308 THE WORLD OF LIFE chap. 



Mr. Henry O. Forbes observed, in Sumatra, that many 

 tropical orchids with showy flowers, which were perfectly 

 adapted for insect-fertilisation, yet produced very few seed- 

 capsules, and in many cases none. Yet the great abundance 

 of seeds, as fine as dust, in a single capsule, together with 

 the long life of most orchids, is quite sufficient, in most cases, 

 to preserve the various species in considerable abundance. 

 When, however, there is any danger of extinction the great 

 variability of orchids, which at first enabled them to become 

 so highly specialised for insect-fertilisation, also enables them 

 (in some cases) to return to self-fertilisation as in our bee- 

 orchis. Should this continuous self-fertilisation at length 

 lead to a weak constitution, then, occasional variations 

 serving to attract insects by nectar or in other ways, with 

 minute alterations of structure, may again lead to fertilisation 

 by insects. 



The other popular objection recently made to Darwin's 

 views on the origin of the flowers is, that the colours and 

 shapes of flowers are often such as to deter herbivorous 

 animals from eating them, and that this is the main or the 

 only reason why flowers are so conspicuous. The special 

 case supposed to prove this is that some buttercups are not 

 eaten by cattle because they are acrid or poisonous, and 

 that the bright yellow colour is a warning of inedibility. 



Even if these statements were wholly correct they would 

 not in the least affect the general proposition that all 

 conspicuous flowers attract insects which do actually cross- 

 fertilise them. But, in the first place, there is much 

 difference of opinion as to the inedibility of buttercups by 

 cattle ; and, in the second, our three most common yellow 

 buttercups (Ranunculus acris, R. repens, and R. bulbosus) are 

 so constructed that they can be cross-fertilised by a great 

 variety of insects, and as a matter of fact are so fertilised. 

 H. Muller grouped these three species together, as the same 

 insects visit them all, and he found that they were attractive 

 to no less than sixty different species, including 23 flies, 11 

 beetles, 24 bees, wasps, etc., and 5 butterflies. 



Any readers who are not satisfied with Darwin's own 

 statements on this subject should examine M tiller's Fertilisa- 

 tion of Flowers (translated by D'Arcy W. Thompson), in 





