Trunk (botany)
In botany, the trunk (or bole) is the stem and main wooden axis of a tree, which is an important feature in tree identification, and which often differs markedly from the bottom of the trunk to the top, depending on the species. The trunk is the most important part of the tree for timber production. Occurrence. Trunks occur both in "true" woody plants as well as non-woody plants such as palms and other monocots, though the internal physiology is different in each case. In all plants, trunks thicken over time due to the formation of secondary growth  (or in monocots, pseudo-secondary growth). Trunks can be vulnerable to damage, including sunburn. Vocabulary. Trunks which are cut down for making lumber are generally called logs; if they are cut to a specific length, called bolts. The term "log" is informally used in English to describe any felled trunk not rooted in the ground, whose roots are detached. A stump is the part of a trunk remaining in the ground after the tree has been felled, or the earth-end of an uprooted tree which retains its un-earthed roots. Structure of the trunk. The trunk consists of five  main parts: The outer bark, inner bark (phloem), cambium, sapwood (live xylem), and heartwood (dead xylem). From the outside of the tree working in: