This experiment was conducted to clarify the effects of different soil moisture levels on the root distribution and root dry matter of upland-cultured paddy rice (cv. Myojoo, Kochihibiki), crossbred rice of paddy rice and upland rice (cv. Ishioka glutinous No.10, Mizuhatamochi), and upland rice (cv. Norin No. 12, Norin No. 21). In the first experiment (1977), the root distribution and dry matter was investigated on the six cultivars which were cultivated under irrigation and nonirrigation. The irrigation treatments were begun at July 18. The soil moisture tension of the two irrigation plots were at pF 2.5 and pF 2.0 at l0 cm depth, respectively. During July 24 to August 8, the soil moisture tension of nonirrigation plot was over pF 2.9 and in the range of pF 2.5 to 2.9, at 10 cm and 30 cm depths, respectively. Therefore, the soil moisture of nonirrigation plots reached to first permanent wilting point at l0 A.M., August 4. Top dry matter, root dry matter and root distribution were investigated at maturity. The investigation of the root distribution was practiced by excavating soil masses, which were sectioned by 7 cm increments up to 35 cm depth. The second experiment (1978) was set up in cylindrical plastic pots of 30 cm height and 25 cm inner diameter using four cultivars (Myojoo, Mizuhatamochi, Norin No. 12, Norin No. 21). Soil moisture treatments composed by two levels of high and low were begun at July 10. That is, high soil moisture plot was irrigated by each pots every day. While, low soil moisture plot was irrigated when every time the soil moisture became to first permanent wilting point. The treatments were continued for 58 days. The results showed that root distribution of the rice plants was effectively influenced by different soil moisture levels. The roots of rice plants distributed in the shallow layer under irrigation, while the roots distributed in the deeper layer under nonirrigation. Root distribution of upland-cultured paddy rice and crossbred rice of paddy rice and upland rice distributed in the shallow layer than that of upland rice. Also, root dry matter was influenced by different soil moisture levels. The root dry matter was increased in drier soil condition, where rice plants proliferated numerous branches to gather a small amount of soil water. The root dry matter of upland rice cultivar 'Norin No. 12' was increased conspicuously in surface layer under nonirrigation. It is suggested that high growth rate of root weights in water stressed rice plants was correlated with drought resistance, because high growth rate of root weight was obtained by upland rice which has drought tore-lance. R-T ratio was increased in drier treatments, because root dry matter was increased and top dry matter was decreased by water stress.

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1. A possibility whether plants react differently to an exogenous growth regulator applied at different times in a day was examined adopting rice plant (Oryza sativa L., cultivar Nipponbare), gibberellic acid (GA₃) and abscisic acid (ABA) as materials. Solutions of the regulators were poured onto the soil surface close to the plant base every mornlng or evening. 2. In the later stage of growth, a difference between morning and evening applications was detected. Applications of GA₃ every evening (GA-E), and ABA every morning (ABA-M) made the flag leaf longer than GA-M or ABA-E respectively. A less conspicuous difference was also observed in the number of expanded leaves. 3. The two growth regulators caused different effects on the final leaf number and the days required from seeding to heading. GA₃ treatments made the final number of leaves less and the days to heading shorter than the water control, while ABA treatments did those slightly more and longer than the control. 4. The present report expects further experiments with more precise methods especially for the applications of plant growth regulators.

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The effect of lodging on the seed yield and the yield components of four cultivars of Italian ryegrass, including two early varieties, VVaseyutaka and Wasehikari and two late ones, Yamaaoba and Nasuhikari was studied in a field trial. To this purpose each variety was given four lodging treatments: natural control (lodged naturally), no lodging (supported mechanically), and artificial lodging at early anthesis (the beginning of anthesis) and at late anthesis (9 to 12 days after the beginning of anthesis). Varietal difference was recognized in the degree of lodging, showing greater differences between the early varieties and between the late ones than between the early and the late ones. In all varieties, the increase in the seed yield was significantly higher by supporting the plant than by any other lodging treatments. The rate ofincrease in the seed yield by supporting the plant was greater in the late variety, but had no relation to the degree of lodging. When compared with the supported plant, the reduction in the seed yield due to lodging at early anthesis was 33to 36%, showing no varietal difference and at late anthesis 9 to 18%, showing a significant varietal difference. The increase in the number of ears was brought about by supporting the plant in the late varieties but not in the early ones. The reduction in the number of ears due to lodging at early anthesis was greater in the late varieties, being 28%, than in the early varieties, being 16%, and the reduction at late anthesis was smaller than at early anthesis. In all varieties, higher seed weight per ear was produced by preventing the plant from lodging. According to this, the increase in the seed yield due to prevention of lodging was recognized to be brought about by the increase in the seed weight per ear in early varieties and by both the seed weight per ear and the number of ears in late ones. The reduction in the seed yield by lodging was found to have relation to decrease in the seed weight per ear in the early varieties and in the number of ears in late ones.

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The present studies were conducted to clarify the effects of high temperature (50°C)treatment to unhulled rice seeds for seven days on the germinability and initial growth of seedlings. The author used 26 new and old cultivars which possessed different degrees of germinability in Hokkaido. The results obtained were summarized as follows: 1. A highly significant correlation existed between the germination coefficients of treated seeds and that of untreated seeds, and the order of the germinability in the cultivars was not affected. 2. Though the heat treatment decreased the germination coefficients by 8% in the mean value of the cultivars, the values of germination coefficient varied depending on individual cultivars. Namely, the coefficients of thirteen cultivars increased, while the others decreased in various degrees. 3. The rate of fluctuation in the germinability caused by the treatment was expressed as a following formula: [numerical formula] The negative and strong correlation was recognized between germination coefficients in the treated and the rate of fluctuation. The treatment improved the degree of germinability in the cultivars of the low germinability. 4. The initial growth of seedlings expressed with plant height and number of roots was inhibited by the treatment in most of cultivars. The correlation between germination coefficients and initial growth of seedlings in the treated group was lessened by the treatment. 5. From the mentioned above, the heat treatment was effective to increase germination coefficients of the promising cultivars possessing a weak degree of germinability.

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It was suggested from the previous investigation that the photosynthetic rate affected by gas exchange rate would be different due to the stomatal aperture in rice plants under different growth conditions even though the rice plants grew under submerged soil condition. The present study was conducted to investigate the difference in gas exchange rate in rice plants under different growth conditions through the measurement of diurnal course of transpiration rate, stomatal aperture and conductance, and xylem and leaf water potentials (Ψ_x and Ψ₁). There were four plots prepared. One was a control, the others were as follows; a plot with additional ammonium sulfate applied to soil several days before measurement to increase nitrogen content in leaves; a plot with soluble starch and additional ammonium sulfate applied to soil several days before measurement to make soil reductive and to decrease root activity without the decrease of nitrogen content in leaves; a plot grown under shading and high humidity for several weeks to decrease the root-top ratio and root-leaf area ratio. The stems of the rice plant in a pot were kept apart from each other by spreading outward with cotton thread in order to minimize mutual shading, so that all leaves on each stem were exposed to the same solar radiation and wind speed when transpiration rate was measured by weighing the pot. Therefore the difference of gas exchange rate through stomata among rice plants can be estimated by simultaneous measurements of transpiration rate. Transpiration rate was higher and stomatal aperture and conductance were larger almost all day long in rice plants with high nitrogen content in leaves induced by additional ammonium sulfate than those in the control. The difference in transpiration rate and stomatal aperture between the two plots was larger in the "Morning" than that in the "Afternoon". Transpiration rate was higher in the afternoon due to high solar radiation, atmospheric vapor pressure deficit and wind speed, so that Ψ₁ was lower in the "Afternoon" than that in the "Morning". It is clear from these results that gas exchange rate through stomata increases due to high nitrogen content in leaves, especially in the "Morning" when rice plants were undcr little water stress. In the rice plants with low root activity induced by the application of soluble starch to soil and with low root-top ratio and root-leaf area ratio induced by shading and high humidity, transpiration rate and stomatal aperture were much lower than those in the control in the "Afternoon." Ψ_x and Ψ₁ were lower in these rice plants than those in the control even though transpiration rate was lower in the former. These results indicate that water absorption decreases due to low root activity and poor development of root system, and it is considered that gas exchange rate through stomata decreases remarkably due to severe water stress under high radiation and atmospheric vapor pressure deficit in rice plants with low root activity and poor development of root system, even though they grew under submerged condition with enough water supply. From the results mentioned above and by the consideration of high correlation between gas exchange rate through stomata and photosynthetic rate, it is suggested that The lncrease of photosynthetic rate owing to higher nitrogen content appears remarkably In the case without or with little water stress, and the decrease of photosynthetic rate owing to the decrease of water absorption appears remarkably under the condition which brjngs on intense transpiration.

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Two soybean cultivars, Tokachinagaha (determinate) and Harosoy (indeterminate), were grown in the equidistant square pattern at five population densities, and dry matter accumulation in plant community were analyzed. The main results obtained were summarized as follows: 1. The maximum dry matter production was 1, 205 g/m² at 25 pls./m² for Tokachinagaha and 1, 123 g/m² at l6 pls./m² for Harosoy at about 120 days after planting. 2. With increase in population density, dry weight of branches decreased more remarkably than that of main stem, and it resulted in varying branch-main stem ratio in the plant community. 3. Relative light intensity at the bottom of the canopy was associated with LAI in whole varietics and growth stages. However, the regression value became larger in the later stage and that of Tokachinagaha (narrow leaf type) was slightly smaller than that of Harosoy (round leaf type) in each stage. The LAI required for 95% light interception was in the range from 3 to 4. 4. The decrease in NAR with increase in LAI initiated from LAI 0.3. This fact was also confirmed in LAI 0.06 to 0.6 for Harosoy at the early growth stage. 5. The estimated value of LAIopt. and CGRmax. varyed with varieties and growth stages. 6. CGR was closely related to photosyntheticallyactive radiation(PAR) intercepted by the canopy. However, the efficiency of dry matter accumulation per unit PAR intercepted (EPAR=CGR/PAR intercepted, dry weight mg/kcal) changed with growth. EPAR attained to the maximum at the young pod stage (near the maximum leaf area stage), then decreased. 7. Significant simple correlation coefficients were recognized between LAIopt., CGRmax. and EPAR, but a partial correlation coefHcient was signiticant only between CGRmax. and EPAR. CGR showed highly positive correlations with EPAR throughout the stages of pod filling.

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Carbon assimilation at low carbon dioxide levels was measured on three Oryza specics (O. sativa L. cv. Toyonishiki, O. officinalis Wall, and O. meyriana Baill.), Brassica napus L. cv. Michinokunatane and Triticum aestivum L. cv. Konosu No.25. Measurements were made at two different oxygen concentrations; 140% and 21% (atmospheric pressure). An improvement in measurement device was made for ensuring an accuracy of the meter readings. That is, a recorder with a modulator was used to enlarge the differences in the carbon dioxide concentration; two- and five-fold for carbon dioxide levels above and below carbon dioxidc compensation point (gamma), respectively. It seems that HEATH and ORCHARD (1968) and HOLMGREN and JARVIS (1967) Changed the carbon dioxide concentration at large intervals, resulting in 3 to 5 measurements below gamma. Such a few measurements would obscure the statistics of the carbon dioxide exchangc rate at low carbon dioxide levels. The changes of carbon dioxide concentration in this experiment, however, were made at intervals of about 2 or 4 ppm from 0 ppm to gamma, resulting in 7 to 14 mean values below it. As the characteristics of carbon dioxide absorption at low carbon dioxide levels, GABRIELSEN (1948) proposed the 'threshold hyPothesis' in which gamma was regarded as a threshold value below which no assimilaton occurred, while HEATH and 0RCHARD (1968) postulated the existence of a 'third process', in addition to ordinary (dark) respiration and assimilation, which could be expected to have a different balance between respiration and assimilation. They denied the adoptation of the threshold hypothesis. From the prescnt experiment in which the carbon dioxide exchange rates were traced by Changing the Carbon dioxide concentrations at very small intervals, hwever, it appeared that the rate of carbon dioxide uptake at low carbon dioxide levels and atmospheric oxygen pressure tended to decrease toward 1/2 gamma carbon dioxide level, and the carbon dioxide uptake seems to cease and only the carbon dioxide release secms to occur below it. In case of measurements at 14% oxygen concentration the situation was similar to those at 2l% oxygen concentration, but a considerable decrease of the value of gamma. Thus, the process of carbon dioxide uptake at low carbon dioxide levels seems to imply the threshold hypothesis and 1/2 gamma seems to be an approximation of the threshold value. The assimilation rate is estimated as the ratio of carbon dioxide concentration differences between ambient air and assimilation center to the sum of diffusion resistances.As an estimate of carbon dioxide levels in the assimilation center in this formula, GAASTRA (1959) proposed zero, while BIERHUIZEN and SLAYTER (1964) adopted the Practise of using gamma to estimate it. From the results mentioned above, we could propose to use 1/2 gamma as its primary approximation because the photosynthetic center would be exposed to this carbon dioxide level but not absorb it.

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[in Japanese]

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[in Japanese]

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Using four varieties of different types, an investigation was made on the varietal differences in the influence of removal at heading of the whole panicles or half of the spikelets of each panicle. Main results were as follows: 1. The total nitrogen and chlorophyll contents on leaf area basis were maintained higher in the whole removal and half removal treatments than in the non-treated control, while photosynthetic activity not always followed the same trend. 2. The ripened grain percentage was improved by both the treatments to greater degrees in those varieties with larger sink, i.e., Tongil and Milyang 23, than in those wlth smaller sink, i. e., T-136 and Kochihibiki. 3. The total accumulation of dry matter aftel. heading was found to decrease by the removal of whole panicles in the three varieties other than T-136.

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IBP (O, O-diisopropyl-S-benzyl thiophosphate) is known as a fungicide. However, in practice, some farmers are believing that IBP has also a preventive effect to lodging. Here we report the findings obtained by laboratory experiments that IBP inhibits the stem growth of intact ricc seedlings in darkness. Rice sceds, Oryza sativa L. cv. Hatishail (indica type), Milyang 23 (indica xjaponica type) and Sasanishiki (japonica type) were used as materials. Seeds were sterilized and placed on culture medium in a test tube (25 X 60 mm). The medium contained 2 ml of water or various concentrations of IBP and/or some other growth regulators. The tubes were kept in darkness or in light condition for l0-12 days at 30-32°C. Results of the tests are as follows: 1. As shown in Fig. 1, the mesocotyls of Hatishail elongated about 110 mm or more in a water alone (0 ppm) under darkness. However, the mesocotyl elongation was markedly depressed by an application of each growth retardant and IBP. The degree of inhibition by IBP (●) was greater than those with B995 (□) or CCC (△), but lesser extent than those with ancymidol (▲) or RH531 (○). In this case, the shoot length was also decreased by an application of the growth retardant, but IBP at 2.5-40 ppm caused the stimulation of shoot growth. When 2.5-40 ppm IBP was applied to the seedlings of Milyang 23 under darkness, marked inhibition of growth of mesocotyls and first internodes occured with the concomitant increase of growth of coleoptiles, first leaves, second leaves and seminal roots. 2. The second internodes seems to be little affected by an application of IBP, whenever the treatment started from 1 to 6 days after immersion under darkness. 3. When IBP at 2.5-160 ppm was applied with GA₃ or ABA to the seedlings of japonica rice, it depressed the stimulative effect on the mesocotylgrowth of both chemicals under dark condition. Under light condition, however, 2.5∼40 ppm IBP did not cause a notable inhibition of growth of the second leaf sheaths when it was applied alone, or with GA₃ or ABA. It may suggest that IBP affect independent-ly with GA₃ or ABA to the stem elongation of ricc seedlings grown under darkness.

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