Transactions of the Horticultural Society. 291 



ment of natural climate. By reflecting on it the cultivator will 

 be convinced of the reasonableness of many parts of practice, 

 which he had, perhaps, followed from habit ; he will see and 

 feel the importance of walls, copings, hedges, protection from 

 the east, from sudden gleams of sunshine, of the warmth re- 

 tained by woody undergrowth s, and, generally, the advan- 

 tages of stagnating air ; of placing gardens on sloping ground, 

 of growing crops on ridges, and a great variety of other 

 things. He will also be able to account for the effects of cold 

 in hollow places ; for the difference of effect between dry 

 cold and moist cold ; for the lower branches of a tree being 

 sometimes injured by frost, when the upper part has escaped 

 injury; of tender plants, in a northern or western exposure, 

 sometimes escaping unhurt, and when those against a south 

 wall have been killed, &c. 



Artificial climates, Mr. Daniell observes, being entirely de- 

 pendant on art, require a more extended acquaintance with 

 the laws of nature, and greater skill and experience in the 

 means of protection. " The plants which require this pro- 

 tection are in the most 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 earthenware, 

 to the interior surface of which the tender fibres quickly pene- 

 trate, 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." 



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

 torrid zone, a climate distinguished by an unvarying high de- 

 gree of heat, and a very vaporous atmosphere. When air is 

 very hot, it will exhale moisture from whatever objects it may 

 come in contact with, which possess that quality. In a hot- 

 houses when all the paths and walls are in a dry state, exhal- 

 ation to an extraordinary degree takes place, from the only 

 sources of moisture, — the leaves of plants and the earth in 

 their pots. This " prodigious evaporation," as Mr. Daniell 

 calls it, is injurious to the plants in two ways ; first, by chilling 

 their roots by evaporation from the surface and sides of the pots, 

 on the same principle that water is cooled in Spain and India, 

 by being put in porous earthen vessels : and, secondly, by ex- 

 hausting the vegetative powers of the plant. Vegetables also 

 have the power of absorbing moisture from the atmosphere, 

 and must consequently suffer in proportion as this is in a dry 

 arid state. Those three considerations show the great im- 

 portance of a vaporous atmosphere in hot-houses ; and the way 



