EXPERIMENTAL STUDY OF HEREDITY 565 



biological science, since 1900, has been largely occupied 

 in trying to answer the questions raised by these men. 



What are these questions? There is not space here 

 even to ask them all, much less to endeavor to answer 

 them even briefly; but they include the following large 

 problems : 



1. What is the mechanism of inheritance? In other 

 words, by what arrangement and interaction of atoms 

 and molecules is it made possible that the peculiar tone 

 of one's voice, the color of a rose, the odor of a carnation, 

 the evenness (or otherwise) of one's disposition, may be 

 transmitted from one generation to another? How may 

 it be transmitted through one generation, without causing 

 any external expression, and reappear in the second genera- 

 tion removed? Is the cytoplasm the carrier, or the 

 chromatin, or both combined, or neither? Is the transfer 

 accomplished by little particles (pangens), as de Vries 

 contends, or by chondriosomes, or otherwise? We do 

 not know. 



2. How may dominance be explained? Why is tallness 

 dominant over dwarfness, brown eye-color over blue, 

 any one character over any other? We have not the 

 faintest idea. 



3. Are acquired characters inherited? In other words, 

 do characteristics acquired after birth by the body or 

 mind of the parent, either by its own activity or as a re- 

 sult of the immediate . effects of environment, influence 

 the germ-cells so as to alter the inheritance which they 

 transmit? Some say yes, others say no; others say, 

 only in part. There seems to be evidence both ways. 

 We can arrive at the correct answer only by careful 

 experimentation, that is, by asking questions of nature. 



