422 SCHREIXER— TOXIC SOIL SUBSTANCES. [April i8, 



soils. The nucleic acid may split off phosphoric acid, or a carbo- 

 hydrate such as the pentose mentioned above, and one or the other 

 of the soil compounds, xanthine, hypoxanthine, guanine, adenine, or 

 cytosine. This illustration serves to make clear the close relation 

 existing between the biochemical changes which take place in the 

 soil and those which take place in the animal. Of course the ulti- 

 mate origin of all these soil compounds are to be found in the plant 

 and animal debris which finds its way into the soil, through maturing 

 plant parts, roots, animal excreta, dead animals, or added in agricul- 

 tural practice in organic fertilizers, such as dried blood, tankage, or 

 in green crops plowed under. In addition to these sources which are 

 extraneous to the soil, there is the synthetic action of the micro- 

 organisms which inhabit the soil, but much further work needs to 

 be done on these biochemical changes in soils before their entire 

 course is understood. The forces which are operative we have 

 already shown to be those of lysis in general, especially hydrolysis, 

 oxidation, reduction, and catalysis. The life forms which produce 

 these forces in the soil are the bacteria, molds, protozoa, yeasts, and 

 the higher plants. All these contribute to the biochemical changes 

 in soils either through the above forces operative as enzymes, or 

 through the synthesis of the organic soil constituents from simpler 

 organic and inorganic material. 



After isolation and identification the soil compounds are studied 

 in respect to their action on growing plants, wheat being usually 

 used as an indicator. At the same time the action of various fer- 

 tilizer salts in diminishing or accentuating the action of the soil 

 compounds on plants is determined. In this manner much informa- 

 tion concerning the physiological action of the compounds, together 

 with suggestions for its neutralization or elimination are obtained. 

 Owing to lack of material not all of the substances isolated have been 

 studied in this comprehensive way, but sufficient information has 

 been obtained to show that among the above enumerated compounds 

 there are some that are distinctly toxic to plants, others that are dis- 

 tinctly beneficial and still others that are either doubtful or inert in 

 so far as direct physiological effects are concerned. 



Among the substances harmful to plants, picoline carboxylic 



