地球上的万千物种都有自己独特的生存本领和生活习性，下面我们托福阅读训练材料中要给大家介绍的就是种子的休眠。 6 _6 z. B! ^7 x+ Y) X
种子休眠是，有生活力的种子由于内在原因，在适宜的环境条件下仍不能萌发的现象。休眠是植物在长期系统发育过程中获得的一种抵抗不良环境的适应性。具有休眠特性的农作物种子在高温多雨地区可防止穗发芽;某些沙漠植物的种子可以休眠状态度过干旱季节，以待合适的萌发条件。种子休眠的原因可归为两大类：第一类是胚本身的因素造成的，包括胚发育未完成;生理上未成熟;缺少必须的激素或存在抑制萌发的物质。用低温层积、变温处理、干燥、激素处理等方法可解除休眠。第二类是种壳(种皮和果皮等)的限制造成的。包括种壳的机械阻碍、不透水性、不透气性以及种壳中存在抑制萌发的物质等原因。用物理、化学方法破坏种皮或去除种壳即可解除休眠。
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- h' ~. n: a4 D7 m9 A% c Learn about seed dormancy on this Moment of Science.
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$ `4 f- s3 E4 |: I _ A man named William James Beal started an experiment in 1879, which has become the longest-running(持续时间最长的) test of seed dormancy in soil.0 T8 d% ]) u, e, E( e2 J
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Beal buried twenty bottles containing sand and seeds from twenty-one common plants. He buried the bottles eighteen inches underground, (1)uncorked(拔去塞子) to allow in oxygen, and upside down to prevent water from accumulating in the bottles and drowning the seeds. The experiment was designed to test how long these various seeds could survive under virtually natural conditions before they would lose their ability to produce a plant.' |1 B( D4 Y/ }' p; R4 W6 _. |
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Seed dormancy is why some seeds wait for the correct season before they (2)germinate(发芽). They’re (3)programmed to(按程序做事) wait for conditions suitable to the plant’s survival. Seed dormancy is also why weeds are never-ending (4)nuisances(麻烦事，骚扰行为). Weed seeds can (5)lurk(潜伏) underground unseen, and then when you till(耕种) soil to make way for a flower bed, the seeds awaken and before you know it, your flower bed is (6)overrun(泛滥) with the pesky(讨厌的，麻烦的) weeds.
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Most of the seeds in Beal’s experiment were still viable(能养活的) after ten years, but as time passed, fewer and fewer of the seeds would germinate. The fifteenth of Beal’s twenty bottles was dug up in 2000, 120 years after it was buried, and two species were successfully germinated–moth mullein(蛾毛蕊花) and a mallow(锦葵) called cheeses. These are also the same two species that grew from the fourteenth bottle in 1980.- n. {; t, H' t9 \5 b3 N
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The plant that holds the record for the longest dormancy is a lotus(莲花) that was sprouted in 1995 from a seed that radiocarbon(放射性碳素) dating estimated to be a whopping(巨大的) 1300 years old. Now that’s one stubborn seed.* E( V7 P( i; N' X. N, Y5 V; V/ P
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注释：
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(1)uncork
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' o* g G1 u+ g' A( i vt. 泄漏;透露;发泄;拔去塞子2 [) ^2 w$ y* T$ k) W. D* T
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DO NOT uncork the champagne but it may be worth cracking open a beer.
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开香槟庆祝也许为时尚早，不过开瓶啤酒痛饮一番还是值得的。
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" r4 }$ r9 Z/ @7 m2 V* v0 N (2)germinate) b8 c) C: K, f
/ P, G. G2 S7 d# G' T1 W2 }+ O vt. 使发芽;使生长
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; f y) }+ I+ ^, d! l vi. 发芽;生长
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1..I don't know how the idea germinated in my mind.
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. ], ~+ S, o- G3 u- Z 我不知道这个想法在我的头脑中是怎么产生的。3 I+ v# Z8 i: }$ w6 N- G: N- c# X
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2.Seeds germinate in the spring.+ \* w5 R3 b0 V) _' ]
/ }+ D+ y. n3 [8 T 种子在春天发芽。( O9 S( z0 u4 F3 V5 s. h9 m5 P
+ e8 B6 t) E, e m% f5 o1 j$ f! M (3)be programmed to do：编制程序去做 编制程序去做
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programmed to do something：按程序做事4 w( R- z4 w0 Y. ?2 O3 h' b9 Y
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1."Relax", said the night man , "We are programmed to receive.& H& U( o2 Q3 k7 M9 I; C( L
1 i! r" s/ q* m5 L 值夜班的人说，“别紧张，我们只是按程序接待。 |
发表于 2012-8-14 23:21:39
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