Cotton: The Fiber of Life

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Coastal Peru

Since time immemorial, plant fibers have been used to make paper, rope, cloth, baskets, roof thatch, mats, and other items. Fibers produced by the cotton plant are classified as textile fibers because they are used to weave cloth (as opposed to cordage fibers, for example, which are used to make rope). Cotton fiber is one of the most economically important nonfood plant commodities on the market, and cottonseed oil, another product of the cotton plant, is the second most important seed-oil crop.

Cotton, Gossypium sp., is in the Malvaceae, a family composed of 80 genera and 1,000 species, many of which are grown as ornamentals. Genera of Malvaceae are found everywhere except in very cold regions, and several of these genera are economically important. For example, the young fruits of Hibiscus esculentus, a mainly tropical genus, are the popular vegetable known as okra. China jute, Abutilon avicennae, yields tough fibers that are used to make many products.

Cotton plants in the field. 
(From Stern, Introductory Plant Biology, 8th ed., © 2000, McGraw-Hill Companies. Reprinted by permission.)

Cotton plants in the field

Depending on the species of Gossypium, the flower color ranges from white to purple.Several species are grown commercially. The flower petals of Gossypium are a source of yellow dye in India, while the endosperm is oily and proteinaceous, yielding a valuable seed oil and a high-protein cattle feed and flour. G. hirsutum, also known as upland cotton, accounts for 90% of the world's cotton crop. G. barbadense, Egyptian cotton, is believed to have been semidomesticated in coastal Peru by 2500 B.C. and was brought to the United States about 1900. Egyptian cotton has a longer fiber than any other cotton and can therefore be woven into much finer fabrics, accounting for the additional cost of products manufactured from G. barbadense.

Although it is almost impossible to determine the origins of the many species of Gossypium, archaeological remains indicate that indigenous people of coastal Peru were harvesting wild populations 10,000 years ago. Fiber and boll fragments were found in the Tehuacan Valley of Mexico dating back 7,000 years, and cotton has apparently been cultivated in Indi
Cross section of fibers. Note the thick walls of each individual cell (in pink).
(From  Stern, Introductory Plant Biology, 8th ed., © 2000, McGraw-Hill Companies. Reprinted by permission.)

Cross section of fibers

a for at least 5,000 years. Cotton arrived in Florida about 1556, making it one of the earliest crops grown by European settlers in the United States.

Technically, a plant fiber is a type of sclerenchyma cell characterized by very thick and toughsecondary walls impregnated with lignin. Commercially, however, the term "fiber" more commonly refers to a mass of elongated plant material that is a collection of either fiber cells or entire vascular bundles. Cellulose, the main structural component of cell walls, is a polysaccharide made up o f anywhere from 100 to 15,000 glucose molecules attached to one another.  In the case of cotton, this creates a strong material that is absorbent, versatile, dyes well, and withstands many washes.   As additional benefits, each cotton plant produces a large amount of fiber, and cotton costs less to process than other plant fibers.

Cotton bolls, as the fruit capsules are known commercially, mature 50-80 days after fertilization. At maturity, they split open to reveal masses of long, white seed hairs (lint), each of which is attached to a black seed. This modification enables the seed to be dispersed by the wind.

Until 1793, when Eli Whitney invented the cotton gin, processing cotton was labor-intensive and time-consuming. 

The gin  removes the seeds so that the lint can be packed into tight bales. The quality and price of cotton are determined based on several factors: length of individual fibers, or staple; grade (color, brightness, and amount of foreign material contaminating the final product); and character (diameter, strength, uniformity, and smoothness of individual fibers).

The ginning of cotton produces tons of seeds, which were once deemed a waste-disposal problem but are now a valuable by-product. The separated seeds go to oil mills, where they are further delinted of the shorter, fine hairs that adhere to the seed coat after initial ginning.   This shorter lint, sometimes called linters, is used to make paper, furniture padding, and the tips of cotton swabs.  The

Arrangement of fibrils, microfibrils, and cellulose in cell walls
Operation of the cotton gin
Operation of the cotton gin
seed is then cracked, the kernel removed, and the oil extracted. The meal that remains is high in protein. While historically most cotton seed was used as fertilizer, it is believed that ancient Hindus extracted the oil from cotton seeds by pounding and then boiling them, skimming the oil from the surface of the water as it boiled. The oil was used medicinally and as lamp oil. By 1900, the chemist David Wesson had perfected the process of purifying the seed oil, setting the standard and starting the modern vegetable oil industry. The first edible cottonseed oil was marketed under the name Wesson Oil; today it has been joined by soybean, canola, and palm oil varieties. Proctor and Gamble introduced the first American vegetable shortening, Crisco, in 1911.

In the United States, the leading cotton-producing states are Texas, California, Georgia, Mississippi, Arkansas, Louisiana, North Carolina, and Arizona. Other leading producers of cotton include China, India, Pakistan, Brazil, and Turkey. While some of the market for cotton is being taken over by synthetic fibers, the cotton plant is still considered the fiber (and oil) of life.

References, Websites, and Further Reading

Heywood, V.H. 1993. Flowering plants of the world. New York: Oxford University Press.

Levetin, Estelle, and Karen McMahon. 1999. Plants and society, 2d ed. New York: McGraw-Hill Companies, pp. 290-94.

Simpson, B.B., and Molly C. Ogorzaly. 2001. Economic botany: Plants in our world, 3d ed. New York: McGraw-Hill Companies.

"Cotton," Microsoft® Encarta® Online Encyclopedia 2000. © 1997-2000, Microsoft Corporation.
http://encarta.msn.com

Journal of Cotton Science
http://www.jcotsci.org/

National Cotton Council of America
http://www.cotton.org/

Related Reading in Stern, Introductory Plant Biology, 8th Edition

Chapter 1: What is Plant Biology?
Human and Animal Dependence on Plants, pp. 4-7

Chapter 2: The Nature of Life
Carbohydrates, including glucose and cellulose, pp. 22-23
Lipids and Oils, p. 23
Proteins, pp. 24-26

Chapter 3: Cells
The Cell Wall, including lignin, pp. 33-36
The Cytoskeleton, pp. 38-39

Chapter 4: Tissues
Simple Tissues, including sclerenchyma, pp. 53-54 Complex Tissues, including xylem, phloem, and vascular bundles, pp. 54-57

Chapter 6: Stems Origin and Development of Stems, including vessels, fibers, and vascular bundles, pp. 86-88

Chapter 8: Flowers, Fruits, and Seeds
Structure of Flowers, pp. 129-32
Fruits, including capsules, pp. 132-39
Fruit and Seed Dispersal, including wind dispersal, pp. 139-42 Seeds, p.143

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