"for all it's mass, a tree is a remarkably delicate thing. all of it's internal life exists within three paper-thin layers of tissue, the phloem, xylem, and cambium, just beneath the bark, which together form a moist sleeve around the dead heartwood. however tall it grows, a tree is just a few pounds of living cells thinly spread between roots and leaves. these three diligent layers of cells perform all the intricate science and engineering needed to keep a tree alive, and the efficiency with which they do it is one of the wonders of life. without noise or fuss, every tree in a forest lifts massive volumes of water - several hundred gallons in the case of a large tree on a hot day - from it's roots to it's leaves, where it is returned to the atmosphere. image the din and commotion, the clutter of machinery, that would be needed for a fire department to raise a similar volume of water to that of a single tree...." - bill bryson, a walk in the woods
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