The substance which constitutes the essential part of
   the solid framework of plants, of ordinary wood, linen, paper, etc. It
   is also found to a slight extent in certain animals, as the tunicates.
   It is a carbohydrate, (C6H10O5)n, isomeric with starch, and is
   convertible into starches and sugars by the action of heat and acids.
   When pure, it is a white amorphous mass. See Starch, Granulose, Lignin.