Chapter 5 - Vascular integration and resource storage

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Surface view of cleared whole mount of a wheat leaf showing large and small parallel veins (mauve). Lines of stomata (orange guard cells) lie along the flanks of these veins. Water evaporates from the wet walls of mesophyll cells below the stomata, drawing water from the veins through sheath cells. Scale bar = 100 um (Photograph courtesy Margaret McCully) 

...what quantities of moisture trees do daily imbibe and perspire: now the celerity of the sap must be very great, if that quantity of moisture must, most of it, ascend to the top of the tree, then descend, and ascend again, before it is carried off by perspiration. (S.Hales,Vegetable Staticks, 1727)