Seed development of Ornithogalum dubium, with special reference to fertilization and the egg apparatus

Abstract

The ovule of Ornithogalum dubium is anatropic, bitegmic and crassinucellate. The integuments are biseriate. Starch grains occur in the outer integument, the funicule and in the intercellular space surrounding the embryo-sac. The embryo-sac development is of the Polygonum type. The synergids are conspicuous and contain a large filiform apparatus. Fertilization is porogamic and occurs 24 h after pollination. The pollen tube enters the egg apparatus in the region of an intercellular space between the micropylar ends of the synergids. Sperm cells in the pollen tube appear to be released through small protuberances of the pollen tube. Migration of the sperm cell to the egg cell is possibly through a gap in the wall between the egg cell and the receptive synergid. Changes in the synergids occur only after a pollen tube has entered the receptive synergid. Changes occurring in the persistent synergid suggest that this cell may be involved in the nutrition of the pro-embryo up to the eight-cell pro-embryo stage. Syngamy is of the post-mitotic type. The first division of the zygote is transverse. The basal cell gives rise to the multicellular suspensor, and the terminal cell to the embryo. The endosperm is of the Helobial type.