Abstract
In the fifth paper of this series, we demonstrated that the most sensitive stage to coolness is at the young microspore stage6). At the same time we also suggested the existence of a secondary sensitive stage before the beginning of meiotic division. For precisely estimating the sensitive stage to coolness in the present study, the same procedures in the previous study were adopted as follows : (1) group uniform panicles belonging to every 1cm range in article distance, (2) estimate the pollen developmental stage at every location of the four (second to fifth) spikelets at the cooling time, and (3) compare the pollen developmental, stage with fertility at the respective locations of spikelets. The trough of the secondary sensitive stage is observed in all the four tested locations of spikelets, though it is not so deep as that of the primary sensitive stage. The critical stage corresponds to just before and at the early leptotene stage.
