root·stock /ˈrutˌstɑk, ˈrʊt-/
 根莖,根源,起源
 Root·stock n. Bot. A perennial underground stem, producing leafly stems or flower stems from year to year; a rhizome.
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 rootstock
      n 1: a horizontal plant stem with shoots above and roots below
           serving as a reproductive structure [syn: rhizome, rootstalk]
      2: root or part of a root used for plant propagation;
         especially that part of a grafted plant that supplies the
         roots