12 THE EVOLUTION OF PLANTS 



Selection is, of course, a metaphorical expression; 

 in Nature it is no conscious being that selects, 

 but it is all the circumstances of life, such as 

 soil, climate and associated organisms, which de- 

 termine the survival of those varieties which are 

 best adapted to them. 



Variations, under which Darwin expressly in- 

 cluded the differences which distinguish one indi- 

 vidual from another, occur in every direction, 

 harmful, indifferent or beneficial; it is on the 

 continual selection for survival of the favourable 

 variations that Evolution depends. Thus, for 

 the first time, the Darwinian theory gave a nat- 

 ural explanation of the process of Evolution, 

 and, at the same time, of the great mystery of 

 adaptation. The universal characteristic of all 

 living things is that their whole structure is a 

 system of mechanisms and devices by which 

 they are enabled to maintain their own life and 

 leave descendants behind them. The whole of 

 Biology bears witness to adaptation; as striking 

 cases among plants, familiar to all, we may 

 mention the beautiful mechanism for securing 

 cross-fertilisation by insects, in the flowers of 

 an Orchid or a Sage; the means of dispersal pos- 

 sessed by seeds or seed-vessels in the Balsam, 

 the Bedstraw or the Dandelion; the climbing 

 organs in the Virginian Creeper, the Clematis or 

 the Ivy. 



