450 
Bulletin No. 161.—1914. 
which two types of white fowl, when mated together, produced 
progeny, all of which were dark colored, thus suggesting that each 
type contained one of the two factors whose combination was neces¬ 
sary in order that pigmentation might result. The observation made 
by Bateson and Punnett naturally suggests the possibility that the 
White Leghorn does not carry the factor, or factors, for black pig¬ 
mentation, but contributes only one (X) of two necessary factors, 
while the White Plymouth Rock contributes the other (Y). This 
point can be tested by properly devised experimental matings and 
it is the aim of the present contribution to report the results of an 
experiment in cross-breeding which has a direct bearing upon it. 
The stock used was pure White Leghorn and White Plymouth 
Rock, line-bred for many generations. The crosses were made 
in only one direction, White Leghorn c? X White Plymouth Rock 9 9. 
The majority of the birds were raised to five months of age, and some 
were kept until they were mature. 
Before presenting the experimental results, a word should be said 
regarding the zygotic constitution of the White Leghorn, since this 
point has an important bearing upon the interpretation of any results 
obtained. This breed is characterized by the so-called “dominant 
white,” as contrasted with the “recessive white” present in the 
majority of other white breeds, including the White Plymouth Rock, 
White Minorca, and White Silky, for example. In crosses between 
the White Leghorn and such black fowl as Black Hamburg, Black 
Minorca, Black Spanish and Black Java, the Fi birds are invariably 
white, frequently showing splashes or flecks of black, and less often 
a barred or partly barred feather. In F 2 the typical Mendelian 
ratio appears, 3 white : 1 dark. The dark birds comprise both 
black and barred individuals in the ratio 1 : 3, as stated in an earlier 
paper.* 
One is naturally led to inquire, — What is the nature of the dominant 
white character in the White Leghorn? The Leghorn white is due 
to the absence of color, but it is illogical to say that the absence of 
* Hadley, P. B., The presence of the barred plumage-pattern in the White Leghorn breed of 
fowls. Amer. Nat., 47, 1913, 418-428. 
