1. ‘water extractable’ (pectic), ‘alkali-extractable’ (hemicellulosic) and ‘residual’ .(cellulosic) substances (Lewis, 1984). This terminology is somewhat mislead¬ing because it implies that all hemicelluloses are chemically related to cellulose. Further problems arise because the molecular composition of the hemicellu¬loses and pectic substances obtained from the tissue of any one species of plant depends on the methods used to isolate the material (Wilkie, 1985).