268 Inheritance in the Groundsel 



Cultures 39 and 35 suggest the possibility of a single pair of factors; 

 cultures 38 and 37, of two pairs of factors, giving the ratio 9 : 7. The 

 difference between the numbers found and those calculated is consider- 

 able. For 97 plants the ratio should be 55 : 42 and not 62 : 35 ; for 

 92 plants, 52 : 40 and not 57 : 35. 



Culture 36 did not segregate, although apparently of an inter- 

 mediate type. It is probably to be regarded as a modified pure red 

 (GO). The facts, as a whole, point unmistakably to segregation for 

 stem colour taking place in the hybrid lanuginosus x multicaulis. 



Culture 33 is of special interest, as there were three pairs of 

 characters involved. Theoretically, there should have been 27 different 

 kinds of plants in this colony. Although there were less than 50 plants, 

 15 of these kinds were found. The segregation for rays, stem colour 

 and hair separately considered was as follows : — 



RR : Rr: rr :: 11 : 25 : 12 

 GG :Gg :gg :: 13 : 20 : 16 

 HH'.Hh.hh :: 14:20: 15 



The detailed analysis of this result suggests that there is possibly 

 a gametic coupling of the form IHG : nHg : nhG : Ihg where ri is a fairly 

 large number. The demonstration of such a coupling, including the 

 determination of the value of n, involves further experiments on a larger 

 scale, and the discussion of this result must be postponed until these 

 have been completed. 



Leaf Colour Factors. 



A brief reference may be made to the factors for leaf colour, the 

 detailed examination of which has scarcely commenced. It is certain 

 that segregation of leaf colour characters takes place in these groundsel 

 hybrids. The foliage leaves of erectus and erectus, radiatus are of a 

 yellowish-green colour, those of multicaulis are of a dark green. Each 

 pure type can be almost said to have its own distinctive shade of green, 

 so that one pair of factors can scarcely suffice to explain the facts unless 

 we assume that the leaf colour factors are affected by other factors. In 

 the F2 generation of the hybrid multicaulis x erectus, radiatus the leaf 

 colour was observed to segregate, but the apparatus necessary for esti- 

 mating the types exactly was not available and therefore no definite 

 analysis was made. It may be provisionally assumed that there is a 

 factor for leaf colour L which determines the darker leaf colour, its 



