330 PRINCIPLES OF GARDENING. [CH. IX. 



apotlieme, rather more than twenty-six parts, and 

 the residue is lime, peroxide of iron, phosphate of 

 lime, and carbonaceous matter. This apotheme 

 is identical with the humic acid of Liebig, the 

 ulmic acid of Braconnot, and the geic acid of 

 Berzelius. It contains 



Carbon 46.6 



Hydrogen 20.0 



Oxygen 33.4 



100.0 



It was once believed, indeed is still believed, by a 

 few men of science, that this apotheme is the imme- 

 diate fertilizing component of organic manures, 

 being soluble under some circumstances, and enter- 

 ing at once into the roots of plants dissolved in the 

 moistui'e of the soil. But every relative research 

 of more modern chemistrv is a^^ainst this conclu- 

 sion, and it is now tolerably certain that a chief 

 nutritive portion of vegetable manures are their 

 carbon converted into carbonic acid, absorbed, either 

 in solution with the earth's moisture, or in a gaseous 

 foi*m, by the roots. Apotheme is only one of the 

 products formed during the progress of putrefaction, 

 and is in its turn a source of carbonic acid. Car- 

 bonic acid has been long since shewn to be beneficial 

 if applied to a plant's roots. It abounds in the 

 sap of all vegetables, though this be drawn from 



