Abstract
The authors intended to examine how the environmental factors affect the seed developmcnt of soybean, and more-over how the influence varv according to varietal diffcrences. Soy-bean varieties used were Kizaya(IIa), Norin No. 2(IIb) and lwate No. 2 (IIc). In natural condition, the ripening period of Kizaya, Norin No. 2 and lwate No. 2 was 48, 66 and 87 days, respectively. By the microscopic observation, it was ascertained that the speed of embryo development was slower in the order of Kizaya, Norin No. 2 and Iwate No. 2. For example, the date of cotyledon emergence was about the 10 th, 15th and 25th day from blooming, respcctively. Under short-day condition, the ripening period was shortened and the degree of shortening was larger in the order of Kizaya, Norin No. 2 and Iwate No. 2. From the the microscopic observation, it was found that there were two stages which were easily affected by short-day condition. The first one was the early period of ripening or the early stage of embryo development, that is from proembryo developmental stage II to first simple leaf deveiopmental stage III, and the second one was the late period of ripening from sccd-length maximum to wholly ripening. in which stock nourishment accumulated in cotyledon. High temperature also hastened seed ripening but the effect of temperature was less than short-day. The elongation of seed- and pod-length was also accelerated by short-day and high temperature, and as a whole, the degree of acceleration was larger in the order of Kizaya, Norin No. 9 and Iwate No. 2.
