p> + Rhamnus catharticus. size of corolla. — frangula. — + lanceolatus. + </p> + <p> + Rhinanthus crista-galli. + </p> + <p> + Rubiaceae. size of anthers. stigmas. number of heterostyled genera. + </p> + <p> + Rudgea eriantha. + </p> + <p> + Rue, the common. + </p> + <p> + Ruellia tuberosa. + </p> + <p> + Salvia. — cleistogama. — Horminum. + </p> + <p> + Satureia hortensis. + </p> + <p> + Scabiosa arvensis. — atro-purpurea. — succisa. + </p> + <p> + Scott, J., on Primula auricula. on Primula vulgaris. on Primula var. + rubra. on Primula Sikkimensis. on Primula farinosa. homostyled Primulae. + hybrids. length of pistil. Hottonia palustris. Androsace vitalliana. + Polyanthus. Mitchella repens. Acanthaceae. Eranthemum ambiguum bearing + three kinds of flowers. + </p> + <p> + Scrophularia aquatica. + </p> + <p> + Serratula tinctoria. + </p> + <p> + Sethia acuminata. — obtusifolia. + </p> + <p> + Smith, Sir J.E., on the carrot. hybrid Verbascums. Serratula tinctoria. + Cnicus. Subularia. + </p> + <p> + Soldanella alpina. + </p> + <p> + Specularia perfoliata. + </p> + <p> + Spence, Mr., on Mollia. + </p> + <p> + Spermacoce. + </p> + <p> + Sprengel on Hottonia palustris. + </p> + <p> + Stellaria graminea. + </p> + <p> + Strawberry, the Hautbois. + </p> + <p> + Subularia. + </p> + <p> + Suteria. + </p> + <p> + Thelymitra. + </p> + <p> + Thomson, Dr., on Campanula. + </p> + <p> + Thrum-eyed, origin of term. + </p> + <p> + Thwaites, Mr., on ovules of Limnanthemum Indicum. Sethia acuminata. + Discospermum. + </p> + <p> + Thymelia. + </p> + <p> + Thymus citriodorus. — serpyllum — vulgaris. + </p> + <p> + Timbal-Lagrave, M., on hybrids in genus Cistus. + </p> + <p> + Torrey, Dr., on Hottonia inflata. + </p> + <p> + Transmission of the two forms of heterostyled plants. + </p> + <p> + Treviranus on Androsace vitalliana. Linum. + </p> + <p> + Vandellia nummularifolia. — sessifloria. + </p> + <p> + Vaucher on the carrot. Soldanella alpina. Lythrum salicaria. — + thymifolia. Ilex aquifolium. on Labiatae. Viola hirta and collina. + </p> + <p> + Verbascum, wild hybrids of. — lychnitis. — phoeniceum. — + thapsus. — virgatum. + </p> + <p> + Viburnum. + </p> + <p> + Vicia. + </p> + <p> + Villarsia. anthers. + </p> +<pre xml:space="preserve"> +Viola alba. +— bicolor. +— biflora. +— canina. +— collina. +— elatior. +— hirta. +— ionodium. +— lancifolia. +— mirabilis. +— nana. + pollen-grains of. +— odorata. +— palustris. +— Roxburghiana. +— Ruppii. +— sylvatica. +— tricolor. +</pre> + <p> + Voandzeia. + </p> + <p> + Walnut, the. + </p> + <p> + Watson, H.C., on cowslips, primroses, and Oxlips. Primula elatior. + </p> + <p> + Weddell, Dr., on hybrids between Aceras and Orchis. + </p> + <p> + Wetterhan, Mr., on Corylus. + </p> + <p> + Wichura, Max, on hybrid willows. sterile hybrids. + </p> + <p> + Wirtgen on Lythrum salicaria. + </p> + <p> + Wooler, W., on Polyanthus. + </p> + <p> + Wray, Leonard, on Fragaria. + </p> + +<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES ***</div> +<div style='text-align:left'> + +<div style='display:block; margin:1em 0'> +Updated editions will replace the previous one—the old editions will +be renamed. +</div> + +<div style='display:block; margin:1em 0'> +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, +so the Foundation (and you!) can copy and distribute it in the United +States without permission and without paying copyright +royalties. 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