On Hybridization of some Species of Salix. II. 
BY 
S. IKENO, F.M.L.S. 
PAGE 
I. Summary of Earlier Results 175 
II. Formation of Hybrids — 
1. General and Generation . . . . .176 
2. F 2 Generation ......... ... 178 
3. Back-crosses ............. 179 
4. Potency . . . . . . .181 
III. Formation of Parental Form 183 
IV. Summary 190 
I. Summary of Earlier Results. 
TZJTRST I will briefly recapitulate here what I have stated in my former 
paper concerning the same subject, 1 in so far as it is related to the 
present communication, because this will conduce much to clearness. 
The hybridizations between two Japanese species of Salix , viz . gracili- 
styla and multinervis, were done in 1910 and 1911. The character which 
sharply distinguishes them is among others the hairy condition of their 
catkin : that of the former is characterized by being densely covered with 
greyish hairs, whilst that of the latter is very sparingly hairy (cf. Ikeno, 1. c., 
PI. I, Figs. 1-2). The cross multinervis xgracilistyla doiie in 1910 has given 
rise to fourteen /q hybrids. The latter were not uniform : eleven were 
provided with catkins densely hairy like gracilistyla (hence called plants of 
G-type ), and three with catkins sparingly hairy like multinervis • (hence 
called plants of M-type ). It is to be noticed that each of the two parents 
was examined in respect to its genetical purity by means of fertilization 
inter se } and found to breed true to its respective type. The fertiliza- 
tion between male and female G-type has given rise in F 2 to many G-types 
and a few M -types, and that between male and female M-type to many 
M-types and a few G-types, while that between male G-type and female 
M-type has produced both types in almost equal number. I have tried to 
explain the formation of two types of progeny in F v despite the apparent 
genetical purity of both parents, by the action of invisible factors. 
1 Journ. of Genetics, 1918, vol. viii, pp. 35-58. 
[Annals of Botany, Vol. XXXVI. No. CXLII. April, 1922.I 
