1915] 



MERRILL ELECTROLYTIC DETERMINATION OF EXOSMOSIS 515 



exosmosis of sugar into the water in which they were placed. 

 Pfeffer (76, 77) and Detmer (79) also confirmed the re- 

 sults above noted regarding the absence of sugar in the water 

 in which roots or other plant parts had been exposed for some 

 time. "Wilson ('81) found that in some cases (Dionaea and 

 Drosera) the excretions may be influenced by external factors, 

 e. g., partly by irritation caused by nitrogenous substances 

 and partly by osmotic action. In general, he believed that the 

 excretion of nectar is caused by the osmotic action of a fluid 

 on the surface of the nectary. Pfeffer ( '86) studied the ef- 

 fects of various organic acids (citric, picric, and tannic) and 

 some inorganic compounds in causing the exosmosis of ab- 

 sorbed methylene blue from Lemna, Trianea, Azolla, and 

 Elodea. 



Wachter ('05) obtained considerable exosmosis of sugar, 

 especially in the case of Allium Cepa ; he found, however, that 

 salts like NaCl and KC1 tended to inhibit this exosmosis. He 

 also investigated the effect of ether on this phenomenon. While 

 he obtained greater exosmosis of sugar the first two days in 

 a solution of ether alone than in one of ether and KC1, he at- 

 tributed this increase to leaching from cells killed as a result 

 of contact with ether, and believed that the ether itself has 

 no effect on the actual process of exosmosis. 



Lepeschkin ('06), from his experimental work on sporangia 

 of Pilobolus, concluded that the exosmosis of water was due 

 to an alteration of the plasma membrane caused by the anes- 

 thetics he used, provided the amounts employed were sufficient 

 to be toxic. Small amounts of ether and chloroform, on the 

 other hand, were found to decrease the exudation of water, 

 and he believed this to be due to a decrease in permeability of 

 the plasma membrane. 



An interesting line of investigation was undertaken by 

 Czapek ('10, '10% '10 b , '11) a few years ago to determine the 

 surface tension relations of the plasma membrane. That work 

 is especially pertinent to our discussion here because of the 

 prominent part exosmosis played in his experiments. He used 

 for the most part species of Echeveria, Spirogyra, and Saxi- 

 fraga, in the cells of which is found a tannoid substance, 



