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

Bark is a protective, outer tissue that occurs on older stems and roots of woody coniferous and angiosperm plants. Bark is generally considered to occur on the outside of the tissue known as wood, or the water-conducting xylem tissues of woody plants. The inner cells of bark, known as phloem, grow by the division of outer cells in a generative layer called the vascular cambium, located between the bark and wood (inner cells of this cambium produce xylem cells). The outer cells of bark, known as cork, grow through cellular division in the cork cambium, present outside of the phloem. The outer part of the bark is a layer of dead cells, which can be as thick as several inches or more, and serves to

protect the internal living tissues from injury, heat, and desiccation.

The generally tough outer surface of bark protects the tree from physical damage. Underneath this surface layer, bark is a conduit for nutrients and waste.

The macroscopic structure of bark varies greatly among species of woody plants. For example, the bark of American beech (Fagus grandifolia ) is distinctively grey and smooth. In contrast, many species have a deeply fissured, rough bark, as in the cases of sugar maple (Acer saccharum ) and spruces (Picea spp.). The color and pattern of fissuring and scaling of bark can often be used to identify species of trees and shrubs.

Some types of bark have specific uses to humans. The young, brownish, inner bark of young shoots of the cinnamon tree (Cinnamomum zeylanicum ), native to Sri Lanka but now widely cultivated in the humid tropics, is collected, dried, and used whole or powdered as an aromatic flavoring of drinks and stews. Some barks have medicinal properties, such as that of the cinchona tree (Cinchona calisaya ), from which quinine has long been extracted and used to reduce the fevers associated with malaria. More recently, taxol, an anti-cancer chemical, has been identified in the bark of the Pacific yew (Taxus brevifolia ). Taxol is now used to treat ovarian cancer, and is also effective against some other cancers.

The bark of some species of trees contains large concentrations of a group of organic chemicals known as tannins, which can be reacted with animal skins to create a tough, flexible, and very useful material known as leather. Tannins will also react with certain metal salts to form dark pigments, which are used in printing and dyeing. Major sources of tannins in North America are the barks of hemlock trees (especially Tsuga canadensis and T. heterophylla ), and oaks, especially chestnut oak (Quercus prinus ) and tanbark oak (Lithocarpus densiflora ). Eurasian oaks and hemlocks are also used, as are several tropical species, such as red mangrove (e.g., Rhizophora mangle ) and wattle (e.g., Acacia decurrens ). The thick, outer bark of the cork oak (Quercus suber ) of Europe is collected and used to manufacture bottle corks, flotation devices, insulation, and composite materials such as parquet flooring. The bark of some conifers is used as a mulch in landscaping, for example, that of Douglas fir (Pseudotsuga menziesii ) and redwood (Sequoia sempervirens ).

Bill Freedman

Bark

Bark is a protective, outer tissue that occurs on older stems and roots of woody coniferous and angiosperm plants. Bark is generally considered to occur on the outside of the tissue known as wood , or the water-conducting xylem tissues of woody plants. The inner cells of bark, known as phloem, grow by the division of outer cells in a generative layer called the vascular cambium, located between the bark and wood (inner cells of this cambium produce xylem cells). The outer cells of bark, known as cork , grow through cellular division in the cork cambium, present outside of the phloem. The outer part of the bark is a layer of dead cells, which can be as thick as several inches or more, and serves to protect the internal living tissues from injury, heat , and desiccation.

The macroscopic structure of bark varies greatly among species of woody plants. For example, the bark of American beech (Fagus grandifolia) is distinctively grey and smooth. In contrast, many species have a deeply fissured, rough bark, as in the cases of sugar maple (Acer saccharum) and spruces (Picea spp.). The color and pattern of fissuring and scaling of bark can often be used to identify species of trees and shrubs.

Some types of bark have specific uses to humans. The young, brownish, inner bark of young shoots of the cinnamon tree (Cinnamomum zeylanicum), native to Sri Lanka but now widely cultivated in the humid tropics, is collected, dried, and used whole or powdered as an aromatic flavoring of drinks and stews. Some barks have medicinal properties, such as that of the cinchona tree (Cinchona calisaya), from which quinine has long been extracted and used to reduce the fevers associated with malaria . More recently, taxol, an anti-cancer chemical, has been identified in the bark of the Pacific yew (Taxus brevifolia). Taxol is now used to treat ovarian cancer , and is also effective against some other cancers.

The bark of some species of trees contains large concentrations of a group of organic chemicals known as tannins, which can be reacted with animal skins to create a tough, flexible, and very useful material known as leather. Tannins will also react with certain metal salts to form dark pigments, which are used in printing and dyeing. Major sources of tannins in North America are the barks of hemlock trees (especially Tsuga canadensis and T. heterophylla), and oaks , especially chestnut oak (Quercus prinus) and tanbark oak (Lithocarpus densiflora). Eurasian oaks and hemlocks are also used, as are several tropical species, such as red mangrove (e.g., Rhizophora mangle) and wattle (e.g., Acacia decurrens). The thick, outer bark of the cork oak (Quercus suber) of Europe is collected and used to manufacture bottle corks, flotation devices, insulation, and composite materials such as parquet flooring. The bark of some conifers is used as a mulch in landscaping, for example, that of Douglas fir (Pseudotsuga menziesii) and redwood (Sequoia sempervirens).

Bill Freedman

Bark

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

Bibliography

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 The protective layer of mostly dead cells that covers the outside of woody stems and roots. It includes the living and dead tissues external to the xylem, including the phloem and periderm. The term can be used more specifically to describe the periderm together with other tissues isolated by the activity of the cork cambium. In some species, such as birch, there is one persistent cork cambium but in the older stems of certain other species a second cork cambium becomes active beneath the periderm and further periderm layers are formed every few years. The result is a composite tissue called rhytidome, composed of cork, dead cortex, and dead phloem cells.