. Contributions from the Laboratory of Plant Genetics. MEXDELIAN FACTORS IN THE GAMETOPHYTE 435 kernels. All ears which had any sugary seeds were classed as segregating. The number of sugary seeds varied on different ears but the number of plants which had no recessive seeds and for that reason would be wrongly classified was probably less than seven percent and was not likely to be enough to disturb the results seriously in view of the wide departure from the normal 1 : 1 ratio obtained. The backcross of pollen from the homo- zygous dominant parent on the heterozygous Fx plants (Susu X SuSu)
. Contributions from the Laboratory of Plant Genetics. MEXDELIAN FACTORS IN THE GAMETOPHYTE 435 kernels. All ears which had any sugary seeds were classed as segregating. The number of sugary seeds varied on different ears but the number of plants which had no recessive seeds and for that reason would be wrongly classified was probably less than seven percent and was not likely to be enough to disturb the results seriously in view of the wide departure from the normal 1 : 1 ratio obtained. The backcross of pollen from the homo- zygous dominant parent on the heterozygous Fx plants (Susu X SuSu) gave 207 segregating and 213 non-segregating individuals. These numbers differ from a 1 : 1 ratio less than the probable error. But the pollen from the heterozygous Fi plants backcrossed on the homozygous dominant parent {SuSu X Susu) gave 88 segregating and 353 non-segregating indi- viduals, a deviation from a 1 : 1 ratio of times the probable error. 'Susu g— susu Rice Pop SuSu-* ,+^^^susu o*— susu. ^ Susu<^^— Selfed— susu Sugary susu-^^ ^^^^"^SuSu <?— Susu SuSu o_— Susu Figure 2. Diagram showing the behavior of the Rice PopXSugary cross when selfed and backcrossed reciprocally with both parents. To sum up, the Fx plants self-fertilized showed a selective action such that more of the gametes carrying the dominant factor united than would be the case in random mating. The heterozygous Fi plants backcrossed with the recessive parent showed no selective action either way the pollin- ations were made. Backcrossed with the dominant parent there was no selective action when the pollen was alike but the pollen from the heter- ozygous F] plants showed a markedly greater pollinating ability on the part of the gametes carrying the dominant factor. These results are shown graphically in figure 2. This series of facts shows that the selective action is not due to differ- ences in the functioning of the pollen alone, although the differe
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