epidermis

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The outermost layer (occasionally several layers) of cells on the primary plant body. Its structure is variable; this article singles out five structural components of the tissue: (1) cuticle; (2) stomatal apparatus (including guard cells and subsidiary cells); (3) bulliform (motor) cells; (4) trichomes; and (5) root hairs.

Leaves, herbaceous stems, and floral organs usually retain the epidermis through life. Most woody stems retain it for one to many years, after which it is replaced. In roots it is usually short-lived. See also Leaf; Periderm.

Cutin is a mixture of fatty substances characteristically found in epidermal cells. It impregnates the outer cell walls and occurs as a continuous layer (cuticle) on the outer surface. The cuticle covers the surfaces of young stems, leaves, floral organs, and even apical meristems. Waxes appear as a deposit on the outside of the cuticle in many plants; the bloom on purple grapes and plums is an example. Most often the waxes are present in small quantity, but the leaves of some plants may be almost white with wax (Echeveria subrigida). The waxes of a few species are of great commercial value in the manufacture of polishes for floors, furniture, automobiles, and shoes. Other substances, such as gums, resins, and salts, usually in crystalline form, may be deposited on the outside of the cuticle.

The apertures in the epidermis which are surrounded by two specialized cells, the guard cells, are known as stomata. The singular form, stoma, is derived from the Greek word for mouth. However, some authorities prefer to include both aperture and guard cells within the concept of stoma. The apertures of stomata are contiguous with the intercellular space system of underlying tissues and thus permit gas exchange between internal cells and the external environment. The opening and closing of the stomatal aperture is caused by relative changes in turgor between the guard cells and surrounding epidermal cells.

Bulliform (motor) cells are large, highly vacuolated cells that occur on the leaves of many monocotyledons but are probably best known in grasses. They are thought to play a role in the unfolding of developing leaves and in the rolling and unrolling of mature leaves in response to alternating wet and dry periods.

Appendages derived from the protoderm are known as trichomes; the simplest are protrusions from single epidermal cells. Included in the concept, however, are such diverse structures as uniseriate hairs, multiseriate hairs (Begonia, Saxifraga), anchor hairs, stellate hairs, branched (candelabra) hairs, peltate scales, stinging hairs, and glandular hairs (see illustration). Cotton and kapok fibers are unicellular epidermal hairs.

geranium (Pelargonium), (b) Unicellular-hooked and uniseriate, club-shaped hairs of the bean (Phaseolus). (c) Uniseriate and glandular hairs of the tomato (Lycopersicon).">
Trichomes. (a) Unicellular and glandular (colleters) hairs of the geranium (Pelargonium), (b) Unicellular-hooked and uniseriate, club-shaped hairs of the bean (Phaseolus). (c) Uniseriate and glandular hairs of the tomato (Lycopersicon).

Root hairs are thin-walled extensions of certain root epidermal cells. They develop only on growing root tips and may arise from any epidermal cell, or from specialized cells known as trichoblasts. The life of a given root hair is usually numbered in days. See also Root (botany); Secretory structures (plant).

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noun

The tissue forming the external covering of the body: integument, skin. See surface/depth.

Outer layer of skin made of stratified epithelium and covered by dead cells impregnated with the fibrous protein, keratin.

(ep-uh-dur-mis)

The outside layers of the skin.

IN BRIEF: The outer skin.

The epidermis of the forearm had a strange rash on it.

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the outermost layer of cells of an animal or plant.
—epidermal adj.

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The outermost and nonvascular layer of the skin, derived from the embryonic ectoderm, the thickness varying between species and in different locations on the body. There are generally five layers, from within outward: (1) basal layer (stratum basale), composed of columnar cells arranged perpendicularly; (2) prickle-cell or spinous layer (stratum spinosum), composed of flattened polyhedral cells with short processes or spines; (3) granular layer (stratum granulosum), composed of flattened granular cells; (4) clear layer (stratum lucidum), composed of several layers of clear, transparent cells in which the nuclei are indistinct or absent; and (5) horny layer (stratum corneum), composed of flattened, cornified, non-nucleated cells. The clear layer is only present in certain areas such as the footpads of dogs and cats and the planum nasale.

• limbic e. — transitional epithelium between limb skin and hoof horn; covers the limbic corium.
• perioplic e. — see limbic epidermis (above).
• tubular e. — covering of the corium of the hoof coronet; produces the tubular horn of the hoof wall.

n

The superficial, avascular layers of the skin.

For a list of words related to epidermis, see:

• Tissue, Fiber, and Integumentary System - epidermis: outside layer of cells

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See words rhyming with "epidermis."

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Dansk (Danish)
n. - overhud, epidermis, yderbark

Nederlands (Dutch)
opperhuid, epidermis

Français (French)
n. - (Anat, Biol, Zool) épiderme

Deutsch (German)
n. - Oberhaut

Ελληνική (Greek)
n. - (ανατ.) επιδερμίδα

Italiano (Italian)
epidermide

Português (Portuguese)
n. - epiderme (f) (Anat.)

Русский (Russian)
эпидермис

Español (Spanish)
n. - epidermis

Svenska (Swedish)
n. - epidermis, överhud

中文（简体）(Chinese (Simplified))
表皮, 上皮

中文（繁體）(Chinese (Traditional))
n. - 表皮, 上皮

한국어 (Korean)
n. - 표피

日本語 (Japanese)
n. - 表皮, 上皮

العربيه (Arabic)
‏(الاسم) بشرة‏

עברית (Hebrew)
n. - ‮קרום העור (בבע"ח), השכבה החיצונה של עלים, גבעולים, שורשים וכו'‬

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