BETWEEN RACES I5I 
leaves so finely divided or dissected into minute seg- 
ments as to resemble a camel’s-hair pencil when re- 
moved from the water. Sooner or later the growing 
terminal bud reaches the surface, and rises above it 
into the air. As soon as this happens, the rudimentary 
leaves just beginning to swell within the bud entirely 
‘change their course of development. They grow now 
into flat-lobed blades, which float upon the surface of 
the water. The change of environment from water to 
air has worked such an alteration in form that no one 
who was not in the secret would suppose that these 
two kinds of leaves could possibly have been borne 
upon the same plant. 
De Vries would say that the tendency to produce 
the floating kind of leaf was latent in the submerged 
plant. In other words, the appearance of any given 
plant, or that of any given part of it, depends partly 
upon its hereditary qualities. and partly to the external 
circumstances to which it is submitted. Many other 
examples of similar changes could be alluded to, and 
one recently described is of rather special interest to 
students of genetics. This relates to a variety of 
Primula sinensis, which, if kept at a temperature of 
30° C., in a moist greenhouse, produces red flowers 
only ; whilst under similar conditions, but at a tem- 
perature of 20° C., bears only pure white blossoms. 
Another variety of the same species exists which only 
produces white blooms when exposed to any condi- 
tions under which it will flower at all. In describing 
the hereditary difference between these two varieties, 
we cannot say that it consists in the former having red 
