INFLUENCE OF ENVIRONMENT 357 



inherited, but rather "Are the hereditary po- 

 tencies of the germ cells altered by stimuli act- 

 ing on the parental body?" This is a very 

 different thing from the inheritance of a par- 

 ticular acquired character, and there is some 

 evidence that such stimuli may in rare instances 

 produce changes in the hereditary constitution 

 of the germ plasm. The observations and ex- 

 periments of deVries on the mutations of the 

 evening primrose, of Hansen on those of 

 yeast and of Fischer, Standfuss, Tower and 

 Morgan on mutations in insects seems to favor 

 such a belief. 



On the other hand certain changes may be 

 produced in germ cells or embryos which last 

 only for a generation or two and then disap- 

 pear. It is well known that plants grown in 

 poor soil are smaller and produce smaller seeds 

 than those grown in good soil, and deVries, 

 Baur and Harris find that such seeds produce 

 smaller plants with smaller seeds than do seeds 

 of normal size. This is an after effect of poor 

 nutrition which changes the amount of food 

 material in the seeds and through this the size 

 of the plant which develops from the seed, but 



