1915] 



MERRILL ELECTROLYTIC DETERMINATION OF EXOSMOSIS 511 



nicht geleugnet werden, wiewohl es moglich ist, dass sie nicht 

 bei alien Pflanzen in gleichem Grade stattfindet." 



Molisch ('87) branched out in a new direction as regards the 

 subject of root excretions ; he held that such excretions exer- 

 cise an influence on organic bodies in the soil which is even 

 more important than that exercised upon the inorganic con- 

 stituents of the same, for he considered the latter merely a 

 dissolving action but the former a real chemical transforma- 

 tion. His main work along this line pertained to a study of 

 the ferments in the root excretions, and their reactions and 

 properties. Johnson ('90), after considering Gyde's results 

 above noted, says that "we may well doubt whether agricul- 

 tural plants in the healthy state excrete any solid or liquid 

 matters whatever from their roots," but that "under certain 

 circumstances, small quantities of soluble salts or free acids 

 may indeed diffuse out of the root-cells into the water of the 

 soil. This is, however, no physiological action, but a purely 

 physical process." Goebel ( '93) found that after the roots of 

 Hordeum and Lepidium plants had been in distilled water for 

 six days the medium gave the reaction for formic acid. 



We thus see that the early work on root excretions was 

 characterized by contradictions and uncertainties. "While the 

 nature of the more recent work has been more exact and com- 

 prehensive, the subject, as we shall see, is still beclouded by a 

 considerable degree of confusion. 



& 



A classic piece of experimental work was undertaken by 

 Czapek ( '96, '96 a ) to determine the exact chemical nature of 

 the excreted substances from roots. In his report ('96 a ) he 

 discussed the earlier work, especially with regard to the rela- 

 tion between excretion from injured cells and actual exos- 

 mosis. In his experimental work he found that root excretions 

 are composed of soluble substances, partly organic and partly 

 inorganic. Of the inorganic, he identified K, Ca, Mg, HC1, 

 H2SO4, and H.JPO4, only the first and last mentioned — in the 

 form of the primary potassium phosphate — being excreted 

 in any quantity. Of the organic substances he identified 

 carbonic acid and also formic acid, the latter in the form of 

 its potassium salt : oxalic acid was also isolated as a primarv 



