18 



On Climate, fyc. 



artificial state, which it is possible to conceive; for, not only 

 are their stems and foliage subject to the vicissitudes of the 

 air in which they are immersed, but, in most cases their roots 

 also. The soil in which they are set to vegetate is generally 

 contained in porous pots of earthen ware, to the interior sur- 

 face of which the tender fibres quickly penetrate and spread 

 in every direction ; they are thus exposed to every change of 

 temperature and humidity, and are liable to great chills from 

 any sudden increase of evaporation. This part of the subject 

 naturally divides itself into two branches. The first regards 

 the treatment of such exotics as are wholly dependent upon 

 the artificial atmosphere of hot-houses : the second refers to 

 the management of those hardier plants which only require 

 to be preserved in green-houses part of the year, 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 

 management of gardeners in this delicate department are 

 those of temperature ; but there are others, regarding mois- 

 ture, which are, I conceive, of at least equal importance. 

 The inhabitants of the hot-house are all natives of the torrid 

 zone, and the climate 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 ex- 



