Experiments were made on morphogenesis of the root nodule of Crotalaria juncea. After the rhizobial invasion had occurred, the characteristic initial infected cells were formed in the first cortical layer adjacent to the root hair cells (Fig. 1-4). Those cells seem to become the places of rhizobial multiplication thereafter. Since we could recognize neither the infection thread formation nor other visible changes in the host cell where rhizobial invasion occurred, it is suggested merely that root hairs become the avenues of entry of rhizobia. The hystological origin of the root nodule in this species is 1-3 layers of the cortex as in soybean, adzuki bean, yellow lupine and Mucuna capitata.