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an Individual. 21 
nica. Of the same nature are the deposits of crystals of calcium oxalate 
In the cell-wall, as for example in the leaves of the citron, the epidermis 
of the root of the Lombardy-poplar, &c. 
The cell-wall consists of a peculiar substance called ce//wlose, having 
the chemical composition C,H,,O,. It is found in the pure state only 
in young cells ; in older cells it is often concealed by other bodies 
which are said to incrust it, or becomes altogether transformed into other 
élasticune. (X 370.) 
Fic. 36. — Scalariform cell 
from the underground stem 
of the brake, Pteris agut- 
lina. (%* 500.) 
‘Substances. Cell-walls are intimately permeated, by means of zucrws- 
tation or infiltration, by other substances which are deposited among 
the particles of cellulose. The cell-walls of many Algze are converted 
__ by incrustation into actual coats of silica, which are often marked with 
very beautiful tracings, so fine that they are used as test-objects under ~— 
the microscope ; and this is especially the case in the diatoms (Figys 
Fic. 37.—Cystoliths from the leaf of Urostigma 
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