Lignin (sometimes "lignen") is a complex chemical compoun most commonly derived from wood and an integral part of the cell walls of plants. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood. It is the most abundant organic polymer on Earth after cellulose, employing 30% of non-fossil organic carbon and constituting from a quarter to a third of the dry mass of wood. The compound has several unusual properties as a biopolymer, not least its heterogeneity in lacking a defined primary structure.