466 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8. 
Sodium chromate of 0.22 M has about the same conductivity as normal 
sea water and has a pH of about 9.5. This is not alkaUne enough to cause 
any appreciable effect, just as a pH of 4.5 was not acid enough to interfere 
with the success of these experiments, as shown by Osterhout (2). Never- 
theless, in order that conditions might be comparable with those in which 
chromium was used as a cation, a solution was prepared consisting of 50 
percent sodium chromate 0.22 M, 50 percent sodium chloride 0.52 M, and 
with just enough chromic acid added to bring the acidity up to that of the 
chromous chloride solution (pH about 4.5). 
The acidity in the case of colored solutions was measured by diluting 
a hundred times, taking the pH of this diluted solution, and then making a 
correction for the increase in dissociation upon dilution. As a check upon 
this method the pH was also determined directly by means of the hydrogen 
electrode. 
The results obtained with the sodium chromate mixture of pH 4.5 are 
shown below and in figure i, B. The figures given are the average of three 
experiments. 
Time in Percentage of Original Probable 
Minutes Resistance Error 
2 93 1% 
5 88 I 
10 85 2 
20 78 2 
40 68 3 
60 62 3 
80 55 5 
It is seen that the initial effect is a fall in resistance. This is to be 
expected since we have here a monovalent cation with a bivalent anion. 
It is also seen that the hydrogen-ion concentration is not responsible for 
the rise in resistance when the chromium has a positive charge. When it 
has a negative charge (even though the hydrogen-ion concentration is the 
same, viz., pH 4.5) the resistance does not increase but, on the contrary, 
decreases from the start. To what extent this is due to the presence of 
the oxygen in the anion can not be determined. 
II. The Effect of Changing the Valency of the Same Ion 
As previously stated, the nature of the charge on the ion seems to be a 
very important factor in determining the initial response of the tissue to 
electrolytes. It is natural to inquire what the result would be if the same 
ion could be used with a varying charge. If an anion with one charge 
causes a decrease in resistance, the same ion with two or three charges 
should cause a more rapid decrease. Similarly, a cation with two positive 
charges should cause a less rise in resistance than one with three provided 
they are used with anions which permit this rise in resistance. Osterhout 
