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 extra- 

 ordinary significance of the discovery was at once 

 apparent. From their experiments, 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 in- 

 heritance, 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 



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