Curves were fitted to the rates of CO2 uptake (P) of single leaves of tomato against light intensity (I). It was shown that an asymptotic curve of the form P = a−bpI gave a consistently better fit to the observed data than the rectangular hyperbola. Saturating rates of photosynthesis, estimated as the asymptote of the curve, showed marked changes with leaf age, being maximal at or shortly after the start of the experiment, in small rapidly expanding leaves, and falling continuously thereafter. Photochemical efficiency, measured as the slope of the curve at zero light intensity, gave no discernable trends with time except in visibly senescent leaves, when the value decreased appreciably.
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W. E. Peat (1970) studied this question.