1) The toughness and the percentages of silica and nitrogen were measured at the tip, middle and basal parts of the leaf blades of rice. 2) The toughness was tested at the motor cell region of tie inner half of a leaf blade by needle puncture method using JOLLY's balance. Rice varieties used for this purpose were Sensyo, Aikoku, Asahi, Ban-Shinriki and Kamairazu. Former two varieties are resistant to the blast disease while remaining three susceptible. 3) The quantities of silica and nitrogen present in these leaf portions were shown in percentage and in "skeleton ratio" or crude fiber ratio. Rice varieties used for this purpose were Totigi-Wase and Togo, wich were in the ripening stage. 4) The resistance of the leaf blade against needle puncture is largest at the basal part, and it is larger at the middle part than near the tip. 5) The percentage of silica is larger near the tip of a leaf blade than at its basal part, while it is contrary in the case of nitrogen. 6) Comparing these results with the infection experiment of Piricularia oryzae, carried out by T. ABE, to the rice leaf horizontally laid, it is evident that the susceptibility of rice leaf to the infection of the blast fungus is proportional to the quantity of nitrogen but inversely to that of silica of the portion of the leaf blade, and that there exists scarcely any relation between the blast resistance and the rate of toughness of the leaf portion.
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