THE CELLULAR BASIS 103 



egg and are not in some mysterious way 

 grafted upon it or transmitted to it. 



Parents do not transmit their characters to 

 their offspring but their germ cells in the 

 coirrse of long development give rise to adult 

 characters similar to those of the parents. The 

 thing which persists more or less completely 

 from generation to generation is the organiza- 

 tion of the germ cells which diiferentiate in 

 similar ways in successive generations if the ex- 

 trinsic factors of development remain similar. 



In short, heredity may be defined as the 

 appearance in offspring of characters whose 

 differential causes are found in the germ cells. 

 Heritage is the sum of all those qualities which 

 are determined or caused by this germinal or- 

 ganization. Development is progressive and 

 coordinated differentiation of this germinal or- 

 ganization, by which it is transformed into the 

 adult organization. Differentiation is the for- 

 mation and localization of many different kinds 

 of substances out of the germinal substance, of 

 many different structures and functions out of 

 the relatively simple structures and functions 

 of the oosperm. 



