LUTHER BURBANK 



THE CONTINUITY OF THE GERM-PLASM 



The full significance, from the standpoint of 

 heredity, of this segregation of the germ-plasm 

 has been appreciated only within comparatively 

 recent years. It was not until Professor August 

 Weismann made special studies in this field, about 

 thirty years ago, that the subject prominently at- 

 tracted the attention of biologists. 



Weismann had been struck by the fact that 

 single-celled organisms, owing to the character of 

 their reproduction by division, are, as he phrased 

 it, ' ' potentially immortal. ' ' They do not normally 

 die, but rejuvenate themselves by division, a given 

 individual becoming two, and these two presently 

 becoming four, and so on in an unending geomet- 

 rical progression, in which the descendants of any 

 generation whatever might be regarded as repre- 

 senting the divided substance and personality of 

 the original ancestor. 



Weismann made application of this thought 

 to the cells constituting the germ-plasm of the 

 higher organisms. These, he said, pass on their 

 substance and hence their potentialities from gen- 

 eration to generation much as does the protozoan ; 

 and this fact of the continuity and virtual im- 

 mortality of the germ-plasm furnishes the simple 

 and obvious explanation of the observed facts 

 of hereditary transmission of qualities from one 

 generation to another. 



In each new generation a certain number of 

 cells are differentiated to form body-plasm, and 



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