1. In the present paper, the results of the experimental studies on the relation of air-humidity to conidial formation of the rice blast fungus on the affected leaves were first described. Then, the characteristics of the strains of the same fungus differing in their pathogenicities were compared in germinating conidia. 2. Rice seedlings of about 20 cm height were sprayed with the suspension of conidia. As soon as the diseased spots appeared on the inoculated leaves, they were put into large desiccators, in which the air was controlled at various constant humidities by the use of different salts or sulphuric acid of varying concentrations. The results show that the causal fungus is capable of producing the conidia on the spots in the air maintaining 93% or higher in relative humidity. Although the size of the spots increased gradually, the conidia were not produced in the air maintaining 88% or lower in the relative humidity. At 90 or 89% they were scarcely produced. 3. The percentage of the germinated conidia and also the length of the germ-tubes seem to have no correlation to the difference of pathogenicity shown by strains of the fungus. However, in the present experiment the tendency of producing two germtubes from a single conidium was higher in a strain of the strongest pathogenicity than in a strain of the weakest pathogenicity.
1. The present paper deals with the results of the writers' investigations on the Phytophthora rot of eggplant which occurs very often on the market in Kyoto as well as in transport from Prov. Tosa in Shikoku. 2. The causal fungus of the disease is quite identical with Phytophthora Melongenae SAWADA described first in Formosa in 1914. But many authors have regarded P. Melongenae SAWADA as identical with P. parasitica DASTUR described in 1913, although LEONIAN noted in 1935 that P. Melongenae SAWADA and P. parasitica DASTUR could possibly be included in P. palmivora BUTLER named first in 1907 as a species of Pythium. 3. The oospores of the causal fungus were found abundantly in three months old cultures of potato decoction agar containing 2% sucrose. They were also produced in the rotted host tissue, the inner portion of which changed almost into liquid. 4. The relation of temperature to the growth of the causal fungus was studied. It was found that the fungus in culture grows at from ca. 16° to ca. 36°C. and the optimum temperature for the mycelial growth seems to lie at from 28° to 32°C. At 3°C. and 40°C. no growth was observed. Consequently the writers came to the conclusion that the causal fungus belongs to a high temperature group of pathogenic fungi of plants. 5. Repeated experiments were made to determine the relation of temperature to infection of the fruit of eggplant and the rate of progress of decay by the fungus in question. The results show that the most favorable temperature for the decay caused by this fungus seems to lie at approximately 28°C. At 5° to 6°C. no infection took place even when inoculated into the wounds. 6. The optimum hydrogen ion concentration of cuture media for the mycelial growth is approximately 6.0 in pH value. In the media indicating pH 3.0 and pH 8.5 no growth was observed. 7. In the atmosphere controlled to 95% or higher in relative humidity, the aerial mycelium of the causal fungus grows vigorously on the affected fruits. On the contrary the conidial formation is apt to be more abundant in the air controlled to 85% or lower in relative humidity than in the air of high humidity. 8. Inoculation experiments performed by the writers demonstrated clearly, that the causal fungus has a power to infect the uninjured fruit of eggplant as well as the young seedlings of the same plant. The fruits of tomato and red pepper are affected by the same fungus only when inoculated into needle wounds.