1826.] Mr. Daniell on Climate. 12$ 



but during the summer months are exposed to the changes of 

 the open air. I shall offer a few remarks first on the atmosphere 

 of a hot-house. 



The principal considerations which generally guide the 

 mianageaient of gardeners in this delicate department are those 

 of temperature ; but there are others regarding moisture which 

 are, I conceive, of at least equal importance. The inhabitants 

 of the hot-house are all natives of the torrid zone, and the cli- 

 mate of this 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 between the 

 tropics, rarely found, at the hottest period of the day, so great a 

 difference as ten degrees between the temperature of the air and 

 the dew-point; making the degree of saturation about 730, but 

 most frequently 5° or 850° ; and the mean saturation of the air 

 could not have exceeded 910. Now I believe that if the hygro- 

 meter were consulted, it would be no uncommon thing to find in 

 hot-houses, as at present managed, a difference of 20° between 

 the point of condensation and the air, or a degree of moisture 

 falHng short of 500. 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, and 

 the exhalations 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 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 precau- 

 tions not to use any water of a temperature at all inferior to that 

 of the hot air of the house ; inattention to this point is quickly 

 followed by diastrous 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 earthen ware, 

 is well known, and the common garden pot is as good a cooler 

 for this purpose as can be made. Under the common circum- 

 stances of the atmosphere of a hot-house, a depression of 

 temperature amounting to 15 or 20 degrees, may easily be pro- 

 duced 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 those integuments 



