492 E. J. LUND 



All that the writer desires to show by these experiments is: 

 1) that the magnitude of the fall of electrical potential differs 

 along the length of the stem and, 2) that under the conditions of 

 these experiments, the direction of the fall of potential may be 

 different in more basal regions than in the apical part of the same 

 stem. This latter result appears somewhat surprising, in view of 

 the general morphological similarity of the different levels of the 

 stem. It appears that the small potential difference (or absence 

 of P.D., table 6 W, 1) shown by the whole pieces between cuts x 

 and z was due to the fact that the apical and basal ends of these 

 pieces were both electronegative to the middle region of the piece. 

 This result suggests a similarity to the results obtained by Miiller- 

 Hettlingen ('83) on growing seedlings. 



CONCLUSIONS 



It is evident that the observations reported in this paper appear 

 complementary to the results reported in the first paper on the 

 effects of an electric current on the regeneration process in the 

 internodes of Obelia. Now, if differences of electrical potential 

 are inseparably associated with structural polarity and apical 

 growth, then it follows that the stem or certain regions of the 

 stem of Obelia^ — and also very probably each branch — serves 

 as a conductor of a continuous electric current of perhaps varying 

 intensity, which passes within the tissues of the stem and com- 

 pletes the circuit in the surrounding sea-water. If the basal 

 region is electronegative to the middle region of the stem, then 

 of course the direction of the current would be the opposite in 

 the lower parts of the stem to that in the apical region of the 

 stem. In any case, if these constant bioelectric currents are 

 inseparably associated with apical or basal growth, it is logical 

 to expect that if they be appropriately opposed or augmented by 

 the application of an external source of E.M.F., then the normal 

 growth processes should show the effects of such interference. 



If this reasoning is correct, then an appropriate application of 

 an external electromotive force to regenerating and growing 

 tissues should be a unique instrument for the investigation of 

 the causes and conditions of structural polarity and symmetries 



