ON VENTILATING HOTHOUSES, AND GLAZING WITH SHEET GLASS. 71 
the admission of chilling draughts. These extremes lie at the door of the operator, \Yith 
whose ignorance we ought not to confound the character of the apparatus provided him. 
It was to be expected therefore, I say, beforehand, that the sheet glass triumph would 
not be complete in its first essa}^ ; and that prejudices would arise which, in my opinion, 
will, before long, be fairly grappled with, and I trust dispersed. 
Now it so happens, according to my view of the matter, at least, that the subject of 
atmospheric moisture is also of necessity woven into this delicate affair. 
Intensity of light leads, in the present forms of gardening structures, to a vast accumu- 
lation of heat ; and these powers, in conjunction, prove so serious a draw on the vital 
forces of vegetables, that some counterpoise must of necessity be provided, or the remedy 
(inordinary language) would prove worse than the disease. The term "flagging" is con- 
ventionally known amongst gardeners to express that condition in vegetable existence 
when the elaborating powers overtake the absorbent ones. If then, I say, this cannot be 
provided against, better give up the idea of more light; a little time, however, will, as I 
think, show that this is by no means an insurmountable affair. I take it for granted, then, 
that a greater amount of atmospheric moisture will, in most cases, be requisite ; and, before 
concluding my remarks, I will endeavour to show how this may be carried out. 
Now, as to the much greater intensity of light produced by the British sheet, I would 
here point to another bearing of the subject ; — I mean the use of shades. Persons not 
well versed in practical gardening may, off-hand, suppose that those who so strongly 
advocate a brighter glass, and talk of systematic shading, are guilty of a great incon- 
sistency; and, according to the ordinary saying, " blowing hot and cold." Nothing is more 
natural than to come to this conclusion ; but to such I would say, that it is not a greater 
intensity of light, when the sun shines, that the British gardener desires ; but a much 
greater amount of light under ordinary circumstances ; as, for instance, on murky days, or 
through the winter, when a dulness prevails, which is little better than a twilight as to its 
effects on vegetation ; more especially in the case of early forcing. 
This point being once established, another consideration arises or naturally grows out 
of it : viz., w^hether it is expedient to use night coverings ; and, if so, whether the same 
material could be made equally applicable to both purposes ? This is a somewhat grave 
consideration, I confess ; inasmuch as all these matters lead to some expense in the first 
outlay : opinions here, then, must be given and received with some caution. As to the use 
of shades, there can be little doubt that, although with an increased amount of ventila- 
ting power, such may not be absolutely indispensable, yet they will be beneficial : and 
I have little doubt that, with a. general adoption of the sheet glass, there will be as 
general a demand for shading, more especially during one of those very bright and hot 
summers, which now and then take us somewhat by surprise. 
What the result of the experiments may be as to the rough plate glass, I of course can- 
not say ; this is at present undetermined : the utility, however, of canvas or other shades 
has long been proved, and these we can for the present refer to in the argument. Night 
coverings have often been recommended by first-rate practitioners, as well as suggested 
by theory ; the argument in favour of their use is, in the first place, that they enable us 
to descend to a lower night temperature than we otherwise dare, in the present state 
of horticulture. It appears tolerably evident that, with the internal air in an all but 
quiescent state, and the capricious interchange occasioned by a cold and of course con- 
densing roof, removed by means of some non-conducting body, that we dare in reality 
suffer vegetation to rest diurnally, as Nature has planned it in most climes. I have now 
been considering the matter of night coverings, chiefly as relates to really tropical pro- 
ductions, such as Orchids, Vines under forcing, &c. ; it remains to view it in another and 
most material point. 
Drip in houses is well known to be a source of great annoyance ; indeed, what comfort 
is there in a conservatory or show house w^hich is liable to these adventitious showers. In 
these stirring times, a very considerable portion of the charms of a gardening establish- 
ment is owing to a gay conservatory during the dull winter months ; when the contrast 
exhibited between the dormancy of Nature uncontrolled without, and assisted within, 
I 
