Epidermis The epidermis of leaves is a continuous layer of cells on all surfaces of the leaf, unbroken except for pores, the stomata ( stoma , singular), which facilitate the exchange of gases between the interior of the leaf and the atmosphere. The parenchyma cells of the epidermis fit together like paving stones and generally contain no chloroplasts except for those in the guard cells of the stomata. A cuticle composed of cutin and wax is deposited on the outer primary walls of the epidermal cells. It varies in thickness among different kinds of plants. Hairs or scales—called trichomes —are extensions of epidermal cells and are present on many leaves. Glands associated with trichomes often produce substances repugnant or toxic to herbivores. The physical presence of a tangle of trichomes on the surface of a leaf also deters many animals from eating or using the leaf.
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