Fig. 1. A schematic illustrating the dependence of c_i on the relationship between stomatal conductance and photosynthetic capacity. In this "A/c_i" plot, the two curved lines rising from near the origin represent the dependence of A on c_i as determined by leaf gas-exchange measurements taken over a range of external CO₂ concentrations. Variation in the initial slope of these curves reflects variation in photosynthetic capacity. The two curved lines are intersected by two straight lines originating at the ambient CO₂ concentration, c_a. The slope of these straight lines is the stomatal conductance to CO₂, g_c. The intersections indicated by numerals represent the "operating" values of c_i (and of A, g_c, and c_i/c_a) for three genotypes of a C₃ species. The data shown here were derived from leaf gas-exchange measurements on three wheat varieties reported in Condon et al. (1990). (Adapted from Condon and Hall, 1997.)

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