50 On Hybridisation of some Species of Salix 



catkin factors themselves, because the latter are retained in the same 

 heterozygous condition in all F^ offspring. What we have seen in F.^, 

 (pp. 42 — 43) is however the segregation occurring on account of the 

 heterozygosity of the catkin factors carried by F^ plants. 



Let us now go to F^. As already described (pp. 42 — 43) the fertilisa- 

 tion 6^-type X (r-type gives rise to many (r-type and few i/-type 

 plants, and the ilZ-type x if -type gives rise to many if-type and few 

 (r-type ones, whilst in the if-type x (r-type plants of both types are 

 produced in almost, though not quite, equal numbers. The explanation 

 of this peculiar mode of i^2-segregation will, as I think, naturally follow 

 from our hypothesis adopted about F^ plants. We have supposed 

 (p. 49) that each of the F^ plants, whether (r-type or i/-type, possesses a 

 similar factorial constitution in respect to the catkin character, which 

 we have represented by Gg ; in F^ we should have then on account of 

 the segregation 



GG-f wGg + gg 



in all cases, n being any positive integer equal to or greater than 2. 



As already - noticed (p. 49) each of the (r-type F^ plants carries 

 besides the factors Gg a certain combination of invisible factors which 

 we may for instance call X, and which acts together with the latter, so 

 as to give rise to (r-type catkins exclusively; accordingly all the F2 

 offspring derived from the fertilisation (r-type x G^-type will contain X ; 

 and so of the F^ plants GG + z^Gg + gg, GG and ?iGg (the latter 

 under the influence of X) should be (r-typed, whilst only gg should be 

 ilf-typed, thus explaining the fact that the F2 offspring consist largely 

 of (r-type plants. 



On the contrary, as each of the if-type F^ plants carries besides Gg 

 a combination of invisible factors which we may call Y, and which acts 

 together with the latter, so as to give rise to if-type plants exclusively, 

 we may, by similar reasoning as above, come to the conclusion that of 

 the offspring GG + ?i . Gg + gg derived from the fertilisation ilf-type x 

 iV/-type, nGg (under the influence of Y) and gg should be il/-type, and 

 only GG, (r-type, thus explaining the fact that the F2, offspring are 

 then largely il/-type. 



In the fertilisation TIf-type x (r-type we have to deal with the two 

 kinds of combinations of invisible factors, X and Y, which are provided 

 with diametrically opposite characters. It is clear that in F^ some 

 offspring will receive X, whilst some others Y, and that then Gg accom- 

 panied by X will be (r-types, whilst other Gg accompanied by Y, will be 



