植物的時空這旅

Sounds like science fiction？ Well， it isn't.

Every year billions of babies are dried and buried， not to be unburied for weeks， months， years or even decades. Don't worry. These are not babies like your little brother or sister； these are baby plants， or as you might call them， seeds. Why would a mom do such a thing？ To answer this question， imagine you are a plant. You have no legs or wings or fins. You can't move from the place where you are rooted. You can't turn on the heat when it gets cold or the air conditioner when it gets hot. If it doesn't rain near you， you can't go get the water from someplace else. Now let's say you're ready to reproduce1）， how could you take care of your babies？ How could you be sure they'd have a good chance at survival？ The answer for mother plants is to pack them up in a special time capsule called a seed.

聽上去像科幻小說？不過這不是。

每年都有數以十億計的小寶寶經過脫水后被埋入地下，此后的數周、數月、數年甚至數十年都在不見天日的地下度過。別擔心，我說的不是像你的弟弟或妹妹那樣的人類寶寶，而是植物寶寶，也許你更習慣叫它們種子。植物媽媽為什么要做這種事呢？要回答這個問題，得先把自己想象成一株植物。沒有腿腳、翅膀，也沒有鰭，你只能扎根在原地不動，天冷了沒法開暖氣，天熱了也沒有空調。如果附近不下雨，你也沒法去別的地方找水。現在假設你已經到了該生兒育女的階段，你怎么照顧自己的小寶寶呢？你怎么確定它們會有良好的存活機會呢？對植物媽媽們來說，解決的辦法就是把孩子們裝入一種特殊的時間膠囊——種子。

How is a seed like a time capsule？

為什么說種子像時間膠囊？

Like a chicken egg， a seed is a package containing the plant embryo2） and food for the baby plant. The package is then covered in a protective hard shell called the seed coat. But unlike chicken eggs， most seeds can remain dormant3） for weeks or years， waiting for the conditions to be right. When the time is right the seed germinates4） and the new plant starts to grow.

與雞蛋類似，一顆種子里面包含著植物的胚胎和供植物幼體消耗的養分，外面還包裹著一層叫做種皮的硬殼，能夠起到保護作用。不過，與雞蛋不同的是，大多數種子都能休眠數周甚至數年，以等待合適的條件生根發芽。當時機來臨，種子就會發芽，長成新的植株。

What conditions do seeds need to start growing？

種子開始生長需要哪些條件？

Sometimes seeds only need water. But other seeds get clues from their environment that tell them the time is right. What kind of clues do seeds need from their surroundings？ Well， that depends on the seed. Seeds of annual plants in the desert wait until it has rained a lot and then germinate. Some seeds on the forest floor wait for a tree to fall and sunlight to hit them. The seeds of the California chaparral5） plants wait for the plants above them to burn. Other seeds need to travel through an animal's gut6） and get scarred7） by the digestive acids in order to germinate.

有時候種子只需要有水就可以生長。但是有些種子需要從外界的環境中獲得某種信號，告訴它們生長時機已到。種子需要從它們周圍的環境中獲得什么樣的信號呢？關于這一點，不同的種子情況不同。生長在沙漠中的一年生植物，其種子要等到大量降雨之后才會發芽。有些落在森林地表的種子需要等待旁邊的大樹倒下，陽光照射到它們的時候才會發芽。加利福尼亞沙巴拉灌木群落里某些植物的種子則要等到野火把原有的植被燒為灰燼后才發芽。還有些種子需要經過動物的消化道，種皮被動物體內的酸性消化液腐蝕后才能發芽。

What kind of information does the seed get from these clues？

種子從這些信號中獲得了什么樣的信息？

These clues let the seed know that it's time to grow. Let's say you're a plant that needs a lot of sunlight to grow well. If you reproduce and spread your seeds all over the forest， a lot of your babies end up underneath other plants where they get too much shade. But remember， a seed is like a time capsule， it can wait， dormant， for a long time. One day the plant that is shading you dies. Light hits you for the first time since you left your mom， and that is the clue you've been waiting for. Now you can germinate， grow big and strong and make new babies of your own.

The seeds of some plants get buried over time. These seeds can't respond to sunlight. They get their clue when the temperature in the soil changes. When the soil warms up， they start growing.

Here's another example. Ever wonder why some seeds won't germinate until after they've been chilled for a few weeks？ This cold temperature is a clue about the time of year. That's right. It tells them it's winter. But why do they need to know when winter has passed？ Well， these plants come from places where the mildest times of the year are spring and fall； these are the times of the year when it's not too cold or too hot. In these places， winters can be so cold that plants die. The seeds need to start growing in the spring so they have enough time to grow up and make their own seeds before winter comes. These seeds won't germinate until it has been cold in the winter and then warm again in the spring.

Sometimes seeds get tricked into growing at the wrong time. For example， when there is long warm spell8） in the middle of winter. They start growing during the warm spell. Then the winter weather returns and the plants die. Other seeds avoid growing at the wrong time by sensing changes in the length of days. In summer days are longer. Days get shorter as the winter approaches. Seeds that need warm weather and longer days will almost always germinate at the right time.

Seeds are actually very amazing time travelers. Just how long they can remain dormant and still germinate is part of an ongoing experiment that began in 1880 by a scientist named William James Beal. This experiment continues even today along with other studies of seeds that show some seeds have been time traveling for even longer—3000 years to be exact.

這些信號讓種子知道，生長的時間到了。假設你是一株需要大量陽光照射才能健康生長的植物，當你開始繁殖并把種子播撒到森林各處，它們中有許多最終會落到其他植物下方，得不到多少光照。不過別忘了，種子就像時間膠囊，可以等待、休眠很長時間。總有一天，擋著你的那棵植物會死去。自從離開母體后，陽光第一次照在你身上，而這就是你一直在等待的信號。現在你可以發芽、茁壯成長并繁育自己的后代了。

有些植物的種子則會隨著時間的推移被漸漸掩埋。這些種子無法對陽光產生反應，它們要從周圍土壤溫度的改變中得到自己的生長信號。當土壤的溫度升高時，它們就會開始生長。

再舉一個例子。有沒有想過為什么有些種子要在受凍幾周后才能發芽呢？低溫是提示季節的信號。沒錯，它讓種子知道自己身處冬季。但是，這些種子為什么需要知道冬季何時結束呢？原因是，在這些植物的產地，一年中氣候最溫和的時期是春季和秋季，這兩個季節正是這一年中既不太冷也不太熱的時候。在這些地區，冬季太過于寒冷，導致這些植物無法存活。因此，它們的種子需要在春天開始生長，以保證在冬季到來前能有足夠的時間成熟結籽。這些種子要經歷寒冷的冬天然后迎來溫暖的春天時才會發芽。

有時，種子也會受騙，在錯誤的時間開始生長。比如，如果冬季持續出現較長時間的小陽春天氣時，就會發生這種情況。種子在小陽春天氣中開始生長，然后隨著冬季回歸、氣溫下降，它們長成的植株就會被凍死。有些種子通過感知白天時長的變化來避免在錯誤的時間生長。夏季白天較長，而當冬季臨近時，白天會縮短。那些需要溫暖天氣和較長日照時間的種子幾乎總能在正確的時間發芽。

種子確實是非常了不起的時間旅行者。一位名叫威廉·詹姆斯·比爾的科學家在1880年開始了一項不間斷的實驗，目的之一就是找出種子在經過多長時間的休眠后仍然可以發芽。這項實驗至今仍在繼續，而同時進行的另外一些對于種子的研究則表明，有些種子已經經歷了比這更久的時間旅行——足足有3000年。

2.embryo [?embri???] n. 【植】胚

3.dormant [?d??（r）m?nt] adj. （指動植物）休眠的

4.germinate [?d???（r）m?ne?t] vi. 萌芽；開始生長（或發育）

5.chaparral [???p??r?l] n. （美國加利福尼亞州南部）沙巴拉群落（由一種能耐干旱及寒冷的灌木植物構成的生態群）

6.gut [ɡ?t] n. 消化道；腸

7.scar [skɑ?（r）] vt. 使結疤；使留下傷痕

8.spell [spel] n. （特定天氣的）一段持續時間