43» 



THE POPULAR SCIENCE MONTHLY 



exactly what one would expect in a Mendelian character in which more 

 than one factor is involved, as, for example, in the case of the color of 

 the sweet peas shown in Fig. 59. Davenport, who has made an ex- 

 tended study of this case concludes that "there are two double factors 

 (.1.1 BB) for hlack pigmentation in the full-blooded negro of the west 

 coast of Africa and these are separably inheritable." These factors are 

 lacking in white persons (this being indicated by oa lib). Since the 

 germ cells carry only single factors and not double ones, the cross be- 

 tween negro and white would have only one set of these factors for 

 black color, as shown by the formula AB X db = ABdb; hence the 

 color of the F, generation is intermediate between that of the two par- 

 ents. In the F 2 generation there should be a variety of colors ranging 

 all the way from white to black, though pure white or pure black would 

 be expected in only a small proportion of the offspring. As a matter of 

 fact it is known that the children of mulattoes vary considerably in 



Fig. 65. Blending Iniieuitance of Size in Rabbits; the skulls of two parents are 

 shown in 1 and 3, of their intermediate offspring in 2. (Prom Castle.) 



color, and in some cases a child may be darker or lighter than either 

 parent, which would indicate that segregation does actually occur. It 

 is very probable that this classical case of "blending" inheritance is 

 really Mendelian inheritance in which several factors for skin color are 

 involved. 



Similar blending inheritance is found in certain other cases where 

 the parents differ in form or size. Thus Castle found that when long- 

 eared rabbits were crossed with short-eared ones the offspring have ears 

 of intermediate length, and in all subsequent generations the ear 



