GENETICS 97 



cytoplasm of individual cells, and so the genes of 

 the germinal chromosomes are held inviolate to a 

 remarkable degree. 



Since the probable modification of genes through 

 the indirect action of environmental factors must 

 rest upon this type of evidence for the present, it 

 is significant to note the expressed conclusions of 

 various writers on the subject: These are only a 

 few of many statements, but they are representa- 

 tive. Troland regards enzyme action as a general 

 solution of many biological phenomena, including 

 variation. ^^ Conklin says: "Various changes in 

 the chemical and physical environment produce 

 abnormalities in the number, distribution and 

 constitution of chromosomes, as was pointed out 

 on a previous page, and it is not antecedently im- 

 probable that such environmental changes may 

 produce similar modifications in genes them- 

 selves." ^^ Cunningham is a little more positive 

 in his statement: "Whenever a changed environ- 

 ment acts upon the organism, therefore, it to some 

 extent affects the normal excretions and secretions 

 of some or all of the various tissues, and these 

 react not only on the tissues themselves, but also 

 to a less degree upon the determinants representing 

 them in the germ-plasm." ^^ Alexander concludes 

 that "the specificity of the germ plasm is evidently 



" Am. Nat, Vol. LI, p. 327, 1917. 



^Sd. Monthly, Vol. X, p. 511, 1919. 



^^ Hormones and Heredity, Ch. XIV, 1921. 



