root, in botany
root, in botany, the descending axis of a plant, as contrasted with the stem, the ascending axis. In most plants the root is underground, but in epiphytes epiphyte (ĕp`əfīt') or air plant,..... Click the link for more information. the roots grow in the air and in hydrophytes (e.g., cattails and water lilies) they grow in water or marshes. Roots function to absorb water and dissolved minerals from the soil, to anchor the plant, and often to store food. There are two main types of root system: the tap-root system, in which there is a main primary root larger than the other branching roots; and the diffuse (or fibrous) root system, in which there are many slender roots with numerous smaller root branches. Tap roots are characteristic of most trees and of many other plants, including the carrot, parsnip, radish, beet, and dandelion. The grasses (e.g., corn, rye, and alfalfa) have diffuse roots; in the sweet potato some of the larger fibrous roots swell to store food—although these should not be confused with the tuber of the Irish potato, which is a modified underground stem stem, supporting structure of a plant, serving also to conduct and to store food materials. The stems of herbaceous and of woody plants differ: those of herbaceous plants are usually green and pliant and are covered by a thin epidermis instead of by the bark of woody
..... Click the link for more information. . Root systems often far exceed in mass the aboveground portions of the plant: alfalfa roots sometimes reach 40 ft (12 m) in length, and the combined length of all the roots of a mature rye plant has been measured at 380 mi (612 km). These ramified root systems are important agents in preventing soil erosion. Roots grow primarily in length; only the older roots may develop a cambium layer that increases their diameter. Protecting the constantly growing tip of the root is a cap of cells that break off as the root probes through the soil; they are replaced by new cells from a layer of meristematic tissue just behind them. In the center of the root the cells formed earlier by the embryonic cells of this layer differentiate into storage tissue and xylem and phloem vessels to conduct sap sap, fluid in plants consisting of water and dissolved substances. Cell sap refers to this fluid present in the large vacuole, or cell cavity, that occupies most of the central portion of mature plant cells.
..... Click the link for more information. upward to the leaves and back down to nourish the root cells. On the surface of the epidermis of the growing portion of the root, tiny cellular projections called root hairs extend into the soil to absorb water and minerals. Although root hairs are less than 1-3 in. (.84 cm) long, their great number enables the plant to collect enormous quantities of water, most of which is promptly lost into the air by transpiration. In spite of their slenderness and delicate structure, the spiraling forward thrust of the root tips and the pressure of their expanding cells is sufficient to split solid rock.
root, in mathematics
root, in mathematics, number or quantity r for which an equation f(r)=0 holds true, where f is some function function, in mathematics, a relation f that assigns to each member x of some set X a corresponding member y of some set Y; y is said to be a function of x, usually denoted f(x) (read "f of x..... Click the link for more information. . If f is a polynomial polynomial, mathematical expression which is a finite sum, each term being a constant times a product of one or more variables raised to powers. With only one variable the general form of a polynomial is a0xn+a
..... Click the link for more information. , r is called a root of f; for example, r=3 and r=−4 are roots of the equation x2+x−12=0, because (3)2+(3)−12=0 and (−4)2+(−4)−12=0. In the special case where f(x)=xn−a for some number a, a root of f is called an nth root of a, denoted by n√a or a1/n. For example, 2 is the third, or cube, root of 8 (3√8=2), since it satisfies the equation x3−8=0. Every number has n different (real or complex) nth roots; e.g., there are two square roots of 9 (3 and −3) since (3)(3)=9 and (−3)(−3)=9.
root
)
root
(1) The top level of a hierarchy. See tree, root directory and root domain.
(2) A person with unlimited access privileges who can perform any and all operations on the computer. Also called "superuser."
root
root [rüt]
Root (botany)
The absorbing and anchoring organ of vascular plants. Roots are simple axial organs that produce lateral roots, and sometimes buds, but bear neither leaves nor flowers. Elongation occurs in the root tip. The older portion of the root, behind the root tip, may thicken through cambial activity. Some roots, grass for example, scarcely thicken, but tree roots can become 4 in. (10 cm) or more in diameter near the stem. Roots may be very long. The longest maple (Acer) roots are usually as long as the tree is tall, but the majority of roots are only a few inches long. The longest roots may live for many years, while small roots may live for only a few weeks or months.
Root tips and the root hairs on their surface take up water and minerals from the soil. They also synthesize amino acids and growth regulators (gibberellins and cytokinins). These materials move up through the woody, basal portion of the root to the stem. The thickened, basal portion of the root anchors the plant in the soil. Thickened roots, such as carrots, can store food that is later used in stem growth. See Cytokinin, Gibberellin
Roots usually grow in soil where: it is not too dense to stop root tip elongation; there is enough water and oxygen for root growth; and temperatures are high enough (above 39°F or 4°C) to permit root growth, but not so high that the roots are killed (above 104°F or 40°C). In temperate zones most roots are in the uppermost 4 in. (10 cm) of the soil; root numbers decrease so rapidly with increasing depth that few roots are found more than 6 ft (2 m) below the surface. Roots grow deeper in areas where the soil is hot and dry; roots from desert shrubs have been found in mines more than 230 ft (70 m) below the surface. In swamps with high water tables the lack of oxygen restricts roots to the uppermost soil layers. Roots may also grow in the air. Poison ivy vines form many small aerial roots that anchor them to bark or other surfaces.
The primary root originates in the seed as part of the embryo, normally being the first organ to grow. It grows downward into the soil and produces lateral second-order roots that emerge at right angles behind the root tip. Sometimes it persists and thickens to form a taproot. The second-order laterals produce third-order laterals and so on until there are millions of roots in a mature tree root system. In contrast to the primary root, most lateral roots grow horizontally or even upward. In many plants a few horizontal lateral roots thicken more than the primary, so no taproot is present in the mature root system.
Adventitious roots originate from stems or leaves rather than the embryo or other roots. They may form at the base of cut stems, as seen in the horticultural practice of rooting cuttings.
| root - 1. See root mode, go root, wheel. |
How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content.
| ?Page tools | ||
|---|---|---|
|