74 
on the contrary, is only decomposable by violent 
chemical action. 
All the hydrogen necessary for the formation 
of an organic compound is supplied to a plant 
by the decomposition of water. The process of 
assimilation, in its most simple form, consists in 
the extraction of hydrogen from water, and car- 
bon from carbonic acid, in consequence of which, 
either all the oxygen of the water and carbonic 
acid is separated, as in the formation of caout- 
chouc, the volatile oils which contain no oxygen, 
and other similar substances, or only a part of it 
is exhaled. 
The formation of acids is accompanied with 
the smallest separation of oxygen; the amount 
_ of oxygen set free increases with the production 
of the so-named neutral substances, and reaches 
its maximum in the formation of oils. Fruits 
| remain acid in cold summers; while the most 
numerous trees under the tropics are those which 
produce oils, caoutchouc, and other substances 
containing very little oxygen. 
Assimilation of Nitrogen.—There is no reason 
for believing that the nitrogen, contained in all 
parts of a vegetable structure, is derived from 
that gas in its free state, for, excepting in the 
case of ammonia, it cannot be made to unite di- 
rectly with any element excepting oxygen. Am- 
monia is a compound of nitrogen and hydrogen, 
and the last product of the putrefaction of animal 
matters. It is capable of undergoing a multitude 
of transformations, in contact with other bodies, 
into the most various forms; either alone or with 
acids, it is very soluble in water; and hence it isthe 
chief form in which nitrogen is conveyed to plants. 
The thousands of millions of men and animals 
by death and decay yield a large quantity of am- 
monia, a portion of which must escape into the 
| atmosphere; and the reason why it has not been 
previously detected is, that the quantity of air 
submitted to analysis is very small. Liebig proved 
its existence in pure rain-water by evaporation 
with muriatic acid ; the sal ammoniac had always 
a brown or yellow colour, with the offensive odour 
of perspiration or animal excrements, from which 
its origin might be inferred. It has since been 
found by many others in rain-water, snow, and 
hail. If we suppose 1 lb. of rain to contain } 
grain of ammonia, then 26,910 square feet (1 
Hessian acre) must receive annually 88 lbs. of 
ammonia or 71 lbs. of nitrogen, which is more of 
the latter (in the form of vegetable albumen and 
_ gluten) than is contained in 2,920 lbs. wood, 
| 3,085 lbs. hay or 10 tons beetroot (the produce 
of such an acre), but less than the grain, straw, 
and roots of grain, on the same surface. 
Ammonia is evidently taken up by the roots 
of plants, and may be detected in many parts of 
their structure, in the juice of the maple tree, in 
the beetroot ; it is obtained in the distillation 
of flowers, herbs, and roots, with water ; the juice 
of the fresh tobacco leaf, and of the vine contains 
ammonia. 
AGRICULTURAL CHEMISTRY. 
The quantity of gluten (a nitrogenous body) 
contained in grain, seems to increase with the 
quantity of ammonia arising from manures. Thus, 
wheat grown in a soil manured with cow-dung 
(containing a little nitrogen) yielded only 11:95 
per cent. gluten, while in a soil manured with 
human urine it afforded 35:1 per cent. Putrefied 
urine contains a large proportion of nitrogen in 
the form of ammoniacal salts. Guano yields also 
much ammonia, and hence a part of its fertiliz- 
ing effects. 
Gypsum (plaster of Paris) acts beneficially by 
fixing ammonia in the soil and preventing its 
evaporation; for the sulphate of lime and carbo- 
nate of ammonia mutually decompose into sulphate 
of ammonia and carbonate of lime. The use of 
burned clay as manure and the fertility of ferru- 
ginous soils depend on the fixation of ammonia 
by alumina and sesquioxide of iron, with which 
it forms chemical compounds. Powdered char- 
coal absorbs 90 times its volume of ammonia, 
decayed wood 72 times (See Apsorprion), and 
hence in part the use of humus. 
The conclusion, then, is well established that 
the nitrogen of plants is derived from the am- 
monia of the atmosphere. 
Inorganic constituents of Plants.—Plants ab- 
sorb the soluble materials in a soil indiscrimi- 
nately, retaining such as are necessary and re- 
turning the others as excrement. The various 
acids in plants are combined with potash, soda, 
lime, and magnesia, which regulate their forma- 
tion, and when the plants are incinerated, these 
salts remain as carbonates, And since certain | 
acids are peculiar to plants and essential to them, 
alkaline bases must be equally necessary. The 
capacity of saturation of these acids being uni- 
form, the quantity of alkaline bases must be in- 
variable. 
The following analyses of ashes of two pine 
trees by De Saussure, and of two fir trees by Ber- 
thier, show that equivalent quantities of alkali 
are present. 
Pine from Mont Breven, 
Carbonate of potash 3°60 contains of oxygen, 0°41, 
< lime 46°34 ss ¢ 7:33 
@ magnesia 6:77 ‘6 1:27 
5671 Total oxygen 9-01 
Pine from Mont La Salle, 
Carbonate of potash 7°36 contains of oxygen 0°85 
G lime 119 ‘ G 8:10 
Gi magnesia 00:00 ss G 
58°55 8:95 
Fir from Allevard, 
Potash ‘ : 4 
REA } ° 16:8 contains of oxygen 3:42 
Lime 29'5 g e 8:20 
Magnesia 32 se f 1:20 
45:5 Total oxygen 12:82 
Fir from Norway, 
Potash 14:11 contains of oxygen 24 
Soda . 20°7 sf ‘ 5:3 
Lime ° 12:3 oe « 3°45 
Magnesia 4:35 ss $ 1:69 
51:45 Total oxygen 12°84 
