Bottom heat, secured by manure in the heating stage, or by hot water or steam, is much used by professional gardeners, and to less extent by amateurs for starting subtropical plants, such as tomato, pepper, egg-plant, and subtropical flowers. After potting, the plants are set in flats and gradually hardened for outdoor planting. As the hot-bed and cold-frame are used also for cuttings, their structure will be given in the chapter devoted to growing plants from cuttings (65. The Hot-bed).