WOOD is the material that makes up most of the trunk of a tree. It is composed of cellulose fibers joined with lignin.

CELLULOSE is a structural polysaccharide formed by glucose that is part of the wall of plant cells. Its functions are to serve as a skeleton for the plant or tree and to give it plant protection. It is very resistant to chemical agents, insoluble in almost all solvents and also unalterable in dry air.

LIGNIN is a class of complex organic polymers that form important structural materials in plant support tissues. Lignins are particularly important in the formation of cell walls, especially in wood and bark, as they lend rigidity and do not rot easily. The word lignin comes from the Latin term lignum, which means "firewood, wood"; thus, plants that contain a large amount of lignin are called woody.