PARTICULATE THEORIES OF HEREDITY 31 



unquestionably important in keeping in the foreground 

 the intimate relation between heredity and cytology. It is 

 difficult for us to estimate to what extent his fascinating 

 speculations have influenced our later attempts to inter- 

 pret heredity in terms of chromosome constitution and 

 behavior. 



These and other earlier speculations have today mainly 

 an historical interest. They do not represent the main 

 path along which the modern theory of the gene has de- 

 veloped, which rests its claims to recognition on the 

 method by which it is derived and on its ability to predict 

 exact numerical results of a specific kind. 



I venture to think that, however similar to the older 

 theories the modern theory may appear, it stands apart 

 from them, in that it has arisen step by step from experi- 

 mentally determined genetic evidence that has been care- 

 fully controlled at every point. The theory need not and 

 does not, of course, pretend to be final. It will, no doubt, 

 undergo many changes and improvements in new direc- 

 tions, but most of the facts concerning heredity, known 

 to us at present, can be accounted for by the theory as 

 it stands. 



