epidermis

epidermis In animals, outer layer that contains no blood vessels. In many invertebrates, it is only one cell thick. In vertebrates, it may comprise several layers and forms part of the skin. In plants, the epidermis is the outermost layer of a leaf or of an unthickened stem or root; it is usually coated in a waxy layer, the cuticle, which reduces water loss.

epidermis The outermost layer or layers of cells in an animal. It is one cell thick in many invertebrates, but many cells thick in vertebrates. In land-dwelling vertebrates its surface layer is formed from dead, hardened (keratinized) cells. See also INTEGUMENT.

epidermis
1. (in zoology) The outermost layer of cells of the body of an animal. In invertebrates the epidermis is normally only one cell thick and is covered by an impermeable cuticle. In vertebrates the epidermis is the thinner of the two layers of skin (compare dermis). It consists of a basal layer of actively dividing cells (see Malpighian layer), covered by layers of cells that become impregnated with keratin (see keratinization). The outermost layers of epidermal cells (the stratum corneum) form a water-resistant protective layer. The epidermis may bear a variety of specialized structures (e.g. feathers, hairs).

2. (in botany) The outermost layer of cells covering a plant. It is overlaid by a cuticle and its functions are principally to protect the plant from injury and to reduce water loss. Some epidermal cells are modified to form guard cells (see stoma) or hairs of various types (see piliferous layer). In woody plants the functions of the shoot epidermis are taken over by the periderm tissues (see cork cambium) and in mature roots the epidermis is sloughed off and replaced by the hypodermis.