Fig. 8. Typical variation over time of Φ_PSII when C_a was changed abruptly from 350 to 4000 ppm around dehydrated leaves of P. sativum plants grown at normal temperature (relative water content of the leaf = 68·2 %). Other experimental conditions were as in Fig. 7. The line parallel to the x‐axis is the mean Φ_PSII value measured on well‐hydrated leaves ± s.e. (dotted lines, n = 4).