It consists of the protoxylem ( formed first ) and metaxylem 包括原生木质部（最早形成的）和后生木质部。
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Protoxylem the primary xylem elements that are formed from the procambium first 原生木质部：初生木质部的成分，最早由原形成层形成。
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Annular thickening rings of thickening laid down on the inner wall of protoxylem vessels and tracheids 环状加厚：原生木质部导管和管胞的内层环状?厚。
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In seed plants the protoxylem occurs at the innermost edge of the vascular bundles in stems , but external to the later - formed xylem in roots 在种子植物中，原生木质部发生在茎的维管束的最内方，但在根中，位于后生木质部的外方。
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4 . the studies focused on the cnz of dianthus barbatus and saponaria offlcinalis seedlings applied two different vascular cylinder types , even through they both were " " - shape exarch and diarch haplostele , their patterns of protoxylem and m 此外，在商陆科的美洲商陆的子叶节区下部发现了一种具有双大括号状( “ { } ” )的维管柱类型。
