The formation of nodules was limited generally at the baseal portion of root or rootlet in leguminous crops even though growing under the different external conditions. These experiments were carried out to make clear the mechanism of the phenomenon above mentioned. 19 species, including 48 varieties, of legminous crops were used as materials just like the previous experiments (KAMATA, 1958 a). All the crops were cultured with different levels of nitrogen supply, under different conditions of shading or on field. The distance from the base of root to nodule, the number of nodules in each level on root and the dry weight of nodules per plant were measured in the progress of growing of each crop. The development of nodules were observed at the basal portion of root or rootlet in all the cases examined, with only one exception, Pisum Sativum var. Beikoku Ohosaya. The relation between the levels of both the differentiation and maturation of tissues in root and the formation of nodules was observed histologically with a serial cross-sections and longitudinal sections of the whole primary root of Glycine Max Mere var. Norin. No. 1, Pisum Sativum var. Nihon Kinusaya and Arachis Hypogaea var. Southern Cross, and the following two cases were found. Rizobium penetrated into the host tissue at the portion of primary root, in which roothairs were growing, in soybeans and peas, but no bacterium was detected under the level of secondary root appearance on the primary root in peanuts. The Glycine Max Mere var. Norin No. 1, Pisum Sativum var. Nihon Kinusaya and Arachis Hypogaea var. Southern Cross were cultured on sand under sterile condition. The primary roots of the seedlings, 12cm in length, were divided into 5 pieces (ca. 2.0∼2.5cm), and the in lateal roots 3 pieces (ca. 2.6cm). The contents of total sugar, reducing sugar and total nitrogen of the pieces obtained from equal level of roots were measured. Both the total and feducing sugar contents increased with aging of tissues, and the basal portion of root or rootlet had the highest concentration of sugars utilizable for the growth of nodule bacteria.