CHAPTER III 



THE FACTORIAL THEORY OF HEREDITY AND 

 THE COMPOSITION OF THE GERM PLASM 



The discovery that Mendel made with edible 

 peas concerning heredity has been found to ap- 

 ply everywhere throughout the plant and 

 animal kingdoms to flowering plants, to in- 

 sects, snails, Crustacea, fishes, amphibians, 

 birds, and mammals (including man) . 



There must be something that these widely 

 separated groups of plants and animals have 

 in common some simple mechanism per- 

 haps to give such definite and orderly series 

 of results. There is, in fact, a mechanism, 

 possessed alike by animals and plants, that ful- 

 fills every requirement of Mendel's principles. 



THE CELLULAR BASIS OF ORGANIC EVOLUTION 

 AND HEREDITY 



In order to appreciate the full force of the 

 evidence, let me first pass rapidly in review a 



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