cellulose, chief constituent of the cell walls of plants. Chemically, it is a carbohydrate that is a high molecular weight polysaccharide. Raw cotton is composed of 91% pure cellulose; other important natural sources are flax, hemp, jute, straw, and wood. Cellulose has been used for the manufacture of paper since the 2d cent. Insoluble in water and other ordinary solvents, it exhibits marked properties of absorption. Because cellulose contains a large number of hydroxyl groups, it reacts with acids to form esters and with alcohols to form ethers. Cellulose derivatives include guncotton, fully nitrated cellulose, used for explosives; celluloid (the first plastic), the product of cellulose nitrates treated with camphor; collodion, a thickening agent; and cellulose acetate, used for plastics, lacquers, and fibers such as rayon.