Encyclopedia of Global Resources part 102 doc

Economically Important Placer Minerals Many types of minerals and rock materials can occur in placer deposits; among the most important are gold, titanium minerals, zircon, tin oxide, di

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mizing the yield per hectare of wooded land He built

a strong U.S Forest Service, financed in part by the

sale of mature timber He actively opposed the

institu-tion of nainstitu-tional parks to be used for recreainstitu-tion,

con-sidering them a waste of natural resources After

leav-ing the U.S Forest Service, Pinchot became active in

the Progressive Party, founded by supporters of

Theo-dore Roosevelt Pinchot became chief forester of

Pennsylvania in 1920, and he campaigned for and

won election as governor of Pennsylvania in 1923 and

again in 1931

Donald R Franceschetti

See also: Conservation; Forest management; Forest

Service, U.S.; Leopold, Aldo; Roosevelt, Theodore

Placer deposits

Categories: Geological processes and formations;

mineral and other nonliving resources

Placer deposits are mechanical concentrations of debris

weathered out of rocks Commonly, economically

im-portant minerals have higher densities, so they are

con-centrated as the lighter-density minerals are winnowed

out by the action of water or wind.

Background

Placer deposits are found throughout the world

wher-ever the mechanisms of concentration, water and

wind, have been active and the resulting concentrates

have not been redispersed by later processes The best

known types of placers occur in river channels and in

beach sediments

The weathering and erosion of rocks release

parti-cles of varying size, shape, and density Soluble

materi-als are dissolved and removed in surface water or

groundwater Some minerals, such as feldspars, are

hydrated and converted into clay minerals, which,

be-ing soft, small, and of low density, are relatively readily

removed in suspension Quartz (SiO2), common in

many kinds of rocks, generally weathers out as

roughly equant grains that, because of their hardness

and insolubility, wash into streams and rivers, where

they are moved by rolling, bouncing, and pushing

along toward the oceans The abundance of quartz

and its resistance to mechanical and chemical

weath-ering results in its being the most abundant placer

mineral and the principal constituent of temperate and cold climate beaches throughout the world During the weathering and erosional processes, other minor or trace minerals, which are resistant to breakdown, are also transported along with the quartz grains and pebbles in river channels to the ocean margins If the mineral particles possess high densities, they may be selectively concentrated as the transporting agent (usually water) more readily re-moves the lighter-density minerals Thus, gold nug-gets, with densities of 15-19 grams per cubic centime-ter, are commonly concentrated in residual materials

as the quartz grains, with a density of about 2.65 grams per cubic centimeter, are removed The densities of several other valuable and resistant minerals are suffi-ciently higher than that of quartz to allow them to also

be concentrated in placer deposits (examples include ilmenite, FeTiO3, 4.8; rutile, TiO2, 4.25; zircon, ZrSiO4, 4.7; cassiterite, SnO2, 7.0; and diamond, C, 3.5)

Economically Important Placer Minerals Many types of minerals and rock materials can occur

in placer deposits; among the most important are gold, titanium minerals, zircon, tin oxide, diamonds, platinum, and sand and gravel Throughout history, gold has no doubt been the most important placer mineral Gold is soft and malleable but is otherwise nearly inert in the weathering realm Hence, once gold is weathered out of the lode deposits where it ini-tially formed, the grains may survive transport in streams and rivers over long distances It was the dis-covery of such gold grains that led to nearly all of the world’s major gold rushes, including the California gold rush in 1849 Gold placers have formed through-out geologic time; the world’s largest gold reserves in South Africa occur in placers formed 2 billion years ago

The titanium minerals, ilmenite and rutile, occur

in minor amounts as small grains in many types of ig-neous and metamorphic rocks These minerals are highly resistant to weathering and hence are liberated intact from their host rocks Although their densities are less than twice that of quartz, they are quite effec-tively concentrated by flowing water in rivers and by the agitation of waves along beaches as the lower den-sity quartz grains are winnowed out The zirconium silicate zircon is a common accessory mineral in alka-line igneous rocks It weathers out as the titanium minerals do and is generally found with those miner-als in river and beach deposits

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The tin oxide cassiterite, like the titanium

miner-als, is heavy, hard, and extremely resistant to

weather-ing Consequently, where there are cassiterite-bearing

lode deposits, the cassiterite weathers out and may be

concentrated into economic placers The hardness of

diamonds and their resistance to normal weathering

agents has allowed them to wash down rivers that

drain from the areas of exposed diamond pipes and

to occur in placer river and beach deposits Because

the density of the diamonds is only about one third

greater than that of quartz, the diamonds are not as

well selectively concentrated in these placers as are

the heavier minerals noted above Platinum, like gold,

is chemically inert and has a high density, 15-19 grams

per cubic centimeter Platinum lode deposits are much

more restricted geologically than are gold deposits; hence, placer platinum deposits occur in only a few places in the world

The sand and gravel deposits found in rivers and lakes and on beaches constitute the largest placer de-posits in that they represent mechanically concen-trated residual materials Although they have a much lower per unit value than many other placer materi-als, the large volumes of sand and gravel mined from these deposits actually make them the most important placer deposits economically

Types of Placer Deposits Placer deposits have been classified into several differ-ent types on the basis of location of formation The

major types include residual placers, eluvial placers, stream or river placers, riverbank and flood placers, eolian placers, and beach placers Residual placers are occur-rences of minerals at or near their point

of release from the original source rocks There has been some degree of enrich-ment of the placer minerals as the result of the removal of other portions of the host rocks by weathering Eluvial placers are transitional placers in which concentra-tions of placer minerals occur downslope from the source rocks but where the val-ued minerals have not yet washed into streams and rivers that would transport them for long distances

Stream or river placers are the best known placers and are the types responsi-ble for most famous gold discoveries The movement of the running water, especially where there is turbulence, is effective in sorting rock fragments and mineral grains according to size and density Because of their higher densities, gold grains and sev-eral other placer minsev-erals settle out They are readily trapped in crevices and irregu-larities on the stream bed or among larger boulders, as the lower density materials are more easily washed away This type of placer sometimes grades into deltaic beds where a river drains into a lake or the ocean

Riverbank and flood placers are depos-its adjacent to streams and rivers that have been left as the rivers meander, cut

A nineteenth century magazine depiction of a miner using a “cradle” to mine a

placer deposit in 1880’s California (Library of Congress)

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ward, or overflow their banks in flood conditions.

During the natural development of rivers, they

com-monly shift laterally across their floodplains, eroding

banks on one side while depositing materials on the

other side In some areas, changes in base levels result

in rivers cutting downward though the sediments they

had previously deposited in their floodplains In both

these circumstances, valuable placer deposits may be

left in the riverbank sediments that are adjacent to the

present rivers Flood placers also occur in the

sedi-ments adjacent to rivers They form during episodic

flooding when water flow is sufficiently rapid and

tur-bulent to transport gold or other valued placer

min-eral grains up and out of the channels onto the

adja-cent floodplains As the water spreads laterally and its

velocity decreases, the gold grains are left as placer

de-posits along the adjacent floodplains

Eolian placers are wind-formed placers that occur

locally in desert regions where high winds have

re-moved lighter mineral grains, thereby enriching the

heavy minerals in the residuum

Beach placers are generally formed by the

com-bined effects of river transport of weathered materials

to coastal margins and the action of tides and storm

waves along beaches The ebb and flow of the waves

and the generation of longshore currents, especially

under storm conditions, can effectively winnow and

sort beach materials such that certain areas are highly

enriched in heavy minerals Gold-bearing beach

plac-ers are known in many localities, but the most famous

are probably those at Nome, Alaska, where the beaches

were actively mined for many years Diamond-bearing

beach placers have been extensively mined along the

west coast of central and southern Africa, where rivers

draining the interior have transported diamonds into

the beach sands Beach placers containing ilmenite,

rutile, and zircon are the world’s major sources of

these minerals

Mining of Placer Deposits

Gold panning is probably the best known method of

exploiting placer deposits A circular motion of water

in a pan containing gold along with other sediments

effectively separates the minerals on the basis of their

densities The same general principle is used in sluices,

channel-like boxes with barriers to create turbulence

in the water so that sorting can take place On a large

scale, modern placers are mined by the scooping up

of the unconsolidated materials and the use of either

spiral classifiers or heavy media to separate the heavy

materials from the light materials The differences in the densities of the minerals allow for effective separa-tion

James R Craig

Further Reading Bell, Fred J., and Laurance J Donnelly “Placer

De-posits and Mining.” In Mining and Its Impact on the Environment New York: Taylor & Francis, 2006 Boggs, Sam, Jr Principles of Sedimentology and Stratigra-phy 4th ed Upper Saddle River, N.J.: Pearson

Prentice Hall, 2006

Dixon, Colin J Atlas of Economic Mineral Deposits.

Ithaca, N.Y.: Cornell University Press, 1979

Guilbert, John M., and Charles F Park, Jr The Geology

of Ore Deposits Long Grove, Ill.: Waveland Press,

2007

Hartman, Howard L., and Jan M Mutmansky Intro-ductory Mining Engineering 2d ed Hoboken, N.J.:

J Wiley, 2002

McCulloch, Robin, et al Applied Gold Placer Exploration and Evaluation Techniques Butte: Montana Bureau

of Mines and Geology, 2003

Macdonald, Eoin H Alluvial Mining: The Geology, Tech-nology, and Economics of Placers New York: Chapman

and Hall, 1983

Valentine, David “Chinese Placer Mining in the United States: An Example from American

Can-yon, Nevada.” In The Chinese in America: A History from Gold Mountain to the New Millennium, edited by

Susie Lan Cassel Walnut Creek, Calif.: AltaMira Press, 2002

Wells, John H Placer Examination: Principles and Prac-tice Washington, D.C.: U.S Department of the

In-terior, Bureau of Land Management, Phoenix Training Center, 1989

Wenk, Hans-Rudolf, and Andrei Bulakh Minerals: Their Constitution and Origin New York: Cambridge

University Press, 2004

Web Site U.S Geological Survey Prospecting for Gold in the United States http://pubs.usgs.gov/gip/prospect2/

prospectgip.html See also: Diamond; Gold; Marine mining; Residual mineral deposits; Sand and gravel; Tin; Titanium; Weathering; Zirconium

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Plant domestication and breeding

Category: Plant and animal resources

Plant domestication and breeding refers to the process

by which wild plants are intentionally bred and grown

to meet human food, fiber, shelter, medicinal, or

aes-thetic needs.

Background

Perhaps any nation’s greatest resource is its ability to

sustain an agricultural system with the capacity to

feed, shelter, and clothe its population The

develop-ment of an agricultural system depends on an ability

not only to cultivate wild plants but also to selectively

breed plants to increase or improve the production of

products that are useful for food, clothing, shelter,

medicines, or aesthetic purposes

No one knows exactly when the first crop was

culti-vated, but most authorities believe that it occurred at

some time between eight and ten thousand years

ago For centuries prior to that time, humans had

known that some wild plants and plant parts (such as

fruits, leaves, and roots) were edible These plants

ap-peared periodically (usually annually) and randomly

throughout a given region Eventually humans

discov-ered not only that these wild plants grew from seed

but also that the seed from certain wild plants could

be collected, planted, and later gathered for food

This most likely occurred at about the same time in

both the Sumerian region between the Tigris and

Eu-phrates rivers in the Old World and in Mexico and the

Central American region of the New World While the

earliest attempts at domesticating plants were

primar-ily to supplement the food supply provided by

hunt-ing and gatherhunt-ing, people soon improved their ability

to domesticate and breed plants to the point that they

could depend on an annual supply of food This food

supply allowed the development of permanent

settle-ments and decreased reliance on hunting and

gath-ering

Early Crop Domestication

By six thousand years ago, agriculture was firmly

es-tablished in Asia, India, Mesopotamia, Egypt, Mexico,

Central America, and South America Even before

re-corded history, these areas had domesticated some of

the world’s most important food (corn or maize, rice,

and wheat) and fiber (cotton, flax, and hemp) crops

The place of origin of wheat is unknown, but many au-thorities believe that it may have grown wild in the Tigris and Euphrates Valleys and spread from there to the rest of the Old World Wheat was grown by Stone Age Europeans and was reportedly produced in China

as far back as 2700 b.c.e Wheat is the major staple for about one third of the people of the world The earli-est traces of the human utilization of corn (or maize,

as it is also called), dates back to about 5200 b.c.e

It was probably first cultivated in the high plateau re-gion of central or southern Mexico and represented the basic food plant of all pre-Columbian advanced cultures and civilizations, including the Inca of South America and the Maya of Central America and Mexico Botanists believe that rice originated in southeast Asia Rice was cultivated in India as early as 3000 b.c.e and spread from there throughout Asia and Malaysia

In modern society, rice is one of the world’s most im-portant cereal grains and is the principal food crop of almost half of the world’s people Hemp, most likely the first plant cultivated for its fiber, was cultivated for the purpose of making cloth in China as early as the twenty-eighth century b.c.e It was used as the cordage

or rope on almost all ancient sailing vessels Linen made from flax is one of the oldest fabrics Traces of flax plants have been identified in archaeological sites dating back to the Stone Age, and flax was definitely cultivated in Mesopotamia and Egypt five thousand years ago Cotton has been known and highly valued

by people throughout the world for more than three thousand years From India, where a vigorous cotton industry was present as early as 1500 b.c.e., the cultiva-tion of cotton spread to Egypt and then to Spain and Italy In the West Indies and South America in the New World, a different species of cotton was grown long before the Europeans arrived Other important plants that have been under domestic cultivation since an-tiquity include dates, figs, olives, onions, grapes, ba-nanas, lemons, cucumbers, lentils, garlic, lettuce, mint, radishes, and various melons

Modern Plant Breeding Genetic variability is prevalent in all sexually ing organisms, and like all other sexually reproduc-ing organisms, plants produce spontaneous mutants Throughout most of history, plant domestication and breeding were primarily based on the propagation of these mutants When a grower observed a plant with

a potentially desirable mutation (such as a change that produced a characteristic such as bigger fruit,

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brighter flowers, or increased insect resistance), the

grower would collect seed or take cuttings (if the plant

could be propagated vegetatively) and produce

addi-tional plants with the desirable characteristic

Advances in the understanding of genetics in the

early part of the twentieth century made it possible to

breed some of the desirable characteristics resulting

from mutation into plants that previously had lacked

the characteristic The obvious advantages of

produc-ing plants with improved characteristics such as higher

yield made plant breeding highly desirable As

popu-lations continued to grow, there was a need to select

and produce higher-yielding crops The development

and widespread successful use of new high-yield

vari-eties of crop plants in the 1960’s is often referred

to as the Green Revolution Basic information

sup-plied by biological scientists allowed plant breeders to

fuse a variety of characteristics from different plants

to produce new, higher-yielding varieties of

numer-ous crops—particularly the seed grains that supply

most of the calories necessary for maintenance of the

world’s population

When a plant characteristic is identified as desir-able, it is studied both morphologically and biochemi-cally to determine the mechanism of inheritance If it

is determined that the mechanism is transferable, at-tempts are made to incorporate the trait into the tar-get plant If the plants are closely related, traditional breeding techniques are used to crossbreed the plant with the desirable trait with the plant that lacks the characteristic Although this process is often tedious,

is sometimes difficult to accomplish, and requires considerable patience and hard work, it is based on a fairly simple concept Basically, pollen from one of the plant types is used to fertilize the other plant type This process often requires specialized handling tech-niques to ensure that only the pollen from the plant with the desired characteristic is allowed to fertilize the eggs of the recipient plant

Sometimes this process involves the use of bags or other materials to isolate the recipient flowers, which are then pollinated by hand Another technique in-volves the introduction of a gene for male sterility into the recipient plant In these cases, only pollen from another plant can be used to fertilize the egg Once plants with the desirable characteristics are devel-oped, the lines are often inbred to maintain large numbers of progeny with the desired traits In many cases, inbred lines will lose vigor after several genera-tions When this occurs, two inbred lines are often crossed to produce hybrids A majority of the hybrid offspring will still contain the desired characteristics but will be more vigorous

Until relatively recently, the use of traditional breeding techniques between two closely related spe-cies was the only means of transferring heritable char-acteristics from one plant to another The advent of recombinant deoxyribonucleic acid (DNA) technol-ogy, however, made it possible to transfer genetic characteristics from any plant (or, in actuality, from any organism) to any other plant The simplest method for accomplishing this transfer involves the use of a vector, usually a piece of circular DNA called a plasmid The plasmid is removed from a microorgan-ism such as bacteria and cut open by an enzyme called

a restriction endonuclease or restriction enzyme A section of DNA from the plant donor cell that con-tains the gene for a previously identified desirable trait is cut from the donor cell DNA by the same re-striction endonuclease The section of plant donor cell DNA with the gene for the characteristic of inter-est is then combined with the open plasmid DNA, and

Agriculturist Edgar E Hartwig, the “soybean doctor,” has spent

more than fifty years breeding crops resistant to diseases and pests.

(United States Department of Agriculture)

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the plasmid closes with the new gene as part of its

structure The recombinant plasmid (DNA from two

sources) is placed back into the bacteria where it will

replicate and code for protein just as it did in the

do-nor cell The bacteria is then used as a vector to

trans-fer the gene to another plant, where it will also be

transcribed and translated

D R Gossett

Further Reading

Acquaah, George Horticulture: Principles and Practices.

4th ed Upper Saddle River, N.J.: Pearson Prentice

Hall, 2009

Adams, C R., K M Bamford, and M P Early Principles

of Horticulture 5th ed Boston:

Butterworth-Heine-mann, 2008

Fennema, Owen R., ed Principles of Food Science New

York: Dekker, 1975

Hartmann, Hudson T., et al Hartmann and Kester’s

Plant Propagation: Principles and Practices 7th ed.

Upper Saddle River, N.J.: Prentice Hall, 2002

Janick, Jules Horticultural Science 4th ed New York:

W H Freeman, 1986

Kipps, M S Production of Field Crops: A Textbook of

Agronomy 6th ed New York: McGraw-Hill, 1970.

Martin, John H., Richard P Waldren, and David L

Stamp Principles of Field Crop Production 4th ed

Up-per Saddle River, N.J.: Pearson Prentice Hall, 2006

Metcalfe, Darrel S., and Donald M Elkins Crop

Pro-duction: Principles and Practices 4th ed New York:

Macmillan, 1980

Rather, Howard C., and Carter M Harrison Field

Crops 2d ed New York: McGraw-Hill, 1951.

Vaclavik, Vickie A., and Elizabeth W Christian

Essen-tials of Food Science 3d ed New York: Springer, 2008.

See also: Agricultural products; Agriculture

indus-try; Biotechnology; Corn; Green Revolution;

Horti-culture; Monoculture agriHorti-culture; Plant fibers; Rice;

Wheat

Plant fibers

Fiber crops provide a natural source of the raw

materi-als used to produce textiles, ropes, twine, and similar

materials.

Background The major fiber plants are cotton, flax, and hemp Less important crops such as ramie, jute, and sisal are produced in small amounts

Cotton With a total annual production approaching 25

mil-lion metric tons in 2008, cotton (Gossypium species) is

by far the most important fiber crop in the world Since humans rely heavily on cotton for clothing and other textiles, it enters the daily life of more of the world’s people than any other product except salt Cotton fiber has been known and highly valued by people throughout the world for more than three thousand years As is true of most crop plants that have been in cultivation for long periods of time, the early history of cotton is obscure A vigorous cotton industry was present in India as early as 1500 b.c.e From India, the cultivation of cotton spread to Egypt and then to Spain and Italy In the New World, a differ-ent species of cotton was grown in the West Indies and South America long before the Europeans ar-rived In the United States, cotton is grown from the East Coast to the West Coast in the nineteen southern-most states

Botanically, cotton is in the mallow family, which includes such plants as okra, hollyhock, hibiscus, and althea The plant has a taproot and branching stems Flowers form at the tips of fruiting branches, and the ovary within each flower develops into a boll which contains the seed, fiber, and fuzz The fiber, most com-monly referred to as lint, develops from epidermal cells in the seed coat of the cottonseed The fiber reaches maximum length in twenty to twenty-five days, and an additional twenty-five days are required for the fiber to thicken Fiber length from 2.0 to 2.4 centime-ters is referred to as short-staple cotton, and fiber length from 2.4 to 3.8 centimeters is called long-staple cotton The boll normally opens forty-five to sixty-five days after flowering Cotton is native to tropical re-gions but has adapted to the humid, subtropical cli-mate, where there are warm days (30° Celsius), rela-tively warm nights, and a frost-free season of at least

200 to 210 days

There are eight species of cotton in the genus

Gossypium, but only three species are of commercial importance Gossypium hirsutum, also known as

up-land cotton, has a variable staple length and is pro-duced primarily in North and Central America

Gossypium barbadense, a long-staple cotton, is primarily

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produced in South America and Africa Gossypium

herbaceum is a shorter-staple cotton native to India and

eastern Asia

Cotton is one of the more labor-intensive and

ex-pensive crops to produce The most opportune time

to plant cotton is at least two weeks after the date of

the region’s last killing frost Prior to seeding, the

field is prepared by plowing to a depth of 2.5

centime-ters Fertilizer, which is applied before seeding or at

the same time the seeds are planted, is placed to the

side and below the cotton seed Once the seeds

germi-nate and emerge from the soil, they often have to be

thinned, and shortly afterward, the producer begins

to apply irrigation water as needed

After the plants have developed a stand, weed

con-trol becomes crucial Weeds are concon-trolled both by

cultivation and chemical herbicides Cotton plants

are subject to invasion by a variety of insect pests such

as the boll worm and boll weevil; therefore

consider-able attention is given to insect control, typically using

a number of different insecticides When the bolls

ripen with mature fiber, the leaves of the plant are

re-moved by the application of a chemical defoliant, and

the cotton fiber is harvested

Harvesting was once done almost entirely by hand,

but today mechanical pickers harvest almost all the

cotton produced in the United States The picked

cot-ton is ginned to remove the seed and compressed into

bales The bales are transported to the cotton mill,

where the cotton is cleaned and spun into yarn, which

is then woven into fabric One kilogram of fiber is suf-ficient to produce up to 10 square meters of the fabric used for shirts and simple dresses

Flax

Flax (Linum sitatissimum) is the natural fiber used to

make linen While some flax is still produced for the purpose of producing this fabric, much of the flax, particularly that grown in the United States, is used to produce the flaxseed from which linseed can be ex-tracted Linen made from flax is one of the oldest fab-rics Flax was definitely cultivated in Mesopotamia and Egypt five thousand years ago, and traces of flax plants have been identified in archaeological sites dat-ing back to the Stone Age Flax was one of the first crops brought to North America by the early settlers Today, most of the flax produced in the United States

is grown in the north-central states

Flax, an annual plant, grows to a height of 60 to 100 centimeters and bears five-celled bolls or capsules with ten seeds each at the ends of fertile branches Since the flax fiber is found in the stems from the ground to the lowest branches, varieties that are long-stemmed with little branching are grown for fiber pro-duction Selection of high-quality, disease-free seed

is essential in flax production Flax fields are usually prepared in the fall to allow the soil to settle before planting Flax is usually sown in early spring two to

three weeks prior to the date of the last killing frost of the region Con-siderable attention is given to con-trolling weeds in a flax field When the crop is harvested for fiber, the plants are pulled from the soil, the seeds are removed, and the flax straw

is “retted” to separate the fiber from the woody part of the stem When the straw is completely retted, it is dried and then broken apart to remove the fifty-centimeter fibers which can be woven into fabrics

Hemp

Hemp (Cannabis sativa), a term used

to identify the plant and the fiber it produces, is used to make the stron-gest and most durable commercial fi-bers available Hemp was most likely the first plant cultivated for its fiber

A hemp stem featuring the plant’s fibers.

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It was cultivated for the purpose of making cloth in

China as early as the twenty-eighth century b.c.e It

was also used as a drug by the ancient Persians as early

as 1400 b.c.e It was used to make the cordage or rope

on almost all ancient sailing vessels Today hemp is

commercially produced for heavy textiles in

numer-ous countries, including Canada, China, Australia,

Russia, and France Hemp production is problematic

in the United States because it is illegal to grow

Canna-bis sativa, as it is the source of marijuana.

Hemp is an annual plant in the mulberry family

The plant is dioecious, meaning that it has staminate

or “male” flowers and pistillate or “female” flowers It

has a rigid stalk which can reach a thickness of more

than 2.5 centimeters in diameter and a height of 5

me-ters The plant has a hollow stem, and the bark or

“bast” located outside the woody shell is used to make

the bast fiber, which is then used to make hemp twine,

ropes, and other textiles where strength and

durabil-ity are desired Humid climates with moderate

tem-peratures and a period of at least 120 frost-free days

are necessary for hemp production Unlike flax, hemp

requires that the soil be plowed and thoroughly disked

or harrowed prior to planting The entire

above-ground portion of the plant is harvested when the

male plants are in full flower After two to three days

the plants are tied in bundles and set in shocks Hemp

fiber is retted and prepared for the mills in a manner

similar to that described for flax, except that heavier

machines are used to handle the stronger hemp stalks

Minor Crops

As for the minor fiber crops, ramie (Boehmeria nivea) is

produced primarily in Asia and is used to make strong

cloth such as Chinese linen Jute (Corchorus capsularis)

is grown primarily in India and Pakistan and is used to

manufacture burlap for bags and sacks Sisal (Agave

sisalana) is produced in East Africa and the West

In-dies and is used to make different types of cordage,

such as baler twine

D R Gossett

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