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AGRICULTURAL CHEMISTRY. 
opposite to that which must be adopted in order 
to produce a maximum of corn from the same 
plant.” 
Nutriment of plants—There are two prevailing 
views in reference to the nutriment of plants: 
the one regarding it as wholly derivable from in- 
organic matter and decomposed organic matter, 
—the other, as partly or even chiefly from unde- 
composed though dead organic matter. The for- 
mer of these views has been ably advocated by 
Liebig by reference to numberless chemical and 
physiological data; and even though it should 
not prove to be wholly correct, his essay can 
scarcely fail to exert a very modifying and im- 
proving influence on many important topics in 
the science of agriculture. The principal advo- 
cates of the opposite opinion are Boussingault, 
Saussure, Hermann, Payen, Mulder, and Madden. 
We shall present a condensed view, first of Lie- 
| big’s theory, and next of that of his opponents. 
| VIEW OF THE THEORY THAT THE NUTRIMENT OF PLANTS 
IS DERIVED SOLELY FROM INORGANIC MATTER. 
There are four elements which in general form 
the organic matter of plants; carbon, hydrogen, 
oxygen, and nitrogen, two or more of which united 
in variable proportions constitute an almost in- 
finite number of proximate principles. Plants 
derive nourishment from the atmosphere and the 
soil. The former consists of carbon from carbonic 
acid, nitrogen from ammoniacal gas, and oxygen 
and hydrogen from watery vapour ; and the latter 
consists of the same elements from decomposed 
organic matters and from water. Humus was 
formerly supposed to yield the principal aliment ; 
but it is now known to be both an indirect and 
a quite secondary source. 
Assimilation of Carbon.—Humus is soluble in 
an extremely minute degree in water, but when 
treated with alkalies, the humic acid formed is 
somewhat soluble. Suppose this acid to be ab- 
sorbed in the form of that salt which is most 
soluble, the humate of lime, and suppose that 
potash, soda, the oxides of iron and manganese 
take up the same quantity of the acid as lime, 
Berthier found that 1,000 lbs. of dry fir-wood 
yielded 4 lbs. ashes, containing 53 per cent. me- 
tallic oxides. A Hessian acre yields annually 
2,920 lbs. fir-wood, containing 6°17 lbs. metallic 
oxides. Then 1 lb. of lime, uniting with 12 lbs. 
humic acid, the 6°17 lbs. of the oxides would in- 
troduce 74 lbs. humic acid, which, containing 58 
per cent. carbon, would correspond to 100 lbs. of 
wood ; but the acre really yields 2,920 lbs. In 
the same way the oxides in wheat straw would 
produce 93:6 lbs. woody fibre to the acre, whereas 
the produce is 1,961 lbs. of straw composed simi- 
larly to woody fibre. 
Calculating the quantity of this acid which 
plants might receive under the most favourable 
circumstances by the agency of rain-water, and 
supposing all the rain which falls on an acre to 
be received by the plants, and all to be saturated 
7] 
by humate of lime, then the plants would receive 
only 330 lbs. humic acid, while the acre produces 
2,843 lbs. of grain and straw, so that the 330 of 
acid would only account for a small quantity of 
the carbon actually obtained. 
Again, the Hessian acre of wood or meadow 
yields 1,109 lbs. carbon in its wood or hay,—1,032 
in the beetroot without the leaves, or 1,124 lbs. 
in straw and grain; equal surfaces of average 
fertility yielding equal quantities of carbon ; and 
yet the conditions in the growth of these plants 
have been very dissimilar. 
Moreover, the soil of meadow and forest, in- 
stead of losing carbon, actually increases its quan- 
tity, notwithstanding the removal of so much in 
the wood or hay, and the soil of a field which is 
manured contains no more than a meadow or 
forest which is not manured. 
These considerations prove that the common 
view of the nutrition of plants by humic acid is 
incorrect. Whence, then, is their carbon de- 
rived ? 
The quantities of carbonic acid in the air aver- 
ages 4 vols. in 10,000 vols., so that the weight of 
carbon which presses on an acre of land is about 
7 tons. The quantity of oxygen estimated to be 
consumed by the respiration of 1,000,000,000 of 
men in one year is 0°79745 cubic miles. A 
town of 7,000 inhabitants consumes annually 
551,000,000 cubic feet of oxygen in the combus- 
tion of wood. Hence we may conceive of the 
enormous quantity of carbonic acid constantly 
thrown into the air by the respiration of men 
and animals, by combustion, and the putrefac- 
tion of animal and vegetable matter. Now, anal- 
ysis shows that the quantity of oxygen is the 
same now as it was 1,000 years since. There 
must be, therefore, some means of replacing the 
oxygen consumed, and of removing the carbonic 
acid which is formed. 
Plants effect both of these changes, absorbing 
carbonic acid, decomposing it and giving off 
oxygen. A plant placed in water containing 
carbonic acid, and exposed to the sun’s light, 
removes the acid and evolves oxygen, which may 
be collected in a receiver and examined ; it in- 
creases in weight more than can be accounted 
for by the carbon taken up, which shows that the 
elements of water are assimilated at the same 
time. The quantity of carbon in the air may be 
shown to be 3,300 billions of lbs., which is more 
than all the plants and the strata of coal on the 
earth. Calculating from the quantity of carbonic 
acid absorbed by a freshly white-washed surface 
in a given time, a Hessian acre might absorb in 
200 days 11°353 Ibs. carbonic acid, containing 
3,304 lbs. carbon, which is 3 times as much as 
obtained from plants growing on the same sur- 
face. 
Carbonic acid is absorbed from the air by the 
leaves, and from the soil by the roots, for it forms 
an atmosphere in the soil around decaying humus. 
When exposed to sun-light it is decomposed while 
