ELECTRICAL POLARITY IN OBELIA 



479 



P.D. inherent in the stem is therefore represented by one-half 

 the difference between the deflections. By proper cahbration 

 of the galvanometer, it therefore would be possible to determine 

 the value of the current due to the P.D. between the ends of the 

 stem, and by direct measurement of the resistance of the stem 

 the P.D. inherent in the stem would of course be known. 



Figure 1 



The second interpretation of the difference in deflection, when 

 the stem occupies the two positions on the electrodes, would be 

 that the current can pass more readily in one than in the opposite 

 direction through the stem. The properties of the stem would 

 therefore partially resemble the behavior of a rectifier toward 

 an alternating current.^ That this possibility should be taken 



2 According to F. Elfving (Bot. Zeit., Bd. 40, 1882, S. 257-263), Kunkel (Arbeit d. 

 bot. Inst. Wurzburg, Bd. 2, Heft 2) found that the resistance of the shoot (seed- 

 lings) when a weak 'current' was passed from base to apex through the shoot was 

 less than the resistance of the same shoot when the 'current' was reversed. No 

 experiments on the root are mentioned, but Elfving briefly states that an electric 



