264 



Inheritance in the Groundsel 



by experiment, it deserves provisional acceptance. It is possible that 

 the presence of the Y factor alone in Exps. 63 and 68 might serve to 

 explain the result. Further experiments are necessary. 



The remaining three experiments are of greater interest, as they 

 were intended to test the behaviour of the progeny of plants homo- 

 zygous for hair and rays. An unexpected segregation occurred in one 

 of them. 



TABLE XV. 



Exp. No. Cross type type H^ H^ H' Eemarks 



Exp. 62 31 Lanuginosus x [ HH rr — — 93YY Hairiness of the lowest 



type and constant. 

 Hairiness probably de- 

 pressed by YY 



Exp. 69 38 Lanuginosus x | HH rr 20yy 49 F?/ 27YY All H^ plants unhealthy. 



Hairiness upon the whole 

 less than in the praecox 

 cross. Exp. 61 



Exp. 70 39 Lanuginosus x ) HH RR — 49 FF — Hairiness not quite equal 

 multicaulis [ toH'. Hence FFplants. 



R raises the grade of 

 hairiness 



The plants of Exp. 62 were all of a very low standard of hairiness. 

 This may be partly accounted for by the absence of R and the presence 

 of F. 



Exp. 69 is comparable with Exp. 67. The Y factor is involved, and 

 the heterozygotes are recognisable. The slight loss of hair may be due 

 to the absence of R. The numbers found correspond very well to the 

 expectation. 



Found :— YY : Yy : yy :: 27 : 49 : 20 



Expected:— :: 24 : 48 : 24 



In Exp. 70 the plants shewed constant hairiness ; they were probably 

 of YY type, the presence of R raising the grade of hairiness from H^ 



The study of the inheritance of hair is no doubt incomplete ; but 

 it is clear that (1) the transmissibility of hair from one type to another 

 is possible ; (2) that two pairs of factors at least are involved, H, h and 

 Y, y ; (3) that consequently there must be at least several grades of 

 hairiness ; and (4) the presence {R) or absence (r) of the ray factors 

 modifies the hairiness due to the proper hair factors. The difficulties 

 of the study are accentuated by the transgressive variability of the 

 segregating characters and by the direct influence of the environment 

 in producing slight non-heritable modifications. 



