Araliaceae, the ginseng family of flowering plants, in the order Apiales, comprising approximately 700 species centred in Southeast Asia and tropical America. Most members are shrubs or trees, though there are a number of climbers and a few herbs. The family has large, usually alternate, compound leaves, five-parted flowers arranged in compound umbels (flat-topped clusters), and a berry or (rarely) a drupe (a one-seeded fruit). Several members of the family are economically important. Ivies (Hedera species) are grown as ornamental plants and houseplants. The rice-paper plant (Tetrapanax papyriferum) is the source of rice paper, and the wood of several species, especially that of Dendropanax arboreum and several members of the genus Didymopanax, provides timber.
Wild sarsaparilla (Aralia nudicaulis) has an aromatic root that is used as a substitute for sarsaparilla. Ginseng root, from Panax ginseng, has long been used by the Chinese in the treatment of various diseases; its American relative, Panax quinquefolium (seephotograph), is used in the United States as a stimulant. Hari-giri, or castor aralia (Acanthopanax ricinifolius), is used in Japan in building and in furniture making.
With the exception of synthetic polymers, most economically important products, such as paper, cordage (cords and rope) and textiles, are derived from plant fibers. Fibers are elongate cells with tapering ends and very thick, heavily lignified cell walls. Fiber cells are dead at maturity and function as support tissue in plant stems and roots. The lumen or cavity inside mature, dead fiber cells is very small when viewed in cross section. Fibers are one of the components of sclerenchyma tissue, along with shorter, thick-walled sclereids (stone cells) which produce the hard tissue of peach pits and the gritty texture in pears. Fibers are also associated with the xylem and phloem tissue of monocot and dicot stems and roots, but generally not in the wood of gymnosperms. In fact, the primary reason why gymnosperm woods are generally softer and lighter than angiosperm woods is the presence in angiosperm wood of dense clusters of heavily-lignified, thick-walled fiber cells. The densely-packed fiber cells greatly increase the hardness and density of angiosperm woods.
Longitudinal section and cross section of a fiber cell.
A Word About Dietary Fiber
Dietary fiber comes from the cell walls of edible plant tissue and in the seeds and gummy sap of certain plants. It is not from bast fibers and tracheids, unless you enjoy eating wood pulp and rope. Plant gums are complex polysaccharides composed of many sugar subunits linked together. They are soluble in water unlike plant resins, such as pine pitch and incense. Plant gums are commonly used as thickening agents and emulsifiers, such as guar gum and gum tragacanth. Gum tragacanth is considered one of the world's best natural plant gums. It come from the sap of several species of spiny, shrubby, Middle Eastern locoweeds of the genus Astragalus. It was largely imported from the Zagros Mountains of Iran, when the United States was on better diplomatic terms with that nation. Locust bean gum, a thickening agent in ice creams and salad dressings, comes from the ground seeds of the carob tree (Ceratonia siliqua). Another valuable plant gum is gum arabic, obtained from the spiny, shrubby Acacia senegal of northeastern Africa. In addition to its use in foods, hand lotions and soaps, it is used in fine water colors, inks and confections. It also produces the water-soluble adhesive on postage stamps and the "lace curtain" on the sides of your beer glass. Plant gums also provide the soluble fiber in a healthy diet by absorbing water and adding bulk to the large intestine. Several dietary supplements contain the powdered husks of psyllium seeds from plantain (Plantago ovata), a herbaceous plant in the plantain family (Plantaginaceae). Insoluble fiber comes from the indigestible cellulose cell walls of fruits and vegetables. This includes several types of plant tissue, including parenchyma, sclerenchyma and collenchyma. Collenchyma tissue produces the stands in the leaf stalks of celery (Apium graveolens) that often get stuck in your incisors while eating. Both types of fiber are beneficial in maintaining a healthy colon, particularly in older adults with diverticulosis.
Fibers are also the basic component of wood products, such as paper. One of the earliest records for making sheets of paper dates back at least 5500 years ago to the ancient Egyptians who pressed together thin strips of papyrus stems (Cyperus papyrus) to write on. Egyptian papyrus belongs to the sedge family (Cyperaceae). The inner pith of the stems was cut into strips after removing the outer epidermal layer. The strips were then laid side-by-side and over one another at right angles to form two overlapping layers, one vertical and one horizontal. This "sheet" was pounded to release a glucose-rich sap which served as a bonding agent. The sheets were hammered to make them more compact and rubbed with a stone or bone to produce a smooth surface. This process is similar to bark paper discussed below. To make a scroll, several of these flat sheets were pressed and bonded together.
|Transparent view of papyrus paper showing the overlapping stems of Cyperus papyrus which have been pressed together. This is one of the earliest types of paper made by people.|
Any discussion of natural paperlike products made from wood pulp or fiber cells should include paper wasps of the yellow jacket family (Vespidae). Some of the earliest paper makers on earth were undoubtedly wasps of the genera Polistes and Vespula. The nest of a paper wasp (Polistes fuscatus) is formed by mixing saliva with fibers rasped from dead wood until a pulp similar to papier-mâché is formed. Yellow jackets (Vespula) also build a nest made of this papier-mâché material. Some species of Vespula are also referred to as hornets. The umbrella-shaped nests of paper wasps are attached by a short stalk to the underside of overhanging surfaces such as the eaves of a house or under bridges. The nests contain a single layer of six-sided chambers or cells that fit neatly together like the cells of a honeycomb. Chambers in the nest contain wasp larvae which are fed caterpillars collected by adult female workers. These wasps are easily provoked and can sting forcibly and repeatedly, as this author can testify. This is especially true of yellow jacket nests. If you find small nests made of a mudlike material on the eaves of your house, they probably are from the mud dauber wasp (Sceliphron caementarium) of the family Sphecidae.
|Close-up view of an adult paper wasp (Polistes fuscatus) and her nest. The rounded, wheel-shaped nest is attached by a short stalk to the underside of overhanging surfaces such as the eaves of a house. The nest contains a single layer of chambers or cells which house the developing larvae. Note the adult female worker at the top of the right nest. Adult wasps gather caterpillars, which they skin and chew before feeding them to the grublike larvae developing in the chambers. Since they kill caterpillars that feed on plants, paper wasps are considered beneficial to gardeners. Paper wasps are closely related to yellow jackets (Vespula). They are distinguished from yellow jackets by their narrowed (threadlike) waste and nearly solid yellow abdomen. Both species of wasps can sting viciously, but yellow jackets are probably more easily provoked.|
Rice paper, another ancient paper from the Orient, was made originally from the pith of the rice paper plant (Tetrapanax papyriferus), a member of the aralia family (Araliaceae). This species is listed in some references (such as your textbook) as Fatsia papyrifera. It is not made from the rice plant (Oryza sativa). Rice paper is utilized to this day as a medium for painting and in the manufacture of imitation flowers; however, today's paper labeled as "rice paper" is made from a meshwork of pressed fibers from the pulp of bamboo, paper mulberry (Broussonetia papyrifera) or another species. It is commonly used in calligraphy and ink paintings. In the case of authentic rice paper, stems of Tetrapanax papyriferus are soaked in water to loosen the pith which is removed and dried. Thin sheets are shaved (peeled) from the pith cylinder, like a veneer is shaved off a tree trunk. The sheets are then cut into various sizes and pressed lightly to flatten. Sheets of pith paper were once used in watercolor and gouache paintings, but have largely been replaced by other types of paper made from pulp. Contrary to some botany texts, the pith was not pounded to make authentic rice paper from Tetrapanax papyriferus.
|Left: Rice paper plant (Tetrapanax papyriferus), a stoloniferous evergreen shrub or small tree native to southern China and Taiwan. The dried pith of the stem is the source of rice paper in China. Right: A painting on modern "rice paper" by the artist Kiyoko Messenger. Although it is called "rice paper" this paper is not from the pith of Tetrapanax papyriferus. Under high magnification, most so-called "rice papers" are composed of a meshwork of pressed fibers from the pulp of another species, such as paper mulberry (Broussonetia papyrifera)|
More About Rice Paper
The following information is summarized from Prue McKay (personal communication, 2001): Tetrapanax pith paper is no longer being made for use by artists. It is still apparently in production in Taiwan for making artificial flowers, and is primarily shipped to South America for this purpose. The art of painting on pith paper essentially died out in the 1920s, although some pith paintings were made in Japan during the Second World War period. Most pith paintings were made solely for export from Taiwan and the southern provinces of China from 1800 to 1920.
Most papers labeled as "rice paper" in China and Japan are made from bast fibers of various trees including the paper mulberry (Broussonetia papyrifera). High quality, Japanese handmade paper (known as Washi) is produced in large volumes. There are different grades according to weight, fiber, color, etc. Chinese paper is generally of lower quality in terms of strength and purity. In both countries, the paper is made from pulp by soaking bast fibers in water and processing the fibers by retting, cooking and beating. A mold (generally made from a fine lattice of bamboo or horse hair) is covered with the pulp and the resulting sheets of paper are placed in a stack, then brushed out onto a flat, vertical surface to dry. There is virtually no paper made from the rice plant (Oryza sativa) except one called "rice straw paper." It is very laborious to make and is done by hand in areas of central Burma.
Before the Spanish conquest, the Aztecs used fig bark to make a kind of paper. In fact, the common Spanish name for many species of Ficus is "amate," from the Nahuatl word "amatl" meaning paper. Both Aztecs and Mayans used bark from native fig trees to make paper for the original Mexican codices. Bark was stripped from the fig tree, soaked in water, washed, boiled and split into thin strips. The strips were then placed on a plank and pounded with a stone until a sheet of paper was formed, a process not unlike the production of papyrus paper by the ancient Egyptians.
Mexican bark paper is still being made to this day, particularly in the state of Puebla. The process is summarized by Anna Lewington in Plants For People (Oxford University Press, 1990). The fibrous inner phloem fibers are separated from the outer bark in strips and boiled for several hours in water containing lime. This procedure softens the fibers and makes them separate more easily. After rinsing, the strips are arranged in a grid pattern on a smooth board and then beaten with a flattened stone until the fibers mesh together. The sheets are left on the boards and allowed to dry in the sun. According to Lewington (1990), the bark of several tree species are used, including Ficus tecolutensis and Morus celtidifolia of the mulberry family (Moraceae) and Trema micrantha of the elm family (Ulmaceae).
Painted bark paper from Yucatan, Mexico.
A process similar to that of bark paper can also be used as a substitute for cloth. The best known bark cloth is called tapa cloth, which was a major source of clothing for native Polynesians. The bark was obtained from the paper mulberry (Broussonetia papyrifera), a member of the mulberry family (Moraceae). Native figs, such as the Polynesian banyan (Ficus prolixa) were also used locally on some islands for bark cloth. Strips of bark were peeled off the trunk, and the outer coating scraped off with a shell. After they were soaked in water and cleaned, the strips were placed on a hard wood surface and pounded with a mallet. Individual strips were fused together by overlapping the edges and beating them together. Depending on the thickness of the sheets, the finished tapa cloth varied in appearance from a muslin-like material to a tough, leather-like cloth.
|Polynesian tapa cloth. For centuries, Polynesians have made bark cloth with unique and beautiful designs, in a seemingly endless array of patterns. In ancient times, tapa was used to denote rank and social status, but today is worn on special occasions. It is still used for weddings and ceremonial dances, and to decorate homes and make handbags, quilts and draperies.|
|Paper mulberry (Broussonetia papyrifera): A. Multiple fruit composed of numerous separate pistils from numerous separate female flowers; B. A small branch showing strips of stringy bark peeled away; C. Strips of stringy bark twisted into a crude twine. The pliability and usefulness of the bark is due to clusters of bast fibers.|
|A Mbuti ceremonial bark cloth shirt from the rain forest of N.E. Zaire. The Mbuti people fashion clothing from the bark of fig trees (Ficus) that grow in the local rain forest. The man makes two horizontal cuts around the trunk and then slices vertically between the cuts. He peels away the rough out bark, and then peels off the inner layer between the sapwood and the bark. Although this layer includes phloem tissue, it usually does not kill the tree. He wets this inner layer with water and hammers it with a mallet made of ivory or wood. After allowing it to dry, he repeats the wetting, pounding and drying process until the bark cloth is pliable and the correct thickness. When the bark cloth is ready, a women paints her unique designs using twig brushes and natural plant dyes from the forest.|
Modern paper is made from wood pulp, a mass of intermeshed fiber cells that are pressed into a thin sheet. This process was first produced by the Chinese nearly 2,000 years ago using the stem fibers of paper mulberry (Broussonetia papyrifera). The fibers were separated from the stems and floated in water. The macerated meshwork of fibers was allowed to settle in a thin film on a screen. After drying, the thin sheet of interlocked fiber cells (paper) was peeled from the screen. If you closely examine coarse blotter paper under a microscope with substage illumination, the meshwork of slender fiber cells can easily be seen, especially near the torn edges of the paper.
|Microscopic view of the torn edge of coarse blotter paper showing tangled meshwork of fibers. [Magnified Approximately 100X.]|
In order to produce pulp, logs and wood chips must be reduced to a mass of fibers. If gymnosperm wood is used, then the pulpy mass is composed essentially of tracheids. Several methods are used to convert wood into pulp, including the ground wood process, sulfite process and the sulfate process. In the sulfite process the chips are cooked in a digester with bisulfites. Hot acid is then pumped into the digester, and the cooking is completed. The softened fibers are then forcibly blown into a chamber to separate them. Paper made from this process has a high acid content and becomes brittle and begins to disintegrate after 100 years. This is why modern textbooks (including the recommended text for this course) often say "printed on acid-free paper." The sulfate process is an alkaline rather than an acid process and uses as digestive agents sodium sulfate, sodium sulfide, and caustic soda (sodium hydroxide). This process is now the most widely used because unlike the sulfite process, the "acid free" paper has greater longevity. The sulfate process also dissolves the resins out of the pulp and can therefore be used for gymnosperm woods such as Douglas fir (Pseudotsuga menziesii) and various pines, including (Pinus ponderosa). After digestion, the tenuously bound fibers are beaten to separate them.
In addition to chemically digesting the wood until it is reduced to its component fibers, the lignin must also be removed in fine quality papers. Cardboard containers and supermarket shopping bags (kraft paper) are stiff and brown because they still contain lignin. Wood pulp is also used for the manufacture of insulating board and fiberboard, such as masonite. Special types of paper, such as photographic paper, are coated so they will be suitable for various printing techniques. Rag paper contains fibers from cotton and linen. It does not become brittle and can withstand repeated folding and creasing. U.S. money is printed on rag paper with scattered colored fibers of silk or nylon to discourage counterfeiting.
Sizing agents are used to make the high quality paper of books, magazines and paper money. Sizing involves the addition of natural thickening agents such as starches, gums and resins to paper and cloth fabrics to stiffen them and to fill surface irregularities. In the paper industry sizing prevents the paper from becoming too absorbent so that writing inks will not bleed or diffuse into the paper. Some of the commonly used sizing agents mixed with paper pulp are potato starch, guar gum, methyl cellulose, alginates and rosin. Different sizing agents are used for specific attributes in the finished paper product. For example, methyl cellulose has excellent oil and grease resistant properties and also helps to give an even finish. Guar gum from the sap of Acacia senegal serves to bond the fibers together and distribute them more evenly. This gives a better sheet formation and improves folding and tensile strength.
Why Paper Money Doesn't Disintegrate In A Washing Machine?
Ordinary notebook paper is made from the intermeshed cellulose fibers of wood pulp. The cellulose fibers absorb water and come apart (dissolve) when they are soaked in water. Paper money is made from textile (rag) fibers, such as cotton and linen. Intermeshed "rag" fibers bond together more firmly and don't separate (dissolve) in water.
The stringy, threadlike strands in the leaves of monocots such as giant yucca (Yucca elephantipes), sisal (Agave sisalana), bowstring hemp (Sansevieria trifasciata) and New Zealand flax (Phormium tenax) are composed of clusters of fiber cells associated with the numerous vascular bundles.
|Thread-like fibers exposed from the leaves of two species of monocots in the agave family (Agavaceae): A. Bowstring Hemp (Sansevieria trifasciata); and B. Giant Yucca (Yucca elephantipes).|
|Magnified view of a Yucca leaf cross section showing dense cluster of fiber cells (pinkish-red cells with very small lumens). Note the thick, waxy layer (cuticle) along the upper side of the leaf that prevents desiccation in a hot desert climate. Also note the deep, sunken stomata with a pair of guard cells at the bottom (red square). Sunken stomata reduce desiccation because the guard cells and stomata (pores) are located in a deep pit (crypt). The leaves can carry on gas exchange through their stomata without being directly exposed to the hot sun and drying winds. [Magnified Approximately 400X.]|
|Magnified view of a Yucca leaf cross section showing dense cluster of fiber cells; pinkish-red cells in upper half of photo with thick walls and very small lumens. [Magnified Approximately 500X.]|
Fibers are also present in the stems of many herbaceous dicots, such as flax (Linum usitatissimum), ramie (Boehmeria nivea) and Indian hemp (Cannabis sativa). The following table shows some of the world's most interesting and economically important fiber plants used for cordage and textiles.
Stem (Bast) Fibers (Dicots)
Leaf Fibers (Monocots)
New Zealand Flax
Seed Fibers (Dicots and Monocots)
Fibers From Seed Pods (Dicots)
Fibers From Seeds And Seed Pods
Cotton "fibers" are made from unicellular hairs that grow out from the surface of the seed immediately after fertilization. The hairs are twisted into usable thread which is tough and strong. Cotton hairs (lint) of tetraploid (4n) species may be up to 50 mm long. In the cotton gin, fine brushes pull the lint off the seed by drawing it through holes too fine for the seeds to pass. Cotton thread is spun from countless billions of microscopic hairs covering the surface of cotton seeds, each hair up to 50 mm (2 inches) in length. The total length of hairs in a single cotton boll (one seed capsule) may exceed 300 miles. Imagine how many miles of cotton hairs are in a standard 500 pound bale. Cotton is the textile produced in the largest volume worldwide.
|A seed capsule (cotton boll) from the cotton plant, a tetraploid cultivar of Gossypium hirsutum or G. barbadense. Several seeds are embedded in the mass of white hairs (two seeds are visible in photograph). Cotton "fibers" are made from unicellular hairs that grow out from the surface of the seeds immediately after fertilization. The hairs are twisted into usable thread which is tough and strong. The total length of hairs in a single cotton boll may exceed 300 miles.|
Kapok hairs are produced on the inner surface of the seed capsule of the kapok tree (Ceiba pentandra). In tropical regions of the New World (including Central and South America), the kapok grows into an enormous rain forest tree with a massive buttressed trunk. The floss silk tree (Chorisia speciosa), another member of the kapok family (Bombacaceae) also produces seed capsules lined with masses of silky hairs. This tree with its distinctive thorny trunk and showy pink flowers is commonly planted in southern California. Kapok hairs are coated with a highly water-resistant, waxy cutin. The empty lumen is larger than cotton hairs and hence the fiber is lighter in weight. Kapok is difficult to spin and is not made into textiles. It is used primarily as a waterproof filler for mattresses, pillows, upholstery, softballs, and especially for life preservers. A kapok-filled life jacket can support 30 times its own weight in sea water. The seeds of North American milkweeds (Asclepias) have a tuft of long, silky hairs at one end. Like miniature parachutes, the hairs aid in the wind dispersal of this interesting North American species. The hairs were used as a substitute for kapok during World War II. The hairs can also be twisted into dental floss. Coir fiber is made from the husk (mesocarp) of the coconut fruit (a dry drupe). In the Orient, it is twisted into rope and twine, and in the West it is made into door mats and stuffing. The dried, seed capsules of North American devil's claw (Proboscidea parviflora) are used by Native American tribes of Arizona and Mexico to weave black designs into their baskets.
|Floss silk tree (Chorisia speciosa), a member of the bombax family (Bombaceae) along with kapok (Ceiba pentandra). The large seed capsule is filled with a mass of silky hairs resembling a large cotton ball.|
|Floss silk tree (Chorisia speciosa), a member of the bombax family (Bombaceae) along with kapok (Ceiba pentandra). The large seed capsule is filled with silky hairs entangled with black seeds. The silky fluff presumably aids in the wind dispersal of the seeds as they fall from branches high above the ground. [Yellow ruler is 6 inches (15 cm) long.]|
Bast Fibers From The Bark Of Stems
Bast fibers are groups of long, thick-walled fiber cells usually occurring in the phloem parenchyma of stems. Bast fibers (and sometimes the associated xylem tissue) constitute the main source of stem fibers. Flax and ramie are fine and white, and are mainly cellulose. Jute and hemp are coarse and brownish, and contain ten to fifteen percent lignin. Flax fibers are made into linen textiles which are soft, lustrous and very water-absorbent. Linen is used for towels and numerous other products. Flax seeds are the source of linseed oil. Ramie fibers are stronger than cotton and flax, and are made into the lustrous "China grass cloth." Jute is woven into burlap, sackcloth and tough twines.
|Burlap is a coarse fabric made from the stem fibers of jute (Corchorus capsularis), a tall, much-branched annual or perennial native to China. It is usually placed in the basswood family (Tiliaceae), although some references place it in the mallow family (Malvaceae). Jute is a very tough fiber composed of heavily lignified cells. In fact, the brown color is due to the high lignin content. Because it is relatively inexpensive and very strong, it is used for large sacks to haul heavy materials. It is commonly used for sand bags, although synthetic fibers are now used extensively. The large sack in the above image was used for cacao (chocolate) beans in tropical America. Jute fabric is also called Hessian cloth and jute bags are called gunny sacks. Jute is also used for brown twine commonly sold in gardening stores.|
Indian hemp (Cannabis sativa) fibers are made into cord and rope, and into some textiles. The male plant yields the best fibers. The best varieties (for fiber) are grown in Italy and are almost white in color and nearly as soft as linen. Female plants are an important source of another economically important plant product (THC) which accounts for the main cash crop in some counties of California. Another Indian hemp (Apocynum cannabinum) was an important traditional fiber plant of native North American people.
|A tall clump of Indian hemp male plants (Cannabis sativa) growing in southern California. The male plants of this fascinating dioecious species yield the best bast fibers. The plants in photo were about fifteen feet tall, taller than the tangelo tree to the right.|
|Various items made from Indian hemp (Cannabis sativa), including twine, purse, shoelaces, colored yarn, wallet, bracelet, and notebook.|
|Linum usitatissimum, the source of linen and one of the world's most valuable fiber plants. This species also produces flax seeds, the source of linseed oil, an unsaturated drying oil used in the original linoleum and in the paint industry. Linoleum was discovered in 1863 by Frederick Walton. He named the product linoleum from linum (flax) and oleum (oil). Oxidized linseed oil was mixed with ground cork and pigments, pressed onto burlap (jute or hemp) or a felt backing, and then baked. The tough, elastic, waterproof qualities of linseed oil produced the fine qualities of linoleum. Modern floor coverings are made from plastic polymers, many of which are still derived from seed oils.|
Fibers From The Leaves Of Monocots
Leaf fibers are derived from long, narrow leaves typical of the monocots. Sisal and henequen come from large, polyploid species of Agave. Agave sisalana is propagated vegetatively from viviparous plantlets that develop high on the inflorescence (flower stalk). Sisal and henequen furnish most of the world's non-naval string and rope. Another leaf fiber plant in the same family as Agave is the genus Yucca. The sun-dried leaves of Yucca elata are used extensively for the main visible white coils in baskets of native North American people, including the Papago, Pima and Havasupai.
Manila hemp or abaca comes from the leaves of a banana species (Musa textilis) which is native to the Philippines. Manila hemp makes the finest ropes which have held ships to docks throughout the world. Manila hemp rope is being replaced by nylon in many parts of the world. In Ethiopia, another banana species (Musa ensete) is similarly used for its strong leaf fibers. Bowstring hemp comes from the leaves of Sansevieria metalaea (syn. S. guineensis & S. hyacinthoides), and other species. The whitish fiber is used in Central Africa for course cloth and fishing nets. Some species of Sansevieria are cultivated for their rosettes of attractive, variegated leaves. Another monocot used in southern California landscaping (such as the campus of Palomar College) with tough, fibrous leaves is New Zealand flax (Phormium tenax).
|Manila hemp or abaca comes from the leaves of a banana species (Musa textilis) which is native to the Philippines. The leaf fibers make some of the finest natural ropes in the world.|
|Stem and leaf fiber plants: A: Indian Hemp (Cannabis sativa), a stem fiber plant; B. Bowstring Hemp (Sansevieria trifasciata); C. Giant Yucca (Yucca elephantipes) with sisal rope from Agave sisalana; D. & E. New Zealand Flax (Phormium tenax).|
Monocot Leaf & Stem Fibers Used In Basketry
|A Chocó basket from the Darién rain forest on the Panama/Colombia border. Fibers obtained from dried palm leaves are dyed with colorful extracts of wild plants, bark and mud.|
Many commercially important textile fibers are made from natural wood cellulose or from synthetic polymers, and two important protein fibers come from a mammal and an insect. Some of the popular synthetic fibers include various polyesters and nylon, and some of these require natural plant products in their manufacture. Castor oil is the primary raw material for the production of sebacic acid, which is the basic ingredient in the production of nylon and other synthetic resins and fibers. Approximately three tons of castor oil are necessary to produce one ton of nylon. Purified wood cellulose (from plant cell walls) is used in the manufacture of a number of synthetic products. Cellophane is made from a viscous solution of wood cellulose that is extruded through a narrow, slit-like opening. In rayon, the viscous solution of wood cellulose is extruded through minute openings called spinnerets to form strong, pliable fibers. Arnel is made from triacetate fibers from purified wood cellulose which has been chemically bonded to acetyl groups. Wool comes from the hair of sheep and silk thread is spun from the cocoon of the silkworm moth.
|An assortment of textiles: A. Wool; B. Nylon; C. Rayon; D. Silk (with 2 silkworm moth cocoons); E. Cotton (with a cotton seed capsule or cotton boll); F. Arnel (triacetate); G. Ramie; and H. Linen.|
Silk From Caterpillars & Spiders
The silk industry depends on moth that feeds on the leaves of mulberry trees. Raw silk actually consists of two proteins, fibroin and sericin. The fibers are very fine and lustrous, about 1/2500th of an inch in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk. Based on 2/3 of mile (1 km) per cocoon, ten unraveled cocoons could theoretically extend vertically to the height of Mount Everest, the world's highest mountain. It is estimated that at least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion pounds of mulberry leaves. According to E. L. Palmer (Fieldbook Of Natural History, 1949), one pound of silk represents about 1,000 miles of filament. The annual world production represents 70 billion miles of silk filament, a distance well over 300 round trips to the sun!
|Although silk thread is synthesized from digested mulberry leaves, it is technically an animal fiber rather than a plant fiber. Another fascinating animal fiber is derived from the webs of spiders. In fact, the world's strongest natural filament comes from the silk strands of a spider's web, specifically orb weaver spiders of the genus Nephila (family Araneidae). The golden silk spider (Nephila clavipes) of the southeastern United States and New World tropics makes a huge web more than three feet (1 m) in diameter.|
The golden orb's web can run from the top of a tree 20 feet (6 m) high and up to six feet (2 m) wide. Unlike the fragile webs of other spiders, the golden orb's web can last for weeks and even months. The silk of Nephila species is so strong that it can trap small birds, which the spider doesn't eat. Trapped birds often destroy the web by thrashing around. To avoid such damage, the spider often leaves a line of insect carcasses on its web (like the safety strip on glass doors), or builds smaller barrier webs around the main web. Matted and twisted webs of Nephila maculata are used by South Sea Islanders for various kinds of bags, fishing lures and traps. Female spiders are induced to build nests on bamboo frames which are then used as fishing nets. In the Solomon Islands, the spider web is collected by winding it around sticks to make large sticky balls which are suspended just above the water. Needle fish are lured to jump out and get entangled in the ball. In Southeast Asia, people make a net by scooping up the web between a stick bent into a loop. Spider webs have also been used as a bandage to stop blood flow from an injury.
The silk of golden orb spiders is almost as strong as Kevlar, a synthetic fiber which is drawn from concentrated sulphuric acid. [According to Stanton de Riel (Personal Communication 2013), literature suggests that ultra-high molecular weight polyethylene (UHMWPE) yield strength: weight ratio (the usual criterion of strength) exceeds that of polyaramid (Kevlar) by 40%.] If spider silk could be manufactured, it would have thousands of uses, including parachutes, bullet-proof vests, lightweight clothing, seatbelts, and light but strong ropes. It could also be used for sutures in operations, artificial tendons and ligaments. It has been estimated that a solid strand of silk from this spider the diameter of a pencil could stop an airliner in flight! This unsubstantiated claim was reported on a TV nature program.
Studies are now being conducted to have genetically engineered plants produce fluid polymers that can be processed into silk. Spiders are not used commercially to produce silk fabric because silkworm moth caterpillars produce twice as much silk and are much easier to culture. Up to 150 meters of silk can be collected from a single individual of Nephila clavipes. It would take approximately 415 spiders to make a square yard of cloth. The same number of silkworm larvae could make twice as much silk, and they don't eat each other. All you need is a plentiful supply of mulberry leaves.
|Close-up view of a female golden silk spider (Nephila clavipes) in her web. The orb web of this species may be over one meter in diameter. This species is also called the golden orb spider because of the golden tinge of the silken web. This large spider is easily recognized by the conspicupous tufts of hair (red arrow) on the femora and tibiae of leg pairs #I, #II and #IV. [For some reason, leg pair #III does not have the characteristic tufts of hair.]|
All text material & images on these pages copyright © W.P. Armstrong