56 On Hybridisation of some Species o/Salix 



III. Conclusions. 



After the appearance of the work of Wichura the view prevailed 

 that hybrids between various species of Salioc breed true in later 

 generations. My hybridisation experiments conducted on a few Salioc- 

 species have shown that this is not true, at least in respect to certain 

 characters. According to these experiments the erect habit of stem is 

 dominant to the spreading, the hairy character of leaves is dominant 

 to the non-hairy in one case, and recessive in another, red stigma is 

 dominant to green, and all these characters were found to exhibit 

 segregation in F2 generation. Hybrids between plants with stipulate 

 and those with exstipulate leaves exhibit a mosaic character, for some 

 leaves have stipules and others none ; the occurrence of segregation of 

 this character in F2 is not yet proven. 



In the hybridisation >S'. multinervis x S. gracilistyla the so-called 

 0-type and the il/-type offspring, differing in catkin character, appear 

 in Fy. This phenomenon has not yet been explained beyond all doubt, 

 and various hypotheses have been proposed for it. Of the latter the most 

 probable is that which supposes that either one of the parents (or both) 

 is heterozygous in some invisible factors; the offspring derived from the 

 hybridisation under consideration will then carry them in different 

 combinations, and this genotypic difference will influence the factors 

 concerning the catkin character, so as to give rise in some cases to the 

 G^-type, and in others to ilf-type. Thus the appearance of the two 

 types of catkins in F^ is not due to the segregation of the catkin factors 

 themselves, for all F^ plants will agree in carrying the latter in the 

 same heterozygous condition. Their real segregation was found to take 

 place first in F^) the peculiar mode of this latter process has been 

 explained on the basis of the hypothesis adopted in the case of F^ 

 plants. 



The segregation of many allelomorphic characters has thus been 

 conclusively proven, but in every case the proportion of individuals 

 bearing each antagonistic character is very different from 3:1, 15:1, 

 63 : 1, etc. etc., usually seen in Mendelian hybrids. It would not how- 

 ever be surprising that I was unable to demonstrate the usual Mendelian 

 ratios in >SfaZiic-hybrids, because neither Lotsy' nor Wichler^ was able to 



^ Zeits. f. ind. Ahstammungs- und Vererbungslehi-e, Bd viii. 1912, pp. 325 — 333; 

 IV ^ Conference Internationale de Genetique, 1913, pp. 416 — 428. 



^ Zeits. f. ind. Ahstammungs- und Vererbuvgslehre, Bd x. 1913, pp. 175 — 232. 



