Anatomical Observations on the Fertilization and Embryogenesis in Sweet Potato, Ipomoea batatas (L.) Lam.

In order to get information of low seed set generally observed in sweet potato breeding, first of all, some observations on the normal process of fertilization and embryogenesis were made on the specimens collected at different intervals after pollinations from the compatible cross combination (Chikei 682-ll×Kyushu No.58). Approximately 4 hours after pollination, the pollen tube enters into one of the synergids through the micropyle. From 6 to 9 hours after pollination the double fertilizations occur, bringing forth the zygote and the endosperm nucleus. 14 and 10 hours after pollination both the former and the latter begin to show their first mitotic divisions, respectively. Approximately 24 hours after pollination, the zygote is to be differentiated into an apical cell and basal one, and the several endosperm nuclei begin to lie in the peripheral layer of the embryo-sac. 48 hours after pollination, the zygote is to be developed. into the embryo and the suspensor consisting of 8 cells, with the endosperm nuclei lying densely in the peripheral layer of the embryo-sac. 3 to 7 days after pollination, the zygote is to be differentiated into the embryo ball and the suspensor, and the formation of the cell walls surrounding respective endosperm nuclei begins from the micropyle side towards the antipodal one. 10 days after pollination, the zygote reachs heart stage, and the endosperm cells begin to be degenerated at the micropyle side. 13 to 17 days after pollination, a rapid elongation comes to be shown by the cotyledon, with the endosperm cells almost degen-erated.