THE ELECTRON MICROSCOPE OBSERVATIONS ON THE STRUCTURE AND FUNCTION OF THE NUCELLUS IN NITRARIA SIBIRICA PALL.

The crassinuccllate ovules develop very well in Nitraria sibirica Pall. According to the ultrastructural characteristic of the nucellar cell, three kinds of cell layers can be distinguished at the stage of proembryo. They are the inactive periphery cell layers(about 4—5 layers), specialized cell layers (about 1—2 layers), and disintegrated cell layers(about 1—2 layers) near the embryo sac.When the nucellar cells begin to degenerate, their wall disperse first in cellulose microfibril, meanwhile the protoplasm disintegrate gradually. During the cell degenerating, lipid bodies are accumulated in them. As the cell wall facing the embryo sac has disappeared, the nucellar cells become open cells. Their protoplasm are free around the embryo sac. A disconnected area of the embryo sac wall between micropylar and chalazal region is obviously observed under electron microscope. Therefore, the free protoplasm of the nucellar cells can be directly transported into the embryo sac. It is important that the rapidly multipiicate free nuclear endosperm needs a supplement of a lot of nutrient materials in short time.There is an obvious area between the plasm membrane and the wall of central cell in which many paramural bodies are observed. The paramural body is possibly another important nutrient pathway from nucellar cells moving into the embryo sac.