represents the advective water flow from the xylem toward the sites of evaporation and back diffusion from the sites of evaporation into the rest of the leaf including the xylem.
The Péclet number is proportional to the transpiration rate (E ) and the effective mixing length (L ) that water takes to move from the veins to the sites of evaporation, and inversely proportional to the molar density of water (C ; 5.56 x 10-4 mol m-3) and the diffusivity of H218O in water (D ; Eqn. 8) (Farquhar et al. 1998; Barbour & Farquhar 2000; Barbour et al. 2000b; Gan et al. 2003; Barbour & Farquhar 2004; Barbour 2007). The diffusivity of H218O in water calculated according to Cuntz et al. (2007).