Ikeno.—On Hybridization of some Species of Salix. II. 1 8 1 
If we compare the results shown in Tables III, IV, and V, we see that 
the deviations from the expectation are very similar to each other (5*6 per 
cent., 6*3 per cent., 6-2 per cent, respectively), which will indicate that the 
degree of failure of dominance is nearly the same in all three cases. In F 1 
generation, however, where the theoretical expectation is too per cent, 
dominants and no recessives, the deviation, i. e. the failure of dominance, 
is 1 6*7 per cent, (see Table II), and consequently much larger than in the 
above three cases. To what cause may such a difference be ascribed ? We 
may make several suppositions. Thus, for instance, in the crosses shown 
in Tables III-V one or both parents are heterozygous, i. e. DR , whilst 
in the cross in Table II both are homozygous ; may not such a circumstance 
lead to the difference in the degree of failure of dominance? We may 
perhaps put forward another consideration : Does not that degree vary 
under the influence of external conditions ? Such questions and all others 
which one may ask are naturally not to be definitely decided without 
further breeding experiments, and I must here be satisfied with simply 
indicating such problems. 
A few words as to the dominance of the gracilistyla catkin. We have 
seen that the hairy condition of catkins of the latter is dominant to the less 
hairy condition of multinervis as a rule. I have observed that in multi- 
nervis xgracilistyla the non-hairiness of leaves is dominant to their hairiness 
(1. c., p. 38), which is consequently very different from what we see in the 
catkins in the same hybrid. Evidently the genetic factors concerning hairs 
covering leaves on one hand and those covering catkins on the other must 
be quite different. 
4. Potency. 
As we can easily see by comparing the results of the various crosses 
above enunciated, the degree of failure of dominance is not the same in 
G-type as in M-type. The question is, Do the G-type plants produce 
a larger proportion of G-type progeny than the M-type ones, and vice 
versa ? Is the degree of ‘ potency ’ (to use the word and the expression 
adopted by Davenport *) inherited ? 
Let us first see what other authors have observed in this respect. In 
their experiment on the crossing between extra toes and normal ones 
in poultry, where the former are dominant to the latter, Bateson and 
r • 
1 Carnegie Institution of Washington Publication, No. 121, 1909. The author says (p. 92), 
‘The potency of a character may be defined as the capacity of its germinal determiner to complete 
its entire ontogeny. If we think of every character as being represented in the germ by a determiner, 
then we must recognize the fact that this determiner may sometimes develop fully, sometimes 
imperfectly, and sometimes not at all. . . . Potency is variable. Even in a pure strain a determiner 
does not always develop fully. . . . But in a heterozygote potency is usually more or less reduced. 
When the reduction is slight, dominance is nearly complete ; but when the reduction is great, 
dominance is more or less incomplete. . . .’ 
