506. Houses for the protection of plants are of various kinds; some merely useful, and others useful and ornamental; some for plants from climates only a little warmer than our own, and which, consequently, require no means of heating, as they are only necessary to protect the plants they contain from severe frosts, and from the excessive damps of our climate; others, which require to give a little warmth, as well as shelter, to the plants placed in them; and others, which are intended for the plants of tropical climates, which must be provided with the means of equalling the heat and moisture of climates of that kind. In the present work, attention will he principally paid to those houses which are intended for ornamental plants, as the houses for growing and forcing fruits have been already amply described in the twin work called The Horticulturist.