REMOVAL OF NUTRIENTS FROM THE SOIL 297 



properties corresponding to those of an oxidizing enzyme. 

 His work has been repeated by others, who have failed to ob- 

 tain similar results, but lately Sehreiner and Reed^ have 

 demonstrated an oxidizing action of roots that is apparently 

 due to a peroxidase. Oxidation alone, however, would hardly 

 suffice to account for the solvent action accompanying the de- 

 velopment of roots, although it is doubtless an important 

 function and useful in other ways. 



Sehreiner and Sullivan^ have demonstrated the presence 

 of reducing substances in media in which plants were grow- 

 ing. This work has recently been corroborated by Lyon and 

 Wilson,^ working with maize, oats, peas, and vetch. They 

 found that the solutions in which the plants had been growing 

 exhibited both reducing and oxidizing phenomena. Reducing 

 substances were always present, but whether oxidizing mate- 

 rials were so consistently produced could not be definitely 

 decided. The peroxidases were rendered inactive by boiling 

 the solutions. The reducing substances did not always disap- 

 pear with such treatment. This would throw some doubt upon 

 the enzymic character of the reducing materials and suggest 

 that non-enzymic catalytic exudates are a possibility. 



The interstices between the larger particles of a normal 

 soil are at least partially filled with colloidal material of a 

 more or less gel-like nature. Moreover, the surfaces of some 

 soil grains may be somewhat coated with the same material. 

 Roots of growing plants have been found to cause coagula- 

 tion of at least some colloids, possibly by leaving an acid 

 residue in the nutrient solution by reason of the selective 



Organische Substanzen; Sitzungsber. Akad. Wiss. Wien-Math. Nat., Band 

 96, Seite 84-109, 1888. Abstract in Chem. Centrlb. f. Agr. Ohem., Band 

 17, Seite 428, 1888. 



* Sehreiner, Oswald, and Beed, H. S., Studies on the Oxidising Powers 

 of Boots; Bot. Gazette, Vol. 47, p. 355, 1909. 



* Sehreiner, 0., and Sullivan, M. K., Studies in Soil Oxidation; U. S. 

 Bept. Agr., Bur. Soils, BuL 73, 1910. 



"Lyon, T. L., and Wilson, J. K., lAberation of Organic Matter by 

 Boots of Growing Plants; Cornell Agr. Exp. Sta., Memoir 40, July, 1921* 



