Electrolytic Solutions upon Permeability of Plant Cells . 593 
about 50 per cent., while in a few cases as high as 6 4 per cent, was 
reached. 
In the experiments with the electrolytic solutions, bottles holding 30 c.c. 
of the liquid chosen were used for the immersion of each five or six sections. 
Sections were removed after known times, soaked in the ferric chloride, 
transferred to a slide and mounted in more of the ferric chloride under 
a large cover-slip, and examined after three minutes altogether in contact 
with the iron salt. The change of permeability was considered complete if 
traces of blue could be seen appearing in about half the cells of the section 
excluding marginal cells. These latter were excluded because it was 
possible they might have been injured in the preparation of the material. 
The colour observed rapidly deepened during the next few minutes. The 
low power had therefore to be used to consider a section as a whole; the 
high power was afterwards used on individual cells to study the appearance 
of the protoplasm. 
Since such methods are open to many sources of error no great 
degree of accuracy was aimed at in preparing the electrolytic solutions. 
The ordinary ‘pure ’ chemicals of a laboratory were used, and a solution of 
each made up. Small quantities were withdrawn and diluted as required 
for the separate tests. The ferric chloride was made up freshly every 
few days. 
To accompany the experiments upon each concentration sections from 
the same part of the plant as those being immersed in the salt solution 
were left in distilled water, and examined from time to time. 
These ‘ control ’ experiments showed that the cells became injured, in 
some cases, after soaking for three days in water alone, so it was thought 
unwise to experiment over periods much above those quoted later. In con¬ 
sequence of this the influence of very dilute solutions of the salts could not 
be studied. 
Rough experiments were first made for each concentration of electro¬ 
lytic solution used. If, after a certain time of immersion no blue appeared 
upon the application of the ferric chloride, either the change in the 
protoplasm had not taken place, or the tannin had had time to diffuse 
out of the cell. To find which of these possibilities was correct one could 
either pour a little alcohol over the solution, or heat the slide to kill the 
cells, to allow the iron compound to pass in, if it had not already been able 
to do so. 
These rough tests served to give the time needed for the change in 
permeability between limits of half to two hours, according to the nature of 
the experiment. 
The sections in the bottles already mentioned were accordingly left 
undisturbed for the shorter time limits, and specimens were then removed 
at intervals of five minutes to twenty minutes according to circumstances, 
