INHERITANCE 



313 



gation, and subsequent fertilization, providing the new turn of the 

 kaleidoscope. 



But since the life of an organism is one continuous series of re- 

 actions with its surroundings, it follows that nurture plays an 

 immensely important part in molding the individual on the basis 

 of its heritage. Indeed we are apt to overlook the fact, already 

 mentioned, that every character is a product both of factors of the 





Fig. 198. — Corn of a single variety (Learning dent): at the left, grown well 

 spaced: at the right, badly crowded. The heredity of each plot of corn is 

 the same; the striking differences in growth are therefore solely due to en- 

 vironment. They are modifications. (From Blakeslee.) 



heritage and of the environment and can be reproduced only when 

 both are present. Those characters that appear regularly in suc- 

 cessive generations are those whose development depends upon 

 factors always present in the normal surroundings. Other charac- 

 ters, potentially present, do not become realized unless the un- 

 usual environmental conditions necessary for their development 

 happen to be met. Heredity and environment are collaborating 

 artists with different roles to play as molders of the individual. 

 To disentangle the closely interwoven influences of heredity and 



