In the Tohoku district, the cooler region in Japan, the cultivatable period of rice plants is shorter, and moreover, the extremely cool weathers have often occured during the important growth periods. Therefore, these periods are necessary to fit climatically in safe time. Such agro-climatological studies for estimating the rice cultivation period have recently developed in Japan and the methods which set the heading to a center of the plan have been established. In earlier studies the earliest and the latest dates of the safe cultivation period were established on the basis of seasonal variation curve of air temperature or of accumulated air temperature usually by the critical temperature free from cool damage, but they have not discussed the products from the quantitative point of view. Therefore, it was difficult to estimate physiologically of economically the most suitable cultivation period considering the management of a farm. For the purpose of settling this difficulties, it is necessary to elucidate the relationships between the changes of climatic conditions and of yield, corresponding to the movement of the important growth periods.
The Authors have found the method for estimating the course of yield index corresponding to the heading by the application of such assumptive decreasing scales of rice yield based on low air temperature at the important periods as Fig. 1. These scales were proposed by Abe et al. (1964) in connection with the study (1960-1961) for estimating the damage by cool weather conditions on rice production.
If the decreasing rates of yields by low temperature at three important periods of rice plants such as the reduction division period, the heading and ripening periods in case of heading on the date i in the year j, are designated by (R₁)_ij, (R₂)_ij and (R₃)_ij respectively, the yield index Y_ij will be as follows.
Y_ij=100(1-(R₁)_ij)(1-(R₂)_ij)(1-(R₃)_ij)
(1)
The mean yield index for n years on a specific date i, Y_i will be written
Y_i=∑nj=1Y_ij/n (2)
From Eqs. (1) and (2), yield index in case of heading on a spontaneous date can be calculated and consequently, the course of yield indexes is drawn in Fig. 2. For instance, the yield indexes and their course calculated from daily air temperature from 1937 to 1963 at the Fujisaka Farm are shown in Fig. 2 and Table 1.
Taking the scale of a farm and working efficiency into consideration, if Y_p is the planned level of yield index per unit area, the heading period obtaining products more than Y_p is the term between H_c and H_l, the crossings of the curve of yield index to Y_p-line, as shown in Fig. 3. But the heading time is apt to delay by the low temperature before them. Therefore, when the number of days of probable lateness, Ll is calculated by the other method, the date Hp, Ll days before H_l is obtained as the planning latest heading date, and the period from H_c to H_p, L_p is obtained as the planning safe heading period.

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気象要素が土壌水分に与える影響のうち, 降水の多さや, 蒸発散能の多さ等は, 土壌水分への影響がすくなく, 降水のないか, もしくは少ない時間数が, 殊に表層土壌の水分に影響し, 植被のある場合は, 表層があたかも根域にまで拡大されたような影響を示す。灌漑の必要度は, 無降水もしくは, 降水の少ない期間の長さに比例して増大する。これはまた集約度が高まるにつれて増大する。

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In winter of 1963, heavy snow fall by unusual cold weather resulted in considerable destroy to trellis and shoots of fruit tree. An analysis was made to clarify the relation of snow depth to mechanical damage of trellis and shoots from the data of this investigation. The results obtained are as follows;
(1) These data show that a snow depth near 150cm was critical for breaking trellis and shoot of fruit tree.
(2) Commercial production of fruit tree are practiced in our country in the regions where snow depth of 150cm occurs every 10 years or more longer intervals as shown in Figure 3.
(3) It would be desirable to culture fruit tree at meteorologically favorable places where the snow depth of 150cm occures every 10 years or more longer intervals.

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It should be noticed that when we grow plants in a closed room like a glasshouse, their environment is quite different from that out of doors. Regarding the concentration of carbon dioxide in the air, it is increased in the glasshouse to get more harvest in recent experiments. But most glasshouses and phytotrons in this counntry maintatin the supply of carbon dioxide by ventilation. A study on this matter was made earlier by MORRIS et al. (1954). Since then, this problem has not been developed further. MORSE and EVANS (1962) designed the CSIRO Phytotron using MORRIS' hypothetical minimum ventilation rate. Furthermore, MORSE (1963) calculated the ventilation rate of the growth cabinet, assuming that the plant net assimilation rate was constant in spite of the large decrease in carbon dioxide concentration in the air. In the present paper, our study is to improve the methods used by MORRIS and MORSE, and to demonstrate the close relationship between the plant net assimilation rate and the ventilation rate in wide range of values of parameters. We assume that the plant net assimilation rate has a linear relation with the concentration of carbon dioxide in the air, i. e.,
a=C-C_c/C₀-C_c-a₀, C≥C_c,
where a is the rate of net assimilation in the glasshouse per unit area per unit time (g/m²hr), C is the concentration of carbon dioxide in the glasshouse per unit volume (g/m³), C_c is that of compensation point (g/m³), C₀ is that out of doors (g/m³), and a₀ is the rate of net assimilation out of doors (g/m²hr). In Fig. 1, the line (A) is used by us, and the other (B) was shown by Morris et al. We also assume that the concentration of carbon dioxide in the atmosphere near the ground is constant in the daytime, the molecule of carbon dioxide in the glasshouse is always mixed uniformly, the influence of the temperature coefficients of respiration and assimilation are small, and the concentration of carbon dioxide is the limiting factor of plant photosynthesis. In this paper we shall confine the discussion to the simple problem of the soil free carbon dioxide in the glasshuose.
We calculated the efficiency of plant assimilation rate in two ways. One is
a/a₀=m·z+2m/m·z+2m+1,
where m is c_e·v/a₀·s, z is ventilation rate (1/h), v is the glasshouse air volume (m³), C_e is C₀-C_c, s is growing area (m²), and a is (a₀+a_i)/2. This equation was solved using a linear approximation in the change of carbon dioxide concentration. The other is the strict solution of this problem, that is, a_i/a₀=1-a₀/c_e·j·z+a₀{1-exp[-(z+a₀/c_e·j)t]} where j is V/S, t is time, a_i is the plant net assimilation rate in the glasshouse. If a₀ and C_e are fixed at 5.0g/m²hr (MORSE and EVANS, 1962) and 0.394g/m³ (Egle 1951) respectively, the ratio a_j/a₀ is the function of t with parameters i and z. Suppose the obtainable values of j are from 1 to 15 and that of z are from 1 to 100, the computation of this equation is very complicated, Taking t from 0.05 to 0.5 at the interval of 0.05 and from 0.5 to 5 at the interval of 0.5, j as integer, and z from 1 to 20 continuously, 25, 30, 40, 50 and 100, we calculated this equation using the electric computer at the Computation Centre, University of Tokyo. Some of the typical exmples are shown in Fig. 3.

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同化箱または蒸散箱による同化量や蒸散量の測定法は農学分野のなかで広く重宝されているにもかかわらず, それらのなかの微気象の研究, とくに微気象の制御の研究は余りなされていない。そこで著者は生育箱内での熱・水蒸気・炭酸ガスの収支式から出発して, 箱内の微気象と換気率との関係を研究した。つぎに, 生育箱内の植被層内部の気象要素の分布を数値計算的にしらべた。それらの結果を要約するとつぎのようである。
箱内の気温は外気温と複合項の和として表わされ, 複合項は純放射に比例し, 総括顕熱伝達係数と換気顕熱伝達係数の和に逆比例することがわかつた (5式参照)。換気顕熱伝達係数は(6)式にみられるように換気率Nに比例するが, その割合は単位壁面あたりの箱容積 (V_c/A_w) によつて変化する。V_c/A_wは保温比(R=A_f/A_w) に箱の平均高さを乗じたものに大体ひとしい。(5) 式からの結果が第1図Aに示されている (50×50×100cm³の生育箱について)。この生育箱では約100回/時間の割りで換気すると, 内外気温の差は3℃以下になることがわかつた。
箱内の水蒸気圧力は(8, 9)式のように示され, 平衡水蒸気圧力は純放射量・ボーエン比・A_f/Qの3量によつて大きく影響されることがわかつた。純放射が多くて蒸発散が多い場合 (湿つてβが小) には内部の水蒸気圧力は著しく高くなる。上と同様な生育箱について(9)式から求めた結果が第1図Bに示されている。
箱内に植被がある場合の炭酸ガス収支式は(10)のように表わされ, これから平衡時の炭酸ガス濃度は(13)式のようになることがわかつた。平衡炭酸ガス濃度は主として単位葉面積あたりの換気量, 外部の炭酸ガス濃度, 葉内と葉外との炭酸ガス拡散のための積分拡散係数とによつてきまることがわかつた。同一生育箱に葉面積指数をかえて植物を入れた場合の炭酸ガス濃度と換気率との関係が第1図Cに示されている。換気がますにつれて箱内濃度は増加して外気のそれに接近するが, 箱内の葉面積指数に応じてある濃度を保つに必要な換気率は大きくなる。箱内と野外の作物の光合成量の比と通気量との関係が第2図に示されている。単位時間単位葉面積あたりの換気量が800cc以下では光合成能率は急減することがわかつた。この模様は第1表に示されているD_tの大小によつて著しく変化する。
生育箱内の気象要素の垂直分布を明らかにするために, 植被層微気象の研究方法を利用した。その結果が第4図に示されている。気温はゆるやかに下から上へむけて高くなるが, 葉温は下層での24℃から上層の33℃まで高まつている。湿度も上にゆくほど高くなつている。普通の Bowen 比と Foliage Bowen ratio とは植被層内での変化の形は似ているが, 絶対値は著しく違うことがわかつた。

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