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 expect 
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 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, 
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 Phillips furnished 
