It was found that the rate of multiplication of the nodule organism was greater in high than in low dilution. It was also noted that Bacillus radicicola of garden pea remained alive in solution for 142 days and that O2 was the limiting factor during the growth of nodule bacteria in solution. Shaking the culture containers helped to introduce O2 and thus to give increased growth. Calcium carbonate added to the media stimulated the growth of B. radicicola more than tricalcium phosphate. B. radicicola of garden pea and sweet clover, also Pseudomonas radicicola of cowpea and soy bean were killed at 10-minute exposure to 50[degree]C, whereas B. radiobacter and Azotobacter chroococcum were not. The solution in which the organisms were suspended had an influence on heat penetration; the denser the solution the slower heat penetrated, and the thinner the solution, the more rapidly heat penetrated. Peat soil maintained the life of nodule bacteria at a much higher temperature than brown silt loam soil. Acid soil decreased the thermal death point of legume organisms, the latter dying in such a soil after a short period of storage. The addition of calcium carbonate to the acid soil increased the thermal death point and the keeping quality of legume organisms. In experiments in which the composition of the normal media was altered, the morphology of nodule bacteria was materially affected. The normal bacteria were smaller in size than the bac-teroids; the latter predominated in these abnormal media. Absence of phosphate or carbonate in the media resulted in the formation of bacteroids. Presence of tricalcium or acid phosphate in the non-carbonated media did not stimulate the production of active forms. Aluminum chloride and hydrochloric acid gave the same effect on the forms of the nodule bacteria, whereas the presence of acetic, nitric and sulphuric acids in the media changed the legume bacteria into the bacteroid stage, and each of these acids affected the form of the organisms specifically.