CHAPTER V 



INTERACTION OF FACTORS 



WE have now reached a point at which it is possible 

 to formulate a definite conception of the living 

 organism. A plant or animal is a living entity 

 whose properties may in large measure be expressed 

 in terms of unit-characters, and it is the possession 

 of a greater or lesser number of such unit-characters 

 renders it possible for us to draw sharp distinctions 

 between one individual and another. These unit- 

 characters are represented by definite factors in the 

 gamete which in the process of heredity behave as 

 indivisible entities, and are distributed according to 

 a definite scheme. The factor for this or that unit- 

 character is either present in the gamete or it is 

 not present. It must be there in its entirety or 

 completely absent. Such at any rate is the view to 

 which recent experiment has led us. But as to the 

 nature of these factors, the conditions under which 

 they exist in the gamete, and the manner in which 

 they produce their specific effects in the zygote, we 

 are at present almost completely in the dark. 



The case of the fowls' combs opens up the im- 

 portant question of the extent to which the various 

 factors can influence one another in the zygote. 



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