26 MODES OF RESEARCH EST GENETICS 



The cytologist is compelled by force of circum- 

 stances to use in the main static material — the 

 dead stained cell. But in the problem of heredity 

 he is concerned with dynamic phenomena — 

 gamete and soma formation. It is obvious that the 

 chances for error in interpretation are very great, 

 and difficult to eliminate or control, when one is 

 compelled to reason from a static, fixed structure, 

 to a dynamic course of events. 



It may fairly be said that a direct connection be- 

 tween a particular chromosome in the gamete and 

 a particular structure in the adult has never yet been 

 completely demonstrated. The closest approach 

 to it, on the directly cytological side, is found in 

 the case of the sex chromosomes, and here a causal 

 nexus is not absolutely proven, though it seems 

 doubtful whether by cytological methods alone it 

 will ever be possible to get essentially nearer to 

 a proof than we now are. The clear-cut and 

 thorough researches of Wilson, in particular, 

 and American cytologists in general, on the sex 

 chromosomes appear to take the problem as far 

 as purely observational methods can take it. 



There has been no lack of cytological hypotheses 

 regarding genetic phenomena in recent years. 

 In particular it has become the practically uni- 

 versal custom to look for the explanation of diver- 

 gent Mendelian ratios in cytological disturbances 

 or deviations of some sort or other. This has con- 

 spicuously been the case in regard to the so-called 



