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+Project Gutenberg Etext of Different Forms of Flowers, by Charles Darwin
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+Title:  The Different Forms of Flowers on Plants of the Same Species
+
+Author: Charles Darwin
+
+Release Date: March, 2003  [Etext #3807]
+[Yes, we are about one year ahead of schedule]
+[The actual date this file first posted = 09/18/01]
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+Language: English
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+Project Gutenberg Etext Different Forms of Flowers, by Charles Darwin
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+This Etext prepared by Sue Asscher   asschers@dingoblue.net.au
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+
+
+THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES
+
+by CHARLES DARWIN, M.A., F.R.S.
+
+
+
+
+TO
+
+PROFESSOR ASA GRAY
+
+THIS VOLUME IS DEDICATED BY THE AUTHOR
+AS A SMALL TRIBUTE OF RESPECT AND AFFECTION.
+
+
+
+
+CONTENTS.
+
+
+INTRODUCTION.
+
+
+CHAPTER I.
+HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEAE.
+
+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.
+
+
+CHAPTER II.
+HYBRID PRIMULAS.
+
+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.
+
+
+CHAPTER III.
+HETEROSTYLED DIMORPHIC PLANTS--continued.
+
+Linum grandiflorum, long-styled form utterly sterile with own-form pollen.--
+Linum perenne, torsion of the pistils in the long-styled form alone.--Homostyled
+species of Linum.--Pulmonaria 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.
+
+
+CHAPTER IV.
+HETEROSTYLED TRIMORPHIC PLANTS.
+
+Lythrum salicaria.--Description of the three forms.--Their power and complex
+manner of fertilising one another.--Eighteen different unions possible.--Mid-
+styled form eminently feminine in nature.--Lythrum 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.
+
+
+CHAPTER V.
+ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS.
+
+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.
+
+
+CHAPTER VI.
+CONCLUDING REMARKS ON HETEROSTYLED PLANTS.
+
+The essential character of heterostyled plants.--Summary of the differences in
+fertility between legitimately and illegitimately fertilised plants.--Diameter
+of the pollen-grains, size of anthers and structure of stigma in the different
+forms.--Affinities of the genera which include heterostyled species.--Nature of
+the advantages derived from heterostylism.--The means by which plants became
+heterostyled.--Transmission of form.--Equal-styled varieties of heterostyled
+plants.--Final remarks.
+
+
+CHAPTER VII.
+POLYGAMOUS, DIOECIOUS, AND GYNO-DIOECIOUS PLANTS.
+
+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.
+
+
+CHAPTER VIII.
+CLEISTOGAMIC FLOWERS.
+
+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.
+
+
+INDEX.
+
+
+...
+
+
+THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES.
+
+
+INTRODUCTION.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.")
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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 [].
+
+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.
+
+
+CHAPTER I.
+
+HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEAE.
+
+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.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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:--
+
+TABLE 1.1.
+
+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.
+
+Short-styled cowslips :  9 : 33 : 199 : 83.
+Long-styled cowslips  : 13 : 51 : 261 : 91.
+
+If we compare the weight from an equal number of plants, and from an equal
+number of umbels, and from an equal number of capsules of the two forms, we get
+the following results:--
+
+TABLE 1.2.
+
+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.
+
+Short-styled cowslips : 10 : 92 :: 100 : 251 :: 100 : 41.
+Long-styled cowslips : 10 : 70 :: 100 : 178 :: 100 : 34.
+
+So that, by all these standards of comparison, the short-styled form is the more
+fertile; if we take the number of umbels (which is the fairest standard, for
+large and small plants are thus equalised), the short-styled plants produce more
+seed than the long-styled, in the proportion of nearly four to three.
+
+In 1861 the trial was made in a fuller and fairer 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:--
+
+TABLE 1.3.
+
+Column 1: Plant.
+Column 2: Number of Plants.
+Column 3: Number of Umbels.
+Column 4: Weight of Seed in grains.
+
+Short-styled cowslips : 47 : 173 : 745.
+Long-styled cowslips  : 58 : 208 : 692.
+
+These figures give us the following proportions:--
+
+TABLE 1.4.
+
+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.
+
+Short-styled cowslips : 100 : 1585 :: 100 : 430.
+Long-styled cowslips  : 100 : 1093 :: 100 : 332.
+
+The season was much more favourable this year than the last; the plants also now
+grew in good soil, instead of in a shady wood or struggling with other plants in
+the open field; consequently the actual produce of seed was considerably larger.
+Nevertheless we have the same relative result; for the short-styled plants
+produced more seed than the long-styled in nearly the proportion of three to
+two; but if we take the fairest standard of comparison, namely, the product of
+seeds from an equal number of umbels, the excess is, as in the former case,
+nearly as four to three.
+
+Looking to these trials made during two successive years on a large number of
+plants, we may safely 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.
+
+In 1860 a few umbels on some plants of both the long-styled and short-styled
+form, which had been covered by a net, did not produce any seed, though other
+umbels on the same plants, artificially fertilised, produced an abundance of
+seed; and this fact shows that the mere covering in itself was not injurious.
+Accordingly, in 1861, several plants were similarly covered just before they
+expanded their flowers; these turned out as follows:--
+
+TABLE 1.5.
+
+Column 1: Plant.
+Column 2: Number of Plants.
+Column 3: Number of Umbels produced.
+Column 4: Product of Seed.
+
+Short-styled :  6 : 24 : 1.3 grain weight of seed, or about 50 in number.
+Long-styled  : 18 : 74 : Not one seed.
+
+Judging from the exposed plants which grew all round in the same bed, and had
+been treated in the same manner, excepting that they had been exposed to the
+visits of insects, the above six short-styled plants ought to have produced 92
+grains' weight of seed instead of only 1.3; and the eighteen long-styled plants,
+which produced not one seed, ought to have produced above 200 grains' weight.
+The production of a few seeds by the short-styled plants was probably due to the
+action of Thrips or of some other minute insect. It is scarcely necessary to
+give any additional evidence, but I may add that ten pots of Polyanthuses and
+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.
+
+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.
+
+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:--
+
+TABLE 1.6. Primula veris.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+22 : 15 : 14 :  8.8 : 62.
+
+Long-styled by own-form pollen. Illegitimate union :
+20 :  8 :  5 :  2.1 : 42.
+
+Short-styled by pollen of long-styled. Legitimate union :
+13 : 12 : 11 :  4.9 : 44.
+
+Short-styled by own-form pollen. Illegitimate union :
+15 :  8 :  6 :  1.8 : 30.
+
+SUMMARY:
+
+The two legitimate unions :
+35 : 27 : 25 : 13.7 : 54.
+
+The two illegitimate unions :
+35 : 16 : 11 :  3.9 : 35.
+
+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.
+
+TABLE 1.7. Primula veris.
+
+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.
+
+The two legitimate unions :
+100 : 77 : 71 : 39 :: 100 : 50 :: 100 : 54.
+
+The two illegitimate unions :
+100 : 45 : 31 : 11 :: 100 : 24 :: 100 : 35.
+
+We here see that the long-styled flowers fertilised with pollen from the short-
+styled yield more capsules, especially good ones (i.e. containing more than one
+or two seeds), and that these capsules contain a greater proportional weight of
+seeds than do the flowers of the long-styled when fertilised with pollen from a
+distinct plant of the same form. So it is with the short-styled flowers, if
+treated in an analogous manner. Therefore I have called the former method of
+fertilisation a 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.
+
+(FIGURE 1.2. Primula veris.
+Graphic representation of two kinds of union between:
+Left: Long-styled form.
+Right: Short-styled form.)
+
+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.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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.
+
+Primula elatior, Jacq.
+Bardfield oxlip of English authors.
+
+This plant, as well as the last or cowslip (P. veris, vel officinalis), and the
+primrose (P. vulgaris, vel acaulis) have been considered by some botanists as
+varieties of the same species. But they are all three undoubtedly distinct, as
+will be shown in the next chapter. The present species resembles to a certain
+extent in general appearance the common oxlip, which is a hybrid 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.)
+
+The results of my trials on the relative fertility of the two forms, when
+legitimately and illegitimately fertilised, are given in Table 1.8.
+
+TABLE 1.8. Primula elatior.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+10 :  6 : 62  : 34 : 46.5.
+
+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.)
+
+Short-styled by pollen of long-styled. Legitimate union:
+10 :  8 : 61  : 37 : 47.7.
+
+Short-styled by own-form pollen. Illegitimate union :
+17 :  3 : 19  :  9 : 12.1.
+
+SUMMARY:
+
+The two legitimate unions together :
+20 : 14 : 62  : 37 : 47.1.
+
+The two illegitimate unions together :
+37 :  7 : 49* :  2 : 35.5.
+(*These seeds were so poor and small that they could hardly have germinated.)
+
+If we compare the fertility of the two legitimate unions taken together with
+that of the two illegitimate unions together, as judged by the proportional
+number of flowers which when fertilised in the two methods yielded capsules, the
+ratio is as 100 to 27; so that by this standard the present species is much more
+sterile than P. veris, when both species are illegitimately 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.
+
+Herr W. Breitenbach informs me that he examined, in two sites near the Lippe (a
+tributary of the Rhine), 894 flowers produced by 198 plants of this species; and
+he found 467 of these flowers to be long-styled, 411 short-styled, and 16 equal-
+styled. I have heard of no other instance with heterostyled plants of equal-
+styled flowers appearing in a state of nature, though far from rare with plants
+which have been long cultivated. It is still more remarkable that in eighteen
+cases the same plant produced both long-styled and short-styled, or long-styled
+and equal-styled flowers; and in two out of the eighteen cases, long-styled,
+short-styled, and equal-styled flowers. The long-styled flowers greatly
+preponderated on these eighteen plants,--61 consisting of this form, 15 of
+equal-styled, and 9 of the short-styled form.
+
+Primula vulgaris (var. acaulis, Linn.)
+The primrose of English Writers.
+
+(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.)
+
+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.
+
+TABLE 1.9. Primula vulgaris.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+12 : 11 : 77 : 47 : 66.9.
+
+Long-styled by own-form pollen. Illegitimate union :
+21 : 14 : 66 : 30 : 52.2.
+
+Short-styled by pollen of long-styled. Legitimate union:
+ 8 :  7 : 75 : 48 : 65.0.
+
+Short-styled by own-form pollen. Illegitimate union :
+18 :  7 : 43 :  5 : 18.8 (This average is perhaps rather too low).
+
+SUMMARY:
+
+The two legitimate unions together :
+20 : 18 : 77 : 47 : 66.0.
+
+The two illegitimate unions together :
+39 : 21 : 66 :  5 : 35.5 (This average is perhaps rather too low).
+
+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.
+
+Primula Sinensis.
+
+In the long-styled form the pistil is about twice as long as that of the short-
+styled, and the stamens differ in a corresponding, but reversed, manner. The
+stigma is considerably more elongated and rougher than that of the short-styled,
+which is smooth and almost spherical, being somewhat depressed on the summit;
+but the stigma varies much in all its characters, the result, probably, of
+cultivation. The pollen-grains of the short-styled form, according to
+Hildebrand, are 7 divisions of the micrometer in length and 5 in breadth;
+whereas those of the long-styled are only 4 in length and 3 in breadth. (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.
+
+TABLE 1.10. Primula Sinensis.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+24 : 16 : 0.58 :: 50.
+
+Long-styled by own-form pollen. Illegitimate union :
+20 : 13 : 0.45 :: 35.
+
+Short-styled by pollen of long-styled. Legitimate union:
+ 8 :  8 : 0.76 :: 64.
+
+Short-styled by own-form pollen. Illegitimate union :
+ 7 :  4 : 0.23 :: 25.
+
+SUMMARY:
+
+The two legitimate unions together :
+32 : 24 : 0.64 :: 57.
+
+The two illegitimate unions together :
+27 : 17 : 0.40 :: 30.
+
+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.
+
+TABLE 1.11. Primula Sinensis (from Hildebrand).
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+14 : 14 : 41.
+
+Long-styled by own-form pollen, from a distinct plant. Illegitimate union :
+26 : 26 : 18.
+
+Long-styled by pollen from same flower. Illegitimate union :
+27 : 21 : 17.
+
+Short-styled by pollen of long-styled. Legitimate union:
+14 : 14 : 44.
+
+Short-styled by own-form pollen, from a distinct plant. Illegitimate union :
+16 : 16 : 20.
+
+Short-styled by pollen from the same flower. Illegitimate union :
+21 : 11 : 8.
+
+SUMMARY:
+
+The two legitimate unions together :
+28 : 28 : 43.
+
+The two illegitimate unions together (own-form pollen):
+42 : 42 : 18.
+
+The two illegitimate unions together (pollen from the same flower ):
+48 : 32 : 13.
+
+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.
+
+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.
+
+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.
+
+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.
+
+[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.)
+
+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.
+
+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.
+
+By the first standard, the fertility of the two legitimate unions of the
+auricula is to that of the two illegitimate unions as 100 to 80; and by the
+second standard as 100 to 15.
+
+Primula Sikkimensis.
+
+According to Mr. Scott, the pistil of the long-styled form is fully four times
+as long as that of the short-styled, but their stigmas are nearly alike in shape
+and roughness. The stamens do not differ so much in relative length as the
+pistils. The pollen-grains differ in a marked manner in the two forms; "those of
+the long-styled plants are sharply triquetrous, smaller, and more transparent
+than those of the short-styled, which are of a bluntly triangular form." The
+fertility of the two legitimate unions to that of the two illegitimate unions is
+by the first standard as 100 to 95, and by the second standard as 100 to 31.
+
+Primula cortusoides.
+
+The pistil of the long-styled form is about thrice as long as that of the short-
+styled, the stigma being double as long and covered with much longer 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.
+
+Primula involucrata.
+
+The pistil of the long-styled form is about thrice as long as that of the short-
+styled; the stigma of the former is globular and closely beset with 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.
+
+Primula farinosa.
+
+According to Mr. Scott, the pistil of the long-styled form is only about twice
+as long as that of the short-styled. The stigmas of the two forms differ but
+little in shape. The pollen-grains differ in the usual manner in size, but not
+in form. The fertility of the two legitimate to that of the two illegitimate
+unions is by the first standard as 100 to 71, and by the second standard as 100
+to 44.]
+
+SUMMARY ON THE FOREGOING HETEROSTYLED SPECIES OF PRIMULA.
+
+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.
+
+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.
+
+Primula veris : 69 : 65.
+
+Primula elatior : 27 : 75 (Probably too high).
+
+Primula vulgaris : 60 : 54 (Perhaps too low).
+
+Primula Sinensis : 84 : 63.
+
+Primula Sinensis (second trial) : ? : 53.
+Primula Sinensis (after Hildebrand) : 100 : 42.
+
+Primula auricula (Scott) : 80 : 15.
+
+Primula Sikkimensis (Scott): 95 : 31.
+
+Primula cortusoides (Scott): 74 : 66.
+
+Primula involucrata (Scott): 72 : 48.
+
+Primula farinosa (Scott): 71 : 44.
+
+Average of the nine species : 88.4 : 61.8.
+
+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.
+
+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.
+
+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.):--
+
+TABLE 1.a.
+
+Primula veris : 71.
+
+Primula elatior : 44 (Probably too low).
+
+Primula vulgaris : 36 (Perhaps too low).
+
+Primula Sinensis : 71.
+
+Primula auricula : 119.
+
+Primula Sikkimensis : 57.
+
+Primula cortusoides : 93.
+
+Primula involucrata : 74.
+
+Primula farinosa : 63.
+
+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.
+
+HOMOSTYLED SPECIES OF PRIMULA.
+
+It has now been shown that nine of the species in this genus exist under two
+forms, which differ not only in structure but in function. Besides these Mr.
+Scott enumerates 27 other species which are heterostyled (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.'
+
+Hottonia palustris.
+
+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.
+
+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:--
+
+TABLE 1.13. Hottonia palustris (from H. Muller).
+
+Column 1: Nature of the Union.
+Column 2: Number of Capsules examined.
+Column 3: Average Number of Seeds per Capsule.
+
+Long-styled by pollen of short-styled. Legitimate union:
+34 : 91.4.
+
+Long-styled by own-form pollen, from a distinct plant. Illegitimate union:
+18 : 77.5.
+
+Short-styled by pollen of long-styled. Legitimate union:
+30 : 66.2.
+
+Short-styled by own-form pollen, from a distinct plant. Illegitimate union:
+19 : 18.7.
+
+SUMMARY:
+
+The two legitimate unions together:
+64 : 78.8.
+
+The two illegitimate unions together:
+37 : 48.1.
+
+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.
+
+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.
+
+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.
+
+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.
+
+
+CHAPTER II.
+
+HYBRID PRIMULAS.
+
+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.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+TABLE 2.14.  Crosses inter se between the two forms of the common Oxlip.
+
+Column 1: Illegitimate union.
+Short-styled oxlip, by pollen of short-styled oxlip: 20 flowers fertilised, did
+not produce one capsule.
+
+Column 2: Legitimate union.
+Short-styled oxlip, by pollen of long-styled oxlip: 10 flowers fertilised, did
+not produce one capsule.
+
+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.
+
+Column 4: Legitimate union.
+Long-styled oxlip, by pollen of short-styled oxlip: 10 flowers fertilised, did
+not produce one capsule.
+
+TABLE 2.15.  Both forms of the Oxlip crossed with Pollen of both forms of the
+Cowslip, P. veris.
+
+Column 1: Illegitimate union.
+Short-styled oxlip, by pollen of short-styled cowslip: 18 flowers fertilised,
+did not produce one capsule.
+
+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.
+
+Column 3: Illegitimate union.
+Long-styled oxlip, by pollen of long-styled cowslip: 11 flowers fertilised,
+produced one capsule, containing 13 wretched seeds.
+
+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.
+
+TABLE 2.16.  Both forms of the Oxlip crossed with Pollen of both forms of the
+Primrose, P. vulgaris.
+
+Column 1: Illegitimate union.
+Short-styled oxlip, by pollen of short-styled primrose: 34 flowers fertilised,
+produced two capsules, containing 5 and 12 seeds.
+
+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.
+
+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.
+
+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.
+
+TABLE 2.17.  Both forms of the Cowslip crossed with Pollen of both forms of the
+Oxlip.
+
+Column 1: Illegitimate union.
+Short-styled cowslip, by pollen of short-styled oxlip: 8 flowers fertilised, did
+not produce one capsule.
+
+Column 2: Legitimate union.
+Long-styled cowslip, by pollen of short-styled oxlip: 8 flowers fertilised,
+produced one capsule, containing 26 seeds.
+
+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.
+
+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.
+
+TABLE 2.18.  Both forms of the Primrose crossed with Pollen of both forms of the
+Oxlip.
+
+Column 1: Illegitimate union.
+Short-styled primrose, by pollen of short-styled oxlip: 8 flowers fertilised,
+did not produce one capsule.
+
+Column 2: Legitimate union.
+Long-styled primrose, by pollen of short-styled oxlip: 8 flowers fertilised,
+produced two capsules, containing 5 and 2 seeds.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+Finally, although we may freely admit that Primula veris, vulgaris, and elatior,
+as well as all the other species of the genus, are descended from a common
+primordial form, yet from the facts above given, we must conclude that these
+three forms are now as fixed in character as are many others which are
+universally ranked as true species. Consequently they have as good a right to
+receive distinct specific names as have, for instance, the ass, quagga, and
+zebra.
+
+Mr. Scott has arrived at some interesting results by 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."
+
+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.
+
+SUPPLEMENTARY NOTE ON SOME WILD HYBRID VERBASCUMS.
+
+In an early part of this chapter I remarked that few other instances could be
+given of a hybrid 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.
+
+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.)
+
+My observations were made in the autumn; so that I was able to collect some
+half-matured capsules from twenty of the thirty-three intermediate plants, and
+likewise capsules of the pure V. lychnitis and thapsus growing in the same
+field. All the latter were filled with perfect but immature seeds, whilst the
+capsules of the twenty intermediate plants did not contain one single perfect
+seed. These plants, consequently, were absolutely barren. From this fact,--from
+the one plant which was transplanted into my garden yielding when artificially
+fertilised with pollen from V. lychnitis and thapsus some seeds, though
+extremely few in number,--from the circumstance of the two pure species growing
+in the same field,--and from the intermediate character of the sterile plants,
+there can be no doubt that they were hybrids. Judging from the position in which
+they were chiefly found, I am inclined to believe they were descended from V.
+thapsus as the seed-bearer, and V. lychnitis as the pollen-bearer.
+
+It is known that many species of Verbascum, when the stem is jarred or struck by
+a stick, cast off their flowers. (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.
+
+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.
+
+
+CHAPTER III. HETEROSTYLED DIMORPHIC PLANTS--continued.
+
+Linum grandiflorum, long-styled form utterly sterile with own-form pollen.
+Linum perenne, torsion of the pistils in the long-styled form alone.
+Homostyled species of Linum.
+Pulmonaria 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.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+FIRST.
+
+Pollen from a short-styled plant was placed on the five stigmas of a long-styled
+flower, and these, after thirty hours, were found deeply penetrated by a
+multitude of pollen-tubes, far too numerous to be counted; the stigmas had also
+become discoloured and twisted. I repeated this experiment on another flower,
+and in eighteen hours the stigmas were 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.
+
+SECONDLY.
+
+Pollen from a long-styled flower was placed on all five stigmas of a long-styled
+flower on a separate plant: after nineteen hours the stigmas were dissected, and
+only a single pollen-grain had emitted a tube, 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.
+
+THIRDLY.
+
+Repeated last experiment, and placed own-form pollen on all five stigmas of a
+long-styled flower; after nineteen hours and a half, not one single grain had
+emitted its tube.
+
+FOURTHLY.
+
+Repeated the experiment, with the same result after twenty-four hours.
+
+FIFTHLY.
+
+Repeated last experiment, and, after leaving pollen on for nineteen hours, put
+on an additional quantity of own-form pollen on all five stigmas. After an
+interval of three days, the stigmas were examined, and, instead of being
+discoloured and twisted, they were straight and fresh-coloured. Only one grain
+had emitted a quite short tube, which was drawn out of the stigmatic tissue
+without being ruptured.
+
+The following experiments are more striking:--
+
+SIXTHLY.
+
+I placed own-form pollen on three of the stigmas of a long-styled flower, and
+pollen from a short-styled flower on the other two stigmas. After twenty-two
+hours these two stigmas were discoloured, slightly twisted, and penetrated by
+the tubes of 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.
+
+SEVENTHLY.
+
+Experiment repeated in the same manner, with the same result.
+
+EIGHTHLY.
+
+Experiment repeated, but the stigmas were carefully examined after an interval
+of only five hours and a half. The two stigmas with pollen from a 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.
+
+NINTHLY.
+
+Put pollen of a short-styled flower on a single long-styled stigma, and own-form
+pollen on the other four stigmas; after twenty-four hours the one stigma was
+somewhat discoloured and twisted, and penetrated by many long tubes: the other
+four stigmas were quite straight and fresh; but on dissecting them I found that
+three pollen-grains had protruded very short tubes into the tissue.
+
+TENTHLY.
+
+Repeated the experiment, with the same result after twenty-four hours, excepting
+that only two own-form grains had penetrated the stigmatic tissue with their
+tubes to a very short depth. The one stigma, which was deeply penetrated by a
+multitude of tubes from the short-styled pollen, presented a conspicuous
+difference in being much curled, half-shrivelled, and discoloured, in comparison
+with the other four straight and bright pink stigmas.
+
+I could add other experiments; but those now given amply suffice to show that
+the pollen-grains of a short-styled flower placed on the stigma of a long-styled
+flower emit a multitude of tubes after an 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.
+
+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.
+
+Linum perenne.
+
+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.
+
+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.
+
+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.
+
+The flowers borne on the thirteen short-styled plants under the net, which were
+not fertilised, produced twelve capsules, containing on an average 5.6 seeds. As
+some of these capsules were very fine, and as five were borne on one twig, I
+suspect that some minute insect had accidentally got under the net and had
+brought pollen from the other form to the flowers which produced this little
+group of capsules. The one uncovered short-styled plant which grew close to the
+uncovered long-styled plant yielded twelve capsules.
+
+From these facts we have some reason to believe, as in the case of L.
+grandiflorum, that the short-styled plants are in a slight degree more fertile
+with their own pollen than are the long-styled plants. Anyhow we have the
+clearest evidence, that the stigmas of each form require for full fertility that
+pollen from the stamens of corresponding height belonging to the opposite form
+should be brought to them.
+
+Hildebrand, in the paper lately referred to, confirms my results. He placed a
+short-styled plant in his house, and fertilised about 20 flowers with their own
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+(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.)
+
+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.
+
+Thus we can understand the meaning of the torsion of the styles in the long-
+styled flowers alone, as well as their divergence in the short-styled flowers.
+
+One other point is worth notice. In botanical works many flowers are said to be
+fertilised in the bud. This statement generally rests, as far as I can discover,
+on the anthers opening in the bud; no evidence being adduced that the stigma is
+at this period mature, or that it is not subsequently acted on by pollen brought
+from other flowers. In the case of Cephalanthera grandiflora I have shown that
+precocious and partial self-fertilisation, with subsequent full fertilisation,
+is the regular course of events. (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.
+
+Linum flavum.
+
+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.
+
+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.
+
+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.)
+
+PULMONARIA (BORAGINEAE).
+
+Pulmonaria officinalis.
+
+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.
+
+TABLE 3.19. Pulmonaria officinalis (from Hildebrand).
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+14 : 10 : 1.30.
+
+Long-styled 14 by own-pollen, and 16 by pollen of other plant of same form.
+Illegitimate union :
+30 : 0 : 0.
+
+Short-styled by pollen of long-styled. Legitimate union:
+16 : 14 : 1.57.
+
+Short-styled 11 by own-pollen, 14 by pollen of other plant of same form.
+Illegitimate union :
+25 : 0 : 0.
+
+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.
+
+Pulmonaria angustifolia.
+
+(FIGURE 3.6. Pulmonaria angustifolia.
+Left: Long-styled form.
+Right: Short-styled form.)
+
+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.
+
+TABLE 3.20.  Pulmonaria angustifolia.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+18 : 9 : 2.11.
+
+Long-styled by own-form pollen. Illegitimate union :
+18 : 0 : 0.
+
+Short-styled by pollen of long-styled. Legitimate union:
+18 : 15 : 2.60.
+
+Short-styled by own-form pollen. Illegitimate union :
+12 : 7 : 1.86.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+Pulmonaria azurea, according to Hildebrand, is not heterostyled. (3/12. 'Die
+Geschlechter-Vertheilung bei den Pflanzen' 1867 page 37.)
+
+[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.]
+
+Polygonum fagopyrum (Polygonaceae).
+
+(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.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+Four heads on short-styled plants similarly received pollen from other short-
+styled plants, and were thus illegitimately fertilised. They produced 9 seeds,
+or 2.25 per flower-head.
+
+The results from fertilising the flower-heads in the above imperfect manner
+cannot be fully trusted; but I may state that the four legitimately fertilised
+flower-heads yielded on an average 7.50 seeds per head; whereas the seven
+illegitimately fertilised heads yielded less than half the number, or on an
+average only 3.28 seeds. The legitimately crossed seeds from the long-styled
+flowers were finer than those from the illegitimately fertilised flowers on the
+same plants, in the ratio of 100 to 82, as shown by the weights of an equal
+number.
+
+About a dozen plants, including both forms, were protected under nets, and early
+in the season they 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.
+
+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.
+
+[Leucosmia Burnettiana (Thymeliae).
+
+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.
+
+Menyanthes trifoliata (Gentianeae).
+
+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.
+
+Limnanthemum Indicum (Gentianeae).
+
+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.
+
+Villarsia [sp.?] (Gentianeae).
+
+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.
+
+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.
+
+Forsythia suspensa (Oleaceae).
+
+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.
+
+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.
+
+Cordia [sp.?] (Cordiaceae).
+
+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.
+
+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.
+
+Gilia (Ipomopsis) pulchella vel aggregata (Polemoniaceae).
+
+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.
+
+Gilia (Leptosiphon) micrantha.
+
+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.
+
+Phlox subulata (Polemoniaceae).
+
+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.
+
+Erythroxylum [sp.?] (Erythroxylidae).
+
+(FIGURE 3.8. Erythroxylon [sp.?]
+Left: Long-styled form.
+Right: Short-styled form.
+From a sketch by Fritz Muller, magnified five times.)
+
+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.)
+
+Sethia acuminata (Erythroxylidae).
+
+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.
+
+Cratoxylon formosum (Hypericineae).
+
+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.
+
+Aegiphila elata (Verbenaceae).
+
+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.
+
+Aegiphila obdurata.
+
+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.]
+
+RUBIACEAE.
+
+This great natural family contains a much larger number of heterostyled genera
+than any other one, as yet known.
+
+Mitchella repens.
+
+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.
+
+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.
+
+TABLE 3.21. Mitchella repens.
+
+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.
+
+Long-styled by pollen of short-styled. Legitimate union :
+9 : 8 : 4.6.
+
+Long-styled by own-form pollen. Illegitimate union :
+8 : 3 : 2.2.
+
+Short-styled by pollen of long-styled. Legitimate union:
+8 : 7 : 4.1.
+
+Short-styled by own-form pollen. Illegitimate union :
+9 : 0 : 2.0.
+
+The two legitimate unions together :
+17 : 15 : 4.4.
+
+The two illegitimate unions together :
+17 : 3 : 2.1.
+
+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.
+
+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.
+
+Borreria, nov. sp. near valerianoides (Rubiaceae).
+
+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.)
+
+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.
+
+Faramea [sp.?] (Rubiaceae).
+
+(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.)
+
+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.
+
+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.)
+
+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.
+
+[Suteria (species unnamed in the herbarium at Kew.) (Rubiaceae).
+
+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.
+
+Houstonia coerulea (Rubiaceae).
+
+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.
+
+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.
+
+Oldenlandia [sp.?] (Rubiaceae).
+
+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.
+
+Hedyotis [sp.?] (Rubiaceae).
+
+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.
+
+Coccocypselum [sp.?] (Rubiaceae).
+
+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.
+
+Lipostoma [sp.?] (Rubiaceae).
+
+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.
+
+Cinchona micrantha (Rubiaceae).
+
+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.
+
+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.)]
+
+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.
+
+
+CHAPTER IV.
+
+HETEROSTYLED TRIMORPHIC PLANTS.
+
+Lythrum salicaria.
+Description of the three forms.
+Their power and complex manner of fertilising one another.
+Eighteen different unions possible.
+Mid-styled form eminently feminine in nature.
+Lythrum 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.
+
+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.
+
+Lythrum salicaria.
+
+(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.)
+
+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.
+
+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.
+
+LONG-STYLED FORM.
+
+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.
+
+MID-STYLED FORM.
+
+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.
+
+SHORT-STYLED FORM.
+
+The pistil is here very short, not one-third of the length of that of the long-
+styled form. It is enclosed within the calyx, which, 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.
+
+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:--
+
+TABLE 4.a. Lythrum salicaria. Diameters of pollen-grains after immersion in
+water.
+
+Column 1: Source of Pollen-grains.
+Column 2: Minimum diameter.
+Column 3: Maximum diameter.
+
+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.
+
+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.
+
+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.
+
+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:--
+
+TABLE 4.22. Lythrum salicaria. Classification according to form of flower.
+
+Column 1: Place of origin.
+Column 2: Long-styled.
+Column 3: Mid-styled.
+Column 4: Short-styled.
+Column 5: Total.
+
+North Wales : 95 : 97 : 72 : 264.
+Hampshire : 53 : 38 : 38 : 129.
+Total : 148 : 135 : 110 : 393.
+
+If twice or thrice the number had been collected, the three forms would probably
+have been found nearly equal; I infer this from considering the above figures,
+and from my son telling me that if he had 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.
+
+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.
+
+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.
+
+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.
+
+ON THE POWER OF MUTUAL FERTILISATION BETWEEN THE THREE FORMS.
+
+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.
+
+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.
+
+TABLE 4.23. Lythrum salicaria, long-styled form.
+
+TABLE 4.23.1. Legitimate union.
+
+13 flowers fertilised by the longest stamens of the mid-styled. These stamens
+equal in length the pistil of the long-styled.
+
+Product of good seed in each capsule.
+
+  36   53
+  81    0
+   0    0
+   0    0
+   0    0
+   -    0
+  45
+  41
+
+38 percent of these flowers yielded capsules. Each capsule contained, on an
+average, 51.2 seeds.
+
+TABLE 4.23.2. Legitimate union.
+
+13 flowers fertilised by the longest stamens of the short-styled. These stamens
+equal in length the pistil of the long-styled.
+
+Product of good seed in each capsule.
+
+ 159             104
+  43             119
+  96 poor seed.   96
+ 103              99
+   0             131
+   0             116
+   -
+ 114
+
+84 percent of these flowers yielded capsules. Each capsule contained, on an
+average, 107.3 seeds.
+
+TABLE 4.23.3. Illegitimate union.
+
+14 flowers fertilised by the shortest stamens of the mid-styled.
+
+   3    0
+   0    0
+   0    0
+   0    0
+   0    0
+   -    0
+   0    0
+   0
+
+Too sterile for any average.
+
+TABLE 4.23.4. Illegitimate union.
+
+12 flowers fertilised by the mid-length stamens of the short-styled.
+
+  20    0
+   0    0
+   0    0
+   0    0
+   -    0
+   0    0
+   0
+
+Too sterile for any average.
+
+TABLE 4.23.5. Illegitimate union.
+
+15 flowers fertilised by own-form mid-length stamens.
+
+   2    -
+  10    0
+  23    0
+   0    0
+   0    0
+   0    0
+   0    0
+   0    0
+
+Too sterile for any average.
+
+TABLE 4.23.6. Illegitimate union.
+
+15 flowers fertilised by own-form shortest stamens.
+
+   4    -
+   8    0
+   4    0
+   0    0
+   0    0
+   0    0
+   0    0
+   0    0
+
+Too sterile for any average.
+
+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:--
+
+   20   20   35   21   19
+   26   24   12   23   10
+    7   30   27   29   13
+   20   12   29   19   35
+
+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.
+
+TABLE 4.24. Lythrum salicaria, mid-styled form.
+
+TABLE 4.24.1. Legitimate union.
+
+12 flowers fertilised by the mid-length stamens of the long-styled. These
+stamens equal in length the pistil of the mid-styled.
+
+Product of good seed in each capsule.
+
+ 138   122
+ 149    50
+ 147   151
+ 109   119
+ 133   138
+ 144     0
+   -
+
+92 percent of these flowers (probably 100 per cent) yielded capsules. Each
+capsule contained, on an average, 127.3 seeds.
+
+TABLE 4.24.2. Legitimate union.
+
+12 flowers fertilised by the mid-length stamens of the short-styled. These
+stamens equal in length the pistil of the mid-styled.
+
+Product of good seed in each capsule.
+
+ 112   109
+ 130   143
+ 143   124
+ 100   145
+  33    12
+   -   141
+ 104
+
+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.
+
+TABLE 4.24.3. Illegitimate union.
+
+13 flowers fertilised by the shortest stamens of the long-styled.
+
+  83   12
+   0   19
+   0   85 seeds small and poor.
+   -    0
+  44    0
+  44    0
+  45    0
+
+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.
+
+TABLE 4.24.4. Illegitimate union.
+
+15 flowers fertilised by the longest stamens of the short-styled.
+
+ 130   86
+ 115  113
+  14   29
+   6   17
+   2  113
+   9   79
+   -  128
+ 132    0
+
+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.
+
+TABLE 4.24.5. Illegitimate union.
+
+12 flowers fertilised by own-form longest stamens.
+
+  92    0
+   9    0
+  63    0
+   -    0
+ 136?*  0
+   0    0
+   0
+
+(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.)
+
+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.
+
+TABLE 4.24.6. Illegitimate union.
+
+12 flowers fertilised by own-form shortest stamens.
+
+   0    0
+   0    0
+   0    0
+   -    0
+   0    0
+   0    0
+   0
+
+Not one flower yielded a capsule.
+
+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.
+
+TABLE 4.25. Lythrum salicaria, short-styled form.
+
+TABLE 4.25.1. Legitimate union.
+
+12 flowers fertilised by the shortest stamens of the long-styled. These stamens
+equal in length the pistil of the short-styled.
+
+  69    56
+  61    88
+  88   112
+  66   111
+   0    62
+   0   100
+   -
+
+83 percent of the flowers yielded capsules. Each capsule contained, on an
+average, 81.3 seeds.
+
+TABLE 4.25.2. Legitimate union.
+
+13 flowers fertilised by the shortest stamens of the mid-styled. These stamens
+equal in length the pistil of the short-styled.
+
+  93    69
+  77    69
+  48    53
+  43     9
+   0     0
+   0     0
+   -     0
+
+61 percent of the flowers yielded capsules. Each capsule contained, on an
+average, 64.6 seeds.
+
+TABLE 4.25.3. Illegitimate union.
+
+10 flowers fertilised by the mid-length stamens of the long-styled.
+
+   0   14
+   0    0
+   0    0
+   0    0
+   -    0
+  23
+
+Too sterile for any average.
+
+TABLE 4.25.4. Illegitimate union.
+10 flowers fertilised by the longest stamens of the mid-styled.
+
+   0    0
+   0    0
+   0    0
+   0    0
+   -    0
+   0
+
+Too sterile for any average.
+
+TABLE 4.25.5. Illegitimate union.
+
+10 flowers fertilised by own-form longest stamens.
+
+   0    0
+   0    0
+   0    0
+   -    0
+   0    0
+   0
+
+Too sterile for any average.
+
+TABLE 4.25.6. Illegitimate union.
+
+10 flowers fertilised by own-form mid-length stamens.
+
+  64?*  0
+   0    0
+   0    0
+   -    0
+  21    0
+   9
+
+(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.)
+
+Too sterile for any average.
+
+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.
+
+SUMMARY OF THE RESULTS.
+
+LONG-STYLED FORM.
+
+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.
+
+Twenty-six long-styled flowers fertilised illegitimately by the other stamens of
+the mid-and short-styled forms yielded only two very poor capsules.
+
+Thirty long-styled flowers fertilised illegitimately by their own-form two sets
+of stamens yielded only eight very poor capsules; but long-styled flowers
+fertilised by bees with pollen from their own stamens produced numerous capsules
+containing on an average 21.5 seeds.
+
+MID-STYLED FORM.
+
+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.
+
+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.
+
+Thirteen mid-styled flowers fertilised illegitimately by the mid-length stamens
+of the long-styled form yielded 54 per cent of capsules, which (excluding one
+with 19 seeds) contained on an average 60.2 seeds.
+
+Twelve mid-styled flowers fertilised illegitimately by their own-form longest
+stamens yielded 25 per cent of capsules, which (excluding one with 9 seeds)
+contained on an average 77.5 seeds.
+
+Twelve mid-styled flowers fertilised illegitimately by their own-form shortest
+stamens yielded not a single capsule.
+
+SHORT-STYLED FORM.
+
+Twenty-five flowers fertilised legitimately by the stamens of corresponding
+length, borne by the long and mid-styled forms, yielded 72 per cent of capsules,
+which (excluding one capsule with only 9 seeds) contained on an average 70.8
+seeds.
+
+Twenty short-styled flowers fertilised illegitimately by the other stamens of
+the long and mid-styled forms yielded only two very poor capsules.
+
+Twenty short-styled flowers fertilised illegitimately by their own stamens
+yielded only two poor (or perhaps three) capsules.
+
+If we take all six legitimate unions together, and all twelve illegitimate
+unions together, we get the following results:
+
+TABLE 4.26.
+
+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.
+
+The six legitimate unions : 75 : 56 : 96.29 : 71.89.
+The twelve illegitimate unions : 146 : 36 : 44.72 : 11.03.
+
+Therefore the fertility of the legitimate unions to that of the illegitimate, as
+judged by the proportion of the fertilised flowers which yielded capsules, is as
+100 to 33; and judged by the average number of seeds per capsule, as 100 to 46.
+
+From this summary and the several foregoing tables we see that it is only pollen
+from the longest stamens which can fully fertilise the longest pistil; only that
+from the mid-length stamens, the mid-length pistil; and only that from the
+shortest stamens, the shortest pistil. And now we can comprehend the meaning of
+the almost exact correspondence in length between the pistil in each form and a
+set of six stamens in two of the other forms; for the stigma of each form is
+thus rubbed against that part of the insect's body which becomes charged with
+the proper pollen. It is also evident that the stigma of each form, fertilised
+in three different ways with pollen from the longest, mid-length, and shortest
+stamens, is acted on very differently, and conversely that 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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+[Lythrum Graefferi.
+
+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.
+
+Lythrum thymifolia.
+
+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.
+
+Lythrum hyssopifolia.
+
+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.
+
+We thus see that within this genus some species are heterostyled and trimorphic;
+one apparently heterostyled and dimorphic, and one homostyled.
+
+Nesaea verticillata.
+
+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.)
+
+Lagerstroemia Indica.
+
+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.)]
+
+Oxalis (Geraniaceae).
+
+(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.)
+
+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.
+
+Oxalis Valdiviana.
+
+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:--
+
+Table 4.b. Oxalis Valdiviana. Diameters of pollen-grains in divisions of the
+micrometer.
+
+Column 1: Source of Pollen-grains.
+Column 2: Minimum diameter.
+Column 3: Maximum diameter.
+
+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.
+
+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.
+
+Table 4.27. Oxalis Valdiviana (from Hildebrand).
+
+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.
+
+Long-styled by pollen of longest stamens of short-styled. Legitimate union :
+28 : 28 : 11.9.
+
+Long-styled by pollen of longest stamens of mid-styled. Legitimate union :
+21 : 21 : 12.0.
+
+Long-styled by pollen of own and own-form mid-length stamens. Illegitimate union
+:
+40 : 2 : 5.5.
+
+Long-styled by pollen of own and own-form shortest stamens. Illegitimate union :
+26 : 0 : 0.
+
+Long-styled by pollen of shortest stamens of short-styled. Illegitimate union :
+16 : 1 : 1.
+
+Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union :
+9 : 0 : 0.
+
+Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union :
+38 : 38 : 11.3.
+
+Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union :
+23 : 23 : 10.4.
+
+Mid-styled by pollen of own and own-form longest stamens. Illegitimate union :
+52 : 0 : 0.
+
+Mid-styled by pollen of own and own-form shortest stamens. Illegitimate union :
+30 : 1 : 6.
+
+Mid-styled by pollen of shortest stamens of long-styled. Illegitimate union :
+16 : 0 : 0.
+
+Mid-styled by pollen of longest stamens of short-styled. Illegitimate union :
+16 : 2 : 2.5.
+
+Short-styled by pollen of shortest stamens of long-styled. Legitimate union:
+18 : 18 : 11.0.
+
+Short-styled by pollen of shortest stamens of mid-styled. Legitimate union:
+10 : 10 : 11.3.
+
+Short-styled by pollen of own and own-form longest stamens. Illegitimate union :
+21 : 0 : 0.
+
+Short-styled by pollen of own and own-form mid-length stamens. Illegitimate
+union :
+22 : 0 : 0.
+
+Short-styled by pollen of longest stamens of mid-styled. Illegitimate union:
+4 : 0 : 0.
+
+Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union:
+3 : 0 : 0.
+
+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.
+
+Oxalis Regnelli.
+
+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.
+
+TABLE 4.28. Oxalis Regnelli (from Hildebrand).
+
+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.
+
+Long-styled by pollen of longest stamens of short-styled. Legitimate union :
+6 : 6 : 10.1.
+
+Long-styled by pollen of longest stamens of mid-styled. Legitimate union :
+5 : 5 : 10.6.
+
+Long-styled by pollen of own mid-length stamens. Illegitimate union :
+4 : 0 : 0.
+
+Long-styled by pollen of own shortest stamens. Illegitimate union :
+1 : 0 : 0.
+
+Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union :
+9 : 9 : 10.4.
+
+Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union :
+10 : 10 : 10.1.
+
+Mid-styled by pollen of own longest stamens. Illegitimate union :
+9 : 0 : 0.
+
+Mid-styled by pollen of own shortest stamens. Illegitimate union :
+2 : 0 : 0.
+
+Mid-styled by pollen of longest stamens of short-styled. Illegitimate union :
+1 : 0 : 0.
+
+Short-styled by pollen of shortest stamens of mid-styled. Legitimate union:
+9 : 9 : 10.6.
+
+Short-styled by pollen of shortest stamens of long-styled. Legitimate union:
+2 : 2 : 9.5.
+
+Short-styled by pollen of own mid-length stamens. Illegitimate union :
+12 : 0 : 0.
+
+Short-styled by pollen of own longest stamens. Illegitimate union :
+9 : 0 : 0.
+
+Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union:
+1 : 0 : 0.
+
+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.
+
+Oxalis speciosa.
+
+This species, which bears pink flowers, was introduced from the Cape of Good
+Hope. A sketch of the reproductive organs of the three forms (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:--
+
+Table 4.c. Oxalis speciosa. Diameters of pollen-grains in divisions of the
+micrometer.
+
+Column 1: Source of Pollen-grains.
+Column 2: Minimum diameter.
+Column 3: Maximum diameter.
+
+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.
+
+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.
+
+Table 4.29. Oxalis speciosa.
+
+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.
+
+Long-styled by pollen of longest stamens of short-styled. Legitimate union :
+19 : 15 : 57.4.
+
+Long-styled by pollen of longest stamens of mid-styled. Legitimate union :
+4 : 3 : 59.0.
+
+Long-styled by pollen of own-form mid-length stamens. Illegitimate union :
+9 : 2 : 42.5.
+
+Long-styled by pollen of own-form shortest stamens. Illegitimate union :
+11 : 0 : 0.
+
+Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union :
+4 : 0 : 0.
+
+Long-styled by pollen of mid-length stamens of short-styled. Illegitimate union
+:
+12 : 5 : 30.0.
+
+Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union :
+3 : 3 : 63.6.
+
+Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union :
+4 : 4 : 56.3.
+
+Mid-styled by mixed pollen from both own-form longest and shortest stamens.
+Illegitimate union :
+9 : 2 : 19.
+
+Mid-styled by pollen of longest stamens of short-styled. Illegitimate union :
+12 : 1 : 8.
+
+Short-styled by pollen of shortest stamens of mid-styled. Legitimate union:
+3 : 2 : 67.
+
+Short-styled by pollen of shortest stamens of long-styled. Legitimate union:
+3 : 3 : 54.3.
+
+Short-styled by pollen of own-form longest stamens. Illegitimate union:
+5 : 1 : 8.
+
+Short-styled by pollen of own-form mid-length stamens. Illegitimate union :
+3 : 0 : 0.
+
+Short-styled by both pollens mixed together, of own-form longest and mid-length
+stamens. Illegitimate union:
+13 : 0 : 0.
+
+Short-styled by pollen of longest stamens of mid-styled. Illegitimate union :
+7 : 0 : 0.
+
+Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union:
+10 : 1 : 54.
+
+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.
+
+Oxalis rosea.
+
+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.
+
+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.
+
+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.
+
+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.
+
+Oxalis (Biophytum) sensitiva.
+
+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.
+
+HOMOSTYLED SPECIES OF OXALIS.
+
+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.
+
+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.
+
+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.
+
+PONTEDERIA [SP.?] (PONTEDERIACEAE).
+
+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.
+
+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.
+
+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.
+
+TABLE 4.d. Pontederia. Diameters of pollen-grains, after having been long soaked
+in water, in divisions of the micrometer.
+
+Column 1: Source of Pollen-grains.
+Column 2: diameter.
+
+Long-styled form, mid-length stamens (Average of 20 measurements): 13.2.
+Long-styled form, shortest stamens (10 measurements): 9.0.
+
+Mid-styled form, longest stamens (15 measurements) : 16.4.
+Mid-styled form, shortest stamens (20 measurements): 9.1.
+
+Short-styled form, longest stamens (20 measurements): 14.6.
+Short-styled form, mid-length stamens (20 measurements): 12.3.
+
+We have here the usual rule of the grains from the longer stamens, the tubes of
+which have to penetrate the longer pistil, being larger than those from the
+stamens of less length. The extreme difference in diameter between the grains
+from the longest stamens of the mid-styled form, and from the shortest stamens
+of the long-styled, is as 16.4 to 9.0, or as 100 to 55; and this is the greatest
+difference observed by me in any heterostyled plant. It is a singular fact that
+the grains from the corresponding longest stamens in the two forms 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.
+
+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.
+
+
+CHAPTER V.
+
+ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS.
+
+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.
+
+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.
+
+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.
+
+Lythrum salicaria.
+
+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.
+
+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.
+
+STANDARD NUMBER OF SEEDS PRODUCED BY LEGITIMATE PLANTS OF THE THREE FORMS, WHEN
+LEGITIMATELY FERTILISED.
+
+Long-styled form:
+Average number of seeds in each capsule, 93;
+Maximum number observed out of twenty-three capsules, 159.
+
+Mid-styled form:
+Average number of seeds, 130;
+Maximum number observed out of thirty-one capsules, 151.
+
+Short-styled form:
+Average number of seeds, 83.5; but we may, for the sake of brevity, say 83;
+Maximum number observed out of twenty-five capsules, 112.
+
+CLASSES 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.
+
+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.
+
+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.)
+
+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.
+
+[PLANT 1.
+
+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.
+
+PLANT 2.
+
+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.
+
+PLANTS 3 AND 4.
+
+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.
+
+PLANT 5.
+
+This long-styled plant, after flowering in 1863 close to an illegitimate mid-
+styled plant, yielded only four capsules, which altogether included only five
+seeds. During 1864, 1865, and 1866, it was surrounded either by illegitimate or
+legitimate plants of the other two forms; but it did not yield a single capsule.
+It was a superfluous experiment, but I likewise artificially fertilised in a
+legitimate manner twelve flowers; but not one of these produced a capsule; so
+that this plant was almost absolutely barren.
+
+PLANT 6.
+
+This long-styled plant, after flowering during the favourable year of 1866,
+surrounded by illegitimate plants of the other two forms, did not produce a
+single capsule.
+
+PLANT 7.
+
+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.]
+
+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.
+
+[PLANT 8.
+
+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.
+
+PLANT 9.
+
+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.
+
+PLANT 10.
+
+This long-styled plant was freely fertilised at the same time and in the same
+manner as the last. Ten capsules yielded an average of 44.2 seeds, with a
+maximum of 69 and a minimum of 25; hence this plant yielded 47 per cent of the
+full complement of seeds.]
+
+The nineteen long-styled plants of the third lot, of the same parentage as the
+last lot, were treated 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.
+
+[PLANT 11.
+
+This long-styled plant produced a large crop of capsules, and in this respect
+was one of the most fertile of the whole lot of nineteen plants. But the average
+from ten capsules was only 35.9 seeds, with a maximum of 60 and a minimum of 8.
+
+PLANT 12.
+
+This long-styled plant produced very few capsules; and ten yielded an average of
+only 15.4 seeds, with a maximum of 30 and a minimum of 4.
+
+PLANT 13.
+
+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.]
+
+CLASS 3. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED WITH
+POLLEN FROM OWN-FORM MID-LENGTH STAMENS.
+
+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.
+
+[PLANT 14.
+
+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.
+
+PLANT 15.
+
+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.
+
+PLANT 16.
+
+This short-styled plant, treated like the two last, yielded from ten capsules an
+average of 77.8 seeds, with a maximum of 97 and a minimum of 60; so that this
+plant produced 94 per cent of the full number of seeds.
+
+PLANT 17.
+
+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.]
+
+CLASS 4. ILLEGITIMATE PLANTS RAISED FROM A MID-STYLED PARENT FERTILISED WITH
+POLLEN FROM OWN-FORM LONGEST STAMENS.
+
+After two trials, I succeeded in raising only four plants from this illegitimate
+union. These proved to be three mid-styled and one long-styled; but from so
+small a number we can hardly judge of the tendency in mid-styled plants when
+self-fertilised to reproduce the same form. These four plants never attained
+their full and normal height; the long-styled plant had several of its anthers
+contabescent.
+
+[PLANT 18.
+
+This mid-styled plant, when freely and legitimately fertilised during 1865 by
+illegitimate plants descended from self-fertilised long-, short-, and mid-styled
+plants, 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.
+
+PLANT 19.
+
+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.
+
+PLANT 20.
+
+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.]
+
+CLASS 5. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED WITH
+POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.
+
+In the four previous classes, plants raised from the three forms fertilised with
+pollen from either the longer or shorter stamens of the same form, but generally
+not from the same plant, have been described. Six other illegitimate unions are
+possible, namely, between the three forms and the stamens in the other two forms
+which do not correspond in height with their pistils. But I succeeded in raising
+plants from only three of these six unions. From one of them, forming the
+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.
+
+[PLANT 21.
+
+This short-styled plant, freely and legitimately fertilised during 1865 by
+illegitimate plants, descended from self-fertilised long-, mid- and short-styled
+parents, yielded an average from ten capsules of 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.
+
+PLANT 22.
+
+This short-styled plant produced perfectly sound pollen, as viewed under the
+microscope. During 1866 it was freely and legitimately fertilised by other
+illegitimate plants belonging to the present and the following class, both of
+which include many highly fertile plants. Under these circumstances it yielded
+from eight capsules an average of 100.5 seeds, with a 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.
+
+PLANT 23.
+
+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.
+
+PLANT 24.
+
+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.
+
+PLANT 25.
+
+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.]
+
+CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH
+POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.
+
+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.
+
+[PLANT 26.
+
+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.
+
+PLANT 27.
+
+This mid-styled plant, fertilised during 1864 in the same manner as the last,
+yielded an average, from ten capsules, of 99.4 seeds, with a maximum of 122 and
+a minimum of 53, thus attaining to 76 per cent of the normal fertility. If 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.
+
+PLANT 28.
+
+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.
+
+PLANT 29.
+
+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.
+
+Plant 30.
+
+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.
+
+Plant 31.
+
+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.]
+
+CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH
+POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.
+
+It was shown in the last chapter that the union from which these illegitimate
+plants were raised is far more fertile than any other illegitimate union; for
+the mid-styled parent, when thus fertilised, yielded an average (all very poor
+capsules being excluded) of 102.8 seeds, with a maximum of 130; and the
+seedlings in the present class likewise have their fertility not at all
+lessened. Forty plants were raised; and these attained their full height and
+were covered with seed-capsules. 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.
+
+[PLANT 32.
+
+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.
+
+PLANT 33.
+
+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.]
+
+CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF THE THREE FORMS OF Lythrum
+salicaria.
+
+From the three forms occurring in approximately equal numbers in a state of
+nature, and from the 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.
+
+[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.
+
+NORMAL STANDARD OF FERTILITY OF THE THREE FORMS, WHEN LEGITIMATELY AND NATURALLY
+FERTILISED.
+
+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.
+
+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.
+
+TABLE 5.30. Continued.
+
+CLASS 1 AND CLASS 2.--ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS
+FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH OR SHORTEST STAMENS.
+
+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.
+
+ 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.
+
+CLASS 3. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH
+POLLEN FROM OWN-FORM SHORTEST STAMENS.
+
+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.
+
+CLASS 4. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH
+POLLEN FROM OWN-FORM LONGEST STAMENS.
+
+18 : Mid-styled  : 102.6 : 131 : 63 : 80.
+19 : Mid-styled  :  73.4 :  87 : 64 : 56.
+20 : Long-styled :  69.6 :  83 : 52 : 75.
+
+CLASS 5. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH
+POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.
+
+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.
+
+CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH
+POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.
+
+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.
+
+CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH
+POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.
+
+32 : Mid-styled   : 127.2 : 144 : 96 :  98.
+33 : Short-styled : 113.9 : 137 : 90 : 137.
+
+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.
+
+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.
+
+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.
+
+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.
+
+OXALIS.
+
+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.
+
+[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.
+
+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.]
+
+PRIMULA.
+
+Primula Sinensis.
+
+I raised during February 1862, from some long-styled plants illegitimately
+fertilised with pollen from the same form, twenty-seven seedlings. These were
+all long-styled. They 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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+SUMMARY ON THE TRANSMISSION OF FORM, CONSTITUTION, AND FERTILITY OF THE
+ILLEGITIMATE OFFSPRING OF Primula Sinensis.
+
+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.
+
+[EQUAL-STYLED VARIETY OF Primula Sinensis.
+
+As any variation in the structure of the reproductive organs, combined with
+changed function, is a rare event, the following cases are worth giving in
+detail. My attention was first called to the subject by 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.
+
+TABLE 5.31. Primula Sinensis. Preponderance of long-styled over the short-styled
+form.
+
+Column 1: Name of owner or place.
+Column 2: Long-styled form.
+Column 3: Short-styled form.
+Column 4: equal-styled variety.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.]
+
+CONCLUSIONS WITH RESPECT TO THE EQUAL-STYLED VARIETY OF P. Sinensis.
+
+That this is a variation, and not a third or distinct form, as in the trimorphic
+genera 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.
+
+[Primula auricula.
+
+Although I made no experiments on the illegitimate offspring of this species, I
+refer to it for two reasons:--First, because I have observed two equal-styled
+plants in which the pistil resembled in all respects that of the long-styled
+form, whilst the stamens had become elongated as in the short-styled form, so
+that the stigma was almost surrounded by the anthers. The 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.
+
+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.
+
+Primula farinosa.
+
+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.
+
+Primula elatior.
+
+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.]
+
+Primula vulgaris, BRIT. FL.
+
+VAR. acaulis OF LINN. AND P. acaulis OF JACQ.
+
+VAR. RUBRA.
+
+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.
+
+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!
+
+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.
+
+TABLE 5.32. Primula vulgaris.
+
+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.
+
+Purple- and yellow-flowered illegitimate long-styled plants, ILLEGITIMATELY
+fertilised with pollen from the same plant :
+72 : 11 : 11.5 : 26 : 5.
+
+Purple- and yellow-flowered illegitimate long-styled plants, ILLEGITIMATELY
+fertilised with pollen from the common long-styled primrose :
+72 : 39 : 31.4 : 62 : 3.
+
+Or, if the ten poorest capsules, including less than 15 seeds, be rejected, we
+get:
+72 : 29 : 40.6 : 62 : 18.
+
+Purple- and yellow-flowered illegitimate long-styled plants, LEGITIMATELY
+fertilised with pollen from the common short-styled primrose :
+26 : 18 : 36.4 : 60 : 9.
+
+Or, if the two poorest capsules, including less than 15 seeds, be rejected, we
+get:
+26 : 16 : 41.2 : 60 : 15.
+
+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.
+
+Or, if the three poorest capsules be rejected, we get:
+20 : 11 : 18.9 : 46 : 8.
+
+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.
+
+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.
+
+Primula veris, Brit. Fl.
+
+Var. officinalis of Linn., P. officinalis OF Jacq.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+[EQUAL-STYLED RED VARIETY OF Primula veris.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+PULMONARIA.
+
+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.
+
+Polygonum fagopyrum.
+
+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.]
+
+CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF HETEROSTYLED TRIMORPHIC AND
+DIMORPHIC PLANTS.
+
+It is remarkable how closely and in how many points illegitimate unions between
+the two or three forms of the 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.
+
+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.
+
+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.
+
+
+CHAPTER VI.
+CONCLUDING REMARKS ON HETEROSTYLED PLANTS.
+
+The essential character of heterostyled plants.
+Summary of the differences in fertility between legitimately and illegitimately
+fertilised plants.
+Diameter of the pollen-grains, size of anthers and structure of stigma in the
+different forms.
+Affinities of the genera which include heterostyled species.
+Nature of the advantages derived from heterostylism.
+The means by which plants became heterostyled.
+Transmission of form.
+Equal-styled varieties of heterostyled plants.
+Final remarks.
+
+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.
+
+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.
+
+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.
+
+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.
+
+Primula veris : 69 : 65.
+
+Primula elatior : 27 : 75.
+
+Primula vulgaris : 60 : 54.
+
+Primula Sinensis : 84 : 63.
+
+Primula Sinensis (second trial) : 0 : 53.
+
+Primula Sinensis (Hildebrand) : 100 : 42.
+
+Primula auricula (Scott) : 80 : 15.
+
+Primula Sikkimensis (Scott) : 95 : 31.
+
+Primula cortusoides (Scott) : 74 : 66.
+
+Primula involucrata (Scott) : 72 : 48.
+
+Primula farinosa (Scott) : 71 : 44.
+
+Average of the nine species of Primula : 88.4 : 69.
+
+Hottonia palustris (H. Muller) : - : 61.
+
+Linum grandiflorum (the difference probably is much greater) : - : 69.
+
+Linum perenne : - : 20.
+
+Linum perenne (Hildebrand) : 0 : 0.
+
+Pulmonaria officinalis (German stock, Hildebrand) : 0 : 0.
+
+Pulmonaria angustifolia : 35 : 32.
+
+Mitchella repens : 20 : 47.
+
+Borreria, Brazilian sp. : - : 0.
+
+Polygonum fagopyrum : - : 46.
+
+Lythrum salicaria : 33 : 46.
+
+Oxalis Valdiviana (Hildebrand) : 2 : 34.
+
+Oxalis Regnelli : 0 : 0.
+
+Oxalis speciosa : 15 : 49.
+
+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.
+
+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.
+
+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.
+
+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.
+
+DIMORPHIC SPECIES.
+
+Column 1: Name of species.
+Column 2: From the long-styled form : relative diameter.
+
+Primula veris : 67.
+
+Primula vulgaris : 71.
+
+Primula Sinensis (Hildebrand) : 57.
+
+Primula auricula : 71.
+
+Hottonia palustris (H. Muller) : 61.
+
+Hottonia palustris (self) : 64.
+
+Linum grandiflorum : 100.
+
+Linum perenne (diameter variable) : 100 (?).
+
+Linum flavum : 100.
+
+Pulmonaria officinalis : 78.
+
+Pulmonaria angustifolia : 91.
+
+Polygonum fagopyrum : 82.
+
+Leucosmia Burnettiana : 99.
+
+Aegiphila elata : 62.
+
+Menyanthes trifoliata : 84.
+
+Limnanthemum Indicum : 100.
+
+Villarsia (sp.?) : 75.
+
+Forsythia suspensa : 94.
+
+Cordia (sp.?) : 100.
+
+Gilia pulchella : 100.
+
+Gilia micrantha : 81.
+
+Sethia acuminata : 83.
+
+Erythroxylum (sp.?) : 93.
+
+Cratoxylon formosum : 86.
+
+Mitchella repens, pollen-grains of the long-styled a little smaller.
+
+Borreria (sp.?) : 92.
+
+Faramea (sp.?) : 67.
+
+Suteria (sp.?) (Fritz Muller) : 75.
+
+Houstonia coerulea : 72.
+
+Oldenlandia (sp.?) : 78.
+
+Hedyotis (sp.?) : 88.
+
+Coccocypselum (sp.?) (Fritz Muller) : 100.
+
+Lipostoma (sp.?) : 80.
+
+Cinchona micrantha : 91.
+
+TRIMORPHIC SPECIES.
+
+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.
+
+Lythrum salicaria : 60.
+
+Nesaea verticillata : 65.
+
+Oxalis Valdiviana (Hildebrand) : 71.
+
+Oxalis Regnelli : 78.
+
+Oxalis speciosa : 69.
+
+Oxalis sensitiva : 84.
+
+Pontederia (sp.?) : 55.
+
+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.
+
+Oxalis rosea, long-styled form (Hildebrand) : 83.
+
+Oxalis compressa, short-styled form : 83.
+
+Pontederia (sp.?) short-styled form : 87.
+
+Pontederia other sp. mid-styled form : 86.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+TABLE 6.35. List of genera including heterostyled species.
+
+DICOTYLEDONS.
+
+HYPERICINEAE:
+Cratoxylon.
+
+ERYTHROXYLEAE:
+Erythroxylum.
+Sethia.
+
+GERANIACEAE:
+Linum.
+Oxalis.
+
+LYTHRACEAE:
+Lythrum.
+Neseae.
+
+RUBIACEAE:
+Cinchona.
+Bouvardia.
+Manettia.
+Hedyotis.
+Oldenlandia.
+Houstonia.
+Coccocypselum.
+Lipostoma.
+Knoxia.
+Faramea.
+Psychotria.
+Rudgea.
+Suteria.
+Mitchella.
+Diodia.
+Borreria.
+Spermacoce.
+
+PRIMULACEAE:
+Primula.
+Hottonia.
+Androsace.
+
+OLEACEAE:
+Forsythia.
+
+GENTIANACEAE:
+Menyanthes.
+Limnanthemum.
+Villarsia.
+
+POLEMONIACEAE:
+Gilia.
+
+CORDIEAE:
+Cordia.
+
+BORAGINEAE:
+Pulmonaria.
+
+VERBENACEAE:
+Aegiphila.
+
+POLYGONEAE:
+Polygonum.
+
+THYMELEAE:
+Thymelea.
+
+MONOCOTYLEDONS.
+
+PONTEDERIACEAE:
+Pontederia.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+THE MEANS BY WHICH PLANTS MAY HAVE BEEN RENDERED HETEROSTYLED.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+TRANSMISSION OF THE TWO FORMS BY HETEROSTYLED PLANTS.
+
+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.
+
+TABLE 6.36. Nature of the offspring from illegitimately fertilised dimorphic
+plants.
+
+Column 1: Species and form.
+Column 2: Number of long-styled offspring.
+Column 3: Number of short-styled offspring.
+
+Primula veris. Long-styled form, fertilised by own-form pollen during five
+successive generations : 156 : 6.
+
+Primula veris. Short-styled form, fertilised by own-form pollen : 5 : 9.
+
+Primula vulgaris. Long-styled form, fertilised by own-form pollen during two
+successive generations : 69 : 0.
+
+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.
+
+Primula Sinensis. Long-styled form, fertilised by own-form pollen during two
+successive generations : 52 : 0.
+
+Primula Sinensis. Long-styled form, fertilised by own-form pollen (Hildebrand) :
+14 : 3.
+
+Primula Sinensis. Short-styled form, fertilised by own-form pollen: 1 : 24.
+
+Pulmonaria officinalis. Long-styled form, fertilised by own-form pollen : 11 :
+0.
+
+Polygonum fagopyrum. Long-styled form, fertilised by own-form pollen : 45 : 4.
+
+Polygonum fagopyrum. Short-styled form, fertilised by own-form pollen : 13 : 20.
+
+TABLE 6.37. Nature of the offspring from illegitimately fertilised trimorphic
+plants.
+
+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.
+
+Lythrum salicaria. Long-styled form, fertilised by own-form pollen : 56 : 0 : 0.
+
+Lythrum salicaria. Short-styled form, fertilised by own-form pollen : 1 : 0 : 8.
+
+Lythrum salicaria. Short-styled form, fertilised by pollen from mid-length
+stamens of long-styled form : 4 : 0 : 8.
+
+Lythrum salicaria. Mid-styled form, fertilised by own-form pollen : 1 : 3 : 0.
+
+Lythrum salicaria. Mid-styled form, fertilised by pollen from shortest stamens
+of long-styled form : 17 : 8 : 0.
+
+Lythrum salicaria. Mid-styled form, fertilised by pollen from longest stamens of
+short-styled form : 14 : 8 : 18.
+
+Oxalis rosea. Long-styled form, fertilised during several generations by own-
+form pollen, produced offspring in the ratio of : 100 : 0 : 0.
+
+Oxalis hedysaroides. Mid-styled form, fertilised by own-form pollen : 0 : 17 :
+0.
+
+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.
+
+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.
+
+EQUAL-STYLED VARIETIES.
+
+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.
+
+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.
+
+FINAL REMARKS.
+
+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.
+
+
+CHAPTER VII.
+POLYGAMOUS, DIOECIOUS, AND GYNO-DIOECIOUS PLANTS.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS.
+
+Euonymus Europaeus (CELASTRINEAE).
+
+(Figure 7.12. Euonymus Europaeus
+Left: Hermaphrodite or male.
+Right: Female.)
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+Fragaria vesca, Virginiana, chiloensis, etc. (ROSACEAE).
+
+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.)
+
+Rhamnus catharticus (RHAMNEAE).
+
+(FIGURE 7.13. Rhamnus catharticus (from Caspary.)
+Left: Long-styled male.
+Right: Short-styled male.)
+
+(FIGURE 7.14. Rhamnus catharticus.
+Left: Long-styled female.
+Right: Short-styled female.)
+
+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.
+
+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.
+
+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.
+
+Rhamnus lanceolatus.
+
+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.
+
+Epigaea repens (ERICACEAE).
+
+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.
+
+Ilex aquifolium (AQUIFOLIACEAE).
+
+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.
+
+GYNO-DIOECIOUS PLANTS.
+
+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.
+
+Thymus serpyllum.
+
+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.)
+
+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.
+
+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.
+
+Thymus vulgaris.
+
+(FIGURE 7.15. Thymus vulgaris (magnified).
+Left: Hermaphrodite.
+Right: Two females.)
+
+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.
+
+Satureia hortensis.
+
+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.
+
+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.
+
+[Scabiosa arvensis (DIPSACEAE).
+
+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.
+
+Echium vulgare (BORAGINEAE).
+
+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.
+
+Plantago lanceolata (PLANTAGINEAE).
+
+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.
+
+Cnicus, Serratula, Eriophorum.
+
+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.)]
+
+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.
+
+
+CHAPTER VIII.
+CLEISTOGAMIC FLOWERS.
+
+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.
+
+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.
+
+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.
+
+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."
+
+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.)
+
+DICOTYLEDONS.
+
+BORAGINEAE:
+Eritrichium.
+
+CONVOLVULACEAE:
+Cuscuta.
+
+SCROPHULARINEAE:
+Scrophularia.
+Linaria.
+Vandellia.
+
+ACANTHACEAE:
+Cryphiacanthus.
+Eranthemum.
+Daedalacanthus.
+Dipteracanthus.
+Aechmanthera.
+Ruellia.
+
+LABIATAE:
+Lamium.
+Salvia.
+
+NYCTAGINEAE:
+Oxybaphus.
+Nyctaginia.
+
+ASCLEPIADAE:
+Stapelia.
+
+CAMPANULACEAE:
+Specularia.
+Campanula.
+
+PRIMULACEAE:
+Hottonia.
+
+COMPOSITAE:
+Anandria.
+
+CRUCIFERAE:
+Heterocarpaea.
+
+VIOLACEAE:
+Viola.
+
+CISTINEAE:
+Helianthemum.
+Lechea.
+
+MALVEACEAE:
+Pavonia.
+
+MALPIGHIACEAE:
+Gaudichaudia.
+Aspicarpa.
+Camarea.
+Janusia.
+
+POLYGALEAE:
+Polygala.
+
+BALSAMINEAE:
+Impatiens.
+
+GERANIACAEA:
+Oxalis.
+
+LEGUMINOSAE:
+Ononis.
+Parochaetus.
+Chapmannia.
+Stylosanthus.
+Lespedeza.
+Vicia.
+Lathyrus.
+Martinsia vel Neurocarpum.
+Amphicarpaea.
+Glycine.
+Galactia.
+Voandzeia.
+
+DROSERACEAE:
+Drosera.
+
+MONOCOTYLEDONS.
+
+JUNCEAE:
+Juncus.
+
+GRAMINEAE:
+Leersia.
+Hordeum.
+Cryptostachys.
+
+COMMELINEAE:
+Commelina.
+
+PONTEDERACEAE:
+Monochoria.
+
+ORCHIDEAE:
+Schomburgkia.
+Cattleya.
+Epidendron.
+Thelymitra.
+
+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.
+
+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.
+
+Viola canina.
+
+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.
+
+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.
+
+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.
+
+Viola odorata (WHITE-FLOWERED, SINGLE, CULTIVATED VARIETY).
+
+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.
+
+Viola hirta.
+
+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.
+
+Viola nana.
+
+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.
+
+Viola Roxburghiana.
+
+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.
+
+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.
+
+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."
+
+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.
+
+Oxalis acetosella.
+
+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.
+
+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.
+
+Oxalis (Biophytum) sensitiva.
+
+This plant is ranked by many botanists as a distinct genus, but as a sub-genus
+by Bentham and Hooker. Many of the early flowers on a mid-styled plant in my
+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.
+
+Vandellia nummularifolia.
+
+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.
+
+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.
+
+Linaria spuria.
+
+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.
+
+Ononis columnae.
+
+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.
+
+Ononis minutissima.
+
+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.
+
+Lathyrus nissolia.
+
+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.
+
+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.
+
+Impatiens fulva.
+
+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.
+
+Impatiens noli-me-tangere.
+
+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.
+
+Drosera rotundifolia.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+Juncus bufonius and Hordeum.
+
+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.
+
+Leersia oryzoides.
+
+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.
+
+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.
+
+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.)
+
+CONCLUDING REMARKS ON CLEISTOGAMIC FLOWERS.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.
+
+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.)
+
+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.
+
+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.
+
+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.
+
+
+INDEX.
+
+Acanthaceae.
+
+Acer campestre.
+
+Adoxa.
+
+Aegiphila elata.
+--mollis.
+--obdurata.
+
+Alefeld, Dr., on Linum.
+
+Alisma natans.
+
+Amphicarpaea.
+
+Amsinckia spectabilis.
+Variability in length of stamens and pistil.
+
+Anchusa arvensis.
+
+Androsace vitalliana.
+
+Anthers, size of, in different forms.
+contabescent.
+
+Arachis.
+
+Arnebia hispidissima.
+
+Ascherson, Dr., on Salvia cleistogama.
+Juncus bufonius.
+Leersia oryzoides.
+
+Asclepias.
+
+Ash, the common.
+
+Asperula scoparia.
+
+Axell on Primula stricta.
+
+Babington, Professor, on Primula elatior.
+Stellaria graminea.
+
+Baillon, emission of the tubes from pollen-grains.
+
+Belhomme, M., on ray-florets.
+
+Bennett, A.W., on Impatiens fulva.
+flowers fertilised whilst in the bud state.
+
+Bentham, Mr., on the differentiation of the sexes.
+on the cleistogamic flowers of Ononis.
+
+Boragineae.
+
+Boreau on cowslip and primrose.
+
+Borreria.
+
+Bouche on Pavonia.
+effect of temperature and light on corolla.
+
+Bouvardia leiantha.
+
+Braun on Dracocephalum.
+
+Breitenbach, W., on Primula elatior.
+
+Bromfield, Dr., on primrose and cowslip.
+Primula elatior.
+Specularia perfoliata.
+
+Brown, Robert, on sexual changes.
+
+Buckwheat, the common.
+
+Caltha palustris.
+
+Campanula colorata.
+
+Cardamine amara.
+
+Caspary, Professor, on Rhamnus catharticus.
+
+Cattleya.
+
+Chamissoa.
+
+Cinchona micrantha.
+
+Cleistogamic flowers.
+list of genera.
+on their origin.
+
+Cnicus acaulis.
+-- palustris.
+
+Coccocypselum.
+pollen-grains of.
+
+Coprosma.
+
+Cordia.
+pistil of.
+
+Corolla, difference in size in the sexes of the same species.
+
+Corydalis.
+
+Corylus avellana.
+
+Cowslip, the common.
+short- and long-styled.
+
+Cratoxylon formosum.
+
+Crocker, C.W., on Plantago lanceolata.
+
+Cryptostachys.
+
+Cuphea purpurea.
+
+Darwin, Charles, on reproductive organs under cultivation.
+intercrossed plants.
+prepotency of pollen.
+insects fertilising flowers.
+Cephalanthera grandiflora.
+Epidendron and Cattleya.
+number of pollen-grains.
+
+Darwin, W., on Pulmonaria angustifolia.
+
+Datura arborea.
+
+Delpino, plants fertilised by the wind.
+on the walnut.
+Polygonaceae.
+pollen-grains.
+Thymus serpyllum.
+closed or cleistogamic flowers.
+Viola odorata.
+
+Dianthus barbatus.
+
+Dickie, Dr., on Eriophorum angustifolium.
+
+Dictamnus fraxinella.
+
+Diodia.
+
+Dioecious and sub-dioecious plants.
+
+Discospermum.
+
+Doubleday, H., on Primula elatior.
+
+Dracocephalum Moldavicum.
+
+Drosera Anglica.
+-- rotundifolia.
+
+Duval-Jouve, M., on Cryptostachys.
+Leersia oryzoides.
+
+Dyer, Thiselton, on Salvia Horminum.
+Cratoxylon formosum.
+
+Echium vulgare.
+
+Epidendron.
+
+Epigaea repens.
+
+Eranthemum ambiguum.
+
+Eriophorum angustifolium.
+
+Erythroxylum.
+pollen-grains of.
+
+Euonymus Europaeus.
+
+Euphrasia officinalis.
+
+Euryale.
+
+Faramea.
+pollen-grains of.
+
+Fitzgerald, Mr., on Thelymitra.
+
+Forsythia suspensa.
+stamens.
+-- viridissima.
+
+Fragaria Chiloensis.
+-- elatior.
+-- vesca.
+-- Virginiana.
+
+Fraxinus excelsior.
+
+Galium cruciatum.
+
+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.
+
+Gentianeae.
+
+Geraniaceae.
+
+Geranium sylvaticum.
+
+Gesneria pendulina.
+
+Gilia aggregata.
+-- coronopifolia.
+-- micrantha.
+-- nudicaulis.
+-- pulchella.
+
+Gillibert on Menyanthes.
+
+Gloriosa Lily, the.
+
+Godron on hybrid Primulas.
+
+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.
+
+Gyno-dioecious plants.
+
+Hart, Mr., on Nepeta glechoma.
+
+Hautbois Strawberry, the.
+
+Hedyotis.
+
+Henslow, Reverend Professor, on hybrid Primulae.
+
+Henslow, Reverend G., on flowers self-fertilised during the winter.
+
+Herbert, Dr., on hybrid Primulae.
+
+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.
+
+Hibiscus, pollen-grains.
+
+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.
+
+Homostyled species of Primula.
+
+Hooker Dr., on Campanula.
+
+Hordeum.
+
+Hottonia inflata.
+-- palustris.
+relative fertility.
+anthers of.
+papillae on stigma.
+
+Houstonia coerulea.
+
+Hoya carnosa.
+
+Hybrid Primulas.
+
+Hydrangea.
+
+Hypericineae.
+Hyssopus officinalis.
+
+Ilex aquifolium
+-- opaca.
+
+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.
+
+Illecebrum.
+
+Impatiens, pollen-grains of.
+-- balsamina.
+-- fulva.
+-- noli-me-tangere.
+
+Juglans regia.
+
+Juncus bufonius.
+
+Jussieu, A. de, on Malpighiaceae.
+
+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.
+
+Kirk, Dr., on Monochoria vaginalis.
+
+Knoxia.
+
+Koch on Primula longiflora.
+
+Krascheninikowia.
+
+Kuhn, Dr., on cleistogamic flowers.
+list of plants producing differently formed seeds.
+heterostyled plants.
+Vandellia nummularifolia.
+V. sessiflora.
+
+Lagerstroemia Indica.
+-- parviflora.
+-- reginae.
+
+Lathyrus nissolia.
+
+Lecoq, H., on the common maple.
+cowslips and primroses.
+Primula elatior.
+Linum Austriacum.
+Lythrum hyssopifolia.
+Rhamnus.
+gyno-dioecious plants.
+Scabiosa succisa.
+Viola odorata.
+
+Leersia oryzoides.
+pollen-grains of.
+
+Leggett, Mr., Pontederia cordata.
+
+Legitimate unions, summary on the fertility of the two, compared with that of
+the two illegitimate in Primula.
+fertility of, compared with illegitimate.
+
+Leighton, Reverend W.A., on the cowslip and primrose.
+Verbascum virgatum.
+
+Leontodon, pollen-grains.
+
+Leptosiphon.
+
+Leucosmia acuminata.
+-- Burnettiana.
+stigma.
+
+Lily, the Gloriosa.
+
+Limnanthemum Indicum.
+pollen-grains.
+anthers.
+
+Linaria spuria.
+
+Lindley on Fragaria elatior.
+
+Linnaeus on Primula veris, vulgaris, and elatior.
+
+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.
+
+Lipostoma.
+
+Lysimachia vulgaris.
+
+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.
+
+Malpighiaceae.
+
+Manettia bicolor.
+
+Maple, the common.
+
+Marshall, W., on Primula elatior.
+Plantago lanceolata.
+
+Masters, Dr. Maxwell, on cleistogamic flowers.
+
+Maximowicz on Krascheninikowia.
+
+Meehan, Mr., on Mitchella.
+Epigaea repens.
+
+Melissa clinopodium
+-- officinalis.
+
+Mello, Correa de, on Arachis.
+Voandzeia.
+
+Mentha aquatica.
+-- hirsuta.
+-- vulgaris.
+
+Menyanthes.
+-- trifoliata.
+
+Michalet on Oxalis acetosella.
+Linaria spuria.
+
+Mitchella.
+-- repens.
+
+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.
+
+Mollia lepidota.
+-- speciosa.
+
+Monnier, M., on Viola.
+
+Monochoria vaginalis.
+
+Mulberry, the.
+
+Muller, D., on Viola canina.
+
+Muller, Fritz, on pollen of the Villarsia.
+Faramea.
+Posoqueria fragrans.
+Nesaea.
+Oxalis.
+Pontederia.
+Oxalis Regnelli.
+Chamissoa.
+
+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.
+
+Myosotis.
+
+Nepeta glechoma.
+
+Nertera.
+
+Nesaea verticillata.
+
+Nolana prostrata, variability in length of stamens and pistil.
+
+Nyctaginia.
+
+Oldenlandia.
+
+Oleaceae.
+
+Oliver, Professor, on ovules of Primula veris.
+Viola.
+Campanula colorata.
+
+Ononis columnae.
+-- minutissima.
+-- parviflora.
+
+Origanum vulgare.
+
+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.
+
+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.
+
+Oxybaphus.
+
+Paeony, pollen-grains of.
+
+Parallelism between illegitimate and hybrid fertilisation.
+
+Pavonia.
+
+Phlox Hentzii.
+-- nivalis.
+-- subulata.
+
+Planchon on Linum salsoloides.
+L. Lewisii.
+on Hugonia.
+
+Plantago lanceolata.
+-- media.
+
+Polemoniaceae.
+
+Pollen-grains, relative diameter of.
+
+Polyanthus.
+
+Polygonaceae.
+
+Polygonum bistorta.
+-- fagopyrum.
+pollen-grains.
+
+Pontederia.
+pollen-grains.
+size of anthers.
+-- cordata.
+
+Posoqueria fragrans.
+
+Primrose, the common.
+
+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
+
+Primula vulgaris, var. rubra.
+
+Prunella vulgaris.
+
+Psychotria.
+
+Pulmonaria angustifolia.
+anthers.
+-- azurea.
+-- officinalis.
+  number of flowers.
+  pistil.
+
+Ranunculus aquatilis.
+
+Ray-florets, their use.
+
+Rhamnus catharticus.
+size of corolla.
+-- frangula.
+-- lanceolatus.
+
+Rhinanthus crista-galli.
+
+Rubiaceae.
+size of anthers.
+stigmas.
+number of heterostyled genera.
+
+Rudgea eriantha.
+
+Rue, the common.
+
+Ruellia tuberosa.
+
+Salvia.
+-- cleistogama.
+-- Horminum.
+
+Satureia hortensis.
+
+Scabiosa arvensis.
+-- atro-purpurea.
+-- succisa.
+
+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.
+
+Scrophularia aquatica.
+
+Serratula tinctoria.
+
+Sethia acuminata.
+-- obtusifolia.
+
+Smith, Sir J.E., on the carrot.
+hybrid Verbascums.
+Serratula tinctoria.
+Cnicus.
+Subularia.
+
+Soldanella alpina.
+
+Specularia perfoliata.
+
+Spence, Mr., on Mollia.
+
+Spermacoce.
+
+Sprengel on Hottonia palustris.
+
+Stellaria graminea.
+
+Strawberry, the Hautbois.
+
+Subularia.
+
+Suteria.
+
+Thelymitra.
+
+Thomson, Dr., on Campanula.
+
+Thrum-eyed, origin of term.
+
+Thwaites, Mr., on ovules of Limnanthemum Indicum.
+Sethia acuminata.
+Discospermum.
+
+Thymelia.
+
+Thymus citriodorus.
+-- serpyllum
+-- vulgaris.
+
+Timbal-Lagrave, M., on hybrids in genus Cistus.
+
+Torrey, Dr., on Hottonia inflata.
+
+Transmission of the two forms of heterostyled plants.
+
+Treviranus on Androsace vitalliana.
+Linum.
+
+Vandellia nummularifolia.
+-- sessifloria.
+
+Vaucher on the carrot.
+Soldanella alpina.
+Lythrum salicaria.
+-- thymifolia.
+Ilex aquifolium.
+on Labiatae.
+Viola hirta and collina.
+
+Verbascum, wild hybrids of.
+-- lychnitis.
+-- phoeniceum.
+-- thapsus.
+-- virgatum.
+
+Viburnum.
+
+Vicia.
+
+Villarsia.
+anthers.
+
+Viola alba.
+-- bicolor.
+-- biflora.
+-- canina.
+-- collina.
+-- elatior.
+-- hirta.
+-- ionodium.
+-- lancifolia.
+-- mirabilis.
+-- nana.
+  pollen-grains of.
+-- odorata.
+-- palustris.
+-- Roxburghiana.
+-- Ruppii.
+-- sylvatica.
+-- tricolor.
+
+Voandzeia.
+
+Walnut, the.
+
+Watson, H.C., on cowslips, primroses, and Oxlips.
+Primula elatior.
+
+Weddell, Dr., on hybrids between Aceras and Orchis.
+
+Wetterhan, Mr., on Corylus.
+
+Wichura, Max, on hybrid willows.
+sterile hybrids.
+
+Wirtgen on Lythrum salicaria.
+
+Wooler, W., on Polyanthus.
+
+Wray, Leonard, on Fragaria.
+
+
+
+
+
+End of this Project Gutenberg Etext of The Different Forms of Flowers on Plants
+of the Same Species by Charles Darwin.
+