1. The outer surfaces of trees and other woody
plants. The inner side of the bark of certain
trees, e.g., birch, has been used in the past as a
surface for writing. Bark books were rather common
in Central Asia and the Far East until
comparatively recent times. Bark is vulnerable to
dampness and curling in climates of high relative
humidity and to cracking in dry areas. 2. See: VEGETABLE TANNINS .