Recent Advances in the Study of Heredity. 243 
the first case was of constitution DD, whilst that of the second was 
DR. The mating was of this nature:— 
DD x DR; giving 50% DD x 50% DR. 
Our interest centres on the DRs produced; and we find that 
the result of their self-fertilization is the production of rounds and 
wrinkleds in the same proportions as those which obtain in the F 2 
resulting from a union between a round gamete borne by a round 
zygote and a wrinkled gamete borne by a wrinkled zygote. 
What makes this case more remarkable is the fact that the 
heterozygote round which bore the gamete with the wrinkled factor 
was not an F, heterozygote, but an F 6 one. That is to say the 
wrinkled zygotes which appeared in normal proportions in the 
• F 2 from the cross in question had no wrinkled individuals in 
their ancestry nearer than the great-great-great-great-great-grand- 
parental generation. 
This particular cross was made without deliberate intention by 
the same pollinations which were designed to effect the cross 
between the pure yellow and the extracted green in F 5 described 
in my last lecture. The F 5 greens used in that experiment had 
been saved from three distinct plants, all of which were of course 
heterozygous in respect of cotyledon colour. With regard to 
cotyledon shape, two happened to be dominant homozygotes the 
other a heterozygote. When I was recording the F 2 from this 
cross (between pure Y and extr. G in F 5 ) I was at first puzzled 
when I found that many of the plants bore wrinkled as well as 
round seeds ; indeed, so far was I from understanding the interest 
of the case that at first I contented myself with recording the fact 
of the plants being heterozygous and did not count the actual 
numbers of rounds and wrinkleds. That the Mendelian interpretation 
of the case which I have suggested is the true one cannot, I think, 
be doubted : for it was found that all the crosses which had given 
wrinkleds in F 2 were made with the heterozygote round referred 
to above. I am aware that it can be urged that there is nothing 
very remarkable in this experiment and that the same thing is 
illustrated equally well, if not better, by the fact that a wrinkled 
zygote is formed by two wr. gametes both of which are borne by 
zygotes, both of which are round, in the mating DR x DR. But 
the ordinary Mendelian cross is so familiar now, that it is difficult 
to illustrate unfamiliar ideas by its means. I give below the 
pedigree (B) of this cross together with that of the cross described 
in my last lecture (A); in both cases the somatic characters of the 
