Lignin is a complex organic polymer that forms the chief constituent of wood and is present in all vascular plants. It is produced by the phenylalanine/tyrosine metabolic pathway in plant cells. Lignin is particularly important in the formation of cell walls, especially in supporting tissues of most plants. It adds compressive strength and stiffness to the plant cell wall and is believed to have played a role in the evolution of terrestrial plants by helping them withstand the compressive forces of gravity. Lignin also waterproofs the cell wall, facilitating the upward transport of water in xylem tissues. Finally, lignin has antifungal properties and is often rapidly deposited in response to injury by fungi, protecting the plant body from the diffusion of fungal enzymes and toxins. Lignin is removed from wood pulp in the manufacture of paper, and it has a number of industrial uses as a binder for particleboard and similar laminated or composite wood products, as a soil conditioner, and as a fuel.