1?LAN* COtJSTlTtJfiNt^ , 3 



the greatest proportion of ash is found ; in the leaves 

 of root crops the ash will amount to 10 — 25 per cent, 

 of the dry matter. 



The incombustible ash always contains six chemical 

 elements — potassium, magnesium, calcium, iron, phos- 

 phorus and sulphur. Iron is present in only very 

 small quantity. These six elements, though forming 

 a very small portion of the plant, are indispensable to 

 its hfe. Besides the elements just named, an ash will 

 generally contain sodium, silicon, and chlorine, with 

 frequently manganese, and perhaps minute quantities 

 of other elements. The supplementary elements just 

 named sometimes form a considerable portion of the 

 ash ; they are not, however, essential to plant life, 

 though some of them discharge useful functions in 

 the plant. 



The metals above-named occur in the plant as salts, 

 being combined with phosphoric, nitric, sulphuric, 

 and various vegetable acids, of which formic, acetic, 

 oxalic, malic, tartaric, and citric acid are the most 

 common. The metals are also frequently present as 

 chlorides. Phosphorus occurs in the form of phos- 

 phates, and to a small extent in organic combination. 

 Silicon is present as silica. Sulphur occurs partly as 

 sulphates and partly as a constituent of albuminoids. 

 In the ash of plants the bases of the nitrates, and of 

 the salts of vegetable acids, are found in the form ot 

 carbonates. 



It is usual to speak of the combustible ingredients 

 of a plant as organic, and of the incombustible in- 

 gredients as inorganic. This distinction is scarcely 

 accurate, as those ash constituents which are indis- 

 pensable parts of plants have, during the life of the 



