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Epidermiscellen hebben doorgaans dikke wanden, bevatten geen bladgroenkorrels (chloroplasten) en sluiten goed op elkaar aan. Ze bieden bescherming tegen a) uitdroging, b) overmatig zonlicht (ultraviolette (UV) straling en hitte), c) mechanische beschadigingen, d) vraat door herbivoren (planteneters van insect tot vee).
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The epidermis is the outermost layer of the leaf, whicht serves to protect the inner tissues. It mostly consists of a single-cell layer, but sometimes multiple-layering can be encountered (see example here below in Ligustrum). In a transverse section of an entire leaf both upper end lower epidermis can be seen (see ivy here above). Often, the upper epidermis differs from the lower epidermis. Epidermal cells are mostly thick walled, they do not contain chloroplasts and they form an unbroken cover. The epidermis protects against a) dehydration, b) intense sunlight, especially ultraviolet (UV) irradiation, c) mechanical stress and d) predation by herbivores (insects, cattle). Among specific adaptations against animals, one can mention the occurance of multi-layered epidermis with thick cell walls, hook-shaped and stingy hairs and the presence of sticky, irritating, toxic or indigestible substances, like tannins. Since dehydration is the major threat for plants, the epidermal cells are covered with a cuticle, a layer of cutin, a tough lipid-like and water impermeable substance. In addition a waxy layer is often present (See image of wax deposition).
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