1954 年 3 巻 4 号 p. 186-192
1) Our "Muro-yosui" is a small artificial irrigation trench, 24 km long, 7 m wide and 70 cm deep, located east parts of Aichi Pref., taking the water out of the middle of a river, Toyogawa and irrigating rice fields of about 3,000 acres near around. It was built in 1890 with the purpose of irrigating. 2) They let water run in this trench from the beginning of May till the end of October every year for the irrigation and, as a rule, leave it dry during the rest period. There are, however, left several exceptional regions, where water runs or water pools are left in autumn and winter. 3) In those regions where water runs abundantly only in summer and the bottom is sandy, we find Vallisneria asiatica community over all and in those where muddy, Hydrilla verticillata community over all. The scale of the both communities is fairly big. 4) In those regions water runs just scarcely or only water pools are left in winter and the bottom is sandy, we find Vallisneria asiatica-Potamogeton distinctus community and in those where muddy, Potamogeton oxyphyllus-P, Maschianus community. In other regions these two communities are found mixed in mosaic way. Moreover, in muddy regions pure communities of Potamogeton crispus are also found. All these communities are small in scale. 5) Thus, the author wants to conclude that the distribution of water plants on the bottom of the trench is dominated by the size of soil rgains of its bottom and the presence or absence of water in it during winter, the latter factor seeming to be greatly concerned with the existence of the plants growing there or their winter buds.