66 Elementary Species 



and even the most skillful historians, by sifting 

 the evidence afforded by the older writers, and 

 that obtained by comparative linguistic investi- 

 gations have been able to do little more than 

 frame the most general outline of the cultural 

 history of the most common and most widely 

 used plants. 



Some authors assume that cultivation itself 

 might have been the principal cause of variabil- 

 ity, but it is not proved, nor even probable, that 

 cultivated plants are intrinsically more variable 

 than their wild prototypes. Appearances in 

 this case are very deceptive. Of course widely 

 distributed plants are as a rule richer in subspe- 

 cies than forms with limited distribution, and 

 the former must have had a better chance to be 

 taken into cultivation than the latter. In many 

 cases, especially with the more recent cultivated 

 species, man has deliberately chosen variable 

 forms, because of their greater promise. 

 Thirdly, wide variability is the most efficient 

 means of acclimatization, and only species with 

 many elementary units would have offered 

 the adequate material for introduction into new 

 countries. 



From this discussion it would seem that it is 

 more reasonable to assert that variability is one 

 of the causes of the success of cultivation, than 

 to assume that cultivation is a cause of variabil- 



