This study examined the influence of relative humidity of the atmosphere on the dry matter production of rice at its seedling stage. The plants were grown in a growth cabinet where the relative humidity was maintained at either 60% (dry treatment), 75% (standard treatment), or 90% (wet treatment) with the day/night temperature of 28/24°C and the illumination of 34-30 klux. The plants grown in a more humid atmosphere produced more dry matter when compared over the same growing period after seeding. But, no difference was detected when compared at the same plant age measured in the number of leaves (Fig. 1). We investigated the characteristics of the leaf blade and leaf sheath and conducted grow h analysis. 1. The top to root ratio was greater in the plants grown in a more humid atmosphere when measured either on the same day after seeding or at the same plant age (Fig. 2). 2. Atmospheric humidity had little effect on the weight and length of the leaf blade. On the other hand, the weight and length of the leaf sheath were strongly influenced: the more humid the atmosphere was, the greater the weight and length of leaf sheaths. 3. With increasing atmospheric humidity, the leaf area increased and the specific leaf area increased: the specific leaf area showed a significant positive correlation with the leaf area (Fig. 4). 4. The leaf area index, which strongly influenced crop growth rate, was larger in a more humid atmosphere, which may be why the dry matter production was higher in a more humid condition when compared at the same growing period (Table 2). 5. The plants grown in a more humid condition had a larger leaves. However they were thinner and had a lower photosynthetic rate (Fig. 6). Therefore, it seemed that there was no difference in the dry matter production of the plants grown in the three different humidifies when compared at the same plant age.

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Eight varieties differed in ear type were used in this study: Stirpe 136 and Anthocyane (javanica) (ear type I: Number of grains on the secondary rachis-branch was abundant in the basal position of ear), Jaekeon (japonica) and Milyang No. 23 (japonica-indica hybrid) (ear type II: number or grains on the secondary rachis-branch was less near panicle base than in ear type: I), Norin No. 8(japonica) and Josaeng Tongil(japonica-indica hybrid) (ear type III: number of grains on the secondary rachis-branch was abundant in the middle position of ear) and Dojinkyo and Panbila (indica) (ear type V: number of grains on the secondary rachis-branch was abundant in thc upper position of ear). After harvesting, number of the primary rachis-branches per ear, and number of grains on the primary rachis-branch, and number or the secondary rachis-branches and their grains at each node of rachis were determined for the ear of the longest stem in the hill in twenty replicates. Under the same level of fertilizer, increase in planting density decreases number of the primary rachis-branches per ear, and the secondary rachis-branches and their grains at all the nodes of rachis, especially, at the basal position of ear. These trends seemed to be intensified by increase in fertilizer level in almost all the varieties (Fig. 2 A-H). Because of the extreme decrease of number of the secondary rachis-branches and their grains at the basal position of ear as mentioned above, Stirpe 136, Anthocyane and Milyang No. 23 changed their ear type, II to III in high fertilizer and dense planting plot (Fig. 2 A, B and C). In the previous experiment which was undertaken under favourable climates for the rice cultivation, Stirpe 136 and Anthocyane, Jaekeon and Panbila showed ear type I, II and V, respectively. However, there existed no those ear types in the present experiment. These may be due to decrease of number of grains on the secondary rachis-branch at the basal (Stirp 136, Anthocyane and Jaekeon) and upper (Panbila) positions, which appeared to have been caused by the low temperature during the present study (Fig. 1). Anthocyane and Panbila were used for determination of ear type in all the tillers of four hills as influenced by fertilizer level and planting density. Number of the primary rachis-branches per ear, number of the secondary rachis-branches and their grains at each node of rachis were determined as for the ear having every different number of the primary rachis-branches per ear in four hills in four replicates. Number of the secondary rachis-branches and their gains decreased at all the nodes of rachis, especially, at the basal position of ear, with reduction of number of the primary rachis-branches per ear. This caused changes in ear type of cars having reduced number of the primary rachis-branches per ear, viz. ear type II to III and further, in some cases, to ear type IV in the hill of Anthocyane (Fig. 3A), but ears of Panbila showed ear type IV or V in all the plots differing in fertilizer level and planting density (Fig. 3B). Increase in fertilizer level and planting density decreases number of the secondary rachis-branches and their grains at all the nodes of rachis, especially at the basal position of ear. For this reason, number of secondary rachis-branches and their grains was almost zero at the panicle base in the plots of high fertilizer level and dense planting density, regardless of number of the primary rachis-branches per ear. Anthocyane and Panbila showed ear type II and IV in the ears with the largest number of the primary rachis-branches, respectively. Number of grains on the primary rachis-branch at almost all the nodes of rachis was about 6 in all the plots, varieties and tillers.

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The grain growth of rice is highly tolerant to water stress throughout the grain-filling period. Despite a large reduction in dry matter production, the grain growth during both the period of active cell division and expansion, and the subsequent period of rapid starch deposition was little affected by water deficits. Reduction in dry matter production due to water stress was almost completely compensated by the increased transfer of reserved assimilates to the grain. But, the plants which experienced drought during the early stage of grain growth and were relieved from the stress thereafter yielded less than the plants which were well watered throughout the grain-filling period. Similar response was observed in wheat, and a deteriorated root function in stressed plants is suggested as a possible factor for this reduced grain yield. It is therefore probable that the yield reduction in rice associated with prolonged drought during the period of grain-filling is a result of the indirect effects of water stress through the function of roots with regard to the production of hormonal substances. However, in view of the highly tolerant nature of the short term grain growth to water deficits, it is more likely that the lack of assimilate supply to the grain is responsible for reduced grain yield in plants under prolonged stress, since there must be an upper limit to the amount of pre-anthesis reserves that can be available for grain growth. This situation has been clearly demonstrated with maize. The objective of this study was to examine the above premise, i.e., the total assimlate supply is the primary factor that controls grain yield in rice droughted during most of the grain-filling period. Rice plants (Oryza sativa L. cv. Nipponbare) were grown in wooden trays (1.05×1.20×0.15 m) containing sandy silt soil. The trays were placed in a vinyl-covered house located in a field and so arranged to form a block of miniature crops that simulates a field density of 95, 200 plants/10a. Part of the block was adequately watered throughout the whole growing period, while water application to the remaining block was restricted after ear emergence so that leaf water potential around midday was maintained at -10 to -15 bars. At intervals during the treatment period, water potential was measured on the flag leaves between 1300 and 1500 hours. During this period, areas of green leaves and grain growth were also monitored. Dry weights of grains, shoots and roots were determined both at the time of ear emergence and at maturity. Daytime water potential in the leaves of stressed plants declined rapidly after the start of treatment, reaching -12 bars 10 days after ear emergence (Fig. 2). Leaf water potentials in the control plants remained at -3 to -6 bars except at the later stage of the growth. Leaf senescence was accelerated in stressed plants, LAI reaching less than 50% of the initial value by the 20th clay after ear emergence, whereas the controls still retained the green leaves of about 60% of the initial value until the full-ripe stage (Fig. 3). Water deficits reduced the dry matter production by approximately 40% (Tables 2 and 3) through the reduction in both the leaf area duration and the average rate of dry matter production (Table 4). Despite this, the grain yield of desiccated plants was only reduce by 16% (Tables 1 and 2), due to the increased assimilate transfer from the shoots to the grain (Tables 2 and 3). Thus the apparent contribution of reserves to grain yield was 34% in the desiccated plants, about three times as high as in the controls (Table 3.). These findings are in agreement with our earlier studies; the grain growth for the first 10 to 20 days after ear emergence was only slightly affected by the water stress (Fig. 4). However, the rate of grain growth declined as the water stress was prolonged. [the rest omitted]

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Effect of nitrogen side-dressing at 10 days after flowering on yield, yield components and protein content of seeds was examined using 12 varieties and ammonium sulfate. 1. Mean yield among 12 varieties supplemented with 120 kg nitrogen per ha increased by 6.7 percent or 250 kg per ha (Table 1). The most affected variety was Chippewa (13.2%) and the least was Waseshiroge (0.1%) (Fig. 1). 2. As to the early or medium varieties, yield increase was mainly due to the increase of 100 seeds weight. As to the late varieties, on the other hand, it was mainly due to the increase of pod number (Fig. 1). 3. Nitrogen or protein content of seeds increased by 3.3 percent on the average of 12 varieties supplemented with 120 kg nitrogen per ha. Protein yield per unit land area increased also by 10.3 percent (Table 2). 4. Effect on yield of supplemental nitrogen was the largest on the least fertile plots, and vice versa. On the least fertile plots all of the yield components, pod number, number of seeds per pod and 100 seeds weight increased. On the most fertile plots, on the other hand, pod number decreased, which negated the increase of 100 seeds weight, hence the least yield increase (Fig. 3). 5. Taking into account of the increase of total revenue due to the increase of yield and input cost for ammonium sulfate and labour for its dressing, the most reasonable amount of supplemental nitrogen was supposed to be around 100 kg per ha. In this case the increase of net revenue was about 35, 000 yen per ha.

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In order to identify the factors which have played a significant role in the increase of rice yield, comparative growth analysis was attempted for several cultivars of rice plant which have been cultivated in the past or currently being cultivated in the south-western part of Japan (Kyushu district). Dry matter production of old and new types of rice cultivars was compared in the field. The old types refer to the ear-weight-type with long culms, vs. the new types or ear-number-type with short culms. The results obtained are as follows: During the growth period before heading, dry matter production was higher in thc old types than in the new types of cultivars (Table 2). This difference was due to the production of dry matter during the ear initiation stage. Dry matter increase was positively correlated with canopy height in this stage (r=0.858^**) (Fig. 2). Further analysis indicated that the canopy of the old types consisted of lower leaf area density as compared to that of the new types of cultivars (Fig. 3). As a result, dry matter increase showed a significant negative correlation with the leaf area density (r=-0.852^**) (Fig. 4), suggesting a possible correlation between CO₂ diffusion and a vertical distribution of leaf area in the canopy. During the growth period after heading, dry matter increase showed a significant positive correlation with the leaf area index (LAI) and net assimilation rate (NAR)(Fig. 5). The new types which showed higher LAI and NAR produced a larger amount of dry matter as compared to the old types of cultivars (Fig. 5). Also, the new types had higher nitrogen content in the leaf blade and lower decrease in thc photosynthetic rate (p₀) and leaf area during ripening stage than the old types of cultivars (Fig. 6, Table 4). The old types of cultivars experienced lodging during the middle and later ripening stages whereas red-kernel rice, regarded as a very old type of cultivar, showed lodging at heading, due to the presence of a long culm. In order to increase dry matter production and hence grain yield, the role of canopy height should be reevaluated in relation to dry matter production both before and after heading.

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イネにおける, 穂上位置による穎花の冷温感受性の差異に関連して, 小胞子初期に冷温処理をした材料および処理しない材料について, 開花期に穂上位置別の穎花について葯長および充実花粉数を調査した(第2～5表). 対照区および冷温処理区における葯長および充実花粉数の4者のいずれにおいても以下の傾向が見出された下位枝梗, 2次枝梗および同一1次枝梗上の下位の穎花は, それぞれ上位枝梗, 1次枝梗および同一1次枝梗上の上位の穎花にくらべて, 葯長は長く, 充実花粉数は多い. これら4者は, 穂上位置に関してお互いに(第6表), また小胞子初期に冷温処理をうけた場合の受精率に対して(第1～4図)高い相関を示した. これらの事実は, 既報において提出された仮説-花粉数が穂上位置による穎花の冷温感受性の差異の原因である-を支持するものである. 穂の上部の穎花は, 下部の穎花にくらべて対照区における充実花粉数が少いばかりでなく, 冷温処理による減少率も高い(第8表). 受精率が90%パーセント以上になるための充実花粉数の限界値は, 小胞子初期に冷温処理をうけた頴花の受精率に対する充実花粉数の回帰線を外挿することにより, 葯当たり640 (あるいは穎花当たり3,840)と計算された(第4図).

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通常の光条件下で生育させたダイズ葉に, 異なる強度と照射時間の組み合わせから成る光照射処理を通常の気体条件下で行い. 処理後に得られた光-光合成曲線から, みかけの飽和光合成速度(P₀)および光-光合成曲線の初期匂配から求められたみかけの量子収量(QY)の光阻害を定量的に調べた. 1. 2700μE/m²/secの光で照射処理された葉では, 処理後2時間で, P₀およびQYに顕著な光阻害が観察されたが, 1760μE/m²/secの光で照射処理された葉では, 12時間後に顕著な光阻害が観察された (Fig. 1 および Table 2). 2. 1760μE/m²/sec以下の光で処理された葉では, 処理後6時間までP₀の光阻害は起こらなかったが, QYには処理後4時間ですでに僅かな光阻害が観察された (Table 2). 3. 光阻害はP₀よりQYにより顕著に起こった (Table 2). 4. 通常の光条件下で生育したダイズ葉は, 通常の気体条件下で光照射された場合, 光阻害-特にP₀の-に関してかなり大きな耐性を備えていることが示された. このことから, ダイズには光阻害の効果的な回避機構が存在する可能性について考察した.

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ダイズ葉の調位運動が強光による光合成の光阻害に対する回避機構の一つとして働いている可能性を探るために, 葉に種々の強度の光を照射し, 水平面入射光強度(HL)と葉面入射光強度(LL)との関係を調査した. 1000μE/m²/sec以下の光を葉に照射した場合には, LLのHLに対する割合(LL/HL)は常に0.9以上の高い値を示し, 光を避けるような調位運動は見られなかった. 1000μE/m²/sec以上の光を葉に照射すると, LL/HLはHLの増大に伴って減少する傾向を示し, 葉は光を避けるような調位運動を行った. この傾向は, 光照射時間が13時間と長くなると極めて顕著になった. 以上の結果から, ダイズ葉の調位運動は, 葉が極めて強い光を長時間受けるような場合, 光合成の光阻害を回避する機構として働いている可能性があるものと考えられた.

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インドネシアのインド型および日本型品種ならびに日本品種の2,4-Dに対する感受性の差異を生理的見地から明らかにするために, 畑の心土を用いて若干のポット試験を行い. 次の結果を得た. 1. インドネシアのインド型品種は日本型品種および日本品種にくらべて2,4-D感受性が大きく, 2,4-Dによる生育阻害(草丈×茎数値, 主茎当たり生存葉数, 葉の緑色程度および地上部の乾物重の減少)が著しかった(第1, 2表, 第1図). 2. 稲品種のエチレンおよびエスレルに対する感受性の順序は2,4-Dに対する感受性の順序とほぼ一致した. 但しエチレンに対する感受性は2,4-Dに対する感受性にくらべて小さかった(第3, 4表, 第1図). 3. 2,4-D施用によって葉から多量のエチレンが発生したが, その発生がインドネシアのインド型品種は日本型品種および日本品種にくらべて著しく大きかった(第2図). 4. インド型品種(IR36)の2,4-D感受性はエチレンの併用によって高められた(第5表, 第3図). 5. 以上からインド型品種の2,4-Dに対する高い感受性は少なくとも一部は 2,4-Dによって生成された多量のエチレンによって高められたと推測される.

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葉から根へ送られる窒素の意義を明らかにする目的で, 穂ぼらみ期の水稲の最上位葉に¹³C標識の炭酸ガスと¹⁵N標識の二酸化窒素を同時に取り込ませ, ¹³Cと¹⁵Nの体内移動および節位別に分級した根中での動態を8日間追跡した. 同化葉からの¹³Cの転流は1日で大部分が終了し, その間に固定された¹³Cの21%が呼吸により失なわれた. 一方, ¹⁵Nの同化葉からの流出は¹³Cに比ベ遅く, かつ実験期間中継続して起った. ¹³Cと¹⁵Nの体内分布パターンの類似性から,少なくとも一次分配過程では¹³Cと¹⁵Nは一緒に師管中を動くと考えられた. 一方, 各部位の¹³C/¹⁵N比に違いが認められたことから, 炭素と窒素の相対的分布はシンク器官の性格によっても影響されていると思われた. 同化後1日目には葉から転流した¹³Cの19%と¹⁵Nの17%が根系ヘ分布した. ¹³Cと¹⁵Nは生長中の上位節根(新根)ばかりでなく, 発育を完了した下位節根へも転流した. 根中の¹³C量は呼吸による放出や地上部への再転流のため, 1日目以降明らかに減少した. 下位節根ヘ転流した¹⁵Nは, その後上位節根や地上部に再転流し, 最終的には根系中の¹⁵Nの大部分は上位節根ヘ集中し, その生長に使われた.

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Formation and morphology of the primary roots on growing shoots were observed in field grown cereals, i.e. Setaria italica Beauv., Panicum miliaceum L., Echinochloa frumentacea Link., Pennisetum typhoideum Rich., sorghum bicolor Moench., Coix lachrymajobi L. and Eleusine coracana Gaertn. All species showed a similar developmental pattern. Although root emergence proceeded keeping pace with leaf emergence, the pace varied from species to species. Among species we also found some morphological differences such as, stem diameters, the number and diameters of the primary roots, and frequency of the secondary roots along the primary root axes. In all species examined, the basal diameter of the primary roots was closely correlated with the diameter of the stem on which they appeared. The root diameter acropetally decreased rapidly in any root parts where the diameter is large. The results were discussed from two aspects, namely, the determining process of the number of the primary roots and formative process of each primary root.

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The factors of the occurrence of straighthead of rice plants are vague yet. The purpose of this paper is to present the effects of the application of barley straws in common paddy fields on the occurrence of the straighthead of rice plants. The summary of the results is shown below. 1) Some plants with high percentage sterility occured in the test plots in which barley straws had been applied. 2) Numerous plants with high percentage sterility occured in the barley straws applied paddy field which was restored to the paddy field last spring after ten years use as an upland. 3) Abnormal rice plants with deformed panicles and spikelets occured in the test plot in which barley straws were applied two years before. Percentage sterility of them were high (Fig. 4). 4) Abundant typical symptoms of straighthead of rice plants were observed in a farmer's paddy field in which much barnyard manure had been applied. 5) From above-mentioned results, it was concluded that straighthead of rice plants occured not only in paddy fields which had been restored after at least more than several years use as uplands but also in common paddy fields in which much organic matter such as barley straws had been applied.

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In order to clarify the roles of EF (epidermis-cortical fiber compound) and P (fundamental parenchyma) in breaking resistance, several dynamic characteristics of the fourth internode from the top of rice culm, var. Koshihikari, were studied at the time of harvesting. Breaking strength and deflection of PEF (whole internode tissues) and P, obtained by shaving off the EF from PEF, were measured with aid of the stalk bending hardness tester (type EO-III). Tensile strength, compressive strength and shearing strength were measured by traditional methods used in the material testing. These data are shown in Table 1. Some calculations with these data verify that EF/P ratio in YOUNG's modulus, tensile strength and compressive strength are 113, 63 and 19, respectively. Besides, the tensile strength of EF in rice internode was ascertained to be almost the same to that of the xylem tissue of boxwood (Buxes microphylla var. suffruticosa Makino). Moreover, about 89% of bending stress (tensile and compressive stress) is supported with EF, and about 78% of shearing stress is supported with P in the bended internode. Therefore, with regard of bending stress, the internode of rice culm can be considered dynamically to be a pipe composed of thin EF as illustrated in Fig. 1. The value of maximum stress M can be obtained by the formula (6), and d²t [(diameter of internode)²×(thickness of EF)] can be considered to be a very important factor in breaking resistance. On the other hand, the main role of P in breaking resistance is to prevent sectional deformation and to maintain cylindrical form in the bended internode. Breaking strength of the fourth internodes with or without leaf sheath was investigated in the ripening period as shown in Fig. 2. The breaking strength had a peak soon after heading and a minimum at 25-30 days after heading. It may be thought that the slight increase in breaking strength at the time of harvesting was caused by reaccumulation of starch in the internode.

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The carbon budget and efficiencies of solar energy utilization for gross and net production of rape plant populations have been calculated from data on diurnal courses of CO₂ exchange and dry matter production. This was done both for individual days at different growth stages and for the whole growth period. The results arc summarized as follows: 1. The daily gross production (Pg), derived from data on diurnal courses of. CO₂ exchange, increased gradually during early stages of growth. At the beginning of bolting (early March), Pg began to increase steeply attaining to a maximum at the beginning of ripening (early May) and then decreased rapidly. The largest value of Pg was 61.53 g CO₂/m²/day (Table 1, Fig. 1). 2. The daily net production (Pn) varied with growth stage in a manner similar to Pg althought the maximum occurred a little earlier than that for Pg. The largest value obtained was 41.14g CO₂/m²day (Table 1, Fig. 1). 3. The Pn/Pg ratio, as well as Pg and Pn, varied largely as a result of changes in daily solar radiation (S). That is, the ratio increased with increasing S approaching a certain level asymptotically. 4. The level of the Pn/Pg ratio, calculated for fine day at each growth stage, remained around 70% during the period from the earliest growth stage to the beginning of ripening and then decreased rapidly. The ΣPn/ΣPg ratio (ΣPn and ΣPg denote total net and gross production for the whole growth period) was fairly constant and fell in the range of 53-56% in the three season's experiments. 5. The efficiencies of solar energy utilization for Pg(Eg) and for Pn(En), based on total solar radiation incident of the field, were high on cloudy days and low on clear days. As for the developmental changes in these efficiencies, it was observed that maxima appeared in the period from the middle of flowering to the beginning of ripening. The averages for days during this period, which included various weather conditions, were 0.85% and 0.47% respectively (Table 4). 6. The proportion of seed to total net production (ΣPn) on a calorie basis was 36%. Oil content of seed on a calorie basis was 62%. Thus, efficiencies of solar energy utilization for seed yield and oil production, based on total solar radiation incident on the field during the whole growth period, were estimated as 0.162% and 0.101% respectively (Table 4). 7. The results of analysis of the yield production process of rape were compared with those from other crops. The authers concluded that it is particularly important in the case of rape plant to promote development of the leaf canopy at early growth stages to increase the interception of solar radiation.

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