568 



THE AMERICAN NATURALIST 



[Vol. LI 



quired characters may at the same time effect chromosome struc- 

 ture and behavior in the germ plasm. The cause for unusual 

 activity on the part of the chromosomes in either case may, how- 

 ever, well be totally different. 



Interesting as are the effects of natural influences on the germ 

 plasm, of greatest importance is the problem whether or not 

 modifications may be produced and controlled artificially. The 

 fact that experimental research is tending to show the specificity 

 of certain chemicals for various organisms or parts of organisms 

 makes hopeful the outlook for finding a specific or many specifics 

 that will act upon the meclianism of heredity or different parts 

 of that mechanism. At present our investigations can only be 

 empirical, trying this or that method more or less blindly. Con- 

 siderable work in this field has already been done. Without 

 entering into a full discussion of the numerous investigations, 

 it may be said that alcohol, temperature, humidity, ether, zinc 

 sulphate and radium have been used in attempts to alter the 

 germinal constitution. Changes indeed have been produced in 

 some cases but the effects have been generally physiological in 

 nature either interfering with development or influencing 

 color, length of hair, etc. In all cases where the offspring re- 

 sembles tlie altered parents the results have been readily inter- 

 preted on the assumption that eggs or embryos are influenced 

 at the same time as were the forms producing them. MacDougal 

 reports having produced changes in one of the (Kuotheras 

 through ovarial injections. Although it niiiy be possible that 



theras is in most ca.M-s -ivar. n\u\ tlir -aiurtir piii'ity of his 



In many ways ])lant.s offer the most favorable material for 

 the study of exi>erimental variation. Many parts of the plant 

 arc adapted to experimentation. The ])ollen may be subjected 



