xy·lem /ˈzaɪləm, ˌlɛm/
  木質部
  Xy·lem n.  Bot. That portion of a fibrovascular bundle which has developed, or will develop, into wood cells; -- distinguished from phloem.
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  xylem
       n : the woody part of plants: the supporting and
           water-conducting tissue, consisting primarily of
           tracheids and vessels