112 OF THE INORGANIC CONSTITUENTS OF PLANTS. 



It is not known in what form silica, manganese, 

 and oxide of iron, are contained in plants ; but we 

 are certain that potash, soda, and magnesia, can be 

 extracted from all parts of their structure in the 

 form of salts of organic acids. The same is the 

 case with lime, when not present as insoluble oxalate 

 of lime. It must here be remembered, that in plants 

 yielding oxalic acid, the acid and potash never exist 

 in the form of a neutral or quadruple salt, but always 

 as a double acid salt, on whatever soil they may 

 grow. The potash in grapes also, is more frequently 

 found as an acid salt, viz. cream of tartar (bitartrate 

 of potash), than in the form of a neutral compound. 

 As these acids and bases are never absent from 

 plants, and as even the form in which they present 

 themselves is not subject to change, it may be 

 affirmed that they exercise an important influence 

 on the development of the fruits and seeds, and also 

 on many other functions of the nature of which we 

 are at present ignorant. 



The quantity of alkaline bases existing in a plant 

 also depends evidently on this circumstance of their 

 existing only in the form of acid salts, — for the 

 capacity of saturation of an acid is constant; and 

 when w^e see oxalate of lime in the lichens occupy- 

 ing the place of woody fibre which is absent, we 

 must regard it as certain that the soluble organic 

 salts are destined to fulfil equally important though 

 different functions, so much so that we could not 

 conceive the complete development of a plant with- 

 out their presence, that is, without the presence of 

 their acids, and consequently of their bases. 



From these considerations we must perceive, that 

 exact and trustworthy examinations of the ashes of 

 plants of the same kind growing upon different soils 

 would be of the greatest importance to vegetable 

 physiology, and would decide whether the facts 

 above mentioned are the results of an unchanging 

 law for each family of plants, and whether an inva- 

 riable number can be found to express the quantity 



