A linear polymer of (1→4)-linked β-D-glucopy­ranosyl units, and the most abundant of all naturally occurring substances. Cellulose constitutes approximately a third of all vegetable matter and thus it exists in far greater quantity than any other polysaccharide. It occurs as a principal structural component of the cell walls of mosses and seaweeds (25–30%), annual plants (25–35%), and trees (40–50%); cotton fiber contains 98% cellulose along with 1% protein, 0.65% pectic substance, and 0.15% mineral matter. Cellulose also is produced by some microorganisms, in a few cases reaching amounts of 20–30%.