223 
ON THE CLIMATE OF HOT-HOUSES. 
BY PROFESSOR DANIELL, KING's COLLEGE, LONDON. 
The principal considerations which generally guide the management of gar- 
deners in this delicate department, are those of temperature ; but there are others, 
regarding moisture, which are, I conceive, of at least equal importance. The in- 
habitants of the hot-house are all natives of the torrid zone ; and the chmate of that 
region is not only distinguished by an unvarying high degree of heat, but also by a 
very vaporous atmosphere. Captain Sabine, in his meteorological researches be- 
tween the tropics, rarely found, at the hottest period of the day, so great a differ- 
ence as ten degrees between the temperature of the air and the dew point ; making 
the degree of saturation about seven hundred and thirty, but most frequently five 
degrees, or eight hundred and fifty ; and the mean saturation of the air could not 
have been below nine hundred and ten. Now I believe that if the hygrometer were 
consulted, it would be no uncommon thing to find in hot-houses, as at present 
managed, a difference of twenty degrees between the point of condensation and the 
air, a degree of moisture falling short of five hundred. The danger of over-watering 
most of the plants, especially at particular periods of their growth, is, in general, 
very justly appreciated ; and, in consequence, the earth at their roots is kept in a 
state comparatively dry ; the only supply of moisture being commonly derived from 
the pots. The exhalation of the leaves is not enough to saturate the air ; and the 
consequence'is, a prodigious power of evaporation. This is injurious to the plants 
in two ways : in the first place, if the pots be at all moist, and not protected by tan, 
or any other litter, it produces a considerable degree of cold upon their surface, and 
communicates a chill to the tender fibres with which they are lined. The danger 
of such a chill is carefully guarded against in the case of watering ; for it is one of 
the commonest precautions, not to use any water of a temperature at all inferior to 
that of the air of the house : inattention to this point is quickly followed by dis- 
astrous consequences. The danger is quite as great from a moist flower pot, placed 
in a very dry atmosphere. 
The custom of lowering the temperature of fluids in hot climates, by placing 
them in coolers of wet porous earthenware, is well known ; and the common garden 
pot is as good a cooler for this purpose as can be made. Under the common cir- 
cumstances of the atmosphere of a hot-house, a depression of temperature, amount- 
ing to fifteen or twenty degrees, may easily be produced upon such an evaporating 
surface. But the greatest mischief will arise from the increased exhalations of the 
plants so circumstanced, and the consequent exhaustion of the powers of vegetation. 
The flowers of the torrid zone are, many of them, of a very succulent nature, 
largely supplied with cuticular pores ; and their tender buds are unprovided with 
* Horticultural Transactions. 
