INOEGANIO CONSTITUENTS OF PLANTS. 131 



Silica . 



Phospliorio acid 



Sulphuric acid 



Chlorine 



Carhonic acid 



Magnesia 



Lime . 



Peroxide of Iron . 



Potash . 



Soda . 



These inorganic elements are variously combined in plants, in the 

 form of sulphates, phosphates, silicates, and chlorides. Some plants, 

 as Wheat, Oats, Barley, and Eye, contain a large quantity of Silica 

 in their straw ; others, such as Tobacco, Pea-straw, Meadow-clover, 

 Potato-haulm, and Sainfoin, contain much lime ; while Turnips, Beet- 

 root, Potatoes, Jerusalem-artichoke, and Maize-straw, have a large 

 proportion of salts of potash in their composition. Sulphates and 

 phosphates are required to supply part of the material necessary for 

 the composition of the nutritive protein compounds found in grain. 



Silica (SiO^) abounds in Grasses, in Equisetum, and other plants, 

 giving firmness to their stems. The quantity contained in the Bamboo 

 is very large, and it is occasionally found in the joints in the form of 

 Tabasheer. Reeds, from the quantity of siliceous matter they contain, 

 are said to have caused conflagrations, by striking against each other 

 during hurricanes in warm climates. In species of Equisetum, the 

 silica in the ash is as follows : — 



Ash. Silica. 



Equisetum arvense . . . 13'84 ... 6-38 



limosum . . . 15-50 ... 6-50 



hyemale . . . 11-81 ... 8-75 



maximum . . . 23-61 ... 12-00 



The third of these furnishes Dutch Reed, used for polishing mahogany. 

 The silica is deposited in a regular manner, forming an integral part 

 of the structure of the plant. Many insoluble matters, as silica, seem 

 to be deposited in cells by a process of decomposition ; thus, silicate 

 of potash in a vegetable sap may combine with oxalic acid, by which 

 oxalate of potash and silicic acid will be produced, as in the cells of 

 Grasses and Equisetum. Chara translucens has a covering of silicic 

 acid, while 0. vulgaris has one composed of silicic acid and carbonate 

 of lime ; and Ohara hispida has a covering of carbonate of lime alone. 

 Silica, the only known oxide of Silicon, contains 28 parts silicon, and 

 32 parts oxygen. It is in reality an acid, though a very weak one at 

 ordinary temperatures. Its insolubility in water prevents the mani- 

 festation of its acid properties under ordinary circumstances. In those 

 plants in which silica most abounds. Fluorine has also been discovered. 



