INFLUENCE OF ENVIRONMENT 349 



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 

 it does not change the hereditary constitution. 

 Woltereck found that in Daphnia there is an 

 after effect of cold lasting for one or two gen- 

 erations, and this he calls "induction" when the 

 effect lasts for one generation, or "preinduc- 

 tion" when it lasts for two or three genera- 

 tions. Whitney found that rotifers poisoned 

 with alcohol were weaker in resistance to cop- 

 per salts and were less fertile than others, and 

 when brought back to normal conditions the 

 first generation was weak but the second was 

 normal. In man also alcohol may have an in- 

 duction effect on offspring, but it does not seem 

 to alter hereditary constitution. Probably of 

 a similar character are Sumner's results; he 

 found that mice raised in the cold have shorter 

 tails than those raised at higher temperatures 



