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This paper gives a description of a two-channel photoelectric planimeter for measuring leaf areas. It is based on the absorption of rays within the range 0.6 to 1.4μ. The flux of radiation is converted to electric signals by argentum sulphide photocells. The difference in the photoelectric currents from the measuring and control channels is amplified by a sensitive and highly stable d.-c. differential amplifier and is indicated by a meter which can be calibrated direct in area units.

The intensity of respiration and of photosynthesis were investigated simultaneously in sugar-beet leaves not detached from the plant. Several hours before the experiment the leaves had assimilated radioactive14CO2 whereafter they were placed into a normal leaf chamber for continuous gasometric estimation of the intensity of photosynthesis, according to the changes in the concentration of carbon dioxide in the passing air. At the same time, the specific activity of C02 was measured in the air that had passed through the assimilation chamber. From the values of the specific activity of CO2 produced by the leaf in the dark the intensity of respiration in mg. CO2 can be calculated.

A study of the effect on the photophosphorylating system of those enzymes, which transform phosphoric esters, may be of great importance for discovering a mechanism in the regulation of some stage of the bioenergetic processes. Enzymes added to intact chloroplasts may interact with intermediates of photophosphorylation or with enzymes of this system, and thus evoke changes in the rate of inorganic phosphate incorporation during photophosphorylation. In this connection the effects of three enzymes — acid and alkaline phosphatases and pyruvate kinase — on the rate of photophosphorylation were studied. The enzymes were introduced into suspensions of chloroplasts at the beginning of or after definite periods of illumination. In the course of the experiment changes in inorganic phosphate and nucleotides were determined.