146 



Controversial Oucstions. 



character which has so often afforded material for sta- 

 tistical investigation. Their variation can be expressed 

 in the form of curves ; the mean for dark green individ- 

 uals which have been liberally watered stands at 13 ray- 

 florets, but for a separate part of the same plant which 

 had been kept relatively dry the mean was 12. 



Fig. 29. Helianthemum vulgar e after G. Bonnier {loc. cit., 

 Plate 20). The plant was divided in two halves of which 

 one (a) was subsequently cultivated in the plain and the 

 other (b) in the Alps. Both halves are reduced on the 

 same scale in the figure. 



In these instances nutritional modifications are seen 

 to be adaptive characters ; in one case these adaptive 

 differences are what we should describe as instances of 

 normal A'ariability ; and they are obviously brought about 



