[Vol. 2 



510 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



same work ('41, p. 411) says that other chemists were unable 

 to obtain results similar to those of Macaire. If they did, they 

 were inclined to ascribe them to injury of the roots examined. 



Various workers were thus attacking different phases of the 

 problem. Chatin ('47) mentioned the excretions from roots 

 and especially considered the elimination of toxic substances 

 by them. Link ('48) held that the slimy drops found on root 

 tips should not be considered as actual excretion inasmuch as 

 they arise from the cast-off cap cells of the root. Garreau 

 and Brauwers ('58) maintained a similar view in regard to 

 the gummy, nitrogenous substance they found given off by the 

 roots to the water in which they were placed. The observa- 

 tions of Liebig ('58) concerning the dissolving action of roots 

 on limestone were later substantiated by the experimental 

 work of Sachs ( '60), which has been so much referred to since 

 that time. Of the two possible explanations Sachs advanced 



excretion of carbonic acid by the roots, and the liberation of 

 acids by the decomposition of the cell walls of the roots — he 

 inclined to favor the latter as being the best explanation for 

 the marble etchings caused by the roots in his experiments. 

 In his extensive series of experiments, Knop ( '60, '61, '62) 

 studied, among other things, the character and amount of 

 root excretions from certain plants placed in distilled water, 

 and the conditions governing the same. His analyses indicated 

 that, in addition to other substances in small amounts, potas- 

 sium, calcium, phosphoric acid, and some organic matter were 

 excreted. The studies of Cauvet ('61) resulted in his declar- 

 ing that physiologically sound roots do not excrete any sub- 

 stances, toxic or otherwise, and that all theories based on the 

 ideas of root excretion advanced by De Candolle and Macaire 

 were necessarily false. Sachs ('65) made further contribu- 

 tions along his line of work indicated above, while Liebig ( '65) 

 says: 



"Wir haben alien Grund zu glauben, dass diese Absonderung 

 an der ganzen Oberflache stattfindet, wir beobachten sie nicht 

 nur am Stamme, sondern auch an den kleinsten Zweigen, und 

 wir miissen daraus sehliessen, dass dieser Excretiorisprocess 

 auch an den Wurzeln vor sich geht. . . . . Eine Aus- 

 seheidunrr von Excrementen kann demnach bei den Pflanzen 



