CHAPTER XIX 



VARIATION OF POLAR REACTION UNDER TISSUE MODIFICATION 



Modification of polar reaction under tissue-changes — Effect of age — 

 After-effect of moderate stimulation — Modified polar effect : excitation, 

 at kathode-make and anode-make ; excitation at kathode-make, 

 kathode-break, and anode-make — General review of polar reactions. 



In the course of my investigations into the effects of currents 

 on the pulvini of different leaves of Mimosa, I found that 

 during the beginning of the summer season the normal 

 effects which have been described occurred uniformly, in 

 their proper sequence. But later in the year, at the end of 

 the rainy season, when the plants had begun to seed, I was 

 puzzled by the appearance of certain new and unexpected 

 types of response with which I had not hitherto been 

 familiar. Thus in the case of certain leaves, with a moder- 

 ate current the excitatory reaction took place only at 

 make of kathode and make of anode. It will be remem- 

 bered that in Amphistigma also this was the characteristic 

 response observed by Verworn. With certain other leaves, 

 again, under fairly strong current, the polar excitations 

 took place at the make of kathode, at the break of 

 kathode, and at the make of anode. This again was like 

 the responsive reaction in Actinosphaerium observed by 

 Kiihne. I found a very large number of leaves which gave 

 these specific reactions, which precluded the idea of their 

 being accidental. These were most frequently exhibited 

 late in the season and also in winter. 



I made many experiments with a view to solve these 

 anomalies, and found that the normal polar reactions of 

 plants are modifiable, to a greater or less extent, by various 



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