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Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner bark, which in older stems is living tissue, includes the innermost area of the periderm. The outer bark in older stems includes the dead tissue on the surface of the stems, along with parts of the innermost periderm and all the tissues on the outer side of the periderm. The outer bark on trees which lies external to the last formed periderm is also called the rhytidome. Products used by people that are derived from bark include: bark shingle siding and wall coverings,〔http://barkhouse.com/〕 spices and other flavorings, tanbark for tannin, resin, latex, medicines, poisons, various hallucinogenic chemicals and cork. Bark has been used to make cloth, canoes, and ropes and used as a surface for paintings and map making.〔Taylor, Luke. 1996. ''Seeing the Inside: Bark Painting in Western Arnhem Land. Oxford Studies in Social and Cultural Anthropology''. Oxford: Clarendon Press.〕 A number of plants are also grown for their attractive or interesting bark colorations and surface textures or their bark is used as landscape mulch.〔Sandved, Kjell Bloch, Ghillean T. Prance, and Anne E. Prance. 1993. ''Bark: the Formation, Characteristics, and Uses of Bark around the World''. Portland, Or: Timber Press.〕〔Vaucher, Hugues, and James E. Eckenwalder. 2003. ''Tree Bark: a Color Guide''. Portland: Timber〕 ==Botanic description== What is commonly called bark includes a number of different tissues. Cork is an external, secondary tissue that is impermeable to water and gases, and is also called the phellem. The cork is produced by the cork cambium which is a layer of meristematically active cells which serve as a lateral meristem for the periderm. The cork cambium, which is also called the phellogen, is normally only one cell layer thick and it divides periclinally to the outside producing cork. The phelloderm, which is not always present in all barks, is a layer of cells formed by and interior to the cork cambium. Together, the phellem (cork), phellogen (cork cambium) and phelloderm constitute the periderm.〔Dickison, WC. 2000. Integrative Plant Anatomy, Academic Press, San Diego, 186-195.〕 Cork cell walls contain suberin, a waxy substance which protects the stem against water loss, the invasion of insects into the stem, and prevents infections by bacteria and fungal spores. The cambium tissues, i.e., the cork cambium and the vascular cambium, are the only parts of a woody stem where cell division occurs; undifferentiated cells in the vascular cambium divide rapidly to produce secondary xylem to the inside and secondary phloem to the outside. Phloem is a nutrient-conducting tissue composed of sieve tubes or sieve cells mixed with parenchyma and fibers. The Cortex is the primary tissue of stems and roots. In stems the cortex is between the epidermis layer and the phloem, in roots the inner layer is not phloem but the pericycle. From the outside to the inside of a mature woody stem, the layers include: *(1) Cork (Phellem) *(2) Cork cambium (Phellogen) *(3) Phelloderm *(4) Cortex *(5) Phloem *(6) Vascular cambium *(7) Xylem. The bark includes (1) through (5), and is composed of periderm and phloem and the cells that produce these tissues. The periderms includes (1), (2) and (3). In young stems, which lack what is commonly called bark, the tissues are from the outside to the inside: epidermis, periderm, cortex, primary phloem, secondary phloem, vascular cambium, secondary xylem, and primary xylem. As the stem ages and grows, changes occur that transform the surface of the stem into the bark. The epidermis is a layer of cells that cover the plant body, including the stems, leaves, flowers and fruits, that protects the plant from the outside world. In old stems the epidermal layer, cortex, and primary phloem become separated from the inner tissues by thicker formations of cork. Due to the thickening cork layer these cells die because they do not receive water and nutrients. This dead layer is the rough corky bark that forms around tree trunks and other stems. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bark」の詳細全文を読む スポンサード リンク
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