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.