[Vol. 1! 



512 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



potassium salt. Czapek believes the reddening of litmus 

 paper by root excretions to be due ordinarily to the acid 

 reaction of monopotassium phosphate, but in the case of 

 hyacinth roots to the primary oxalate. The corrosion of 

 marble he attributed to the dissolving effect of carbonic acid. 

 While considering as possible the results obtained by Molisch 

 ('87), who claimed that diastatic ferments were normally 

 present in the root excretions, Czapek 's own work in repetition 

 of Molisch 's experiments offered only negative results. 



Prianischnikov ('04) performed some experimental work 

 dealing with the action of organic acids on phosphates. It will 

 be remembered that because the roots did not attack aluminum 

 phosphate Czapek concluded that organic acids were not ex- 

 creted by them, inasmuch as this substance is soluble in cer- 

 tain organic acids. Prianischnikov found that phosphates 

 derived from different sources were utilized by various plants 

 but in different degree, and he suggested that this might be 

 correlated with a different amount of CO2 excretion, in which 

 case the presence of organic acids would not be necessary. 



Kunze ('06) found that free mineral acids are not excreted 

 from the roots of higher plants and concluded that any acidity 

 in the excretions is probably not due to the presence of acid 

 salts of mineral acids, but to excreted organic acids. These, 

 however, were present in such minute amounts as to be below 

 the sensitiveness of litmus. He held that a greater effect is 

 produced on the soil by fungi than by the roots of the higher 

 plants. Lemmermann ('07) held views similar to those of 

 Kunze. 



Stoklasa and Ernest ( '08) disagree with the findings of both 

 Czapek and Kunze. No potassium or phosphoric acid were 

 ever found as a result of their determinations, and they main- 

 tain that in the economy of the plant the excretion of such 

 useful or necessary substances is unthinkable. Only COu was 

 found to be excreted under conditions of normal aerobic res- 

 piration of the root system; no other free inorganic or organic 

 acids were detected. In aerobic respiration of the root system, 

 they believe the organic acids in the living cells would be split 

 up to give CO2 and Ho, the latter then being oxidized to H2O. 



