112 Heredity and Eitf;eiiies 



unchanging. Such a conception would be mechanical and 

 not biological. These changes must aiTect the germ cell 

 structurally to be inherited. They may be large, they rhay 

 be small. We may call them mutations with DeVries, or 

 we may use the simpler and broader term, inherited varia- 

 tions. When they occur, new varieties may be isolated 

 in which they are present, and these may be considered 

 to be relatively permanent as compared with the non- 

 inherited fluctuations that continually occur due to varying 

 en\'ironment. 



One may question the stability of unit-characters as does 

 Castle, but I cannot see how this affects the truth of the 

 genotj-pe conception as a help toward an idea of the process 

 of heredity. Stability is a relative thing. Why is there not 

 a scale of stability in biology even as in chemistry ? Many 

 unit-characters are high in the scale of stability, others may 

 be low. Certain characters ordinarily transmitted perfectly 

 may possibly be modifiable by selection. We might imagine 

 their factors to be huge chemical molecules, stable as a whole 

 but modifiable by isomerism or even the dropping ofi" or 

 adding on of unimportant radicles. This is a smaller issue, 

 unimportant when compared with the genot>T3e conception 

 as a whole. The important point as the foundation of the 

 modern view of heredity I give in Johannsen's own words: 

 "Personal qualities are the reactions of the gametes joining 

 to form a zygote; but the nature of the gametes is not deter- 

 mined by the personal qualities of the parents or ancestors 

 in question." 



