380 
PHYSIOLOGY. 
BOOK II. 
rally contains a fluid charged with nitrogen ; and he thence 
infers that the substances employed to prevent the decomposi- 
tion of wood do so by acting upon the azotised matter, which 
they coagulate and render insoluble in water. (Comptes 
rendus^ vi. 102. 132., vii. 889.) The accuracy of these state- 
ments, although opposed to the opinions formerly entertained 
by vegetable chemists, seems generally admitted. The cause of 
the importance of nitrogen to vegetation having been so long 
overlooked, is well explained by the committee which re- 
ported to the Institute upon M. Boussingault’s observations, 
[Comptes rendus, vi. 130.) One has been involuntarily led 
to suppose that nitrogen takes no part in the phenomena of 
vegetation, because we know that in its gaseous state it enters 
into combination with much difficulty. Sufficient attention 
has not been paid to the facility with which, on the other 
hand, dissolved nitrogen forms energetic combinations, nor 
to the pasturage of cattle on high mountains, whence there is 
annually abstracted, in the form of fat or milk, so much 
nitrogen, which nevertheless can scarcely reach such situations 
except by the atmosphere.” 
The result of the foregoing phenomena is, the formation 
of numerous principles peculiar to the vegetable kingdom, 
and the deposition of others which are foreign to plants, but 
which have been introduced into their system in the current 
of the sap. Thus are produced the silex of the Grass tribe; 
the sugar of the Cane, and of various fruits ; the starch of Corn, 
Potatoes, and other farinaceous plants; the gum of the Cherry; 
the tannin of the Oak ; and all those multitudes of alkaline, 
oily, resinous, and other principles, of which the modern 
chemist has ascertained the existence. These, belonging to the 
province of Chemistry rather than of Botany, need not be 
recapitulated here. It will be more useful to make some 
general observations upon the practical application of the 
physical laws we have been examining. 
It is, however, desirable to explain that the old ideas of 
certain secretions of inorganic matter being formed by the 
vital forces of plants are altogether disproved. It has, in par- 
ticular, been asserted that silex is formed by the vis formatrix 
of vegetation : but Dr. Daubeny has shown, by well conducted 
