Abstract
1. The number of differentiated spikelets is firstly affected by the amount of nitrogen absorbed by the time of late spikelet differentiation and secondly by the amount of carbohydrates produced during the period from the neck-node differentiation stage to the late spikelet differentiation stage. 2. The number of degenerated spikelets is found to be determined by the interrelationship between the number of differentiated spikelets and the amount of carbohydrates produced during the period from the late spikelet differentiation stage to the heading stage. The amount of nitrogen in leaf-blades during the period of determining the number of degenerated spikelets has no immediate effect, but has a mediate effect on determining the number of degenerated spikelets by influencing the rate of carbon assimilation. 3. Both the number of differentiated spikelets and the number of degenerated spikelets have nothing to do with the amount of carbohydrates accumulated in the rice plant. 4. It has already been pointed out by the other research workers that the nitrogen content in leaf-blades is strongly correlated with the number of spikelets per panicle, and also the weight of leaf-blades per hill or the amount of total nitrogen in leaf-blades per hill at the heading stage is closely correlated with the number of spikelets per hill, but it has also been clarified by the present experiments that the above-mentioned facts can hardly be generalized and they hold true only in the following cases:-(1) an identical variety is used and it is sown or transplanted on an identical date, (2) the period of determining the number of panicles is not overlapping with the period of determining the number of spikelets, and (3) the amount of dry-matter increased during the period from the initial stage of reduction division to the heading stage is positively correlated with the amount of nitrogen in leaf-blades at the heading stage.
