The present paper deals with the changes in the forests and the climate in Southern Saghalien and Hokkaido, studied by means of pollen analysis. The writer first made a thorough study of the recognized methods of pollen analysis, adopted by workers aboard, and then developed a new method by which have accurate results can be obtained. He carried out pollen analysis in many of the peat-bogs in Southern Saghalien and Hokkaido, and from the results attained was able to visualize the historical changes in the forests and the climate since the Diluvium epoch. The conclusions of this study are summarized in the following paragraphs: In 1930, when this study of pollen analysis was begun, there was in this country no adequate study of pollen grains. Consequently, the first step taken by the writer was to sketch and measure the pollen grains and spores of 172 kinds of plants found in and about the former Saghalien Experiment Station of Kyoto University. Next, he determined the significance of pollen analysis, as a means of determining the historical changes in the forests and the climate of Japan since the Diluvium epoch. Study was made of the usual methods of treating peat for extracting pollen grains, in conformity with the chemical consideration of the structure of the pollen-membrane of the components of peat. The writer pointed out some defects theoretically inevitable in these procedures, and finally devised a new method of treating peat. In brief, this new procedure corrects a major defect in the alkaline and dehydrated acetic acid methods, usually adopted for the treatment of peat, which do not take it into consideration the fact that the content ratio of the principal substances of peat, such as humic acid, lignine and cellulose, generally shows certain gradual changes from the upper strata of peat down to the lower ones. In addition, as regards the representation of the percentage of pollen grains, the writer improved upon the usual method and adopted the new proce