Wilson — Unsound Mendelian Developments. 407 



This result corresponds with the results given in Professor Punnett's 

 " Mendelism,"' excepting that there the combless fowl are all lumped together 

 as " Bredas," and the numbers of individuals in each group are not given. 

 Had the Bredas been grouped and counted, tlie evidence would have been 

 complete. As it is, it is very strongly presumptive that the constitution 

 assumed for the Breda is correct. In anj' ease the foregoing is an example 

 of liow the Mendelian formnlte may be applied, and may help us to follow 

 the working of the presence and absence theorj'. 



Unfortunately this theory has not yet been fully explained. It has, 

 however, been used frequently for analytical purposes, and, from statements 

 made in cases in wliioli it has been so used, its general purport can be made 

 out ; but, since the underlying logic has not been exhaustively expounded, 

 the principle desired to be established may be difficult to find. 



Tlie tlieory originated at the time the fowls' combs were being studied, 

 and was first used to explain the experimental results in that case, which 

 seemed unusual. Its authors took a different view from that taken in tliis 

 paper as to the factors concerned in the production of rose, pea, and single 

 combs. Althougli it seems impossible to think otherwise than that, when a 

 set of second crosses split into four groups standing to each other, as regards 

 the numbers they contain, in the ratio 9:3:3:1, there must be two pairs of 

 differentiating characters concerned, and that each group must bear at least 

 two characters, they took the view tliat rose, pea, and single comb are each 

 the result of one factor only. Holding this view they saw nothing unusual 

 in the walnut resulting from the mating of rose and pea. It was a com- 

 pound character, one of a kind " produced by the mutual interaction of 

 factors belonging to distinct allelomorphic systems." The difhculty arose 

 when two first-cross walnut combs mated produced a single comb. How was 

 tills to be accounted for ? Professor Punnett puts the case thus : — " How are 

 we to express the fact tliat while single behaves as a simple recessive to 

 either pure rose or to pure pea, it can yet appear in F2 " (i.e., in the second 

 crosses), " from a cross between those two pure forms, thougli neither of 

 them should, on Mendel's view, contain the single ? "■ (" on Mendel's view " 

 ought rather to be on the view that rose and single combs are due to single 

 characters). 



The explanation given of the anomaly is that, while walnut is the com- 

 bined result of the rose and pea factors, and tlie other combs are each the 

 result of their own individual factors, the single comb emerges from the 



' p. 37, Diagram =p. 31. 



SCIENT. PBGC. E.D.S., VOL. XIII., NO. XXVII. 3 P 



