Fertilized 



egg 



Germ plasm 



Body 1 



perm plasnt 



Body 2 



iGerm plasm 



Body 3 



Germ 



plasm 



After Wcismaiin 



THE IDEA OF GERM PLASM 



We commonly think of germ cells as produced by the organisms which bear them. 

 We may also think of the fertilized egg as dividing into cells that become a body 

 and others that continue as germ plasm, which later gives rise to new individuals — 

 and more germ plasm. The stream of germ material persists indefinitely, carried 

 through successive generations in the bodies — which it produces 



ment, it is not enough to compare two individuals or two groups of individuals. 

 The problem really involves four sets of questions. We can see this if we 

 generalize it to cover all essentials. 



1. How do organisms of uniform genetic constitution develop in en- 

 vironment A} 



2. How do organisms of uniform genetic constitution develop in en- 

 vironment B} 



3. What is the effect of a particular environment upon the development 

 of organisms having constitution C? 



4. What is the effect of the same environment upon the development of 

 organisms having constitution D} 



These are practical questions for all who have to raise plants or animals, as 

 well as for breeders. Some varieties or strains of plants and some kinds of 

 animals — including human beings — can thrive in one setting but not in an- 

 other. We invite failure if we plan to raise bananas in Kansas or to run a fox 

 farm in Florida. But we have to be discriminating even if we plan to raise 

 wheat or corn in Kansas and oranges in Florida. 



The physician and the nurse, the politician and the teacher (as well as the 

 poultryman or the rancher), have to know that you cannot treat all individ- 

 uals alike if the individuals are to develop to their full capacities. The old 

 saying that you cannot make a silk purse out of a sow's ear still holds true. 

 We must recognize that individuals of one constitution will make aviators, 



508 



