114 INORGANIC CONSTITUENTS OF PLANTS. 



Ash. Silica. 



Equisetum arvense 13-84 6'38 



limosnm 15'50 



hvemale H-81 8'75 



Telroateia 23'61 12-00 



The third of these furnishes Dutch Rush, 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 be mixed 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 C. vulgaris has one composed of silicic acid and carbo- 

 nate of limp ; and Chara hispida has a covering of carbonate of lime 

 alone. 



227. JLime is found in all plants, and in some it exists in large 

 quantity. It occurs sometimes in the form of carbonate on the sur- 

 face of plants. Thus, many of the Characeas have a calcareous encrus- 

 tation. The crystals or raphides (^ 18) found in the cells of plants, 

 have lime in their composition. 



228. Soda and Potash occur abundantly in plants. Those grow- 

 ing near the sea have a large proportion of soda in their composition, 

 while those growing inland contain potash. Various species of Salsola. 

 Salicornia, Halimocnemum, and Kochia, yield soda for commercial pur 

 poses, and are called Halophytes AJ, salt, and Qvroy, plant). The 

 young plants, according to Gobel, furnish more soda than the old ones 

 There are certain species, as Armeria maritima, Cochlearia officinalis, 

 and Plantago maritima, which are found both on the sea-shore, and 

 high on the mountains removed from the sea. In the former situation 

 they contain much soda and some iodine ; while in the latter, accord- 

 to Dr. Dickie, potash prevails, and iodine disappears. 



229. iron, manganese, and Copper, especially the two last, exist 

 in small quantity in plants. Copper was detected, by Sarzean, in 

 coffee. 



230. All these inorganic matters are derived in a state of solution 

 from the soil, and plants are said to have, as it were, a power of selec- 

 tion, certain matters being taken up by their roots in preference to 

 others. Saussure made a series of experiments on this subject, and 

 stated that when the roots of plants were put into solutions contain- 

 ing various saline matters in equal proportions, some substances were 

 taken up by imbibition in larger proportion than others. Bouchardat 

 doubts the accuracy of Saussure's conclusions on this point. He thinks 

 that errors arose from the excretions of the plants and other causes. 

 He performed similar experiments with plants of Mint, which had been 

 growing for six months in water previous to experiment, and he found 



