bark1 / bärk/ • n. the sharp explosive cry of certain animals, esp. a dog, fox, or seal. ∎ a sound resembling this cry, typically one made by someone laughing or coughing: a short bark of laughter. • v. 1. [intr.] (of a dog or other animal) emit a bark: a dog barked at her. ∎ (of a person) make a sound, such as a cough or a laugh, resembling a bark: she barked with laughter. 2. [tr.] utter (a command or question) abruptly or aggressively: he began barking out his orders [with direct speech] “Nobody is allowed up here,” he barked [intr.] he was barking at me to make myself presentable. ∎ [intr.] call out in order to sell or advertise something: doormen bark at passersby, promising hot music and cold beer. bark2 • n. the tough, protective outer sheath of the trunk, branches, and twigs of a tree or woody shrub. ∎ this material used for tanning leather, making dyestuffs, or as a mulch in gardening. • v. [tr.] strip the bark from (a tree or piece of wood). ∎ scrape the skin off (one's shin) by accidentally hitting it against something hard. DERIVATIVES: barked adj. [in comb.] the red-barked dogwood. bark3 • n. (also barque) a sailing ship, typically with three masts, in which the foremast and mainmast are square-rigged and the mizzenmast is rigged fore-and-aft.
Bark is the outer protective coating of the trunk and branches of trees and shrubs and includes all the tissues outside of the vascular cambium. A typical bark consists of several layers of different types of tissue. The inner bark, or bast, is living and contains the conductive tissue, called phloem, by which sugars are transported from the leaves in the crown of a tree to the roots, and from storage tissues to other parts of the plant. The outer bark is layered, with the inner layer consisting of the cork cambium, a meristem that produces cork cells to the outside. The cork cells are usually tightly packed and have fatty substances deposited in their thick walls. In contrast to the cork cambium, cork cells are dead and filled with air, making cork lightweight and insulating.
The appearance of a bark depends on the type of cork cells produced by the cork cambium, the relative amount of cambial products, and the amount of secondary conducting tissue (phloem). In some species, such as the cork oak (Quercus suber ), the cork cambium is very active and produces a thick layer of cork, which is extracted and used commercially. Other species, such as birch trees, have a papery bark because the cork cambium alternatively produces several layers of thin-walled cells. These are fragile, and the thicker layers can come off as sheets. In habitats where natural fires occur, such as tropical savannas and the pine and redwood forests of California, trees tend to have a thick, corky bark to insulate them from the heat of fires. In some arid regions many trees have chlorophyll-containing bark to continue the process of photosynthesis when the leaves are absent during long periods of drought. The varied texture and thickness of bark is often a function of the environment in which the tree grows. The variation in the structure of bark often gives a tree its characteristic appearance, for example, the hairy look of the shagbark hickory. A forester can recognize the species of trees by the differences in their bark either externally or by cutting a small slash to examine the inner structure.
Bark is used in many ways and is of considerable economic importance. Many indigenous peoples have made clothes, canoes, houses, drinking vessels, arrow poisons, and medicines from bark. Bark has also provided commercial medicines such as quinine and curare, and is also the major source of tannins for the leather industry and cork for wine bottles. In horticulture, bark is used for mulch. Some of our favorite flavors and spices, such as cinnamon and angostura bitters, come from bark. Bark is much more than the protective skin of trees; it is one of the most useful products of nature.
see also Stems; Tissues; Tree Architecture; Trees.
Ghillean T. Prance
Junikka, L. Survey of English Macroscopic Bark Terminology. Leiden, The Netherlands: Hortus Botanicus, 1994.
Prance, G. T., and A. E. Prance. Bark: The Formation, Characteristics, and Use of Bark Around the World. Portland, OR: Timber Press, 1993.
bark (in botany)
bark, outer covering of the stem of woody plants, composed of waterproof cork cells protecting a layer of food-conducting tissue—the phloem or inner bark (also called bast). As the woody stem increases in size (see cambium), the outer bark of inelastic dead cork cells gives way in patterns characteristic of the species: it may split to form grooves; shred, as in the cedar; or peel off, as in the sycamore or the shagbark hickory. A layer of reproductive cells called the cork cambium produces new cork cells to replace or reinforce the old. The cork of commerce is the carefully harvested outer bark of the cork oak (Quercus suber), a native of S Europe. The phloem (see stem) conducts sap downward from the leaves to be used for storage and to nourish other plant parts. "Girdling" a tree, i.e., cutting through the phloem tubes, results in starvation of the roots and, ultimately, death of the tree; trees are sometimes girdled by animals that eat bark. The fiber cells that strengthen and protect the phloem ducts are a source of such textile fibers as hemp, flax, and jute; various barks supply tannin, cork (see cork oak), dyes, flavorings (e.g., cinnamon), and drugs (e.g., quinine). The outer bark of the paper birch was used by Native Americans to make baskets and canoes.