ON THE FOOD OF PLANTS. 1^3 



with water, appears to be carbonic acid ; but as 

 it has not been proved, that in this state it is, by 

 any application, capable of producing anything 

 like the quantity of carbonaceous matter required 

 to sustain a plant in health and vigour, it may 

 justly be concluded that carbonic acid, like coal, 

 is, by its constitution, restricted in its operation. 

 That process of decomposition, therefore, which 

 can be conducted so as to produce the required 

 state of solution and separation, without its run- 

 ning into the excess of carbonic acid or charcoal, 

 must be the most efficient ; and the chemical 

 terms which best express this state, appear to 

 me to be vegetable and animal oxydes ; and my 

 opinion as to the best mode of producing and 

 applying this, I shall hereafter explain. 



Sir Humphry Davy says, " There is no ques- 

 " tion on which more difference of opinion has 

 " existed, than that of the state in which ma- 

 *' nure ought to be ploughed into the land ; 

 " whether recent, or when it has gone through 

 " the process of fermentation. And this ques- 

 " tion is still a subject of discussion ; but whoever 

 ♦' will refer to the simplest principles of che- 

 ♦' mistry, cannot entertain a doubt on the subject. 



" As soon as dung begins to decompose, it 

 " throws ofi' its volatile parts, which are the 



