Investigations have been carried out to determine the protein, fat, ash, phosphorus, potassium, and magnesium content of rice kernel of 4 lowland non-glutinous varieties at intervals of 10 days from dough ripening (20 days after heading) to over ripening (70 days after heading). From dough ripening to full ripening, the chemical composition varied widely and each of the components decreased on dry matter and increased in 1000 kernels. After full ripening, the chemical composition had a tendency to vary slightly. The protein and fat content decreased and the ash and potassium content increased on dry matter. On the other hand, the protein content increased or decreased after the initial increasing and the ash, phosphorus, potassium, and magnesium content increased and the fat content decreased in 1000 kernels.

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In order to investigate the effects of high temperature in young stage of tobacco leaf on the final leaf shape, tobacco (flue-cured variety, BY-4), planted in the pot of 1/2000 a, was grown in four plots in the controlled conditions, i.e., (Plot 1) 20°C (9:00-17:00) /15°C (17:00-9:00) for 4 weeks from April 10 (the 5th day after planting) in 1969 (control), (Plot 2) 35°C/15°C for 2 weeks from April 10 and 20°C/15°C for the successive 2 weeks, (Plot 3) 20°C/15°C for 2 weeks from April 10 and 35°C/15°C for next 2 weeks, (Plot 4) 35°C/15°C for 4 weeks from April 10, in the phytotron of Okayama Tobacco Experiment Station (Table 1). And in the field, tobacco (BY-4) was grown in three plots, i.e., Non-covered plot (control), Plot covered with polyethylene film for 21 days after planting, on April 2 in 1971, Plot late covered with polyethylene film for 13 days (from the 34th day to the 47th day after planting) (Table 2). The following results were obtained; 1. In Plot 2, width/length ratio of the mature leaves under the 16th leaf (numbered from cotyledons) got greater than that of the comparable leaves in Plot 1 (Fig. 3). 2. In Plot 3, the mature leaves above the 15th leaf got broader than the comparable leaves in Plot 1, but there was little difference in width/length ratio of the mature leaves under the 15th leaf between Plot 3 and Plot 1, in spite of smaller size of them in Plot 3 than the comparable leaves in Plot 1 (Figs. 1, 3). 3. In Plot covered after planting, width/length ratio of the mature leaves under the 15th leaf got greater than that of the comprable leaves in Non-covered plot, and in Plot late covered, the upper leaves from the 21st leaf got broader than the comparable leaves in Non-covered plot (Fig. 8). These results indicates that the final leaf shape of tobacco was distinctly affected by high temperature in the young stage of the leaf and that high temperature little affected the final shape of the leat except its size, which has been comparatively large.

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Mesophyll protoplasts of Nicotiana tabacum. cv. Bright Yellow mutant Aurea and Burley 21, and of N. rustica. cv. Rustica were prepared from leaf tissue by enzymatic digestion and were fused with the aid of polyethylene glycol. When the fused protoplasts were plated on an agar medium or in a liquid medium for cell culture, new cell walls were regenerated from them and the first cell division could be seen beginning on the 12th day of culture, and cell division process took place on and after the 21th day (Fig. 1). After one month culture, almost all of the surviving fused protoplasts grew to cell colonies of 1-2 mm in diameter. The cell colonies were subcultured on an agar medium for callus culture. On the medium, they grew vigorouly and formed calli of 2 cm in diameter after 2 months culture. At this stage, the hybrid calli showing greenish white with a compact appearance were selected in contrast to parental type calli tinged with white or green color (Fig. 2). Ten somatic hybrid calli of the combination of Aurea and Rustica and 3 calli of the combination of Burley 21 and Rustica were obtained. Many plantlets were differentiated from these calli when transfered to a medium enriching zeatin (Fig. 3). All of the mature flowering plants showed to be perfectly hybrid, and the shape of the leaves and flowers indicated an intermediate between N. tabacum and N. rustica (Fig. 5, 6). The plant height of the normal hybrid morphologically was higher than that of the parent plant and all of the hybrid plants were highly resistant to the tobacco mosaic virus (Fig. 4, Table 1, 2). The chromosome numbers of the somatic hybrids showed to be the aneuploid type having from 60 to 91 chromosomes (Table 1, 2). The normal hybrid plants morphologically, however, have a pollen fertility, and seeds and progenies were obtained from 4 of the Aurea-Rustica hybrids and 3 of the Burley 21-Rustica hybrids (Table 1, 2).

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The present investigation was undertaken to clarify the relationship between the behaviour of stomata and water absorption through thc roots in rice plants grown under submerged condition by measuring the diurnal course of stomatal aperture in rice plants with partially excised root system. No difference of stomatal aperture was found between plants with non-excised and partially excised root system in early morning when transpiration was not so remarkable and water content of leaf blades was still high (Fig. 2, 3). After about 11 a.m. on a fine day accompanied by intense transpiration, stomata closed to a more considerable extent in plants with partially excised root system than that of non-excised one, due to decrease of water content of leaf blades (Fig. 2, 3). The extent of stomatal closure is severer in lower leaves than in upper ones, especially in plants with partially excised root system, so that the difference of stomatal aperture between lower and upper leaves became larger in the afternoon (Fig. 4, Table 1). Leaf water content on an areal basis followed the diurnal variation pattern of taking the maximum value in early morning and decreasing towards atternoon. The decrease of leaf water content was rather remarkable in plants with partially excised root system than that of non-excised one on fine days, but the difference was smaller than was expected (Fig. 5). Leaf water saturation deficit was different significantly between plants with non-excised and partially excised root system in the afternoon on the fine day at the ripening stage (Table 2). From these results and the close relationship between stomatal aperture and photosynthetic rate, it is suggested that the decrease of water absorption in rice plants grown under submerged condition has much caring on the efficiency of light utilization in photosynthesis because of the stomatal closure in the afternoon on a fine day, in the same manner as the effect of water deficit in the soil.

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1. Stomatal frequency (stomatal number per unit leaf area, abbreviated Sf) of a flag leaf was high at the middle of the leaf and low at the leaf margin. It was low at the leaf base and the leaf apex (Fig. 1, 2). Sf in a leaf in upper leaf position on a stem was higher than that in lower leaf position. Sf in lower leaf surface was higher than that in upper leaf surface (Fig. 3). 2. Sf of upland rice cultivars was lower than that of lowland rice cultivars (Fig. 3). Sf of Indica type rice was higher than that of Japonica rice (Fig. 4, 6). Sf of leaves grown in different years (Fig. 4), in different transplanting dates (Table 4) and in low-land and upland field (Table 3) correlated highly in positive way. Sf of L₂ and Lf (Table 2) and Sf in lower and upper leaf surface (Table 3) correlated highly also in positive way. 3. Fertilizer application at lag stage caused an increase of Sf leaf size and total stomates of a flag leaf (Table 1, Fig. 5). Sf decreased with a shortening of the growing period (Table 5, 7). In comparison among cultivars of lowland rice, Sf of cultivars having a large leaf was high (Table 5). But in comparison among cultivars containing upland rice, Sf of cultivars having a large leaf was low (Table 7). Values of genetic correlation between Sf and leaf size (Table 6) explained this tendency quite well. Values of environmental correlation between them were low (Table 6). Sf of lowland rice grown in lowland field was higher than that in upland field. In case of upland rice, however, difference between Sf grown in lowland and upland field was not so clear (Fig. 3).

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The present investiagation was undertaken to examine possible change of the diurnal course of stomatal aperture in rice plants grown under different environmental conditions from the transplanting to the day of stomatal measurement. The environment was much different between the border and the interior of rice population of paddy fields, i.e., light intensity was weaker due to mutual shading, humidity higher and wind lower in the interior of paddy fields (Table 3). The stomatal aperture was both measured in rice plants grown in the border and interior of paddy fields and in those grown in the pots buried in the places mentioned above. Furthermore, the stomatal aperture of the rice plants which had grown in the interior was measured in the almost same condition as the border by reaping several rows in the south or west side of these rice plants by 10 m wide on the day just before the stomatal measurement. And also the stomatal aperture was measured in rice plants grown in the pots transported from the interior to the border on the day just before stomatal measurement. In this paper rice plants subjected to the two treatments mentioned above were represented by "Interior to Border", and rice plants grown and measured in the interior and border were represented by "Interior"and "Border", respectively. The stomatal aperture of rice plants which had grown under different environmental conditions was compared in the same border environment by measuring the diurnal course of stomatal aperture of "Interior to Border" and "Border". The stomatal aperture of rice plants which had grown under the same interior environmental conditions was compared in the different environment by measuring the stomatal aperture of "Interior" and "Interior to Border". The results obtained are as follows. On a cloudy day the diurnal course of stomatal aperture was practically the same in "Interior", "Interior to Border" and "Border" except when the stomatal aperture was smaller due to the severe decrease of radiation (Fig. 1. A.). On a fine day the stomatal aperture was not so different among three kinds of rice plants in early morning, but about 9 a.m. the stomata in "Interior" closed to a lesser extent than those in "Interior to Border" and "Border", due to weaker light intensity, higher humidity and lower wind in the interior of rice population, so that the stomatal aperture was larger in "Interior" compared with those in "Interior to Border" and "Border" at all growing stages (Fig. 1. A., Fig. 2-4). Furthermore, the extent of stomatal closure in "Interior to Border" was severer than that of "Border" in the afternoon on a fine day with intensive transpiration except for the two stages, i.e., the maximum tillering stage when rice plants did not grow so thick and the ripening stage when rice plants in the border were mature earlier than those in the interior (Fig. 2, 3). Attention should be paid to both facts that the stomatal aperture of rice plants grown in the pots buried in the border was larger in the afternoon on a fine day compared with those grown in the pots transported from the interior to the border, and the facts that the stomatal aperture in the pots transported from the border to the interior ("Border to Interior") was also larger compared with those in the pots buried in the interior (Fig. 4). The stomata of lower leaves closed to a more considerable extent in the afternoon than those of upper ones in "Interior to Border" compared with stomatal closure of upper and lower leaves in "Border" at the same hours (Fig. 5, 6. Table 5). [the rest omitted]

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Field experiments were carried out from 1966 to 1972 using rice varieties "Hoyoku'' and "Shiranui" both in normal season culture and early planting culture to find out relationship between yield or yield components and climatic factors or other factors. Results obtained are as follows. 1. Mean temperature for 3 weeks from heading did not show significant simple correlation with yield, but, it showed significant negative partial correlation with yield. It suggests that yield tends to decrease with increase of the mean temperature of that period, when excluding the effect of other factors. 2. High negative correlation was found between mean temperature for 3 weeks from heading and 1000 kernel weight, and it was supposed that this fact corresponded to the significant negative partial correlation found between yield and the mean temperature for 3 weeks from heading. 3. Positive correlation was found between number of ears per m² and ratio of solar radiation to mean temperature during the period from transplanting time to 6 weeks before heading, showing that abundant solar radiation and low temperature in tillering stage was apt to produce a large number of ears. 4. Positive correlation was found between spiklet number per m² and solar radiation during the period 6 weeks before heading, and negative partial correlation was found between spiklet number per m² and mean temperature during the same period. 5. Negative correlation was found between 1000 kernel weight and calculated value of respiration after heading.

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This study was undertaken to determine the influence of upright leaves, at various populations in two row widths (50 cm and 150 cm); on the light distribution, dry matter production and grain yield of field grown corn (variety Azumayellow). Upright leaves were obtained by mechanically supporting leaves above the first ear node in an elect position since 1 week later from silking time to date of maturity. The results are as follows. 1. At both row widths, the effect of upright leaves on light distribution was seen only at 900 plants/a. 2. In two row widths, upright leaves affected differently on dry matter production at 900 plants/a. The dry matter production was increased in 50 cm row, but decreased in 150 cm row. As a result, optimum population for dry matter production was heightened at 50 cm row and lowered at 150 cm row. 3. The dry matter production increased as LAI increased to 6-7, but no further increases above an LAI of 6-7. And it became advantageous to reduce light extinction coefficient to optimum value by upright leaves with narrow row. 4. Effects of upright leaves on grain yield were similar to that on dry matter production. When leaf angle were compared for best grain yield, upright leaves outyielded the normal by 27% (107 kg/a).

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It is very important to determine the optimum planting density giving the highest yield and also to understand the effect of plant height on growth and yield. This experiment was conducted to investigate the effect of the planting density and the plant height on dry matter production and yield performance under three different planting densities with three grain sorghum varieties in 1977. The tall and short line in each variety used for this experiment were isogenic having a common genetic background. The main results obtained are summarized as follows. 1. There were statistically significant differences in tiller number, dry matter weight and leaf area per unit area among planting densities. These characters were larger in high density than in low desnity. No significant differences were shown in tiller number and leaf area between tall and short isogenic line. 2. There were significant differences in NAR and CGR among varieties in t₂ (29, June-11, July) and t₃ (11, July-25, July). The tall lines exceeded significantly the short ones in NAR and CGR (Table 1). 3. With the increase of LAI, NAR decreased, while CGR increased (Figure 1). The best fitting regression of NAR on LAI was curvilinear while that of CGR on LAI was straight. This relationship was common among varieties and lines. But the tall lines showed higher value of NAR and CGR than that of the short ones at the same LAI level. 4. As the grain yield was closely related with CGR and LAI at t₁ (16, June-29, June), t₂ and t₃ (Table 3), the higher yield will be attainable when both CGR and LAI are higher from early growth stage. 5. The positive significant correlation between grain yield and LAI at heading stage was observed. The optimum LAI may occur over higher level obtained in this experiment. 6. The grain yield of tall lines significantly exceeded that of short ones and the grain yield of tall and short lines increased with the increase of planting density (Table 1, 4). The optimum may occur outside the range of density used in the experiment. 7. It has been said that the taller the plant height, the better the distribution of light within a plant population. It may be concluded that the tall line is more advantageous in the efficiency of dry matter production and in getting higher yield than short line, whereas lodging must be noted.

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Existence of considerable amounts of gibberellins in crop residual was detected in rice and barley straw, bean pericarps after full ripening and abscind bean cotyledons. Gibberellin activity was detected even when the straw of rice and barley, and full ripened bean pericarps were air-dried for a long time before the extraction of gibberellins. The gibberellin activity in the rice straw was found only in the acidic ethylacetate fraction and no activity was detected in the acidic n-butanol fraction (Fig. 1). On the other hand, in the barley straw and the bean pericarps, the activity was detected in both fractions (Fig. 2). In the kidney bean, the full ripened and then air-dried pericarps contained almost the same amount of gibberellins in both fractions as the developing one (Fig. 3). The abscind bean cotyledons were also found to contain almost the same amount of gibberellin in both fractions as in the cotyledons at their early stage of germination (Fig. 4). It may be concluded from these results that gibberellins are widely detected in the crop residuals that already accompanying no growth. Moreover, gibberellins may play certain roles not only in their own growth of the organs that containing those gibberellins but also in other physiological phenomena such like as translocation of nutrients. It is also speculated that if these crop residuals are returned into the field, the gibberellins in the residuals would also be returned into the soil.

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[in Japanese]

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This research was carried out to determine the effect of plant densities on leaf water potential, leaf diffusive resistance during drought stress period and grain yield of grain sorghum, and also to confirm the effect of drought at three growth stages on yield as done in previous years. The results obtaincd are as follows: No consistant relationship was recognized between plant densities and leaf water potential, leaf diffusive resistance in irrigated treatment. However, high plant densities of non-irrigated treatment during drought stress period showed lower leaf water potentials and higher leaf diffusive resistances, and suffered severer water stress (Fig. 1, 2). Total evapotranspiration (consumptive water use) in both treatments during drought stress pcriod increased with increased plant densities (Fig. 3). Grain yields were the highest in 250, 000 plants density and the lowest in 400, 000 plants density per ha in irrigated treatment and in non-irrigated treatment increased as plant densities decreased. However, stover yields were higher in higher plant densities in both treatments. The effect of drought at three growth stages was the severest at boot stage and also showed the highest reduction rates of grain yields at the same stage (Table 2).

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The position of the formation of "stunted roots" within a hill of rice plants was examined, using samples taken from 6 different paddy fields at Sakata City, Yamagata Prefecture. "Stunted roots" were found to occur rather abundantly in the following position within a hill; 1) in the higher "shoot-units" of each stem, 2) in the upper parts within a "shoot-unit", 3) in the central stems of a hill, as compared with the peripheral ones, and 4) in the stem parts where another tiller is in contact with. The number of "stunted roots" as well as the percentage of the number of the total differ markedly according to the growing conditions of the plants examined. The plants taken from 6 different paddy fields were thus divided into two groups, A and B. The group A is characterized by the abundant "stunted root" formation, with relatively more "stunted roots" at the middle "shoot-units" along the stems. In the B group, on the contrary, "stunted roots" were less in number, however, the number increased towards the higher "shoot-units". The plants belonging to the group A were found, as compared with those of the group B, to receive more nitrogenous chemical fertilizer as basal and top dressing. Some possible mechanisms underlying the "stunted root" formation were discussed in relation to their position. Those are 1) the competition of assimilates during the later stages of the plant development, 2) the mechanical stress exerted by crowding together of many stems, 3) the changes of nutritional status brought about by the excess nitrogen application, and so on.

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The test material was ripening plants. The plants were grown in 150 paddy fields at Aomori, Akita, Yamagata, Fukushima, Chiba, Saitama, Nagano, Fukui, Hiroshima, Kouchi and Saga prefectures in Japan (Table 1). Superficial roots were collected by means of the soil-core sampling method. Core, consisting of a cylindrical tube with an internal diameter 5 cm and 5 cm height, was pressed vertically into the soil up to 5 cm in ten places in the middle of intrarow spacing (Fig. 1). The degree of superficial root formation is shown by the average weight of roots involved in the soil core. Value of yield of hulled rice was calculated in terms of field per 10 are. It has been found that superficial root weight is correlated with the field of hulled rice (Fig. 3). In case of the fields which produced yields between 180 kg and 600 kg hulled rice, superficial root weight and yield of hulled rice showed a considerable value of correlation coefficient (r=+0.831). In case of the fields which produced yields between 601 kg and 801 kg of hulled rice, superficial root weight and yield of hulled rice showed relatively lower correlation coefficient (r=+0.313) as shown in Fig. 4. From these results, it has been assumed that superficial root formation contributed to rise of the yield of hulled rice. Also it can be reported that, the importance of root system is not only due to its superficial root but also contributed to the root grown into both the plow layer and subsoil.

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In rice plants, the diameter of root, thickness of cortex, number of cortical cell layers and width of cortical cells were measured in both mature and apical parts of crown roots. In mature part of roots, it could be proved that the thickness of cortex was in harmony with the diameter of root, but in the case of stele diameter, only slight change was noticed. The thickness of cortex was more dependent on the width of cortical cells than the number of cortical cell layers, because the former was proportional to the cortex thickness, but the latter was only decreasing with the distance from the base of root (Figs. 2, 3, 4). In the apical part of roots, at 200 μm level, the width of cortical cells was proved to be constant (3.8 μm) irrespective of root diameter or cortical cell layer number. Moreover, the width of cortical cells increased basipetally and it ranged from 13 to 31 μm in mature part (Table 1). In 1 mm diameter roots, the width of cortical cells increased basipetally up to 8 mm from the apical tip, at which the epidermal cell length reached its maximum (Fig. 9).

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The experiment on competition between upland crops and weeds was conducted with four upland crops which were typical in the Kanto plain. And from aspect of the effects of different periods of weed-free maintenance on the crop yields, adequacy of the period for weed-free maintenance hypothesized in the previous report was estimated. 1. In upland rice and soybean cropping plots, plant length of large crab-grass (Digitaria adscendence Henr.) at the plots of 0 and 30 days weed-free maintenance extended up to the upper part of crop canopies which maintained the relative light intensity under 10%. On the other hand, that at the plots of 47 and 58 days weed-free maintenance was limited to the lower part of crop canopies. In peanut cropping plots, even that at the plot of 58 days weed-free maintenance extended up to the upper part of crop canopies. As the plant height of corn was high, even that at the plot of 0 day weed-free maintenance was kept to the lower part of crop canopies. 2. The later the time of competition with weeds started, the smaller the ratio of weed weight to total community weight became. The ratio of weed weight to total community weight in corn was the smallest of all crops, that is, was under 25% at the plot of 0 day weed-free maintenance, and was under 5% at the plots of 30 and 47 days weed-free maintenance. The ratio of weed weight to total community weight in upland rice and soybean was large at the plots of 0 and 30 days weed-free maintenance, but was small at the plots of 47 and 58 days weed-free maintenance. That of peanut was the largest, and was over 30% even at the plot of 58 days weed-free maintenance at harvesting. The amount of weeds at harvesting were little in corn, medium in upland rice and soybean, and much in peanut. And those showed approximately similar results to the ratio of weed weight to total community weight. Namely, the smaller the weed weight to total community weight was, the less the amounts of weeds at harvesting became. 3. Effects of weeds on crop yields were reflected in results of competition between crops and weeds. The yields of upland rice and soybean reduced at the plots of 0 and 30 days weed-free maintenance, as growth of weeds was not diminished greatly by crop canopies. But reduction of yields did not occur at the plots of 47 and 58 days weed-free maintenance, as growth of weeds was diminished greatly by crop canopies. The yields of peanut reduced at all plots of competition with weeds, as weeds grew rampant. In corn, significant reduction of weights of ears did not occur even at the plot of 0 day weed-free maintenance, but weights of stems and leaves reduced. Crop yield reduction due to weeds did not occur at the plots of 30 and 47 days of weed-free maintenance. 4. From above results, it was clear that hypothesis about the period for weed-free maintenance after seeding required to escape crop yield reduction due to weeds had high adequacy.

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The crown root primordia of rice plants appeared to undergo a "dormant" stage before their emergence. The number of these "dormant" root primordia was found to increase successively from 9th "shoot unit" (S.U.) to the 13th S.U. (Fig. 4). The total number of crown roots including these root primordia formed was found to increase successively in the upper S.U. However the development of upper roots was less regular than the lower ones (Fig. 5). The influence of growth conditions on total number of root primordia formed in the 9th S.U. was examined and it was revealed that in the plants grown under low nitrogen supply and low degree of light intensity, the formation of the total crown root primordia had considerably reduced, when compared to those of the control (Fig. 10). This decrease of total number of crown root primordia was due to the decreased number of upper root primordia, since different nitrogen and light intensity treatments did not show any significant variation in the formation of lower root primordia. The number of the upper root primordia which were formed away from the midrib had decreased considerably in the case of plants grown under low nitrogen supply and low degree of light intensity (Fig. 16). It might be concluded from the above study that the upper root primordia of any S.U. were more sensitive to the various physiological factors concerned with the root initiation than the lower ones of the same S.U. The root primordia which were formed away from the midrib were also appeared to be sensitive to the various physiological factors than those found nearer to the midrib. The diameter of the primordia, and stele, thickness of cortex and the number of cortical cell layers of the primordia of rice plants grown under different growth conditions have also been investigated. However, no significant differences were observed in this study (Tables 2, 3).

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In the previous report, it was considered that the slight variation of leaf water content on an areal basis (leaf water content) gave much influence upon stomatal aperture). The present study was conducted to establish other measurement methods of water status in the rice plant, i.e., leaf water potential and water saturation deficit (WSD), and to discuss which of them was satisfactory for measuring water status in the rice plant. The results obtained are as follows: Three hours for equilibration of water potential between gas phase and rice plant leaves in psychrometer chamber were required for leaf water potential measurement (Fig. 1) and full turgidity was attained in four hours after immersing leaves in water for WSD measurement (Fig. 2). Diurnal changes of water status in leaf blades were measured by leaf water potential, leaf water content and WSD. The results were that water in leaf blades was contained sufficiently in the early morning and it decreased in the daytime and again increased towards the evening (Fig. 3 and 4). Close correlation was found between leaf water potential and leaf water content, and between leaf water potential and WSD at each leaf position on the stem, and the height of those regression lines was different from each other depending on leaf position on the stem (Fig. 5). In the early morning when there was no water stress in the rice plant, leaf water potential was constant being about -2 bars through all leaf position investigated. On the contrary, leaf water content and WSD were different from each other depending on leaf position on the stem, i.e., the maximal values of leaf water content and WSD were obtained for 11th and 12th leaves, 10th and 11th leaves, respectively. The values of leaf water content and WSD gradually decreased both to upper and to lower leaves as they were away from the leaves with maximum values (Fig. 6). At the same degree of wilting of leaves or when apparent photosynthetic rate was reduced to zero due to water deficit in leaves, leaf water potential was almost constant through all leaf position investigated, but leaf water content and WSD were different from each other depending on leaf position on the stem (Table 1 and 2). From the results mentioned above and that the standard deviation of measured values of leaf water potential at the same water status was much less than that of leaf water content and WSD, it is considered that leaf water potential expresses leaf water status physiologically and it is more suitable for measurement of water status in the rice plant of which stomatal aperture is much influenced by the slight variation of water status. It is assumed that stomatal aperture changes with leaf water potential and that the stomata of the rice plant begin to close due to the slight decrease of leaf water potential.

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The present investigation was undertaken to clarify the relationship between nitrogen content in leaf blades and stomatal aperture at different growth stages, by using rice plants with different nitrogen content. There were two plots prepared. One was a control, the other was a plot with additional nitrogen applied to soil several days before stomatal measurement (Table 1). The results obtained are as follows. For the plants, received additional application of ammonium sulfate, there was higher content of nitrogen in leaf blades regardless of leaf position on the stem and of growth stage (Table 2). On fine days the stomatal aperture was larger in higher nitrogen plot compared with that of the control especially from the morning until the aperture reached to the maximum of the day. After the stomata started to close in the afternoon the difference of stomatal aperture became very small or negligible due to more considerable extent of stomatal closure in higher nitrogen plot (Fig. 1). On the contrary, on cloudy days accompanied with lesser evaporation, the difference of the stomatal aperture between the two plots could be found from the morning to the evening even though it became smaller in the afternoon compared with that in the morning (Fig. 2). In addition, the larger difference of the aperture between two plots was found in upper leaves compared with lower leaves at all growth stages independent of weather condition (Fig. 3 and 4). A high positive correlation between nitrogen content and stomatal aperture was clarified in leaves on the different position of the stem at different growth stages (Fig. 5 and 7). In Fig. 5 and 7, examined in detail, it was found out that the stomatal aperture of lower leaves was smaller compared with that of upper leaves in the almost same nitrogen content and that the stomatal aperture of rice plants after heading stage was also smaller even in the same leaf position compared with that before heading stage (Fig. 6). It is assumed from these results that the difference of stomatal aperture between rice plants with higher and lower nitrogen content appears only in the case with sufficient water content of leaf blades, but that it cannot be found in leaves under water stress. Furthermore, it is also suggested that the increase of stomatal aperture owing to higher nitrogen content has much bearing on the increase of photosynthetic rate in leaf blades, considering high positive correlation between stomatal aperture and photosynthetic rate in rice plants.

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Morphological changes of the rice plant under and after submersion were studied in relation to the lodging resistance of the rice plant. Results are summarized as follows. 1. Leaf blade and leaf sheath of young plant grown under submersion elongated remarkably and wilted due to strong dehydration after recession of water. 2. Submersion inhibited tillering at basal portion of rice plant and sometimes increased number of nodes in main culm. 3. The internode near the ground elongated abnormally under submersion, and the lodging resistance of rice plant was reduced. 4. Submersion after booting stage stimulated the growth of highernodal tillers and unbalanced growth stratum of rice plant. 5. Submersion at each stage accelerated aging of organs at the lower part and inhibited the development of subterranean part of the rice plant.

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The reduction of lodging resistance of rice plant due to submersion was analyzed. The results are summarized as follows. 1. The sheath of leaf embracing the culm prevents the plant from lodging. 2. The longer the length of internode at the basal portion is, the weaker the internode becomes. 3. The strength of each portion of internode with leaf sheath is larger at its lower part than the upper one due to the embracement of leaf sheath, but the strength of internode without leaf sheath is weaker at the lower part because of its low density of structure. 4. Submersion deteriorates the lodging resistance of rice plant by the following reasons. (1) The strength of leaf sheath is weakened. (2) The folding tension of leaf sheath in culm decreases due to swelling. (3) The strength of basal internode decreases due to abnormal elongation. (4) The flexural rigidity is weakened due to the decrease of dry matter. (5) The thickness of culm wall is diminished. (6) The tissue in leaf sheath is degenerated and the formation of silica cell is inhibited.

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[in Japanese]

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This study was undertaken to elucidate the growth process of young panicle of rice. The growth of each spikelet was investigated in relation to the positional differences and was compared with that treated with thinning and top-dressing at the end of spikelet differentiation stage (16 days before heading). Three spikelet positions, the upper (T-1), the middle (M-2) and the lower (B-2'), were selected for this experiment (Fig. 1a, b). The results obtained are summarized as follows: 1. In controls, the length of lemma, empty glumes and the width of spikelet at maturation decreased on lower position. But there was little differences in the length of anther and pistil, and the diameter of pollen among the spikelets at different positions on panicle (Fig. 2, Table 3 and 4). 2. The growth of each spikelet proceeded succesively from the upper to the lower position on panicle (Fig. 3). 3. Interrelationships of the growth of each spikelet organ were almost the same in all spikelets on panicle. Lemma, anther and pistil in a spikelet began to grow simultaneously. Marked growth occurred in lemma from 16 to 8 days before flowering, in anther and pistil from 16 to 3 or 2 days before flowering, and in the width of spikelet from 16 to 6 days before flowering (Fig. 4). 4. Regardless of spikelet position on panicle, meiosis of pollen was found to occur in the anther of the same length. However, the lemma length at meiotic stage in the upper spikelet was different from that in the lower one. Meiosis of the upper spikelet occurred when it was smaller than the lower spikelet (Fig. 2 a, c). 5. When the nutritive conditions were improved by thinning and top-dressing, the length of panicle, the number of spikelet, the length of primary branches and the diameter of rachis increased. The increase of the spikelet number was due to the decrease of degenerative spikelets (Table 1 and 2). 6. The lemma length of middle and lower spikelets, the length of empty glumes and pistil of all spikelcts, were increased by the treatment. The anther length and the pollen diameter in all spikelets were not increased and the growth period of anther in the lower spikelet was shortened by the treatment. The growth of the upper spikelet was not promoted by the treatment (Fig. 5, Table 3 and 4). Thus, the spikelet organs, which seemed to be differentiated in various manner from the apex, showed the different responses to the treatment. From these results, it is assumed that the positional differences in the spikelet growth were not only dependent upon the distribution of translocated substances but also upon the physiological specificity of each organ of the spikelet.

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The experiments were made to determine the effect of photochemical oxidants on physiological activitics of rice plants. Rice plants were fumigated with ozone at concentration of 0.12-0.20 ppm for 2-3 hr to investigate the accute injury and at 0.05 and 0.09 ppm for daily exposure from 3.0 leaf stage to assess the effect of ozone on growth. 1. It was observed that malondialdehyde produced by disruption of the components of membrane increased in the leaves exposed to ozone. 2. Ozone reduced the RuBP-carboxylase activity in both of young and old leaves 12-24 hr after fumigation and then in the young leaves the activity of this enzyme recovered to some extent after 48 hr, but it did not show any recovery in the old leaves. On the otherhand, ozone remarkably increased the peroxidase activity and slightly increased acid phosphatase in any leaves. 3. Abnormally high ethylene evolution and oxygen uptake were detected in leaves soon after ozone fumigation. 4. In general, high molecular protein and chlorophyll contents in the detached leaves decreased with incubation in dark, particularly in the old ones. These phenomena were more accelerated by ozone fumigation. Kinetin and benzimidazole showed significant effect on chlorophyll retention in ozone-exposed leaves. 5. Reduction of plant growth and photosynthetic rate was recognized even low concentration of ozone in daily exposure at 0.05 and 0.09 ppm. From these results it was postulated that ozone may act the senescence of leaves in rice plants.

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