212 Walter Stiles 
It is not clear, however, how far this result is to be attributed to toxic 
action. 
S. C. Brooks (1916 b) treated strips of peduncle of Taraxacum 
with solutions of respectively 0-22 M sodium chloride, 0*17 M calcium 
chloride and 0-05 M cerium chloride for 20 or 25 minutes, then trans¬ 
ferred the tissue to distilled water and measured the increase in 
electrical conductivity of the latter. He assumed that exosmosis 
during the first 30 minutes is due to diffusion into the water of the 
salt previously absorbed, and that subsequent exosmosis can be 
regarded as due to exosmosis of electrolytes from the protoplasm. 
Since it was found that after 30 minutes exosmosis from tissue that 
had been treated with calcium chloride was less than that from tissue 
which had not been in contact with any salt solution, it was concluded 
that calcium chloride brings about a decrease in permeability of the 
tissue, while as from tissue treated with sodium chloride exosmosis 
after 30 minutes was greater than from the control which had not 
been in contact with salt solution, it was concluded that sodium 
chloride brings about an increase in permeability. Cerium chloride 
was regarded as bringing about first a decrease in permeability which 
is followed by an increase. 
To the present writer these conclusions appear of little value for 
the following reasons. The recorded observations are few in number, 
the recorded differences are small, and it is not shown that they lie 
outside the limits of experimental error. It is necessary to show this, 
especially as electrical conductivity can be used only as an approxi¬ 
mate, but not as an accurate, measure of the exosmosis of electrolytes, 
while it is unlikely that diffusion of the experimental salt out of the 
tissue should end, and that of other substances in the cells begin, at 
any particular moment, or at the same time with different salts. 
Experiments with the tissue tension method and the diffusion 
method described in the last chapter led Brooks to similar con¬ 
clusions, namely, that salts of univalent kations (and also sucrose) 
increase permeability, while salts of divalent and trivalent kations 
at first bring about a decrease in permeability. But these methods 
also are not free from serious objections, and the legitimacy of the 
conclusions drawn appears to the present writer very doubtful (cf. 
Chapter xi). 
As indicated in the last chapter Osterhout (1912 a, b) found that 
thallus of Laminaria when transferred from sea water to sodium 
chloride having the same conductivity as sea water, underwent a 
gradual loss of electrical resistance until the tissue was quite dead. 
