Each 24 hours a layer of cellulose is deposited in the form of a growth ring on the inside of the fiber around the cell lumen. This process continues until the fiber is mature or until adverse environmental conditions stop the growth processes in the plant. Because environment does play a role in this development, the number of growth rings in mature fibers of bolls set at different periods of the season can vary widely. Bolls maturing early may have fewer growth rings (20-25) as compared to others (30-40 rings). Also, the walls of early maturing fibers frequently are thicker than those of later maturing fibers, resulting in higher micronaire readings.