Abstract
1. In Kagoshima Prefectural Agricultural Experiment Station, 38 varieties of Paddy Rice were sown on July 5, 1958, and the sunshine was limited by victorial lawn. By this treatment daily maximum temperature was about 4°C lower than natural temperature and the heading of many varieties was accelerated. From this result it is distinct that the heading of rice is restrained under the natural condition in the warm districts as Kagoshima. 2. When the varieties were sown every month from March to July, the later was the date of seeding, the shorter was the period from seeding to heading. But in some varieties, the number of days from seeding to heading increased conversely in the June seeding in comparison with the May seeding in spite of the temperature of growing period was higher. And these reversals of number of days from seeding to heading were more remarkable in the green house than in the field, and in Oshima (locates in Km south of Kagoshima) than in Kagoshima. The varieties that showed the reversal of the number of days are not sensible to short day, and on the other hand, the difference of photoperiod between the growing peiod of May seeding and that of July seedig is very small. From these reasons it is conceivable that the high temperature and sensibility to high temperature are responsible for the reversal of the length of growth period. In these varieties whose heading time was accelerated by limiting sunshine, and number of days from seeding to heading was prolonged in the warmost growing time, the heading time of plant sown on July 1st was delayed by 4 to 10 days in the green house than in the field. From these results it is clear that these varieties are commonly sensible to high temperature. On the contry, when the varieties insensible to high temperature were sown on July 1st the heading time both in green house and in field was the same. These facts indicate the existence of the "excessive high temperature to their heading". 3. The delay of the heading time by high temperature mainly depend upon the delay of the time of differentiation of panicle primordium. 4. In the green house the time of differentiation of panicle primordium delayed more than two weeks as compared with the plants in the field, but the speed of leaf emergence was equal in both conditions. So the speed of leaf emergence and the advance of the inner condition to the differentiation of panicle primordium are greatly different in the sensibility to high tmperature. The whole number of leaves are decided by the mutual relation between the speed of leaf emergence and the length of periods from germination to the differentiation of panicle primordium, and they are considered to react separately to the environments.
