ORIGIN AND FORMATION' OF SOILS. 141 



alumina, while in the ashes of juniper, growing beside 

 the Lycopodium, this substance was absent, examined 

 the rootlets of both plants, and found that tlie former had 

 an acid reaction, while the latter did not affect litmus- 

 paper. Salm Ilorstniar supposed that the alumina of 

 the soil finds its way into the Lycopodium by means of 

 this acid. Ritthansen has shown that the Lycopodium 

 contahis malic acid, and since all the alumina of the plant 

 may be extracted by water, it is probable that the acid 

 reaction of the rootlets is due, in part at least, to the 

 presence of acid raalate of alumina. {Joxr. fnr. Prakt. 

 Chem. LIIL 420.) 



At Liebig's suggestion, Zoller made the following ex- 

 periments. A number of glass tubes were filled with 

 water made slightly acid by some drops of hydrochloric 

 acid, vinegar, citric acid, bitartrato of potash, etc. ; the 

 open end of each tube was then closed by a piece of 

 moistened bladder tied tightly over, and various salts, in- 

 soluble in water, as phosphate of lime, phosphate of am- 

 monia and magnesia, etc., were strewn on the bladder. 

 A^ter a short time it was found that the ingredients of 

 these salts were contained in the liquid in contact with 

 the under surface of the bladder, having been dissolved 

 by tlie dilute acid present in the pores of the membrane, 

 and absorbed through it. This is an ingenious illustra- 

 tion of the mode in which the organic aciils existing in 

 the root-cells of plants may act directly upon the rock or 

 soil external to tliem. By such action is doubtless to be 

 explained the fact mentioned by Liebig hi the following 

 words : 



" We frequently find in meadows smooth limestones 

 with their surfaces covered with a network of small fur- 

 rows. "When these stones are newly taken out of the 

 ground, we find that each furrow corresponds to a rootlet, 

 which appears as if it had eaten its way into the stone." 

 {31odern Ag p. 43.) 



