植物界中有这样一类植物，它们的茎是细长而柔软的．不能直立，而要缠绕在其它物体上才能向上生长。如牵牛、菜豆、忍冬等，就是缠绕植物。缠绕植物的茎为什么会具有缠绕本领呢？著名博物学家达尔文很早就注意到这个问题。他找到了～种叫做蛇麻草的植物，并且把它栽种在家里， There are such plants in the plant kingdom. Their stems are slender and soft. Can not stand upright, but must be wrapped around other objects to grow upward. Such as cows, beans, honeysuckle, etc., is winding plants. Why does the stem of a winding plant have winding power? Darwin, a famous naturalist, noticed this problem very early. He found a plant called hop and planted it at home.