In the previous paper (SAKAI, 193-a) the writer has reported that cytokinesis is entirely inhibited in rice by exposing the pollen mother cells to low temperature below 15°C. The writer's further investigations revealed that the same phenomenon as above mentioned has also taken place in embryosac mother cells. Following to the absence of the cell-wall formation during the macrosporogenesis, micropylar and chalazal cells fail to differentiate, the multinucleate macrospore being formed. Then it degenerates and becornes impossible to develop into the functional embryosac cf. Figs. 1-8). Frequencies of appearance of such abnonrmal macrospores which were calculated in the experiment of 1937 are given in Table 1. Diurnal periodicity of cytokinesis in micro-and macrosporogenesis was investigated (Tables 2 add 3). Occurrence of cytokinesis is 0.46 by day (8 AM to 5 PM) and O.54 by night (8 PM to 5 AM) in the next morning) in pollen mother cells and 0.54: 0.46 in the case of embryosack mother cells. According to the writer's experiment (SAKAI 1937b), it was evident that the formation of the abortive pollen grains and the decrease of fertility occur in plants when they are exposed to such a Iow temperature as above mentioned, at the stage of meiosis of the pollen mother cell. The facts presented above seem to give a possible interpretation for the occurrence of the decrease in fertility of rice in Hokkaido where the harmful low temperature attack on rice-plants not infrequently during the season of its culture, accompanying their reduction of yields.