Epicuticular wax (ECW) The aerial surfaces of plants are covered with a wax layer that is primarily a waterproof barrier but that also provides protection against environmental stresses. The ubiquitous presence of cuticular wax is testimony to its essential function. The epidermis constitutes the leaf surface. The most characteristic trait of epidermal cells is the fact that they have the cuticle on the outer periclinal wall. The cuticle coats nearly continuously all mature parts of the leaf, and the only breaks or gaps are stomata the pores between guard cells. The cuticular layer, outside the cell wall, consists of lipid substances (such as waxes, cutin and cutan polysaccharides (cellulose and pectins). The cuticular layer is coated with the cuticle proper which lacks polysaccharides and contains more waxes than the underlying layers. On top, there is the epicuticular wax layer, without cutin or cutan. The cuticle proper is covered by a smooth amorphous wax film. Outside the wax film we can find waxes in more ordered form. They form a layer with considerable ultrastructural and chemical diversity. Epicuticular waxes are composed of a mixture of chemical compounds: hydrocarbons, primary alcohols, aldehydes.