Fig. 4.

CO₂ assimilation of detached sycamore branches allowed ¹³CO₂-labelled water to transpire for 4.75 h in sunlight. Each branch was measured at two locations (lower, ∼ 25 cm from the cut end, and upper, ∼ 60 cm from the cut end). Assimilation was determined by two methods, ¹³C analysis and efflux calculated from measurements made with an infrared gas analyser. Efflux measurements were made in sunlight after the branches had taken up CO₂-enriched water for at least 2 h, and were repeated after the branches equilibrated in the dark for at least 2 h. Branches were harvested after 4.75 h in the dark for ¹³C analysis.