Effect of light on uptake by photosynthetic tissues in the absence of co2. —The effect of light and of CO2on the uptake of86Rb and-32P by isolated leaves of Elodea canadensis has been studied. The uptake of both these ions is strongly stimulated by light both in the presence and in the absence of CO2. In the case of phosphate, light stimulates uptake and inhibits the leakage of the ion from the tissues.