2022. Where wall-fruit is an object of consideration, the whole of the walls should be flued or cellular, in order that in any wet or cold autumn, the fruit and wood may be ripened by the application of gentle fires, night and day, in the month of September. It is an error to light the fires of hot-walls only in the evenings, the effect of heat in the process of maturation being much greater when accompanied by light. In all hot-walls one precaution must not be neglected, the building in, on the inferior or outer side, small cast-iron doors, or framed stones, which may be opened at pleasure, in order to withdraw the soot. They must be made perfectly air-tight, which is readily accomplished by having double cast-iron doors, in what is called Count Rumford's manner.