A carbohydrate-digesting enzyme (a carbohydrase) that hydrolyses cellulose to sugars, including cellobiose (a disaccharide consisting of two β‎-(1,4) linked molecules of glucose) and glucose. Cellulase breaks the β‎-glycosidic links that join the constituent sugar units of cellulose. It plays an essential part in abscission in plants, while microbial cellulases enable the digestion of plant material by herbivores. See also ruminantia.