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Show 32R DARWINISM CHAP, How the Struggle for Existence Acts among Flowers. Let us now consider what will be the action of the ~truggle for existence under the conditions we hav~ seen to exist .. E ver,y w here ac nd at all times some spec•i esb of dp' la.n.ts hw' 1ll b. e d omm· an t a nd aabaor ess· ive '· while others Wlll e Imims mg m numbers, reduced to occupy a sr:1aller area, and generally l VI.n(T a haru stru(T()'le to maintam themselves. Whenever al as elfo- fertilising plabnot is thus reduce~ m. r:u:n: b ers 't '11 b 1 WI e · d· aer of extinction because, bemg hmited to a small In, a'ntb w ill suffer from t' he effects of too um' fo rm con dI' tw· n::; area, I . . · B h'l h' . which will produce weakness and mfertihty. . ut. ":' 1 e t 1 ~ h ae 1·s in pro(Tress any crosses between mdiVllluals of c ano b ? • • • 1 d 11 .. slightly different c.onstitt~twn Wlll be beneficm , an a. vana,~ tions fa.vouring c1ther msect agency on. the one hand, 01 wind-dispersal of pollen on the other, will le~d to the production of a somewhat stronger and more fertile stock. I ncreased size or <l'reatcr brilliancy of the flower, mo~·c abunda.nt nectar, sweeter odonr, or adaptations for more efiectu~l. c.ros::;fertilisation woul<l all be preserved, and thus wou.ld be nutmt ~d some form of specialisation for inse.ct agen?y m cross- fertd ·sation · and in every different species so circumstanced the ~·esult ~vonld be different, depending as it would on many and complex combinations of variation of parts. of the ~OVI~cr, a.nd of the insect species which most abounded 1~ the d1stnd. Species thus favourably modified might begm a new. era of development, and, while spreading over. a somewhat wid?l area, give rise to new varieties or speCies, all .a.dal~ted 111 various degrees and modes to secure cross-fert1hsat10n hy insect agency. But in course. of ages s_ome change. of co~lchtions might prove adverse. Either the msects reqmred nul?ht diminish in nurn bers or be attracted by other competmg flowers or a. chan(Te of climate rnig,ht give the advantage to oth~r more vigo~ous plants. Then self-fertilisation with <treater means of eli persal might be more advantageous j the flowers mirrht become smaller and more numerous j the seeds smaller and lighter so as to be more e~sily dis_persed by .t~c wind while some of the special adaptatiOns for msect fer tlh::;ation' being useless would, by the absence of selectio?- and hy the law of economy of growth, be reduced to a rudimentary xr THE SPECIAL COLOURS OF PLANTS 329 form. \Vith these modifications the species might extend its range into new district., thereby obtaining increased vi(Tom· bJ:" the change of conditions, as appears to have been the ~ase ~Ith. so many.of the sm~ll flowered self-fertilised plants. Thus It might contmue to cx1st for a long series of ages, till under other changes-geographical or biological-it mi(j·ht a(Tain .cr f . . b b suuer rom competitiOn or from other adverse circumstances and be at lenoth ag:J.in confined to a limited area, or reduced to very . canty nurn hers. But when thi~ cycle of change had taken place, the species would be very different from the original form. The flower would have been at one time modified to favour tho vi. its of insect and to sect~·e cross-fertilisation by their aid, and when the need for tlus passed away, some portions of these structures would remain, though in a reduced or rudi~ entary condition. But when insect agency became of Importance a second time, the new modifications would start from a different or more advanced basis, and thus a more complex result might be produced. Owing to the u~equal rates at which the reduction of the various parts might occur, some amount of irregularity in the flower mio·ht arise, and on a second development towards in ect cr~ssfertjli~ ation this irregularity, if useful, might be increased by vanation and selection. The rapidity and comparative certainty with which such changes as are here supposed do really take place, arc well shown by the great differences in floral structure, as reaard. the mode of fertilisation, in allied genera and species, and 0even in some cases in varieties of the same species. Thus in the Ranunculacere we find the conspicuous part of the flower to he the petals in Ranunculus, the sepals in Helleborus, Anemone, etc., and the stamens in most species of Thalictrum. In all these we have a simple regular flower, but in Aquil gia it is made complex by the spurred petals, and in Delphinium and Aconitum it becomes quite irregular. In the more simple clas self-fertilisation occurs freely, but it is prevented in the more complex flowers by the stamens maturing before the pistil. In the C~prifoliacere we have small and regular greenish flowers, a m the moschatel (Adoxa) j more conspicuous regular open flowers without honey, as in the elder (Sambucus) j and |