1 10 SILEX. 



is present, and that by its means combinations 

 are produced; but the manner of their produc- 

 tion is as yet a mystery. 



It is, however, probable that a silicate of 

 potash is formed by some process in nature, 

 which is either entirely or sparingly soluble in 

 water; and this admitted, the difficulty at once 

 ceases. In this state it is absorbed by the 

 spongelets of the roots, the silex is assimilated 

 in the straw, and the potash exists to enter into 

 compounds with the various other substances 

 present, and to perform the functions elsewhere 

 described. 



Silex is one of the most abundant products 

 in nature; it constitutes a principal ingredient 

 in granite, it composes a large portion of the 

 sand found in beds of rivers, and on the sea 

 shore, and it enters largely into several mine- 

 rals of rarer occurrence, such as rock crystal, 

 quartz, cornelian, &c. 



Its mechanical use in agriculture is very 

 great, as it serves to render heavy soils porous, 

 and open to the transmission of moisture, and 

 with this view it is extensively used ; although 

 this action must not be confounded with the use 

 of the calcareous sand in Cornwall, the western 

 part of Ireland, and other places, where the be- 

 nefit derived arises entirely from the calcareous 

 nature of the sand so employed. 



This then concludes the description of those 

 substances which are assimilated by plants. 



It has been showed, it is hoped satisfactorily, 

 the sources from which these simples are de- 

 rived, their mode of action, and the compounds 

 they enter into, and the analysis of the various 



