CH. II.] THE ROOT. 101 



employed be pure. Xo wonder that experiments are 

 discrepant, when Mr. E. Solly has detected adultera- 

 tions in fertilizers to the amount of 97 per cent. ! 

 Even when the dung of animals is employed, it 

 varies most essentially, and according to the food on 

 which tliey are kept The richer their nourishment 

 the more abouncUng are their excrements in the salts 

 of ammonia and other fertilizing matters. 



Some manures ameliorate a soil by absorbing 

 moisture from the atmosphere. This property is at 

 least as beneficial to ground that is aluminous, as to 

 that which is siliceous ; for it is equally useless to 

 either duiing such periods of the year as are charac- 

 terised by a plentiful deposition of rain ; but in the 

 drought of summer, when moistui'e is much wanting 

 to plants, it is beneficial to both : m very dry 

 seasons it is even of greater importance to clayey 

 than to light soils ; for vegetation on the former 

 suffers more from long continued drought than 

 on the latter, inasmuch as that moisture being 

 equally exhaled from each, the surface of the clayey 

 soil becomes caked and impervious to the air, the 

 only grand source of compensatoiy moisture that is 

 available to the languishing plants, and which is more 

 open to those which grow on light and, consequently, 

 more pervious soils. 



The following table of the comparative absorbent 

 powers of many manui'es is extracted chiefly from 



