2007. Haythorn's pits for cucumbers and melons (fig. 566.) may be of any convenient length, according to the mode in which they are heated. On the supposition that smoke-flues are employed, the length may be from 30 to 40 ft., and the breadth 13 ft., including the brick path. Each pit has one fire and a flue, which makes three courses, two under the pit (a a), and one along the pathway, to heat the air of the house (b). Over this last flue is a narrow pit or box, in the way of border (c), for holding the earth for the cucumbers or small melons, which are trained to wires suspended from the roof (d). The soil in this border may be increased by laying one or more courses of bricks along its outer curb (e). Steam may be produced by pouring water over the cover of the flue (b); and also, if desirable, under the bed of earth, by introducing water through a pipe with a funnel (k); all the flues being furnished with a course of bricks along the outer edges of the cover, so as to form a trough between them. The mushroom house (g) is a vault between the two pits; and, by means of small openings (i), to be closed at pleasure by bricks, may receive heat from either or both of the pits; but, except in the most severe weather, the warmth incident to its situation will be sufficient for the growth of mushrooms. It may be fitted up with shelves (h) in the usual way; and may also be used for forcing succory, rhubarb, sea kale, winter potatoes, &c.