ON YENTILATING HOTHOUSES, AND GLAZING WITH SHEET GLASS. 73 
doubt that much of the burning must be attributed to imperfect ventilation — imperfect, 
at least, as regards the sheet glass. 
There has been an increasing desire in later years to accomplish the back ventilation 
of hothouses by means of clappers or flaps in the back walls. This was certainly a most 
laudable attempt at progress, inasmuch as the old plan of sliding down the back lights was 
liable to some serious objections. The glass was very liable to get broken ; the lights were 
liable to get fast, and were, moreover, rather cumbrous affairs to wind up ; and, worse 
than all, they had to be drawn up hastily when a sudden shower occurred. Such, succeeded 
by as sudden a burst of sunshine, has been the cause, in many instances, of leaf scorching. 
These back ventilators or clappers, however, have, in nearly all instances whicli have 
come under my notice, been insufficient in point of size to prove a proper equivalent for 
the sliding light. It has not been sufficiently considered, that hot air lodged in the 
uppermost angle of the roof will more speedily rush through an opening straight overhead 
than by a side aperture, which becomes, in the case of a north wind, as much a point of 
ingress as of egress. If, then, such were inadequate to the purpose with a roof of crown-glass, 
ventilated by a thousand laps in addition, what could be expected in reglazing such roofs with 
the bright sheet glass, with no extra provision for ventilation ? I know a case, within fifty 
miles of where I write, in which a new range of houses had to be built for a wealthy 
proprietor : no expense was to be spared to render them complete. The gardener, being 
jealous of the plans as to their efficiency in point of ventilation, and some other matters 
(such plans having been concocted by the architect), called on me, in company with the 
clerk of the works, to ask my opinion. I at once protested against the imperfect ventilation, 
such being small clappers in the back wall — their incapacity being manifest, at a glimpse, to 
the merest tyro. I have since found that my advice was set aside, the building gentlemen 
not considering it weighty enough to disturb the original plan; and I am given to 
understand, by a proper authority, that during the last summer, at certain periods, the 
thermometer was much above a hundred degrees, in defiance of every ventilating aperture 
being wide open, and the very doors of the houses open likewise. The same authority has 
informed me, also, that the Grapes have actually been coloured at the top of the house, 
whilst those at the bottom remained quite green. These things ought not to be ; they are 
a serious hindrance to the free progress of horticulture, besides great individual loss. 
Before concluding my remarks, I may be permitted perhaps to make a few general 
observations on the above matters. 
To revert to a point about which I offered a few observations previously, viz., 
atmospheric moisture, I must with deference add, that many forcing or plant-houses are 
still somewhat deficient in regard of a permanent supply. About half a score years since, 
it was a common affair to talk about steaming the houses, by pouring water on highly 
heated flues or pipes. This was at one period considered very sound doctrine ; but who 
talks of steaming now ? 
The great desideratum, it would appear, is a permanency of supply, regulated at all 
times by the demand on the vegetable fabric, through solar light and heat. The only 
question that remains, if such be admitted, is how it may be produced. Hot steam, it 
appears, is repudiated. Open tanks are very good things ; but when stronger fires are 
wanted, in order to ward off low temperatures, the amount of hot steam produced, if they 
be uncovered, is in some cases inconvenient. To be sure, the tanks may be covered; 
but then another extreme occurs, and we are just in the position that we should have 
been with the ordinary piping. I may here be permitted to describe a house lately erected 
here for Orchids, and which appears to answer the purpose admirably. The house is a 
" lean-to," or roof sloping to the south, forty feet in length by about twelve feet in breadth. 
A front shelf of open lattice-work runs from one end to the other along the front ; this 
shelf is about thirty inches wide, and much the same height from the floor level. A 
walk of three feet intervenes between this and the back stage, the lower shelf of which 
commences at precisely the same height from the ground as the front shelf, and thence to 
the back wall in the ordinary way. A sunken panel or cavity, of nearly two inches in 
depth, occurs through the whole area, beneath the front shelf and the back stage 
VOL. I.-— NO. III. L 
