Chapter I: Front Matter

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.