182 Bulletin No. 155.— 1913. 



IV. General Discussion of Results. 



The experimental data presented in the foregoing pages make it 

 clear that a type of barred plumage-pattern has arisen in F2 from the 

 mating of white with black birds. First of all we may ask : Where 

 did this barring, manifested in a few feathers of a small nmnber of Fi 

 individuals but appearing as a fully developed barred pattern in a 

 certain proportion of F2 progeny, have its origin? As stated at the 

 beginning of this paper it was tentatively assumed, when the present 

 investigations were planned in 1909, that barring represented a 

 heterozygous condition resulting from the crossing of light colored 

 with dark colored birds. This tentative assumption was based on 

 the fact that breeders* have commonly made the observation that 

 the crossing of Blacks X Whites occasionally gave some birds 

 with good barring. Thus the barred plumage-pattern was considered 

 by some as a mosaic made up of black and white. It is now clear, 

 however, that this view is not supported by any evidence supplied by 

 the present investigations. In Fi, contrary to expectation, the degree 

 of dominance of white in all the White Leghorn X Black crosses was 

 so great that the presence of black pigment was usuallj- manifested 

 only as flecks on an otherwise pure white plumage, or, in a smaller 

 number of cases, as a partly barred feather among the white. If the 

 barred pattern were of the nature of a mosaic, it should appear most 

 definitely in Fi; one would not be led esp)ecially to anticipate its 

 appearance in F2, — at least in a well developed condition. But as 

 shoTMi in all the tables giving data on the F2 birds this is exactly 

 where the most extended and most clear-cut barring did appear. 



In contrast to the view outlined above, several other invest igationsf 

 dealing with the type of barring found in Barred Plymouth Rocks 

 have shown that this character as there found may behave in in- 

 heritance like a unit-character; it is separately heritable. In other 

 words, birds that show this barred pattern may be assimied to possess 

 the factor for barring; and without the presence of this factor in the 



♦See Davenport (1906); Wright (1905); Hurst (1905). 

 tGoodale (1909); Pearl and Surface (1910). 



