ABSORPTION OF NUTRITIVE SALTS 407 



were not. He concludes that if the tracings are due to 

 acids excreted by the plant roots, the acids so excreted 

 must be those that have no solvent action on aluminium 

 phosphate. This would limit the excreted acids to car- 

 bonic, acetic, propionic, and butyric. Czapek also re- 

 plies to the argument that the acids producing the tracings 

 must be non-volatile ones because of the definite lines 

 made in the mineral, by stating that the excretion of 

 carbon dioxide alone would be suflBcient to account for 

 the observations since it dissolves in water to form car- 

 bonic acid, and that carbonic acid is always present in 

 the cell walls of the root epidermis. By means of micro- 

 chemical analyses of the exudations of root-hairs grown 

 in a water-saturated atmosphere, Czapek found potassium, 

 magnesium, calcium, phosphorus, and chlorine in the 

 exudate. He concludes that the solvent action of plant 

 roots is due to acid salts of mineral acids, particularly 

 acid potassium phosphate. He has not proved, however, 

 that the exudations were not from dead _ root-hairs nor 

 from the dead cells of the rootcap. In either case they 

 would have some solvent action, but whether sufficient 

 to make them of importance is doubtful. 



323. Secretion of an oxidizing enzyme by plant roots. — 

 Molisch 1 found that root-hairs secrete a substance having 

 properties corresponding to those of an oxidizing enzyme. 

 His work has been repeated by others who have failed to 

 obtain similar results, but lately Schreiner and Reed ^ have 



1 Molisch, H. Ueber Wurzelaussoheidungen xmd deren 

 Einwirkung auf Organische Substanzen. Sitzungsber. Akad. 

 Wiss. Wien-Matb. Nat., Band 96, Seite 84-109. 1888. Ab- 

 stract in Chem. Centrlb., Band 18, Seite 1513, 1888, and in 

 Centrlb. f. Agr. Chem., Band 17, Seite 428, 1888. 



^ Schreiner, Oswald, and Reed, H. S. Studies on the Oxidiz- 

 ing Powers of Roots. Bot. Gazette, Vol. 47, p. 355. 1909. 



