i8o Ikeno. — On Hybridization of some Species of Salix. II. 
In respect to the back-cross DR x R we have to distinguish between 
two cases, viz. G-type x multinervis and M-type x multinervis. They were 
carried on in 1918, and the results as studied in 1920 and 1921 are as 
follows : 
Table IV. 
No. and Nature of Experiment. 
G-type. 
Progeny. 
M-type. 
Totals. 
4. (G-type 5 x multinervis (g) ... 
125 
88 
213 
5 * (M-type <j> x ,, ,,)... 
H 
9 1 
105 
Totals 
139 
179 
318 
% 
43-7 
56-3 
Deviation from 50 % : 50 % expectation 
-6.3 
+ 6.3 
Since the segregation occurs according to 3 : 1 fashion, we expect 
to have in DR x R 50 per cent. G-types and 50 per cent. M-types. 
Actually we have 43*7 per cent, of the former and 56-3 per cent, of the 
latter. The deviation is therefore + 6*3, and is positive on the side of the 
M-type, just as was the case in F 2 (see Table III) ; this is evidently to be 
ascribed to the fact that in certain cases the usual dominance fails, i. e. — 
DR x RR = (50 — 6*3) per cent. DR + 6*3 per cent. (DR) + 50 per cent. 
RR =43*7 per cent. G-type + (6*3 + 50) per cent. M-type = 43*7 per cent. 
G-type 4* 56*3 per cent. M-type. 
(DR) denotes, as before, the zygotes where dominance fails. 
In the back-cross DR x D we have to distinguish between G-type x 
gracilistyla and M-type xgracilistyla. These crosses were performed in 1919.. 
and the results as studied in 1921 are as follows : 
Table V. 
No. and Nature of Experiment. 
G-type. 
Progeny. 
M-type. New type. 
Totals. 
6. (G-type £ y. gracilistyla og) . . . 
184 
8 
192 
7. (M-type $x „ 
76 
9 11 
96 
Totals 
260 
17 11 
288 
% 
93-8 
6-2 
Deviation from 100 % : 0% expectation 
-6.2 
+ 6-2 
In the above table the new type is not taken into consideration for 
counting the percentage. 
Since the above crosses correspond to DR x D we expect to have 
100 per cent. G-types and no M-types at all. Actually we have 6* 2 
per cent, of the latter, so that the deviation from the theoretical expectation 
is +6*2, which is again positive on the side of M-type, i. e. — 
DR x DD — 50 per cent. DD + (50 — 6*2) per cent. DR + 6 * 2 per cent. 
(DR) = 93*8 per cent. G-type 4-6*2 per cent. M-type. 
(DR) — zygotes where dominance fails. 
