1)The Helminthosporium disease lesion of rice leaf will be enlarged to a peculiar ring spot in a few days, if the diseased rice seeding is treated with ether vapor for 24 hours. 2) It was found from patho-histologic observation that the actual invasion of mycelium upon the outer tissue of the original lesion is a more essential factor in comparison with the toxic pre-effects of this fungus upon the development of this lesion. 3) Mycelial invasion were favourably proceeded through the part of vascular bundle of rice leaf in the case of long axis of lesion and through the part of vascular bundle branch in the case of short axis respectively.