CHAPTER IV 



THE PRESENCE AND ABSENCE THEORY 



It was fortunate for the development of biological 

 science that the rediscovery of Mendel's work found a 

 small group of biologists deeply interested in the problems 

 of heredity, and themselves engaged in experimental 

 breeding. To these men the extraordinary significance of 

 the discovery was at once apparent. From their experi- 

 ments, undertaken in ignorance of Mendel's paper, de 

 Vries, Correns, and Tschermak were able to confirm his 

 results in peas and other plants, while Bateson was the 

 first to demonstrate their application to animals. Thence- 

 forward the record has been one of steady progress, and 

 the result of ten years' work has been to establish more 

 and more firmly the fundamental nature of Mendel's 

 discovery. The scheme of inheritance, which he was the 

 first to enunciate, has been found to hold good for such 

 diverse things as height, hairiness, and flower colour and 

 flower form in plants, the shape of pollen grains, and the 

 structure of fruits ; while among animals the coat colour 

 of mammals, the form of the feathers and of the comb in 



poultry, the waltzing habit of Japanese mice, and eye 



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