雅思阅读动植物类真题及答案：ThePearl

雅思阅读动植物类真题：The Pearl

The Pearl

A

Throughout history, pearls have held a unique presence within the wealthy

and powerful. For instance, the pearl was the favored gem of the wealthy

during the Roman Empire. This gift from the sea had been brought back from

the orient by the Roman conquests. Roman women wore pearls to bed so

they could be reminded of their wealth immediately upon waking up. Before

jewelers learned to cut gems, the pearl was of greater value than the diamond.

In the Orient and Persia Empire, pearls were ground into powders to cure

anything from heart disease to epilepsy, with possible aphrodisiac uses as well.

Pearls were once considered an exclusive privilege for royalty. A law in 1612

drawn up by the Duke of Saxony prohibited the wearing of pearls by nobility,

professors, doctors or their wives in an effort to further distinguish royal

appearance. American Indians also used freshwater pearls from the Mississippi

River as decorations and jewelry.

B

There are essentially three types of pearls: natural, cultured and imitation. A

natural pearl (often called an Oriental pearl) forms when an irritant, such as

a piece of sand, works its way into a particular species of oyster, mussel, or

clam. As a defense mechanism, the mollusk secretes a fluid to coat the irritant.

Layer upon layer of this coating is deposited on the irritant until a lustrous

pearl is formed.

C

The only difference natural pearls and cultured pearls is that the irritant is

a surgically implanted bead or piece of shell called Mother of Pearl. Often,

these shells are ground oyster shells that are worth

significant amounts of money in their own right as

irritant-catalysts for quality pearls. The resulting

core is, much larger than in a natural pearl. Yet,

as long as there are enough layers of nacre (the

secreted fluid covering the irritant) to result in a

beautiful, gem-quality pearl, the size of the nucleus

is of no consequence to beauty or durability.

D

Pearls can come from either salt or freshwater sources. Typically, saltwater

pearls tend to be higher quality, although there are several types of freshwater

pearls that are considered high in quality as well. Freshwater pearls tend to

be very irregular in shape, with a puffed rice appearance the most prevalent.

Nevertheless, it is each individual pearls merits that determines value more

than the source of the pearl. Saltwater pearl oysters are usually cultivated in

protected lagoons or volcanic atolls. However, most freshwater cultured pearls

sold today come from China. Cultured pearls are the response of the shell to a

tissue implant. A tiny piece of mantle tissue from a donor shell is transplanted

into a recipient shell. This graft will form a pearl sac and the tissue will

precipitate calcium carbonate into this pocket. There are a number of options

for producing cultured pearls: use freshwater or seawater shells, transplant

the graft into the mantle or into the gonad, add a spherical bead or do it nonbeaded.

The majority of saltwater cultured pearls are grown with beads.

E

Regardless of the method used to acquire a pearl, the process usually takes

several years. Mussels must reach a mature age, which can take up t0 3 years,

and then be implanted or naturally receive an irritant. Once the irritant is

in place, it can take up to another 3 years for the pearl to reach its full size.

Often, the irritant may be rejected, the pearl will be terrifically misshapen, or

the oyster may simply die from disease or

countless other complications. By the end

of a 5 t0 10 year cycle, only 50% of the

oysters will have survived. And of the pearls

produced, only approximately 5% are of

substantial quality for top jewelry makers.

From the outset, a pearl fanner can figure

on spending over 0 for every oyster

that is farmed, of which many will produce

nothing or die.

F

Imitation pearls are a different story

altogether. In most cases, a glass bead is

dipped into a solution made from fish

scales. This coating is thin and may

eventually wear off. One can usually

tell an imitation by biting on it. Fake

pearls glide across your teeth, while the

layers of nacre on real pearls feel gritty.

The Island of Mallorca (in Spain) is known for its imitation pearl industry.

Quality natural pearls are very rare jewels. The actual value of a natural pearl

is determined in the same way as it would be for other “precious” gems.

The valuation factors include size, shape, color, quality of surface, orient

and luster. In general, cultured pearls are less valuable than natural pearls,

whereas imitation pearls almost have no value. One way that jewelers can

determine whether a pearl is cultured or natural is to have a gem lab perform

an x-ray of the pearl. If the x-ray reveals a nucleus, the pearl is likely a beadnucleated

saltwater pearl. If no nucleus is present, but irregular and small dark

inner spots indicating a cavity are visible, combined with concentric rings of

organic substance, the pearl is likely a cultured freshwater. Cultured freshwater

pearls can often be confused for natural pearls which present as homogeneous

pictures which continuously darken toward the surface of the pearl. Natural

pearls will often show larger cavities where organic matter has dried out and

decomposed. Although imitation pearls look the part, they do not have the

same weight or smoothness as real pearls, and their luster will also dim greatly.

Among cultured pearls, Akoya pearls from Japan are some of the most lustrous.

A good quality necklace of 40 Akoya pearls measuring 7mm in diameter sells

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