1^2 ON THE FOOD OF PLANTS. 



to charcoal, by the operation of fire, but would 

 they in this state have afforded as much of the 

 basis of charcoal in a soluble state, as by the result 

 of oxydizement or fermentation ? Certainly not ; 

 then it may be inferred, that to furnish charcoal, 

 or a substance capable of being converted into 

 charcoal, is not enough. Carbon must be pre- 

 sented in that state which admits of its perfect 

 solution and combination with water. And even 

 after this is produced, it clearly appears that some 

 co-operating agent is necessary, either to release 

 it fi*om the natural attachment of some other 

 princij^le or substance, which is obnoxious to 

 plants, or to stimulate the plant to receive it ; 

 ibr it is found that the black residuum of veget- 

 ables, spontaneously decomposed byputrefaction, 

 will not of itself sustain such plants as are objects 

 of cultivation in agriculture ; nor will simple 

 calcareous earths ; but these two substances 

 blended in due proportions, constitute the most 

 fertile soils. Hence, as is well known, black 

 soils, which are constituted wholly of vegetable 

 matter, are sterile, and that by the simple com- 

 bination of lime they are rendered fertile. Then 

 what is this principle of fertility ? this is an im- 

 portant question. 



The most complete solution of carbon, or that 

 state which admits of the most perfect union 



*5 



