In leaf anatomy, xylem is located towards the upper (adaxial) epidermis, while phloem is towards the lower (abaxial) epidermis. This dorsal-ventral arrangement is called amphistomatic leaf organization. The upper-side position of xylem facilitates efficient water delivery to the photosynthetic mesophyll cells. Bundle sheath surrounds the entire vascular bundle, and mesophyll is the photosynthetic tissue between the epidermal layers.