NATURAL SELECTION. 107 



Certain plants excrete sweet juice, appar- 

 ently for the sake of eliminating something in- 

 jurious from the sap : this is effected, for instance, by 

 glands at the base of the stipules in some LeguminoscB, 

 and at the backs of the leaves of the common laurel. 

 This juice, though small in quantity, is greedily sought 

 by insects ; 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 num- 

 ber of plants of any species. Insects in seeking the nectar 

 would get dusted with pollen, and would often transport 

 it from one flower to another. The flowers of two dis- 

 tinct individuals of the same species would thus get 

 crossed ; and the act of crossing, as can be fully proved, 

 gives rise to vigorous seedlings, which consequently would 

 have the best chance of flourishing and surviving. The 

 plants which produced flowers with the largest glands or 

 nectaries, excreting most nectar, would oftenest be visited 

 by insects, and would oftenest be crossed ; and so in the 

 long run would gain the upper hand and form a local 

 variety. The flowers, also, which had their stamens and 

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

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

 degree the transportal of the pollen, would likewise be 

 favored. We might have taken the case of insects visitr 

 ing flowers for the sake of collecting pollen instead of 

 nectar ; and, as pollen is formed for the sole purpose of 

 fertilization, its destruction appears to be a simple loss 

 to the plant ; yet if a little pollen were carried, at first 

 occasionally and then habitually, by the pollen-devour- 

 ing insects from flower to flower, and a cross thus 

 effected, although nine tenths of the pollen were de- 

 stroyed, it might still be a great gain to the plant to 

 be thus robbed ; and the individuals which produced 



