CHAPTER II 



THE PHYSIC\L BASIS OF HEREDITY AND EVOLUTION 

 FROM THE CYTOLOGICAL STANDPOINT 



Heredity involves not only the transmission of similarity 

 in structure, but also the transmission of dissimilarity. 

 Likeness means close relation to the parent forms; unlike- 

 ness means individuality. It is not generally appreciated 

 that individuality expresses itself just as certainly among 

 plants and animals as among human beings. We have 

 learned to recognize the marks of individuality among 

 human beings through long acquaintance, but we should 

 realize also that no two plants or animals are exactly alike. 

 It is this individuality that is called variation, and variation 

 is the basis of evolution. The phenomena of heredity 

 established as facts by series of cultures under rigid control, 

 however, must be recognized as the end results, between 

 which and the act of fertilization there extends a series of 

 unknown processes, wdth which as yet only scientific imagi- 

 nation deals. 



The purpose of this chapter is to inquire whether there 

 is any physical basis for the transmission of like and unlike 

 characters, in the same sense that protoplasm was long ago 

 called "the physical basis of life." This phrase only means 

 that protoplasm is the material substance in which the 

 phenomena of life are manifested. Is there any substance 

 or structure by means of which the phenomena of heredity 

 manifest themselves ? 



The answer to this question would be given more appro- 

 priately by some biologist who has made it the special 



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