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 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.

bark The outer skin of a tree trunk, outside the secondary, vascular, cambium. It is composed of phloem tissues, which occur as living inner and dead outer zones. The outer zone is penetrated by the cork layers (or periderms) formed from cork cambia (or phelloderms), and is sometimes called the rhytidome. The bark surface is variously sculptured, e.g. smooth, scaly, or fissured; and these surface features are partly determined by the arrangement of the phloem tissues and periderms.

bark Outer protective covering of a woody plant stem. It is made up of several layers. The cork layer, waxy and waterproof, is the thickest and hardens into the tough, fissured outer covering. Lenticels (pores) in the bark allow gas exchange between the stem and the atmosphere. See also cambium