Occasionally some plants are fruited in these pits, especially at Kew, but, in general, they are removed to a low house (fig. 15.) of a most economical and judicious construction, and calculated both for the growth of Pines and Vines. This house is fifteen feet wide within walls; the pit (_a_), is nine feet wide; the back path (_b_), forms a border for the roots of the Vines; the pit is surrounded by a flue (_c_, _d_); the curb, or plate is two feet three inches from the glass in front (_e_), and four feet eight inches from it behind (_f_); the Vines are planted in the back border (_b_), and trained under the roof directly over it and over the back flue; and others are planted in the front border (_g_); and trained up the rafters. The length of the houses in the royal gardens at Kensington, varies from thirty-three to fifty feet (fig. 16.): each house has two furnaces, one for constant use, and another for giving an extra supply of heat in very severe weather. The first (_a_), proceeds directly to the front corner (_b_), thence along the front to the opposite end (_c_), then along the back of the pit (_d_, _e_), passing under the back path, or border, and terminating in a chimney (_f_) beside the furnace. [Illustration: 16] The other furnace is placed at the opposite end of the house (_g_); has a short flue under the back path, which conducts it to the back course of the principal flue (at _d_), which it joins, and the smoke of the two fires moves in the same tunnel, (from _d_ to _e_) and passes out by the same chimney. When this second furnace is not in use, its connection with the flue of the first is cut off by a damper at the point of junction (_d_). A very small fire made in this furnace in severe weather, not only adds to the heat of the house by its own power, but by increasing the draught, or rate of burning, of the fire in the other furnace. [Illustration: 17] In addition to the fire heat, a steam apparatus has been lately erected, and the tubes conducted round the houses on the tops of the flues (fig. 15. _d_, _e_); this is found to give a great command of heat, and also to admit of filling the house with vapour at pleasure. The height of the house from the ground to the top of the back wall, is only nine feet (fig. 17.); the rafters of the roof are placed about four feet apart, centre from centre; or about twenty-four sashes are given to every hundred feet; the front sashes (_a_), are only eighteen inches high, and slide past each other; the middle end sash (_b_), also slides; the sill of the door (_c_), and the back path, or border, are on a level with the outer surface of the ground, to admit the easy wheeling in of tan, &c.; the front border (_d_), is raised considerably above it, on account of the wet bottom; the back sheds are low and neat, and the furnaces sunk three feet below the surface (fig. 16, _h_ _h_) to give them a better draught; and this also serves to drain the back border.