The floor may be of paving tiles, or bricks, laid on concrete: a skylight or two may be fixed in the roof, for the purpose of admitting a little light, and air when necessary. The engraving (fig. 2), shows a house of this description, 12 feet wide by 20 feet long, inside measure, but, of course, the length may be extended as circumstances may require. As it is of importance in mushroom-growing that the air of the house should be kept moderately moist, the underside of a slate or tile roof should be lathed and plastered. [Illustration: Fig. 3. View of unheated mushroom-house.] [Illustration: Fig. 4. Section of preceding figure.] Figure 3 represents a mushroom-house suitable for people of small means, or those who cannot adopt plan No. 1. It is designed with a view to growing mushrooms during the greater part of the year, without the aid of artificial heat. To this end it is constructed in such a way as not to be affected by changes of the external temperature, as will be seen by the engraving. The walls are hollow, and banked round with the soil excavated from the interior. The roof is thatched with reeds, and the ends stud-work, lined inside with boards, and outside with split larch poles: the cavity to be filled with sawdust or cut straw; a small diamond-shaped ventilator, hung on pivots, to be fixed in each end. The floor may be of concrete, or burnt clay well rammed; and the beds are retained in their place by boards nailed to good oak posts. Care should be taken to put in efficient drains, so that no stagnant damp may exist about the building. [Illustration: Fig. 5. Section of mushroom-house at Frogmore.] Though the preceding cuts show how we may best attain our object, a few more illustrations of mushroom-houses are desirable here. Figures 5 and 6 exhibit the plan of the mushroom-houses at Frogmore, obligingly communicated by Mr. Rose. [Illustration: Fig. 6. Ground-plan of mushroom-house at Frogmore.] It need hardly be said that in such large mushroom-houses rhubarb and sea-kale may be easily forced, and barbe de capucin, endive, &c. blanched. A small hot-water apparatus, with a 3-inch flow and return pipe, affords the best means of heating a mushroom-house which is not so situated that it may be heated from the boilers of adjacent hothouses. The best position for the mushroom-house is against a north wall. The usual precautions for guarding against damp walls and floor should be adopted in the case of the mushroom-house, and the walls should be hollow. Forsyth’s mushroom-house is described by the designer in Loudon’s _Gardener’s Magazine_. Fig. 7 is a transverse section, showing the arches under and over the beds, the thoroughfare _a_ is the middle, and the position of the hot-water pipes, _c_; _b_ is an open shed and general workshop, the receptacle of everything requiring protection, and too clumsy to be otherwise housed. [Illustration: Fig. 7. Mushroom-house under shed.]