HYBRID OF DIGITALIS. 



367 



Now, if the two homologous factors (P and Y) had remained 

 unaltered in the hybrid, half of the offspring of the lutea backcross 

 {5th column) should cluster about the hybrid mean (grade 390-429) 

 and half about the lutea mean (grade 310-349), but there 

 is no tendency for this condition. In the case of the backcross 

 with gloxinia 'flora (3rd column) the number of the plants is few, 

 but there is no indication of a dimorphic series. 



If it is supposed that corolla-length depends on two or more 

 independent factors, results would be less simple, but in such case 

 the backcrosses should, at least, exhibit very considerable varia- 

 bility, and reference to the table shows that the variation is 

 remarkably small. 



Flower: Intensity of Purple Colouration.- — The scale of 

 colour intensity, which was employed, is the same as that previously 

 described. 1 



In all the lutea plants used in the experiment the purple 

 colouration was exceedingly slight, and was confined to a very 

 inconspicuous patch at the base of the filaments of the stamens; 

 but among some other hi tea plants growing elsewhere, the inside 

 of the base of the corolla was found to be distinctly purple, and 

 the filaments were coloured along their whole length. The gloxinice- 

 flora plants varied from quite pale purple to an intense purple. 

 In the hybrids the mean intensity of colouration (34) was nearly 

 intermediate between the means of the two parent species. The 

 mean of the gloxinia' flora backcross (39) is very much nearer to the 

 hybrid mean (34) than to the gloxiniceflora mean (82), but the 

 mean of the lutea backcross (7) is much nearer to the lutea mean 

 (5) than to the hybrid mean (34). 



Intensity of Purple Colouration. 



(1) Loc. cit. " Biometrika," 1917. 



