tubular flowers increasing in length and irregularity, till in some, like our common honeysuckle, they are adapted for fertilisation by moths only, with abundant honey and delicious perfume to attract them. In the Scrophulariaceae we find open, almost regular flowers, as Veronica and Verbascum, fertilised by flies and bees, but also self-fertilised; Scrophularia adapted in form and colour to be fertilised by wasps; and the more complex and irregular flowers of Linaria, Rhinanthus, Melampyrum, Pedicularis, etc., mostly adapted to be fertilised by bees.
In the genera Geranium, Polygonum, Veronica, and several others there is a gradation of forms from large and bright to small and obscure coloured flowers, and in every case the former are adapted for insect fertilisation, often exclusively, while in the latter self-fertilisation constantly occurs. In the yellow rattle (Rhinanthus Crista-galli) there are two forms (which have been named major and minor), the larger and more conspicuous adapted to insect fertilisation only, the smaller capable of self-fertilisation; and two similar forms exist in the eyebright (Euphrasia officinalis). In both these cases there are special modifications in the length and curvature of the style as well as in the size and shape of the corolla; and the two forms are evidently becoming each adapted to special conditions, since in some districts the one, in other districts the other is most abundant.[1]
These examples show us that the kind of change suggested above is actually going on, and has presumably always been going on in nature throughout the long geological epochs during which the development of flowers has been progressing. The two great modes of gaining increased vigour and fertility—intercrossing and dispersal over wider areas—have been resorted to again and again, under the pressure of a constant struggle for existence and the need for adaptation to ever-changing conditions. During all the modifications that ensued, useless parts were reduced or suppressed, owing to the absence of selection and the principle of economy of growth; and thus at each fresh adaptation some rudiments of old structures were
- ↑ Müller's Fertilisation of Flowers, pp. 448, 455. Other cases of recent degradation and readaptation to insect-fertilisation are given by Professor Henslow (see footnote, p. 324).
