ON THE THEORY OF PH BANDS IN CHARACEAN ALGAE

We show that if we take into account the acido-basic reactions in whic h the ions H+ and HCO3- are involved, the observed characteristics of the steady band patterns which develop around the characean internodal cells can be reasonably explained. The bands result from an instabili ty of the steady state with uniform membrane potential in which the de stabilizing influence is caused by the symport H+/HCO3-. When this inf luence overcomes the stabilizing effect of the proton pump, which is t he case when the external pH of the medium is approximatively between 6 and 10, ionic currents develop. As observed in experiments, their wa velength is between 1 to 10 mm and they flow from the acid to the alka line regions.