No. 556] SHORTER ARTICLES AND DISCUSSION 241 



shown, believers in the Mendelian theory would expect to find 

 separate "gens" or discrete particles of some sort to represent 

 the various characters of the adult animals or plants. The gens 

 that represent the characters of different parents are supposed to 

 remain entirely distinct and to find their ways into different 

 germ-cells. Each germ-cell of a hybrid is supposed to receive 

 only a single set of these hypothetical character-units or gens, 

 representing the contrasted characters of the parents, and the 

 sets are supposed to be made up by chance assortment. Thus the 

 different germ-cells produced by a hybrid are supposed to repre- 

 sent all the combinations of the contrasted parental characters 

 that are theoretically possible under the laws of chance. 



The theory of Mendelism has greatly stimulated the study of 

 cytology, in the hope of finding the supposed character-germs as 

 actual, visible particles in the protoplasm. Some writers have 

 argued that the chromosomes or chromomeres represent the char- 

 acters, or at least the contrasted Mendelian characters, and have 

 attempted to trace a definite relation between the behavior of 

 the chromosomes and the inheritance of the characters. Other 

 writers do not indulge in such speculations, but believe in alter- 

 native transmission for mathematical reasons. Typical cases of 

 Mendelism are relied upon as affording sufficient proof of the 

 theory of alternative transmission. The Mendelian theory ac- 

 cords with the numerical facts of Mendelism, but this is not a 

 sufficient proof of its correctness, for it is not the only interpre- 

 tation that the facts will admit. Elaborate Mendelian computa- 

 tions create in the casual reader an impression of mathematical 

 certainty, but the same computations could be made under other 

 theories of alternative inheritance. 



Alternative Inheritance and Normal Diversity 

 The facts of alternative inheritance are not at all confined to 

 cases where the characters show the exact numerical proportions 

 typical of Mendelism. Alternative inheritance is a general law 

 that applies even in the vast and highly diversified groups of 

 interbreeding individuals that constitute natural species. The 

 typical Mendelian cases usually appear as results of previous 

 artificial breeding of pure strains. 2 



The normal diversity (heterism) everywhere manifested among 

 "Cook, O. P. "Pure Strains as Artifacts of Breeding," The American 



