There are a number of plants, however, in temperate regions which have aerial roots. These are chiefly used to give the stem support as it climbs on trees or on walls. They are sometimes called clinging roots. A common example is the climbing poison-ivy (Rhus radicans), the trumpet creeper, etc. Such aerial roots are called _adventitious_ roots. =797. Bracing roots, or prop roots.=—These are developed in a great variety of plants and serve to brace or prop the plant where the fibrous-root system is insufficient to support the heavy shoot system, or the shoot system branches so widely props are needed to hold up the branches. In the common Indian corn several whorls of bracing roots arise from the nodes near the ground and extend outward and downward to the ground, though the upper whorls do not always succeed in reaching the ground. The screw-pine so common in greenhouses affords an excellent example of prop roots. The roots are quite large, and long before the root reaches the soil the large root cap is evident. The banyan tree of India is a classic example of prop roots for supporting the wide-reaching branches. The mangrove in our own subtropical forests of Florida is a nearer example. [Illustration: Fig. 448. Bracing roots of Indian corn.] [Illustration: Fig. 449. Buttresses of silk-cotton tree, Nassau.] =798. Buttresses= are formed at the junction of the root and trunk, and therefore are part root and part stem. Splendid examples of buttresses are formed on the silk-cotton tree. They are sometimes formed on the elm and other trees in low swampy ground. =799. Fleshy roots, or root tubers.=—These are enlargements of the root in the form of tubers, as in the sweet potato, the dahlia, etc. They are storage reservoirs for food. Portions of the roots become thick and fleshy and contain large quantities of sugar, as in the sweet potato, or of _inulin_ (a carbohydrate) in the root tubers of the dahlia and other composites. =800. Water-roots and roots of water plants.=—These are roots which are developed in the water, or in the soil. Water-roots are sometimes formed on land plants where the root comes in contact with a body of water, or a stream. Water-roots usually possess no root hairs, or but a few, as can be seen by comparing water-roots with soil-roots, or by comparing roots of plants grown in water cultures. The greater body of water in contact with the root and the more delicate epidermis of the root render less necessary the root hairs. The duck-meats (Lemna) are good examples of plants having only water-roots. Other aquatic plants like the potamogetons, etc., have true roots which grow into the soil and serve to anchor the plant, but they are not developed as special organs of absorption, since the stem and leaves largely perform this function.