450 EXPERIMENTS WITH PLANTS 



able that it is a latent character, which has long lain 

 dormant, but is now brought out by some unknown 

 cause. This phenomenon is called atavism and the 

 plant is called an atavist (see p. 420). If the seeds 

 of such a plant are sown, probably few atavists or 

 none at all will appear in the progeny. It is to be 

 classed as a sudden variation. 



If, now, we should find a plant all of whose leaves 

 showed an increased number, say nine, and all of 

 whose descendants showed the same number coming 

 perfectly true to seed, and kept this up without any 

 need of selection, this would constitute a mutation. 1 

 Such a plant has not been found,< but Professor de Vries 

 hopes it may occur, and is continuing his propagation 

 of the Red Clover with this end in view. 



The example of Clover makes clear Professor de 

 Vries' ideas as to the kinds of variation. We have, 

 first, ordinary fluctuating variation (due partly or 

 wholly to differences in nutrition caused by external 

 conditions): second, sudden variations, e. g., mon- 

 strosity, atavism, etc. (due to causes wholly unknown) ; 

 if these should come true to seed they would be called 

 mutations, otherwise not. A mutation is a sudden 

 variation which comes true to seed, and he believes 



1 This would constitute an extreme case. The mutation might, and 

 probably would show fluctuating variation in the leaf numbers, so that 

 not every leaf would be a nine -leaf but the type would be (for explana- 

 tion of type see page 420), and this type would remain absolutely constant 

 without selection. 



