A MICROCHEMICAL STUDY OF HEMICELLULOSES OF ENDOSPERMS AND COTYLEDONS

Abstract

Hemicelluloses occur in several plant tissues, particularly in wood, seed coats, and endosperms, and in fungi. Very little is known about their exact character as they occur in cell walls. Their presence is determined macrochemically by the products of their hydrolysis with weak acids. A review of the literature shows a considerable variation in properties of hemicelluloses obtained from different sources. Consequently definitions for the hemicelluloses as a distinct class of compounds do not entirely agree. Differences of opinion result from the number of hemicelluloses studied and from the methods of study used. The macrochemical methods consist of hydrolyzing the tissues with dilute acids or, more commonly, of extracting tissue with one to five percent alkali and testing the alcoholic precipitate from the extract. This precipitate is called hemicellulose and its properties are considered to be identical with those of hemicellulose regardless of the fact that the tissue from which the extract was obtained may contain non-hemicellulose compounds such as pectic compounds, soluble in dilute alkali and capable of precipitation by alcohol. The main difficulty, however, of arriving at an acceptable definition of the hemicelluloses as a group lies in the heterogeneity of the various hemicellulose substances. An account of the opinions of the more prominent workers will demonstrate the diversity of the hemicelluloses as well as the scarcity of knowledge concerning them. Schulze and Tollens (33) worked with thickened walls both microchemically and macrochemically. They suggested that the term hemicellulose be given to cell wall substances which differ from cellulose in their non-resistance to dilute acids or alkalies but are like cellulose in that they I Papers from the Department of Botany, the Ohio State University, No. 247. [The Journal for January (I7: I-II5) was issued Feb. IO, I930.]