328 DARWINISM 



How the Struggle for Existence Acts among Flowers. 



Let us now consider what will be the action of the struggle 

 for existence under the conditions we have seen to exist. 



Everywhere and at all times some species of plants will be 

 dominant and aggressive ; while others will be diminishing in 

 numbers, reduced to occupy a smaller area, and generally 

 having a hard struggle to maintain themselves. Whenever 

 a self-fertilising plant is thus reduced in numbers it will be 

 in danger of extinction, because, being limited to a small 

 area, it will suffer from the effects of too uniform conditions 

 which will produce weakness and infertility. But while this 

 change is in progress, any crosses between individuals of 

 slightly different constitution will be beneficial, and all varia- 

 tions favouring either insect agency on the one hand, or 

 wind-dispersal of pollen on the other, will lead to the pro- 

 duction of a somewhat stronger and more fertile stock. In- 

 creased size or greater brilliancy of the flower, more abundant 

 nectar, sweeter odour, or adaptations for more effectual cross- 

 fertilisation would all be preserved, and thus would be initiated 

 some form of specialisation for insect agency in cross -fertil- 

 isation ; and in every different species so circumstanced the 

 result would be different, depending as it would on many 

 and complex combinations of variation of parts of the flower, 

 and of the insect species which most abounded in the district. 



Species thus favourably modified might begin a new era 

 of development, and, while spreading over a somewhat wider 

 area, give rise to new varieties or species, all adapted in 

 various degrees and modes to secure cross -fertilisation by 

 insect agency. But in course of ages some change of condi- 

 tions might prove adverse. Either the insects required might 

 diminish in numbers or be attracted by other competing 

 flowers, or a change of climate might give the advantage 

 to other more vigorous plants. Then self-fertilisation with 

 greater means of dispersal might be more advantageous ; the 

 flowers might become smaller and more numerous ; the seeds 

 smaller and lighter so as to be more easily dispersed by the 

 wind, while some of the special adaptations for insect fertilis- 

 ation being useless would, by the absence of selection and by 

 the law of economy of growth, be reduced to a rudimentary 



