十万个为什么·科学阅读30篇（6）
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How Do Seeds Know When to Start Growing?
种子是如何知道何时开始发芽的？
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Seeds wait for the right mix of water, warmth, and light.种子等待水分、温暖和光照恰到好处的组合。
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A special coat keeps them safe until conditions are just right.一层特殊的种皮在条件适宜前保护它们。
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Inside each seed, hormones watch for signals like longer days or more rain.每颗种子内部，激素会感知日照变长或降雨增多等信号。
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Some seeds need cold weather first, then warmth, to break dormancy.有些种子需先经历低温，再遇温暖，才能打破休眠。
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Others need fire or passing through an animal’s stomach.另一些则需要火烧或经过动物胃部消化。
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Once triggers match, roots push down and shoots reach up.一旦触发条件满足，根向下伸展，芽向上生长。
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Tiny root hairs begin drinking water from the soil at once.细小的根毛立刻开始从土壤中吸收水分。
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This careful timing helps young plants survive their first days.这种精准的时机把握，帮助幼苗度过最初几天。