482 E. J. LUND 



different levels in the sanie stem. The resistance of pieces of 

 living stems 25 mm. in length varied, in a considerable number 

 of determinations, from about 180,000 to 280,000 ohms, depend- 

 ing upon the diameter of the stem and certain other conditions. 

 The resistance of the galvanometer was 1000 ohms and that 

 of the copper — sea-water electrodes was 5300 ohms. Constancy 

 of the deflection when the electrodes are constant will therefore 

 largely depend upon the constancy of the resistance of the stem. 



In table 1 A are given five series of tests upon the main stems 

 of five different colonies designated by the numbers at the top 

 of the table. The apical three-fourths of th^ main stem was 

 isolated from its branches in each case. Immediately after 

 removal of the branches, the tests were made in the manner 

 described above. It will be seen by comparing the differences 

 between deflections that a definite and marked difference of 

 electrical potential occurs. The average differences between 

 the deflections in the last five tests in A were 6.1, 8.1, 3.8, 9.6, 

 8.6 mm. There is a perfect uniformity in direction of the P.D. 

 inherent in the stem, such that the apical end is electronegative 

 to the basal end. These pieces of stem ^vere now placed in finger- 

 bowls in fresh sea-water and allowed to regenerate for twenty- 

 four hours. The tests were then repeated with the results given 

 below in table 1 B. Comparison of the differences between 

 deflections will show that these have decreased markedly during 

 the preceding twenty-four hours. The differences are, however, 

 quite definite and generally in the same direction as in the pre- 

 vious tests. 



Two more experiments were carried out in which a total of ten 

 stems were used. The period of regeneration between the tests 

 was forty-eight hours. A marked decrease in the P.D. occurred 

 in nine of the stems, but the original direction of the P.D. was 

 apparently retained. One stem showed no P.D. between its 

 ends at the end of the forty-eight-hour period. 



The following tentative explanation of this decrease in P.D. 

 is offered at the present time. From the above experiments and 

 others to follow it is easily shown that the apical end which 

 is the actively growing region of the stem is electronegative to 



