SEARCH Articles Figures Tables A schematic representation of the process of deposition of cell wall components and the heterogeneous formation of protolignin macromolecule. ML, middle lamella CC, cell corner P, primary wall CML, compound middle lamella S1 S2, and S3, outer, middle, and inner layer of secondary wall H, G, and S,p-hydroxy-, guaiacyl-, and syringylpropane units. [Publishers Imprint]