Abstract
The propagation of sweet potato just after its introduction into Japan was mainly carried on the plant-setting method and this method was gradually adopted with the progress of the technics of nursery bed preparation. Thus the sweet potato propagated by transplanting, and the small tuber-setting method which was being tried in dome places remained unnoticed by the majority though it seemed to be very effective. The writers had found out new method of sweet potato culture, namely, small tuber-setting cultivation with increased yield of fleshy roots preventing the setting-tuber from getting fleshy by exposing it to the light after its sprout. In this experiment the authors tried to clarify the mechanism about inhibition of setting-tuber's getting fleshy by its exposure. Main factors effecting growth in flesh of setting-tuber are temperature, light, and humidity in the ground. In this experiment, temperature and humidity were not immediate causes, but light was most effective for the refleshiness of the setting-tuber. The authors, therefore, conjecture that the cause of inhibition of setting-tuber growth is the radiation of light around it.
