ALLELOMORPHIC RELATIONSHIPS IN MEN DELI SM 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 maternal parent. The maternal type 

 of grains is always produced in such reciprocal crosses. Following up 

 this experiment, when F\ corneous grains of the cross corneous 9 X 

 floury cf 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 cf when grown and selfed likewise pro- 

 duce ears showing distinct segregation into 1 flinty : 1 floury. Evidently 

 the FI 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 /, the zygote of a flinty corn is FF, but the endosperm 

 connected with it is FFF. Correspondingly for the floury race the zygote 

 is //, and its endosperm ///. In the fertilization of flinty by floury corn, 

 the egg nucleus proper, the genetic constitution of which is F, is fertil- 

 ized by an / 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, FF, 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 /. 

 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 // with a pollen 

 nucleus bearing the factor F. It, therefore, has the genetic constitution 

 ffF and it is floury because the two doses of / determine the phenotypic 

 expression to the exclusion of the single dose of F. In F z the hybrid 

 flinty grains from the cross flinty 9 X floury cf give exactly the same 

 results as the hybrid floury grains from the cross floury 9 X flinty d". 

 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 



