Fig. 6. Glucose (A) and sucrose (B) concentrations in cambial zones of tubers produced in plants exposed to light (shade or control illumination) and CO₂ (350 or 700 µmol mol^–1) treatments at tuber initiation (TI) and tuber bulking (TB). Plants were harvested 2 (TI) or 4 weeks (TB) after transfer to short days, with exposure to treatments for 2 weeks prior to harvest in each case. Bars represent the s.e.m. Means labelled with different letters differ significantly (P ≤ 0·05).