When the putrefactive process of plants is completed, there remains a soft black mass, known as vegetable mould, or humus. One hundred parts of the humus of wheat straw have of extractive or apotheme, 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

It was once believed, indeed is still believed by a few men of science, that this apotheme is the immediate fertilizing component of organic manures, being soluble under some circum-stances, and entering at once into the roots of plants, dissolved in the moisture of the soil. But every relative research of more modern chemistry is against this conclusion, 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 gaseous form 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. Carbonic acid has been long since shown to be bene- | ficial if applied to a plant's roots. It abounds in the sap of all vegetables, though this be drawn from their very lowest parts, whereas apotheme is injurious to them if they are grown in a solution of it, and minutest analyzers have failed to detect it even within the extreme vessels of roots. - Prin. of Gard.