56 A MANUAL OF MENDELISM 



This comb was mated with both single and rose 

 combs. When mated with singles, the hybrids had 

 " a large double comb formed as two divaricating 

 singles, not unlike that of the Egyptian." Thus the 

 Breda comb carries the dominant factor for splitting 

 just as the Cairo comb does. It also carries the factors 

 X and y, for, had it carried either X or Y, its hybrids 

 with single comb would have been something else than 

 singles. But it carries still another factor, for, though 

 merely a rudiment, its hybrids with single comb are real 

 combs, not rudiments. Thus it carries a factor for a 

 rudimentary comb which is recessive to a factor for 

 a real comb in the single. If we symbolize these two 

 factors by r and R, then the factors now known to be 

 carried by the Breda comb are xySr and by ordinary 

 single comb xysR. The other real combs, walnut, rose, 

 and pea, must also carry R. 



This finding was confirmed when the Breda comb was 

 mated with rose comb. If Breda carry the characters 

 xySr and rose comb XysR, then the two differ in three 

 pairs of characters, and, while their hybrids should be 

 split rose combs showing the characters XySR, their 

 hybrids' progeny should consist of the eight kinds 

 formed by all the possible combinations of the three 

 pairs of factors X and x, S and s, and R and r, with the 

 factor y common to all. The hybrids were actually 

 split rose combs, but, unfortunately, in their progeny, 

 only six different kinds were distinguished. Six is an 

 impossible number, however, and two groups must 

 have each consisted of two kinds which were not 

 separated. The following table gives the eight groups 

 which should have been found and the six actually 

 found: 



