THE LAWS OF HEREDITY 



ing to hypothesis upon modifications of the 

 germ-plasm. 



But a& nowadays it is fully admitted that all 

 forms of life have undergone change in the past 

 higher forms evolving from lower ones through 

 modification it is obvious that each stream of 

 ancestral germ-plasm must have been more or less 

 subject to influences that modify it. 



As much as this at least is admitted by every 

 biologist, whatever his view toward the allied 

 question of the heritability of modifications that 

 affect the body-plasm of an individual rather than 

 the germ-plasm a question, by the way, that will 

 claim our attention in another connection, but 

 which need not becloud our vision at the moment. 



It must be understood, however, that the modi- 

 fications that can be introduced in the germ- 

 plasm in any given organism, through whatever 

 environmental changes, are relatively slight as 

 contrasted with the totality of qualities of that 

 germ-plasm. 



It is inconceivable, for example, that the germ- 

 plasm of a brier should be so modified that its 

 offspring will be bearers of grapes; or that the 

 germ-plasm of a thistle shall become so trans- 

 formed that the body-plasm sprouting from it in 

 the next generation shall produce figs to revert 

 to the familiar illustration with which we set 

 out. 



To be sure, the vine that bears grapes and the 

 tree that bears figs were doubtless originally as 

 different from their present states as they still are 



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