PLANT ADJUSTMENTS AND APPLICATIONS 563 



of success. Altogether, variation is one of the most universal attri- 

 butes of living things, and the outcome of natural selection upon 

 the varying populations of successive generations is persistence of 

 the forms possessing the most beneficial characters— or, as it is fre- 

 quently called, ' survival of the fittest '. 



Whether or not we accept this explanation of evolution by natural 

 selection approximately as propounded nearly a century ago bv 

 Charles Darwin — and most biologists nowadays believe that it is 

 only a partial elucidation of the mechanisms involved — the fact that 

 evolution takes place is now almost universally accepted. Moreover 

 there can be few if any who would deny that the common course of 

 evolution is through forms which, as it proceeds, become more and 

 more closely aligned with the demands of particular habitats or 

 groups of habitats, its outcome being then in races or higher taxa 

 that are more or less closely adapted to the conditions in which they 

 grow. That is the keynote of the plant geographical aspect of the 

 subject ; and whereas we could go on explaining and exemplifying 

 ad nauseam, it seems best to leave matters here. For there can 

 scarcely be any group of plants that does not afford instances of 

 adaptations to the particular environmental factors under which one 

 or more of its members grow, and which thereby affect its distribu- 

 tion in actuality or potentiality. 



On the utilitarian side we should note that, with crops and trees 

 — including Maize in the mid-western United States and Conifers 

 in Scandinavia — it has sometimes been observed that seed from 

 acclimatized local plants gives better results than seed imported from 

 even a relatively short distance away. This ' regional adaptation ' 

 tends to be especially marked when the testing-ground lies in an 

 area of unusually diversified climatic or other conditions. The 

 reason appears to be that the ' native ' strains have been rendered 

 appropriate to the local conditions through the action of natural 

 selection on a population that was once more mixed genetically. 

 Nature, as it were, is in this way doing the plant breeder's work for 

 him. Yet the basis here is Man's husbandry and, usually, importa- 

 tion of seed in the first instance. 



Man-made Adjustments 



When we come to consider Man's direct and deliberate manipula- 

 tion of certain characteristics of individual plants or, particularly, 

 kinds of plants, we are dealing to a considerable extent with processes 



