bark science definition

The protective outer covering of the trunk, branches, and roots of trees and other woody plants. Bark includes all tissues outside the vascular cambium. In older trees, bark is usually divided into inner bark, consisting of living phloem, and outer bark, consisting of the periderm (the phelloderm, cork cambium, and cork) and all the tissues outside it. The outer bark is mainly dead tissue that protects the tree from heat, cold, insects, and other dangers. The appearance of bark varies according to the manner in which the periderm forms, as in broken layers or smoother rings. Bark also has lenticels, porous corky areas that allow for the exchange of water vapor and gases with the interior living tissues.