A. H. Trow 261 



analy.'sis of the F„ generation. It is well known that the .safest test (as 

 well as the most troublesome) for a presumed heterozygote is to raise 

 a colony of plants from it. 



Ten of the eleven colonies raised shewed that the constitution of 

 the parent plants had been correctly estimated with respect to hairiness. 



Exp. 70 39 / HH HH RR 50 



The eleventh (Exp. 62) marked Hh, proved to be constant for hairi- 

 ness, all the F3 plants conforming to the standard H\ The plants were 

 all rr; if we assume that the non-radiate condition has the effect of 

 depressing hair development, we secure at least a provisional explanation 

 of this case. The original analysis, however, becomes as a whole subject 

 to an error of 10 °/^, and one must admit that the results are to be 

 accepted only with such reservations. 



Let us now note the result of the examination of the segregation 

 of the hair in the Hh types of Table XII, and take in order the rr, RR 

 and Rr groups. The results are presented in Table XIII. The numbers 

 accord fairly well with the expectations. The divergences are partly 

 due to the attempt to recognise the heterozygotes. 



The most hairy types in No. 29 were as hairy as lanuginosus — in 

 the three cultures Nos. 34, 35 and 33 this was not the case. We may 

 assume that typical multieaulis carries a factor Y which depresses the 

 development of the hair character. In its absence (y) hair is fully 

 developed if the factor for hair, H, is present. Pure praecox is a yy 

 plant, midticaulis is YY. This hypothesis will also enable us to explain 

 the interesting result of Experiment 36. Two types of hairy plants 

 appeared in this case : (a) very hairy — H^ — like lanuginosus, and 

 (6) hairy— //=— like the HH plants of No. 35. The 13 very hairy 



