8 Plant Genetics 



biologists, while his theory of germinal selection has 

 been practically discarded. A brief explanation of these 

 two theses is as follows. 



Germinal continuity. — ^A statement of this theory 

 in the words of the author is as follows : 



I believe that heredity depends upon the fact that a small 

 portion of the effective substance of the germ plasm remains 

 unchanged during the development of the egg into an organism, 

 and that this part of the germ plasm serves as a foundation 

 from which the germ cells of the new organism are produced. 

 There is a continuity of germ plasm from one generation to 

 another . . . hence it follows that the transmission of acquired 

 characters is an impossibility, for if the germ plasm is not formed 

 anew in each individual, but is derived from that which preceded 

 it, its structure, and above all its molecular constitution, cannot 

 depend upon the individual in which it happens to occur; but 

 such an individual only forms as it were the nutritive soil, at 

 the expense of which the germ plasm grows, while the latter 

 possessed its characteristic structure from the beginning, namely, 

 before the commencement of growth, but the tendencies of 

 heredity, of which the germ plasm is the bearer, depend upon its 

 molecular structure, and hence only those characters can be 

 transmitted through successive generations which have previ- 

 ously been inherited, namely, those characters which were poten- 

 tially contained in the structure of the germ plasm. It also follows 

 that those other characters which have been acquired by the 

 influence of special external conditions during the lifetime of the 

 parent cannot be transmitted at all. 



This is the theory of germinal continuity and it is in 

 general agreement with the results of biological work 

 today (see fig. i). 



Germinal selection.— The purpose of the con- 

 ception of germinal selection was to construct a theory 

 of variation, and therefore of evolution, which does not 

 involve the inheritance of acquired characters. When 



