ON THE FOOD OF PLANTS. 121 



can be no doubt,) the basis of charcoal must, in 

 that part of the food of plants which is supplied 

 by artificial means, form almost an integral ; 

 and how to prepare, collect, and apply this sub- 

 stance, is the grand desideratum. 



As Sir Humphry Davy says, mucilaginous, 

 gelatinous, saccharine, oily, and extractive fluids, 

 and solutions of carbonic acid in water, are sub- 

 stances that in their unchanged states contain 

 aljnost all the principles necessary for the life of 

 plants J and all that is contained in these sub- 

 stances, except the basis of charcoal, is contained 

 in water ; viz. oxygene, nitrogene, and eartli. 

 In the preparation of food for plants, therefore, 

 the principal object must be to produce and 

 apply carbon, and the manner of effecting this is 

 still an object of doubt, difficulty, and uncer- 

 tainty, which is evinced by the opinions even of 

 those great philosophers which I have quoted. 



What Mr. Kirwan says respecting coal, is true 

 enough ; but as to coal in itself, being made to 

 form any part of the food of plants, I have never 

 seen it proved ; that it has been applied as manure 

 with good effect, may be, but its operation must 

 have been as an alterative in the soil, and a pre- 

 ventative of putrefaction, and not as alibrding 

 carbonaceous matter to the plant. Tlie shavings 

 of wood, no doubt, might have been reduced 



