| Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher; the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest trees, have unusually low root pressures. If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask: how does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion (the attraction between water molecules) are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken. | |
| 大气压能够支持10米高的水柱，但植物可将水送得更高。美洲红杉就能把水泵到地面以上100多米高的树顶。直到19世纪末，水在树木和其它高大植物中的输 送还是一个谜。一些植物学家假定植物中的活细胞充当了水泵的角色。但许多实验表明细胞都已死亡的植物茎干仍能将水输送到相当可观的高度。对于植物中输送水 的其它解释都基于根压--植物底端的根对水的推动。但根压完全不足以将水推到树顶。况且，最高树木中的松柏只有很低的根压。 如果水不是被泵到高树的树顶，也不是被推到树顶，那么我们会问：它是怎样到达树顶的呢根据目前为人们所接受的内聚压力的理论，水是被拉到上面去的。一株植 物中作用于一个正在升高的水柱之上的拉力来自该植物顶部水的蒸发。由于水从叶子表面丧失，一个负压力，或张力就得以产生。蒸发出去的水被植物里流动的水代 替。这些水形成水柱从植物顶端一直延伸到根部。在任何水样中造成表面张力的力支持着这些不断的水柱。当水被限制在内径很小的管道中时，内聚压力(水分子之 间的相互吸引力)是如此之大以致一支水柱的强度相当于一根直径相同的钢丝的强度。这种内聚压力使得水柱被拉到非常高的地方而不会断裂。 |
| Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest trees, have unusually low root pressures. If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask: how does it get there? According to the currently accepted cohesiontension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion the attraction between water molecules are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken. | |
| da qi ya neng gou zhi chi 10 mi gao de shui zhu, dan zhi wu ke jiang shui song de geng gao. mei zhou hong shan jiu neng ba shui beng dao di mian yi shang 100 duo mi gao de shu ding. zhi dao 19 shi ji mo, shui zai shu mu he qi ta gao da zhi wu zhong de shu song hai shi yi ge mi. yi xie zhi wu xue jia jia ding zhi wu zhong de huo xi bao chong dang le shui beng de jue se. dan xu duo shi yan biao ming xi bao dou yi si wang de zhi wu jing gan reng neng jiang shui shu song dao xiang dang ke guan de gao du. dui yu zhi wu zhong shu song shui de qi ta jie shi dou ji yu gen ya zhi wu di duan di gen dui shui de tui dong. dan gen ya wan quan bu zu yi jiang shui tui dao shu ding. kuang qie, zui gao shu mu zhong de song bai zhi you hen di de gen ya. ru guo shui bu shi bei beng dao gao shu de shu ding, ye bu shi bei tui dao shu ding, na me wo men hui wen: ta shi zen yang dao da shu ding de ne gen ju mu qian wei ren men suo jie shou de nei ju ya li de li lun, shui shi bei la dao shang mian qu de. yi zhu zhi wu zhong zuo yong yu yi ge zheng zai sheng gao de shui zhu zhi shang de la li lai zi gai zhi wu ding bu shui de zheng fa. you yu shui cong ye zi biao mian sang shi, yi ge fu ya li, huo zhang li jiu de yi chan sheng. zheng fa chu qu de shui bei zhi wu li liu dong de shui dai ti. zhei xie shui xing cheng shui zhu cong zhi wu ding duan yi zhi yan shen dao gen bu. zai ren he shui yang zhong zao cheng biao mian zhang li de li zhi chi zhe zhei xie bu duan de shui zhu. dang shui bei xian zhi zai nei jing hen xiao de guan dao zhong shi, nei ju ya li shui fen zi zhi jian de xiang hu xi yin li shi ru ci zhi da yi zhi yi zhi shui zhu de qiang du xiang dang yu yi gen zhi jing xiang tong de gang si de qiang du. zhe zhong nei ju ya li shi de shui zhu bei la dao fei chang gao de di fang er bu hui duan lie. |
| Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest trees, have unusually low root pressures. If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask: how does it get there? According to the currently accepted cohesiontension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion the attraction between water molecules are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken. | |
| dà qì yā néng gòu zhī chí 10 mǐ gāo de shuǐ zhù, dàn zhí wù kě jiāng shuǐ sòng dé gèng gāo. měi zhōu hóng shān jiù néng bǎ shuǐ bèng dào dì miàn yǐ shàng 100 duō mǐ gāo de shù dǐng. zhí dào 19 shì jì mò, shuǐ zài shù mù hé qí tā gāo dà zhí wù zhōng de shū sòng hái shì yí gè mí. yī xiē zhí wù xué jiā jiǎ dìng zhí wù zhōng de huó xì bāo chōng dāng le shuǐ bèng de jué sè. dàn xǔ duō shí yàn biǎo míng xì bāo dōu yǐ sǐ wáng de zhí wù jīng gàn réng néng jiāng shuǐ shū sòng dào xiāng dāng kě guān de gāo dù. duì yú zhí wù zhōng shū sòng shuǐ de qí tā jiě shì dōu jī yú gēn yā zhí wù dǐ duān dì gēn duì shuǐ de tuī dòng. dàn gēn yā wán quán bù zú yǐ jiāng shuǐ tuī dào shù dǐng. kuàng qiě, zuì gāo shù mù zhōng de sōng bǎi zhǐ yǒu hěn dī de gēn yā. rú guǒ shuǐ bú shì bèi bèng dào gāo shù de shù dǐng, yě bú shì bèi tuī dào shù dǐng, nà me wǒ men huì wèn: tā shì zěn yàng dào dá shù dǐng de ne gēn jù mù qián wéi rén men suǒ jiē shòu de nèi jù yā lì de lǐ lùn, shuǐ shì bèi lā dào shàng miàn qù de. yī zhū zhí wù zhōng zuò yòng yú yí gè zhèng zài shēng gāo de shuǐ zhù zhī shàng de lā lì lái zì gāi zhí wù dǐng bù shuǐ de zhēng fā. yóu yú shuǐ cóng yè zi biǎo miàn sàng shī, yí gè fù yā lì, huò zhāng lì jiù dé yǐ chǎn shēng. zhēng fā chū qù de shuǐ bèi zhí wù lǐ liú dòng de shuǐ dài tì. zhèi xiē shuǐ xíng chéng shuǐ zhù cóng zhí wù dǐng duān yī zhí yán shēn dào gēn bù. zài rèn hé shuǐ yàng zhōng zào chéng biǎo miàn zhāng lì de lì zhī chí zhe zhèi xiē bù duàn de shuǐ zhù. dāng shuǐ bèi xiàn zhì zài nèi jìng hěn xiǎo de guǎn dào zhōng shí, nèi jù yā lì shuǐ fèn zi zhī jiān de xiāng hù xī yǐn lì shì rú cǐ zhī dà yǐ zhì yī zhī shuǐ zhù de qiáng dù xiāng dāng yú yī gēn zhí jìng xiāng tóng de gāng sī de qiáng dù. zhè zhǒng nèi jù yā lì shǐ de shuǐ zhù bèi lā dào fēi cháng gāo de dì fāng ér bú huì duàn liè. |
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