Precise Measurements of Carbon Dioxide Exchange by Illuminated Leaves near the Compensation Point

The results of precise measurements of rates of carbon dioxide assimilation at low external concentrations of carbon dioxide and of rates of carbon dioxide output into virtually carbondioxide-free air show that linear extrapolations of the carbon dioxide intake curve plotted against the external concentrations of carbon dioxide give an exaggerated estimate of the rate of carbon dioxide output from illuminated leaves into carbon dioxide-free air. The shape of the exchange curve suggests that the rate of endogenous production of carbon dioxide changes at external concentrations in the region of the carbon dioxide compensation point (Г).