The genus Pythium(aquatic fungi)is distributed widely in Japanese lakes, occurring both in the water and the bottom mud. So far as the researches are concerned, the following characteristics may be given with regard to the condition of distribution of the genus Pythium. 1. The amount of zoospores of Pythium in lake water fluctuated seasonally. The feature of seasonal rhythm differend with different lakes. The maximum was observed in winter and the minimum in summer. 2. The vertical distribution of zoospores of Pythium differed seasonally. The zoospores were distributed homogeneously from the surface to the bottom layer during the circulation period and only in the epilimnion during the stagnation period. 3. The distribution of the genus Pythium had close relation to the lake types. They were distributed abundantly in harmonic lakes, while they were very rare in dystrophic and acidotrophic ones.
SUZUKI(1952)reported the ratio of variation (r) on the distribution of a plant community by using the following equation : [numerical formula], where d is distance (meter)between two quadrats, x_a and x_b are measuring value of species at each plot. In of d is constant, the ratio of variation between two quadrats can be compared with each other by that equation. Mean while, we observed the rise and fall of the dominance of each species in a grassland community. If the quadrats are arranged on a line such order as 1,2,3,...n ; with a constant distance between each, the total of the pairing groups is equal to[numerical formula]. For example, if 5 quadrats (z_1,z_2,z_3,z_4,z_5)are arranged on a line with a constant distance between each, the pairs of quadrats can be expressed as follow : (z_1,z_2)(z_1,z_3)(z_1,z_4)(z_1,z_5)(z_2,z_3)(z_2,z_4)(z_2,z_5)(z_3,z_4)(z_3,z_5)(z_4,z_5) Next, both the ratios of variation where the distance is variable (r) and the distance is the median of total length (r') are computed. If the arithmetic means of r' and r'are R and R'respectively, the difference between : R and R'is regarded as the difference of variation ratio(D)by the author. We can find whether a grassland is homogeneous or not by the value of D.
1. Some studies on population ecology were performed by using Drosophila melanogaster, that had been cultured previously by PEARL's medium. 2. When the larvae were cultured in CARPENTER'S medium (Table 1), some characters of the larvae and the adults showed various degrees of variations according to the population densities. With increasing of the densities, the rate of the development of the larvae tended to delay, the emergence rate and the fecundity of female flies emerged from these larvae tended also to decrease. On the other hand, if the population was too scarce (as only one individual per vial), the same detrimental effects were observed. These are the ALLEE'S effect. 3. When the densities of the yeast contained in the food media were different, the flies showed various changes in some characters according to them. In this case also the intermediate density of the medium (standard CARPENTER's medium shown in Table 1 by using 25 g of yeast) was the optimum. The lower or the higher the densities than the optimum, the slower the rate of development of the larvae. The body length and the fecundity of the adult flies also showed the maximum condition at the optimum density of food as mentioned above. 4. No difference in the rate of development of the larvae and the emergence rate was observed among the three different media, namely, PEARL'S medium, CARPBNTER'S medium and CARPENTER'S medium without MOLDEX. However, the lengths of body and wing of the adult flies grown up in the last medium were the largest, and on the contrary, the fecundity was the smallest.
The effluents of three mines, the Kamioka Mine in Gifu Prefecture, the Ogoya Mine in Ishikawa Prefecture and the Hosokura Mine in Miyagi Prefecture were studied, with regard to their effect on stream organisms. The water insects were collected quantitatively at several stations of the rivers in the drainages of the mine-water(Figs. 1,2,3,4,5,6). 1. At the kamioka Mine, the effluents influence the aquatic insects of the Takahara River, as far as to 19 km downstream, it seems to recover in confluence with the Miya River. 2. Ogoya Mine, the Mine, the mine-effluents influence the aquatic insects of the Hashigo River, as far as to 16.5 km downstream (at Karumi). 3. Hosokure Mine, the mine-effluents influence the aquatic insects to the hazama River, as far as to 19.5 km downstream(at Obayashi).
There are two types of females in a social halictine bee, Halictus(Seladonia)aerarius(SMITH). One is large and macrocephalic with dark-coloured mandibles, labrum, legs and metasomal sterna, while the other, which involves the majority of the specimens examined, shows the opposite tendencies in the characters concerned. The two types are distinct from each other in the extremes, although connected by intermediate individuals. Seemingly, this morphological differentiation corresponds to the functional differention of the queen(macrocephalic)and worker(microcephalic). But it was observed that a microcephalic female can occasionally found a nest independently, suggesting a slight discrepancy between morphological and functional differentiation;nevertheless the former attains the highest level of the caste differentiation among the social halictine bees so far studied. As another Japanese species of the same subgenus, H. (S.)tumulorum LINN'E has a simple, solitary life history, the subgenus Seladonia offers a further instance to the co-existence of both solitary and social species within one subgenus;such instances are frequent among halictine bees.