THE FRAGRANT CALLA 27 



periods of their life history, and which thus in- 

 sure a degree of variation that will make racial 

 evolution possible. 



The authority of de Vries sufficed to give wide 

 vogue to his theory ; yet it must be admitted that 

 the explanation offered lacks tangibility and at 

 best amounts to little more than begging the 

 question. 



To say that altered nutrition produces varia- 

 tion in a plant is in effect to state the funda- 

 mental truth that all plants are more or less 

 responsive to their environment. 



But there is nothing specific in the case of the 

 primrose that explains in any precise way the 

 relation of the change to the particular differ- 

 ences, let us say, between the soil of the original 

 home of the primrose and the soil of Holland. 

 Moreover in numberless other instances plants 

 have been transplanted from one region to an- 

 other without showing any such pronounced 

 tendency to develop new races. 



It was recognition of the difficulties thus 

 presented, undoubtedly, that led Professor de 

 Vries to devise the rather visionary hypothesis of 

 periods of mutation with which his theory was 

 cumbered. 



But it is a well-recognized law of logic that one 

 should never seek remote and obscure expla- 



