THE ASH OP PLLNTS. 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 plant? 

 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, (Masa textilis,) 

 aloe-hemp, (Agave Americana,) common flax, and New 

 Zealand flax, (P/iormium tenax,} 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,&quot; 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 ; 8.32 ; 9.77 ; 21.35. 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 ; 

 3.57 ; 4.65 ; 5 08 ; 7.81 ; 11.88 ; 17.12. (Journal farprakt. 



