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 Tri folium incarnatum quadrifolium and 
Ranunculus bulbosus semiplenus, but especially with the 
true middle races, Trifolium pratense quinque folium, and 
Chrysanthemum scgetum 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 
