108 NATURE AND PROPERTIES OF SOILS 



Hentriacontane — C 3J H 64 Histidine — C 6 H 9 2 N 3 



*>/ Dihydroxystearic acid — Trithiolbenzaldehyde — 



C 18 H 36 4 (C.H.CSH),. 



Succinic acid — C 4 H 6 4 Creatinine — C 4 H 7 ON 3 



Picoline carboxylic acid — Salicylic Aldehyde — 



C 7 H 7 2 N C 6 H 4 OHCOH 



57. Relation of organic compounds to plants. — So far as 

 the plant is concerned, organic compounds may be divided 

 into three groups: those that are beneficial, those that are 

 neutral, and those that are toxic or harmful in their effects. 

 As an example of the first group, histidine and creatinine x 

 may be mentioned. Here is a case in which the compounds 

 in the soil organic matter may exert a stimulating effect on 

 plant growth, supplementing the nitrates 2 to a certain extent. 

 That the nitrogen of the soil organic matter may be utilized 

 by plants is well summarized by the publications of Hutchin- 

 son and Miller. 3 As an example of a harmful compound aris- 

 ing from the decomposition of the organic matter, dihydroxy- 

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

 compound was the first to be isolated and identified by the 

 Bureau of Soils and is very toxic. 



The discovery of such compounds in the soil has revived the 

 old theory of toxicity, 4 by which the infertility of certain 

 soils was accounted for. Root excretions were also held to be 

 detrimental to succeeding crops of the same kind. The toxic 

 materials of the soil organic matter largely originate under 



1 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, O., and Skinner, J. J., Nitrogenous Soil Constituents and 

 Their Bearing upon Soil Fertility; U. S. Dept. Agr., Bur. Soils, Bui. 87, 

 p. 68, 1912. Also, Schreiner, O., and Others, A Beneficial Organic Con- 

 stituent of Soils; Creatinine; U. S. Dept. Agr., Bur. Soils, Bui. 83, p. 44, 

 1911. 



8 Hutchinson, 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. 



*See Schreiner, O., and Reed, H. S., Some Factors Influencing Soil 

 Fertility; U. S. Dept. Agr., Bur. Soils, Bui. 40, pp. 36-40, 1907. 



