32 A MANUAL OF MENDELISM 



The dominance of both rose and pea to single comb 

 was referred to as a new phenomenon. This can now 

 be explained. Rose carries the characters Xy while 

 single carries the characters xy. Thus they differ in 

 only one pair of characters, X and x, and, by carry- 

 ing the dominant of the differing pair, rose behaves 

 as a simple dominant to single. Similarly, pea and 

 single differ in only one pair of characters, Y and y, 

 and, by carrying the dominant of the differing pair, pea 

 also behaves as a simple dominant to single. In such 

 circumstances the progeny of the hybrids between rose 

 and single and pea and single should consist of three 

 roses to one single on the one hand and three peas to 

 one single on the other. 



A parallel example might make the case clearer : if 

 round peas with green albumen were mated with 

 wrinkled peas with green albumen — green being common 

 to both — their hybrids' progeny would consist of three 

 round with green albumen to one wrinkled with green 

 albumen ; and, if wrinkled peas with yellow albumen 

 were also mated with wrinkled peas with green albumen 

 — wrinkled being common to both — their hybrids' 

 progeny would consist of three wrinkled peas with 

 yellow albumen to one wrinkled with green albumen. 



In connexion with this case, it may have been noticed 

 that the progeny of the hybrid walnut combs were not 

 too close to the ratio 9:3:3:1. The total number 

 was 555, and this should have divided approximately 

 into 313, 104, 104, and 34, instead of 279, 99, 132, and 

 45. By some statisticians this discrepancy might be 

 considered serious, but the inference from the numbers 

 was proved by other tests, one of which only need be 

 quoted. It will be remembered that Mendel, to prove 



