190 Ikeno. — On Hybridization of some Species of Salix. IT. 
some cases. Thus, for instance, in Bryonia dioica Bitter has obtained 
nine parthenogenetic plants, all of which were male. 1 In Thalictrum 
fnrpurascens the sex of the progeny due to this process is not specially 
mentioned. 2 In Antennaria alpina males are very rare, and partheno- 
genesis seems to be chiefly thelytokous. 3 In Char a crinita , known long 
since as the classical example of natural parthenogenesis in plants, Ernst 4 
has recently discovered that there are two strains : in one, which re- 
produces itself by normal fertilization, males and females are produced 
in almost equal number, whilst in the other, which reproduces itself by 
parthenogenesis, plants are exclusively female, i. e. parenthogenesis is thely- 
tokous. Since in our Salix species our repeated observations have proved 
that even in the case of normal fertilization females are much superior in 
number to males, the fact above enunciated, that all fifty offspring are 
female, might be due simply to the latter circumstance, inasmuch as had we 
had more than fifty plants it would have been possible that some male 
offspring might have been obtained. If, however, parthenogenesis in our 
Salix should prove really to be thelytokous, the fact is easily compre- 
hensible, whether the female is homozygous or heterozygous in respect 
to the sex-determining factors ; because, since in our case egg-cells are 
supposed to develop without undergoing any reducing division of chromo- 
somes, they will remain always in the state of the so-called female-producing 
ones,' JW in the first case and WZ in the second according to the well- 
known nomenclature of Morgan. 
IV. Summary. 
1. By pollination of Salix mnltinervis by S. gracilistyla we get 
hybrids, as well as nndtinervis exactly similar to the mother-plant. 
2. Two kinds of hybrids appear in F v The one characterized by 
its densely hairy catkin is called G-type ; the other characterized by its 
less hairy catkin is called M-type , and is produced in much less number 
than the other (for instance, 37 per cent, against 83 per cent, in 
round numbers). Though the two differ externally they are genetically 
equivalent. 
3. From the study of various crosses we are led to the conclusion that 
the hairy catkin of gracilistyla is dominant as a rule to the less hairy 
one of mnltinervis. If we represent them by D and R respectively 
the F x progeny agree in being DR. 
4. That in F x some DR individuals are G-type and others M-type 
is due to the imperfection of dominance : in a few cases dominance fails, 
1 Abhandl. d. Naturwiss. Yereins zu Bremen, Bd. xviii, Heft i, 1904. Original not seen. 
2 Overton, 1 . c. 
3 Juel : Kongl. Svenska Vetenskaps Akademiens Handlingar, Bd. xxxiii, 1900, p. 11. 
4 Bastardierung als Ursache der Apogamie im Pflanzenreich, Jena, 1918. Cf. especially 
chapter iii, pp. 49 ff. 
