312 



Nutrition and Selection. 



latter character to the true elementary species in which 

 the character of the parent species has become completely 

 latent, for in this case the variation of the new character 

 of course conforms to the general laws of variability. 



We have studied this relation of variability to nutri- 

 tion from various points of view in our researches with 

 the half races of Trifoliiiin incarnatnni quadrifolinin and 

 Ranunculus bulbosus scniiplenns, but especially with the 

 true middle races, Trifolinm pratense qidnquefoliuni, and 

 Chrysanthcminn segetuni plenum as well as with anal- 

 ogous groups. 



Fig. 57. Lysimachia vulgaris. Transverse sections of two 

 buds which were to develop into upright stems in winter. 

 A, quaternary, and B, trimerous symmetry. 



It should be remembered that in all these cases we 

 are dealing with variability in the restricted sense and 

 not with mutability. How one race is transformed into 

 another, we do not know. The phenomenon is as yet 

 far too rare and has not yet been adequately investigated. 

 The variability of the eversporting races is of the trans- 

 gressive kind; but it does not lead, as a rule, to muta- 

 bility. 



Finally I wish to illustrate by means of a scheme the 

 relation between the variability of semi-latent characters 

 and the external conditions of life, and I select as material 



