48 071 Hybridisation of some Species of Salix 



discovered that in crosses of some silk-worms which spin yellow and 

 white cocoons, respectively, the dominance is variable, because in some 

 yellow is dominant to white, while in others the reverse takes place ; 

 this is due, as the latter author thinks, to strain or individual idiosyn- 

 crasies, but Toyama^ has proved experimentally that this phenomenon 

 may be better explained as the effect of a mixed breed, containing 

 recessive as well as dominant whites, than as that of individual idiosyn- 

 crasies. Almost a similar explanation is applicable to what Correns 

 and Lock have observed in hybrids of Maize. In Maize, alha x cyanea, 

 where blue is dominant to white Correns found in F^ 94 °/^ blue 

 individuals and 6 °/„ white ones^ ; also in Maize, Moore's Concord 

 (white) X Black Mexican (black) Lock found that black was dominant 

 to white, but that sometimes the reverse takes placed As first pointed 

 out by East^ and afterwards by Lock himself^ this was due to the fact 

 that "a supposed pure white strain" used in the hybridisation was 

 composed in reality of a number of genotypically different individuals 

 which, though pure for white when selfed, differ among themselves in 

 carrying some invisible factors which react differently in the production 

 of colour^ Thus we have here to deal, not with the "reversal of 

 dominance," but with a " mixed breed," almost in the same way as in 

 the case of the silk-worms above enunciated. It may perhaps be 

 reasonably doubted, whether also in the so-called "reversal of dominance" 

 in poultry we have not to deal with similar circumstances as in Maize 

 just mentioned. 



Our case in Salix is however somewhat different from that of Silk- 

 worms or Maize, inasmuch as the fourteen F^ hybrids are derived from 

 one and the same female plant fertilised by pollen taken also from one 

 and the same male plant, so that if our case were really explicable on 

 the basis of the hypothesis founded on the reversal of dominance it 

 must necessarily follow that the G^-typed catkin is sometimes dominant, 

 sometimes recessive to the if-typed one in the same individuals, which 

 does not seem very probable. It appears to me much more reasonable 

 to consider that though either one of the two types of catkins, for 

 instance the (r-typed one, is in reality always dominant to the other, 



1 Zeits.f. ind. Abstammungs- u. Vererbungslehre, Bd vii. 1912, pp. 252 — 288. 



2 Bibliotheca Botanica, Heft liii. 1901, pp. 53 — 55. 



3 Ann. B. Bot. Garden Peradeniya, Vol. iii. 1906, pp. 117—129. 



4 The Connecticut Agric. Exp. Station, Bull. 167, 1912, pp. 57—100. 



5 Ann. B. Bot. Garden Peradeniya, Vol. v. 1912, pp. 257—264. 



6 Lock, I. c. p. 257. 



