ALLELOMORPHIC RELATIONSHIPS IN MENDELISM 151 
When a floury corn is pollinated by a flinty corn the grains which 
result show no effect of the flinty pollination, they are floury grains of 
the same character as those of a pure floury race. Similarly when a 
flinty corn is pollinated by a floury corn, the grains are flinty. Again 
they are of the same character as the maternalparent. The maternal type 
of grains is always produced in such reciprocal crosses. Following up 
this experiment, when F, corneous grains of the cross corneous 2 X 
floury o’ are grown and selfed, the ears produced show distinct segre- 
gation into flinty and floury corn in the ratio 1 flinty: 1 floury. F floury 
grains from floury 9 X flinty @ when grown and selfed likewise pro- 
duce ears showing distinct segregation into 1 flinty :1 floury. Evidently 
the F; grains although different phenotypically display the same genetic 
phenomena. 
Cytological research has shown that in the fertilization of maize 
and other plants there is a double fertilization, one fertilization giving 
rise to the embryo and the other to the endosperm. In the case of the 
embryo, an egg nucleus unites with a nucleus from the pollen grain 
and from this fusion the embryo develops. In the fertilization which 
gives rise to the endosperm two nuclei from the female unite with one 
from the male, so that the cells of the endosperm contain 3x chromo- 
somes rather than the duplex number characteristic of the cells of the 
embryo. If the flinty factor be represented by F’, and the contrasted 
factor for floury by f, the zygote of a flinty corn is FF, but the endosperm 
connected with itis FFF. Correspondingly for the floury race the zygote 
is ff, and its endosperm fff. In the fertilization of flinty by floury corn, 
the egg nucleus proper, the genetic constitution of which is F, is fertil- 
ized by anf pollen grain, giving a hybrid zygote of the constitution Ff. 
The endosperm which surrounds this embryo, however, arises from the 
fusion of the two endosperm nuclei, ’F, with a single nucleus from the 
pollen grain, giving a zygote of the constitution FFf. This endosperm 
is flinty because two doses of F are apparently dominant to one dose of f. 
On the other hand, when floury corn is pollinated by flinty, the embryo 
has the same genetic constitution, namely Ff, but the endosperm sur- 
rounding it arose by union of two endosperm nuclei ff with a pollen 
nucleus bearing the factor F. It, therefore, has the genetic constitution 
{fF and it is floury because the two doses of f determine the phenotypic 
expression to the exclusion of the single dose of F. In F»2 the hybrid 
flinty grains from the cross flinty 9 X floury o” give exactly the same 
results as the hybrid floury grains from the cross floury @ X flinty o’. 
Here the ratio is 1 flinty: 1 floury in each case, and half the members 
of each class are heterozygous and will reproduce the same ratios in the 
succeeding generation. 
It would be difficult to conceive of a more beautiful illustration of 
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