166 Messrs Bateson and Punnett, A suggestion as to 



pollen of bomostyles is of the pin type. The corollas, however, 

 are peculiar in that they always have a yellow flush which extends 

 the " eye " far up the petals (whence the best known homostyle 

 strain derives the name of " Primrose Queen "). 



In the course of the work thrum was crossed with homostyle, 

 giving F ± ordinary thrum without the yellow flush. But F 2 con- 

 sisted of four types : (1) thrum without yellow flush ; (2) thrum 

 with yellow flush ; (3) pin without yellow flush ; (4) homostyles 

 with yellow flush. The ratios were evidently 9:3:8:1. The 

 form pin, not introduced as an original parent, thus appears in F 2 

 as a novelty. 



The interpretation is obvious. The allelomorphic pairs are 

 clearly two. (1) Thrum (D) and pin (R). (2) No yellow flush (D) 

 and yellow flush (R) ; and the homostyle is merely a zygotic state 

 occurring when yellow flush and pin coincide. The pin therefore 

 appears as a novelty by the meeting of pin and "no yellow 

 flush." 



This observation naturally suggested that the single comb in 

 F 2 from r x p might have a similar mode of origin. Applying this 

 hypothesis the original parents, r and p, are regarded as respec- 

 tively rose + no-pea, and pea + no-rose. The allelomorphs are 

 (1) rose and absence of rose ; (2) pea and absence of pea. The 

 rose and the pea characters belong to distinct allelomorphic pairs. 

 When therefore r meets p the zygote would be walnut, and the 

 single is regarded as constituted by the meeting of gametes 

 bearing neither rose nor pea. In this way all the phenomena are 

 brought into simple relation with each other and the case is 

 exactly comparable with that of any other dihybrid. This suggestion 

 has the merit that it obviates any appeal to resolution, and that 

 the gametic synthesis apparently occurring in the case of the rp 

 character becomes an ordinary phenomenon of dihybrid inheritance. 

 Finally, the fact that r xp cannot be distinguished from rp xs 

 finds a ready explanation. 



If we do not look beyond the special case of the walnut combs, 

 this account seems so complete as to make further discussion 

 unnecessary. We can only express surprise at our failure to 

 perceive it sooner. This failure was of course due to the pre- 

 conception that the types of comb were definite entities alternative 

 to each other, while, as is now evident, the presence of a given 

 modification must be regarded as allelomorphic to the absence 

 of the same modification. The essential feature of the rose comb 

 is its papillosity, while the ridges mark the pea. The single comb 

 is thus to be regarded as a comb into which no such additional 

 element is introduced, being neither papillose nor ridged, and is 

 thus a factor common to all the other types, rose, pea, and 

 walnut. 



