Source : Webster's Revised Unabridged Dictionary (1913)

Liber \Li"ber\ (l[imac]"b[~e]r), n. [L. See {Libel}.] (Bot.)
   The inner bark of plants, lying next to the wood. It usually
   contains a large proportion of woody, fibrous cells, and is,
   therefore, the part from which the fiber of the plant is
   obtained, as that of hemp, etc.

   {Liber cells}, elongated woody cells found in the liber.