ON THE CLIMATE OF HOT-HOUSES. 
227 
winter, might, without much trouble, be fitted to slide over the hot-houses during 
the severe season ; and in the spring, when they are wanted for other purposes, their 
places might be supplied at night by mats or canvass. 
The principles which I have been endeavouring to illustrate, should be, doubt- 
less, extended to the pinery and the melon-frame, in the latter of which a saturated 
moisture might be maintained by shallow pans of water. An increase in the size of 
the fruit might be anticipated from this treatment, without the loss of flavour^ which 
would attend the communication of water to the roots of the plants. I have but few 
additional observations to offer upon the artificial climate of a greenhouse. The 
remarks which have been made upon the atmosphere of the hot-house are applicable 
to it, though not to the same extent. The plants which are subject to this culture 
seldom require an artificial temperature of more than forty or fifty degrees ; and few 
of them would receive injury from a temperature as low as thirty-five degrees. 
When in the house, they are effectually sheltered from the effects of direct radiation, 
which cannot take place through glass ; but the glass itself radiates very freely, and 
thus communicates a chill to the air, which might effectually be prevented by rolling 
mats. With this precaution, fire would be but rarely wanted, in a good situation to 
communicate warmth ; but in this damp climate it may be required to dissipate 
moisture. The state of the air should be as carefully watched with this view, as 
where a high temperature is necessary to guard against the contrary extreme. Free 
transpiration, as I have before remarked, is necessary to the healthy progress of 
vegetation ; and when any mouldiness or damp appears upon the plants, the tempera- 
ture of the air should be moderately raised, and free ventilation allowed. When the 
pots, in the proper season, are moved into the open air, it would contribute greatly 
to their health, and preserve them from the effects of too great evaporation, to em- 
bed them, well in moss, or litter : as a substitute for this precaution, the plants are 
generally exposed to a northern or eastern aspect, where the influence of the sun 
but rarely reaches them ; but which would be very beneficial, if their roots were 
properly protected. The advantage of such a protection may be seen, when the pots 
are plunged into the soil; a method which communicates the greatest luxuriance to 
the plants, but unfits them to resume their winter stations. 
When a greenhouse is made use of, as it often is after the removal of the pots, 
to force the vine, the same precaution should be attended to as in the management 
of the hot-house ; and the elasticity of the vapour should be maintained by wetting 
the floor ; but after a certain period, a greater degree of dryness should be allowed to 
prevail, to enable the tree to ripen its wood, and form the winter productions for its 
buds. In this its treatment differs from that of the tropical plants, which require 
no such change, and to which, on the contrary, it would be highly detrimental. The 
same observation applies to forcing-houses for peaches and other similar kinds of 
trees. As soon as the fruit is all matured, they should be freely exposed to the 
changes of the weather. 
