A. D. Darbishire. 
242 
part which it plays in the interpretation of sex-inheritance and also 
because familiarity with it is necessary for an understanding of an 
experiment which I shall now proceed to describe. 
We have spoken a great deal about the characters of an 
organism being determined not by the somatic characters of its 
parents and ancestors, but by the potentialities existent in the two 
germ-cells which give rise to it; but we still speak loosely of “ mating 
two individuals”; and it is very important that we should make our 
conception as to what we mean by such a statement perfectly clear. 
Now if it is really the case that the characters of a zygote are 
determined solely by the potentialities existent in the gametes which 
by their union give rise to it, the characters of the parents which 
produce these gametes should be immaterial; and if we were to 
isolate a green gamete and a yellow one and allow them to conjugate 
the result should be the same as the result of the union of a green 
gamete borne by a green Pea and a yellow one borne by a yellow 
Pea. It is not possible to do this; but it is possible to do what is 
far more striking, and that is to witness the result of the union of 
a gamete bearing the D character with one bearing the R character, 
when both gametes are produced by parents exhibiting the D 
characters. 
This I have effected, not with the pair of characters yellow and 
green in the cotyledons of Pisnin, but with another character of 
the cotyledons, namely their shape. This pair of characters was, as 
is well known, the first on the list of seven characters with which 
Mendel himself dealt in his classical experiments. The two 
characters are round and wrinkled, of which round is dominant, 
wrinkled recessive; segregation occurs, so far as the evidence goes, 
according to exactly the same scheme as that to which the cotyledon 
colour-characters conform. 
When we cross a round with a wrinkled Pea we are of course 
merely bringing together a gamete bearing the factor for roundness 
and one bearing the factor for wrinkledness. But because we 
invariably do this by transferring pollen from a plant whose first 
two leaves, or cotyledons, were round, to the pistil of one whose 
cotyledons were wrinkled (or vice versa), we are apt to slide 
unconsciously into the belief that the characters of the actual 
parents have something to do with the result. Now in the mating 
which I am about to describe, the round gamete was borne by a 
plant whose cotyledons were round ( i.e ., by a round zygote), and so 
also was the wrinkled gamete ; only, of course, the round zygote in 
