1915] 



MERRILL ELECTROLYTIC DETERMINATION OF EXOSMOSIS 509 



capillary action played a role in Macaire's experiments 

 whereby he obtained an excretion of lead acetate into distilled 

 water, as noted above. Boussingault ('45) considered that 

 under ordinary conditions radicular excretion is doubtful, and 

 that any excretion from the roots in water is caused by dis- 

 ease. He also advanced various arguments opposing De 

 Candolle's theory. 



Gyde ('47) grew various agricultural plants in soil for a 

 time and then, after carefully washing the roots, placed them 

 in pure water. After 3-17 days, during which the plants con- 

 tinued in good condition for the most part, the water was 

 evaporated. The finding of a residue of yellowish or brown 

 matter, part organic and part inorganic, caused him to con- 

 clude that plants excrete both organic and inorganic substances 

 in minute quantities, similar in composition to the sap. But 

 he denied that root excretions have any injurious effect upon 

 plants later grown in the same medium. 



An examination of the literature on the subject of root ex- 

 cretions reveals the tendency among the workers of the par- 

 ticular period at which we have now arrived in our review, to 

 pay more attention to the morphological and chemical aspects 

 of root excretions, and perhaps not so much to the purely agri- 

 cultural phases. Hence we find from this period on, consider- 

 able emphasis laid on the structure of the root and a more 

 detailed account given regarding the chemical nature of the 

 substances excreted from the roots, even though the experi- 

 mental methods were somewhat crude in most cases. Further- 

 more, it should be said that opinion was divided on the ques- 

 tion of whether or not there is an actual excretion from the 

 roots. 



Among those whose influence was felt in the development 

 of the chemical aspects of the subject at this time Liebig should 

 probably be mentioned first. In the American edition of his 

 work ( '41, p. 195) occurs the following statement: "It is evi- 

 dent that plants, also, by producing carbonic acid during their 

 decay, and by means of the acids which exude from their roots 

 in the living state, contribute no less powerfully to destroy the 

 coherence of rocks. ' ' An appended note by Dr. Webster in the 



