CAUSE OF HYBRID VIGOR 187 



tion of dominant factors are not then two unrelated hy- 

 potheses to be held up for the choosing of the one from 

 the other. The outstanding feature of the latter view is 

 that there is no longer any question as to whether or not in- 

 breeding as a process in itself is injurious. Homozygosity, 

 when obtained with the combination of all the most favor- 

 able characters, is the most effective condition for the 

 purpose of growth and reproduction. 



