140 now CROPS FEKD. 



]y with other Lases, as lime, oxide of iron, etc. These 

 alkali-salts, then, should attack the minerals of the soil in 

 a manner similar to carbonic acid. The same is probably 

 true of crenic and npoorenic acids. 



d. It scarcely requires mention that the ammonia salts 

 and nitrates yielded by the decay of plants, as well as the 

 organic acids, oxalic, tartaric, etc., or acid-salts, and the 

 chlorides, sulphates, and phosphates they contain, act upon 

 the surface soil where they accumulate in the manner al- 

 ready described, and that vegetable (and animal) remains 

 thus indirectly hasten the solution of mineral matters. 



Action of Living Plants on the Minerals of the Soil.— 



1. Moisture and Carbonic Acid. — The living vegetation 

 of a forest or prairie is the means of perpetually bringing 

 the most vigorous disintegrating agencies to bear upon 

 the soil that sustains it. The shelter of the growing 

 plants, not less than the hygroscopic humus left by their 

 decay, maintains the surface in a state of saturation by 

 moisture. The carbonic acid produced iu living roots, 

 and to some extent, at least, it is certain, excreted from 

 them, adds its effect to that derived from other sources. 



2. Organic Acids 'within the Plant. — According to 

 ZuUcr, ( Vs. St. \. 45) the young roots of living plants 

 (what plants, is not mentioned) contain an acid or acid- 

 salt which so impregnates the tissues as to manifest a 

 strong acid reaction with (give a red color to) blue litmus- 

 paper, which is permanent, and therefore not due to car- 

 bonic acid. This acidity, Zuller informs us, is most in- 

 tense in the finest fibrils, and is exhibited when the roots 

 are simply wrapped in the litmus-paper, without being at 

 all (?) crushed or broken. The acid, whatever it may be, 

 thus existing within the roots is absorbed by porous paper 

 placed externally to them. 



Previous to these observations of ZuUer, Salm Horst- 

 mar {Jour. far. Prakt.Chem. XL. 304,) liaving found in the 

 ashes of ground pine {Lycopodium, com^planatum), 38° j^, of 



