Root

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Root (botany), organ of higher plants, usually subterranean and having several functions, including the absorption and conduction of water and dissolved minerals, food storage, and anchorage of the plant in the soil. The root is distinguished from the stem by its structure, by the manner in which it is formed, and by the lack of such appendages as buds and leaves. The first root of the plant, known as the radicle, elongates during germination of the seed and forms the primary root. Roots that branch from the primary root are called secondary roots. In many plants the primary root is known as a taproot because it is much larger than secondary roots and penetrates deeper into the soil. Beets and carrots are examples of plants with very large taproots. Some plants having taproots cannot be transplanted easily, for breaking the taproot may result in the loss of most of the root system and cause the death of the plant.

Roots arising from the stem are known as adventitious roots. Such roots may be seen near the base of a corn stem. Adventitious roots formed high up on a stem are termed aerial roots or prop roots. Such roots aid in supporting the stem, as in the banyan, the mangrove, and certain orchids.

The root is composed of three types of tissue: the epidermis, or surface layer; the ground tissue, or cortex; and the vascular core, situated at the center of the root. Certain cells of the epidermis are modified for an absorptive function. Long, tubelike projections, called root hairs, grow from these cells into the absorptive surface of the root and anchor the root to soil particles. Water absorbed by root hairs is transferred across the cortex, the region of water and food storage, and into the vascular core, which carries it up into the stem. Organization of the vascular core in a root is markedly different from that in a stem. In the stem the vascular tissues xylem and phloem are grouped together in vascular bundles. In the root a central core of xylem has radial bands that extend outward toward the cortex, and between these bands are strands of phloem. In aerial roots the xylem core, which is usually solid in subterranean roots, often has a central zone of pith.
For more information about roots, read the full articles in wikipedia.org.

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