In some woody plants, adjusting leaf size (via epidermal cell size) balances water supply (veins) with transpirational demand (stomata). However, it is unclear whether this is a general pattern among plant species.
Carins Murphy et al. compare relationships between vein and stomatal density, epidermal cell size and leaf size in pairs of related herb and woody species from four plant families grown under sun and shade. Correlations between modelled (assuming veins and stomata are passively diluted by epidermal cell expansion) and observed relationships indicate that fluctuations in epidermal cell size constitute a responsive mechanism, by which the plants maintain a constant ratio between the anatomical traits that control leaf water fluxes.