Read it through once

This curious contrivance is only a development of a very common arrangement. In most leaves you will find that rainwater is intended to run in a particular direction. There are little grooves and canals down which it is supposed to go, and dry, thirsty hairs may be found so arranged as to intercept part of it. Thus in summer the plants are not confined entirely to the water from the ground, but are also refreshed by the rain from above.