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Let us, for instance, notice some of the ordinary plants to be found along a riverside. Willows and Alders are the ordinary trees, because they are specially fitted to stand the danger of being regularly overflowed. They easily take root, so that branches broken off and floated down are enabled to form new trees without much difficulty. In the United States, it has become a custom to plant Willows along the banks, because they are then not so liable to be broken down and worn away. Yet when a big Willow tree has become undermined, the weight of the trunk may cause it to fall over towards the water, so that a large section of the bank may be loosened and serious damage may be done if it is torn away by a heavy flood.