Abstract: Embryo sac development in Phaius tankervilliae(Aiton)Bl.was observed under transmission electron microscope.Three phases of functional megaspore and two phases of mature embryo sac were captured in this study.At the functional megaspore and 4-nucleate embryo sac stages,plasmodesmata were present between nucellar cells and embryo sac at the chalazal end.Plasmodesmata are cellular communicating junctions that link adjacent cells to form symplast of a plant.They provide a direct channel for material transport and signal transduction,therefore megagametogenesis is not at an absolutely insulated situation.A big vacuole was observed at the early stage of functional megaspore before it disappeared during the first mitotic division.However,many small vacuoles appeared at the interspaces of separating chromosomes.Distinct vacuoles were also observed in the synergid cells and egg cell during the early stage of mature embryo sac,but vanished when synergid cells degenerated.The change of vacuoles probably resulted from the cell physiological change.Our results may provide insights into reproductive biology of Phaius tankervilliae.