18 
of their truth in every respect ; for we believe 
that, although he has adopted a true method in 
elevating agriculture and physiology by the appli- 
cation of chemical principles, he has by no means 
proved that carbonic acid, water, and ammonia 
constitute the sole source of the organic parts of 
plants. We therefore offer the opinions of others 
likewise grounded on experimental evidence. 
VIEW OF THE THEORY THAT PLANTS DERIVE THEIR 
NUTRIMENT FROM ORGANIC AND INORGANIC MAT- 
TER. 
Saussure has conducted some very able experi- 
ments which seem to prove that some plants do 
take up humus, not in the form of carbonic acid. 
He showed, contrary to the experiments of Har- 
tig, that humus extracted from mould by alkali is 
absorbed by the roots ; and that since a strongly 
coloured solution of humate of potassa becomes 
discoloured in the Polygonum Persicaria, while 
other colouring matters, such as ink, unfitted for 
nutrition, are not—that this humic material is 
assimilated. Without denying that carbonic acid 
and water are assimilated as nutritive matter, 
he holds humic extract is likewise useful to 
plants ; that plants produced by the former 
alone are not as thrifty as with the use of mould. 
The following are his general conclusions :— 
1, That fertile soil contains a mixture of solu- 
ble and insoluble organic matter ; and that the 
introduction of the former by the roots into a 
plant is a powerful aid to that nutrition which 
is afforded by the atmosphere and water. 
2. That the insoluble organic, greatly prepon- 
derating over the soluble, undergoes, by the as- 
sistance of water, slow fermentation, hence pro- 
ducing soluble nutritive matter. 
3. That plants receive their nitrogen almost 
entirely by absorption of soluble organic matter. 
4, That those coloured substances adapted to 
the nutrition of plants change colour, while those 
not nutritious enter a plant without undergoing 
decomposition. 
Hermann has discovered that the chief part of 
the extractive matter in the juice of plants con- 
sists of similar constituents to humus, containing 
humic acids, crenic and apocrenic acids, and ex- 
tractive humus. See Humus. 
Mulder’s experiments lead to the conclusion 
that, by the decay of vegetable substances, ulmin 
and ulmic acid are formed when the air is not 
freely admitted, and these again, by the action 
of the air, pass into humin and humic acid. His 
analyses of the humic acid in turf, decayed wood, 
and vegetable mould from various localities, 
prove that it is combined with ammonia, and the 
remarkable resemblance in the deduced formule, 
seems to prove conclusively that there is a class 
of humus bodies, which, although differing among 
each other, must be ranked together. 
Mulder supposed this ammonia to have been 
abstracted as such from the air, but Hermann’s 
experiments prove that during the decay of wood 
AGRICULTURAL CHEMISTRY. 
1 volume of nitrogen and 2 vols. of oxygen are 
absorbed from the air, and 4 vols. carbonic acid 
given off, and that ammonia is a residual trans- 
formation. 
These researches of Saussure, Mulder, and 
Hermann are certainly opposed to the views of 
Professor Liebig, and we may add to them the 
elaborate researches and conclusions of Boussin- 
gault and Payen. The following is the definition 
of powerful manures by the two last-named chem- 
ists :—Manure is the more valuable in proportion | 
as the quantity of nitrogenous organic matter is 
greater than the non-nitrogenous organic mat- 
ter; and in proportion as the decomposition of 
quaternary compounds acts gradually, and agrees 
with the progress of vegetation. They have there- 
fore constructed a table showing the value of man- 
ures, that is, the quantity of nitrogen they con- 
tain. See Manure. 
Boussingault holds that plants receive a large 
proportion of nutriment from the air, but also 
recelve no inconsiderable amount of organic ma- 
terial directly from the soil. He believes that 
the process of fallowing has chiefly the advantage 
of destroying weeds; that the system of rotation 
of crops does not depend on the injurious action 
of the excrements of plants, since Braconnot’s 
experiments prove that such excrements are not 
produced, but it rather depends on the alterna- 
tion of such plants as only extract nutrition from 
the soil, like the Graminez, and of such as take 
much nutriment from the air, like the Legumi- | 
nos, and whose stubble ploughed under is in 
itself a good manure. 
In conclusion, we may remark that Liebig has | 
shown that a large proportion of the organic 
matter of plants is due to the assimilation of car- | 
bon from carbonic acid, but not that it is wholly | 
He has not shown that their | 
nitrogen is obtained chiefly from the ammonia | 
of the atmosphere; while the formation of am- | 
due to this cause. 
monia by the decomposition of animal manures, 
seems distinctly to indicate that one great source | 
of nitrogen lies within the soil, a view strength- 
ened by the experiments and inferences of Bous- 
singault and Payen. Whether we adopt with the 
former the view that nitrogen is the measure of 
nutrition, we hold with him that the nitrogenous 
compounds in the soil are partly useful because of 
the more ready decomposition of compounds con- 
taining nitrogen, so that the carbon and hydrogen 
of such substances are more readily assimilated. 
Again, Liebig censures the application of the 
principles of animal nutrition to vegetable phy- 
siology, and yet more than once draws such a 
comparison himself. It may be wrong to apply 
these principles in the same manner in both 
cases, but the principles themselves may hold 
good of both. Thus, while he has shown the 
importance of one constituent of the air, car- 
bonic acid, another acts an equally important 
part to animals; for, without the action of the 
oxygen in producing internal transformations 
