Abstract
In order to compare Oryza species regarding the pattern of secondary association in meiosis, PMC's of O. sativa, O. sativa f. spontanea, O. glaberrima, O. breviligulata, O. officinalis, O. australiensis, O. brachyantha, O. ridleyi and O. subulata were observed. Of these species, O. ridleyi is allotetraploid (n=24), while the rest are diploid (n=12). The results may be summarized as follows: 1) All diploid species showed the same type of maximum secondary association, 2(3)+3(2). Also in the mean number of secondary associations per cell, they showed no significant difference. 2) The pattern of secondary association in O. ridleyi could be accounted for on the same basis as for the diploid species. The frequency distribution of cells with different numbers of secondary associations did not fit the Poisson distribution, in the same manner as formerly pointed out by the writer for O. sativa and O. glaberrima. 3) It was concluded that these facts would be in favor of the hypothesis of secondary polyploidy of Oryza, and the doubling of genetic materials in remote ancestry might have played an important role in the evolution of the genus.
