Ultrastructural features during endosperm development of Plantago major L.were viewed and described by means of transmission electron microscope(TEM).The results are as follows:(1)Cellular type endosperm.The primary endosperm nucleus divides into a micropylar and chalazal chamber.The micropylar chamber becomes 8-celled in two tiers by two vertical and a transverse divisions.The four cells in the micropylar tier develop into four micropylar haustoria.The lower four cells develop into endosperm propers.The chalazal chamber develops into a binucleate haustorium by mitosis without division of cytoplasm.(2)The tubular micropylar haustorium penetrates into integument and its micropylar wall has a large amount of ingrowths and a few branches.There are a lot of mitochondria,rough endoplasmic reticulum,golgi bodies and plastids etc.around the ingrowths.The nucleus and nucleolus are obvious and the cytoplasm is dense.The metabolism is exuberant.During the period of global embryo,the micropylar haustorium shows the maximum size and integument around micropylar haustorium is hydrolyzed and resulted in a cavity.Micropylar haustorium absorbs and transforms nutrition from integument to endosperm proper to engage in forming endosperm proper and storing nutrition.At the later stage of global embryo,the micropylar haustorium degenerates gradually.(3)The four original cells of endosperm proper have vigorous meristematic ability,and divide anticlinally and periclinally.The endosperm proper surrounding the embryo is spherical-shaped.The nutrition absorbed by the haustorium and integument tapetum is stored in the endosperm proper.With degeneration of the suspensor,the endosperm proper is hydrolyzed in the period of later global embryo.(3)The two nuclei and nucleoli of chalazal haustorium are large.Mitochondria,plastids,golgi bodies and rough endoplasmic reticulum are located around the nucleus.Chalazal haustorium becomes high vacuolated.Along with the embryo and endosperm proper increasing in size,chalazal haustorium expends towards the chalazal end of the ovule while the chalaza surrounding the chalazal haustorium is hydrolyzed gradually,resulting in a cavity.Chalazal haustorium absorbs and transforms nutrition to the endosperm proper to engage in forming endosperm proper and storing nutrition.During the later period of global embryo,the chalazal haustorium loses its function and degenerates gradually.