2146. It has long been a desideratum in hothouse culture to combine heating with ventilation, or, in other words, to produce an agitation of warm air in plant-houses, in imitation of the natural movement of the wind in the open air. The principal difficulty in effecting this has been to find a means of warming the air before it is admitted into the house; as though ventilation or a current of air through a plant-house is easily obtained by opening the sashes at the lowest part in front, and at the highest part of the roof, the air admitted being that of the atmosphere is necessarily colder than that of the house; and of course, if not warmed, it will produce a chilling effect upon the plants.
