the outer layer of a tree stem outside the vascular cambium derived from cell division of the phellogen —note 1. the anatomical structure of bark is more complex than that of wood and has higher lignin and lower cellulose content —note 2. in older trees, bark is generally divisible into inner bark and outer bark and, in any growing season, into early bark consisting typically of sieve tubes with companion cells or sieve cells (soft bark), and late bark consisting typically of parenchyma and a few small sieve cells (hard bark) —see bark thickness, peridermThis definition last updated 07/16/2008