These structures are what we call plant-houses; and they are not only divided into hothouses for tender plants, and greenhouses for half-hardy plants, but subdivided into various kinds to suit the various climates in which plants are found. These climates, however, are not so numerous as might at first be supposed; as it is a curious fact in the history of plants, that many of the most ornamental grow in patches in some parts of the world without being found anywhere else, as, for example, the pelargoniums or shrubby geraniums at the Cape of Good Hope. Even when the same plant is found in different parts of the world, it is generally in the same climate, though in different countries; and thus pines and firs, oaks and birches, spread like belts or zones round the globe, from Asia, through Europe, to America, almost in the same degree of latitude, making an allowance for islands being warmer than continents, and mountains colder than valleys; as you must always remember that knowing the degree of latitude from which a plant comes is not sufficient to teach its culture, unless we know also whether it grows on the mountains or in the valleys, and whether the climate of the locality is moist or dry. A plant will be soon killed by a dry atmosphere, if it requires a moist one; and it will be as much injured by being kept too hot as too cold. Furze and heath will not grow within the tropics; and the first camellias introduced into England were killed by being kept in a hothouse. From what I have said, you will perceive that as plants will only thrive in climates suitable to them, it is not enough to have a hothouse for tropical plants, and a greenhouse for those of moderately warm countries, but that you must have three or four houses imitating different climates, if you wish to grow different kinds of plants to perfection. Philosophers who have written on the subject describe sixteen distinct kinds of climate, including our own; but, as these would be too many to imitate, gardeners are obliged to content themselves with the following kinds of plant-houses and pits. The _dry stove_ is generally kept at a heat of from 70° to 84° in the day, and never allowed to fall below 65° at night, even in winter. It should be placed in a situation sheltered from cold winds, but quite open to the sun; as the plants grown in it require a strong light, most of them being natives of dry sandy plains, on which there is no tree high enough to cast a shade. The plants are grown in pots, which are generally placed on a frame or stage of wooden or stone shelves, so as to have abundance of air around them; and the stove is best heated by flues. The plants suitable for a stove of this kind are some of the kinds of Cactàceæ, such as the genera Melocáctus, Epiphýllum, and Cèreus, with the tender kinds of Euphórbium, Mesembryánthemum, Stapèlia, Crássula, Sèdum, Sempervìvum, and Agàve, and some kinds of bulbs.