H. Ikrno 49 



it« apparent r^oeanffeneaa is ciuitkHl in buiiu' cii»«'h by the inHui?nce of 

 other factors contniiUHi in tluMn, c'H|K'cially Moinr inviHihh* facU)rH, an 

 explanation similar U) that Hrst j)n)|M>.stM| by Ktwi about the Maizr- 

 cross just cite<i. Let u\v thru describe bc*low my views re^anljn^ this 

 question. Sup|)08e that either one of the two jNirents urnlrr eon- 

 sidemtion, iS. wultincrvis, for instance, carries some such fjictors in .i 

 heten)zyg<.»us condition'. In gametic fonnation thf latter will undergo 

 segregation, so as to give rise to gameti*8 containing ditVerent combirui- 

 tions of invisible fjict^irs. In the fertilisation betw('<«n mah- and frmair 

 plants of this species ganietes ditTering in respect to invisible factors 

 may come to copulation, yet the (►flfspring will always breed tru<' to 

 their pjirent type, at least all of them will agree in their catkin 

 chanicter, bi^nuse since the factors for the latter character an- in th<« 

 same homozygous condition in all of them, there will be no nason 

 why the catkin belonging to any other than the J/-type will come to 

 development, so that in this case the difference of invisibh; factors in 

 different offspring will be perfectly indifferent towards the development 

 of this character. 



Quite different results may however be expected in the hybrid is^i- 

 tion S. muUinervis x S. gracilistyla. All F^ hybrids will agree now in 

 carrying the same factors concerning the catkin character in the sfime 

 heterozygous condition, for instance Gg'-, while they will differ am<jng 

 themselves in containing invisible factors differently combined, just as 

 in the former aise. It is then reasonable to consider that these 

 invisible factors, owing to the difference in the mode of their combina- 

 tions in the various offspring, will co-operate with Gg, so as in the one 

 case to let G dominate over g, and in the other to induce just the 

 contrary effect, thus producing, respectively, the G- or the J/-type in 

 different individuals. In short, whether the one or the other type of 

 catkins will make its appearance, may be regarded as being due to the 

 influence of invisible factors accompanying the catkin factors. Thus if 

 our view be true, the phenomenon seen in F^ is to be regarded as 

 being due to the segregation of invisible factors, but not to that of the 



' Factors may be present, which do not by themselves aluue produce any visible effect, or 

 at least can produce some effects which are so inpignificnnt as to escap<^ our eyes. Such 

 factors are "invisible ones"' which are able to produce visible effects only in co-operati<fn 

 with other ones, either visible or invisible. Further, it is here supi>08ed that only one of 

 the parents carries invisible factors, but it will make no difference whatever in our loj^'ic. if 

 we consider them to be carried by both parents. 



2 G =: G-type, g = absence of G - J/-type ; the factorial composition may really be much 

 more complex, but it is here so represented for the sake of simplicity. 



Joarn. of Gen. viii 4 



