The environmental factors infiuencing the activities of Oncomelania nosophora (ROBSON) were analysed. The observations were made at Mamezu (Saga) in a grassy river-bed of the Chikugo River during 1956 and 1957. Under the seasons of favorable conditions this snail shows daily rhythmic activity that belongs to a type of dependent rhythmicity having two peaks in the night. During daytime it almost rests, but resumes its normal activity after sunset when light intensity reduces to about 0 lux, and after a few hours the activity reaches the maximum. Thereafter the activity declines slightly, but when light intensity increases over about 0 lux, the snails begin to resume their activity. Then after sunrise it gradually declines and scarcely moves. The first peak of activity corresponds to their feeding behavior and the second represents their returning behavior to the rest place during daytime. The principal environmental factor conditioning the daily rhythmicity is the light under the conditions of optimum temperature and wet habitat. When the temperature is lower than 10℃ and the habitat is dry, the activities of these snails are limited, while the rainfall accelerates them. In the habitat under observation their normal activities are seen in spring, autumn and rainy summer.
Using 39 typical varieties of sesame collected in seven countries including Japan as material, experiments were carried on the relation between germination temperature and varietal difference, and the correlation between germination, seed weight and percentage of oil content. In germination experiments for which a Jacobsen germinater was employed, 12 stairs at intervals of 5 degrees with 5℃ as the lowest and 60℃ as the highest temperature was contrived to grade germination temperature; and the germination rate and the germination ratio were 3 and 10 days respectively. The materials employed in the experiments were obtained from the 1957 crop and the experiments carried on at the Shikoku Agricultural Experiment Station in the same year. The results of the experiments are : (1) There was no germination of any variety at either 5℃ or 60℃. It was found that the germination temperature of sesame ranges from 10℃ to 55℃, the proper temperature being between 30℃ and 35℃. (2) The germination temperature of all varieties collected in Israel was 15℃ at the lowest and 50℃ at the highest ; of all the varieties employed for the experiments the Israeli varieties had the narrowest range of germination temperature and the lowest germination coefficient. (3) On the whole, American, Japanese and Chinese varieties had a wide range of germination temperature, and their germination was satisfactory at both low and high temperatures. (4) It was found that, generally, the varieties growing in tropical regions show poor germination at low temperature and good germination at high temperature, while those cultivated in northern regions not only retain the quality of germinating well at high temperature but also germinate fairly well even at low temperature. (5) The covariance of seed weight and the germination coefficient at 15℃ showed that in the case of the Japanese varieties all the light-seed varieties had high germination coefficient, while in the case of the American varieties some of the light-seed varieties had high, and the others, low germination coefficient. In the case of 45℃, the Japanese varieties had (-) correlation as in the case of 15℃; the African varieties had 1 per cent significant of (+), and the Indian varieties almost 5 per cent significant of (+), correlation ; the American varieties, as in the case of 15℃, had high-germination coefficient ones and low-germination coefficient ones mixed in them. (6) The covariance of percentage of oil content and the germination coefficient at 15℃ showed that, on the whole, the higher the percentage of oil content was, the higher the germination coefficient; especially the American varieties had much of this tendency. There were some exceptional varieties, however, such as the Indian varieties, whose germination coefficient was extremely low in spite of their high percentage of oil content. In the case of 45℃, the general situation was much the same as in the case of 15℃, except for the Indian varieties which had nearly 5 per cent significant of (-) correlation. (7) It seemed that there was a fairly close correlation between germination temperature and light sensitivity. Those varieties of low light sensitivity to both short-day and long-day, or those of low short-day sensitivity and high long-day sensitivity had, on the whole, a wide range of germination temperature. It was also found that those of high light sensitivity to short-day and long-day showed poor germination at low temperature and good germination at high temperature.
In plant containers, such as bamboo vase in graveyard, bamboo stub, tree hall and so on, Diptera larval associations, which are formed by various combinations of different species of mosquitoes and Eristalis, were usually observed. To know the factors which play an important role in forming these associations, the following experiment was made. The internodes of the canes of the bamboo Phyllostachis mitis, were used as a container instead of the plant container in natural state. They were set in the shady place of a hill in the campus of the Tohoku University, and filled with sterilized tap-water. In a few days after setting, Diptera larval association began to appear in these water, and with the lapse of time it changed into other ones. In this experiment, the larval fauna found in the water of each bamboo containers, of which bamboos were two months, three months, a year and a half, two years, and three years after budding, were compared and examined. The results are as follows : 1. The appearance of Diptera larvae was characteristic in the containers made of the bamboos of different ages. 2. The diverse distributions of Diptera larvae are likely to be defined by the difference in pH of the water and by the timely appearances of the gravid females. 3. In adult Eristalis, the selection in egglaying was recognized, but when its density was remarkably high, it became loose. 4. The larvae of eggs of Aedes flavopictus became extinct affected by the sudden rise of pH.
Studies were made on the relations between the quantities of air in the sewage and protozoan fauna, by observing experimentally the successions of the protozoan fauna in good aerated condition and in bad aerated or anaerobic condition. The ciliates in the activated sludge have been hitherto classified into three groups (life forms) from the practical point of view and various discussions have been made on this classification. Discussions are presented on the conditions of sewage purification. based upon the three life forms and also on each species of organisms. The results can be summarized as follows : (1) The successions of protozoan biomass in the various experimental conditions are schematicaily graphed in Fig. 6. (2) (i) Vorticella is dominant when the sludge is in the best condition. (ii) Aspidisca occurs in the same case, but not so dominant as Vorticella. (iii) Epistylis and Tokophrya have larger ecological value than Vorticella and Aspidisca. (iv) Epistylis and Tokophrya are dominant when the sludge is a little putrefactive. (v) The succession-curve of Amphileptus has two peaks. The development of Amphileptus seems to be oppressed by Vorticella, Epistylis etc., in the best condition of medium. (vii) Monas, having the largest ecological value, occurs in comprehensive conditions.
1. Nineteen vegetation stands of a grazing grassland, located at Sayoto in the Chugoku Mountains were investigated as to the distributional pattern of plant populations and the indicator plants for disturbance. Each stand was sampled with 250 quadrats of (20×20cm), and the quantitative relations of the plant populations were expressed as frequency percentages. 2. The distributional interchange of four principal species was tested by the method of the leading dominant, and the adaptation number for these species was decided (Table 1). To express the numerical distance between the treated stands, frequency index of each stand was calculated by the following formula : Frequency index =((a×1)+(b×2)+(c×3)+(d×4))/(a+b+c+d)×100 in which a, b, c, and d are the frequency percentage of Miscanthus sinensis, Arundinella hirta, Zoysia japonica, and Plantago asiatica, respectively. The resulting index has a range from 100 to 400,and in this study from 133 to 390. The treated stands were arranged along the numerical order of the index (Table 2). 3. The frequency percentage of each species in each stand was plotted in the above mentioned order of stands. The distributional curve of each species was drawn through these points (Fig. 1). From the resulting curves, it is recognized that the distributional curve is generally of a binomial or bell-shaped form or a portion of it, that the plant species differ from each other in either the optimum range of development or the tolerance, or in both, and that the investigated grassland vegetation represents a continuum in which the principal species distribute continuously from the one end dominated by Miscanthus sinensis, through the intermediate stands dominated respectively by Arundinella hirta and Zoysia japonica, to the other end dominated by Plantago asiatica. It may be convenient for communicative purpose that, dividing the vegetational continuum, the community-type is designated with a single dominant species in this study, for the vegetation type in which Miscanthus sinensis is dominant, although the community-types are neither homogeneous within a particular type nor discrete between them. 4. Occurrence frequencies of dungs and trails of livestock, which indicate indirectly the degree of disturbance caused by treading, were examined in the treated stands. It is found that both frequency percentages increase from the stands of low frequency indices to those of high ones (Table 3). This fact shows that the vegetational continuum of the grazing grassland is pararell with the gradient of the disturbance pressure, from light to heavy conditions, and that, therefore, the plant populations can be used as an indicator for the disturbance condition. 5. Component species of the investigated vegetation were grouped into five groups in terms of the optimum range of development as (Fig. 2) : 1). species group, the optimum range of development of which is in Miscanthus community (Frequency index 100〜150), and which indicates the light conditions of disturbance and includes shrubs, tall grasses, and tall forbs; 2) species group, the optimum range of which in Arundinella community (F. I. 150〜250), and which indicates the medium conditions ; 3) species group, the optimum range of which in Zoysia community (F.I. 250〜350), and which indicates the medium conditions; 3) species group, the optimum range of which in Plantago community (F.I. 350〜400), and which indicates the heaviest conditions of disturbance and includes annual plants and ruderal weeds seen in the grassland; 5) accidental species group which has no indicator value.
(1) Three artificial pools, where the investigations were carried out, are situated in Shinjukuku, Tokyo, Japan. They are made of concrete, of rectangular shape (4×10m^2) and of the same depth of 2.5m. They were built as water reservoirs for fire protection in 1940. The water is humus brown, and is so turbid that SECCHI'S disc was often invisible at 0.5m. The three pools were designated as A, B and C. The pool A is situated in the open. The water edge of the western part of pool B and of the northern part of pool C were covered with the canopy of tree (5〜8m high), which are the main agencies giving rise to the difference of the nature of the waters. (2) The stratification and the seasonal succession of the number of phytoplankton were investigated. Stratifying samplings of phytoplankton were made monthly by using a siphon water sampler. They were measured by the precipitation method. (3) The similar mode of vertical stratification of phytoplankton was seen in the three pools. The maximum concentration of the total phytoplankters was seen in the upper layers (0-1m deep) during the spring and the early autumn overturns. It was seen in the middle and bottom layers (1-2m deep) during the winter. (4) Cyanophyceae and Desmidiaceae were commonly distributed in the upper layers during the summer stagnation. The surface water was rich in Peridinium and Phacus, but Trachelomonas assemble in the bottom layer. In the winter Synedra increased in the lower layers and in the spring and the autumn in the upper layers. (5) The seasonal succession of the individual number took place differently in the three pools both qualitatively and quantitatively. the annual yield of phytoplankton at C was larger than at B in 1952,and the reverse in 1953. It was less at A than in the other two pools every year. Two maxima were found in the spring and in the autumn, and two minima were seen in the winter and the mid-summer at every pool. (6) Cyanophyceae did not appear at A, and Flagellatae were mostly abundant in each pool Cyanophyceae, Diatomaceae and Desmidiaceae were scarce. The pool C was rich in Chlorophyceae. Other groups of phytoplankton occurred in about the same degree at every pool. (7) At A, Chlamydo onas (in 1951 and 1952), Trachelomonas and Peridinium (in 1953) dominated during the luxuriant period, while at B Trachelomonas was abundant every year, and at C Trachelomonas, Peridinium and Synedra and Melosira surpassed in all pools during the cold season, though some exceptions were recognized.
1. The present paper deals with the ecology of benthic insects living in pools of the River Yagi, which represents the upper course of the Maruyama River system. In the summer of 1957,I surveyed four pools in this river, the depths and the lengths of which ranged between 1.5〜3.5m and 13〜56m respectively. The topography of the pools and the result of collection are shown in Figs. 1〜4 and Tables 1〜5. 2. On the bottom of these pools, mayfly nymphs such as Ecdyonurus yoshidae, Potamanthus Kamonis, and chironomid larvae are the dominant species constituting the benthic insect community (Table 6). The dominant species of the pools differ widely from those of rapids (Table 8). 3. The dominant species of the deep bottom are the best indicators of the characteristics of the pools. 4. The standing crop in the deep bottom is the most scanty comparing with that of other parts in a pool (Table 7). 5. The standing crops of the surveyed pools ranged between 1.9 to 4.0 g per m^2,and these values represented 11 to 37 per cent of the standing crops of the rapids discharging into these pools. These values are shown in Tables 9 and 10.