igoS] IN MENDELIAN INHERITANCE. 63 



hybrid from the base of the beak to in front of the nostrils ; some- 

 times incompletely, occupying only the anterior half or fourth of the 

 beak. It seems to me clear that in the varying proportions of this 

 median comb in the hybrids we have at once evidence for, and a 

 measure of, varying intensity of dominance. Now it may reason- 

 ably be asked whether, when the long-combed and short-combed 

 hybrids are mated together, the long comb dominates over the short. 

 The answer is complicated by the fact that the Polish "horns" 

 reappear in this second generation ; but, leaving this aside, we find 

 that there is a greater preponderance of long median combs than 

 simple mendelian expectation calls for and this indicates that the 

 longer median comb tends, but not always perfectly, to dominate the 

 shorter median comb ; or, in other words, the more intense deter- 

 miner dominates the less intense. 



To sum up, I think it is clear that dominance in heredity appears 

 when a stronger determiner meets a weaker determiner in the germ. 

 The extreme case is that in which the strong determiner meets a 

 determiner so weak as to be practically absent as when a red flower 

 is crossed with a white. In such cases we have the clearest exam- 

 ples of mendelian inheritance. But there is an entire gamut of cases 

 where the opposed determiners are of varying relative potency. The 

 phenomenon of determinance is seen in these cases also ; but the 

 mendelian law in them is sometimes obscured and sometimes merely 

 not applicable. 



Cold Spring Harbor, Long Island, N. Y., April, 1908. 



PROC. AMER. PHIL. SOC. XLVII. l88 E, PRINTED JULY lO, I( 



