POSITIVE ELECTRIC RESPONSE IN HYDRILLA JJ 



of light. On the stoppage of light the unmasking of A is 

 seen in the positive after-effect. For the recovery does not 

 stop at the zero base-line, but goes beyond it towards the 

 positive direction and then returns to zero (fig. 19). 



The phenomenon of overshooting after neutralisation. — 

 I have succeeded in demonstrating the A effect by a different 

 method, where the positive, previously masked, exhibits 

 itself by ' overshooting.' Under the continuous action of 

 light the negative response undergoes a decline almost to 

 neutralisation. This is due to the joint effects of fatigue 

 and of increasing positive reaction which neutralises the 

 negative. On the stoppage of light, the A effect, hitherto 

 masked, exhibits itself by an overshooting of response in the 

 positive direction (fig. 20). 



Positive Electric Response in Hydrilla 



The Hydrilla plant readily absorbs C0 2 from water, and 

 the anabolic activity A is quite evident from the rapid rate 

 of evolution of oxygen during photosynthesis. No doubt 

 the excitatory D process is also in operation, but I hoped 

 that in very active specimens the anabolic A would be 

 sufficiently pronounced not to be completely masked by the 

 catabolic D. My anticipations were fully verified, as in the 

 following experiments. 



Two middle portions of Hydrilla stems bearing leaves 

 were employed as the two plates of the photo-electric cell, 

 electric connections with the galvanometer being made by 

 gold wires thrust through the interior of the stems. After 

 a suitable period of rest the normal activity of the plant 

 was found to be restored. The photo-electric cell was filled 

 with tank-water containing a sufficient amount of C0 2 . 

 Alternate exposure of the two plants to sunlight (suitably 

 reflected by a mirror) caused photosynthesis, evidenced by 

 the evolution of oxygen by each plant in turn. The photo- 

 electric cell was enclosed in a dark box provided with a 

 photographic shutter for giving the necessary exposure. 



