132 INORGANIC CONSTITUENTS OF PLANTS. 



The test for the presence of the latter rests in acting on the fluoride 

 with concentrated sulphuric acid, and so producing hydrofluoric acid, 

 which possesses the property of etching glass ; the glass being coated 

 with wax, and the design to be etched traced with a pointed instru- 

 ment. 



Lime is found in all plants, and in some it exists in large quantity. 

 It occurs sometimes in the form of carbonate on the surface of plants. 

 Thus, many of the Characese have a calcareous encrustation. The 

 crystals or raphides (p. 10), found in the cells of plants, have lime in 

 their composition. In the roots of Turkey and East India Ehubarb 

 the crystals of oxalate of lime have been estimated at about 25 per 

 cent, while in those of the English plant the proportion is about 10 

 per cent. In the Cactus tribe crystals of the same kind have been 

 observed, the presence of which, in excessive quantity, imparts brittle- 

 ness to the stem of the old plant. 



Soda and Potash occur abundantly iu plants. They are taken 

 up from the soil in combination with acids. Those growing near the 

 sea have a large proportion of soda in their composition, while those 

 growing inland contain more potash. Various species of Salsola, 

 Salicornia, Halimocnemum, and Kochia, yield soda for commercial 

 purposes, and are called Halophytes (ciX?, salt, and ip-jrov, plant). 

 The young plants furnish more soda than the old ones. There are 

 certain species, as Armeria maritima, Cochlearia officinalis, Plantago 

 maritima, and Silene maritima, which are found both on the sear 

 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, potash prevails, and iodine disappears. 



Ieon, Manganese, and Ooppee, especially the two latter, exist 

 in small quantity in plants. Iron exists in the soil either as an 

 oxide, sulphide, or carbonate, usually occurring as peroxide. Iron 

 when held in solution as carbonate is capable of being absorbed into 

 the vegetable tissues. ' Copper has been detected in coffee. 



All these inorganic matters are derived in a state of solution from 

 the soU, and plants are said to have, as it were, a power of selection, 

 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 containing 

 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 experi- 

 ment, and he found that in watery solutions of mixed salts the plant 

 ' absorbed all in equal proportions. Daubeny states, that if any par- 



