72 A MANUAL OF MENDELISM 



But, by this arrangement, white and red must differ 

 in two pairs of characters, which is not in accordance 

 with the facts. Obviously, if each colour is the result 

 of more than one factor, two must always differ in more 

 than one pair ; and this they do not do. Thus the 

 only possible solution of the problem is that each colour 

 is the result of one factor only and that the factors are 

 polygamous : the factor for black, say, mating with 

 that for red, or white, or brown, or light dun ; and so 

 on all round. Unfortunately this solution cannot be 

 tested satisfactorily, because some of the necessary 

 crosses are seldom made and, if made, are not re- 

 corded. Putting the initial letters of the colours for 

 the factors producing them, blue roan (BW) by 

 red roan (RW) should produce 1 black (BR) : 1 blue 

 roan (BW) : 1 red roan (RW) : 1 white (WW). In 

 Ireland, here and there, are a few blue-grey heifers and 

 cows which are mated with Shorthorn bulls, and the 

 Department of Agriculture's County Instructors and 

 Overseers very kindly took notes of what information 

 they could gather as to the results of mating blue 

 roans with red roan Shorthorns. The blue roans were 

 mostly in the hands of small farmers who found 

 greater difficulty than Shorthorn breeders in distin- 

 guishing not only red from roan but black from blue. 

 They were inclined to call red roans red and blacks 

 with white spots blue. Besides, in cases, they spoke 

 from memory of animals no longer in their possession. 

 As collected the figures are : 



Black Red Blue Red White 

 Roan Roan 



12 7 38 26 30 



