Botanically, there are three principal groups of cotton that are of commercial importance. The first, (Gossypium hirsutum), is native to Mexico and Central America and has been developed for extensive use in the United States, accounting for more than 95 percent of U.S. production. This group is known in the United States as American Upland cotton, and varies in length from about 7/8 to 1 5/16 inches. A second botanical group, (G. barbadense), which makes up the balance of U.S. production, is of early South American origin. Varying in length from 1 1/4 to 1 9/16 inches, it is known in the United States as American Pima, but is also commonly referred to as Extra Long Staple (ELS) cotton. A third group, (G. herbaceum and G. arboreum), embraces cottons of shorter length, 1/2 to 1 inch, that are native to India and Eastern Asia. None from this group is grown in the United States.
In a single pound of cotton, there may be 100 million or more individual fibers. Each fiber is an outgrowth of a single cell that develops in the surface layer of the cotton seed. During the early stages of its growth, the fiber elongates to its full length as a thin–walled tube. As it matures, the fiber wall is thickened by deposits of cellulose inside the tube, leaving a hollow area in the center. When the growth period ends and the living material dies, the fiber collapses and twists about its own axis.
NOTE: The text is from an official USDA publication Agricultural Handbook 566 that was last updated in 2001. Several changes have occurred since that time including closure of two classing offices and the leaf grade is now determined by HVI® line instead of human classer. However, while this publication is not completely up to date it is still the best source of information to overall explain the classification of cotton. USDA-AMS is working to provide an updated version of this information which will be posted here when available.
Dissemination of Data
Equipment Performance Specifications
Selection of Cotton for Calibration Usage
Establishing Values for Calibration Cotton
Calibration of Instruments
Color Chart for American Upland Cotton
Color Chart for American Pima Cotton