g6 An Examination of Weismannism. 



occur in a single shoot depends on the changes explained above, 



which occur in the idio-plasm during the course of its growth, 

 as a result of the varying proportions i which the ancestral 

 idio-plasms may be contained in it l . 



The meaning here appears to be twofold. For 

 there are only two ways of explaining the phenomena 

 of bud-variation. Either they are due to the influ- 

 ence of external conditions acting on the particular 

 bud in question, or else they are due to so-called 

 "spontaneous" changes taking place within the bud 

 itself. Possibly it may be both, but at least it must 

 be either. Well, in the above passage, Weismann 

 appears to assume that it is both. For at the begin- 

 ning of the passage he speaks of the " germ- plasm of 

 the first ontogenetic stage " becoming " altered so 

 far as to correspond with the altered structure of the 

 individual which arises therefrom," and he goes on 

 to say that the alteration " may depend chiefly on 

 the changed conditions of development " — that is, as 

 I understand, the influence of external conditions. 

 But at the end of the paragraph he says that '"the 

 changes which occur in the idio-plasm during the 

 course of its growth " in the sporting bud, are due to 

 " the varying proportions in which the ancestral idio- 

 plasms may be contained in it." Thus, I take it, 

 Weismann here entertains both explanations of the 

 phenomena in question : he appears to regard these 

 phenomema as partly due to peculiar admixtures of 

 ancestral idio-plasms in the bud itself (or '-spon- 

 taneous " variation ), but partly also to an alteration 

 of the germ-plasm by its changed condition of develop- 

 ment (or variation caused by external conditions;). 



1 Essays, 2nd Ed., pp. 331-2. 



