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.

Source: Webster's Revised Unabridged Dictionary (1913)