INFLUENCE OF ENVIRONMENT 341 



that where plants or animals are grafted to- 

 gether each would modify more or less the 

 hereditary constitution of the other. But this 

 does not occur. Everybody loiows 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 ani- 

 mal grafts. Harrison cut in two young tad- 

 poles 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 preserved its 

 own peculiarities even up to the adult condi- 

 tion (Fig. 80). 



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 transplantations in the case of 



