PHENOMENA OF INHERITANCE 437 



crossed with varieties having white glumes the ratio of 3 white to 1 

 black was usually found in the second generation; but one variety of 

 black oats when crossed with white gave in the second generation ap- 

 proximately 15 blacks to 1 white, which is the dihybrid ratio. From this 

 and other evidence he concludes that in this variety of oats two heredi- 

 tarily separable factors are involved in the production of black. In 

 crosses between red-grained and white-grained wheat he usually got in 

 the second generation the monohybrid ratio of 3 red : 1 white, but tliree 

 strains gave the dihybrid ratio of 15: 1 and two gave the trihybrid ratio 

 of 63 : 1. Consequently he concludes that while the red color of wheat 

 grains is usually due to one factor for red, it may in some cases be due 

 to two or even three factors; notable departures from expected ratios 

 may thus be explained. 



Blending Inheritance 



But the most serious objections which can be presented against the 

 universality of the Mendelian doctrine are found in phenomena of 

 "blending" inheritance. In some instances contrasting characters of 

 parents appear to blend in offspring and even in the F 2 in subsequent 

 generations the descendants remain more or less intermediate between 

 the parents. One of the best known illustrations of this is found in the 

 skin color of the mulatto, which is intermediate between the white parent 

 and the black one, and even in the F 2 and in subsequent generations 

 mulattoes do not usually, if ever, produce pure white or pure black 

 children, though the children of mulattoes show considerable variation 

 in color. Here there is an apparent failure of the Mendelian principle 

 of segregation. 



But white skin is not really white nor is black skin ever perfectly 

 black. Davenport has shown that there is a mixture of black, yellow and 

 red pigment in both white and black skins, though the amount of each 

 of these pigments varies greatly in negroes and whites. A white person 

 may have a skin color composed of black (b) 8 per cent., yellow (y) 9 

 per cent., red (r) 50 per cent., and absence of pigment or white (w) 

 33 per cent. On the other hand a very black negro may have b 68 per 

 cent., y 2 per cent., r 26 per cent., w 4 per cent. The nine children of 

 two mulattoes, the father having 13 per cent, of black and the mother 

 45 per cent., ranged all the way from 46 per cent, to 6 per cent, of 

 black— the latter so far as skin color is concerned being virtually white. 

 On the other hand, where both parents have about the same degree of 

 pigmentation the children are more nearly uniform in color ; thus seven 

 children of two mulattoes, the father having 36 per cent, and the mother 

 30 per cent, of black, ranged only from 27 per cent, of 39 per cent, of 

 black. 



Such variations in color in the F 2 and in subsequent generations is 



