234 Heredity and Environment 



were pure white all the offspring of the F x generation were black 

 because they came from "black" eggs and black is dominant over 

 white. The fact that these "black" eggs developed in the body of 

 a white female did not in the least change their hereditary con- 

 stitution. 



Dominants and Recessives Remain Pure. A still more inti- 

 mate union takes place when the dominant and recessive char- 

 acters come together in any zygote. These characters, or rather 

 the factors which determine them, may be intimately associated 

 in every cell of the organism throughout an entire generation 

 and yet we may get a clean separation of these characters in the 

 next generation ; in many cases neither the dominant nor the re- 

 cessive character has been at all modified by its most intimate 

 association with the other. 



Climatic Effects Not Inherited. A striking instance of the 

 purely temporary effect of the environment and of the long 

 persistence of hereditary constitution amidst new environmental 

 conditions, which have greatly changed the appearance of the 

 developed organisms, is found in the case of alpine plants. Nageli 

 says that such plants, which have preserved the characters of high 

 mountain plants since the ice age, lose these characters perfectly 

 during their first summer in the lowlands. 



Summary. If acquired characters were really inherited we 

 should expect to find many positive evidences of this instead of a 

 few sporadic and doubtful cases. In particular why do we not 

 find in plant or animal grafting that the influence of the stock 

 changes the heredit?ry potencies of the graft? Why do we not 

 find that transplanted ovaries show the influence of the foster 

 mother as Guthrie supposed a thing which has been disproved 

 by Castle (Figs. 86 and 87) ? Why do dominant and recessive 

 characters remain pure, even after their intimate union in a 

 hybrid, so that pure dominants and pure recessives may be ob- 

 tained in subsequent generations from this mixture? Why does 

 every child have to learn anew what his parents learned so la- 



