72 THE FIRST PRINCIPLES OF HEREDITY 



combined influence of these homologous determinants 

 which finally determines the character of any given part 

 of the offspring. 



We can now, after the above explanation, understand 

 how it comes about that, in the crossing of two closely 

 related varieties, the resulting hybrid shows characteristics 

 intermediate between those of the parents. The two crossed 

 varieties possess an equal number of determinants, which 

 are all homologous, but heterodynamous. Both kinds of de- 

 terminants will, therefore, exert the same determining power 

 on the cells they impress, so that the result will be equal 

 representation of both kinds of determinants or a blend of 

 both parental qualities. A good instance of blended in- 

 heritance is presented by crossing of the white and black 

 races of man, where the children (mulattoes) are neither 

 white nor black, nor a mixture of white and black patches 

 (piebald), but an intimate blend of both colours — viz., a 

 chocolate brown. 



For plants we give the accompanying illustration (Fig. 40) 

 as an example. 



(b) Exclusive Inheritance. 



Exclusive or prepotent (preponderant or unilateral) in- 

 heritance in hybrids may be due to two causes. Firstly, 

 one of the parents may possess a greater number of Idants 

 and Ids, which would, therefore, become predominant in 

 their effect over the Ids of the other parent. Or even with 

 an equal number of Ids in both parents, the determining 

 power of the respective biophors of each parent may be 

 unequal, a struggle of the biophors taking place, and re- 

 sulting in the overpowering expression of one set of bio- 

 phors. For in the last instance, the biophors into which 

 the determinants dissolve determine the character of the 

 cells ; the biophors from one parent, though equal in 

 number to the other, may be stronger, may lead to 

 the suppression of the weaker biophors from the other 

 parent, and thus to an apparently one-sided inheritance. 



