THEORIES IN PRACTICE 373 



and quality of fruit — these are matters that are 

 subject to modification because they have not as 

 yet established themselves as fundamentally 

 necessary in any detail of form or color to the 

 species. These fall within the scope of Men- 

 delian testing. 



For hundreds of thousands of years, doubtless, 

 the progenitors of plants that now have flowers 

 were provided with roots and stems and leaves, 

 and with essential reproductive organs, but had 

 no blossoms. In comparatively recent times the 

 blossoms were developed. And the modifica- 

 tions of color of the blossoms in the case of any 

 given species are, as we have found reason to 

 suppose, of still more recent origin. 



These modern details, then, and their like, 

 are the ones that are subject to variation and 

 that are still matter for change and adaptation; 

 still in the experimental stage, as it were. And 

 precisely because such is their status, these are 

 the things that are subjected to the Mendelian 

 test when they are brought in juxtaposition, 

 through hybridizing, with forms that differ as 

 to these details. 



And as only the relatively new structures 

 Mendehze, so it is the newer member of any 

 pair that assumes prepotency or dominance. 

 Contrariwise, the older member is recessive. 



