1. In view of the fact that precipitation constitutes the primary source of the salt of inland waters, comparison was made between sea water and rain and snow for major salt components in order to discuss the cause of difference in relative composition between these two different categories of water.
2. The next step was to compare rain and snow, and inland waters, whereby possible factors contributing to the deviation of the concentrations of Na and Cl and the ratio Na/Cl in inland waters from those in rain and snow were made clear. As such factors, dissolution of windborne salt, erosion of rock and soil materials, addition of mineral and thermal spring waters, agriculturally used chloride manure, sodium chloride waste from domestic life including excreta, sodium and chloride contained in mine and other industrial wastes were considered. Climatic factors were also to be considered, and among them annual averages of regional temperatures are especially important in relation to evaporation and soil erosion. Furthermore, annual precipitation is one of the fundamental factors.
3. The magnitude of contribution by some of these factors to the Japanese inland waters was estimated by using the data available. The data for rain and snow were from the author's own laboratory, those for river waters from J. KOBAYASHI and those for ground water from S. OANA'S laboratory, Institute of Earth Sciences, Nagoya University.
4. The conclusion is :
a). In comparison with the waters in the regions facing the Pacific Ocean, those in the regions facing the the Japan Sea are enriched by Na and Cl with a low Na/Cl. The strong winter monsoon from Siberian air mass transports sea spray from the Japan Sea into the regions facing that sea, where the spray falls down in the forms of snow and rain.
b). Geologically speaking, the Japanese inland waters are categorized into three fundamental types : volcanic material type, granitic material type and sedimentary rock type.
The waters of Hokkaido, the northernmost island, and the Tohoku District, the northernmost region of Honshu, the Main Island of Japan, represent the volcanic material type and are characterized by high contents in Na, Mg, Cl, SO₄and SiO₂ with a low Na/Cl. The waters of the Kyushu District, the southernmost among the four large islands constituting Japan, are also of volcanic material type. The waters, however, are characterized by less enrichment of chloride with a higher Na/Cl.
The waters of the Chugoku District, the southwestern part of Honshu, where granite is dominant, represent the granitic material type characterized by a low salinity. It is evident that rocks of granite type are less soluble than other types of rocks such as sedimentary or volcanic.
The characteristic of sedimentary rock type water is richness in Ca. There is no calcite area extensive enough to form a special district representing this type of water. The waters of the Kanto District with Tokyo on its verge are of composite nature of two water types, volcanic and sedimentary rock.
5. Finally, the ratio Na/Cl of inland waters was reviewed world-wide, and explanations were given to unusually low Na/Cl for some Antarctic waters and the water of the Dead Sea.

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1. Ponds, as lakes and rivers, are one of the important inland water. In Japan where rice-culture is carried on extensively, there is a wide distribution of man-made 'tame-ike' ponds in addition to natural ones. Unlike lakes, they are small both in area and in depth, and besides being easily subject to the influences of environmental conditions, they have a distinctive character of their water-volume which is able to be regulated artificially. The studies of such 'tame-ike' ponds have so far been rather neglected, and many problems still remain unsettled about them, and in particular as the basis of utilizing for pisciculture. The present paper aims at the analytical study of their environmental factors, the elucidation of the relationship between such factors and plankton communities, with which the writer tried to make clear the organic production and metabolism in such a kind of ponds.
2. From the above-stated viewpoints, an attempt was made, (1) to make comparative studies extensively, (2) to perform detailed observations of representative 'tame-ike' ponds in regard to their physical and chemical factors, as well as diurnal and seasonal fluctuations of plankton communities. With the three dimensional aspect obtained from the vertical distribution of temperature, pH, O₂, &c., and the recovery of planktonic organisms from the drying-up subsequent to drainage, the writer has made an endeavour to reveal the characters of 'tame-ike' ponds.
3. In making comparative studies, the pond groups on different geological formations were taken up in the suburbs of Osaka. Aside from the alluvium, geological formations had little effect with the difference from one pond to another. A fairly remarkable difference due to artificial contamination among the pond groups on the diluvium was detected in the water quality, and in the number and quantity of planktonic species.
4. The coastal areas of the Inland Sea have a dense distribution of 'tame-ike' ponds hardly seen elsewhere in Japan. As a result of comparative studies of representative ponds in such prefectures as Osaka, Hyogo, Okayama, Kagawa and Ehime, natural eutrophication was usually found in a more advanced stage with inland 'tame-ike' ponds. Those 'tame-ike' pond groups lying near the seashore exposed to either monsoons or typhoons have a larger Cl^- content. On the Islands of Sadoga-shima and Okino-shima, where there comes a strong monsoon from the continent, the pond groups on the western coast have a larger Cl^- content than those on the eastern coast, which shows the effects of sea-breezes undoubtedly. The Cl^-content, however, is seldom found to exceed 100 mg/l and the ponds remain within the confines of freshwater ones, so that the plankton communities in them are composed of freshwater species. The same is not true only in those ponds which are invaded by seawater or which had at one time been connected with the sea.
5. In the coastal areas of the Japan Sea, the pond groups at the seaside of the Tottori sand dunes, or at Kisagata and Konoura beach, Akita pref., at Tsugaru, Aomori pref. are all exposed to the onset of strong monsoons in winter, so that, as a matter of course, they all have a larger Cl^- content than any of inland 'tame-ike' ponds, but with 44 mg/l at Kidaka beach, Tottori pref. as its maximum, the rest of these pond groups shows smaller contents without exceptions. The 'tame-ike' ponds in Akita and Aomori prefectures are not so typical dystrophic as those in Hokkaido, but they have nevertheless a distinctive character of dystrophic ponds in the cold northern districts.

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