Investigations of the cell-wall substances of plants, with special reference to the chemical changes taking place during lignification

Abstract

The substances which accompany cellulose in the cell-walls of plants may be divided into 3 classes: lignins, hemicelluloses, and pectins. The products belonging to the 2 latter classes are formed by conjugation of glycuronic and galacturonic acids with sugars. These acids are, using Ling''s suggestion, designated uronic acids, and the hemicelluloses and pectins seem to belong to a distinct chemical group, for which the name polyuronides is suggested. The pectins contain a much larger uronic acid content than do the hemicelluloses, while the uronic acids are absent from the lignins. Lignified tissues contain lignins and hemicelluloses in large amounts, with only traces (if any) of pectins. Non-hgnified tissues contain relatively large amounts of pectins and small amounts of hemicelluloses. Pectins undergo decarboxylation on treatment with weak alkaline solutions, even at room temp. On this treatment they yield, among other products, hemicelluloses, which still contain uronic groups, but which resist decarboxylation on treatment with alkalis, and which resemble in all respects the hemicelluloses isolated directly from timbers. These results indicate that decarboxylation takes place when plant tissues lignify. No direct connection has yet been traced between the pectins and lignins.