A mathematical model to compute hourly change of the greenhouse environment was designed. The system considered comprises the soil, crop, air and glass or vinyl cover. The feedback effect of the crop on the greenhouse environment is built in, and the temperature and humidity fields are simultaneously solved. Boundary conditions are the incident short-wave irradiance, the downward long-wave radiant flux density, the air temperature, the air humidity, the wind speed, all measured outside the greenhouse, and the water potential of soil in the greenhouse. The system is characterized by its scale, its properties regarding the heat transfer, the ventilation rate, and physiological characteristics of the crop about the water exchange. With these system parameters and boundary conditions, the model calculates not only the air temperature and humidity inside the greenhouse, but also the radiation balance, sensible and latent heat flux densities on the cover, the heat flux density through the cover, the latent and sensible heat exchange by ventilation, the radiation balance on the crop surface, the surface temperature of crop, and transpiration rate from the crop. The model was used to simulate the air temperature and humidity inside the greenhouse as affected by the ventilation rate. The results accorded qualitatively with experimental results so far reported.

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Transpiration rates, leaf temperatures and stomatal apertures in C₃ plants (7 species) and C₄ plants (19 species) were measured in a growth room maintained at an air temperature of about 36°C, a light intensity of 0.48ly/min, a windspeed of about 4m/sec, and a relative humidity of 80% (wet) or 40% (dry). The results obtained are as follows:
1) Transpiration rate
Under the dry condition, transpiration rates of C₃ plants (5.17-3.09gH₂O/100cm²/hr) were higher than those of C₄ plants (2.83-0.94gH₂O/100cm²/hr). Under the wet condition, transpiration rates of C₃ plants (3.08-2.09gH₂O/100cm²/hr) were also higher than those of C₄ plants (2.21-0.64gH₂O/100cm²/hr).
Under both dry and wet conditions, the mean transpiration rates of C₄ plants were about half of those of C₃ plants.
2) Leaf temperature
Under both dry and wet conditions, leaf temperatures of C₃ plants were lower than those of C₄ plants.
The temperature difference between leaf and air was correlated negatively with the transpiration rate.
3) Stomatal aperture
There was no difference in stomatal aperture between C₃ plants and C₄ plants. For both the plants the stomatal aperture under wet condition was larger than that under dry condition, except in the adaxial surface of goosegrass.
On the basis of the above results, a discussion is given on the difference in water requirements and geographical distributions between C₃ plants and C₄ plants.

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Time series of two kinds of climatic indices, the warmth index (WI) and the coldness index (CI), which were proposed to correlate the geographical distribution of plants with thermal resources, were analyzed mainly statistically in order to make clear the long-term change and the variability of climatic resources for natural vegetation. Meteorological data of about 230 stations including around 80 stations in Japan were used in calculations. The results obtained can be summarized as follows.
1. The warmth index representing the total amount of heat available for the growth of plants showed a clear systematic fluctuation during the past 80 years, although there is some difference in the amplitude and the phase among stations. At almost all stations in Japan, the increase of WI values was observed between 1950's and 1960's. Since then it seems to be continuously decreasing to date. The fluctuation of CI was found to be nearly inverse to that of WI in the phase, indicating that there is a negative correlation between |CI| and WI values. Fig. 3 illustrates an influence of the urbanization on the climatic conditions in large cities such as Tokyo, Osaka and Fukuoka. The values of WI at Tokyo with a population of about 9 million and an energy consumption density of 420×10⁹ kcal/km² increased by a rate of 2.7°Cmonth/10 year during the period from 1900 to 1975. The value of CI decreased inversely by a rate of 0.05°Cmonth/10 year during this period. Although similar changes of WI and CI were also observed at Osaka and Fukuoka, the rates of change of WI and CI values were about two-thirds of that at Tokyo.
2. The latitudinal average of WI near the equator was retained at the level of around 240°C month. Poleward of the latitude 25°N it showed a drastic decrease with latitude and became zero at about 70°N. The latitudinal distribution of WI shown in Fig. 4 agreed well with that of the sum of effective temperature (Uchijima, 1976a). On the other hand, the value of |CI| was zero in latitudinal bands lower than 25°N and increased rapidly poleward of this latitude. The latitudinal distributions of both indices were well approximated by Eq. (3).
3. The frequency distribution curves of WI and CI varied appreciably with the place. The standard deviations characterizing the frequency distribution curves of WI and CI increased proportionally with the square root of the mean value of those quantities, as indicated in Fig. 6. The dependence of standard deviation and coefficient of variance on the mean value was found to be in good agreement with the relationships derived from the gamma distribution function (Eq. 6). The scale and shape parameters obtained for the distribution function of CI varied also clearly with the mean value (see Fig. 7). This result indicates that the gamma distribution function is applicable to analyzing the chance occurrence of WI and CI for vegetation growth.
4. The correlogram and the power spectrum of the fluctuations of WI and CI were calculated by the conventional method. As shown in Fig. 8, the correlogram for the time fluctuations of 10 yearly running means of both the indices has a relatively long tail compared with those of the original fluctuations. The correlogram of the fluctuations of 10 yearly running means of CI at Okayama, Kochi, Miyazaki and Kagoshima showed a wavy tail with a clear peak in the lag-time of 20 to 30 years. Such a wavy variation of the correlogram was not obtained for Hokkaido district.
The power spectrum of the original fluctuations of both indices was mainly in the frequency range from 0.1 to 0.5 cycles/year at almost all stations except Hamamatsu where there was a clear peak in the frequency band between 0.04 and 0.07cycles/year.

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The cost of maintaining the desired temperature in winter is a principal element in the production of vegetables in greenhouse culture. Consequently, much lower costs of heat and more profitable operations will be possible if warm water from the condenser of a power plant can be used as the heat source for greenhouse heating.
In order to investigate the possibility of utilizing thermal effluent as the heat source of greenhouse heating, the experiments by a miniature greenhouse equipped with PVC-pipes as indirect heat exchangers were carried out (see Fig. 1).
The results obtained can be summarized as follows.
1. Under the conditions of warm water of 25.5°C and an outside air temperature of -6.8°C at calm clear night, air temperatures at inlet and outlet of the heat exchanger pipes in the greenhouse were 9.0°C and 16.5°C, respectively (see Fig. 2).
2. From an experimentally obtained relationship between the heat transfer coefficient and air speed in the pipes, the heat transfer coefficient at an air speed of 10m/sec was 2.5 times as much as that at 2m/sec (see Fig. 3).
3. From a theoretically obtained formula yielding required number of pipes for the model greenhouse utilizing thermal effluent, it was shown that 16 PVC-pipes, 23m long and diameter of 20cm, were required to maintain 12°C inside the greenhouse with thermal effluent of 25°C and an outside air temperature of -10°C (see Fig. 5, Fig. 6 and Fig. 7).

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A model describing the heat exchange in the plastic greenhouse with a storage-type heat exchanger was made in order to examine the feasibility of the storage-type heat exchanger for controlling the temperature and humidity in the plastic greenhouse. Relatively good agreement was obtained between measured and calculated environmental conditions in the plastic greenhouse with the storage-type heat exchanger.
The magnitude of the heat storage ratio, defined as the ratio of the amount of heat accumulated in water as a heat accumulator to the amount of heat transferred from crop and soil surfaces into the house, was considerably influenced by factors such as short-wave irradiance, ventilation rate and difference in the operation of air circulation system. Sample calculations indicated clearly that under high irradiance the latent heat due to the condensation of water vapor on the inside surface of heat exchange pipes plays an important role for the accumulation of heat.

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