MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 387 



Allen, :03) that, in crosses between pure races of pigmented and albino mice, the 

 pigmented character invariably dominates in the offspring. 



2. It shows that cross-breeding may bring into activity latent characters or 

 latent elements of a complex dominant character. The pigmented parent in Dar- 

 bishire's crosses bore only yellowish ("fawn") pigment, but the hybrid offspring 

 produced by a cross with albinos, in all except sixteen out of one hundred and fifty- 

 four cases, bore also black pigment, which when present with yellow produces the 

 complex character gray. In nine of the sixteen cases mentioned black pigment 

 alone was present, and in the remaining seven cases yellow pigment alone was present. 



3. These facts show that cross-breeding may cause one element of a dominant 

 character to disappear (become latent), while a different element (previously latent) 

 takes its place. This is what happened in nine of the sixteen cases mentioned; in 

 these nine cases fawn (present in the pigmented parent) disappeared, while black 

 (undoubtedly latent in one or both parents) became active. 



Darbishire is unable to regard albinism as beyond qualification recessive, in 

 the Mendelian sense, because white does not entirely disappear from the bodies of 

 the offspring in his first cross. The condition observed by him is indeed somewhat 

 unusual, though entirely in harmony with Mendelian principles. The thing which 

 demands explanation in such cases as this is, not that the offspring are spotted, for 

 this may be regarded as a case of simple dominance of the character of the pigmented 

 parent, but the fact that the dominant and recessive characters occur together in 

 the spotted parent. Two explanations have been offered for such (mosaic) conditions. 

 Correns ( : 03) regards mosaic individuals as due to alternative dominance of the two 

 parental characters. He considers the anlagen of both characters to be present 

 together throughout the soma, but in one region of the body one character dominates, 

 in another region the other. He supports this idea with the observation that in parti- 

 colored flowers which bear stamens, some in the pigmented, others in the unpigmented 

 parts of the flower, pollen taken from stamens of either region transmits both the 

 pigmented (dominant) and the unpigmented (recessive) characters. This observa- 

 tion, however, proves only that the germ-cells may have a character different from 

 that of the soma. The assumption made by Correns that soma and germ-cells are 

 of the same nature in particular regions of the flower is, in our opinion, without 

 sufficient warrant. 



The facts observed by Darbishire, as well as certain observations of our; own, 

 accord better with a different explanation, suggested byBateson and Saunders (:02). 

 On this view, which one of us has recently elaborated (Castle, : 03 a ), a mosaic condition 

 of the soma is due to a mosaic condition of the germ which produced j the mosaic 



