Ikeno . — On Hybridization of some ■ Species of Salix . II. 189 
animals, as Rhabditis aberrans (Nematoda) studied by Krueger. 1 Thalic - 
purpurascens as well as certain species of Hieracium , where some 
ovules are parthenogenetic and others normal, may be considered to be 
in their way of this transition. 2 Our multinervis is also to be 
ranked among such transitional forms, and in view of the extreme rarity 
of parthenogenetic ovules, as well as of the fact that parthenogenesis is 
not always autonomous but in many cases induced (considering my sup- 
position above expressed to hold good), we may regard our Salix as being 
in the very beginning of such transition. 
The opinion was expressed by some authors that parthenogenesis 
has taken its origin in consequence of the abortion of pollen and the 
decline of sexuality, while that of others, especially Winkler, is quite op- 
posed to it. 3 Now if such were really the case we should also observe 
such phenomena in our Salix , but we can there recognize neither 
abortion of pollen nor decline of sexuality. For instance, Nohara has 
examined the germinating power of pollen of our Salix by the use of 2-3 
per cent, cane-sugar solution, and found it to be as high as 98 per cent. 4 
I asked him to examine the germinating power of seeds of this Salix 
species, and he found that out of 721 seeds, taken from four catkins arti- 
ficially pollinated by a male plant of the same species, 655 came to 
germination, i. e. 92-2 per cent. The results of these observations are 
obviously decidedly in favour of the opinion of Winkler. 
We come finally to the problem of the sex of our apomictic progeny. 
As before stated, nearly fifty multinervis individuals resulting from the 
experiment in 191 1 were female without any single exception ; so also were 
two multinervis obtained by the pollination done in 1918 (cf. Nos. 26 and 
29 in Table I). The sex of nine midtinervis derived from the pollination 
made in 1939 (Table VII) is yet unknown. In view of the small number of 
the multinervis progeny resulting from the experiment of 1918, we are not 
able to make any inference about them, but the fact that all midtinervis 
offspring derived from the experiment of 1911, numbering almost fifty, are 
female, can hardly be without a certain significance. Before going farther, 
let us see first what we know about the sex of the progeny arising by 
parthenogenesis in animals and plants. In the former it is arrhenotokous 
(males produced exclusively), thelytokous (females produced exclusively), or 
amphiterotokous (both males and females produced) in different, cases. 5 
Concerning a few dioecious plants where natural parthenogenesis has been 
discovered, the sex of the progeny arising by this process is known in 
1 Cf. Winkler, 1 . c., pp. 28 ff. 
2 Certain species of Rubus may also belong to such transitional form. (Cf. Lidforss, Zeits. f. 
indukt. Abstamm.- u. V ererbungslehre , Bd. xii, 1914, pp. 1-13). 
3 Parthenogenesis und Apogamie im Pflanzenreich, pp. 1 33 ff. 
4 Bot. Mag., Tokyo, vol. xxvii,. 1913, p. 185. 
5 Cf. Winkler : Ursache und Verbreitung der Parthenogenesis, p. 15. 
