Abstract
A plant chamber for the measurement of photosynthesis was devised by the auther to study photosynthesis in tobacco plants. The dimensions of the chamber were 70 by 70 by 120 centimeters. The temperature was controlled by a household air conditioner installed in the wall, which circulated the air in the chamber at the speed of 50 centimeters per second. Using a CO2 enriching apparatus, the concentration of CO2 in the chamber was kept at 300 ppm by changing the flow rate of supplying air. The results obtained were summarized as follows: 1. With regard to the diurnal change of photosynthesis in the individual plant, the so-called "mid-nap" was not observed, which had been pointed out by some investigaters, but photosynthesis was constant from 8 a. m. to 5 p. m. in a day in June. Photosynthesis of the individual tobacco plant was satulated at the same light intensity as in the case of a single leaf. 2. Photosynthesis in the individual plant attained to the highest value at the time before topping, but the respiration in it at the time of topping. The ratio of respiration to photosynthesis was lowest when photosynthesis showed the highest value, and the ratio was retained at 0.1 to 0.15. 3. Photosynthesis per unit leaf area reached a peak about 30 days after the time of topping. The similar results were obtained with the detached leaves grown in the field. 4. High correlation has been observed between protein nitrogen content per unit leaf area and photosynthetic activity per unit leaf area through out the growing season.
