1898] PHYSIOLOGICAL ACTION OF PLASMOLYZING AGENTS 413 
together perhaps in the most complete and convenient form in 
the work of Landolt and Bornstein (7), one can readily estimate 
the number of undissociated molecules and of ions in the solu- 
tion. This number will express the osmotic value of salt when 
that of cane sugar is taken as one. Knowing, therefore, the 
boundary concentration of sugar and the osmotic value of NaCl 
at the different degrees of dilution, we are able to find a theo- 
retical boundary concentration for NaCl, assuming for it a purely 
osmotic action. 
As appears in the table, Spirogyra first survives in NaCl at a 
concentration of 0.1 gm. mol. per liter instead of 0.46 gm. mol., 
the approximate boundary required by purely osmotic action. 
Since the plants succumb ina solution of NaCl hardly one-fourth 
as concentrated as would be required by pure osmotic action, as 
seen in sugar, either the method of exerting this osmotic effect 
is much more disastrous than is seen in the case of sugar, or 
some form of toxic activity is here exerted by the NaCl. Since 
the boundary concentration is so dilute (0.1 gm. mol. per 1.), it 
seems extremely improbable that the mere withdrawal of water 
from the cell sap by the salt solution could exert a harmful effect 
commensurate with the numerical disparity here observed. 
In the case of potassium nitrate (KNO,), a result very simi- 
lar to that seen in the case of NaCl was obtained. The salts 
dissociate in about the same degree under like conditions. A 
concentration of KNO, equal osmotically to the boundary con- 
centration of sugar would be about 0.47 gm. mol. per liter. If 
the physiological action of KNO, were totally osmotic the Spi- 
rogyra should first survive in about this concentration. The 
boundary concentration of KNO, determined experimentally 
was found to be 75 gm. mol. per liter. With an osmotic activity 
very nearly identical with NaCl, a boundary is found at a greater 
dilution, indicating a degree of toxic activity somewhat greater 
than that of NaCl. 
In the course of a study by Dr. Kahlenberg and myself of 
the sodium salts of a number of acids, mainly organic, the boun- 
dary concentrations for Spirogyra were obtained. A wide range 
