CONSTITUENTS OF PLANTS. 95 



line bases. Culture alone will be able to cause a 

 deviation. 



In order to understand this subject clearly, it 

 will be necessary to bear in mind, that any one of 

 the alkaline bases may be substituted for another, 

 the action of all being the same. Our conclusion 

 is, therefore, by no means endangered by the exist- 

 ence of a particular alkali in one plant, which may 

 be absent in others of the same species. If this 

 inference be correct, the absent alkali or earth must 

 be supplied by one similar in its mode of action, or 

 in other words, by an equivalent of another base. 

 The number of equivalents of these various bases, 

 which may be combined with a certain portion of 

 acid, must necessarily be the same, and, therefore, 

 the amount of oxygen contained in them must 

 remain unchanged, under all circumstances, and on 

 whatever soil they grow. 



Of course, this argument refers only to those 

 alkaline bases, which in the form of organic salts 

 form constituents of the plants. Now, these salts 

 are preserved in the ashes of plants, as carbonates, 

 the quantity of which can be easily ascertained. 



It has been distinctly shown by the analyses of De 

 Saussure and Berthier, that the nature of a soil exer 

 cises a decided influence on the quantity of the dif- 

 ferent metallic oxides contained in the plants, which 

 grow on it ; that magnesia, for example, was con- 

 tained in the ashes of a pine-tree grown at Mont 

 Breven, whilst it was absent from the ashes of a tree 



