484 E. J. LUND 



potential should approach that of the apical end, with the result 

 that the potential difference between the basal and apical ends 

 should tend to disappear, which it does. 



PROOF THAT THE DIFFERENCE OF ELECTRICAL POTENTIAL IS 

 ASSOCIATED WITH THE LIVING TISSUE IN THE STEM 



Differences in electrical potential such as described above for 

 Obelia and originally for Tubularia, Pennaria, and Campanu- 

 laria by Mathews ('03) might readily be conceived to originate 

 elsewhere than in the living tissues of the stem. It is therefore 

 necessary to remove completely any doubt on this point before 

 we proceed with the analysis of the problem. Three different 

 methods of testing the question will be given. 



Dead stems. Table 2 shows the results of tests on stems iso- 

 lated from colonies left to die and macerate in sea-water in the 

 laboratory for several weeks. It is clear from a comparison of 

 the differences between deflections that no detectible P.D. 

 exists between the ends of the stem. 



Living stems from which the tissue has been removed mechanically. 

 The most striking proof of an inherent P.D. in the coenosarc of 

 the stem is given in table 3. Stems isolated from five different 

 actively growing colonies were tested immediately. The results 

 are given in table 3 A. All the tests show that a marked P.D. 

 exists between the ends of the stem and that the apical end of the 

 stem is electronegative to the basal end. After the tests in A 

 were completed, the coenosarc was mechanically removed by 

 rolling the round end of a glass rod along the stem. The perisarc 

 tube is elastic and returns perfectly to its original shape, auto- 

 matically becoming w^ashed free from cells and finally filled with 

 sea-water instead of the living tissue. In this way an ideal con- 

 trol for a crucial test is provided. Table 3 B gives the results of 

 the tests on the perisarc tubes filled with sea-water. No potential 

 difference is evident. But, as w^as explained above in connection 

 with table 1, the deflections in successive tests on the same peri- 

 sarc tube decreased. This is due to an increase in ohmic resist- 

 ance of the stem perisarc, caused by evaporation. The results 



