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Show 330 DARWINISM CITAP. tubular flowers increasing in length and irregubrity, till in some like our common honeysuckle, they arc adapted for fertilisation by moths only, with abundant honey . and delicious perfume to attract them. In the Scrophu~anace::c we find open, almost regular flowers, as Veromc~. and Verbascum, fertilised by flies and bees, but also self-f~~t1hsed; Scrophularia adapted in form and colour. to be fert1hscd by wasps ; and the more complex and I.rregu~ar flowers of Linaria, Rhinanthus, Melampyrum, Ped1Cular1s, etc., mostly adapted to be fertilised by bees. . In the genera Geranium, Polygonum, V cromca, and sev?ral others there is a gradation of forms from. large and lmgh t to small and obscure coloured flowers, and m every cas~ the former are adapted for insect fertilisation, often exclusiVely, while in the latter self-fertilisation constantly occurs. In the yellow rattle (Rhinanthus Cr~sta-galli) ~here are tv~o ~orms (which have been named ma;o~ and mtn~r/, t~1c lar gCl and more conspicuous adapted to msect fert1h~at~on only, t~e smaller capable of self-ferti.lisatio~; ~nd two similar forms ex1st in the eyebright (Euphrasm officmahs). In both these cases there are special modifications in the length and curvature of the style as well as in the size and sha.pe of the corol1a; and the two forms are evidently becoming each ad~ptcd to special conditions, since in some districts the one, m 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 a~ways been goina on in nature throughout the long geolog10al ep~chs duri~a which the development of flowers has been progre s.n.lg. The t~vo great modes of gaining increa~cd vigour and fertlhty --intercrossing and dispersal over wider areas-have been resorted to again and again, under the pressure o~ a constn.nt struaale for existence and the need for adaptatiOn to cvercha;~ ng conditions. During all the modifications that emmed, useless parts were reduced or suppressed, owing to the ahscn <:c of selection and the principle of economy of growth ; a.nd th ns at each fresh adaptation some rudiments of old structures were 1 Muller's Fertilisation of Flowers, pp. 448, 455. Otb~r cases of recent degradation and readaptation to iusect-fertili:-;ation are gtven l>y Prof~ssur Henslow (see footnote, p. 324). XI THE SPECIAL COLOURS OF PLANTS 331 re-~e:eloped, but not unfrequently in a different form and for a distmct purpose. . ~he chief types of flowering plants have existed during the mllhons of ages of the whole tertiary period, and during this ~normou.s la~se of ti~e many of them may have been modified m the ~~ect.wn of msect fertilisation, and again into that of self-fertlhsatwn, not once or twice only, but perhaps scores or e:en hun~reds of times; and at each such modification a ~Ifference m the environment may have led to a distinct hnc of deve~opment. . At one epoch the highest specialisation of structure m adaptatiOn to a single species or group of in ·ects may ~ave saved a plant from extinction; while, at other times, the simplest. mode of self-fertilisation, combined with greater P?wers of dispersal and a con titution capable of supportina di~crse physical conditions, may have led to a similar resull Wit~ some groups the tendency seems to have been almost contmuously to greater and greater specialisation while with ?thers a tendency to simplification and degradation'has resulted m such plants as the grasses and sedges. We are now enabled dimly to perceive how the curious anomaly ?~ ve:y simple and very complex methods of securing cross-fertilisatiOn-both equally effective-may have been brought ~bout. . The simple modes may be the result of a comparatively direct .modification from the more primitive typ.es of flow:e~s, whiCh w~r~ occas~onally, and, as it \vcre, accidentally VISited and fertilised by msects · while the more complex modes, existing for the most part in the highly irregular ~owers, m.a! r~sult from those cases in which adaptation to mse?~-fe~tihsat10n, and partial or complete degradation to selffertilisatiOn or to wind -fertilisation, have aaain and aaain re~~rred, each time p~oducing some additio~al comple;ity, ansmg from the workmg up of old rudiments for new purposes, till there have been reached the marvellous flow er structur~s of the papilionaceous tribes, of the asclepiad , or of the orchids. vVe thus see that the existing diversity of colour and of structure in flowers is probably the ultimate result of the ever-recurring struggle for existence, combined with the evercha~ ging relations between the vegetable and animal kingdoms durmg countless ages. The constant variability of every part |