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How does lignin make plant cell walls stronger and more rigid?

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Cutaway illustration of a plant cell showing labeled internal structures including the nucleus, nucleolus, chloroplast, mitochondrion, vacuole, endoplasmic reticulum, ribosomes, Golgi apparatus, cell wall, and other key organelles. — Cell wall Cutaway drawing of a plant cell, showing the cell wall and internal organelles.

Lignin strengthens and stiffens plant cell walls primarily by forming tight, three-dimensional networks through the cross-linking of its polymer components.12

As a complex phenolic compound deposited largely within the secondary cell walls, lignin acts as a structural reinforcement that provides the necessary rigidity for terrestrial vascular plants to withstand the compressive forces of gravity. The diversity and density of these cross-links create a robust matrix that not only enhances mechanical strength but also serves as a formidable barrier against the penetration of fungi and other microbes. Additionally, lignin contributes to the plant's structural integrity by waterproofing the cell wall, which facilitates the efficient upward transport of water through xylem tissues.312