A bright, dry day晴朗乾燥的一天
Watch one bead travel from a root to a leaf. Then look for the vapor above the tree.
盯著一顆珠子，看它從根走到葉子。再找找樹上方的水氣。
Living Things · Unit 2 · Lesson 7 · 生命與生態 單元二 第七課
How Does Water Reach the Top of a Tree?水怎麼爬到樹頂？
A tall tree lifts water higher than a ten-story building, every day, without a pump and without a heart. In a 3D model, watch a thread of water run from the roots to the leaves, and find out what is doing the lifting. Turn off the sun, dry out the soil, or fill the air with mist, and see the flow slow down or stop. Last, compare some real trees with the highest that sucking alone can ever raise water.
一棵大樹每天都把水送到比十層樓還高的地方，沒有幫浦，也沒有心臟。在 3D 模型裡，看一條水柱從根一路通到葉子，找出到底是誰在出力。把太陽關掉、讓土乾掉，或是讓空氣充滿水氣，看水流怎麼變慢、甚至停下來。最後拿幾棵真的樹，和「只靠吸」最多能把水抬到的高度比一比。
Big idea · 一句話看懂
A tree has no heart to push water up. The water is pulled up from the top. Water evaporates out of the leaves through tiny pores, and each bit that leaves pulls the next bit up behind it, because water clings to itself. The pull reaches all the way down the trunk to the roots, through very narrow tubes. The sunnier and drier the day, the harder the leaves pull.
樹沒有心臟可以把水往上推。水是從上面被拉上去的。水從葉子上很小的孔蒸發出去，每離開一點，就把後面的那一點往上拉，因為水會緊緊黏住自己。這股拉力沿著樹幹一路傳到根，走的是非常細的管子。天氣愈晴朗、愈乾燥，葉子拉得就愈用力。
3D Model · 3D 模型
Pulled Up from the Top 從上面拉上來
Drag to turn the model, and scroll or pinch to zoom. The blue beads are water, and you can see through the trunk. First watch where the water goes when it reaches the leaves. Then slide Sunlight down to zero. What happens to the beads? Bring the sun back, and try very damp air, and then very dry soil. Each one slows the water for a different reason.
拖曳可以旋轉模型，滾輪或雙指可以縮放。藍色的珠子是水，樹幹畫成透明的，讓你看得到裡面。先看水到了葉子之後去了哪裡。接著把「陽光」拉到零，珠子怎麼了？把太陽加回來，再試試很潮溼的空氣，然後是很乾的土。每一種都會讓水慢下來，但是原因各不相同。
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
This 3D model needs WebGL, which this browser does not support. The reading and the cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的課文與卡片一樣能看懂。
- Blue beads: water, moving as one chain
藍色的珠子：水，連成一條鏈子在走 - Pale dots: water vapor leaving the leaves
淡色的小點：離開葉子的水氣 - Green: the leaves, which turn yellowish when the tree is short of water
綠色：葉子；樹缺水的時候會偏黃 - Brown: the trunk, branches, and roots, drawn see-through
咖啡色：樹幹、樹枝和根，畫成透明的
A teaching model. A real trunk holds a huge number of very narrow tubes, and the model draws three thick ones. The percentages on the sliders and the speed of the water are examples. Real water in a tree moves much more slowly than the beads do. The model also leaves out the small push that roots can give from below.
這是教學用的模型。真的樹幹裡有數量極多、非常細的管子；模型只畫了三條粗的。滑桿上的百分比和水的速度都是示意，真的樹裡的水走得比這些珠子慢得多。根從下面能給的那一點點推力，模型也沒有畫。
Model drawn by My Culture Connect as a teaching diagram. The ideas follow the sources listed at the bottom of this page. · 模型由人師教育協會自繪示意；原理依本頁最下方列出的出處。
Reading · 英文閱讀
7
Unit 7: How Does Water Reach the Top of a Tree?
Stand under a tall tree and look up. Every leaf at the top needs water, and all of that water came in through the roots, far below your feet. Your heart pumps blood around your body. A tree has no heart. So how does the water get up there?
站在一棵大樹下往上看。樹頂的每一片葉子都需要水，而這些水全都是從你腳底下很深的根吸進來的。你的心臟把血液打到全身；樹沒有心臟。那麼水是怎麼上去的？
You might guess that the tree sucks it up, the way you drink through a straw. But sucking has a limit. Hundreds of years ago, people who built pumps found that suction could not raise water more than about ten meters, however hard they tried. Many trees are much taller than that.
你可能會猜：樹是把水吸上去的，就像你用吸管喝飲料一樣。可是「吸」有極限。幾百年前，做抽水機的人就發現，不管怎麼努力，靠吸的最多只能把水抬高大約十公尺。很多樹比這高得多。
The answer starts in the leaves. A leaf is covered with tiny pores. They open in the daytime to let in the gas the leaf needs for making food. While they are open, water inside the leaf evaporates and drifts out into the air.
答案要從葉子說起。葉子上佈滿了很小的孔。這些孔在白天打開，讓葉子做食物所需要的氣體進來。孔開著的時候，葉子裡的水就蒸發，飄到空氣裡去。
Here is the important part. Water clings to itself very strongly. Inside a tree the water fills very narrow tubes, and it forms one unbroken column from the leaves all the way down to the roots. When a little water leaves at the top, it pulls the whole column up behind it, like a chain being drawn up through a pipe.
接下來是關鍵。水會非常緊地黏住自己。在樹裡面，水裝在非常細的管子裡，從葉子到根連成一條不斷的水柱。上面走掉一點水，整條水柱就被往上拉，像一條鏈子從管子裡被拉上去一樣。
So the tree does not spend energy to lift the water. The sun and the air do the work by drying the leaves. On a bright, dry day the pull is strong. On a damp day it is weak, and at night it nearly stops.
所以樹並沒有花力氣把水抬上去。出力的是太陽和空氣：它們把葉子弄乾。晴朗乾燥的日子，拉力很強；潮溼的日子拉力弱；到了晚上，幾乎就停了。
A tree uses only a tiny part of this water to grow. Nearly all of it, from 97 to more than 99 parts in every hundred, passes straight through and out into the air. That may sound like waste, but the stream carries minerals up from the soil, and the evaporation cools the leaves.
這些水，樹只用掉極小的一部分來生長。幾乎全部——每一百份裡有 97 份到 99 份以上——都只是穿過樹身，散到空氣裡去。聽起來很浪費，不過這股水流把礦物質從土裡帶了上來，而蒸發也讓葉子降溫。
Read aloud · 課文朗讀
Questions · 閱讀理解
Why can a tree not simply suck water up, like a straw?
Suction cannot raise water more than about ten meters, and many trees are much taller than that.
What happens to water when it reaches the leaves?
It evaporates and drifts out into the air through tiny pores.
Why does the water in a tree move as one column?
Water clings to itself very strongly, so when a little leaves at the top, it pulls the rest up behind it.
Words & Phrases · 生字及片語
tree(n.)樹The tree is taller than our school.這棵樹比我們學校還高。trunk(n.)樹幹Water rises through the trunk.水沿著樹幹往上走。branch(n.)樹枝A bird sat on a high branch.一隻鳥停在高高的樹枝上。straw(n.)吸管She drank the juice through a straw.她用吸管喝果汁。evaporate(v.)蒸發Water evaporates from the leaves.水從葉子上蒸發。pull(v. / n.)拉；拉力The leaves pull the water up.葉子把水往上拉。tube(n.)管子The trunk is full of thin tubes.樹幹裡滿是細細的管子。damp(adj.)潮溼的Clothes dry slowly on a damp day.潮溼的日子，衣服乾得慢。
Quick Check · 小測驗
1. What moves water up a tree?
2. Where does most of the water go after it reaches the leaves?
3. Why does the water move as one unbroken column?
4. When does water rise fastest in a tree?
5. What does a tree do when the soil dries out?
How High? · 有多高？
Taller than any straw 比任何吸管都高
The blue bar is ten meters, about the highest that suction alone can raise water. Choose a tree and compare.
藍色的那一條是十公尺，大約是「只靠吸」能把水抬到的最高高度。選一棵樹來比一比。
Choose a tree · 選一棵樹
Suction works by letting the air outside push the water up, and the air can only push so hard. A tree gets past this limit because its water is pulled from above as an unbroken column.「吸」其實是讓外面的空氣把水推上來，而空氣能推的力氣有限。樹能越過這個極限，是因為它的水是連成一條不斷的水柱，從上面被拉上去的。
This tree is · 這棵樹的高度是
×
the height that suction alone can lift water, at tall · 「只靠吸」能把水抬高的高度的這麼多倍
Try It in the Model · 在模型裡試試
Four kinds of weather 四種天氣
In every case the beads stay evenly spaced. If the column of water ever broke, the leaves above the break would have nothing to pull on.
不管哪一種情況，珠子之間的距離都一樣。水柱要是斷了，斷口上面的葉子就沒有東西可以拉了。
Night夜晚
The beads stop, but the column is still whole. It is ready to move again at sunrise.
珠子停了，不過水柱還是完整的，等太陽出來就能再動。
A misty day起霧的日子
The sun is up and the pores are open, and still the water barely moves. Why?
太陽出來了，氣孔也開著，水卻幾乎不動。為什麼？
No rain for weeks好幾個星期沒下雨
Look at the color of the leaves and the soil. The tree has shut its pores to hold on to its water.
看看葉子和土的顏色。樹把氣孔關上了，好留住水分。
Go Further · 延伸閱讀
The pores, and where the water goes 氣孔，還有水的去向
Living Things · Lesson 2 · 生命與生態 第二課How Does a Leaf Make Food from Sunlight?葉子怎麼用陽光做出食物？See the same pores at work, letting in the gas the leaf needs.看同樣的氣孔在工作：讓葉子需要的氣體進來。Go to the lesson · 前往這一課 →Earth and Weather · Lesson 6 · 地球與天氣 第六課Why Does It Rain?為什麼會下雨？Follow the water vapor after it leaves the tree.跟著離開樹的水氣，看它接下來去哪裡。Go to the lesson · 前往這一課 →
Trees by the Numbers · 樹的數字
Six numbers about water in trees 六個和樹裡的水有關的數字
How high, how much, and since when we have known.
多高、多少，還有人類是什麼時候知道的。
10 mthe limit of suction · 吸力的極限
A suction pump cannot raise water higher than about this.抽水機用吸的，最多只能把水抬到大約這個高度。
116 mtallest known · 已知最高
The tallest known living tree, a coast redwood in California, is about this tall.已知最高的活樹是美國加州的一棵海岸紅杉，大約這麼高。
84.1 min Taiwan · 在台灣
The tallest tree known in Taiwan, a Taiwania confirmed in 2023.台灣已知最高的樹：一棵 2023 年確認的台灣杉。
97–99.5%passes through · 只是路過
This share of the water a plant takes up is lost to the air. Only a little is used for growth.植物吸進來的水，有這麼高的比例散到空氣裡去，只有一點點用來生長。
0energy spent · 花的力氣
Moving water up through the tubes costs the plant no energy. The tubes are made of dead cells.水沿著管子往上走，植物不必花能量。這些管子是死掉的細胞構成的。
1894the year · 年
John Joly and Henry Dixon proposed that water is pulled up as an unbroken column.喬利和狄克森提出：水是連成一條不斷的水柱被拉上去的。
Tree Stories · 樹的故事
A stubborn pump, a careful vicar, drops at dawn, and a sword that touches the sky 不聽話的抽水機、細心的牧師、清晨的水珠，還有一把倚天劍
How people worked out what trees were doing all along.
人們是怎麼弄懂樹一直在做的這件事的。
1600s · 十七世紀
The pump that would not go higher再也抽不上去的抽水機
People who built pumps in Italy had a problem. A suction pump could not raise water more than about ten meters, no matter how it was built. Galileo wrote about the puzzle, and his student Evangelista Torricelli solved it. The pump does not pull the water. The air outside pushes it, and the air has only so much weight. Trees, it turned out, must be doing something else.
義大利造抽水機的人遇到一個難題：用吸的抽水機，不管怎麼造，都沒辦法把水抬高超過大約十公尺。伽利略寫下了這個謎題，他的學生托里切利解開了它：抽水機並沒有在「拉」水，是外面的空氣把水「推」上來的，而空氣的重量就只有那麼多。這麼說來，樹一定是用了別的辦法。
1727
The vicar who weighed plants替植物秤重的牧師
Stephen Hales was an English clergyman who loved to measure things. In a book published in 1727 he described his experiments on plants. He compared how much water a plant took in with how much it gave off through its leaves, and his numbers showed water passing through the plant and out into the air.
海爾斯是一位熱愛測量的英國牧師。在 1727 年出版的書裡，他記錄了自己對植物做的實驗：比較一株植物吸進多少水、又從葉子散出去多少水，他的數字顯示：水穿過植物，散到了空氣裡。
Dawn · 清晨
Drops on the tips of leaves葉尖上的水珠
Roots can also push a little. At night, when the leaves are not pulling, the roots of some plants go on taking in water, and the pressure builds from below. By morning it forces drops of sap out at the tips or edges of the leaves. They look like dew, but they came from inside the plant. This push is much too weak to supply a tall tree.
根也會推一點點。夜裡葉子不拉水的時候，有些植物的根還是繼續吸水，壓力從下面慢慢累積；到了早上，就把一滴一滴的汁液從葉尖或葉緣擠出來。它們看起來像露水，其實是從植物裡面出來的。這股推力太弱，供應不了一棵大樹。
Taiwan · 台灣
The tree that touches the sky倚天而立的樹
In January 2023, a team from the Taiwan Forestry Research Institute and National Cheng Kung University walked for days into the mountains of the upper Da'an River. They had picked out one treetop from laser maps made from the air. They climbed the tree and measured it at 84.1 meters, the tallest tree known in Taiwan and in East Asia. It is a Taiwania. Because it stands out above the giants around it, the team named it the Da'an River Yitian Sword. Every drop of water at its top has been pulled up the whole way.
2023 年 1 月，林業試驗所和成功大學組成的團隊，在大安溪上游的山區走了好幾天。他們事先從空中雷射測繪的資料裡，挑出了一個特別高的樹頂。隊員爬上那棵樹實地測量，結果是 84.1 公尺——台灣、也是東亞已知最高的樹。它是一棵台灣杉；因為它在周圍眾多巨木當中特別挺拔，團隊把它取名為「大安溪倚天劍」。它樹頂的每一滴水，都是這樣一路被拉上去的。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Trees suck water up like a straw.樹像吸管一樣把水吸上去。
✓ Fact · 事實Suction stops at about ten meters. The water is pulled up as a column, by evaporation from the leaves.用吸的只到大約十公尺。水是連成一條水柱，被葉子上的蒸發拉上去的。
✗ Myth · 迷思The roots pump the water to the top.是根把水打到樹頂的。
✓ Fact · 事實Roots can push only a little. Almost all of the lifting comes from the pull at the leaves.根只能推一點點。幾乎所有的力氣，都來自葉子那一端的拉力。
✗ Myth · 迷思A tree uses up all the water it drinks.樹把喝進去的水都用掉了。
✓ Fact · 事實It keeps only a tiny part. Nearly all of the water passes through and into the air.它只留下極小的一部分；幾乎所有的水都只是穿過樹身，散到空氣裡。
✗ Myth · 迷思Water rises in a tree at the same speed all day.樹裡的水整天都以同樣的速度上升。
✓ Fact · 事實It rises fastest on bright, dry days and nearly stops at night, when the pores are shut.晴朗乾燥的時候最快；到了晚上氣孔關上，就幾乎停了。
Remember It · 記憶口訣
The climb in a sentence 一句話記住水怎麼往上
No heart, no pump沒有心臟，沒有幫浦
The tree spends no energy on lifting.
樹不花力氣把水抬上去。
Pulled from the top從上面拉
Water evaporates from the leaves.
水從葉子蒸發出去。
Water clings to water水黏著水
So the whole column follows.
所以整條水柱都跟上來。
The weather sets the speed天氣決定速度
Sun and dry air pull hardest.
太陽和乾燥的空氣拉得最用力。
Classroom Activity 1 · 課堂活動一
A Bag on a Branch 套在樹枝上的袋子
You need · 準備材料
- A clear plastic bag and a piece of string一個透明的塑膠袋和一段繩子
- A leafy branch on a living tree or bush, in the sun一根長在活的樹或灌木上、曬得到太陽、葉子多的枝條
Steps · 步驟
- Slip the bag over the end of the branch so that several leaves are inside. Do not break the branch.把袋子套在枝條的末端，讓幾片葉子在袋子裡。不要把樹枝折斷。
- Tie the mouth of the bag gently around the stem.把袋口輕輕綁在枝條上。
- Look at the bag after one hour, and again after three hours. What do you see on the inside?一小時後看看袋子，三小時後再看一次。袋子裡面出現了什麼？
- Try a second bag on a branch in the shade. Which bag collects more?在陰影裡的枝條上再套一個袋子。哪一個袋子收集到的比較多？
The drops are water that came up from the roots and out through the leaves. Take the bag off on the same day, so that the leaves are not harmed.
那些水珠是從根上來、再從葉子散出去的水。當天就把袋子拿下來，免得傷到葉子。
Classroom Activity 2 · 課堂活動二
Celery and Colored Water 芹菜和有顏色的水
You need · 準備材料
- A stalk of celery with its leaves, or a white flower一根帶葉子的芹菜，或一朵白色的花
- A glass of water with food coloring in it一杯加了食用色素的水
Steps · 步驟
- Ask an adult to cut the bottom off the stalk, and stand it in the colored water.請大人把芹菜的底部切掉一小段，然後把芹菜插在有顏色的水裡。
- Leave it in a bright place. Look at the leaves after a few hours, and again the next day.放在明亮的地方。幾小時後看看葉子，隔天再看一次。
- Ask the adult to cut across the stalk. Where exactly is the color?請大人把芹菜橫切開。顏色到底在哪裡？
- Set up a second stalk in a dark cupboard. Does the color travel as fast?再準備一根，放在暗的櫃子裡。顏色走得一樣快嗎？
The colored dots in the cut stalk are the tubes that carry water. Do not eat the celery afterward.
切面上那些有顏色的小點，就是運水的管子。做完之後這根芹菜不要吃。
Sources · 資料出處
Facts and numbers on this page were checked against these sources (October 2026). · 本頁的事實與數字依下列資料查證（2026 年 10 月）。
- Transpiration is the movement of water through a plant and its evaporation from leaves, stems, and flowers; it is a passive process that requires no energy expense by the plant; it cools plants and carries mineral nutrients; of the water taken up, 97–99.5% is lost by transpiration and guttation; plants close their stomata to reduce water loss when uptake by the roots is less than the loss蒸散是水在植物體內移動並從葉、莖、花蒸發的過程；是被動的，植物不需耗能；能讓植物降溫並帶動礦物養分的輸送；吸收的水有 97–99.5% 經蒸散與泌溢散失；根吸水不足時植物會關閉氣孔減少失水Wikipedia, “Transpiration” ↗
- The tubes of the xylem are dead at maturity and transport is passive; evaporation from the leaf cells creates a tension that pulls water up from the roots; the vessels must be very narrow or the water column would break; when the soil is dry a bubble can form and block the tube; the cohesion-tension theory was proposed in 1894 by John Joly and Henry Horatio Dixon; water transport is considered to limit the maximum height of trees木質部的管狀細胞成熟後是死細胞，輸水是被動的；葉肉細胞表面的蒸發造成張力，把水從根部拉上來；導管必須很細，否則水柱會斷；土壤乾燥時可能產生氣泡堵塞（栓塞）；內聚力—張力學說由喬利與狄克森於 1894 年提出；一般認為輸水的難度限制了樹的最大高度Wikipedia, “Xylem” ↗
- Most plants need their stomata open in the daytime; water vapor leaves the leaf through the stomata多數植物的氣孔在白天打開；水氣經由氣孔離開葉子Wikipedia, “Stoma” ↗
- A suction pump could raise water only to a height of about 10 meters, a problem recounted by Galileo and resolved by Torricelli's work on the pressure of the air抽水機用吸的只能把水抬高約 10 公尺；伽利略記述過這個難題，托里切利關於大氣壓力的研究解開了它Wikipedia, “Evangelista Torricelli” ↗
- Stephen Hales's Vegetable Staticks (1727) describes experiments comparing the water taken in by a plant with the water leaving through its leaves海爾斯《植物靜力學》（1727）記錄了比較植物吸水量與葉片散失水量的實驗Wikipedia, “Stephen Hales” ↗
- At night in some plants, root pressure forces drops of sap out at the tips or edges of leaves; when transpiration is high the sap is under tension instead有些植物夜間因根壓而從葉尖或葉緣泌出汁液（泌溢）；蒸散旺盛時，木質部汁液處於張力之下Wikipedia, “Root pressure” ↗
- Hyperion, a coast redwood in California, is the world's tallest known living tree, at about 116 meters美國加州的海岸紅杉「亥伯龍」是已知最高的活樹，約 116 公尺Wikipedia, “Hyperion (tree)” ↗
- A team from the Taiwan Forestry Research Institute and National Cheng Kung University confirmed a Taiwania in the upper Da'an River valley at 84.1 meters, the tallest tree recorded in Taiwan and in East Asia, and named it Da'an River Yitian Sword (reported January 30, 2023)林業試驗所與成功大學組成的「找樹的人」團隊，在大安溪上游確認一棵高 84.1 公尺的台灣杉，創下台灣及東亞最高樹紀錄，取名「大安溪倚天劍」（2023 年 1 月 30 日報導）公視新聞網〈84.1公尺台灣杉「大安溪倚天劍」 創東亞最高樹紀錄〉 PTS News ↗