EXPERIMENT STATION BULLETINS. 405 



the formation of amino acids. About ten per cent of the total nitro- 

 gen is due to the presence of acid amides. From the worlv of Schreiner 

 and Shorey purine, pyrimidine and pyridine compounds constitute a 

 part of the remainder. The greater part is, however, present in forais 

 concerning which we know nothing and which may represent the most 

 important factors in aiding or inhibiting plant growth. It seems prob- 

 able, from the Avork done so far, that the classes of compounds consti- 

 tuting this unknown residue are many. If this is true the possibility 

 of ever getting a simple laboratory method for determining the so-called 

 availability of organic nitrogenous material seems hopeless, as the dif- 

 ference in the action of soil agents upon different substances is un- 

 doubtedly very marked. The factor of toxicity must also be taken into 

 consideration. Even though some method might be devised for imita- 

 ting the action of soil agents in breaking down soil organic matter the 

 presence of substances poisonous to plant growth is always a possibility 

 until sufficient knowledge has been obtained of the kinds and amounts 

 of the various compounds present for us to make positive statements to 

 the contrary. The greatest need at present in determining the value of 

 the organic nitrogenous material of peat and humus is a closer knowl- 

 edge of the individual substances actually present in such material and 

 those which may possibly be formed by natural agents in the soil. Until 

 this knowledge shall have been gained all attempts at the utilization of 

 this material must be made more or less blindly and by empirical and 

 uncertain methods. 



In conclusion the author wishes to express his thanks to Dr. D. D. 

 VanSlyke of the Rockefeller Institute for Medical Research for his 

 kindly interest and helpful suggestions regarding this work. 



