Abstract
Embryo-sac development and fertilization processes of Japanese persimmon (Diospyros kaki L. f.) cv. Fuyu were histologically investigated to clarify the cause of variations inseed formation among the trees.
1. The embryo-sac was formed after meiotic division of the embryo mother cell about 2 weeks before anthesis. One nucleus in the embryo-sac divided into 8 nuclei and the embryo-sac was completed after the antipodal cell disappeared.
2. Abnormal embryo-sac formation was observed : a) presence of a nucellus but lacking an embryo-sac, b) multiplied embryo-sacs, c) aborted embryo-sacs, and d) embryosacs with more or less than normal 8 nuclei.
3. Pollen tubes reached the micropyles 24 or more hours after pollination, but their numbers were few.
4. Most fertilization of eggs occurred 3 days after anthesis. Without zygote formation embryo-sacs began to degenerate in about 7 days, followed by the inner walls of the nucellus fusing together.
5. On vigorous shoots, meiotic division of the embryo-sac mother cell began earlier and the development of the embryo-sacs was faster than on less vigorous shoots. However, there were no differences in the percentage of abnormal embryo-sacs at anthesis and seed numbers per fruit on shoots of different lengths.
6. The percentage of abnormal embryo-sacs was low in the tree which produced many seeds per fruit and, conversely, it was high in the tree which produced a few seeds per fruit.
We conclude that the variations in seed formation among the trees probably resulted from their difference in the frequency of abnormal embryo-sacs.
