418 EUROPEAN AGRICULTURE. 



LXXV. THEORY OF AGRICULTURE. 



The present theory of agriculture assumes that plants consist 

 of two species of matter vegetable and mineral ; that the former 

 is derived wholly from water and the air, and the latter from the 

 soil. The plant is not perfected without the conjoint aid of 

 both. The former consists of oxygen, hydrogen, carbon, and 

 nitrogen ; and the latter of at least eight different kinds of mineral 

 substances. The latter are found in the ashes of plants, and are 

 indestructible. They consist usually of four acids arid four 

 alkalies ; silicic acid, phosphoric acid, sulphuric acid, and mu 

 riatic acid ; and, of the alkalies, potash, soda, lime, and magnesia. 

 Other mineral substances are found ; but these which I have 

 enumerated are the principal. Boussingault thus designates 

 them : &quot; The residue left by the combustion is commonly com 

 posed of salts ; alkaline chlorides, with bases of potash and soda ; 

 earthy and metallic phosphates ; caustic or carbonated lime and 

 magnesia ; silica j and oxides of iron and of manganese. Several 

 other substances are also met with there, but in quantities so 

 small that they may be neglected.&quot;* 



The mineral substances found in the ashes of plants may be 

 supplied by art ; yet whether to be applied to the land in a direct 

 and simple, or in a combined or mixed form, and, if so, how com 

 bined and mixed, are points not as yet determined. It is certain 

 that there is only one form in which they can be taken up by 

 the plants, and that is, in as extreme a degree of solubility as 

 they are capable of being reduced to. Whether they shall be so 

 reduced before they are applied, whether, for example, they shall 

 be presented to the plants in a solid or a liquid form, or whether 

 they shall be by any art prepared, or it shall be left to the vital 

 operations of the plant to prepare them, are points yet to be 

 determined. These questions will naturally present themselves 

 again when the subject of manures is considered. 



In respect to the organic parts of vegetables, those which form 

 their largest portion, and consisting of oxygen, hydrogen, carbon, 

 and nitrogen, the two former are understood to be supplied by 

 water, the carbon by the atmosphere, and the nitrogen, consti- 



* Boussingault, p. 54. 



