Some characteristics on the control of CO₂concentration were tested with the automatic CO₂controlling and recording system, which was attached to the newly constructed phytotron.
The mode of action of this system is as follows (see Fig. 1) ;
1, The CO₂concentration in the chamber (90 × 90 × 120 cm³) or room is able to be controlled at arbitral concentration from 0 to 3, 000 ppm. And CO₂uptake and exhaust are measured at the same time.
2. In the light, CO₂enriched air of arbitral concentration, which is selected to be most suitable for the control of the concentration in the chamber or room, is stored in a gas holder by on-off action, and is flown to the chamber or room through the controlling system.
3. CO₂concentration in the chamber or room is controlled by compound PID (parallel, integral and differential) action of flow rate control valuve from the result of CO₂analysis.
4. In the dark, CO₂increase is controlled by CO₂free air from CO₂absorbing column of moleculer shieve.
5. In the natural light condition, the shift of action from the light to the dark or its reverse action is switched automatically by the signal from the CO₂analyzer of the chamber or room (Fig. 2) .
Using this system, the effect of inlet CO₂concentration upon CO₂uptake of tobacco plants was measured. The CO₂uptake was not affected by the inlet CO₂concentration, however (Table 1) .
Also the effect of CO₂concentration in the chamber upon the CO₂uptake by the plants was tested. The satulation point to CO₂concentration under the artificial light condition of 0.75 cal⋅cm^-2⋅min^-1 was about 1, 200 ppm (Fig. 3) .
The photosynthesis-light curves were figured from the results of the measurement of diurnal changes in net CO₂exchange. Then it was obseved that the tobacco plants in the chamber were satulated with light at the light intensity about 0.75 cal⋅cm^-2⋅min^-1 (Figs. 4, 5) .

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The present study was conducted in order to investigate the effect of pre-or post-irradiation treatment with visible light on UV-induced killing, using the first instar larvae from strains of Cambodge and5mAas materials.
1. The duration and the intensity of subsequent illumination with visible light necessary for obtaining saturation in photoreversing effect were 120min and 500lux, respectively.
2. The dose response curve for UV-induce killing without visible light illumination was sigmoid indicating that killing was multi-hit in character. The D₃₇values forCambodgeand 5mA were 2.05×10⁴and 5.89×10⁴ergs/mm², respectively.
3. By the post-treatment with visible light, UVinduced killing forCambodgeand5mA could be reversed up to 50% and 33%, respectively.
4. The killing action of UV was also reversed by the pre-irradiation treatment with visible light.

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Various kinds of heterozygous striped (p^s/+^p) F₁larvae were irradiated with γ-rays at the dosage of 2, 000 R in the second or the third instar in order to investigate the effect of environmental conditions on the frequency of γ-ray induced white spots due to the elimination ofp^s-carrying chromosome fragment.
1. It was found that the inductions of white spot with γ-rays are photoreactivable in varying degrees, depending upon the strains of silkworm, to the extent of 10 to 50%.
2. Frequencies of white spots induced by γ-irradiation at 24 hrs after the second ecdysis have been influenced to a great extent by the differences of temperature after irradiation, resulting in higher frequency at high temperature (25°C or more) during the third and fourth instars, and in lower frequency at low temperature (16°C) during the third or the fourth instar.
3. The effects of implantation of brain, suboesophageal ganglion, corpus allatum or prothoracic gland on the frequencies of γ-ray induced white spots were investigated. The endocrine organs were transplanted into striped F₁larvae immediatly after the second ecdysis, then these larvae were irradiated at 24 hours after transplantation. Though the transplantation of brain, suboesophageal ganglion or corpus allatum did not show any significant effects, the larvae transplanted with prothoracic gland exhibited the decrease in their frequency of white spots up to 54% of control.

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Photo- or thereto-sensitivity in the germination of potato seeds varied with the variety and the progress of after-ripening of the seeds. The effect was markedly greater in light irradiation than in high-temperature treatment, and low-temperature treatment had a little effect.
When the application of GA brought about high germination at constant temperatures in continuous darkness. But the effect of GA was also considerably various with the variety and the physiological state of the seeds.

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Three years have past since the phytotron was established in '67 at the institute, and it is now running under good conditions. The analysis of the frequency and cause of troubles which was observed in each field of apparatus during the past three years is considered to be useful for the good maintenance of the phytotron.
The average frequency of the failures of electric power and the suspension of water-supply was 35.7 and 9.3 times per year, respectively, and the number of the troubles which actually had effect on the room temperature control was 38 per cent in the former and 75% in the latter. In the refrigerating system, gas-leaks from the joints of the distributor, gauges and so on showed the highest frequency of troubles, followed by the breakage of parts and the malfunction of the water regulating valves and thermostatic expansion valves etc.
As for the controller, the thermal controller showed the highest frequency of troubles. These troubles were comprised of the inoperative kind of troubles between the cam and the electric contacts and slips between the coupling and the drum. Another controller, i. e.the humidity controller and modutrol motor operated almost without any important troubles, but showed an increasing tendency in the occurrence of these compared each proceeding year. Troubles in the electric system were those concerning the fuse, the cable, the parts, the trans-former and the motor. A highest frequency of troubles occurred in the breakage of stabilizers of lamps due to the high temperature of their location. The number of lamps which burned out in the lightroom was 9 in average per year in a set of 339. The highest frequency of trouble in relation to the building was the breakage of the glass of the glassrooms, followed by water-leaks from the ceiling of the glass-room, breakage of the flexible board of the light-room and so on.
In order to decrease the occurrence of these types of troubles, the following are considered necessary : (1) a sufficient maintenance budget is needed; (2) a greater capacity reserve and a dual system of apparatus is desirable; (3) the maintenance of a good source of electric power and water supply, independent of the phytotron, is deemed essential; and (4) the recording and analysis of all troubles which occurred in previous years will be most practical.

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