Ikeno . — On Hybridization of some Species of Salix. II. 19 1 
and the recessive character appears externally, giving rise to M -types. 
The appearance of two types in F\ is not to be regarded as Mendel ian 
segregation. 
5. The segregation occurs first in F 2 as usual. The F 2 generation 
resulting from the cross between the P\ progeny is variously composed : 
G-type ? x G-type cF produces chiefly G-types and a few M-types, 
M-type ? x M-type cF chiefly M-types and a few G-types, M-type ? x 
G-type cF both types in almost equal number. 
6. If we add the results of the above three crosses together we find that 
we have G-types and M-types in the approximate proportion of 3:1, 
with a certain positive deviation on the side of the latter type : this 
deviation is due to the imperfection of dominance of the factor D in 
relation to the factor R. 
7. The above conclusion has been fully confirmed by the results of 
back-crosses, either DR x R or DR x D. 
8. The degree of potency is inherited: i.e. G-type plants produce 
a much larger proportion of G-type progeny than do M-type plants, 
and vice versa. 
9. Rarely multinervis x gracilistyla gives rise to nmltinervis progeny 
which breed true in later generation. Their production from a imdtinervis 
mother without any pollination at all has been also observed, though 
very rarely. Whether the embryo formation from nucellar cells or par- 
thenogenesis is the real cause of such 4 apomictic * development is not 
definitely established. 
10. We have here to deal with parthenogenesis, which is very 
occasionally autonomous ; in many other cases, however, it seems possible 
that it is induced by the stimulating action of foreign pollen (pseudogamy). 
11. If parthenogenesis is derived phylogenetically from normal fer- 
tilization, and if this transition is gradual, our Salix multinervis may 
perhaps be regarded as being in the way of such transition, and in its very 
beginning. 
12. Neither abortion of pollen nor decline of sexuality is to be 
detected in our Salix , which contradicts the view often expressed that 
parthenogenesis sets in in consequence of such circumstances. 
13. All plants of imdtinervis produced by apomixis are female, with- 
out any exception. The explanation for it is given. 
All expenses needed for carrying out the experiments contained in 
this paper were partly defrayed out of grants from the Department of 
Education and the ‘Keimeikwai’ (a society whose object is to give 
pecuniary assistance to scientific investigators, &c., &c.) in Tokyo. 
