132 
GARDENING AS A SCIENCE. 
air have been already alluded to under their proper head ; what we want to know, 
or rather what many persons are solicitous to ascertain is, how, and by what 
agency, the gas called nitrogen and azote becomes united with the other more 
general components of living vegetable bodies. Before reference to any theory, it 
must be clearly understood that the presence of nitrogen is essential in all the 
processes of fermentation ; hence it is always found in wheat, gluten, and the leven 
of fruits — of the grape particularly. Nitrogen is also one of the chief ingredients 
of the volatile alkali called ammonia. 
Now, the theory of the great Liebig may be adduced in a very few lines: — he 
inquires (p. 69, 70)— " How, and in what form, does nature furnish nitrogen to 
vegetable albumen, gluten, fruits, and seeds V The solution of this question he 
finds very simple. " Plants grow perfectly well in pure charcoal, if supplied at 
the same time with rain-water. Rain-water can contain nitrogen only in two 
forms, either as dissolved atmospheric air or as ammonia. Now the nitrogen of 
the air cannot be made to enter into combination with any element except oxygen, 
even by employment of the most powerful chemical means. We have not the 
slightest reason for believing that the nitrogen of the atmosphere takes part in the 
processes of assimilation of plants and animals ; on the contrary, we know that 
many plants emit the nitrogen which is absorbed by their roots, either in the 
gaseous form, or in solution in water. But there are on the other hand numerous 
facts, showing that the formation in plants of substances containing nitrogen, such 
as gluten, takes place in proportion to the quantity of this element which is 
conveyed to their roots in the state of ammonia, derived from the putrefaction of 
animal matter." 
This is the theory of Liebig, which by some is stoutly combated. In truth, 
we know not what nitrogen is, though we can prove that it constitutes four-fifths 
of the atmospheric volume. It may be simple and elementary, yet the conjecture 
may be hazarded as far more probable, that itself is a compound, and therefore 
decomposable by organic life. 
Ammonia is certainly traceable in rain-water ; but it is extremely difficult to 
determine whether the atmospheric vapours receive it altogether from the putrefac- 
tion of dead bodies, and of the decomposing masses of manure, &c, or in a certain 
degree from the quantity of soot which passes into the air. 
Be this as it may, rain-water certainly owes its softness not only to the absence 
of the chalk, but to the existence of a small quantity of that volatile alkali called 
ammonia. 
It therefore appears of little consequence, whether the nitrogen be derived from 
the air, or by the introduction of ammonia with rain into the roots ; and subse- 
quently, from the decomposition of that alkali in the vegetable cells, whereby its 
nitrogen and hydrogen are separated, and become united to other substances in 
order to form compounds, specific to each individual plant. 
While we admit that Liebig may justly claim the presence of nitrogen in the 
