Chapter XI 



THE NATURE OF HEREDITY AND THE PROBLEM 



OF ITS MECHANISM 



Heredity the Chief Present-day Stronghold of Biological 



Element alism 



BIOLOGICAL elementallsm of to-day undoubtedly has 

 its chief stronghold In the realm of heredity. The 

 germ-plasm theory, accepted by probably a majority of 

 biologists as an absolute monarch in the empire of biological 

 tliought, was elaborated for the sole purpose of explaining 

 herecHty. In the third chapter of the present work we 

 looked at certain subsidiary aspects of this theory. The 

 time has now come for scrutinizing the theory itself. 



Heredity has come so conspicuously to the front lately 

 in connection with plant and animal breeding, in social ques- 

 tions, and in eugenics, that almost every educated person has 

 learned something about the splendid progress of knowledge 

 concerning it. All who have glanced through some of the 

 numerous books on the subject have seen the pictures of 

 chromosomes represented as the bearers or the mechanism 

 of hereditv. They have also learned more or less about unit 

 characters, so prominent, biologically speaking, in con- 

 nection with the mode of inheritance discovered by Gregor 

 Mendel. If the learner's efforts have gone beyond the rudi- 

 ments of the subject he has become acquainted with "deter- 

 miners" and "unit factors" of the germinal substance which 

 are held to explain the characters of full-grown organisms. 

 There is something bewilderingly fascinating in the qual- 



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