Abstract
In this review article, the physical and chemical characteristics of lignins are discussed and a list of degradative products is given. The formulas proposed by several investigators, as well as their theories concerning lignin formation, are presented. The long postulated role of phenylpropanes in lignin formation is said to be proven. Derivatives of p-hydroxyphenylpropane are required as lignin precursors. These may be transformed by peroxidases or other phenol oxidizing enzymes into polymers with the physical and chemical properties of lignins. Polymerization appears to be rapid in the presence of cells or cell-wall fragments, slow in cell-free systems. There are 60 references.