150 Half-hoariness In Matthiola 



B. Cases where the expectation is 81 // : 175(t. 



Result obtained in F» Expectation in F^ 



The agreement between expectation and the results actually 

 obtained is sufficiently ccmvincing. If these same ^i crossbreds are 

 crossed back with a glabrous type instead of being self-fertilised, 

 another series of ratios is obtained. The F^ ratio in these cases depends 

 upon how many of the 4 factors have been introduced into the p)edigree 

 more than once in the coarse of the two matings. We may state the 

 results of the various possible combinations in general terms as 

 follows : 



Various ratios obtainable 

 in F2 when a hoary Fj 



crossbred is bred baclc Conditions under which these different 



with a glabrous type ratios are obtained 



(1) IH : IG if 3 out of the 4 factors be introduced more than once 



(2) IH : 'iG if 2 out of the 4 factors be introduced more than once 



(3) IH : "iG if 1 out of the 4 factors be introducetT more than once 



(4) IH : 15G if none out of the 4 factors be introduced more than once 



(5) all // if each of the 4 factors be introduced more than once 



Since in the early experiments, one case excepted, only 3-factor 

 glabrous types were available, viz. CRH, CRK, CHK, RHK. the results 

 obtained from breedings in the form heterozygous hoary x glabrous 

 all fall into either the first or last category given above. As, 

 by suitable breeding, material in which the several factors have been 

 eliminated is obtained, the ratios with the higher proportions of 

 glabrous to hoary can be shown to occur. This has already been done 

 in case (2). From a breeding of the form (GK x RHK) x GK in which 

 the F^ expectation is IH.SG, two F^ plants yielded respectively 



8H : 2W, 

 IH: no. 

 To obtain the two higher ratios 1H:7G and \H:15G is merely a 

 question of further elimination, identification, and suitable mating. 



We may there/ore regard the conclusions formulated in the earlier 

 paper quoted above^ as fully established. Stated in the briefest possible 

 way they amount to this : That the inter-relations of the fully hoary and 

 the glabrous types depend upon two pairs of factors {indicated by GR 

 and HK) which segregate in the normal way, the one pair being essential 

 for the production, of sap-colour, the other for hoai'iness, the latter pair 



' See note 1, p. 148. 



