Fig. 4.
The stable carbon isotope ratio of the dry matter (δ 13Cp) of young and mature leaves plotted against instantaneous measurements of the ratio of intercellular to ambient CO2 concentrations (ci/ca) in the same leaves. The solid line represents the theoretical relationship according to the model of Farquhar et al. (1982a). The broken lines represent least-squares regressions through the mature and young leaves. The regression equation for mature leaves is δ 13Cp = −10.4 – 23.8(ci/ca) (R2 = 0.90), and that for young leaves is δ 13Cp = −7.8 – 22.3(ci/ca) (R2 = 0.64).