ELECTRICAL POLARITY IN OBELI A 481 



of six pairs of tests was approximately ten minutes. It will be 

 noted that the magnitude of the deflections decreased as time 

 went on, but the differences between the deflections were about 

 the same after the first test. The decrease in deflection is caused 

 by the increase in resistance of the stem due to evaporation of 

 the trace of water on its surface after removal from sea-water. 

 A proof that this is the correct explanation will be given later 

 when the tests on dead stems are considered. The stems were 

 manipulated by means of a w^et camel's-hair brush. In a series 

 of tests on the same piece the distance between the electrodes 

 was necessarily always the same. In the above tests it was 

 24 mm. 



In the last column of the table above are given the differences 

 between the successive galvanometer deflections. The — sign 

 indicates that the apical end is electronegative to the basal end 

 and, as in the tables which follow, the + sign indicates that the 

 apical end of the piece is electropositive to the basal end.^ 



Since, for lack of space, it is impossible to publish the actual 

 readings of the galvanometer deflections, the differences only 

 between successive galvanometer deflections are given in the 

 tables to follow. One important thing to be noted is, that since 

 the deflections typically decreased in magnitude in successive 

 tests on the same stem, then if, as sometimes happened, the 

 difference of potential in a stem w^as small and at the same time 

 the fall in total deflection due to drying was rapid, the differ- 

 ences between such successive deflections would have a + sign, 

 and therefore apparently indicate that the apical end was elec- 

 tropositive to the basal end. Such a condition sometimes oc- 

 curred in the tests in the tables given below. Therefore, the 

 occasional occurrence of a + sign opposite a small (0.5 to 1.5 mm.) 

 difference in deflection in some of the following tables does not 

 necessarily indicate that the apical end was electropositive. 

 Only a consistent occurrence of the + sign in successive large 

 (2 to 10 mm.) differences between deflections can be taken as 

 evidence that the apical end is actually electropositive. 



The ohmic resistance of equal lengths of stem from different 

 colonies varies. This is also true of pieces of equal length from 



• * This refers to the current inside the stem. 



