On the mode of Inheritance of certain Characters etc. 299 
(2) All the pollen grains of such strains appear to carry doub- 
leness: that is to say, in these strains the distribution of the factors 
for singleness (X and Y) is limited to the gametes of one sex. 
(3) The ovules in every individual belonging to these strains are 
mixed, the proportion of those carrying singleness and doubleness is 
presumably the same as the proportion of singles and doubles among 
the offspring, since the pollen is uniform. 
(4) The proportion of 7+x single to 9— x double is most easily 
explained on the supposition (I) that two factors at least are con- 
cerned (X and Y), (2) that the zygote is heterozygous in regard to 
both, and (3) that in the case of the ovules these factors show 
partial coupling of the kind with which we are already familiar in 
the Sweet Pea(!). Though, however the scheme of coupling is based 
on the same principle in the two cases, there is in the Stocks an 
additional complexity owing to the limitation of the power of carrying 
these factors to the gametes of the female sex. 
(5) The scheme of coupling is such that the combinations of the 
allelomorphs XxYy carried by almost all the ovules in an eversporting 
individual are the combinations borne respectively by the male and 
female germs which united to produce that individual; the rarer 
terms in the series are those which represent recombinations of these 
factors, one factor in the recombination being derived from the male 
parent, the other from the female. The number of gametes required 
to exhibit the whole series being taken as 2n, we may represent the 
gametic series in the eversporting forms in general terms thus: 
Ovules Pollen 
n-ı XY all xy 
I Xy 
T xy. 
n-I xy 
where XY represent factors required for singleness, and where the 
zygote has arisen from the union of an XY ovule with an xy pollen 
grain. 
(6) White plastids result from the presence of a factor (W), cream 
plastids from absence of the same factor (w). 
(7) Pure white and cream races are homozygous in W and w 
respectively, but the sulphur-white race is heterozygous in regard to 
this factor which is present in some only of the ovules, and absent 
(1) See Bateson and Punnett, Proc. Roy. Soc. Series B. Vol. 84, p. 3; also Re- 
ports to the Evolution Committee of the Royal Society, Rep. III p. 9, Rep. IV p. 3. 
20* 
