204 PLANT RESPONSE 



plants, and first I shall take those in which the A stage was 

 exhibited, that is to say, those in which the anode as well as 

 the kathode showed excitation at make. 



Experimental verification of A stage effects. — With 

 the plant Biophytum, I have always found, without exception, 

 that up to thirty-two volts, or thereabouts, the polar effect was 

 normal ; that is to say, excitation was produced at the kathode 

 at make and not at the anode. On using an E.M.F. of forty- 

 eight volts, however, with a certain specimen, I obtained 

 excitatory response at make, at both anode and kathode. 

 That this anodic effect was not due to transmission of ex- 

 citation from the kathode, was seen in the fact that some 

 of the interpolar leaflets were not affected, as all would have 

 been had the wave of excitation passed from kathode to 

 anode. 



I shall next describe experiments made on Mimosa, in 

 which, as has been said, the two electrodes can be separated 

 by a longer tract of tissue. In the case of this plant, the 

 value of the E.M.F. which is required to bring on the A stage 

 effect, is much higher than in Biophytum. I have occasionally 

 obtained it with no, but more usually with 220 volts. In 

 order to show how at this stage the anodic and kathodic 

 effects tend to become interchangeable, 1 shall describe three 

 experiments. 



In the first of these, an E.M.F. of 1 10 volts was used. At 

 make, the kathodic leaflets fell energetically, while the anodic 

 fell but slightly, and after a little delay. Here we see that 

 though reversal is setting in, yet the normal kathodic effect 

 is relatively predominant. 



In the second of these experiments, I used 220 volts. 

 The anodic fall now took place slightly earlier than the 

 kathodic. The current was maintained till the leaflets 

 recovered. On now breaking the circuit, there was a slight 

 anode-break excitation, but none at the kathode. In this 

 case, though from the slight priority of the anodic excitation 

 we infer some predominance of the anode, yet the fact that 

 the effect at break is normal shows that we are still in the 



