POLAR EFFECTS UNDER STRONG CURRENTS 257 



obtained with a given pulvinus when it was carried through 

 the usual cycle of kathode-make, kathode-break, anode- 

 make, and anode-break. It will be noticed that excitation 

 took place here at each of these phasic changes. 



In the case of the particular specimen whose consecutive 

 changes have been traced, from the first type to the fourth, 

 it will be noticed that it was subjected to a long-continued 

 series of experiments. After this, however, I took up fresh 

 specimens, with a view to the immediate observation in their 

 case of Type III. and Type IV. There could here be no 

 possible suspicion of changes induced by previous currents 

 too protracted. Thus in a certain fresh specimen the 

 third-stage effect was obtained with a current of 9*1 micro- 

 amperes. When this was further increased to I2'6 micro- 

 amperes the excitatory reaction was transformed into that 

 of Type IV. It will be remembered that with less sensitive 

 specimens a higher intensity of current is necessary for the 

 induction of any particular type of effect. Thus with a 

 certain less sensitive Mimosa a current of 14 micro-amperes 

 was required to induce responses of Type III. The current 

 had in this case to be increased to 32 micro-amperes before 

 the effects were transformed to those of Type IV. 



The particular excitations that appear extraordinary in 

 these higher types are those at anode-make and kathode- 

 break. The anode-make effect, as has been shown, can be 

 induced in the initial response of a fresh specimen. But to 

 obtain that at kathode-break — since this presupposes a 

 previous kathode-make which, if sudden, has caused excita- 

 tion — a certain time must be allowed to elapse after make, 

 in order that the leaf under the continuous action of the 

 current may re-erect itself, with restoration of its sensitive- 

 ness. Lest the long-continued action of the current should 

 here have induced some unknown change to which the 

 excitation at kathode-break might be attributable, I have 

 carried out a number of test-experiments in which the 

 kathodic increase of current was made gradually, though 

 in a comparatively short time, without allowing any 



