THE ASH OF PLANTS. \ 185 
the cell-wall, that when the organic matters are destroyed 
by burning, or removed by solvents, the form of the cell 
is preserved in a silicious skeleton. This has long been 
known in case of the Equisetums and Deutzias. Here, the 
roughnesses of the stems or leaves which make these plants 
useful for scouring, are fully incrusted or interpenetrated 
by silica, and the ashes of the cuticle present the same ap- 
Pearance under the microscope as the cuticle itself. ; 
Lately, Kindt, Wicke, and Mohl, have observed that the 
hairs of nettles, hemp, hops, and other rough-leaved plants, 
are highly silicious. 
The bark of the beech is coated with silica—hence the 
smooth and undecayed surface which its trunk presents. 
The best textile materials, which are bast-fibers of various 
plants, viz., common hemp, manilla-hemp, (Musa textilis,) 
aloe-hemp, (Agave Americana,) common flax, and New 
Zealand ‘flax, (Phormium tenaz,) are completely incrusted 
with silica. In jute, (Corchorus textilis,) some cells are 
partially incrusted. The cotton fiber is free from silica. 
Wicke, (loc. cit.,) suggests that the durability of textile 
fibers is to a degree dependent on their content of silica. 
The great variableness observed in the same plant, and 
in the same part of the plant, as to the content of silica, 
would indicate that this substance is at least in some de- 
gree accidental. 
In the ashes of ten kinds of tobacco leaves, Fresenius 
& Will found silica to range from 5.1 to 18.4 per cent. 
The analysis of the ash of 13 samples of pea-straw, grown: 
on different soils from the same seed during the same year, 
under direction of the ‘“ Landes Oeconomie Collegium,” of 
Prussia, gave the following percentages of silica, viz: 
0.56; 0:75; 2.30; 2.32; 2.80; 3.29; 3.57; 5.15; 5.82; 
8.03 ; 8.382; 9.77; 21.385. Analyses of the ash of 9 samples 
of colza-straw, all produced from the same seed on differ- 
ent soils, gave the following percentages: 1.00; 1.14; 3.02; 
8.57; 4.65; 5.08; 7.81; 11.88; 17.12. (Journal fur prakt. 
