68 ILLUSTKATIONS OF THE ACTION OF [CHAP. IV. 



the juice or nectar was excreted from the inside of the flowers of 

 a certain number 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 distinct in- 

 dividuals 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 favour in any degree the transportal of the 

 pollen, would likewise be favoured. 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 

 fertilisation, 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 continued, had been 

 rendered highly attractive to insects, they would, unintentionally 

 on their part, regularly carry pollen from flower to flower ; and 

 that they do this effectually, I could easily show by many striking 

 facts. I will give only one, as likewise illustrating one step in the 

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

 male flowers, which have four stamens producing a rather small 

 quantity of pollen, and a rudimentary pistil ; other holly-trees 

 bear only female flowers ; these have a full-sized pistil, and four 

 stamens with shrivelled anthers, in which not a grain of pollen 

 can be detected. Having found a female tree exactly sixty yards 

 from a male tree, I put the stigmas of twenty flowers, taken from 

 different branches, under the microscope, and on all, without 

 exception, there were a few pollen-grains, and on some a pro- 

 fusion. As the wind had set for several days from the female to 

 the male tree, the pollen could not thus have been carried. The 

 weather had been cold and boisterous, and therefore not favour- 

 able to bees, nevertheless every female flower which I examined 

 had been effectually fertilised by the bees, which had flown from 

 tree to tree in search of nectar. But to return to our imaginary 

 case : as soon as the plant had been rendered so highly attractive 

 to insects that pollen was regularly carried from flower to flower 



