Abstract
1. Allo-octoploid plants (2n=96, CCCCDDDD) were induced by treating the germinating seeds of allo-tetraploid species, Oryza latifolia DEsv. (2n=48, CCDD) with 0.05% colchicine solution. 2. In the octoploid-latifolia, anther development is delayed and the meiosis in PMCs begins only when the top floret of panicle is just coming out of the flag-1eaf sheath. 3. At MI in PMCs, tetravalent chromosomes ranging from O to 10, on the average 4.11 per PMC are formed, the mode being 2. Trivalent chromosomes are rarely met with, while univalent chromosomes are observed rather frequently, 8 in maximum. Thus, the average number of bivalents per PMC was calculated as 39.19. 4. Octoploid-latifolia gives gigas-type in most characters, showing thick culm, thick and coarse leaves, thick and large auricles. The length of ligules, panicles and awns, and the size of stomata, pollen grains and spikelets increased. Especially the increase of spikelet size is conspicuous, but the number of spikelets per panicle showed a reduction. Under short-day condition it headed about 5 days later than its original species. 5. The seed fertility was low, recording 33 % in selfed condition. The crossability with tetraploid-sativa, however, increased remarkably in comparison with that between undoubled species
