104 BREEDING 



which produces only yellow rounds, or only yellow 

 wrinkleds, or only green rounds, we can be sure that 

 it is pure in respect of both colour and shape, and will 

 continue so. And it may be laid down as a general 

 rule that the permanent combination of two recessive 

 characters may be effected in the second hybrid 

 generation, but that the permanent combination of 

 a recessive and a dominant character (belonging, of 

 course, to distinct pairs), or of two dominant 

 characters, cannot be effected till the third hybrid 

 generation. It is curious that the great majority of 

 tne best culinary peas are green wrinkled. But this 

 fact is probably not merely due to the facility with 

 which these two characters can be combined ; for 

 though there is no advantage, from the culinary 

 point of view, in the green over the yellow, the 

 advantage of the wrinkled over the round will be 

 seen to be very great. 



An instance of the value a familiarity with this 

 9:3:3:1 ratio, as a help to understanding otherwise 

 unintelligible results of cross-breeding, will now be 

 given. One of the characteristics which distinguish 

 the various breeds of poultry is the form of the comb. 

 The commonest type of comb, and that possessed by 

 the wild ancestor of our domestic poultry, is known 

 as the single comb, which is represented in Fig. 22. 

 The comb is flat from side to side, and its free edge 

 is marked by deep indentations. Another type of 

 comb, which characterises the Wyandottes, is shown 

 in Fig. 23, and is known as the " rose " comb. It is 



