Constitution of the White Leghorn Breed. 205 



-constitution of the W. L. 9 with reference to the factor I; (2) the 

 presence of factor C, or other factors for black pigmentation, in the 

 W. L. d^; (3) the possible identity between the factor I in the 

 W. L. and Bateson and Punnett's factor /, of the Brown Leghorn, — • 

 an inhibitor of the Silky tA'pe of mesodermal pigmentation in crosses 

 between the B. L. and W. S.; (4) the possible occurrence of barring 

 in other breeds of fowl possessing the "R-white." These points 

 may be taken up in the order of their presentation. 



L — The constitution of the White Leghorn 99 with respect to factor 

 I. — In order to throw light on this point crosses were made during 

 the season of 19L3 between the B. H. d^ and W. L. 99, these being 

 the reciprocal of crosses mentioned earlier in this paper. Fi gave 

 only white birds, thus indicating the homozygous nature of the W. I;. 

 99 for the inhibiting factor. This result was naturally expected. 



2. — The factor for black ^pigmentation in the W. L. cT. — It has been 

 assumed in this study that the W. L. d^ is essentially a black bird in 

 which the pigmentation is obscured b}^ the action of the inhibiting 

 factor I. It is now necessary to present the data upon which this 

 assumption is based. First it may be said that this assumption 

 regarding the zj^gotic constitution of the W. L. is in harmony with the 

 majority of the experimental results already presented. To assume 

 that the W. L. d^ lacks the factor for black pigmentation is not in 

 agreement with the results observed. But it has seemed possible to 

 throw light upon this matter by other means. If the W. L. d^ were 

 mated witn an R- white, such as the White Plymouth Rock, F2 

 should yield some pigmented birds in which the factors / and C had 

 become separated from each other. We may tentatively regard the 

 zygotic constitution of the W. P. R. 9 as C2B6F/12 forming gametes 



cBJi ■ cbFi 

 "The mating would then be represented: 



d^ CBU ' CBfl X 



9 cBfl • cbFi = 



9 C cBhFf I i — white 



<d^ CcB2f2li — white 



