Potato is known to produce stable tuber yield as compared with other field crops. For a better understanding this reason, we observed growth pattern and tuber yield in the two years (1982 and 1983) under different climatic conditions in the early half of the growing seasons. Five main cultivars, early to late, were grown and the observation was made at the same date in the both years. 1. Climatic conditions before early August were substantially contrast between the two years; they were dry with abundant radiation in 1982, while wet with short radiation and low temperature in 1983. After middle August, however, they became near to those of the average year in the both years (Fig. 1). 2. Growing period and tuber dry matter yield were not significantly different between the years, although tuber fresh yield was significantly larger in 1983 than in 1982 (Table 1.). Patterns of total and tuber dry matter accumulation were quite different between the years (Fig. 2). The rates of dry matter production in the early season were smaller in 1983. On July 15th, there were large differences in percentages of dry weight in each organ ; they were smaller in leaf and stem, and larger in tuber dry weight in 1982 than those in 1983 (Table 2). 3. Leaf area index (IJAI), crop growth rate (CGR), net assimilation rate (NAR) and tuber growth rate (TGR) showed quite different seasonal changes between the years (Fig. 3). LAI in 1982 and CGR, NAR and TGR in the early growing season of l983 were rather low values. Significant differences were also found in specific leaf area (SLA) between the years, the values in 1983 were higher than those in 1982 (Table 3). 4. During the experimental period, the solar radiation in 1983 amounted to only 75% of that in 1982. However, there was no signifierence between the years in intercepted photosynthetically active radiation by crops (ΔPAR), because of larger LAI in 1983. The efficiencies of dry matter accumulation per ΔPAR (E_PAR) in 1983 were slightly larger than those in 1982 (Table 4). Tuber dry yield was correlated positively with ΔPAR (r=0.760^*).

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It had been reported by the authors that leaf stomatal aperture in the rice plant under submerged condition decreased in fine midday with high evaporative demand and that close relation was found between diffusive conductance and photosynthetic rate in rice leaves. From these results it had been predicted that photosynthesis would reach the maximum early in the morning and then decrease gradually toward the afternoon with increase in light intensity and vapour pressure deficit. This study was conducted to ascertain this prediction by measuring the diurnal courses of photosynthetic rate (P), transpiration rate (T), P/T ratio (water use efficiency) and diffusive conductance in the single-leaf of the rice plant in paddy field under submerged condition on fine and cloudy days and to clarify the factors determining the diurnal courses of photosynthesis in a fine day using the simultaneous measurement system of photosynthesis and transpiration developed by K_OCH, S_CHULTZ and L_ANGE (Siemens Co. Ltd.). The photosynthetic rate on a fine day increased with increase in light intensity, reached the maximum early in the morning and then gradually decreased down to 75% of the maximum rate toward afternoon even under sufficient light intensity and this was accompanied by a decrease of diffusive conductance (Figs. 2A and 4). The photosynthetic rate in the morning was higher than that in the afternoon under the same light intensity more than 600 μE/m²/sec (Fig. 3A). Transpiration rate increased toward the midday with the increase of light intensity and vapor pressure deficit, and reached the maximum at about 13:00 PM. Water use efficiency was higher early in the morning and late in the evening and lower in the midday (Fig. 2A). The photosynthetic rate, transpiration rate and diffusive conductance on a cloudy day changed according to the change in light intensity (Figs. 2B and 3B). Therefore, light intensity was the dominant factor determining diurnal courses of photosynthetic rate and transpiration rate on a cloudy day. It was found that the time of the daily maximum of diffusive conductance was different from the time of that of photosynthetic rate in their diurnal changes, that is, diffusive conductance had already started to decrease even before the photosynthetic rate reached the maximum early in the morning. Under sufficient light intensity with artificially reflected sunlight by the mirror when diffusive conductance reached the maximum early in the morning, the time when both photosynthetic rate and diffusive conductance reached the maximum coincided. The maximum rater of the photosynthesis was higher than that of the day without the reflected light (Fig. 5). This result suggested that leaf photosynthetic capacity was not always fully realized in diurnal courses of photosynthesis on a fine day. To examine the factor reducing the photosynthetic rate on a fine day, diurnal courses of photosynthetic rate was measured under lower vapor pressure deficit by humidifying air in the chamber. The photosynthetic rate was much higher under lower vapor pressure deficit at least up to noon compared with that under the same vapor pressure deficit as outside (Fig. 6). This fact showed that water stress related to high vapor pressure deficit was the main factor for the decrease of photosynthesis in the midday even though the effects of photosynthate accumulation in the leaf blade and photoinhibition could not be neglected. From these results it was clarified that leaf photosynthetic rate in the rice plants under submerged condition decreased to some extent in the midday on fine days and they could not utilize high solar energy fully for dry matter production. [the rest omitted]

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Soybean plants grown in a green house were allowed to assimilate ¹³CO₂ for 10 hrs under steady-state conditions at 13 (Exp. 1), 26 (Exp. 2) and 40 (Exp. 3) days after anthesis. The partitioning of labelled carbon into individual plant parts and th significance of carbon assimilated at different growth stages for seed-filling were investigated by periodic sampling of labelled plants until harvesting time (50 days after anthesis). The plants were treated with (+N plants) or without (-N plants) supplement nitrogen 9 days after anthesis. Carbon assimilated 13 days after anthesis (Exp. 1) was most actively used for pod formation. Incorporation of labelled carbon into seeds was continued until harvesting time. Fifty per cent or more of labelled carbon found in the seeds at harvesing time was transported mainly from the leaves, pods and stems + petioles during the late reproductive stage from 26 to 50 days after anthesis (Fig. 2). Carbon assimilated 26 (Exp. 2) and 40 (Exp. 3) days after anthesis was utilized mainly as carbon sources for seed-filling. In these experiments, however, the most of labelled carbon found in the seeds at harvesting time was transported into the seeds directly from the leaves within 4 days after the ¹³CO₂ assimilation (Fig. 2). Contribution of assimilated carbon to seed production was highest in Exp. 2 accounting for 4.37% in -N plants and 4.21% in +N plants. They accounted respectively for 1.25 and 1.66% for Exp. 1, and 2.70 and 2.15% for Exp. 3 (Table. 1). Supplement application of nitrogen increased seed yield at about 7% (as carbon content). This increase was due mainly to the efficient contribution of carbon assimilated during the early stage of seed filling.

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Petioles of sugar beet plants, Beta vulgaris var. saccharifera Alef. serve not only as conductive tissues but also as intermediate storage pools^{11∼14, 18)}. Enzymatic conversion systems of sugars should be localized within the phloem and parenchyma cells of the petiole. In the previous papers, the histochemical detection of UDPG-pyrophosphorylase⁶⁾, phosphoglucomutase⁷⁾, phosphoglucose isomerase⁸⁾ and glucose-6-phosphatase⁹⁾ in the petiole tissues were reported. In this paper, The histochemical detection of phosphorylase in the petiole tissues is described. The histochemial method described by Y_IN and S_UN¹⁷⁾ was employed with slight modification. The reaction mixture was summarized in Table 1. Based on the formula (1), newly synthesized polysaccharides were detected with iodine reaction technique¹⁵⁾. (GlP)_n + (Starch)_m ⇆ (Starch)_m+n + nH₃PO₄ ···(1) Procedure : Non-fixed sections obtained from the fresh petioles of sugar beet cv. Mono-hikari were used. After infiltration in distilled water under reduced pressure¹⁰⁾, the sections were incubated in the test solution covered with toluene (Table 1)²⁾ and kept for 1-3 days at room temperature. Before observation under a light microscope, the sections stained with the diluted Gram's iodine solution were mounted on slides, covered with iodine glycerol (Gram's iodine solution : glycerol/1 : 10) and sealed with paraffin¹⁰⁾. Histochemical observations : The site of newly synthesized polysaccharides stained clear deep blue with iodine indicates the localization of phosphorylase. In the epidermal system of the abaxial side of young petioles, guard cells exclusively showed marked formation of polysaccharides in the section incubated in the test solution (Figs. la and lb). In the pith parenchyma cells, the newly synthesized polysaccharides were deposited as tiny granules independently of intracellular particles and nucleus (Fig. 2). In the xylem, phosphorylase activity was not detected in most of its parenchyma, but in the parenchyma cells surrounding the vessel, the vigorous activity was observed frequently (Fig. 3). In the phloem and cambium, phosphorylase activity was not almost observed, but is some cases, marked activity was detected in companion cells and phloem parenchyma (Fig. 4). In the bundle sheath, the newly synthesized polysaccharides appeared in two different states, one gathered around one pole of each cell forming a large ellipsoid, and the other scattered in the cytoplasm forming tiny granules (Fig. 5). From the observation mentioned above, phosphorylase activity occurred in the pith parenchyma cells of young petioles where polysaccharides were not present but large amounts of glucose were stored¹⁰⁾ physiologically. This discrepancy remains to be resolved.

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The present study was aimed to obtain basic knowledge to monitor remotely the physiological-ecological functions and status of crop community. In this paper the features of canopy temperature in corn crop field and its relations with climatic factors measured simultaneously by a multi-sensing system were investigated. The results obtained are summarized as follows: 1. The coefficients of variance of canopy temperature were as small as around 1% for uniform communities (Table 1). 2. The mean temperature of leaves measured by thermocouples differed between adaxial and abaxial surfaces by 0∼0.3°C under cloudy conditions and 0.1∼1.2°C under sunny conditions. The temperature of adaxial surface was always higher than abaxial one. The coefficients on variance of leaf temperature within upper layer of crop community were 1.3∼2.5% under cloudy conditions and 2.5∼6.5% under sunny conditions. 3. The canopy temperature measured by an infrared thermometer was relatively lower than the mean temperature of upper layer of the crop community measured by thermocouples. Because of high correlation between them, the latter could be successfully estimated by the former (Fig. 2, Eq. 1). 4. The canopy temperature varied in the same pattern as that of ambient air temperature keeping lower by 2∼5°C under steady conditions of the other factors. A very high correlation was observed (r = 0.989) between the simultaneous values of them. The time constant of the response of canopy temperature was estimated to be very short and the temperature seemed to respond almost instaneously (Fig. 3). 5. A linear relationship (r = 0.8) was obtained between the air-canopy temperature difference and the vapor pressure deficit of air, and the canopy temperature decreased in proportion to the increment of the vapor pressure deficit (Fig. 4). The depression of the canopy temperature is caused by the cooling effect of the transpiration. It is considered that this relationship was brought about under such conditions that crop water deficit was so small as to give no significant influence on stomatal resistance and the potential transpiration. The above result suggests that the air-canopy temperature difference may be a good index of crop water stress in arid zones where the deficits of air vapor pressure and soil water, both, are large. 6. According to a multiple regression analysis, variance of canopy temperature was estimated almost fully by the three climatic factors ; air temperature, vapor pressure deficit and PAR (r = 0.91∼0.96). Canopy temperature had close relation with these three variables as indicated by the partial correlation coefficients : 0.87 for air temperature, -0.74 for VPD and 0.82 for PAR. And the mean ratio of the contribution of them were estimated as 0.86 for air temperature, -0.62 for VPD and 0.60 for PAR. These relationships were obtained within a wide range of those three factors (Table 2, Fig. 5).

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It was clarified in the previous papers that leaf water potential, stomatal aperture and photosynthetic rate in rice plants decreased with increase in solar radiation and vapor pressure deficit even though rice plants grew under the condition where sufficient water was supplied to roots in submerged paddy field, and that the decrease in leaf water potential, stomatal aperture and photosynthetic rate were more remarkable in rice plants with low root activity or with poor root system. The present study was conducted to investigate the relationship between water uptake and transpiration rates and the effects of this relation on leaf water potential and stomatal aperture through their diurnal changes, and to discuss the characteristics for maintaining water balance in rice plants. Transpiration rate was higher than water uptake rate in the morning when transpiration was increasing rapidly with rapid increase in solar radiation and vapor pressure deficit. Both rates were practically the same in the midday and then transpiration rate was lower than water uptake rate in the evening when transpiration rate was decreasing rapidly with rapid decrease in solar radiation and vapor pressure deficit (Fig. 2 A). The difference between water uptake and transpiration rates was very small even when transpiration rate was changing rapidly (Fig. 2 B). In case of reduced water uptake due to low water potential of culture solution or NaN₃ treatment to roots, transpiration rate decreased remarkably due to increase of stomatal closure in the daytime (Figs. 3 and 4). Therefore, the difference between water uptake and transpiration rates did not increase so much and leaf water potential decreased a very little even in the midday with high transpiration demand compared with decrease of water uptake rate and stomatal aperture (Figs. 3 and 4). These results suggested that water balance in rice plants was maintained by the process as follows: There is too much transpiration in the daytime with high solar radiation and valor pressure deficit, so water uptake could not overtake the transpiration, and leaf water potential decreased to a certain extent. As stomata in rice plants were very sensitive to change of leaf water potential compared with those of other plants, stomata closed very rapidly with response to the decrease of water potential, so that transpiration rate decreased to almost the same as water uptake. Therefore, the difference between water uptake and transpiration rates was very small, and decrease of leaf water potential was prevented. Futhermore, in case of rice plants with reduced water uptake due to low water potential of culture solution or NaN₃ treatment to roots, all were the same as in the process of maintaining water balance. From these results and the high correlation between stomatal aperture and photosynthetic rate, it was considered that water uptake ability directly affected photosynthetic rate under sufficient solar radiation in rice plants with stomata responding very sensitively to change of leaf water potential. Futhermore, it was suggested that rapid wilting often observed in rice, soybean and cucumber under very large vapor pressure deficit or on water saturated soil in rainy season, baiu, could arise from both decrease of water uptake ablility and loss of sensitivity of stomata to decrease of leaf water potential.

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前報で報告した¹⁴C-ロイシン及び¹⁵N-アンモニウムのイネ幼根および6葉期幼植物の蛋白分画への取込みの低温による阻害の機構を明らかにするため, イネ幼根から抽出したポリソームを用いて無細胞系を構成し, その¹⁴C-ロイシン取込みの温度依存性を検討した. イネ幼根ポリソーム及びコムギ胚抽出蛋白(コムギ胚ホモジェネートの170,000×g遠沈の上清中の蛋白分画)とで構成した系に於て, トリクロロ酢酸不溶分画ヘの¹⁴C-ロイシンの取り込みが認められ, かつ, その取込みはシクロへキシミドで阻害されるが, クロラムフェニコールでは阻害されなかった. 従って, 収込みは混入した微生物によるのではなく, 構成した系によると推定された. ¹⁴C-ロイシン取込みのアレニウスプロットは, 30℃から8℃迄の間で一本の直線を示し, 18-20℃での変化は認められなかった. 一方, コムギ胚抽出蛋白の代わりに, イネ幼根抽出蛋白(イネ幼根ホモジェネートの170,000×g遠沈の上清の濃縮液中の蛋白分画)を用いた系では, ¹⁴C-ロイシン取込みのアレニウスプロットに於て, 19℃付近にブレーキングポイン卜が認められた. 更に, 13℃または10℃で低温前処理したイネ幼根から抽出したポリソームのショ糖密度勾配遠沈の沈降プロフィールに於て, 沈降度の大きい重いポリソームが低温処理によって減少する傾向は認められず, 寧ろ増加の傾向を示した. 以上から, 前報で認められた in vivo での蛋白合成の低温による阻害は, 蛋白合成系に対する低温の直接の作用によるものと推定される. また, コムギ肛抽出蛋白を用いた無細胞系の¹⁴C-ロイシン取込みのアレニウスプロットと, イネ幼根抽出蛋白を用いたそれとの差異は, 両抽出蛋白中に存在する蛋白合成系の可溶性因子, 恐らく伸長因子あるいは終了因子, の差異によると推測される.

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The following system was devised to meet the requirement to measure carbon exchange rate (CER) and the related factors of single rice leaves in situ efficiently. 1. A small leaf chamber (100 × 23 × 8 mm) which is connected with two differential type IRGAs (one is for CO₂ and the other for H₂O), is attached to a central part of a leaf blade and CER and transpiration rate are measured (Fig. 2). 2. Leaf temperature is measured with two thermocouples simultaneously with CER and transpiration rate. Based on the transpiration rate, absolute humidity of the surrounding air of the leaf and leaf temperature, "stomatal conductance" (g_s, CO₂ diffusion conductance for the path from the surrounding air to the intercellular space of leaf) is evaluated. 3. The time required to measure CER and g_s of a single leaf is about 1.5 min. The g_s value evaluated in such a way is considered to be that corresponding to stomatal aperture just before attaching the leaf chamber. It was proved that repeated attachment of the chamber to leaves has little aftereffect on g_s and CER of the same leaves. 4. Light intensity, temperature and CO₂ concentration inside the leaf chamber are similar to those outside the chamber. 5. From the above mentioned, this system is considered to be suitable for measuring CER of many single leaves in situ to examine its dependence on related factors, especially on g_s under field conditions.

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ロゼル(タイケナフ)の乾物生産過程の基本的特徴を明かにするため, 1985年, 品種Nonsoon-2を用い, タイ国コンケン畑作試験場において, 標準的な条件(無潅がい, N, P₂O₅, K₂O施肥量各25 kg/ha)の下に圃場試験を行った. 4月20日に播種し, 30日おきに開花期過ぎまで合計6回, 毎回1区30個体ずつ4反復, 合計120個体を抜き取り, 生長解析を行って次のことを明らかにした. 1) 全乾物重の増大は播種後30日頃から急速となり, 120日頃まで続き, 最終乾物重(183日)は2,142g/m²に達した. 播種後30日から90日まで相対生長率(RGR)はほぼ一定値(5-7%/day)を示した. 個体群生長率(CGR)は播種後60-90日に最大値34.9g/m²/dayに達したが, これは温帯, 熱帯を通じてC₃種としては著しく高い値に属する. 2) LAIは播種後120日で最大値6.3に達した. 3) 全乾物に対する根重の割合は全生育期間を通じてほぼ一定の著しく低い値(7-9%)を示すという特異な現象が見られた. これに対し, 茎重の割合は最初の34%からほぼ直線的に増大して183日目には87%となり, 繊維収量に最も密接な関係をもつ皮部の割合は播種後120日目の32%から最終日の38%まで増大した.

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タイ国東北部の4試験地において, 品種Ton-Kiewを用い, 2年間圃場試験を行った. 4月下旬を第1回として20日おきに3回播種し, それぞれ播種後75日を第1回として15日おきに210日後まで刈取りを行ない, 繊維収量と気象条件を調べ, 次の結果を得た. 1. 播種期が早いほど繊維収量は高かった. 収穫期に関しては, 播種後165日の開花期ころの刈取りが最高収量(3播種期, 4試験地の平均で, 1979年2,775kg/ha, 1980年1,965kg/ha)を示し, 210日刈取りでは30%以上減収した. 2. 各刈取間隔15日間の収量相対生長率と気象要因との単および偏相関を調べた結果, 雨量はあるレベルまでは収量に対して促進的に働くが, それを越えると減収方向に働くこと, また日照時数は現存量の著しく大きくなる開花期前後には多いほど収量を増すことが推定された.

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株間距離と条間距離を組合わせて個体密度を41.6個体/m²に一定に保ちつつ, 条間距離を20cmから80cmまで7段階に変えて, ロゼルをタイ国東北部の4試験場で圃場栽培し, 次の結果を得た. 元のデータを4試験場で平均した場合の繊維収量は条間距離によってほとんど変動せず, ただ30cm条間区に小さな極大値が見られるだけであった. しかし, 生産力の高い2試験場とその低い2試験場とで別々に平均収量を求めてみると, 前者では40 cm条間区に極大値が現われるのに対し, 後者では30cm 条間区に極大値が見られた. さらに, 40cmから80cmまで条間を増した場合, 2グループ間で収量は正反対の反応を示した. すなわち, 生産力の高い試験場では条間距離の増大につれて収量が低下したのに対し, 生産力の低い試験場では収量が増大した. イネの場合との相似点と相違点が論議された.

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二培地法により培養したイネ分離種子根の4週間までの培養期間における, 胚盤柔細胞および胚盤上皮細胞の微細構造を, 透過型電子顕微鏡で観察し, 発芽種子の構造と比較した. 発芽2週間後の胚盤では, 細胞内容物が著しく減少しているのに, 培養条件下の胚盤細胞は多くの内容物を含み, 特に粗面小胞体の層状構造がしばしば観察され, 胚盤細胞の生理活性が長期間活発であり, その細胞の蛋白合成能の高いことが明らかとなった. これらの結果から, 胚盤細胞の崩壊に対する幼芽の役割について論議した.

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イネの色素体発達に及ぼす光の強さと温度の影響を, 特に「弱光プロラメラボディ」の形成に注目して研究した. 光の強さと温度は, 弱光プロラメラボディの形成に重要な関係をもっている. すなわち, この構造体は26℃では50ルクス以下にならないと形成されないが, 30℃では400ルクスで, 色素体の発達過程の後半に形成された. これらの事実は, イネの弱光プロラメラボディがゴガツササゲに比べて形成されにくく, 外界要因に対する色素体の応答性は植物の種類によって違うことを示唆する. 40℃の暗所でエチオプラスト内に形成された多数の小胞は, 形態変化をしてプロラメラボディの細管になることができず, 直径1μmの集塊として存在した.

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コムギの干ばつ耐性の測定法として SULLIVAN^8,9) がソルガムに用いた方法を取りあげ, コムギに対する本法の有効性ならびに適用の際の留意点を検討した. 予備試験の結果から, 分げつ最上位の展開葉を1 cmの長さに切断し, この1gサンプルをポリエチレングリコール600 (PEG)の高張水溶液(春播きコムギではPEG 20%, 秋播きコムギではPEG 60%)に24時間浸漬する方法を用いた. 浸漬処理によって生じた細胞膜の損傷程度は, 処理後サンプルを脱イオン水中に浸漬し, 浸出した電解質の量を電気伝導度計で測定することにより評価した. 春播きコムギ11品種および秋播きコムギ14品種にこの方法を適用したところ, 損傷程度に大きな品種間差異が認められ, 干ばつ耐性の測定法として本法が有効であることが示された. しかし, 損傷程度は, 葉位, 葉齢, 葉身上の部位, 季節, 生育中に与えられた水分ストレスの程度やその時期などにより大きな影響を受けたので, 測定に際してはこれらの要因について十分留意する必要があることが認められた。また本法の有効性をより明らかにするために, 本法により評価される干ばつ耐性の生理的, 遺伝的基礎および栽培的意義についてさらに検討が望まれた.

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植物群落内の光環境に対する植物の生育反応を明らかにするため, 植物葉類似の分光透性を示す試作フィルター透過光(人工緑陰)と寒冷紗透過光(中性遮光)下で, 陽地植物としてイネ(日本晴)とダイズ(農林2号), 陰地植物としてカカオとウリカワを用いて2-5週間における幼植物の生育反応を調べた. 光強度は, 対照の白色強光区(BOCランプ+ハロゲンランプ, W比6.4:3.0)では708μmol m^-2s^-1 (400-700nm), 人工緑陰区および中性遮光区ではともに同157および73の明・暗2段階とした. 赤色光(660±5nm)と遠赤色光(730±5nm)の光量子比(R/FR)で表わした光質は, 対照区および中性遮光区では1.31-1.52, 人工緑陰区では0.26-0.51であった. イネとダイズでは, 遮光下で伸長促進, 葉の発達抑制および乾物生産の著しい低下がみられた. 伸長促進程度は, ダイズで大きくイネでは小さかったが, 両種とも人工緑陰下の方が同じ光強度の中性遮光下よりも明らかに大で, とくに処理初期(約1週間以内)に著しかった. 一方, カカオでは, 遮光によって茎の伸長, 葉の発達および乾物生産が著しく増大した. ウリカワでは, 葉の伸長促進, 葉面積の抑制および乾物生産の低下が起るが, その変化の程度は上記陽地植物よりも小さかった. カカオとウリカワに共通した反応は次のとおりである : a) 人工緑陰下の光質によってひき起される伸長促進反応は, 陽地植物と異なり, 処理初期に小さくその後増大する : b) 葉の発達は, 同一光強度レベルでは, 人工緑陰下でより強く促進される : c) 遮光下における乾物生産および葉面積当たり乾物重の相対値は, 陽地植物よりも明らかに高く, 人工緑陰の光質の効果は光強度およびR/FR比が高い場合に促進的に, 低い場合には抑制的に作用する. 葉緑素含量は, ウリカワでは遮光下で著しく増大し, イネでもやや大となったが, 他は大差がなかった. 葉緑素a/b比は, 遮光によってイネとダイズではやや低下したが, カカオとウリカワでは増大する傾向を示した. 人工緑陰下の光質は葉緑素含量および同a/b比の両方を低下させることが, 供試4種に共通して認められた. 以上から, 遮光下では, 陽地植物とくにダイズは弱光回避種と類似の反応をし, 供試した陰地植物は部分的に弱光耐性種に似た反応を示すことが判明した. 後者の高い弱光適応性は, カカオでは主に葉面積の発達により, ウリカワでは葉緑素含量の増加によると考えられた.

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ポット栽培したダイズ(品種農林2号)を用いて, 葉の生長を葉の"伸長性"(葉片に錘りをかけたときの, 葉片の単位時間あたりの伸び量, Ex)と, 圧ポテンシャル(P)との両面から検討した. 得られた結果の大要は, 以下の通りである. 1) 給水を停止すると, 土壌水分含量は低下し, それに伴ない葉の生長速度は低下して, 土壌水分レベルが45%(対圃場容水量)に達したとき, 葉の生長は完全に停止した. その後, 土壌水分レベルを45%に保ったところ, 葉は再び生長を始めた. このことから, 葉の生長において乾燥への馴化がおこると考えられた. しかし, 生長再開後の葉の生長速度は十分に給水した対照区(土壌水分レベル80%)の葉と比べて, 小さかった. 2) 給水停止後, 葉の生長速度が低下したときには, PとExの両者が共に減少した. その後Pは, 対照区のレベルにまで回復し, このことが葉の生長の再開を可能にしたと考えられた. Pの回復は, 浸透ポテンシャルの低下, すなわち浸透調節によりもたらされた. いっぽう, Exは, 低い値にとどまり, 回復しなかった. 低水分状態が維持されたときに, Pが完全に回復するにもかかわらず, 生長の回復が不完全な程度にとどまるのは, Exが低い値にとどまることによると考えられた. 3) 植物体を低水分下に置いた後, 十分給水すると葉の生長は回復するが, 対照区にはおよばなかった. 乾燥処理後の再給水により, Pは十分回復したが, Exの回復は不十分であり, このことが, 生長回復の不十分さの基礎となっていると考えられた. またこのことから, Pはその時々の条件に応じすみやかに変化しうるが, Exは低水分条件により, かなり不可逆的な減少をきたすようであった. 4) 本実験の結果の全体をみると, 葉の生長速度は, P, Exの両者と正の相関を示したが, 後者との間の相関のほうがより密接であった.

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湛水(W)・適湿(M)・乾燥(D)の土壌條件下で, 生育させた9種類の夏作イネ科作物の出葉間隔, 乾物生産と蒸散係数の変化の程度を, 4回の実験を通じて比較検討した(第1表). M区に比べてD区では, すべての種の出葉間隔が長くなったが, W区では水稲・陸稲, シコクビエ, ハ卜ムギ, ヒエで短くなり, キビ, 卜ウジンビエ, アワ, モロコシ, トウモロコシで長くなった(第1図). 植物体と穂の乾物重にもとづくW/M比が, D/M比より大きいか, またその逆の関係かどうかによって, 供試作物は2群に大別された(第2, 3, 4図. 第2, 3, 4, 5表). その一つは, D/M比よりもW/M比の方が大きい群で, 水稲・陸稲, シコクビエ, ハトムギ, ヒエを含む. 他の一つは, W/M比よりもD/M比の方が大きい群で, キビ, トウジンビエ, アワ, モロコシ, トウモロコシを含む. 前者の群を耐湿性程度が大きい群(LWTC群), 後者の群を耐旱性程度が大きい群(LDTC群)とした. W・M・D区の各作物の蒸散係数を, 地上部乾物重当リ(TCs)だけでなく, 植物体全乾物重当リ(TCp)と穂乾物重当リ(TCe)でも求めた(第6, 7表). 各作物のTCsとTCpにもとづくD/M比は, 約1.00であったが, W/M比は種によって変異を示した(第5図B, C). SHANTZとPIEMEISEL の知見にもとづいた「TCeにおけるW/M比またはD/M比が, 1.00を大きく上回れば上回るほど, 湛水または乾燥條件はその種の生育にとって不適当な環境であることを示す」 とする假説によって, 各作物の耐湿性・耐旱性程度を評価した(第5図A). この評価法による各作物の耐湿性と耐旱性程度の大きさの順位は, 穂乾物重のW/M比とD/Mによる順位とほぼ一致した. そして, この評価法によってLWTC群とLDTC群は, さらに2つの亜群に分けえた. LWTC群は, (1) 湛水條件でもっとも安定しているが, 乾燥條件に対する感受性がもっとも高い種である水稲・陸稲, ハトムギを含む亜群と, (2) 湛水條件でも乾燥條件でも比較的安定している種であるシコクビエ, ヒエを含む亜群に分かれた. 一方, LDTC群は, (1) 湛水條件に対する感受性は比較的高いが, 乾燥條件では安定している種であるキビ, トウジンビエ, モロコシ, 卜ウモロコシを含む亜群と, (2) 湛水條件に対する感受性がもっとも高いが, 乾燥條件では安定している種であるアワを含む亜群に分かれた.

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