Abstract: This paper is the first time to describe the ultrastrueture of milk veleh root nodules because of the plants growing only in our country. The nodules with terminal meristem are morphologieally very similar to those of clover, alfalfa and pea that they are elongated and eylindrieal in shape. According to the anatomical arrangement of the nodules which provides an excellent development gradient of the symbiotic proeess along its length, the nodules were sectioned into three equallengh portions, and the central tissue of middle one was used as exprimental material whieh may show ultrastrueture of mature cells infeeted by rhizobia and have the funetion of nitrogen fixation. Most of the ceils in eentral tissue were infeeted by rhizobia whieh entered the host eells also in a way of in'feet,ion thread. The baeteriods developed from released rhizobia are enclosed by envelope membranes. In general, each envelope membrane packs one baeteriod. The envelope membranes can be extended by fusing themselves with vesieles or small vaeuoles in eytoplasm of host cells, and finally enclose the baeteriods from tight to loose. Both the envelope membranes and the surfaee of baeteriods have protrusions, and some of them touch and fuse together to form a pipe-like canal. The relationship between the kinetic change in envelope membranes and the senescence of baeteroids, as well as the material exehange between baeteroids and host cells are diseussed. It is pointed ont that, the baeteriods loose enclosed by envelope membrane and the existence of electron-empty spaee, possibly represent a mature stage of baeteroid development. The structure of pipe-like canals between baeteroids and envelope membranes of host cells is considered probably to be an expression of material exchange function.

Key words: Root nodule, Beeteroid, Cell structure, Cell interaction