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In biology, a tunica () (plural tunicae) is a layer, coat, sheath, or similar covering. The word came to English from the New Latin of science and medicine. Its literal sense is about the same as that of the word ''tunic'', with which it is cognate. In biology one of its senses used to be the taxonomic name of a genus of plants, but the nomenclature has been revised and those plants are now included in the genus ''Petrorhagia''. In modern biology in general, ''tunica'' occurs as a technical or anatomical term mainly in botany and zoology. It usually refers to membranous structures that line or cover particular organs. In many such contexts ''tunica'' is used interchangeably with ''tunic'' according to preference. An organ or organism that has a tunic(a) may be said to be ''tunicate'', as in a ''tunicate bulb''. This adjective ''tunicate'' is not to be confused with the noun ''tunicate'', which refers to a member of the subphylum ''Tunicata''. ==Botanical and related usages== In botany there are several contexts for the term. *As a general, but not comprehensive, descriptive term in botanical anatomy John Lindley in the 19th century defined tunica as "any loose membranous skin not formed from epidermis".〔Lindley, John. The Treasury of Botany. Pub. William Wood 1872. May be downloaded from: ()〕〔Jackson, Benjamin, Daydon; A Glossary of Botanic Terms with their Derivation and Accent; Published by Gerald Duckworth & Co. London, 4th ed 1928〕 *The apical meristem, in particular in Angiosperms, has an outer layer of cells called the tunica; its role in growth and development differs from that of the inner meristem, or ''corpus''.〔Mishra, S.R. Understanding Plant Anatomy. Publisher: Discovery 2009. ISBN 978-8183564571〕 *Bulbs and corms often have protective outer coverings of dead material. Particularly in fields such as horticulture and taxonomic description, such bulbs and corms are said to be "tunicate" — having tunics. Usually such a tunic is derived from the bases of sacrificial dead leaves, often cataphylls specialised for the purpose and dying in place. Such tunics may be delicate, brittle membranes such as those around the bulbs of onions, but the many variations reflect a wide range of adaptations in various species. Many of the larger Amaryllidaceae in particular, for example ''Boophone'' species, accumulate thick layers of rot-resistant leaf-base material around their bulbs. Again, corms of Iridaceous species, such as some Watsonias and the larger species of Gladiolus, accumulate thick, reticulated, fibrous or woody defences. *More generally than in describing tunics of bulbs etc., any leaf-sheath or protective bract remaining attached to the plant after the leaf has died may be called a tunica or tunic.〔 *The testa or spermoderm of a seed is sometimes called the tunic, especially in older books.〔 *In fungi the peridium may be referred to as the tunica.〔 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「Tunica (biology)」の詳細全文を読む スポンサード リンク
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