572 Species According to the Theory of Mutation. 
of a flower may be brought about even by only one of 
these elementary characters becoming inactive. 
Retrogressive mutations give the impression of some- 
thing being lost ; some character or other disappears from 
the picture. But everything seems to point to the con- 
Fig. 133. Castanea vesca. Ab- 
normally leaved catkins. A, 
with two leaves ; B and C, with 
one leaf each. C has also a 
lateral twig, a male, b female 
flowers ; c normal leaf. Apel- 
doorn, 1896. Collected by Dr. 
P. F. ABBINK-SPAINK. 
Fig. 134. Mercunalis annita. A 
sprig of the male plant with 
stray fruits on the long thin 
ears. On the female plants the 
fruits are inserted on short 
stalks in the axils of the leaves. 
elusion that, in the vast majority of cases at least, this 
loss is only an external one ; and that the factor remains 
in the inner organization of the plant, in an inactive state. 
This view is especially supported by those cases in which 
a systematic character which has become latent is occa- 
