Why does lignin make xylem tissue strong?

Lignin is a complex organic polymer that contributes to the structural integrity of xylem tissues by adding stiffness and compressive strength to the plant cell walls.1

By reinforcing these cell walls, lignin allows terrestrial plants to withstand the compressive forces of gravity, providing the necessary rigidity for plants to grow upright on land. In addition to its mechanical role, lignin waterproofs the cell walls, which is essential for facilitating the efficient upward transport of water and dissolved minerals through the xylem. This combination of structural support and waterproofing is a critical adaptation that enables vascular plants to maintain their form and transport nutrients over long distances.12