Where ϕx is the fraction of leaf water in the xylem, and Pr and Pm are the xylem and mesophyll Péclet numbers, respectively. This model allows for different Péclet effects in each tissue type (Gan et al. 2003; Holloway-Phillips et al. 2016). The influence of the xylem Péclet depends on physiological traits such as E that regulates flow velocity and anatomical traits, such as vein density, fraction vein volume, stomatal density and size, and specific water content (Sternberg & Manganiello 2014; Larcher et al. 2015; Song et al. 2015; Holloway-Phillips et al. 2016; Liang et al. 2018). Potentially multiple other anatomical traits that influence the movement of water along the transpiration pathway and in the leaf alter Δ18OLW. The Farquhar-Gan model can be modified by excluding the mesophyll Péclet if it is small or nonexistent compared to xylem Péclet (Eqn. 11). Therefore, the Péclet effect