双语有声阅读：沙漠中的植物
时间：2019-02-25 作者：英语课 分类：双语有声阅读
英语课
Plants in the Deserts
Some cacti 1, like the saguaro, grow to tree size, but true trees need more moisture than most desert environments can supply, so they are scarce on deserts. Close to streambeds, cottonwoods can sometimes be found. Though these streams are dry most of the year, water flows there longest and is usually available fairly close to the surface. Elsewhere, trees must send taproots deep into the hard baked desert soil to draw on underground water. Perhaps the most widespread family of trees on the world's deserts is the acacia, whose taproots drill down as far as 25 feet (7. 5 meters). The mesquite common on North American deserts in both tree and shrub 2 forms,does not begin to grow above ground until its root system is completely developed, ensuring the plant a supply of moisture. The roots of shrubs 3 and trees help to hold the desert soil in place. Their stalks and branches also act as screens to keep the wind from sweeping 4 great drifts of sand along the surface. These services are vital if a desert is to support life. Scientists estimate that a desert needs year round plant cover over 20 to 40 percent of its surface. If shrubs are too far apart-separated by a distance greater than five times their height - soil around them is likely to blow away. Without the shelter of established shrubs, new seedlings 5 will have difficulty in getting a start.
On the other hand, plants that are too close together may compete for underground moisture. To protect themselves from this competition some shrubs give off a substance that kills young plants that sprout 6 too close to them. In addition to a few varieties of trees and tough shrubs, most deserts have grasses, herbs, and other annual plants. These do not compete for moisture with the longer lived growth. They spring up quickly after rains, when the surface is moist. Then, for a brief time, the desert can be literally 7 carpeted with color. Almost as quickly as they appeared,these small plants die away. But they have developed special ways of ensuring the life of another generation when rains come again.
Some cacti 1, like the saguaro, grow to tree size, but true trees need more moisture than most desert environments can supply, so they are scarce on deserts. Close to streambeds, cottonwoods can sometimes be found. Though these streams are dry most of the year, water flows there longest and is usually available fairly close to the surface. Elsewhere, trees must send taproots deep into the hard baked desert soil to draw on underground water. Perhaps the most widespread family of trees on the world's deserts is the acacia, whose taproots drill down as far as 25 feet (7. 5 meters). The mesquite common on North American deserts in both tree and shrub 2 forms,does not begin to grow above ground until its root system is completely developed, ensuring the plant a supply of moisture. The roots of shrubs 3 and trees help to hold the desert soil in place. Their stalks and branches also act as screens to keep the wind from sweeping 4 great drifts of sand along the surface. These services are vital if a desert is to support life. Scientists estimate that a desert needs year round plant cover over 20 to 40 percent of its surface. If shrubs are too far apart-separated by a distance greater than five times their height - soil around them is likely to blow away. Without the shelter of established shrubs, new seedlings 5 will have difficulty in getting a start.
On the other hand, plants that are too close together may compete for underground moisture. To protect themselves from this competition some shrubs give off a substance that kills young plants that sprout 6 too close to them. In addition to a few varieties of trees and tough shrubs, most deserts have grasses, herbs, and other annual plants. These do not compete for moisture with the longer lived growth. They spring up quickly after rains, when the surface is moist. Then, for a brief time, the desert can be literally 7 carpeted with color. Almost as quickly as they appeared,these small plants die away. But they have developed special ways of ensuring the life of another generation when rains come again.
n.（复）仙人掌
- There we could see nothing but cacti.那里除了仙人掌我们什么也看不到。
- Cacti can survive the lack of rainfall in the desert.仙人掌在降水稀少的沙漠中也能生存下去。
n.灌木，灌木丛
- There is a small evergreen shrub on the hillside.山腰上有一小块常绿灌木丛。
- Moving a shrub is best done in early spring.移植灌木最好是在初春的时候。
灌木( shrub的名词复数 )
- The gardener spent a complete morning in trimming those two shrubs. 园丁花了整个上午的时间修剪那两处灌木林。
- These shrubs will need more light to produce flowering shoots. 这些灌木需要更多的光照才能抽出开花的新枝。
adj.范围广大的，一扫无遗的
- The citizens voted for sweeping reforms.公民投票支持全面的改革。
- Can you hear the wind sweeping through the branches?你能听到风掠过树枝的声音吗？
n.刚出芽的幼苗( seedling的名词复数 )
- Ninety-five per cent of the new seedlings have survived. 新栽的树苗95%都已成活。 来自《现代汉英综合大词典》
- In such wet weather we must prevent the seedlings from rotting. 这样的阴雨天要防止烂秧。 来自《现代汉英综合大词典》
n.芽，萌芽；vt.使发芽，摘去芽；vi.长芽，抽条
- When do deer first sprout horns?鹿在多大的时候开始长出角？
- It takes about a week for the seeds to sprout.这些种子大约要一周后才会发芽。