In the field, the primary infections of scab to the heads of wheat occurred by the natural inoculation with ascospores or conidiospores flying in the air; whereas the artificial inoculation of scab is usually carried out by spraying a mixed suspension of spores and hyphae of the fungus. In this experiment of the improved method of scad inoculation, the possibility was tested that the hyphae alone might be infected to leaf blade or ears, as spores do. For this purpose, the hyphae as well as the spores were taken from the scad cultured on the potato agar medium. It was found that the infection could be also obtained by inoculating the hyphae alone, though the conidiospores were successfully used in the infection, of course. The materials (wheat varieties; Nobeoka-bouzu and Wheadling) used in this experiment were much more resistant to scab than the variety Shin-chunaga, which is recognized one of the most resistant varieties in Japan. Nevertheless, no difference was seen in the susceptibility to scab between these resistant varieties and the less resistant ones reported in our previous papers. This fact supports our previous assumption that both the resistant varieties and the susceptible ones show the nearly same degree of infection when the scab was inoculated into leaf blade. From the results of our previous studies concerning the scab infections to leaf blade, head and rachis of wheat by the improved method of inoculation, the conclusions with regard to the mechanisms of infection, resistance or susceptibility to scab were drawn as follows: (1) The absence of natural infection of scab on the leaf blade of wheat in the field may well be due to the fact that it has no morphological and histological factors (steps) to promote the germination of scab spores and the subsequent intrusion of hyphae into the tissue of leaf blade. But by the improved method of inoclation, scab fungus is able to intrude easily into leaf blade, and to show a symptom of scab infection on it, owing to the supply of moisture and nutrient. (2) The fact that the natural infection of scab to wheat is restricted to heads suggests the existence of various morphological and histological factors (steps), which are needed for the intrusion of scab into heads of wheat. Such factors as number of anthers caught by glumes, pollens, number and size of stomata on the inner parts of outer glumes were recognized as the important factors influencing the entrance of scab into heads. Furthermore, the resistance or susceptibility of wheat varieties to scab might be attributable mainly to the characteristic differences of these factors on the head of each variety. (3) The foliage lesion of scab inoculated by the improved method was similar in both the resistant and susceptible varieties. This similarity was explained by the fact that any of the wheat varieties is never immune or even highly resistant to scab constitutionally, and that all the varieties are equally susceptible rather than resistant to scab. (4) The degrees of lesion in various varieties infected by the improved method of inoculation on heads or rachises did not always coincide with those of the varieties whose resistances were judged by the degrees of damages received in the field. The possible explanation of this fact may be that when the tissues of heads or rachises were directly inoculated by the improved method, the tissues permit the entrance and spreading of fungus without the aid of any of the factors above-mentioned. In spite of this fact, however, the existence of slight but recognizable differences of varietal resistance in the predisposition cann't be completely excluded. The available data do not permit the definite conclusion, and these phenomena are open for further research.

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[in Japanese]

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Physiological changes induced in rice plant following defoliation were studied from 1961 to 1968. In the defoliated plants, the water and nitrogen content (%) increased with a concomitant increase in transpiration per unit weight of shoot as compared with those of the untreated control (fig. 1, 2). Recovery was most rapid in leaf formation and nitrogen absorption with the reduction of carbohydrate content in the stem and leaf-sheath (fig. 3). The Total-N/TAC ratios of shoot, therefore, were higher in the defoliated plant (fig. 4), indicating a more juvenile state. Chlorophyll content was also higher in the treated plant with a higher photosynthesis (fig. 7, 8 table 1). During 10 days following defoliation, the root activity expressed in the ability of TTC reduction was lower due to the stoppage of new root formation. After that, however, as the new roots emerged and elongated, the activity of the treated plant surpassed that of the control the roots of which were becoming gradually less active (fig. 9, 10). Higher growth rate in the later half-life of the defoliated plant was considered to be caused by the physiological juvenilization induced from the later formation of new roots and their longer persistence.

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Influence of oxygen concentration in the culture medium on the translocation of assimilated ¹⁴CO₂ into roots was studied on the tobacco seedling. The major results were as follows: 1. The translocation of ¹⁴C from top to root and its storage in the root was greater under aerobic condition than under anaerobic one. 2. The specific activity of ¹⁴C in the top scarcely decreased by the preceding anaerobic treatment, whereas that in the roots decreased conspicuously. 3. Exchange of anaerobic condition into aerobic one gave little influence on the specific activity in the top or decreased it to some extent, whereas that in the roots increased obviously.

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Application of nitrogen at different growth stages varied the total dry weight at the ear emergence and at maturity. The early application of nitrogen increased the total dry weight and straw weight at the ear emergence and at maturity much more than late ones. But the dry weight of ears at maturity and the grain yield had not always definite relation with the time of application of nitrogen. In case of the time of application of nitrogen being different, the dry weight of ears at maturity had not always definite relation with the dry weight produced after the ear emergence nor the number of spikelets, in spite of it being strongly affected by them. Except the treatment applied nitrogen after the rate spikelet initiation stage, the dry weight of ears at maturity was positively correlated with the dry weight produced after the ear emergence. But in all the treatments applied nitrogen after the late spikelet initiation stage, the dry weight of ears at maturity was positively correlated with the number of spikelets. So, the dry weight of ears at maturity was determined by the inter-relationshp of the number of spikelets and the dry weight produced after the ear emergence as reported previously. Dry weight of shoots increased after the ear emergnce was represented as the difference of the dry weight produced after the ear emergence and the dry weight which ears needed. The number of spikelets was determind by the interrelationship of the amount of nitrogen absorbed by the late spikelet initiation stage and that absorbed during the period from the late spikelet initiation stage to the ear emergence as reported previously. And the dry weight produced after the ear emergence was positively correlated with the product of the amount of solar radiation during the ripening period by the sum of the amount of nitrogen in leaf-blades at the ear emergence and the amount of nitrogen absorbed after the ear emergence. So, the dry weight of ears and shoots, the dry weight ratio of ear to shoot at maturity could be represented as a function of the amount of nitrogen absorbed at different growth stages. In this experiment, the dry weight ratio of ear to shoot had not definite relation with grain yield, the percentage of ripened grains and the amount of carbonhydrates in shoots at maturity, respectively. So, it could not always be taken as the index of the diagnosis of the yield, the percentage of ripened grains and the translocation of carbohydrates from shoots to ears, but could be taken as the index of the diagnosis of the interrelationship of the dry weight production at different growth stages and the number of spikelets, or the index of diagnosis of the interrelationship of nitrogen absorbed at different growth stages.

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In the previous paper, it was found that top dressing with nitrogenous fertilizer at full heading stage increases their percentage of ripened grains and results in an increase in yield. On the other hand, it is known that the protein content of rice is increased by the application of nitrogenous fertilizer after heading stage. Based on those results, the present experiments were carried out to prove the possibility of increasing the protein yield and the nutritional value of rice by nitrogen dressing. Basal dressing and top dressing at panicle formation stage did not always affect the total nitrogen content ( : protein content) but top dressing at full heading stage increased the total nitrogen content by 15∼30 per cent. In the case of increasing not only the total nitrogen but the grain yield by top dressing at full heading stage, the total nitrogen yield was greatly increased by the interaction. With respect to a given quantity of top dressing after full heading stage (2∼8 Ng/m²), it was shown that the more the fertilizer applied, the more the total nitrogen content was increased. When an identical amount of the dressing was applied in the period from full heading stage to 30 days after it, it was the more effective at the nearer stage to full heading. The total nitrogen was less in milled rice than in brown rice and the decreasing rate of total nitrogen by milling was lower in the brown rice of high total nitrogen content increased by top dressing at full heading stage. This finding indicates that the increased protein is stored in the endosperm. The total nitrogen content in both the brown and the milled rices showed negative correlations with lysine and methionine contents to 16g total nitrogen but positive correlations with lysine, threonine and methionine contents on dry matter. As the results, it is presumed that top dressing at full heading stage serves to increase the protein content and the nutritional value of rice, and also the protein yield in case of the percentage of ripened grains being increased.

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[in Japanese]

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In order to see the mechanisms of pod break down in peanut, the strength requisite for detaching the pod from the gynophore was examined, firstly. In this experiment, the pod break down occured by the breaking at the junction of gynophore and pod, or gynophore itself. The strength was measured with unbonded gauge type transducer (LT 51kg) and automatic null balancing recorder (fig. 1). Varieties were Java No. 13, Kikuyo and Chiba-handachi. Materials were taken at 5, 10, 20, 30, 40, 50, 70, 90, 110 and 130 days after flower open. Each experimental lot consisted of about 15 pods. Results were as follows. 1. The strength requisite for detaching the pod from gynophore increased with the number of days after flower open. At 30 days in Java No. 13, 40 days in Chiba-handachi and 50 days in Kikuyo after flower open, the strength was maximum. It was about 1.6kg in Java No. 13 and Chiba-handachi, and about 1.3kg in Kikuyo, respectively. Thereafter, the strength decreased with the number of days in gradually. At 50 days in Java No. 13 and at 70 days in Kikuyo after flower open, the strength was 1.1 kg in the former and 0.7 kg in the latter. In these two varieties, the strength was almost the same from this time to harvest time. In Chiba-handachi, on the other hand, the strength decreased from the time of maximum strength to harvest time. 2. At the time of maximum strength, seed size (weight of seed dry matter) were about 1/4 in Chiba-handachi, about 1/3 in Java No. 13 and about 2/3 in Kikuyo as compared with that at harvest time. In these three varieties, effect of seeding time on the strength was not obvious. Maximum strength at the duration from 50 days after flower open to harvest time was about 1.1∼1.3 kg in Java No. 13, about 1.2 kg in Kikuyo and 1.2∼1.4 kg in Chiba-handachi. On the other hand, the strength at harvest time (about 110 days after flower open) were about 1.1∼1.3 kg in Java No. 13, about 0.8 kg in Kikuyo and about 0.7 kg in Chiba-handachi, respectively.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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The conception has been prevailing for a long time that the crop plants grown under permanent wilting at several stages of the development always show a decrease in yield. For the improvement of irrigation method the authors scrutinized what disparity exhibited in growth and production of dry matter of corn plants as a provender, cultivated under the influence of successive wilting treatments at some stages of the development. This investigation was practised with the potted plants arranged in the green house condition. Wagner's pots were filled up with diluvial soil containing few organic matter. The potted plants presented the phenomenon of wilting in conformity to discontinued irrigation and soil aridity level was brought on several changes by the period to rewatering. The influences of wilting treatment on corn plants were as follows: 1. When corn plants were passed through successive wilting at the early stage of growth up to 6 leaves age, the growth and fodder yield decreased visually, but they showed an increase when corn plants were passed through only temporary wilting at same stage. 2. On any age between 9 leaves age when the lower internodes began to elongate and 15 leaves age when they were established, not only the growth and fodder yield did not decrease by the successive wilting but they often increased. However, they always showed a decrease when the plants were passed through more hardy successive wilting. 3. When corn plants were passed through successive wilting on the 18 leaves age when the stem began to elongate vigorously, they showed a decrease without restoring in the growth and fodder yield. 4. It may be very interesting phenomenon that the growth and the production of dry mater show the tendency to increase by rewatering after the plants were passed through temporary wilting at the early stage of growth up to 6 leaves age and they were passed through successive wilting for few days at the early stage of stem elongation.

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It has been known that the organs and tissues developed under wilting show the various morphological changes in the xerophyte plants and that the morphological changes due to dryness itself may not be able to increase the yield because all cells, tissues and organs diminish in size because of water deficit. The authors reported in previous paper that the fodder yield does not always decrease by the treatment of successive wilting. At the same time they observed such phenomena seemed to be the cause of the increased fodder yield by some morphological changes resulted from successive wilting at some stages of the developments. In the present paper the phenomena, i. e. the elongation of lower internodes and the appearance of the root developments by the wilting treatment are reported. 1. The elongation of lower internodes which developed during the wilting period from 6 or 9 leaves age to 12.5 leaves age, was retarded and the length of lower internodes became short. On the contrary the growth of upper internodes became supplementally vigorous. As the result of shorting of the lower internodes, the more nodes may be covered with soil easily by the work of hilling. 2. The brace roots from lower nodes begin to elongate from the lowest node at first and thereafter regularly from the upper ones. This pattern seems to indicate that there may be some relationship between rooting and internodal elongation. Under the unsuitable circumstances the brace roots stop to elongate about 3∼5 cm in length without branching and after then, even if the circumstances become better they do develop no longer, though the development of brace roots from the upper nodes is accelerated. 3. On corn plants experienced the successive wilting a number of roots become elongate after rewatering and as the results the number increase when wilting is not so hard, though they decrease when it is hard. The number of roots that begin to elongate during wilting period have the inclination to be reversed. 4. The influence of GA treatment on the growth of corn plants and the behavior of rooting was discussed from the hormonal stand point of view referring to the effects of gibberellin on them carried out by the writer and others.

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Dry matter production was compared between the two groups of four grass species which differ in photosynthetic capacity and optimum temperature for growth. The species were oats, Avena sativa L. Italian rye grass, Lolium multiflorum, (species of low photosynthetic capacity and low optimum temparature), barnyard grass, Panicum Crus-galli var. echinata and sorgo, Sorghum vulgare (species of high photosynthetic capacity and high optimum temperature). Experiments were carried out from summer to autumn in 1966 for 74 days with two sowing densities and for spring in 1967 for 51 days with one sowing density. The results of high density plot only were described. Panicum and Sorghum produced much higher dry matter and had higher crop growth rate (CGR) then Avena and Lolium (Fig. 1 and 4) in the experiment in 1966. It was shown that the former species had the higher leaf area indeces (LAI) in an early growth stage (Fig. 2) and had the higher net assimilation rate (NAR) even in the growth stage of high LAI than the latter species (Fig. 3). The comparison was also made in dry weight ratio of nonphotosynthetic system to photosynthetic system and specific leaf area, but no consistent result with dry matter production was obtained (Table 3). In the experiment in 1967, which was carried out for a period of lower temperature, longer day length and for younger stage, than the one of 1966, sorghum showed higher CGR, higher relative growth rate, higher relative leaf growth rate and higher NAR than Lolium (Table 5). It was noticed that NAR was one of the most important factor for dry matter production in the young stage with low LAI. From these results, the significance of NAR or photosynthetic capacity per unit leaf area (P) in dry matter production was discussed. It was concluded that not only leaf area but NAR or P were important and that the high dry matter production of forage grasses could be achieved with the species which possess both the ability of high NAR or P and of high growth rate in leaf area simultaneously.

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In the present investigation, the authors observed the changes caused during the storage in the quality of rough rice grains harvested by the combine harvester (cylinder speed, 1, 100-1, 700 m/min). For this purpose, sample rough rice were harvested by the combine on September 7 and November 8, 1966, and were conditioned at five moistur-content levels, approximately at 16, 18, 20, 22, and 24%, and stored for 30 days at temperature of 23°C, 28°C, 32°C and variable (in a barn of wooden construction, room temperature 25.8°C to 17.6°C) in case of samples harvested on Sept. 7; and 13°C, 18°C, 23°C and variable (room temperature 15.2°C to 7.5°C) in case of samples harvested on Nov. 8. The results are summarized as follows: 1. In the case of samples containing less than 20% moisture, any appreciably great changes in moisture content were not noticed during the storage period, irrespective of the different harvesting dates, while in the samples containing more than 20% moisture, moisture content increase at the latter storage stage when stored at tempratures of 23°C, to 32°C. 2. The occurence of deteriorated grains in the course of storage for 30 days was on the upward trend accordiny as the moisture-content and storage temperature became higher, and when stored at variable temperature in a barn of wooden construction, the grains harvested on earlier date tended to become more liable to be deteriorated. In the case of grains of moisture-content of less than 18%, little or no deteriorated grains were noticed during the 30 days storage at the respective temperatures ranging from 13°C to 32°C, irrespective of different harvesting dates In the course of storage for 30 days, the rough rice grains heavested by the combine were more often deteriorated than the grains threshed using the self-feeding thresher. 3. Viabilty of embryos (TZ values) both of the grains harvested on earlier date and on later date tended to decrease more rapidly at the latter storages according as the moisture-content and the storage temperature became higher. 4. In case where 23.6% moisture-content grains harvested on Sept. 7 were stored at temperatures of 23°C to 32°C and variable, grains could safely be stored only for one day, while in case where grains containing 18% moisture heavested on Sept. 7 or grains of less than 18.9% moisture heavested on Nov. 8 were stored at temperatures of 13°C to 23°C and variable, both grains could safely be stored for 30 days without any deterioration in their quality. In case of the grains of the same moisture-content, the maximum safe storage duration of the rough rice harvested by the combine was shorter than that of the grains threshed by the selffeeding thresher. This was thought chiefly due to the fact that the percentage of the injured grains harvested with combine was higher than that threshed by the self-feeding thresher.

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Relationships of corn plant population rates, soil fertility levels and varieties with grain yield, total dry matter and composition of corn leaves were examined in 1967. The results are as follows. 1. The logarithm of grain yields per plant decreased linearly as plant population was increased. By using the linear relationships between the logarithm of the grain yields per plant and the number of plants per land area of one are, the maximum grain yields and optimum plant populations on each soil fertility level were determined after Duncan's example. The highest value of the calculated maximum grain yield was 87.1 kg per are at 749 plants per are on the high fertility soil for Tomorokoshi Ko No. 7 (variety cross), and 67.7 kg per are at 562 plants per are on the high fertility soil for Yellow Dent corn (openpollinated variety). 2. There were also the linear relationships between the logarithm of total dry matter yields per plant and the number of plants per are for Tomorokoshi Ko No. 7. The logarithm of total dry matter of a plant decreased linearly as plant population increased. The highest total dry matter yield was 202kg per are at 932 plants per are on the high fertility soil. The optimum plant populations for the highest total dry matter production were higher than those for the highest grain production on each soil fertility level. 3. Tomorokoshi Ko No. 7 required higher populations than Yellow Dent corn to reach the point of maximum yields on each soil fertility level. It is suggested that Tomorokoshi Ko No. 7 possess an inherent capacity to perform better than Yellow Dent corn under the stress of high population rates. 4. As the soil fertility increased, the number of plants per are required for maximum grain yields and maximum total dry matter yields increased. The higher maximum grain yields and maximum total dry matter yields were obtained on the higher soil fertility level than on the lower. It is suggested that increase of plant population for higher grain yields and total dry matter yields should keep pace with increase of soil fetility. 5. Chemical analysis of the leaves on the nodes just below the primary ear for total N, P and K at silking stage showed that the yields of Yellow Dent corn increased with increase of N and P contents when N and P were below 2.4% and 0.26%, respectively. But little or no yields increased when they exceeded 2.4% N and 0.26% P. The yields of Tomorokoshi Ko No. 7 increased with increase of N and P contents within the limits of observation in these experiments. There was little change in K contents with difference of plant population and soil fertility. 6. The conclusions drawn from these experiments are that for Tomorokoshi Ko No. 7 high yields above 850 kg per are may be obtained at plant populations above 650 plants per are when N and P contents of the leaf are above 2.5% and 0.34%, respectively, and that for Yellow Dent corn, likewise, higer yields above 650 kg per are, at plant populations above 450 plants per are when N and P contents, above 2.4% and 0.26%, respectively.

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Studies were made in order to find out the ecological factors on the deep plowing culture of sweet potato. Deep plowing culture was carried out by plowing 25 cm deep, and compound fertilizer was applied to both shallow and deep layers of soil. Nutrients treatments are as follows (kg/10 a): ordinary culture, compound fertilizer (3-10-10) 100; heavy manuring culture, 200; deep plowing culture, 100 (shallow) plus 100 (deep). The ordinary and heavy manuring culture were applied only a shallow layer. For growth analysis, whole plants were taken seven times every three weeks after transplanting and divided into each organ. Leaf area was estimated by the leaf punch method and various ecological indexes were calculated from the values of leaf area and dry weights of the plant. In order to analyze the photosynthetic ability of leaves physiologically, three major elements (N, P, K, ) and carbohydrate contents were determined. The results obtained are as follows: 1. Fresh weight of tuberous roots of the deep plowing culture was greater about 22% than the ordinary culture or the heavy manuring culture. 2. LAI at the vigorous stage was the smallest in the deep plowing culture. At the harvest time, LAD of the ordinary, the heavy manuring and the deep plowing culture were 53.7 (week), 59.3 and 49.6, respectively. In the deep plowing culture the dry weight of stems (containing petioles) was not so much as other treatments. 3. NAR and (Leaf)/(Stem) which shows the structural efficiency of the vegitation were generally high throughout the growth stage in the deep plowing culture. 4. The coefficient of the economic efficiency of photosynthesis (Keco.) proposed by NICHIPOROVICH and MEDINETS, is defined by [yield (fruits, tuberous roots, etc.)/total weight] and indicates how amount of total photosynthates is used for the economic part of a plant. In this experiment, Keco, is (TR)/(T) in table 1. Keco. of the deep plowing culture kept high extent throughout the growth stage. 5. It is well known that K content of leaves correlate highly with the photosynthetic ability, and K/N of tuberous roots also correlate with the growth of tuberous roots. Both values of the deep plowingculture were higher than the other two. 6. Total carbohydrate contents were not largely diffent between the treatments. And high yield culture did not lower the carbohydrate content of tuberous roots. 7. From the resuls described above, it can be concluded that photosynthetic ability of the deep plowing culture was higher and photosynthates translocated very efficiently into the tuberous roots.

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Experiments were undertaken to examine the relation between photosynthetic rate, air-temperature, concentrations of sulfur dioxide and treatment time for which rape and barley were exposed to the gas. The results obtained were as follows : 1. Photosynthetic rate of rape and barley was markedly decreased with an increase in the concentration of sulfur dioxide and an extention of treatment time exposed to the gas, especially in the plots treated by 5 and 10 ppm-SO₂, it was found that respiration exceeded photosynthesis. 2. The rate of apparent photosynthesis was decreased by about 160% in 8 hours after barley exposed to 10 ppm-SO₂, and about 140 % in 7 hours after rape exposed to 5 ppm-SO₂, comparing with the control (0 ppm-SO₂), respectively. The rate of decrease of apparent photosynthesis (R) was calculated by the following formula : R(%)=(A-B)/A×100 Where, A and B denote the apparent photosynthesis of the control (0 ppm-SO₂) and that of each treatments (5, 10 and 20ppm-SO₂), respectively. 3. Making a comparison between the rate of decrease of the apparent photosynthesis to 0 ppm-SO₂ of rape and barley under the condition of 20°C, there were frequent occasions when that of barley showed higher than that of rape. 4. As the result of experiment, the rate and degree of the apparent photosynthesis to 0 ppm-SO₂ [showed generally higher values under the condition of 20°C than 10°C in both plants. From the present experiment, an injurious effects of sulfur dioxide on the apparent photosynthesis of rape and barley varied with difference of air-temperature during treatment with sulfur dioxide, the concentrations of sulfur dioxide and treatment time for which both plants were exposed to the gas.

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In order to establish the direct-seeding cultivation of rice on the submerged paddy field in such cool region as in Hokkaido, it is very important to stabilize the germination after seeding and to stabilize the subsequent standing of seedlings. Standing of seedlings is affected seriously by the root development conditions at the earlier stage. In view of this, in order to clarify the relation between the viability of rice seeds to germinate at low temperature (having close bearings on the stability of germination of seeds) and the viability of roots to develop at earlier plant growth stage, the authors made the experiments in 1967 under the conditions of the direct-seeding on the submerged paddy fields (indoor) by using 23 varieties as samples. The results of the experiment are summarized as follows : 1. With respect to the relation of the viability of paddy rice seeds to germinate at low temperature to the some properties of roots (the number of roots, the maximum length of roots, and the weight of roots of the seedlings), significant or some positive correlations were observed in both cases of 10-day old seedlings and 20-day old ones, irrespective of the difference in water depth (3 cm and 6 cm), but in the case of 20-day old ones, the correlations were observed more clearly than in the case of 10-day old ones. 2. Regarding the inter-or intra-relations among the number of roots, the maximum length of roots and the weight of the seedlings, very high correlationships were noticed, irrespective of difference in the water depth as well as in the number of days after seeding. Even at the relatively early stage after seeding, the same varietal differences were observed under different conditions such as depth water. 3. On the other hand, with respect to the relation between the plant height and the root development, very high positive correlation was observed. When authors tried to find out the partial correlations among the germination rate of seeds at low temperature, plant height and the root development at earlier stage, the significant correlation was observed between the plant height and the root development at earlier stage, excepting the effect of the germination of seeds at low temperature. 4. Viewed from the above test results, the positive correlation found between the germination rate of seeds at low temperature and the root development at earlier stage is regarded as the derivative action through the plant height. However, the significant correlation between the germination rate of seeds at low temperature and plant height of seedings was observed as reported in preceding paper (SASAKI, 1968), so, authors dissussed that it was very significant to use the rice varirties high in germination rate at low temperature to ensure the stability of direct-seeding rice culture on the submerged paddy field in such cool region as in Hokkaido.

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Photosynthesis in the communities of various plant spacings in plant bed was tested with ecological methods. From the analysis of dry matter production (Fig. 2, Table 1), field-density effect seemed to appear at the stage when the value of leaf area index exceeded more than 4. From the study of photosynthesis-light curves in plant communities, light satulation was observed even at the stage when the density effect had already appeared (Fig. 3). Changes in the pattern of light curves were not obsered in relation to plant spacings or stage of seedlings. This might be due to the apparent photosatulation by tobacco seedlings in the community, where owing to shading effect whole photosynthesis would be represented by photosynthesis of the surface layer of leaves. Logarithmically linear relation was shown between photosynthesis per unit leaf area and leaf area index (Fig. 4), so the photosynthesis seemed to decrease with the increment of leaf area index. Photosynthesis is decreased in relation to the protein nitrogen content in leaves (Fig. 5), but the decreace in the protein nitrogen content might be due to the reduction in the supply of photosynthate for the protein synthesis. Comparison of leaf number and the ratio of stem dry weight to total dry weight showed that the narrower the spacing of seedling of seedlings, the worse the quality of seedlings became.

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Following the previous report, two experiments were carried out to analyse further the photosynthesis in plant communities in plant bed. In the first experiment, of which nitrogen supply was changed, the pattern of the photosynthesis-light curves was almost the same irrespective of the treatment, as shown in the previous report (fig. 2). Logarithmically linear relation was also shown between photosynthesis per leaf area and leaf area index (fig. 3). Further analysis of this relation led to the following formula; P=C(SA)^α(LA)^1-α Where, P : Photosynthesis per seedling in plant community. SA : Plant bed area per seedling. LA : Leaf area per seedling C : Parameter which expresses photosynthetic ability per leaf area in the community where any mutual shadowing does not appear. α : Expornent which expresses the extent of influence of leaf area index on photosynthesis per leaf area. Commenting this formula, the photosynthesis per plant in plant bed community would be decided by spacing at first, and by leaf area expansion at second. In the second experiment, effect of plant growing conditions, such as water, light and temperature, upon the relation between photosynthesis per leaf area and leaf area index were investigated (fig. 4). The effect of these factors was shown as the slope in the above mentioned relation. And the extent of these factors to restrict leaf area expansion was larger in the order of water, temperature and light. As the quality of seedlings becomes worse with the excess increment of leaf area, it is necessary to restrict leaf area expansion through the growing conditions, with which the depression of photosynthesis is brought about.

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