POLYGAMOUS FACTORS 75 



has the effect of mixing the coloured hairs with white — 

 the animal carrying the mixture being then called a 

 roan — while the recessive leaves the coat unmixed. 

 Thus there are chestnut roans, black roans, bay roans, 

 dun roans, and grey roans ; but the last cannot be 

 distinguished from ordinary greys unless the animals be 

 very young. The roan factor has effect upon the body 

 only and leaves the face and lower limbs the normal 

 colour ; but it has effect from birth. A grey horse, on 

 the other hand, is usually born black and does not begin 

 to turn grey till its first coat has been cast. The grey- 

 ing begins about the head and face. Thus a foal with 

 black face and legs and the rest of its body a mixture 

 of black and white hairs is not a grey but either a black 

 roan or a grey roan. If its face remains black it is a 

 black roan, if its face turns grey it is a grey roan. 



Two roans are seldom mated, consequently few horses 

 pure for roan can be found. So far only one — in America 

 — has been identified, but, as hybrid roans produce equal 

 numbers of roans and normals when mated with normals 

 and two normals do not produce a roan, the dominance 

 of the factor for roan is clear. 



The first important evidence as to the inheritance of 

 horse colours was that collected from the records of 

 German official studs by Doctors M. Wilckens and 

 H. Crampe and published as far back as 1887 and 1888 

 in volumes xvii and xviii of Landwirtschaftliche Jahr- 

 biicher. Dr. Crampe makes two very significant obser- 

 vations, namely: 



(1) That chestnuts with chestnuts have chestnut 

 foals, including chestnut roans and chestnut greys. 



(2) That blacks with blacks have both black and 

 chestnut foals, and roans and greys of these colours. 



