82 THE MENDEL JOURNAL 



which was born after his death and was called 

 " Postnmus " (Plate 1), and is now in training at 

 Kingsclere. This colt was and is grey. 



For breeders of race-horses " Postnmus " is a 

 specially interesting horse. First of all, it was 

 thought by some that " Postumus " did not fall 

 into line with the Mendelian principles, and that 

 even a pure (D D) bay parent did not breed true. 

 But they overlooked the very important fact, that 

 the pureness of the (D D) bay character only holds 

 with regard to bayness and to colours recessive to 

 it, and that it can be best tested by mating it with 

 a chestnut. The question at stake is simply this : 

 Is the bay colour of this stallion dominant to the 

 chestnut colour ? It is answered by the fact that 

 "St. Simon's" offspring out of chestnut mares were 

 invariably bays. So it is proved that " St. Simon" 

 was (D D) for bay, since were he a (D R), that is 

 carrying the dominant (D) bay colour and also the 

 recessive (R) chestnut colour, he would have pro- 

 duced, as some other bays which are (D R^) have 

 done, chestnut foals as well as bays. 



If "St. Simon" is thus a pure bay, the greyness 

 of his last foal " Postunms " is of some interest. 

 Among horse breeders, it has been attempted to 

 frame an explanation of the appearance of this grey 

 foal upon the fanciers' old conceptions of inheritance. 

 We will first deal with these attempted explanations, 

 and then view the matter from the Mendelian stand- 

 point. We shall see how well the Mendelian 

 interpretation harmonises with the facts in the 



