not know. Some suppose it to be held in 

 check by an additional unit-character, an in- 

 hibiting factor, but we have no direct evidence 

 that such a factor exists. All that we are 

 warranted in saying at 'the present time is 

 that black and white in poultry represent dif- 

 ferent conditions of pigmentation, alternative 

 to each other in heredity. In crosses of the 

 two, white is ordinarily dominant over black, 

 but in crosses between certain strains of white 

 and black poultry this relationship is reversed, 

 as Bateson has shown. 



In still other cases, a cross of white with 

 black fowls produces offspring which resemble 

 neither parent closely, but which are in reality 

 intermediate. They are known as blue or 

 Andalusian fowls. They manifest a dilute 

 condition of black, such as one might obtain 

 by mixing lampblack with flour; they are in 

 reality a fine mosaic of black with white. 

 Such a condition has thus far been obtained 

 only from a cross of black fowls with a pecu- 

 liar strain of impure sooty whites. This strain 

 undoubtedly contains the mosaic pattern but 

 without sufficient black pigment to make it 



55 



