1. Conspicuous morphological change was observed in rice pollen grains when they were left in the air after shedding.
2. Within a few minutes, a lot of vacuoles appeared around each pollen grain. Inclusion of the vacuoles was exuded from inside of pollen grains, but chemical analysis has not been carried out in the present study.
3. However, a rapid alteration in the physiological condition might have occurred to result in a decrease of germinability of pollen grains. And in part, this has been proved by TTC test.
4. Above described transformation of the pollen grains was characteristically occurred when they were shed sparsely on the slide glass. But when they were scattered densely, there were also observed a few pollen grains which kept the viability for longer time.
5. It was concluded that the rice pollen grains rapidly lost their viability by losing inner substances when they were left in the drought condition in the air. Further study on the physiological and metabolic disturbances in the course of losing viability, will throw light on the problem of longevity in rice pollen grains.