130 ACTION OF SALTS. 



plants exert and keep up this influence. Salts act in a simi- 

 lar way, but above all, over all, influencing all, is the living 

 plant. This electric action induced, extends to undeternriined 

 distances ; hence there is a transfer, as is usual in all cases 

 of galvanic decomposition, of substances remote from the 

 plant, to its root, where they are taken up. It is not the 

 potash and lime, &c., immediately in contact with the root, 

 which alone supplies the plant, but under the galvanic influ- 

 ence, an undetermined portion of soil is decomposed. This 

 decomposing agency of plants wholly destroys all confidence 

 in experiments, undertaken to prove that pure water alone 

 can nourish plants. The containing vessel, that is the vessel 

 in which the experiment is made, is itself always decom- 

 posed. If, to guard against an error, glass is used, it has 

 already been shown that this is only a combination of sili- 

 cates, and these will be transferred from the glass to the 

 plant. 



By the experiments of Weigmann and Polstorff*, it ap- 

 pears that plants constantly discharge, while growing, car- 

 bonic acid from their roots. This acid decomposed the 

 silicates in a soil, which had resisted the action of nitro- 

 muriatic acid. It eliminated elements from supposed pure 

 quartz, whose existence there had been proved in no other 

 mode. 



