lignin, a highly polymerized and complex chemical compound especially common in woody plants. The cellulose walls of the wood become impregnated with lignin, a process called lignification, which greatly increases the strength and hardness of the cell and gives the necessary rigidity to the tree. It is essential to woody plants in order that they stand erect.

Complex oxygen-containing organic compound, a mixture of polymers of poorly known structure. After cellulose, it is the most abundant organic material on Earth, making up one-fourth to one-third of the dry weight of wood, where it is concentrated in the cell walls. Removed from wood pulp in the manufacture of paper, it is used as a binder in particleboard and similar products and as a soil conditioner, filler in certain plastics, adhesive ingredient, and raw material for chemicals including dimethyl sulfoxide and vanillin (synthetic vanilla flavouring).

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