Comparisons of physiological and anatomical characteristics between two cultivars in bi-leader apple trees ( Malus  ×  domestica Borkh.) 1 1Abbreviations: Chl, chlorophyll; DABB, days after bud break; Gs, stomatal conductance; Ψleaf, leaf water potential; ΨMD, midday leaf water potential; ΨPD, pre-dawn leaf water potential; LEC, lower epidermis cell; PPFD, photosynthetic photon flux density; Pn, net photosynthesis rate; Sd, stomatal density; SLW, specific leaf weight; UEC, upper epidermis cell; Ve, vessel; VPD, vapor pressure deficit; Xr, xylem rays.