THE ASH OF PLANTS. 161 



is to be gathered both from the table of ash-percentages 

 and from experiments like that of Wiegmann & Polstorf, 

 above described. 



III. We have reason to believe that each part or organ 

 (each cell) of the plant contains a certain, nearly invaria- 

 ble, amount of fixed matters, which is indispensable to the 

 vegetative functions. Each part or organ may contain, 

 besides, a variable and unessential or accidental quantity 

 of the same. What portion of the ash of any plant is es- 

 sential and what accidental is a question not yet brought 

 to a satisfactory decision. By assuming the truth of this 

 proposition, we account for those variations in the 

 amount of ash which cannot be attributed to the causes 

 already noticed. The evidences of this statement must 

 be reserved for the subsequent section. 



SPECIAL COMPOSITION OF THE ASH OF AGBICFLTUBAL 

 PLANTS. 



The result of the extended inquiries which have been 

 made into the subject of this section may be convenient- 

 ly presented and discussed under a series of propositions, 

 viz. : 



1. Among the substances which have been described 

 ( I) as the ingredients of the ash, the following are in- 

 variably present in all agricultural plants, and in nearly 

 all parts of them, viz. : 



f Potash, K,O. f Chlorine, Cl. 



Soda, Na,O. Sulphuric acid, SO S . 



Bases J. Lime, CaO. Acids J. Phosphoric acid, P,O B . 



Magnesia, MgO. Silicic acid, SiO,. 



I^Oxide of iron, Fe 2 O 3 . ^Carbonic acid, CO 2 . 



2. Different normal specimens of the same kind of 

 plant have a nearly constant composition. The use of 

 the word nearly in the above statement implies what has 

 been already intimated, viz., that some variation is noticed 

 in the relative proportions as well as in the total quantity 



11 



