也叫“水肺”，海参类动物的呼吸器官。由消化管末端的一部分伸入体腔，然后在体腔中不断分支，形成树枝状，因而叫做“呼吸树”。除有呼吸作用外、还有排泄功能。
凉爽的晨风吹拂着他们的脸颊，每一次呼吸肺里都充满了纵树的芳香。
A cool morning breeze fanned their cheeks, and the spicy fragrance from the fir-trees filled their lungs with every breath.
大约需要7到8棵树产生足够一个人呼吸一年的氧气。
It takes about 7 to 8 trees to make enough O2 for one person to breathe for a year.
因为自己没有叶绿体，它们无法合成呼吸需要的某种细胞，因此它们依赖树的能力去完成。
Having no chloroplasts of their own, the fungi cannot synthesize the precursors of respiration, and so they piggyback on the trees' ability to do this.
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