138 THE ORIGIN OF SPECIES 



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 nec- 

 taries, 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 

 visiting 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-devouring 

 insects from flower to flower, and a cross thus effected, 

 although nine-tenths of the pollen were destroyed it 

 might still be a great gain to the plant to be thus 

 robbed; and the individuals which produced more and 

 more pollen, and had larger anthers, would be selected. 

 When our plant, by the above process long contin- 

 ued, had been rendered highly attractive to insects, they 

 would, unintentionally on their part, regularly carry pol- 

 len from flower to flower; and that they do this effect- 

 ually, I could easily show by many striking facts. I 

 will give only one, as likev-^ise illustrating one step in 

 the separation of the sexes of plants. Some holly-trees 

 bear only male flowers, which have four stamens produc- 

 ing a rather small quantity of pollen, and a rudimentary 

 pistil; other holly -trees bear only female flowers j these 



