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. A re 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. 
