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Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The word ''xylem'' is derived from the Greek word ξύλον (''xylon''), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant. The basic function of xylem is to transport water, but it also transports some nutrients. == Structure == The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called ''vessels''. Xylem also contains two other cell types: parenchyma and fibers.〔(Xylem ). Encyclopædia Britannica〕 Xylem can be found: * in vascular bundles, present in non-woody plants and non-woody parts of woody plants * in secondary xylem, laid down by a meristem called the vascular cambium in woody plants * as part of a stelar arrangement not divided into bundles, as in many ferns. In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain ''primary xylem'' only. The branching pattern exhibited by xylem follows Murray's law. 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「Xylem」の詳細全文を読む スポンサード リンク
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