WATER CONTENT AND ASH OF PLANTS l6l 



in the elementary or free state, as free sodium or free 

 silicon, but they are always in chemical combination, 

 forming salts, or are combined with the elements 

 which constitute the organic part of the plant. The 

 ash elements are never present in the form of free acids or 

 free bases, although, in chemical analyses, they are ex- 

 pressed as acid or basic oxides. Phosphorus, for exam- 

 ple, never exists in the plant as free phosphorus or as 

 phosphoric acid, but either as a phosphate or combined 

 with some of the elements which constitute the organic 

 part. 



209. Amount of Ash in Plants. While the amount 

 of ash in plants is fairly constant, it will be found to vary 

 with the stage of growth, climatic conditions, and na- 

 ture of the soil. In mature agricultural plants, the amount 

 rarely exceeds 10 per cent, of the dry weight of the ma- 

 terial. Clover grown in different localities is found to 

 contain from 6 to 8.5 per cent, ash; other crops also 

 show limited variations. The ash is not evenly dis- 

 tributed throughout all parts of a plant ; the leaves, for 

 example, contain a larger amount than the seed. In the 

 case of corn, the amount of ash in different parts is as 

 follows : 



Per cent. 



Mature plant 5.8 



Roots 3.5 



Leaves 8. i 



Stems entire 6.6 



Grain 1.4 



As previously stated, the ash elements of a plant, to- 

 gether with the nitrogen and water, represent all of the 



