Description
The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialised parenchyma cells, but the established modern preference has long been to classify the epidermis as dermal tissue, whereas parenchyma is classified as ground tissue. The epidermis is main component of the dermal tissue system of leaves (diagrammed below), and also stems, roots, flowers, fruits, and seeds; it is usually transparent (epidermal cells lack chloroplasts, except for the guard cells.)
The cells of the epidermis are structurally and functionally variable. Most plants have an epidermis that is a single cell layer thick. Some plants like Ficus elastica and Peperomia, which have periclinal cellular division within the protoderm of the leaves, have an epidermis with multiple cell layers. Epidermal cells are tightly linked to each other and provide mechanical strength and protection to the plant. The walls of the epidermal cells of the above ground parts of plants contain cutin, and are covered with a cuticle. The cuticle reduces water loss to the atmosphere, it is sometimes covered with wax in smooth sheets, granules, plates, tubes or filaments. The wax layers give some plants a whitish or bluish surface color. Surface wax acts as a moisture barrier and protects the plant from intense sunlight and wind. The underside of many leaves have a thinner cuticle than the top side, and leaves of plants from dry climates often have thickened cuticles to conserve water by reducing transpiration.
The epidermal tissue includes several differentiated cell types: epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichomes). The epidermal cells are the most numerous, largest, and least specialized. These are typically more elongated in the leaves of monocots than in those of dicots.
Trichomes or hairs grow out from the epidermis in many species. In root epidermis, epidermal hairs, termed root hairs are common and are specialized for absorption of water and mineral nutrients.
In plants with secondary growth, the epidermis of roots and stems is usually replaced by a periderm through the action of a cork cambium.
Read more about this topic: Epidermis (botany)
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