Abstract
1. Cytological studies on tbe sterility of rice plants irrigated with cool water have been conductcd in Kamikawa Rice Breeding Inttitute of Hokkaido Agricultural Experiment Station during these two years in order to make clear the cause of their sterilities. 2. Sterilities were far more higher in the treated plants than those in normai conditions, and abnormalities found to occur in their pollen formation were to follow: 3. The rate of microsporogenetic development was significantly retarded in the treated plants which possibly being the cause effecting in inmature pollen at the anthesis. 4. Various abnormalities in the behavior of pollen mother-cells were also found. i. e. asynapsis, lagging and non-orientation of dividing chromosomes, failure of meiotic cytokinesis, and the abnormal hypertropy of tapetal cells. 5. Such abnormalities appeared to be of the same nature to those occuring under low air-temperatures as having been detdcted in our laboratory.
