Morphological and Physiological Studies on Occurrence of Abortive Seeds in Leguminous Forage Crops : III. Formation of one-seeded pod in sweet clover

Abstract

Usually the pod of sweet clover, when matured, contains only one seed, while the ovary at its young stage involves several ovules, ranging 2-5. In this experiment, some embryological observations were carried out, using four-ovuled ovaries, on the process of above-mentioned one seed formation and abortion, and the results obtained were summarized as follows : (1) The abortion of ovules is partially due to fertilization failure. Namely, 27.0 % of ovules observed were not fertilized. Out of them ; 22.0 % were abnormal ovules in which the embryo-sac was not normally formed, and the remained 5.0 % were normal but non-fertilized ovules. Therefore, the main cause for non-fertilization is owing to embryo-sac failure. (2) When the ovaries are classified by numbers of fertilized ovules involved, 12.0 % of them contained only one fertilized ovule and these ovaries should grow into one-seeded pods. The remained 88.0 % were the ovaries consisting of more than two fertilized ovules, especially, 38.0 % were the ovaries in which all ovules were fertilized. Nevertheless, when observed on the 10th day after pollination, 97.4 % were the ovaries in which more than two fertilized ovules never developed evenly and all but one were arrested their growth, and consequently they grew into one-seeded pods. (3) The degeneration of fertilized ovules began from about 5th day after pollination, and one-seeded pods were confirmed on about 7th day. (4) As to the position of normal seeds in the pods, there was a marked tendency that the seed-setting increased from the stylar (apical) end toward the basal end of the ovary. So far as this experiment is concerned, 85.7 % were the pods in which either basal or subsequent ovule developed into normal seed.