Fig. 4.
(A) Observed relationship between vein density and epidermal cell size (black solid line) compared with the modelled relationship (black dashed line, see the Materials and Methods for details). Vein density in all species follows a dependency on epidermal cell expansion similar to stomata, but vein density per epidermal cell size is significantly greater under sun conditions. The modelled effect of epidermal cell size on vein density is shown for the mean stomatal index across all species. Symbols show the mean observed values ± s.d. of the five woody species (including Toona ciliata) and the four herbaceous species grown in sun and shade (symbols as in Fig. 1) (sun and shade species pairs joined by a black dotted line). The observed relationship is not significantly different from the modelled relationship. Linear regressions describe the relationship between vein density and epidermal cell size under sun and shade conditions; DV under sun conditions = 0·143 × 1/√SEC + 2·102 (r2 = 0·88, F1,7 = 49·27, P < 0·001), DV under shade conditions = 0·145 × 1/√SEC + 0·984 (r2 = 0·85, F1,7 = 39·78, P < 0·001). Also shown are representative paradermal sections from leaves of (B) Ocimum basilicum and (C) T. ciliata. Note the higher density of veins in T. ciliata.