148 Messrs. Prout and Bacot. On Cross-breeding of [Jan. 8, 



20 would be called dark, but there is no clear line of demarcation. The 

 return to a darker type might be called atavistic, but more probably the 

 actual parents — which are not known — happened to be among the darkest 

 ones of F 9 . 



(5) From a dark <$ x light ? , F 7 consisted of 21 specimens (labelled 

 D ^ vii (7) ), all normal intermediates, with no appreciable variation. The 

 strain was unfortunately lost. 



C. General Conclusions. 



From the foregoing mass of detail a few facts emerge with conspicuous 

 clearness, and certain other points are sufficiently suggested to be worth 

 putting forward, at least tentatively. 



In the first place, there is most certainly no Mendelian dominance in 

 coloration in the cross of the dark (London) race of Acidalia virgularia with 

 the light (Hyeres) race. With remarkable persistence, a first cross of the 

 pure races produced a form intermediate in coloration. The sole exception, 

 out of two dozen such crossings, is the brood noticed above as F, No. (1). 



But, in the second place, it is perfectly well known that colour-dominance 

 is not the essential feature of Mendelism. As Mr. Bateson says,* " The 

 essential fact which Mendel discovered is the segregation of characters in 

 gametogenesis." Now, as the intermediate form, which was so nearly universal 

 in the first crosses, did not appear in either of the " pure " strains, it may well 

 be taken as the normal manifestation of hybridity in this blend, correspond- 

 ing to the " blue " Andalusian fowl and other well-known cases ; and it is 

 certainly noteworthy that a rough resolution into a wider range of forms 

 proved quite general in the F 2 generation. That proportions did not agree 

 with expectation might be due to defective analysis. For example, the said 

 " hybrid " or " intermediate " might have a wider range of variation than had 

 been discovered by the investigators, who might thus have referred some 

 hybrids to one of the " pure " forms. But a glance at our actual results 

 convinces us that it is not generally too few intermediates that we obtained 

 in F 2 but too many ; and fortunately we know very accurately the limits of 

 the variation of at least one of the pure races (L), so that there seems no 

 chance, on the assumption of gametic purity, of our having classified pure 

 " lights " as " intermediate." It is, however, further noteworthy that some, 

 at least, of the extracted strains (light x light, ex hybrid, viz., A (2) in 

 generation F 7 ,f ? B in generation F 5 (1), b xf |£>] in generations F 9 and ? ~F W > 



* ' Progressus Eei Botanicse,' 1906, p. 368. 



t But if this was really "pure" whence came the single "intermediate" $ in its. 

 offspring ? 



