1915] OSTERHOUT—PERMEABILITY 473 
In order to observe the effect of a tetravalent kation, 1 gm. 
Th(NO,),-4 H.O was added to 300 cc. sea water, making the con- 
centration 0.006 M. ‘Tissue which had in sea water a resistance 
of 690 ohms was placed in this solution; the resistance rose in the 
course of half an hour to 750 ohms; at the end of one hour it was 
760 ohms; after this it fell slowly, and at the end of 40 hours was 
sto ohms. The results are shown in table VII and fig. 7. 
Summary 
All of the trivalent kations investigated (La, Ce, Y, Fe, Al) 
and the tetravalent kation Th are able to decrease permeability to 
a marked degree. 
LABORATORY OF PLANT PHYSIOLOGY 
HARVARD UNIVERSITY 
