580 



SCIENCE 



[N. S. Vol. XXXVI. No. 931 



Pentose, 

 Agrosterol, 



Choline, 

 Creatinine. 



In addition to those here mentioned, a 

 number of others are already isolated and 

 will soon be reported. 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 chemical relation- 

 ships, origin and processes of change ac- 

 cumulated in such other lines can be di- 

 rectly applied to the understanding of the 

 biochemical changes in soils and the con- 

 stitution of soil organic matter. 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 con- 

 tained 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 soils only 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 derivatives. It 

 is my purpose, however, to bring strongly 

 before you the fact that these soil constit- 

 uents affect plants directly. 



As scientists personally interested in all 

 that has to do with plant life and develop- 

 ment, 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 function in the soil 

 may be. Indeed, the reason why this in- 



vestigation 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 some- 

 thing detrimental to crops rather than an 

 absence or deficiency of the usual beneficial 

 elements like nitrogen, phosphorus or po- 

 tassium. This harmful effect on plant 

 growth can be shown very readily by any 

 one with such a soil under investigation. 

 The soil is shaken with distilled water for 

 several minutes, allowed to settle, and the 

 supernatant liquid filtered off, which must 

 usually be done with a Pasteur-Chamber- 

 land filter in an apparatus specially de- 

 signed 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 cul- 

 tures. A control in pure distilled water, 

 or in an extract from a fertile soil, should 

 be run at the same time. In such cases 

 the plants grown in the extract from the 

 poor soil will show many peculiarities not 

 shown by the plants either in the pure dis- 

 tilled water or in the extract from the 

 good soil. The plant will be smaller, less 

 developed in top and root, the latter often 

 showing dark and swollen tips, which are 

 sometimes bent into hooks, a phenomenon 

 characteristic of certain toxic action. The 

 growth in this soil extract may even be 

 greatly less than the growth in the distilled 

 water, although the soil extract naturally 

 contains plant nutrients, whereas the dis- 

 tilled water contains none. 



If a separate portion of the original ex- 

 tract be treated with carbon black, made 

 from natural gas by imperfect combustion 

 much as lampblack is formed on lamp 

 chimneys, agitated and filtered, the filtrate 

 will be a good medium for the growth of 

 the seedlings. This simple treatment with 

 carbon black has, therefore, removed by 

 absorption the harmful properties of the 



