Alkali solubility of hemicelluloses in relation to delignification

The polysaccharide composition of bark from Pinus radiata, Salix fragilis, and Populus euramericana has been determined. All the barks contained lower levels of cellulose and hemicellulose than the corresponding woods; cellulose: hemicellulose ratios were also lower in the barks. Alkali extracted all of the hemicellulose-A but only half of the hemicellulose-B from P. radiata bark without prior delignification. Similar alkaline extraction removed almost all of the hemicellulose (A + B) from ryegrass leaves without delignification. With the other samples tested only a part of the hemicellulose A and B is extracted without delignification. It is suggested that the polysaccharide so extracted represents wall hemicellulose which is not linked to lignin or other wall constituents by alkali-stable links.