1917] BROOKS—PERMEABILITY 317 
hours. The disks were still brown and apparently uninjured even 
after 48 hours in the apparatus. Certain experiments with lan- 
thanum salts indicated that the effect of lanthanum would resemble 
that of calcium, differing chiefly in that the alterations of per- 
meability would take place more rapidly. 
Summary 
1. The protoplasm of Laminaria is normally permeable to the 
salts of sea water. 
2. Sodium salts cause an increase of permeability which cul- 
minates in death. 
3- Calcium and lanthanum salts cause a decrease in per- 
meability, followed by an increase which culminates in death. 
LABORATORY OF PLANT PHYSIOLOGY 
HarvVARD UNIVERSITY 
