230 Heredity and Environment 



There still remains the question of the inheritance of certain 

 characters due to environment, though here also the most clear- 

 .cut evidence is against this proposition. That unusual conditions 

 of food, temperature, moisture, etc., may affect the germ cells so 

 as to produce general and indefinite variations in offspring is 

 probable, but this is^a very different thing from the inheritance 

 of acquired characters. The germ cells being a part of the paren- 

 tal organism may be modified by such changes in the environment 

 as affect the body as a whole, they may be well nourished or 

 starved, they may be. modified by changed conditions of gravity, 

 salinity, pressure, temperature, etc., and these modifications of the 

 germ cells probably lead to certain general modifications of the 

 adult, which may be larger or smaller, stronger or weaker, accord- 

 ing as the germ is well or poorly nourished, but it is incredible that 

 the environment which produces rickets, or hypertrophied heart, 

 or loss of sight in one generation should modify the germ cells 

 in such a peculiar and definite way that they should give rise in 

 the" next generation to these particular peculiarities, in the absence 

 of the extrinsic cause which first produced them. The inheri- 

 tance of acquired characters is incredible, because the egg is a 

 cell and not an adult organism ; and in this case there is no suffi- 

 cient evidence that the thing which is incredible really does hap- 

 pen. 



No Inherited Influence of Stock on Graft. If specific changes 

 of environment produced specific changes in heredity we should 

 expect to find that where different plants or animals are grafted 

 together each would modify more or less the hereditary consti- 

 tution of the other. But this does not occur. Everybody knows 

 that when a branch of a particular kind of fruit tree is grafted 

 upon a tree of a different variety the quality of the fruit borne by 

 that branch is not altered by its close union with the new stock. 

 The same is true of all* forms of animal grafts. Harrison cut in 

 two young tadpoles of two species of frog, Rama sylvatica and 

 Rana palustris, and spliced the anterior half of one to the posterior 

 half of the other. These frogs and their tadpoles differ in color 



