OF GARDENING AS A SCIENCE. 
83 
matter, is woody fibre, reduced by a still slower process of combustion, (that is, by 
decay,) to which Liebig has adapted the very expressive term of Eremacausis. 
By metallic oxides we understand, chiefly, the alkalies called pearl-ash and 
lime, products of the metals 'potassium and calcium ; though the small quantity of 
iron traceable in wood ashes is also included. “ Now, according to the estimates 
of Malaguti and Sprengel, 1 lb. Hessian of lime combines chemically with 10 T ^ 
lbs., Hessian, of humic acid ; lbs. of the metallic oxides would accordingly in- 
troduce into the trees 61 lbs. Hessian of humic acid, which, admitting humic acid 
to contain 58 per cent, of carbon, would correspond to 91 lbs. Hessian of dry 
wood.” But we have seen that 2650 lbs. of fir wood are really produced! Again, 
according to the same data — 
“ It will be found that the wheat growing on 40,000 square feet of land would 
receive, in that way, 574- lbs. Hessian of humic acid, corresponding to 85 lbs. 
Hessian of woody fibre. But the extent of land just mentioned produces, 
independently of the roots and grain, 1780 lbs. Hessian of straw.” 
He next proceeds to calculate the utmost quantity of humus which plants 
could take up by the solvent power of rain-water, independently of any chemical 
agency : thus— - 
“ The quantity of rain which falls at Erfurt, one of the most fertile districts of 
Germany, during the months of April, May, June, and July, is stated by Schubler 
to be 174 lbs. Hessian over every square foot ; 40,000 square feet consequently 
receive 700,000 lbs. Hessian of rain water. Suppose that not a pound of this water 
evaporates, except from the leaves of the plants, and, if we further assume, that 
the water thus absorbed is saturated with humate of lime ; then the plants thus 
nourished would not receive more than 300 lbs. Hessian of humic acid, since one 
part of humate of lime requires 2,500 parts of water for solution. But since it is 
known that only a small portion of the rain water, which falls upon the surface of 
the earth, evaporates through plants, the quantity of carbon which can be conveyed 
into them in any conceivable manner, by means of humic acid, must be extremely 
trifling in comparison with that actually produced in vegetation. Other consider- 
ations, of a higher nature, confute the common view respecting the nutritive office 
of humic acid, in a manner so clear and conclusive, that it is difficult to conceive 
how it could have been so generally adopted.” 
He then states the calculation of various products from fertile land — trees, 
beet-root, rye, hay, and the like ; from which, as facts incontestable, he infers 
“ that equal surfaces of cultivated land, of an average fertility, produce equal 
quantities of carbon;” and adds — “yet how unlike have been the different con- 
ditions of the growth of the plants from which this has been deduced !” 
But the soil, instead of becoming exhausted of humus, “ becomes every year 
richer in this element. A certain quantity of carbon is taken every year from the 
forest or meadow, in the form of wood or hay, and in spite of this, the quantity of 
carbon in the soil augments ; it becomes richer in humus.” 
