308 BOTANICAL GAZETTE [OCTOBER 
The solution used in the lower cells was either sea water or a 
pure salt solution of the same conductivity; while the upper cells 
contained a solution of half the concentration of that in the corre- 
sponding lower cell. Solutions of equal conductivity were used 
in order to facilitate comparison with the work of OSTERHOUT.’ 
Sources of error 
In order to obtain accurate data, the following precautions were 
taken: 
1. The solutions were made up with distilled water, which had 
a specific conductivity of about 2X10-*® ohms. The sodium 
chloride used was Baker’s “analyzed”; the calcium chloride, 
Kahlbaum’s; and the lanthanum nitrate, Eimer and Amend’s 
“Tested Purity.” For this work an error of 1 per cent in the con- 
centration of the solutions was considered allowable. 
2. In order to prevent dissolving of electrolytes from any part 
of the apparatus, the cells were made of Durox glass, and both 
cells and rubber thoroughly steamed immediately before each 
experiment. An apparatus of this type, set up with no Laminaria 
tissue, but with a thick layer of the vaseline-beeswax cement, and 
filled with distilled water, gave off only traces of electrolytes. The 
change in conductivity of the water in such a cell during 48 hours 
was equivalent to an increase of concentration of sodium chloride 
of less than 1X10-7M. Dissolving of electrolytes from the 
apparatus has therefore no significance in the experiments. 
3. It was necessary to eliminate the influence of temperature. 
As it was impracticable to conduct the experiments at constant 
temperature, the cells were placed outdoors, the temperature vary- 
ing from —3° to +9° C. This amount of fluctuation produced no 
appreciable change in the rate at which salts passed through the 
tissue, and the low temperatures were exceedingly favorable to the 
maintenance of normal permeability.* 
? Unpublished data of OstErRHouT show that differences of osmotic pressure 
the magnitude of those produced by the use of solutions of equal conductivity bare 
little effect on the permeability of Laminaria during the ape of time occu y 
these experiments. 
3 Laminaria lives much longer when the temperature is low. While it may be 
en hy alive under laboratory conditions several weeks ‘at o° C., it perishes rapidly at 
