12 
CONSTRUCTION OF PLANT-HOUSES. 
really believe the quantity required to be very small) can be sup¬ 
plied without the aid of sliding sashes in the roof, our conclusions 
will be easily arrived at. To render the matter as plain as pos¬ 
sible, we will take the case of both the lean-to and span roof— 
the most usual forms for all purposes. To ventilate the first 
without moving any part of the top, is quite easy, if the back 
wall is independent, that is, does not form the side of another 
building, to its entire height, it can then be effected by means of 
sliding shutters, to cover apertures in the wall corresponding 
with the front sashes. When both of these are open, a current 
of air will pass from the front of the house out at the back, 
sufficient even for heaths, or any other plants. An improve¬ 
ment even on this may be managed by introducing similar air- 
valves in the front walls, beneath the sashes. This height from 
the floor of the inside is the usual position of the pipes or other 
heating apparatus ; and the air, being admitted immediately on 
to them, by contact becomes slightly warmed, before it approaches 
the plants, a matter of some consequence in early growths, whe¬ 
ther of plants or vegetables. In the unusual case of the back 
wall of such a house being occupied, so as to prevent the egress of 
air, the same object may be gained by causing a portion of each 
end to be made moveable : a comparatively small sash, hinged in 
the gable of both ends, has been found to answer all the purposes 
and quite as effectually, as the sliding down of half a dozen or 
more in the roof of the house. In the same manner, the span, 
or double roof may be ventilated: one or both of its gables being 
open, will carry off heated air in the proportion that the fresh 
cold air is admitted by the front lights or shutters ; and thus 
every advantage is gained at much less trouble; and it is evident 
that smaller timbers and fewer of them will suffice, to the great 
improvement of the stock to be grown and the removal of much 
anxiety from the mind of the gardener, together with an increase 
of pleasure, because of the superior condition of the collection, to 
the proprietor. We have only to add, that a house ventilated in 
the manner described, or, indeed, by any other, should have a thin 
blind, fixed on rollers, to be used as occasion may require, in 
order to intercept the force of a sudden sun-burst, or the intense 
light of long-continued bright weather. The benefit of this pre¬ 
caution is so well understood, that we need not enlarge on its 
importance. Editor. 
