15 



so duly prepared, as to be fit for their assimilation. 

 Warmth in the soil, acts beneficially also, by preventing 

 the sudden or undue interruption of the excitability of 

 plants growing in it, which would be likely to result from 

 the lowering of the temperature of the plants by evapora- 

 tion, were it not for the action of the antagonist force, 

 existing in and exercised by the heated soil, which heat, 

 is communicated to, and absorbed by the plants. 



It may be regarded as an established and universal 

 rule, that all plants require the soil, and the atmosphere 

 in which they are cultivated, to correspond with the natu- 

 ral circumstances under which they nourish ; and as it 

 has been repeatedly ascertained that the soil is naturally 

 a degree or two above the temperature of the atmosphere, 

 we have certain and unerring data for the application of 

 bottom heat, and no more powerful evidence than this 

 can be desired, to condemn at once the application of a 

 very powerful degree of heat, at the roots of plants. 



The importance of bottom heat in the culture of tender 

 plants, being a practical fact established beyond question, 

 another consideration arises as to the best means of pro- 

 ducing it, and of regulating its application. Various 

 substances and materials have been submitted to a pro- 

 cess of fermentation, and so employed to effect it: stable 

 manure, tanner's bark, and the leaves of trees, are among 

 the principal of these materials, and either of them will 

 supply just what the plants require, as truly as these 

 wants can be supplied by any other means ; but from 

 their very nature, they are violent, and fluctuating, and 

 ephemeral in their action, and setting aside the labour 

 which the employment of them necessarily involves, we 

 have in these particulars, the special points in which the 

 tank system of applying bottom heat far excels them: 

 it is unrform, and constant, in its action ; there need 

 be no apprehension of the soil becoming overheated, for 

 the source whence it derives its warmth ought never to 



