你是否注意到,在晴朗的夜晚,植物会改变叶子的位置。你会看到,羽扁豆(lupinus)的叶子低垂下来,而萝卜的叶则在那里直立着。人们把植物的这种现象叫做感夜运动,或通俗地叫“睡眠”。为什么会出现这种现象,问题争论了十几年。其实,达尔文早就发现,叶子的垂直取向可以保护叶子免在夜间遭受冻害,如果阻止叶子的这种自由运动,霜冻和冷害就容易发生。然而这个发现被后来解释达尔文工作的科学家们强调得过分了。事实上在没有霜冻的地方植物也会发生感夜运动。于是,解释这种现象的许多假说提了出来。最流行的一种认为, Did you notice that on a clear night the plants change the position of the leaves. You will see that the leaves of the lupineus are hanging down, while the leaves of the radish stand upright. People call this phenomenon of plants a sense of nocturnal exercise, or “sleep” in the popular. Why this phenomenon occurs, the issue of controversy for more than a decade. In fact, Darwin has long found that the vertical orientation of the leaves protects the leaves from frost damage at night, and frost and chilling can easily occur if this free movement of the leaves is prevented. However, this finding was over-emphasized by scientists who later explained Darwin’s work. In fact there is no night-time movement of plants in the absence of frost. As a result, many hypotheses explaining this phenomenon have been proposed. The most popular one thinks,