1. There are the following methods to measure the water color in the field.
1. FOREL'S color standards method a. Serié FOREL centesimale b. Serié FOREL pour de la mer
2. ULE's color standards method
3. HAZEN'S Platinum-Cobalt scale method
4. Glass-disks method (the convenient method of HAZEN'S method)
5. BREU'S supplementary standards to FOREL'S color standards
6. ELSTER'S colorimetric scale method
2. Many studies have been done on the water color and on the relation between it and the limnological phenomena. To study more exactly, however, I think, the color standards and scales cited above are not sufficient, as many authors have criticised, because they have failed to regard the chromatolological theory of color specification.
3. The chromatological theory of color specification is based upon GRASSMAN'S Laws on color language, according to which three values, hue, value, and chroma, should be also given in limnological water color specification. From the view of physical color specification, FOREL-ULE'S color standards method expresses only hue of the three values and has a disregard for the other two. HAZEN'S Platinum-Cobalt Scale method also expresses value and chroma indirectly but ignores hue.
It is necessary, however, to indicate the three values in water color, and as the three values are independent each other, limnological significance of each value must be studied.
As the representative methods which can indicate the three values, there are C. I. E. (Commission Internationale de 1'Eclaisage) Color language and MUNSELL color notation. These two color specifications are adopted internationally at present. The former is based on the physical theory, while the latter is based on the sensible uniform chromaticity scale. The author is therefore of opinion that the C. I. E. color language may be more suitable for the specification of water color with modern chromatological trends.
RUDOLFS and HANLON used a spectrophotometer to measure water color, and : afterwards the photometric method with three tristimulus filters was devised. Both of these methods are used to measure the water color of sewage and industrial waters in the United States. YAMAZAKI and WATANABE have also devised a new field method which can indicate the three values of the C. I. E. color language under the principle of “additive color mixture.” They used a MAXWELL'S disc to measure the water colors of gold-fish ponds. NAKAMURA measured the water color of eel-culturing ponds by using the “MUNSELL Book of Color”, and specificatied the water color by MUNSELL Color system. COSS and NEMEROW devised a stream colorimeter by using a photometer and three tristimulus filters to measure water color of rivers.
All the methods mentioned above have been developed after 1950, and all methods have adopted the C. I. E. color language except NAKAMURA'S method. Asto the measurements of natural water color in the field, there are only two methods, i. e. YAMAZAKI-WATANABE'S and NAKAMURA'S. The other methods are not always suitable to such a purpose, because their devisers did not desire to measure the natural water color as it is, and their apparatus is too heavy to carry it in the field.
The author improved the authors' method to use as convenient as possible, but this improvement will be informed in more detail in a forthcoming report.

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The ecological studies on lacustrine bacteria were carried out in the Goshiki-numa Lake Group of Volcano Bandai, Eukushima Prefecture, Japan. The amount of bacteria is relatively scarce in the acidotrophic lakes, while it is large in the water and bottom mud of the harmonic lakes. The differences in the multiplication of bacteria are observed with different lake types. The rate of multiplication is large in the harmonic lakes.
Some experiments were carried out in the laboratory on the resistibility of water bacteria to sulfur compounds. The results indicate that the resistibility to sulfur compounds is greater in the bacteria of the acidotrophic lakes than those of the harmonic lakes. So far as the present investigations are concerned, the physiological nature of bacteria differs between those of the harmonic lakes and of the acidotrophic lakes.

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The ecological studies on aquatic fungi were carried out in the Shiga Lake Group, Nagano prefecture, Japan. The lakes under consideration consisted of two different types, acid and neutral. The lake waters of the former type were colored with humus colloids, while those of the latter were clear.
The zoospores of aquatic fungi were very rich in the lake water. The distribution of fungus species differed with lake types. Pythium sp. was distributed only in the lakes of neutral water and was never found in those of acid water. On the other hand, Saprolegnia diclina, Aplanes Braunii, and Leptolegnia caudata were found only in the acid water lakes.
The zoospores of aquatic fungi were distributed in the lakes uniformly from the surface to the bottom during the circulation period. The forms of distribution differed with different genera ; Saprolegnia was distributed in the upper layer, while Achlya and Aphanomyces were found mostly in the deeper layer.
The fungi were scarce in the bottom mud. Aphanomyces sp. was the dominant species, and Pythium sp. was distributed only in the muds of the neutral water lakes.
So far as the fungus productivity is concerned, the lakes of the Shiga Group are divided into the following three groups : a) Shibu-ike group : the fungus productivity is very high and is characterized by the absence of Pythium in the lake water as well as in the bottom mud. h) Maru-ike group : the fungus productivity is the same as that of deep eutrophic lakes. c) Onuma-ike group : the fungi are very scarce.

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The diatom- and desmid-flora of the reclaimed paddy-fields by drainage in the city of Toyohashi, Aichi prefecture, were studied by the author in August, 1958. Jinnoshinden which has an area of 16 km² is one of the largest reclaimed paddy-fields in Toyohashi and its vicinity. The results obtained are as follows :
1. The pH value of the water ranges from 6.3 to 7.1 ; and the chlorinity is roughly 0.02-0.4 g/l. The chlorinity is considerably high (175-396 mg/l), in the region 100-150 m distant from the sea shore, while it is remarkably low (19-42 mg/l) in the region 500-1500 m far from the shore.
2. The diatoms of these paddy-fields are composed of 9 families, 28 genera, and 92 species, 43 per cent of which belong to the genera Navicula, Nitzschiq Pinnularia. Among them, the widely-distributed species are as follows : Melosira varians, Cyclotella Meneghiniana, Achnanthes hungarica, Auliscus caelatus, Caloneis silicula, Diploneis ovalis, Navicula exigua, Pinnularia viridis, P. gibba var. subundulata, Nitzschia tryblionella var. victoriae, and Surirella tenera var. nervosa.
The dominant and subdominant species are Achnanthes hungarica, Bacillaria paradoxa, Navicula elegans, N. exigua, Gomphonema parvulum, and Cyclotella Meneghiniana. The occurrence of thesse species in this area differs, as shown in Table 3, gradually from the polyhaline to oligohaline species.
The common diatoms in brackish water are enumerated 38 % of the whole species appeared (excl. fossil diatoms which are contained in the soil of paddy fields).
3. The desmids are composed of 30 species, belonging to 4 genera, Pleurotaenium, Closterium, Cosmarium, Euastrurn, among which Cosmariurn is rich in the number of species.
The desmid flora well resembles that of the inland paddy-fields of the Kinki district (exc. N₁).

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Yubara-ko is a reservoir which was constructed in damming up the upper course of the Asahi-gawa River at the town of Yubara, Maniwa-gun in Okayama prefecture, for the purpose of storaging water to hydro-electric power stations. It was filled with water in March, 1955, and five years have passed after the appearance of this artificial lake up to the beginning of 1959. The writer began the investigations of this lake, concerning its water quality, the vertical distribution of plankton in summer, and the annual succession of net-plankton during the period from September 1958 to August 1959. The results obtained are as follows :
The metaliumion developed in the layers of 4-20 metres deep in Aug. ; the pH values were 6.0-7.2, the amounts of nutritive salts for phytoplankton (NO₃-N, NH₄-N and PO₄-P) being 0.01-0.02 mg/l, 0.01-0.03 mg/l, and 0. 005-0.006 mg/l respectively. This lake seems to be remained still at an oligotrophic condition. The plankton reached the maximum in numbers (1006/l) in the layer of 10 m. deep, and the minimum (41/l) in the layer of 45 m deep (bottom layer). Ceratium hirundinella was the dominant species throughout the layers. In general, the plankton were rich in individual numbers in the layer of 10 m deep, i. e. the middle layer of the rnetalimnion where the dissolved oxygen and the pH values decreased remarkably.
The annual succession of plankton showed that the number of species and the amount of plankton were rich in summer and poor in winter. During the period from September 1958 to August 1959, there occurred 41 species of plankton animals and plants, of which 17 were the phytoplankters and 24 were the zooplankters. The dominant species of plankton animals and plants in each month were as follows :
September Difflugia corona
October Synedra sp.
November-December-January Bosmina longirostris
February Synchata stylata
March Asplanchna priodonta
April Ploesoma truncaturn
May Keratella cochlearis
June Bosminopsis deitersi
July-August Ceratiuin hirundinella

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Year after year, during the period from the late summer to early autumn, there develops a conspicuous turbid layer which is alkaline in some measure in the thermocline of Lake Noziri etc.
On August 26th of 1959, however, its development in the thermocline of Lake Noziri was faint, and, besides, the water in it was almost neutral (pH=7.2). The author considers this phenomenon to be attributed to the circulation, though not perfect, of the lake water caused by the heavy rainfall which had lasted without intermission for about eleven hours immediately before the time of observation.
After the heavy rain, fine weather lasted with high atmospheric temperature ; on September 5th of this year a turbid layer which was markedly alkaline (pH=8.1) was observed in the thermocline of this lake.

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Five species found in the phytoplankton collected in the area of Kobe city are reported here as new to Japan. They are : 1. Oscillatoria kawamurae NEGORO, 2. Scenedesmus diagonalis FANG, 3. Desmidium baileyi NORDST. forma tetragonum NORDST., 4. Streptonema trilobatum WALLICH, and 5. Spirulina princeps W. et G. S. WEST. The former four species are interesting with respect to their rather rare distribution.

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