214 PLANT RESPONSE 



At break — No effect at anode, but feeble augmentation 

 of luminosity at kathode. 



These results afford us some insight into that obscure 

 phenomenon of the modified condition of tissue by which 

 reversal of response is brought about. 



We have seen that in the case of Biophytniii, the polar 

 effects are alvvaj-s found to be normal, within rather a wide 

 range of E.M.F., that is to say, up to about thirty volts. The 

 kathode here excites at make, and the anode at break. I 

 have carried out several hundreds of experiments with this 

 plant, but have not once come across any deviation from this 

 normal action. 



As the E.M.F. was progressively increased, however, we 

 found in this and other plants a tendency towards the 

 reversal of these normal polar effects. During the first, or 

 A, stage of this reversal, the excitatory value of the kathode 

 was seen to undergo a diminution, and the anode, which 

 normally had a depressing influence, was observed to have 

 its property reversed, and to produce excitation. The result 

 during this stage, therefore, was the exhibition of excitation 

 at both kathode and anode at make. 



With still higher E.M.F. the B stage was reached, and 

 here there was a complete reversal of the normal polar effects. 

 It was then found that the anode produced excitation at 

 make, and the kathode at break. This reversal of polar 

 effects under a high E.M.F. was further demonstrated by 

 means of Death-response in plants, and Glow-response in 

 animals. 



We have also seen that in consequence of progressive 

 molecular change induced by fatigue, the normal polar effect 

 tended to be reversed, and we have been able to trace the 

 successive stages of such a reversal, in experiments on the 

 plant Mimosa and on the firefly. 



And, finally, specimens are occasionally found which, 

 owing to molecular modifications of their tissues— modi- 

 fications that a knowledge of their previous history could 



