Plants in Deser Only special_考试试题_职称英语

试题来源：职称英语模拟题-综合类-阅读判断
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Plants in Deser

Only special plants can survive the terribleclimate of a desert, for these are regions where the annual range of the soiltemperature can be over 75℃. Furthermore, during thesummer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drivesmall, sharp particles of sand into the plants, tearing and damaging them. Themost difficult problem for all forms of plant life, however, is the fact thatthe entire annual rainfall occurs during a few days or weeks in spring.

Grasses and flowers in desert survive from oneyear to the next by existing through the long, hot, dry season in the form ofseeds. These seeds remain inactive unless the right amount of rain falls. If norain falls, or if insufficient rain falls, they wait until the next year, oreven still the next. Another factor that helps these plants to survive is thefact that their life cycles are short. By the time that water from the springrains disappears --- just a few weeks after it falls-such plants no longer needany.

The perennials have special features whichenable them to survive as plants for several years. Thus, nearly all desertperennials have extensive root systems below ground and a small shoot systemabove ground. The large root network enables the plant to absorb as much wateras possible in a short time. The small shoot system, on the other hand,considerably limits water loss by evaporation.

Another feature of many desert perennials isthat after the rainy season they lose their leaves in preparation for the long,dry season, just as trees in wetter climates lose theirs in preparation for thewinter. This reduces their water loss by evaporation during the dry season.Then, in next rainy season, they come fully alive once more, and grow newbranches, leaves and flowers, just as the grasses and flowers in desert do.

EXERCISE:

1. Ordinary plants are unable to survive in thedesert mainly because of the changeable weather.