A. H. Trow 259 



include apparently two types more and less hairy respectively; the 

 less hairy were added to the hh group, and the more hairy constituted 

 the presumed Hh heterozygotes. Under these circumstances, it should 

 be understood that the result shews little more than that segregation 

 actually occurs in this case. The aberration is probably due to trans- 

 gressive variability, which makes it impossible to fix exactly the limits 

 of the three types. A nearer approximation is gained by applying 

 the law of dominance, but this procedure reveals nothing new. All 

 groundsels, even the most glabrous types, vary a little in hairiness, 

 and in such sunny weather as that of last summer (1911) to a con- 

 siderable extent. It is possible that the multicaulis strain introduced 

 an unknown disturbing factor. 



We may now turn our attention to the relation of the factors for 

 rays and hairiness when they act together. Lanuginosus {RRHH) 

 X praecox (rrhh), erectus (rrhh) or multicaulis (rrhh) might be expected 

 to produce nine types of plants in the F, generation. Table X shews 

 both the expectation and what was actually found. 



TABLE X. 



9 Types 



h 



Confining our explanations to Exps. 23 and 25, in which Hh and Rr 

 taken separately segregate normally, we note that the heterozygotes for 

 hair are distributed fairly, according to the usual law, among the three 

 types RR, Rr and rr. There are, however, too many plants of HHRR 

 type and too few of hhRR, and also too many plants of hhi^ and too few 

 of HHrr. In other words, hairy radiate types and smooth non-radiate 

 types are produced in greater relative abundance than glabrous radiate 

 or hairy non-radiate types. In Exp. 27, which although anomalous, 

 agrees with Exps. 23 and 25 in these respects, only one plant was 

 HHrr and could therefore be of the type of a hairy multicaulis or 

 non-radiate lanuginosus. In Exp. 25 there was only one HHrr plant, 

 and in Exp. 23 only two. Hence it is clear that the production of a 

 hairy praecox, erectus or multicaulis, or of a non -radiate lanuginosus^ 



