ORGANIC CONSTITUENTS OF SOILS. 13 



elated with animal material, but in addition to finding it in soils we 

 have also found it in many plant materials, such as wheat seeds, 

 wheat seedlings, wheat bran, rye, clover, alfalfa, cowpeas, and pota- 

 toes; and if, as is suggested by several investigators, creatinine 

 in the animal occurs as the result of the breaking up of albumin, 

 then it seems reasonable to expect that creatinine will be found in 

 practically all plants. From the standpoint of root excretion, I 

 should also mention the fact that of samples of the same soil, planted 

 and unplanted, the planted soils give larger amounts of creatinine, 

 thus showing that the increase in creatinine is connected in some 

 way with plant growth. When the roots of wheat were bathed 

 in water the creatinine could also be found in the culture water. 

 One of the sources of creatinine in soils would seem, therefore, 

 to be found in plants, since by their decay and by direct sloughing, 

 or even by excretion, the creatinine is left in water and soil. Its 

 occurrence in stable manure and also in green manures suggests 

 another source of supply, and its formation by soil organisms may 

 be another. Whatever its origin, it occurs in soils, appearing to be 

 a normal and frequently occurring constituent, and is present in 

 amounts comparable with the amounts of soil nitrates found in 

 ordinary agricultural soils. Its effect on plants, as I have implied 

 earlier, is decidedly beneficial. When a series of cultures containing 

 only potash and phosphates in varying proportions is set up together 

 with another set containing in addition some 50 parts per million 

 of creatinine the increased growth hi the latter set is rather striking, 

 being fully comparable with the increased growth produced by 

 nitrates under the same circumstances. When nitrates are present 

 at the same time the additional effect of the creatinine is not so 

 marked, but an analysis of the culture solution reveals the fact that 

 far less nitrate is used by the plants in the presence of the creatinine, 

 although a larger plant growth takes place. In other words, the plants 

 absorb the creatinine, make use of it in building up tissue, and in so 

 doing a lighter draft is made on the supply of nitrates. It appears, 

 therefore, that this soil constituent is fully as valuable as soil nitrates, 

 can be present in amounts comparable to the amounts of nitrates in 

 soils, and is able to replace the latter in its effect on plant growth. 

 The significance of this in agricultural investigations is apparent. 



Nor is creatinine the only constituent that behaves in this manner. 

 The same beneficial characters are shown by other soil constituents 

 by hypoxanthine and xanthine, by argininc and histidine, and 

 by nucleic acid. All these show the same influence on plant growth 

 and the same effect on the consumption of nitrate. Based on the 

 results of these rather extensive investigations, I am ready to for- 

 mulate the theory that these degradation products of protein are 

 absorbed by the plant directly from the soil and that the plant uses 



