Lignin: The Natural Glue That Holds Wood Together

The substance that binds wood fibers (cellulose) into a rigid, strong material is lignin.

• Chemical Nature: A complex, cross-linked organic polymer (phenolic) deposited in plant cell walls.
• Function: Provides compressive strength, rigidity, and waterproofing to vascular tissue (xylem), enabling trees to grow tall and transport water.
• Color: Lignin is responsible for wood's characteristic brown color; it darkens on exposure to light and air.
• Industrial Relevance: In papermaking, lignin is largely removed (pulping) to yield white cellulose fibers. It's a byproduct (black liquor) burned for energy or used in adhesives, dispersants, and bio-based materials.

Without lignin, plants would be herbaceous; with it, they become woody, forming the forests that shape terrestrial ecosystems.