36 -Fallow Land. [BookVlIL 



cerated in diftilled water, produced a black colour 

 with galls. The leaves of a plant of mint, which had 

 been nourlfhed by water alone, when tried by the 

 fame teft, produced no colour whatever. Trifling as 

 this experiment may appear, it proves two points; 

 that plants have not the power of rejecting even inju- 

 rious matters when prefented to their roots - f and that 

 other matters befides water and air are capable of being 

 abforbed'by them* 



Agriculture feems yet to be nearly in its infancy, 

 and even the benefit produced by the common cuftom 

 of letting lands lie fallow, has not yet been fatisfacto- 

 rily explained. Something may no doubt be attri- 

 buted to the deftrudtion of weeds, but more probably 

 to fome change produced in the foil by its being ex- 

 pofed to the action of the fun and air. The manage- 

 ment of nitre- beds may tend to throw fome light on 

 this fubje<5t. Thefe are compofed of calcareous earth 

 and dung cemented together. After being expofed 

 for fome months to the air, they are found to contain 

 a quantity of nitrous acid, which, uniting to the cal- 

 careaus earth, forms a kind of fait, which is extracted 

 by lixiviation. Now calcareous earth .and dung are 

 two of the molt powerful kinds of manure, and it doe;! 

 not feem improbable that their fertilizing powers may 

 be in fome manner connected with tlieir property &f 

 affording nitrous acid. 



