Fig. 2.

Mean rates of internal ¹³CO₂ label assimilation of tissues of detached sycamore branches after 4.75 h water uptake in sunlight as determined by ¹³C analysis. One-half of the branches were harvested at the end of the uptake period, and one-half were harvested after an additional 4.75 h in the dark. (Pooled data shown.) Treatment branches (n=18) were labelled by allowing them to take up water enriched with 99 atom% ¹³CO₂ at a concentration of 0.0116 mol l⁻¹. Control branches (n=6) took up water enriched with 0.0114 mol l⁻¹ CO₂ at atmospheric isotope composition (∼1 atom% ¹³C). Bars are standard error of the mean. Control branch assimilation of ¹³CO₂ was not significantly different from zero (t=0.774, P=0.440, n=66, pooled data of all tissues).