Fig. 5. Relationship between the PhRUE calculated with the simple method (PhRUE_HL) and that calculated with data on actual leaves (PhRUE_50L). The dotted line (barely visible because it overlaps with the solid line) is a linear fit with zero intercept to all data on almond and walnut, including data for clear days (open circles), overcast days (closed circles) and data on aubergine (open squares) from Rosati and DeJong (2003). The solid line is a linear fit with zero intercept to all data except data on overcast days. The equation parameters are: y = 0·982x, r² = 0·81, P < 0·001 for all data and y = 0·989x, r² = 0·91, P < 0·001 for clear days only (including aubergine data).