482 
W. J. V. OSTERHOUT 
therefore evident that this process is different from false plasmolysis, 
although false plasmolysis may occur later if the exposure be suffi- 
ciently prolonged. 
None of the other salts examined produced the characteristic 
contraction at such dilutions. SrCl2 produced it at a higher concen- 
tration (.001 M and higher) but CaCl2 and MgCU did not produce it 
even at concentrations which plasmolyzed; the same is true of MnCl2, 
CdCl2, NiCl2, C0CI2, NaCl, KCl and NH4CI. As long as we work 
with very dilute solutions the effect of barium appears to be specific. 
Even if it should turn out that other salts can produce this effect 
(the action of trivalent kations was not investigated) the striking 
fact remains that calcium and magnesium, which are chemically 
closely related to barium, do not produce it at all. 
It would appear that further investigation of this and similar 
cases is desirable in order to discover what constituents of proto- 
plasm make this specific action possible. 
Harvard University, 
Laboratory of Plant Physiology 
