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-char- 

 acter is either present in the gamete or it is not present. 

 It must be there in its entiretv or completelv 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 important 



question of the extent to which the various factors can 



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