ARE ACQUIRED CHARACTERS HEREDITARY? 333 



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 parental 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 modi- 

 fications of the adult, which may be larger or smaller, stronger or 

 weaker, according as the germ is well or poorly nourished, but it is 

 incredible that the environment which produces rickets, or hyper- 

 trophied 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 

 inheritance 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 happen. 



No inherited influence of stock on graft. — -If specific changes of 

 environment produced specific changes in heredity we should e.xpect 

 to find that where different plants or animals are grafted together each 

 would modify more or less the hereditary constitution 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 quahty 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, 

 Rana 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 as well as in other respects, R. sylvatica being more deeply 

 pigmented than R. palustris. In the grafted tadpoles each half pre- 

 served its own peculiarities even up to the adult condition. 



A still more striking case of the persistence of heredity in spite of 

 environmental changes is found in experiments in which the ovaries 

 are removed from one variety of animal and transplanted to another 

 variety. Guthrie made such transplation in the case of fowls and 

 concluded that there was some influence of the foster mother upon the 

 transplanted ovary, but Davenport, who repeated his experiments, was 

 unable to confirm his results. Finally Castle and PhiUips furnished 



