lignin

A complex carbohydrate polymer making up about 25% of the wood of trees and also found in the cell walls of schlerenchyma tissues and vessels, fibres, and tracheids at maturity. It increases the strength of such tissues making them more resistant to compression and tension. Lignin is formed by condensation of the phenolic compound coniferyl alcohol. Its distribution in tissues can be shown by staining with acidified phloroglucin, which turns lignin red.