ORGANIC CONSTITUENTS OF SOILS. 9 



In addition to those here mentioned a number of others are already 

 isolated and will soon be reported. 1 It is obvious that definite 

 chemical information of this kind sheds much light upon the nature 

 of soil organic matter and the processes going on in the soils. The 

 compounds encountered are the same as those encountered in other 

 lines of biochemistry, and, therefore, the knowledge in regard to chem- 

 ical relationships, origin, and processes of change accumulated in 

 such other lines can be directly applied to the understanding of the 

 biochemical changes in soils and the constitution of soil organic mat- 

 ter. It is not my purpose to discuss the biochemical changes here, 

 other than to say, in passing, that the occurrence of these products 

 which have an obvious chemical relationship with the great classes of 

 tissue material contained in the plant and animal debris that gets into 

 the soil, the carbohydrates, the fats, the proteins, the nucleic acids, 

 the lecithins, etc., proves conclusively that the process of humification 

 is not a mysterious process which takes place in the soil and can not 

 be understood, but rather that the process of change in the soil is, 

 after all, very closely paralleled by the processes known to take place 

 in the laboratory when the complex organic substances are split by 

 hydrolysis, oxidation, reduction, or deamidization, into simpler deriv- 

 atives. It is my purpose, however, to bring strongly before you the 

 fact that these soil constituents affect plants directly. 



As scientists personally interested in all that has to do with plant 

 life and development you will be glad to learn that we have studied 

 as many as possible of these compounds in such a way as to determine 

 what their possible functions in the soil may be. Indeed, the reason 

 why this investigation of the organic matter in soils was undertaken 

 is to be found in the fact that certain soils and soil extracts behaved 

 toward plants as if they contained something detrimental to crops. 

 This harmful effect on plant growth can be shown very readily by 

 anyone with such a soil under investigation. The soil is shaken with 

 distilled water for several minutes, allowed to settle, and the super- 

 natant liquid filtered off, which must usually be done with a Pasteur- 

 Chamberland filter in an apparatus specially designed for such work, 

 in order that all solid material may be removed. The clear filtrate 

 is then used as a medium for the growth of wheat seedlings in bottle 



i These compounds have since been reported in Bulletin No. 88 of the Bureau of Soils, entitled: "Some 

 Organic Soil Constituents," by Edmund C. Shorey, and, in addition to the classes of compounds enumer- 

 ated above, contain aldehydes, sugars, and sulphur derivatives. The soil compounds described in this 

 bulletin are: 



Acrylic acid. Oxalic acid. Sulphur. 



Adenine. Rhamnose. Trimethylamine. 



Lysine. Saccharic acid. Trithiobenzaldehyde. 



Mannite. Salicylic aldehyde. 



Nucleic acid. Succinic acid. 



The isolation of guanine from a heated soil is described in Bulletin 89 of the Bureau of Soils, entitled: 

 " The Chemistry of Steam Heated Soils," by Oswald Schreiner and Elbert C. Lathrop. 



-Cir. 7413 2 



