For gold-fish farmers at Koriyama near Nara, so-called “Mizutsukuri” (“water-making”) is an important but arduous daily task so as to maintain the pond water containing adequate quantity of phytoplankton, upon which the gold fish production depends. The decision of the suitability of “Mizutsukuri” is always given by the gradation of color of pond water derived from phytoplankton which has increased in adding sufficient fertilizers. FOREL-ULE'S color standards widely used in limnology is not suitable for the indication of the color grades of pond water, because they express only hue of the three values in GRASSMAN'S law of color language which is now adopted internationally (Commission Internationale de l'Eclaisage). Therefore, the writers have developed a new easy field method which can indicate the three values of the C. I. E. color language in combination with the principle of “additive color mixture” by using a MAXWELL'S disc.
In studying by this method of about eighty gold-fish ponds, at Koriyama the writers have succeeded in representing all the water colors of them in mixing the color-discs of yellowish green, orange and black which have spectral reflectance curves as shown in Fig. 3. Table 1 shows the tristimulus value, chromatic coefficient, wavelength and excitation purity of three color discs. The apparatus used is as follows : Each disc has a radial slit extending from the center hole to the circumference so that three discs, when put upon with each other, may be intermingled with a portion of each which remains visible. When such discs are rotated by a miniature motor connected to two 1. 5 v dry cells producing a speed of more than 35 times per second, they are visible as an individual color. The color resulting from this mixture depends upon the relative amount of the exposed areas of the discs used. In order to compare the mixed paper color with the color of pond water under the same condition, a gray-colored paper mask with two windows of the same size and form is used (Fig. 4). Table 2 indicates the water colors of 30 gold-fish ponds which were selected at random in September, 1954. The chromaticity positions of each water color thus obtained were given on the C. I. E. diagram in Fig. 5 in using each chromatic coefficient in Table 2.
The results obtained on the water colors of gold-fish ponds are as follows :
1). The wavelengths are distributed between 560 mμ, and 590 mμ, mostly between 560 mμ, and 570 mμ, (Table 3).
2). The brightness is distributed uniformly between 4.0 and 16.0 per cent (Table 4).
3). It is remarkable that about 70 per cent of the ponds examined has given excitation purity at the values between 30 and 40 per cent (Table 5).
4). It was obtained a positive correlation between the brightness and the excitation purity, as shown in the graph of Fig. 6 and as denoted as Y= 0.279, Pe +0.05, and the correlation coefficient (r) being 0.763.
In the waters which have become extremely eutrophic like the goldfish ponds under consideration, the factors deciding the water colors are the quantity of phytoplankton which consists chiefly of blue-green and green algae especially Microcystis and Scenedesmus in dominancy throughout the year. If the water color be investigated in such a relation as mentioned above, the significance of each value of the wavelengths, the brightness and the excitation would become clear, and the method discussed would be able to apply to practical purposes.

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Although considerable attention has been paid to a limiting factor of the phytoplankton growth and many studies have been made about it, we have as yet very little information as to the relation between the carbon dioxide supply and the phytoplankton growth. So the present study was designed to secure this information. The results obtained are as follows.
1). We calculated the relation between alkalinity and total carbon dioxide at various hydrogen ion concentrations. The results are shown in Fig. 1 and Table 1.
2). We also calculated the relation between pH and alkalinity when the total carbon dioxide contained in the water was wholly assimilated by the phytoplankton (Fig. 2). From Fig. 2, it seems possible that only by the measurement of pH and alkalinity we detect whether or not the carbon dioxide supply is a limiting factor of the phytoplankton.
3). The common planktonic alga, Scenedesmus obliquus was cultured in the media of different alkalinities, and during this cultivation daily changes of pH and water temperature were observed (Table 2). Each maximum value of pH obtained in this experiment agrees with the theoretical values that are calculated supposing the phytoplankton consumed the total carbon dioxide wholly.

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An enormous occurrence of water-bloom due to the pollen grains of pine (Pinus densiflora) and to male flowers of Vallisneria asiatica biwaensis has been frequently observed in Lake Biwa, especially in its auxiliary basin.
The pollen grain water-bloom is found in early and middle May. These pollen grains are supplied from the pine forests on the west and east coasts of the main basin of the lake, and are drifted away by southward wind forming certain large groups floating at the surface of water (Fig. 1, P). Thence they are carried by water current from the main basin to the southern auxiliary basin through the narrow channel. When large floating masses of pollen grains arrive the area off the city of Otsu, they spread over the surface of the auxiliary basin as the consequence of gradual spreading. This phenomenon is continuing in one month or more after pollen production of pine trees began.
In early autumn there occurs water-bloom due to a considerable masses of male flower of Vallisneria, which makes up more than 40 per cent of the amount of water plants in the shallow water of the lake. When Vallisneria is in full-bloom, numerous male flowers (Fig. 2), which came off from the bracts float up the surface of water making water-bloom. Owing to the influence of the current of lake water and of the wind, the water-bloom thus formed is usually condensed at the middle area of the axillary basin of the lake (Fig. 3).
The “pollen-grain water-bloom” has been noticed by German authors (WASMUMD 1930, SCHMITZ 1930) in regard to its occurrence and significance for pollen analysis of cores of bottom deposits of lakes. In a deep oligotrophic lake like Lake Biwa, such a kind of bloom may be less significance for pollen analysis but is noteworthy to report regarding the water color and the movement of surface water.

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