THE ASH OF PLANTS. 17? 



on the unmanured soil, and on the same, after applica- 

 tion of the substances specified below : 



1234 56 



Unma- Chloride Nitrate Carbonate Su'phate Carbonate 

 nured. of of of of of 



sodium, potash, potash, magnesia. lime. 



100.0 100.0 100.0 100.0 100.0 100.0 



It is seen from these figures that all the applications 

 employed in this experiment exerted a manifest influ- 

 ence, and, in general, the substance added, or at least one 

 of its ingredients, is found in the plant in increased 

 quantity. 



In 2, chlorine, but not sodium ; in 3 and 4, potash ; 

 in 5, sulphuric acid and magnesia, and in 6, lime, are 

 present in larger proportion than in the ash from the 

 unmanured soil. 



6. What is the normal composition of the ash of a 

 plant ? It is evident from the foregoing facts and con- 

 siderations that to pronounce upon the normal composi- 

 tion of the ash of a plant, or, in other words, to ascer- 

 tain what ash-ingredients and what proportions of them 

 are proper to any species of plant or to any of its parts, 

 is a matter of much difficulty and uncertainty. 



The best that can be done is to adopt the average of a 

 great number of trustworthy analyses as the approximate 

 expression of ash-composition. From such data, how- 

 ever, we are still unable to decide what are the abso- 

 lutely essential, and what are really accidental, ingredi- 

 ents, or what amount of any given ingredient is essential, 

 and to what extent it is accidental. Wolff, who appears 

 to have first suggested that a part of the ash of plants 



