Plant cell walls are composed of polysaccharides and, in the case of higher plants, lignin. The economic significance of plant cell walls arises largely from three types of uses: (1) use of whole tissues or slightly processed tissues whose constituents are primarily cell-wall components (wood and other plant fibres); (2) use of delignified and extracted tissues (pulp); (3) use of extracted, and in some cases chemically modified, water-soluble cell-wall polysaccharides (pectins, seaweed polysaccharides, hemicelluloses). Other substances that can be extracted from plant tissues are generally extraneous to the cell wall.