Abstract: The formation and development of the wall of embryo sac, from functional megaspore to mature embryo sac of rice ( Oryza sativa L. ), were studied with transmission electron microscopy. Results showed that the embryo sac wall was derived from the wall of the functional megaspore. Later, it became much thickened mainly due to the piling up of wall remains from the degenerated nucellar cells. Plasmodesmata were frequently observed in the wall near the chalazal pole of the func-tional megaspore. Some of these plasmodesmata persisted through the stage of eight-nucleate embryo sac formation. At the four-nucleate embryo sac stage, wall ingrowths began in the micropyle region. At the eight-nucleate embryo sac stage cells began to form in the embryo sac but the patterns of development of wall ingrowths in these cells were different. In the central cell, wall ingrowth appeared in the region of the embryo sac wall adjacent to the nucellar, cells, especially in the region near the micropyle and the chalaza pole. Wall ingrowths were quite well developed in the wall near the micropyle region and much more well,developed in the mature cell. Ingrowths failed to develop in other parts of the cell wall. In the antipodals, ingrowths developed only in the region of the embryo sac wall adjacent to nucellar cells. Ingrowths were absent in other regions of the wall of the antipodals. In the synergids, only the common wall between the synergids developed wall ingrowths. These wall ingrowths later formed part of the filiform apparatus which could be observed clearly before the embryo sac was obviously enlarged. In the egg cell, ingrowths were limited only in the wall adjacent to the synergids. The reasons and the functional significance of the formation of wall ingrowths in various parts of the embryo sac were discussed.

Key words: Rice, Embryo sac, Wall of embryo sac, Ingrowth, Plasmodesmata