136 SOILS: PROPEETim AND MANAGEMENT 



histidine and creatinine^ may be mentioned. Here is 

 a case in which the compounds found in the soil humus 

 may exert a stimulating effect on plant growth, and 

 may also be a source of plant-food, supplementing the 

 nitrates ^ to a certain extent. That the nitrogen of the 

 soil organic matter may be utilized by plants is well sum- 

 marized by the publications of Hutchinson and Miller.^ 

 As an example of a harmful compound arising from the 

 decomposition of the organic matter, dihydroxystearic 

 acid^ may be mentioned as one of the best known. This 

 compound was the first to be isolated and identified by 

 Schreiner, and is very toxic. 



93. To3dc material in the soil.— The discovery of 

 such compounds in the soil has revived the old theory 

 of toxicity,^ by which the infertility of certain soils is 

 accounted for. Root excretions are also held to be 

 detrimental to succeeding crops of the same kind. The 



^ Skinner, J. J. Effect of Histidine and Arginine as Soil 

 Constituents. Eighth Internat. Cong. App. Chem., Vol. XV, 

 pp. 253-264. 1912. Also, Beneficial Effects of Creatinine 

 and Creatine on Growth. Bot. Gaz., Vol. 54, No. 2, pp. 152- 

 163. 1912. 



2 Schreiner, 0., and Skinner, J. J. Nitrogenous Soil Con- 

 stituents and Their Bearing upon Soil Fertility. U. S. D. A., 

 Bur. Soils, Bui. 87, p. 68. 1912. Also, Schreiner, 0., and others. 

 A Beneficial Organic Constituent of Soils; Creatinine. U. S. 

 D. A., Bur. Soils, Bui. 83, p. 44. 1911. 



^Futehinson, H. B., and Miller, N. H. J. The Direct 

 Assimilation of Inorganic and Organic Forms of Nitrogen by 

 Higher Plants. Jour. Agr. Sci., Vol. 4, Part 3, pp. 282-302. 

 1912. 



^ Schreiner, 0., and Skinner, J. J. Some Effects of a Harm- 

 ful Organic Soil Constituent. TJ. S. D. A., Bur. Soils, Bui. 70. 

 1910. 



^See Schreiner, 0., and Reed, H. S. Some Factors Influ- 

 encing Soil Fertility. U. S. D. A., Bur. Soils, Bui. 40, pp. 36- 

 40. 1907. 



