Abstract
1) Both in the early (from late March to middle of August) and the late cropping (from middle of July to late October), the "number of days from seeding to heading (D. H.)" of the seedlings detained in the nursery bed including the early and late varieties were same with the thin or dense seeding despite of the delay of the speed of leaf appearing or the diminishing of the numbers of leaves in the dense seeding. On the other hand the so-called short-day varieties differentiated the young ears under the comparatively long day-length (13∼14 hours) both in the early and late croppings. From these results it is conceivable that the (D. H.) of rice under the natural day-length is mainly affected by temperature and that when the effects of temperature are amounted to some definites the heading is taken place, so that the "accumulated temperature (A. T.)" is concerned. 2) The (A. T.) from seeding to heading was larger in the early cropping than in the late cropping in all varieties. From this ahd the results of above, the ideas of the "uneffective temperature (x)" and the "quantity of the effective temperature (y)" are notable. From these ideas the author calculated (x) and (y) as follows. (D. H)=y/Average temperature of everyday-x………(1) y={(A. T.) in the early cropping}-{(D. H.) in the early cropping}×(x)…………(2) y={A. T.) in the late cropping}-{(D. H.) in the late cropping}×(x)…………(3) The data from these calculations reveal that the (x) is smaller in the early varieties than the late varieties and the (y) is varied according to the varieties. 3) Moreover the existence of the supra-maximum temperature was conceivable from other results.
