NEO-MENDELISM IN PLANTS 



427 



variation within the species. Darwin depended upon it as the basis of 

 his theory of natural selection as the origin of species; in fact, ever 



IK 



Pure Red 



While 



Intermediate Grades 



FIG. 86. Diagram illustrating Nilsson-Ehle's 63 : i ratio. (From Coulter 

 and Coulter.) 



since Darwin's Origin of Species, individual variation has been funda- 

 mental in our conceptions. To account for this universally recog- 

 nized phenomenon, Darwin proposed his transportation hypothesis as 



