Paddy rice plants, variety Norin No. 29, cultured under various light intensities and levels of nitrogen were examined for sterility. The results obtained are summarized as follows: 1) The occurrence of sterility increased, associated with an increase in the level of nitrogen and a decrease in the light intensity during a month prior to heading. 2) A negative correlation was consistently observed between the occurrence of sterility and number of pollens on a stigma counted about 1.5 hours after flowering. 3) It was observed that the sterility under high levels of nitrogen and low light intensities was caused by inhibition of pollination resulted from incomplete dehiscing of anthers and abnormal behaviour of filament at the time of flowering.
