MANURES. 85 



not much matter whether it be potash or soda ; but in 

 general it will be more productive if both these alkalies 

 are present. For plants which naturally inhabit the sea- 

 shore, such as asparagus and sea kale, its presence in the 

 form of common salt (Chloride of sodium) is indispensa- 

 ble. (Lindley.} The nitrate of soda is similar in its 

 beneficial action upon plants to the nitrate of potash, but 

 it is not yet settled whether the good effects of these salts 

 are owing to their nitrogen, or in part to their alkali. 



Phosphoric Acid, Next to ammonia, this is usually 

 the most necessary application to soils, because the first 

 element exhausted. Where not present in sufficient quan- 

 tity, its supply, artificially, is even of more urgent neces- 

 sity. A supply of ammonia may, in some measure, be de- 

 rived from the atmosphere, but the phosphates must be 

 restored by man. The presence of the phosphates in the 

 soil is required that ammonia may have its full effect. 



u In wild plants, the phosphates are less abundant than 

 in cultivated crops. The latter produce a large quantity 

 of blood, forming food in a short space of time ; hence 

 more phosphates are required. All plants that are useful 

 for animal food have great power of taking up the phos- 

 phates, and cultivation increases this power. Evergreen 

 and perennial plants extend their vegetating processes 

 over many years, and do not in a given period require so 

 large a quantity of the phosphates as the ordinary culti- 

 vated plants, and their falling leaves restore much of the 

 inorganic matter to the soil. But cultivated plants are 

 mostly annual and herbaceous, grow rapidly, and require 

 an abundance of phosphates, which are annually removed 

 with the crop. If the crop, like that of wild plants, was 

 left upon the soil, the plants in their decay would restore 

 all they had taken. Phosphoric acid is present in the 

 blood, is a constituent of the brain and nerves, and enters 

 largely into the bones of the animals that consume these 

 plants or their seeds and roots. Providence never per- 



