1. The runners of the healthy and the diseased sweet potatoes were inserted in the bottles filled with KClO3 solutions, 0.01, 0.025, 0.05, 0.25, 1.O per cent respectively, and the injurious effects were compared. 2. The healthy sweet potato was more endurable than the diseased to KClO3 solution in the concentration of O.05 to O.25 percent with the, Chugoku No.2, and of O.05 to 1.O per cent with the Norin No. 2.