Lowering the pH of sea water from 8.2 to 6.4 lowers the positive P.D. of Halicystis reversibly (this does not happen with Valonia).

Exposure to sea water at pH 6.4 does not affect the apparent mobility of Na+ or of K+ (this agrees with Valonia).

Guaiacol makes the P.D. of Halicystis less positive (in Valonia it has the opposite effect).

Exposure to guaiacol does not reverse the effect of KCl in Halicystis which in this respect differs from Valonia.

The P.D. can be changed from 66 mv. positive to 23 mv. negative by the combined action of KCl and guaiacol.

Exposure to guaiacol affects Halicystis and Valonia similarly in respect to their behavior with dilute sea water. Normally the dilute sea water makes the P.D. more negative but after sufficient exposure to guaiacol dilute sea water either produces no change in P.D. or makes it more positive. In the latter case we may assume that the apparent mobility of Na+ has become greater than that of Cl- as the result of the action of guaiacol. (Normally the apparent mobility of Cl- is greater than that of Na+.)

In Halicystis, as in Valonia and in Nitella, an organic substance can greatly change the apparent mobilities of certain inorganic ions (K+ or Na+).

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