Abstract:There were three methods used to introduce the invasion of Rhizobium astragai Huakui and R. sesbania sp. into the roots of barley ( Hordeum vulgare L. ) and rice ( Oryza sativa L. ) with subsequent formation of pseudonodules on their roots. One was to treat rhizobia and plants first with a certain strength of magnetic field, to inoculate rhizobia to plants, and then to culture them togather. Secondly, the rice plants were innoculated with rhizobium cultured medium containing the root extract of rice seedlings. And thirdly, plants were treated with exogenous 2,4-D before rhizobium innoculation. The cell structures of pseudonodules were very fine with organelles and infection threads, from which bacteria were released into the cytoplasm. Bacteria were enclosed in a paribacteroid membrane becoming the bactereid. These morphological structures were similar to those of legumes nodules with symbiotic characteristics, but the bacteroids were vesiculated. In the pseudonedules on rice roots formed by R. sesbania sp. cultured in the medium containing rice extract, the bacteria were distributed both in the intercellular and intracellular spaces. Here the structures of the infected cells were coarse containing free bacteria without paribacteroid membrane. The character of the pseudonodules formed after 2,4-D treatment were the same as those described above, but a large amount of bacteria were present in the central vascadar system of parent roots. These kinds of structures were completely different from those of legume nodules. The morphological relationship between the bacteria and plants could be attributed to an asymbiotic association.