510 BOTANICAL GAZETTE [DECEMBER 
experiments on this tissue the distilled water was obtained by dis- 
tillation from an apparatus made entirely of glass, and which had 
been in constant operation for several weeks prior to the collection 
of the sample here used.?_ All the kations were used in the form of 
chlorides, thus making it possible to determine their concentration 
in the upper cell by two entirely independent methods. The con- 
ductance of known concentrations from 10~7 M to 1073 M of the 
salts used was determined and a curve plotted showing for each 
salt the concentrations corresponding to any given conductance. 
The concentration of a given salt diffusing into the distilled water 
in the upper cell was then ascertained by comparison of the con- 
ductance of the solution in the upper cell with the curve for the 
corresponding salt. In addition, the chlorides in the upper cell 
were determined nephelometrically by the method of RICHARDS 
and WELLs.3 
In neither living nor dead tissues could the presence of chlorides 
in the upper cell in excess of 3X10~5M be detected nephelo- 
metrically, even during experiments whose duration exceeded 24 
hours. The changes in conductivity were also such as would indi- 
cate a negligible increase in the concentration. It seems therefore 
that little or no salt can pass through the epidermis. 
Experiments were then tried to determine the permeability 
of the tissue to dyes. The diffusion of Bordeaux red through the 
diaphragm from an o.1 per cent aqueous solution in the lower cell 
into distilled water in the upper during 96 hours was insufficient 
to cause any visible change in the color of the distilled water. A 
similar experiment, in which the lower cell contained a 1 per cent 
aqueous solution of eosin (Merck’s eosin bluish), was continued 
for 7 days; at the end of that time the distilled water in the uppet 
cell could not be distinguished in color from fresh distilled water, 
even by the use of a colorimeter. 
The experiments on dyes (as well as those on acids and alkalies, 
subsequently described) were performed on dead tissue. 
? Water distilled from glass becomes better the longer distillation is continued, - 
since the constant exposure to steam and hot water soon removes the more soluble 
constituents of the glass. Water such as that here used may be regarded as having no 
appreciable toxicity. 
3 Ricuarps, T. W., and Wexts, R. C., The nephelometer, an instrument for 
detecting and measuring opalescent precipitates. Amer. Chem. Jour. 31:235- 194 
