1897] BEES AND THE DEVELOPMENT OE E LOWERS 105 



Those flowers of the original race which were cross-fertilised should 

 have survived rather than those self-fertilised. The passage from 

 perfect adaptation for cross-fertilisation to perfect adaptation to 

 self-fertilisation is a long one, and must have been spread over 

 many generations in each of which the latter was an advantage, if 

 it is to be accounted for on the principles of natural selection. 

 But it has been suggested that the change has been due to the 

 absence of insects and that thus only those plants which were able 

 to fertilise themselves survived. If, however, we suppose that in the 

 ancestral orchid the apparatus for cross-fertilisation was as perfect 

 as in many species at the present day, it would be incapable of 

 self-fertilisation, and therefore die out in the absence of insect 

 visits. Even if it could in a few cases fertilise itself, how could its 

 fewer and weaker progeny compete with the stronger seedlings of 

 nearly related and cross-fertilised species probably occupying the 

 same station ? If, however, in the ancestral orchid the arrangement 

 for fertilisation was such that self-fertilisation usually took place 

 in default of insect visits, then no benefit would arise from change 

 of form to perfect adaptation for self- and avoidance of insect- 

 fertilisation. With regard to the benefits resulting from cross- 

 fertilisation generally, Professor Henslow points out that orchids, 

 the most remarkably adapted of all plants for cross-fertilisation by 

 insects, " set the least amount of seed even when fully exposed to 

 insects." 



Another fact established by Darwin in relation to cross-fertilisa- 

 tion is that the offspring of the cross is more vigorous when between 

 slight varieties of the same species, or between individuals grown 

 under slightly different conditions. This fact is also adverse to the 

 theory of the development of a species of flower by the selective 

 action of the bee. For among the offspring of the crosses affected 

 by it those will be strongest which occur between varieties, or be- 

 tween plants grown at a distance, and therefore likely to differ 

 slightly from each other. But these are precisely the individuals 

 in which the incipient characters tending to the formation of a 

 new species will be least marked. Hence the action of the bee is 

 rather to retard development ; and Darwin himself has remarked 

 that frequent in-crossing tends to give uniformity to species varying 

 slightly as they do in a state of nature. 



A brief allusion to Professor Henslow's amendment of the 

 Darwinian insect selection theory will suffice. Apart from the 

 extreme improbability — as shown by recent research — that such 

 acquired characters as the lengthening of the petal of a flower by 

 the weight of an insect stretching it, or the coloration caused by 

 the irritation of an insect's feet, are transmitted, Professor Hens- 

 low's theory splits on the same rock as the older one. For, like the 



H 



