290 Genetic Studies in Poultry 



to be the case the evidence from the Silky suggests that either factor, 

 if two are concerned, is capable by itself of giving rise to broodiness. 



We do not know of any instance in which broodiness has arisen 

 through the crossing of two strains which experience had shown to be 

 pure for the non-broody character. In the course of our experiments 

 during the past ten years we have tested considerable numbers^ of hens 

 arising from complex crosses between the three non-broody breeds, 

 Pencilled Hamburghs, Sebrights, and Brown Leghorns. Not a single 

 bird has appeared which showed the slightest sign of broodiness. Such 

 data as we have accumulated afford no grounds for the suggestion that 

 the broody habit may depend upon the meeting of complementary 

 factors ^ 



Broodiness and dark eggs. 



It is well known that most of the races of poultry that lay dark 

 eggs belong to the broody section, whereas the non-broody strains lay 

 white eggs. These facts suggest that there may be some form of linkage 

 between egg-colour and broodiness, a point upon which we hoped that 

 our experiments would throw some light. Figs. 12 and 13 show the 



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123 4 56789 10 11 



Fig. 12. Distribution of grades of egg-colour in the F^ broody birds 

 ex Brown Leghorn $ x Langshan ^. 



distribution of egg-colour in relation to broodiness in the Langshan- 

 Leghorn cross. For the non-broody birds the average grade of egg- 

 colour is 3*8, while for the broody ones it is 4*9. The numbers are 

 however too few to lay any stress on this small difference. It is con- 

 ceivable that one of the factors upon which egg-colour depends may be 

 linked with broodiness, and that the slightly higher grade of colour 

 among the broody birds is significant. Nor must it be forgotten that 

 the non-broody birds were, with few exceptions, only tested during their 

 pullet year. Some of them were doubtless potentially broody, and if 



1 Certainly more than 200. 



2 Broody birds, as is well known, may appear in breeds which are nominally non- 

 broody, e.g. White Leghorns. We are inclined to think that in such cases the cock is 

 responsible. After an occasional cross with a broody race it is not enough to rebuild the 

 strain solely by selection of non-broody hens. The cock may also carry broodiness, and 

 should be carefully tested before he is put into the breeding pen. 



