有些不法分子盗剥名贵植物杜仲的树皮作药材，致使树木死亡，这主要是因为树皮中的什么结构遭到了破坏（   ）

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    Do you like traditional Chinese paper-cutting? Ding Xiang, a student at Nongsishi Middle School in Xinjiang, is really good at it. At the eighth National Excellent Talents Competition last month in Beijing, the 15-year-old girl got the gold award（金奖） for her paper-cutting skills.

    At the competition, Ding cut a piece: Millennium Dream（千年梦想）. The piece has two papers. One shows an ancient cave painting(壁画) and the other a Chinese-made spaceship. The two papers form a sharp contrast（对比）. Ding said she wanted to show three things with the piece: China's long history, China's rapid development, and her hope for the future of paper-cutting. This piece helped Ding walk away with the gold award.

    "I was very surprised to get the award." Ding said in an interview with Yili Daily, a Xingjiang newspaper. "I should thank paper-cutting for bringing me the award."

    All the hard work has paid off. In two years, Ding's skills have improved a lot, and she has the gold award to prove(证明) it.

    Ding said she has learned a lot from paper-cutting. "I have learned to observe things carefully," Ding told Yili Daily. "I have become more confident, too. It is a great help in my studies. Also, I have learned a lot of history from the art."

藻类、苔藓和蕨类植物的共同特征是（　　）

种子萌发所需的环境条件有充足的空气和一定的水分、____ 。