218 RESEARCHES ON IRRITABILITY OF PLANTS 



upon the required point and immediately washing it off with 

 water. A minute speck of kaolin paste is then attached to 

 each of the electrodal spots, with the point of a fine brush. 

 The electrical contact with the moistened thread is now 

 found to be perfect. 



The e.m.f. is then applied and gradually increased, till 

 the minimally effective intensity is found. If the two sub- 

 petioles be equally excitable, then the same minimal stimulus 

 will excite both to the same extent. If their sensitiveness 

 be slightly different, then the extent of excitatory trans- 

 mission will be different in the two cases. In the present 

 case the excitabilities of the two sub-petioles were practically 

 the same, and the minimally effective e.m.f. was found to 

 be 4 volts. The exciting current was 7 micro-ampere. 

 When the current was suddenly made by turning the Pohl's 

 commutator to the right, kathode-make, or Km, was effected 

 on R, and anode-make, or A'm, on L. No effect was found 

 to be induced at A'm, but excitation was induced at Km. 

 This excitation not only caused closure of the pair of leaflets 

 at the kathodic point but was irradiated in both directions 

 from this point. Eleven consecutive pairs of leaflets under- 

 went successive closure in the intra-polar tract, and three 

 pairs in the extra-polar — a fact which may be indicated 

 by the symbol 11 <- -> 3. In this convention it will al- 

 ways be understood that <- indicates intra-polar and -> 

 extra-polar transmission. Having observed the effects of 

 Km and A'm, the circuit was then broken, thus causing 

 kathode break, Kb, at R, and anode-break, A'b, at L. No 

 excitatory effect was induced. 



In order to test these results further, the key was now 

 tilted to the left, making L kathode and R anode. This, 

 it will be noted, is the reverse of the previous arrangement. 

 The excitatory effects were now found to have changed 

 their places, the new kathode K' at L showing excitation at 

 make, with a similar overflow as before — namely, 11 *- ■* 7. 

 It is obvious that only by accident could the excitability 

 and conductivity of two different sub-petioles be exactly the 



