276 PHYSIOLOGICAL GENETICS 



L929). And the introduction of the term plavmon by Wettstein 

 for the entity of cytoplasmic net ion in heredity may be considered 

 an outward sign of such a tendency. I cannot refrain from 

 expressing my opinion that the facts do not encourage such a 

 view (see also I last, 1934). Where it was possible in the just- 

 quoted cases to base the analysis upon individual gene-controlled 

 traits, it was shown that no cytoplasmic heredity comes into play 

 but only a differential action of different plasmata as substratum 

 upon the action of the genes in controlling the differentiation of 

 definite characters. I do not think that a single case is known 

 of a definite hereditary character that is determined as such by 

 the hereditary constitution of the protoplasm, aside, of course, 

 from the special case of plastid characters. In only one way can 

 I conceive of the facts that have been reported: I assume that 

 genes act in controlling the differentiation of hereditary traits 

 through the control of chains of reaction of definite velocity. 

 Whatever these reactions may be in individual cases, one thing 

 may be regarded as certain; viz., their velocities will be dependent 

 among other things upon the substratum in which they take 

 place, i.e., the cytoplasm. The specificity of the cytoplasm in 

 question may be physical, e.g., a matter of viscosity or permea- 

 bility; or it may be chemical like the pH situation; but in any 

 case there is no reason to assume that it is of a type similar to 

 the difference between two genes. It is then not a plasmon, 

 acting in some way as an independent part of the germ plasm, 

 which is responsible for the phenomena in question, but simply a 

 physical or chemical property of the cytoplasm of the species. 

 Its most probable action is the inhibition or, in other cases, aug- 

 mentation of velocities of gene-controlled developmental reac- 

 tions, resulting in visible influences of cytoplasmic constitution 

 upon such characters, which are influenced predominantly in 

 their development by relative speeds of differentiation. In 

 addition, of course, a kind of poisoning effect of w r rong cytoplasmic 

 surroundings might be involved in cases of sterility and the like. 



E. Cytoplasmic Inheritance and Dauermodification 



Arrived at this point, we have to return to a fact that w r e have 

 mentioned repeatedly, viz., the incomplete knowledge of the 

 behavior of the cytoplasmic influence in further generations of 

 extracted homozygotes. The importance of this point for a final 



