Lignin is the fiber in our food, the thing that makes vegetables crunchy and firm. It is a polymer found extensively in the cell walls of all woody plants, Lignin, one of the most abundant natural polymers, constitutes one-fourth to one-third of the total dry weight of trees. It combines with hemicellulose materials to help bind the cells together and direct water flow. Lignin is formed by removal of water from sugars to create aromatic structures. These reactions are not reversible. Lignin resists attack by most microorganisms, and anaerobic processes tend not to attack the aromatic rings at all. Aerobic breakdown of lignin is slow and may take many days. Lignin is nature's cement along with hemicellulose to exploit the strength of cellulose while conferring flexibility.