FIGURE 4.

Sketches (from light microscopic images) of representative minor loading veins from fully expanded leaves of Verbascum phoeniceum grown under a 9-h photoperiod of 400 μmol photons m ^–2 s^–1 at an average day/night leaf temperature of 25° C/20° C (warm) or 14° C/8° C (cool) and of minor loading veins from fully expanded leaves of cucumber and pumpkin grown under a 14-h photoperiod of 1000°mol photons m^–2 s^–1 at an average day/night leaf temperature of 25° C/20° C. Filled dark gray cells are intermediary (companion) cells (IC), filled light gray cells are phloem parenchyma cells (PC), small white cells are sieve elements (SE), and cells with light gray adjacent to the cell walls are tracheids (T). Photosynthetic capacities (light- and CO₂-saturated rates of oxygen evolution, P_max in μmol O₂ m^-2 s^-1) ± standard deviation obtained from one leaf from each of four plants (n = 4) per growth condition provided above each sketch. Mean photosynthetic capacities between V. phoeniceum leaves grown at the two different temperatures, and between cucumber and pumpkin grown under the common conditions, were significantly different at p < 0.001 (Student’s t-test).