Dr. Weismann's Theory of Heredity applied 



to Plants. 



THE essential point of Dr. Weismann's theory of reproduction is the 

 assumption of a special reproductive substance or germ-plasm, 

 distinct from the rest of the protoplasm, which is somatic, serving to 

 nourish the germ-plasm and maintain the growth of the individual. 

 There is a continuity of this reproductive substance from one 

 generation to another, each passing on to its offspring a certain 

 amount of germ-plasm which, nourished by the somatoplasm, is 

 increased in the individual but undergoes no change in kind, so long 

 as it simply perpetuates the species. 



Nageli distinguished two parts in the protoplasm ; an active 

 organising portion termed idioplasm being separated from the rest 

 which is merely nutritive. But while Nageli's idioplasm is regarded 

 as forming a continuous network throughout the organism formed 

 by growth from the idioplasm of the spore, Weismann's germ-plasm 

 is confined only to a certain series in the soma and a few special cells 

 of the individual, which are accordingly distinguished as reproductive 

 from all the rest which are merely somatic. 



In the following observations on Dr. Weismann's theory,^ I 

 propose limiting my remarks to the consideration of three points only, 

 as follows : — 



1. That there is a continuity of germ-plasm, from the germ-cells 

 of the parent to those of the offspring (p. 173) in a certain series of 

 somatic cells only (pp. 197, 207). 



2. That the characters acquired by the individual through " use, 

 disuse, practice, neglect, nutrition, light, moisture, and climate," 

 (p. 387) cannot produce any effect in the transformation of species 

 (p. 388) and cannot be transmitted at all (p. 267). 



3. That the transformation of species is due (i.) to direct changes 

 in the germ-plasm effected by external influences (pp. 327, 388, 396, 



1 Biological Memcirs, Authorised translation, Oxford. The pages given in the text 

 refer to the First Edition, 1889. 



