2054. To ascertain the principles of action, it is always necessary to begin by considering the end in view. The object or end of plant-houses is to form habitations for vegetables, and either for such exotic plants as will not grow in the open air of the country where the habitation is to be erected, or for such indigenous or acclimated plants as it is desired to force or excite into a state of vegetation, or accelerate their maturation at extraordinary seasons. The former description are generally denominated greenhouses or botanic stoves, in which the object is to imitate the native climate and soil of the plants cultivated; the latter comprehend forcing-houses and culinary stoves, in which the object is, in the first case, to form an exciting climate and soil, on general principles; and in the second, to imitate particular climates. The chief agents of vegetable life and growth are heat, light, air, soil, and water; and the merit of artificial climates consists in the perfection with which these are supplied.