Studios on the Photoperiodism with Special Reference to the Physiological Distinction between the Spring and Winter Typos in Wheat and Barley

[摘要] The present paper contains the reports on the author's experiments which were carried out from 1931 to 1934, in order to know the photoperiodic responses of wheat and barley, with special reference to the physiological distinctions between the spring and winter varieties. On Nov. 2, 1931, seeds of each two varieties of wheat and barley were sown in pots, and plants of these varieties at various stages of their growth were brought under the lengthened light period (24-hour day) for different lengths of time. In one of the wheat varieties and in both of the barley varieties, a long light period at the earlier stage of developm nt was found to retard the transition of the vegetative growth stage to the reproductive one, whileas at the later stage, the development was accelerated under the same long-day condition. In the next year 85 varieties of wheat and barley were sown in pots and immediately after their emergence, they were grown under 24-hour day for a month. An interesting fact observed was that the plants in which the development was retarded, were all of winter types amounting to 35 per cent in number of the varieties investigated. At the later stage, however, they were all forced into the reproductive stage under the same daily light condition. Therefore, when they were grown under the long daily light period continuously from emergence until heading, the hastening effect was less marked than in the case when they were brought under the long day about a month later. In the spring varieties, however, the development was accelerated at every stage. The fact that the photoperiodic response in the winter varieties is less pronounced than that in the spring ones, may be attributed to the cancelling action of the two contrary effects of the long light period at the earlier and the later stages of growth. On Apr. 6, 1932, seeds of wheat variety Akagawa'aka, a typical winter one were sown in pots and during the first 20 and 40 days after emergence they were grown under different day-length conditions. The plant with 8-hour day for the first 20 days came into heading on July 29, and the plant with the same short daily light period for 40 days headed a week earlier than the former, while both the control plant and the one with 24-hour illumination for these days, failed to head. It may be therefore concluded, that the failure by spring sowing of winter cereals to head may be attributed to the excessive length of daylight period for their seedling growth. The extent to which the wheat and barley plants can produce heads normally by delaying the date of spring sowing, differs for different varieties ; the spring types having the capacity to head even in the latest sowing, whereas the winter ones failing in the earlier one. Between these two extreme types there are many intermediate ones as to the extent or the limit of capacity in normal production of head by spring sowing ; i. e. there are many grades of spring sowing habit between a typical spring and an extreme winter types. In order to complete the plant development most rapidly, the optimum day length for the young seedlings of these cereals is different for different varieties. According to the results of the spring sowing experiment with 17 wheat varieties of various grades, it was 8-hours for the winter types, 24-hours for the spring ones and the natural length of day (ca. 13 hours) for the intermediate ones. In the older stage of development, however, the long daily light period forced the plant into the reproductive stage without regard to the grades of spring habit. Ther esults of the experiment in which each two varieties of wheat and barley were sown in the fa'l of 1931, showed that the short daily light period at the earlier stage of growth has no appreciable effect on the development of plants. However, four or five months after emergence, there was found a stage that was especially responsive to the retarding effect of the short day length. It can be concluded, from

[学科分类] 农业科学（综合）