[Certation experiment concerning competition between pollentubes under the influence of the locus Ga in Oenothera].

The material for the experiments were two Oenothera-Hybrids with the complexes (h) hookeri and flavens which were heterozygous for the gametophytic gene ga and for the genes s and de. Certation experiments were done by pollinating the styles of Oe. hookeri sulfurea with different amounts of pollen grains and by interruption of pollen tube growth by cutting off the styles at different times after pollination.There is no correlation between the experimental treatment and the segregation for the two genes in the progeny. The competition between pollen cells with the alleles respectively ga (+) and ga (-) therefore cannot be due to differences in growth rates during the developmental stage of pollen tube-growth in the style but must occur during the germination of the pollen on the stigma or in the last stage of development of the pollen tubes shortly before fertilization. The data reveal great variability of crossing-over in the chromosome-region under investigation.