Ice and water samples were collected from Lake Haruna, Gumma Prefecture, in the winter, 1962. The vertical change of the concentration of several components (UV-absorbance, COD, Cl, and Ca+Mg) at the lake surface was investigated with the following results.
1. All the components are less concentrated in ice than in water which bordered it.
2. The degree of concentration from water to ice in regards to each component is expressed in the ratio (concentration in ice) / (concentration in water).
The ratio is is larger for Cl than for the other components. This fact means that in the course of freezing of lake water the desalting effect is less for Cl than for the others.
3. The ratio is found to be minimum in the deepest layer of ice contacting with lake water the ratios for E₂₂₀, COD, Cl and Ca+Mg are 1/10, 1/10, 1/3 and 1/20 times those of lake water respectively.

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The present paper deals with the relation of the primary production of lakes to the trophic degree, with special reference to the nutritive salt conditions.
1) The ratio of the production of phytoplankton to that of rooted aquatic plants are examined in some Japanese lakes. If the whole area of a lake is concerned, rooted aquatic plants which take part in the primary production can be neglected except the shallow lakes where the aquatic plants are growing luxuriantly.
2) The phytoplankton production and the mean chlorophyll content in the euphoric zone are small in deep lakes and large in shallow lakes.
3) There are two types in seasonal variation of chlorophyll content in the euphoric zone, i. e. the one is seen in the shallow eutrophic lakes where its maximum content is found in midsummer, and the other is that of the deep oligotrophic as well as mesotrophic lakes where two maxima occur, one in autumn and the other in spring.
4) The total nitrogen and total phosphorus contents of lake waters were measured during the circulation period. The inverse curve linear relation could be found between the mean depth of lakes and the content of each element as well as of chlorophyll.
5) The content of different mineral elements in lake waters was compared with the minimum requirements of various phytoplanktonts for the corresponding elements. It was shown that the lake waters contained the least nitrogen and phosphorus for the requirement of phytoplankton. It could be found a fairly direct linear relationship between the chlorophyll content and the total phosphorus content of the surface waters of lakes, when they were plotted on the logarismic scales.
6) The relation between the daily production rate of phytoplankton and the total phosphorus content of the lake water was calculated theoretically. On the basis of the results thus obtained, the balance of phosphorus was calculated between the part incorporated in the newly produced plankton bodies and that contained in the lake water. From these results it could be surmised that most part of phosphorus incorporated in the newly produced plankton bodies, especially of those of the eutrophic lakes, should come liberated from dead plankton bodies and mud.

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The algae attached to the stones were studied on the basis of three samples which were collected by Prof. M. TSUDA in the streams in Kauai, the northernmost island of the Hawaiian Islands, in August, 1961.
1. Many species of diatoms, blue-green algae, green algae and Conjugales were found. They are mostly of cosmopolitan species.
2. The diatoms consist of 19 genera, 61 species, 24 varieties and 3 forms (cf. Table 1, Plates 1-3), of which 21 species are cosmopolitan, while the other 40 species are distributed mostly in the warmer regions.
The diatom flora in the streams in Kauai resembles that in the streams of Japan rather than that in the streams in the tropical islands, Sumatra, Java and Bali. (of. HUSTEDT 1938, 1939).
3. WATANABE'S biotic indices of water pollution based upon the species number of Bacillariophyceae were calculated upon the samples from the three stations under consideration ; the values are as follows :
st.1……+118 st.2……+132 st.3……+200
From the above values, the water of the station 1 seems to be slightly polluted ; it may be polluted naturally, not artificially, by fallen leaves, &c. in the woods. The value of the biotic index of the station 2 is nearly equal to the values obtained in the mountain streams of Japan. The station 3 is considerably high, it showing the highest value which can be obtained by this method of biotic index. The flora of diatoms at this station resembles very much that of high moors in Japan.

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The vertical differences in the activity of bacteria were observed by culture method in some Japanese lakes. The multiplication of bacteria occurred at the surface (0-2 m), the layer above thermocline and the bottom layer during the stagnation period. On the other hand, the activity of bacteria was observed at the surface (0-2 m) and bottom layer during the circulation period.
The vertical differences in the activity of bacteria in lake water seem to have close relation to the distribution of plankton and also to multiplication of floating bacteria.

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The present paper deals with the ecology of aquatic Hyphomycetes in the inorganic acidotrophic lakes of Japan. Six species of fungi were obtained by the writers from these lakes. Tricladium gracile var. oxyphilum and Anguillospora longissima were the preponderant species. Lemonniera aquatica, Lunulospora curvula, Tetrachaetum elegans and Tricladium gracile were found only in the weak acidic lakes. But no aquatic Hyphomycetes was seen in Lake Kata-numa (pH=1. 9) and Akadoro-numa (pH=2.75).
Experiments were carried out in the laboratory on the effect of mineral elements upon the formation of conidia. So far as the experiments are concerned, the amounts of iron and the pH value of the lake water are the essential factors to determine the distribution of aquatic Hyphomycetes in the acidotrophic lakes.

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The plankton and algal studies have been made on Mizoroga-ike Pond in Kyoto from 1950 to 1960, during which there were found 66 species of diatoms and 62 species of desmids. The results obtained were compared with those of the other six ponds in Kyoto (Ariga-ike, Ko-ike, Hojojuno-ike, Ôsawano-ike, and Kyoyono-ike), with special reference to the chemical qualities of the pond waters.

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The Kuwabara area lying on the fan of the Sano River is situated on the southwestern side of the Zenkoji valley, in the northern part of Nagano Prefecture. In this area, there are 10 ponds (artificially constructed ponds) and 2 springs. The writer visited them twice in 1958 to collect plankton.
The results obtained are as follows :
1. The three ponds, namely Karizuka-ike, Nashikubo-ike and Daiunjiuchi-ike are of inorganic acid water (pH value below 5. 3), and the other 7 ponds, Yakushi-ike, Daiunjisoto-ike, Shigawa-ike, Kosaka-ike, Harutaminami-ike, Harutakita-ike and Ryutôin-ike are of neutral water. Of the two springs, the Ichiriyama-shimizu spring is of inorganic acid water (pH value below 4. 3) and the Nanme-shimizu. spring is of neutral water.
2. The plankton of these ponds and springs consist of 89 species, of which 32 are phytoplankters and 57 zooplankters.
The dominant species in the acid water, are Scapholeberis mucronate., Acanthodiaptomus pacificus, Brachionus quadridentatus var. cluniorbicornis, Hormidium sp., Microspora tumidula. Mougeotia sp., Eunotia septentriontms, Frustultia rhomboides var. saxonica and Pinnularia Braunii var. amphicephuta, while Moira weismanni, Bosmina longirostris, Cyclops vicinus, Brachionus angularis, Asplanchna sp., Anabaena circinalis, Chlamydomonas sp., Mougeotia sp., Dinobryon divergens, D. sertularia, Melosira italica and Gornphonema acurninatum occur in the neutral water.

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