Chap. IV. NATURAL SELECTION. 95 



was successful in its battle for life, it would slowly spread from 

 a central spot, competinp^ Avitli and conf[U(>rinof the uncluuifred 

 individuals on the niar<>-ins of an ever-increasing circle. But 

 to the subject of intercrossing we shall have to return. It may 

 be objected by those who have not attended to natural history, 

 that tlie long-continued accumulation of individual differences 

 could not give rise to parts or organs which seem to us, and 

 arc often called, new. But, as we shall hereafter find, it is dif- 

 ficult to advance any good instance of a really new organ ; 

 even so complex and perfect an organ as the eye can be showa t(< 

 graduate downward into mere tissue sensitive to diffused light 

 It may be worth Avhile to give another and more complex 

 illustration of tlie action of natural selection. Certain plants 

 excrete sweet juice, apparently for the sake of eliminating 

 something injurious from their sap: this is effected, for in- 

 stance, by glands at the base of the stipules in some Legunii- 

 nosa^, and at the backs of the leaves of the common laurel. 

 This juice, though small in quantity, is greedily sought by in- 

 sects ; but their visits do not in any way benefit the plant. 

 Now, let us suppose that the juice or nectar was excreted 

 from the inside of the flowers of a certain number of plants of 

 anv species. Insects in seeking the nectar would get dusted 

 with pollen, and would certainly often transport it from one 

 flower to another. The flowers of two distinct individuals of 

 the same species would thus get crossed ; and the act of cross- 

 ing, as Ave have good reason to believe, would produce vigor- 

 ous seedlings, which consequently would have the best chance 

 of flourishing and surviving. The plants which produced flow- 

 ers with the largest glands or nectaries, excreting most nectar, 

 would oftencst be visited by insects, and would oftenest be 

 crossed ; and so in the long-run would gain the upper hand and 

 form a local variet}'. The flowers, also, wliich had their sta- 

 mens and pistils placed, in relation to the size and habits of the 

 particular insect which visited them, so as to favor in any 

 dcgr(>e the transportal of the pollen, would likewise be favored. 

 AVe might have taken the case of insects visiting flowers for 

 Ihc sake of collecting pollen instead of nectar; and as pollen is 

 formed for the sole purpose of fertilization, its destruction ap- 

 pears to be a simple loss to the plant ; 3-et if a little pollen 

 "were canied, at first occasionally and then habitually, by the 

 pollen-devouring insects from flower to flower, and a cross thus 

 ellected, although nine-tenths of the pollen were destroyed, it 

 might still be a great gain to the plant; and the individuals 



