1. The present paper deals with the results of the writer's exp riments on the relation of air humidity to germination and the effect of low temperature on the vitality of the urediniospores of Puccinia glumaruns, Puccinia triticina and Puccinia Lolii which cause the cereal loss in the vicinity of Kyoto. 2. Either a saturated atmosphlre or a drop of precipitated moisture was almest ideal for germination of the urediniospores of P. triticina On the contrary those in dry condition kept in 99% relative humidity showed very low germinability, averaging 4.29%. In 95% it is very questionable whether any germination took place. 3. In the case of P. glumarum, the percentage of the germinated spores in the saturated atmosphare without a film of water was very low as compared with that of the germinated spores sown in water drops. In 99% relative humidity they germinated about 1.5%. 4. The germinability of the urediniospores of Puccinia Lolii in dry condition kept in the saturated atmosphere was a little lower than that of the spores sown in water drops, but in 99% relative humidity they germinated about 17%. 5. The results obtained seem to support the opinion of ward, Lauritzen and others that the uredinicspores to germinate in an atmosphere at or near the point of saturation and, therefore, a film of water covering the leaf surface is not essential to infection. 6. By the microscopical examination at the end of 24 hours, it was learned that water conylenses around the dried spores in 100 and 99% relative humidity, and only after this can gerru-nation take place. No such water film, however, was formed in 95 or 90%. Hence the opinion of Beauvérie, Melhus and Durrell and Stock that direct contact with water is essential for germination of the urediniospores seems to be supported by these experiments. 7. The urediniospores of P. triticina and P. Lolii together with their host-leaves were held in a refrigerator at the constant temperature of-8°to-9°C. A few spores of both the fungi did not lose their vitality even after 44 days, although the former seemed to be more resistant for refrigeration than the latter. A suspension of the urediniospores, of P. Lolii was held and frozen in the same refrigerator for 24 hours. The germin bility of such spores was decreased to ca. 4%.