356 The Unity of the Organism 



spending in form to the seeds of both their grandparents, it 

 is certain that the germs of their parents must have con- 

 tained some sort of a combination between round-producing 

 and angular-producing capacities of the germs, cvi-u 

 thougli those parents revealed nothing of that capacity so 

 far as their own seeds were concerned. And it is certain, 

 too, that whatever the nature of the combination in the 

 germs of the F t generation, it is such as to permit a separa- 

 tion of the capacities for the seeds of the F 2 generation. 



In 1865, when Mendel announced these observations, noth- 

 ing was known about pea germs, or for that matter about 

 any other germs, that could remotely suggest what their 

 constitution is in virtue of which they possess peculiar ca- 

 pacities. Nor was it until cytological research had accu- 

 mulated a good deal of knowledge of the chromosomes that 

 positive light from the side of germ morphology and 

 physiology was thrown on the subject. 



Chromosomes and the Mendelian Mode of Inheritance 



The pregnant hypothesis that the combination and the 

 separation of hereditary attributes in the fashion discovered 

 by Mendel is not only paralleled but explained by combina- 

 tions and separations of chromosomes in the germ-cells, was, 

 according to Morgan, Sturtcvant, Bridges, and Mtiller, first 

 stated "in the form in which we recogiii/e it to-day," by W. 

 S. Button. E. B. Wilson has informed us how the idea came 

 to expression almost simultaneously by Mr. Button, then a 

 student of zoology in Columbia University, and W. A. Can- 

 non, a botanical student in the same University. 



The basis and formulation of the hypothesis are pre- 

 sented by Mr. Button in two papers published in the same 

 volume of the Biological Bulletin. In order to appreciate 

 the full cogency of the argument in favor of the hypothesis, 

 it is necessary to go a little farther than we have hitherto 



