70 OF THE INORGANIC CONSTITUENTS OF PLANTS. 



and magnesia, can be extracted by means of water 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 the 

 neutral oxalate or quadroxalate, but always as a binoxalate, on 

 whatever soil they may grow. The potash in grapes is always 

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

 and never 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 salts of certain acids, — for the capacity of saturation of an acid 

 is constant. 



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 im- 

 portance 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 invariable number can be 

 found to express the quantity of oxygen which each species of 

 plant contains in the bases united with organic acids. In all pro- 

 bability such inquiries will lead to most important results ; for it 

 is clear that if the production of a certain unchanging quantity 

 of an organic acid is required by the peculiar nature of the 

 organs of a plant, and is necessary to its existence, then potash 

 or lime must be taken up by it in order to form salts with this 

 acid ; that if these do not exist in sufficient quantity in the soil, 

 other alkaline bases, of equal value, must supply their place ; 

 and that the progress of a plant must be wholly arrested when 

 none are present. 



Seeds of the Salsola kali, when sown in common garden soil, 

 produce a plant containing both potash and soda ; while the planti 



