186 ROOTS DISENGAGE CARBONIC ACID. [BOOK n. 



disengage carbonic acid, and that this acid is capable of decom- 

 posing the silicates of the soil, which even resist the action of 

 nitro-muriatic acid. This most curious discovery throws a new 

 light upon the importance of carbonic acid to vegetation, and 

 explains clearly what has been by no means evident, namely, 

 the manner in which flinty substances prove beneficial to 

 vegetation, and how minerals so hard as felspar are made to 

 contribute to the maintenance of plants. Plants of Tobacco, 

 Oats, Barley, Clover, &c., were grown in quartz-sand, which 

 had been heated red-hot, and then digested for sixteen hours 

 in dilute nitro-muriatic acid. One would have thought that 

 after such treatment the quartz could have contained nothing 

 capable of sustaining vegetable life ; nevertheless, the plants 

 grew in it, and their ashes were found to contain potassa, 

 lime, magnesia, and siliceous earth, which had been obtained 

 from the decomposition of the quartz-sand by the carbonic 

 acid of the roots. Dr. Jackson of Boston U. S., has also 

 observed that glasses in which Hyacinth bulbs had been 

 grown, were corroded. He had also noticed the same effects 

 on bottle glass, which had lain in garden mould, and supposes 

 that plants have the power of decomposing glass as well as 

 the felspar of granite, and of appropriating to their use the 

 potash contained in it, and that this is the source of the 

 potash contained in the ashes of plants. (Proceedings of 

 Boston Society.} 



