The cross section below shows the many structures of a leaf blade. Palisade and spongy cells serve as food producers. In the veins, xylem tissue distributes water, and phloem tissue carries away food. Stomata (pores) on the underside of the blade enable gases to enter and leave the leaf. Guard cells regulate the amount of carbon dioxide and water vapor that pass through a stoma. The stomata are usually open while the leaf is making food.

SOURCE
World Book Encyclopedia Chicago: World Book-Childcraft International, Inc., 1979

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