On Modern Improvements of Horticulture, 273 



mates : heat, that powerful agent in the development of vegeta- 

 tion, we can have in any degree, by stoves, by fermenting sub- 

 stances, and from the steam of boihng water : light, a no less 

 necessary agent in the maturation of fruits, we combine with 

 the former, by glazed houses and frames. 



The various expedients for obtaining the necessary degree of 

 heat, are, first, the most simple method of a stove, with its flue 

 passing through or round the floor of the house, and this for 

 warming the air within ; but in this case, as the roots of the 

 plants do not suffiGiently, it is supposed, receive the proper 

 degree of heat, various fermenting substances, as recent stable- 

 yard dung, tanners' bark, oak and other leaves of trees, &c. are 

 formed into beds, on which the compost of earth is placed, as 

 in hot-bed frames, or in which the pots containing the plants 

 are placed, or plunged, as in a hot-house. To obtain the same 

 effect, borders within houses are formed for the roots, having 

 an excavated heat-chamber beneath, supplied by simple stove 

 flues, or from the fermenting substances above named, or from 

 steam admitted for the purpose. This mode of supplying an 

 equal degree of heat to the roots, as well as to the leaves and 

 branches of a plant, is plausible, and cannot be far wrong, 

 because it has been attended with success: but there is, 

 perhaps, more attributed to it than it deserves, because the 

 region or stratum of the soil, which is naturally occupied by 

 roots, differs, in respect of temperature, much less over the 

 whole surface of our globe, than is commonly imagined. The 

 heat of the air in different latitudes ranges from several degrees 

 below zero to 110 degrees of Fahrenheit's scale ; but the tem- 

 perature of the earth eighteen inches below the surface, it is 

 probable, does not vary more than ten or fifteen. In England 

 spring water varies only two degrees, viz. from 42 degrees in 

 summer to 40 degrees in winter ; and the effects of our hardest 

 frosts very rarely penetrate deeper than nine inches ; but it is 

 necessary to observe, that, in such cases, as well as in hotbeds, 

 we force as well as defend ; and probably, by such mode of 

 applying heat and moisture, nutritious gases may be commu- 

 nicated, which may be no small advantage. Besides, the 

 atmosphere of the house can (as is done) be impregnated 

 with the same qualities and degrees of heat and humidity (a 



