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The length of the roots is very great in most of the broom-like, "hedgehog," and other plants. A quite small plant not more than six or eight inches high will have a root as thick as one's thumb. Even at a depth of four or five feet below the surface its root will be as thick as the little finger, so that the root-length is at least twenty times the height of the visible part above ground. These thirsty roots explore the ground in every direction, and go very deep downwards in their search for water.