3 2 4 
A. D. Darbishire. 
that this case is not precisely parallel to that which we have 
described in the inheritance of the characters of the seed-coat in 
Pisuin. 
The other answer to the imaginary objection to the suggestion 
that all cases which are now explained on the hypothesis of a single 
pair of characters are really cases of 3 : 9 : 4, the objection that in 
all cases of 3 : 9 : 4 the hybrid is reversionary is contained in the 
following question. Do we know that such a thing as simple 
dominance ever occurs ? Can we be certain that the apparent 
similarity of hybrid and dominant parent is not due to our inability 
to detect the differences between them? In the case of roundness 
and wrinkledness in Peas, the first character on the list of the seven 
with which Mendel dealt, the answer to this question is—no. For 
we now know that although the hybrid round and its round parent 
are indistinguishable to the naked eye, they differ radically from 
one another in two characters. A figure was given in my last 
lecture of the starch grains which distinguish these two types of 
Peas, and I give here a figure of the starch grains of the hybrid 
round. A reference to the figures of the parental types of grain 
will show that those of the round are single and nearly twice as 
long as broad, whilst the grains of the wrinkled Pea are compound 
and almost round, the number of component pieces varying 
between 2 and 8, the commonest number being 6. The grain of 
the hybrid Pea is, as will be seen from the figure given here, 
almost exactly intermediate between its two parental types. Its 
length-breadth index is intermediate; and the compoundness of 
the grains in the aggregate is intermediate. In the first place 
(in the case of the Pea from which the grains figured were taken) 
about half the grains are compound and half single ; and the 
compoundness in those that are compound is intermediate between 
singleness on the one hand and the degree of compoundness 
exhibited by the grains of wrinkled Peas on the other. For whilst in 
these latter the number of component pieces ranges between 2 and 8 
and the commonest is 6; in those of the hybrid Pea the number 
ranges from 2 to 4 and the commonest is 3. Again, mention was 
made in my last lecture of the difference in the absorptive capacity 
in the two types of Pea; the absorptive capacity of the hybrid 
round Pea is very nearly intermediate between that of its two 
parents. It will be remembered that the absorptive capacity of a 
set of round Peas was given as 86%, and that of a set of wrinkled 
ones as 120%. The absorptive capacity of a Pea derived from the 
