The results are shown in Fig. 1 and 2. In the case of Motosu-ko, an oligotrophic lake, any essential difference cannot be noticed between MIYADI'S data obtained in 1930 and the present ones in 1953. But in the case of Syôzi-ko, an eutrophic lake, changes towards a greater degree of eutrophy seem to have occurred during the twenty years since MIYADI'S observation.
