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 the former had 
an acid reaction, while the latter did not affect litmus- 
paper. Salm Horstmar supposed that the alumina of 
the soil finds its way into the Lycopodium by means of 
this acid. Ritthausen has shown that the Lycopodium 
contains 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 malate of alumina. (Jour. fir. Prakt. 
Chem. LITT. 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, bitartrate of potash, ctc.; 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. 
After 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 the 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 acids existing in 
the root-cells of plants may act directly upon the rock or 
soil external to them. By such action is doubtless to be 
explained the fuct mentioned by Liebig in 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.” 
(Modern Ag. p. 43.) 
