Abstract: Ultrastructural and cytochemical methods were used to study egg development of the liverwort Marchantia polymorpha L.Egg development of M.polymorpha was divided into young egg,middle egg,and mature egg stages.Well-developed plasmodesmata existed between the egg,the ventral canal and the neck canal cells in the young egg stage.However,the plasmodesmata between the egg and the ventral canal cells degenerated soon after the egg was formed.At this stage,the egg cell contained numerous transparent vesicles distributed evenly in the cytoplasm.In the middle egg stage,lipid bodies were found in the vesicles of the cytoplasm.The ventral canal cell degenerated obviously.Mucilaginous materials accumulated in the vesicles and resembled that in the chamber around the egg.The mucilaginous materials showed a PAS positive reaction and were most likely polysaccharide.In the mature stage of the egg,the ventral canal cell and the neck canal cell degenerated completely.A layer of mucilaginous polysaccharide encompassed the matured egg.The nucleus showed an irregular profile and apparent nuclear evaginations were produced.The nucleus appeared to show blebbing,because a numerous small vesicles occurred close the nucleus.The lipid bodies formed clusters around the nucleus,while other organelles were indistinguishable.During egg development,the plastids possessed no starch granules;the mitochondria degenerated,while and the Golgi bodies became more abundant.The features of the egg development of M.polymorpha were different from those in pteridophytes.