242 A BOOK OF INSECTS 



vested with a kind of glamour which inevitably casts 

 its spell over the mind. Staid men of science have ex- 

 perienced this enchantment, and there can be little doubt 

 that their judgment has been occasionally influenced 

 thereby. They have observed that plants which are 

 habitually self-fertilised are often small weeds and annuals, 

 and that their flowers are usually insignificant when com- 

 pared with those which are frequently visited by insects. 

 These facts have prompted the assumption that there 

 is something infelicitous in self-fertilisation, and that 

 plants which have been able to secure an interchange 

 of pollen have climbed, as it were, out of the ruck to 

 their abiding advantage. But this is only one aspect 

 of the question ; for botanists tell us that self-fertilised 

 plants invariably set an extraordinary abundance of good 

 seed, that they tend to monopolise the soil, and that they 

 are more widely distributed on the face of the earth than 

 any others ; whereas those plants which depend solely 

 upon the chance visits of insects are relative failures in 

 the struggle for existence. Indeed, it is said that whereas 

 cross-fertilisation is at first a stimulating process, re- 

 sulting in the production of "fine" plants in the popular 

 sense of the word, its long continuance tends to reduce 

 fertility almost to zero. This is made manifest in the 

 case of the orchids, most of which cannot set seed at 

 all unless they are visited by the right kind of insect. 

 The Rev. G. Henslow mentions a tropical orchis 

 (Dendrobium speciosum), growing in the open in its 

 native country, which bore 40,000 blossoms but produced 

 only one pod. 



These facts seem at first to hint at a flaw in Nature's 

 scheme. But we must remember that " evolution is no 

 mechanical tendency making for perfection ; it is simply 

 the continual adaptation of plastic life, for good or evil, to 



