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The disease known under the name of "Bakanae-Byo" is one of the destructive diseases of the rice-plant in Japan. Commonoly the disease occures in seed-beds, but does no kill the attacked seedlings immediately. The diseased seedlings grow somewhat abnormally, showing a taller and more slender appearende in leaves and culms than those of normal growth. Their colour becomes, therefore, yellowish-green to pale in the advanced stage. Such an abnormal growth of the aerial parts is supposed to be caused by the presence of the mycelium of a species of Fusarium in the tissue of the foot of the plants attacked. The present paper deals with the occurrence of the disease by inoculation of the causal organism and also of seemingly the same appearance of seedlings without this organism. The latter case is called "Bakanae" phenomenon in the present paper. The pathological meaning of the distinction between the "Bakanae" disease and the "Bakanae" phenomenon is discussed in detail. The summarized conclusions are briefly stated as follows. 1. The "Bakanae" disease was proved to be caused by a species of Fussarium isolated from the tissues of the infested plants. According to the writer's experiments it is clear that the fungus has the power of attacking rice-seedlings germinated in perfect health, causing the characteristic overgrowth. 2. The fungus in question has never shown any pathogenicity to check the growth of the seedlings, as shown by Piricularia Oryzae Br. et Cav., Helminthosporium Oryzae Brada de Haan, and Hypochnus Sasakii Shirai. On the contraty, it has rather tended to stimulate its abnormal growth. 3. The filtrate of the cultured solution of the causal fungus-Knop's solution containing glucose in variouspercentages-was able to produce the phenomenon characteristic of the "Bakanae" disease, as recently mentioned by Kurosawa. Owing to the absence of the mycelium of the causal fungus, the writer considers it correct to call it the "Bakanae" phenomenon, as compared with the natural condition in the occurrence of the disease. 4. Differing from the filtrate of the fungus in question, the filtrate of the cultured solution of Helminthosporium Oryzae Breda de Hann parasitic commonly to the leaves of the rice-plant failed to produce any overgrowth of the leaves and culms.