PROOFS OF ACID SOILS. 73 



until we may suppose the recent supply of acid to have been re- 

 moved by cultivation and other causes, 



It may be objected that, even if fully admitted, my authorities 

 prove only the formation of a single vegetable acid in soil, the acetic 

 that my facts show only the production of a single acid plant, 

 sorrel and that the acid which sorrel contains is not the acetic, 

 but the oxalic.* In reply to such objections, it may be said, that 

 from the application of acids to recently ploughed land, no acid 

 plant except sorrel is made to grow, because that one only can 

 spring up speedily enough to arrest the the fleeting nutriment. Po- 

 verty grass (Aristida gracilis or A. dichotoma) grows only on the 

 same kinds of soil, and generally covers them after they have been 

 a year free from a crop, but does not show sooner ; and pines re- 

 quire two years before their seeds will produce plants. But when 

 pines begin to spread over the land, they soon put an end to the 

 growth of all other plants, and are abundantly supplied with their 

 acid food, from the dropping of their own leaves. Thus they may 

 be first supplied with the vegetable acid ready formed in the 

 leaves, and afterwards with the acetic acid, formed by their sub- 

 sequent slow decomposition. It does not weaken my argument, 

 that the product of a plant is a vegetable acid different from the 

 one supposed to have nourished its growth. All vegetable acids 

 (except the prussic), however different in their properties, are com- 

 posed of the same three elementary bodies, differing only in their 

 proportions')- and consequently are all convertible into each other. 

 A little more, or a little less of one or the other of these ingre- 

 dients, may change the acetic to the oxalic acid, and that to any 

 other. We cannot doubt but that such simple changes may be 

 produced by the chemical powers of vegetation, when others are 

 effected far more difficult for us to comprehend. The most tender 

 and feeble organs, and the mildest juices, aided by the power of 

 animal or vegetable life, are able to produce decompositions and 

 combinations which the chemist cannot explain, and which he would 

 in vain attempt to imitate. 



4th. This ingredient of soils, which nourishes acid plants, also 

 poisons cultivated crops. Plants have not the power of rejecting 

 noxious fluids, but take up by their roots everything presented in a 

 soluble forin.^ Thus the acid also enters the sap-vessels of culti- 

 vated plants, stints their growth, and makes it impossible for them 

 to attain that size and perfection which their proper food would 

 insure, if it were presented to them without its poisonous accom- 

 paniment. When the poorest virgin wood-land is cut down, it is 



* Agr. Chem. Lecture 3. 



f Carbon, oxygen, and hydrogen. Agr. Chem. Lecture 3, p. 78. 



J Agr. Chem. Lecture 6, page 186. 



