Barley. Vetches.

Muriate of Ammonia 257.2 176.4
Carbonate of Ammonia 123.6 173.8
Sulphate of Ammonia 203.6 125.2

These experiments not only prove that ammonia can be absorbed, but they
also indirectly confirm the statement already made, that humus is not
necessary; for in some instances the produce was higher than that
obtained from the uncalcined soil with the same manures, although it
contained four per cent of humus.

On such experiments Liebig rests his opinion that ammonia is the
exclusive source of the nitrogen of plants, and although he has recently
admitted that it may be replaced by nitric acid, it is obvious that he
considers this a rare and exceptional occurrence. The evidence, however,
for the absorption of nitric acid appears to rest on as good grounds as
that of ammonia, for experience has shown that nitrate of soda acts
powerfully as a manure, and its effect must be due to the nitric acid,
and not to the soda, for the other compounds of that alkali have no such
effect. Wolff has illustrated this point by a series of experiments on
the sunflower, of which we shall quote one. He took two seeds of that
plant, and sowed them on the 10th May, in a soil composed of calcined
sand, mixed with a small quantity of the ash of plants, and added at
intervals during the progress of the experiment, a quantity of nitrate
of potash, amounting in all to 17.13 grains. The plants were watered
with distilled water, containing carbonic acid in solution, and the pot
in which they grew was protected from rain and dew by a glass cover. On
the 19th August one of the plants had attained a height of above 28
inches, and had nine fine leaves and a flower-bud; the other was about
20 inches high, and had ten leaves. On the 22d August, one of the plants
having been accidentally injured, the experiment was terminated. The
plants, which contained 103.16 grains of dry matter, were then carefully
analysed, and the quantity of nitrogen contained in the soil after the
experiment and in the seed was determined.

Grains.
Nitrogen in the dry plants 1.737 }
" remaining in the soil 0.697 } 2.434

" in the nitrate of potash 2.370 }
" in the seeds 0.029 } 2.399
------
Difference 0.035

Hence, the nitrogen conta