THEORIES IN PRACTICE 371 



Yet this aspect of the subject, even if not all- 

 important, has obvious interest. And the ques- 

 tion naturally arises as to which ones among the 

 numberless hereditary factors in the case of any 

 given organism will "Mendelize" in the main, 

 and why these factors will thus Mendelize while 

 others fail to do so. 



The answer is found, apparently, in the simple 

 assumption that the factors that show the phe- 

 nomena of dominance and recessiveness are those 

 that are relatively new acquisitions in the germ 

 plasms of the species under observation. Traits 

 that have been the common heritage of the an- 

 cestry for untold generations, constituting the 

 fundamental structures of the organism, do not 

 Mendelize. They have proved their merit, and 

 are accepted as part of the necessary equipment 

 of the plant, not subject to the testing process 

 that Mendelism essentially constitutes. 



Such fundamental structures are, for example 

 the root and stem and leaves and stamens and 

 pistils of a flowering plant. As to their broad 

 essentials of form and structure, these funda- 

 mental organs are inherited en bloc, and never 

 jeopardized by being weighed in the Mendelian 

 scale. 



But the newly acquired characteristics, such 

 as details of leaf form, or color of petals, or size 



