THE ABSORPTION OF CARBON DIOXIDE BY UNILLUMINATED LEAVES

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Abstract
All leaves so far examined, although unilluminated, absorb CO2 in excess of the amt. ascribable to the water they contain. This absorption is not necessarily a function of the living processes of the leaves; sunflower leaves killed either by heating or by freezing absorb more CO2 than do similar living leaves. It is unlikely that chlorophyll participates to an appreciable extent in this absorption inasmuch as etiolated, yellow and albino leaves absorb as much CO2 as do green leaves. Furthermore, neither chlorophyll-containing leaf residues (obtained by extraction of frozen leaves with aqueous solns. of CO2), isolated chlorophyll, nor pheophytin combine chemically with CO2. In sunflower leaves, water, buffer substances contained in the sap, and alkaline-earth carbonates present in the solid leaf material, all take part in the absorption of CO2. The alkalinity of the sap expressed from sunflower leaves is increased by storage of the leaves in an atmosphere of CO2. This increase may be correlated with the increased conc. of alkaline-earth bicarbonate caused by such treatment. Analytical and physico-chemical data concerned with the reactions of CO2 in sunflower leaves are given. The apparatus used for making the measurements is descr.

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