The cross-section of a leaf reveals its complex structure ... It's on the surface of the leaf and its main job is to prevent water loss as the plant needs this water. It also protects the plant.

Because water must cross cell membranes (e.g ... Is it a matter of phloem unloading? Plant Science 180, 604-611 (2011). Sack, L. & Holbrook, N. M. Leaf hydraulics. Annual Review of Plant Biology ...