50 QUARTERLYJOURNAL. 



only the power of absorbing food, but also of throwing off those 

 matters which are taken up with the food and are not necessary 

 for the growth or sustenance of the plant. Amongst the experi- 

 ments instituted to determine this point, we find but one in which 

 there is any evidence of an acid being excreted, and in this case it 

 was united with a base. When the ground upon which the poppy 

 had been grown was washed, a considerable quantity of acetate of 

 lime was found. 



But if free acids exist in soils they must be dissolved in the wa- 

 ter which passes through, and will then appear in springs and 

 wells, which we believe is never the case, although these waters 

 always contain some salts. There is an apparent exception to this, 

 but it is only apparent, in the case of carbonic and sulphuric acids 

 as they exist in some springs and as they are produced beneath 

 some soils in overwhelming quantities, so as to destroy all vegeta- 

 ble life. The presence of these acids depends upon some local 

 cause for which there is no remedy. 



Nothing has been said thus far of humic acid, which is known 

 to abound in soils chiefly composed of vegetable matter, because 

 this acid is utterly insoluble, and can therefore have no injurious 

 effect upon vegetation. We are only considering such free acids 

 as are prejudicial, and which of course must be soluble. It cannot 

 be assumed that soils abounding in this acid due from this cause un- 

 productive. They are so, not because they contain the acid, for it is 

 generally admitted to be, under proper circumstances, an abundant 

 source of nourishment to plants, but because the acid is insoluble, 

 and cannot in this state be conveyed into the mouths of plants. 



But after all, the question must be decided by analysis. It can- 

 not be reasoned thus — because such a plant grows upon a soil, that 

 soil is sour. The only evidence of its being sour is the actual 

 finding an acid in it, and if one is there it can certainly be found. 

 Besides, this question cannot be decided from the effect of alkalies, 

 and till some acid is found in the soil, the cause of the benefit fol- 

 lowing theit use, must be looked for in something else than their 

 neutralizing power. 



