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THE ROLE OF THE CYTOPEASM 233 



hybrids obtained were fertile, the cytoplasm would be found to play a 

 more prominent differential role in character determination than it does in 

 l^ure lines and intraspecific hybrids. 



Emphasis upon the nucleus as a system of elements necessary to 

 development and upon its chromosomal organization as the key to the 

 Mendelian phenomenon is surely warranted, but it should not obscure the 

 fact that "the physical basis of heredity" in a broad sense includes all 

 relatively stable protoplasmic elements affecting the characters developed, 

 wherever these elements are located and whether their activitj' results 

 in likeness or unlikeness in the characters. Even if one inclines to view 

 the cytoplasm as a "culture medium" in which the nucleus somehow 

 works out the characters, it must be remembered that this medium, even 

 more than the characters themselves, is a direct inheritance from previous 

 generations. 



