z^72 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, h female 

 flowers; c normal leaf. Apel- 

 doorn, 1896. Collected by Dr. 

 P. F. Abbink-Spaink. 



Fig 



134. MercuriaUs annua. 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 tliose cases in wliich 

 a systematic character which has become latent is occa- 



