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THE AMERICAN NATURALIST [Vol. XLV 



as if the superstructure of this conception were too 

 elaborate to rest upon a simple foundation ; yet I can not 

 see but that the basis of the entire hypothesis is the fact 

 that a fluctuation is a non-inherited variation produced 

 upon the soma by environmental conditions, while the 

 inherited variation, the mutation if you will, is any 

 variation qualitative or quantitative, that is germinal 

 in character. This being so, it seems scarcely necessary 

 for an elaborate proof of the proposition, for it is noth- 

 ing but a corollary to that part of Weismannism which 

 was already generally accepted. 



Of course it is recognized that pure Lamarckism still 

 has followers to whom neither Weismannism in any 

 form nor the genotype conception of heredity could ap- 

 peal. But to thorough Weismannians and to those who 

 believe in occasional germinal response to environmental 

 conditions, it seems as if both propositions must be ac- 

 ceptable and their interdependence apparent. 



Let us follow this line of reasoning to its logical con- 

 clusion in regard to the physiology of heredity. The 

 Mendelian notation has been generally accepted as a con- 

 venient way of accounting for the facts of heredity in 

 certain markedly discontinuous characters. It has been 

 questioned by many, however, whether the Mendelian con- 

 ception is not rather an apparent interpretation of a rela- 

 tively small number of facts than a general law. De Vries 

 has even suggested that there are definite physiological 

 reasons why certain characters should Mendelize and 

 others should not. His idea is that Mendelian segrega- 

 tion occurs when a germinal determinant for a character 

 (Anlage) meets an opposing determinant, and when no 

 such opposition exists the character in the cross-bred 

 organism breeds true. Now the universal tendency of the 

 facts of breeding is towards an interpretation the oppo- 

 site of this. When a determinant from one j)arent meets 

 with no such determinant from the other parent (pres- 

 ence and absence hypothesis), Mendelian segregation 

 appears. When the same determinant is received from 



