1 68 Plant Genetics 



vigor and size of sporophytes, therefore, it might be 

 expected to increase the size of endosperms also. 

 Furthermore, endosperms have considerable advantage 

 over sporophytes as material for such investigation. We 

 say that hybrid sporophytes are more vigorous than 

 pure-bred sporophytes, but just how much more vigor- 

 ous cannot be stated with exactness. In order to 

 demonstrate this clearly it would be necessary to have 

 the hybrid and the pure-bred stock growing side by side 

 in exactly the same conditions, but such conditions 

 cannot be controlled with exactness. The environ- 

 mental factors affecting the size and vigor of a corn plant 

 are numerous, complex, and to a large extent uncon- 

 trollable. Thus two different plants, growing side by 

 side, might be in a distinctly different environment 

 without the fact being recognized. It cannot be 

 said, therefore, with much certainty that one plant 

 shows hybrid vigor and one does not when there are 

 so many other unknown factors that might affect size 

 and vigor. On the other hand, if it is claimed that the 

 endosperm of one grain shows hybrid vigor while the 

 endosperm of the grain next to it upon the same ear 

 does not, the statement would be more exact, for the 

 two endosperms have developed under conditions which 

 are unquestionably much more constant than the condi- 

 tions surrounding the different sporophytes in a corn- 

 field. 



JONES selected a plant with white endosperm and 

 pollinated it with a mixture of its own pollen and pollen 

 from a yellow endosperm race. In the mature ear, 

 therefore, he had a mixture of yellow endosperm grains 

 and white endosperm grains. The former grains of 



