Dn the distribution of desmids from the rice-fields in the caldera of Mt. Aso

Abstract

The caldera of Mt. Aso is divided by the central cone into two parts : Aso-Valley and Nango-Valley. Rice-fields are cultivated inside the slope of caldera at Kugino, on a sharp inclination of the mouth of caldera at Tateno, on a easy slope of central cone at Bochu, and at Narukawa midst the Plain of Aso-Valley. Phycological and ecological survey was carried out at these 4 stations.
In these fields cultivated on the slope or inclination, water is supplied from the adjoining upper field and flows down into the lower. Desmid is scanty even the water is comparatively poor in chlor and calcium. On the other hand desmid occurs luxuriantly at Narukawa in spite of considerable amount of both minerals, because the water is stagnant. In comparison with alluvial lowland of Yatsushiro-Plain, Kumamoto Pref. and calcareous district of Hiraodai-Plateau, Fukuoka Pref., Narukawa is the poorest in desmid among these fields. At Hiraodai the water contains corresponding amount of calcium to Narukawa but less of chlor. The water of Narukawa is richer than the lowland both in chlor and calcium. At Bochu the amount of both minerals is exceedingly rich and desmid can hardly be encountered. Accordingly desmid in Mt. Aso is scanty in general and chlor is also related to the distribution of desmid. It has been hitherto remarked that Cosmarium or Closterium dominates in the water which is rich in minerals or organic matter. The association of desmid in the caldera of Mt. Aso is chiefly composed of Cosmarium and Closterium and in this meaning resembles to that of alluvial lowland.