226 RESEARCHES ON IRRITABILITY OF PLANTS 



e.m.f. still further, I found the characteristic effects of 

 Type II. to take place under an e.m.f. of 30 volts, the 

 resulting current being n micro-amperes. Excitation thus 

 takes place, with moderate currents, at the make of kathode 

 and the break of anode. This result was borne out without 

 any exception by a series of experiments on five different 

 specimens. 



It will be seen that, in this case as in others, with feeble 

 current kathode alone excites at make, and with moderate 

 current excitation takes place at make of kathode and 

 break of anode. 



Leaflets of Averrhoa carambola 



These leaflets are as a general rule but slightly sensitive, 

 and require a comparatively high e.m.f. to induce excitation. 

 The bi-polar connections are here made on two points of the 

 same leaf, separated from each other by a distance of 7 cm. 

 The electrical resistance of the petiole is high, being about 

 5 million ohms when the connections are as described. The 

 velocity of transmission of excitation, also, is relatively 

 feeble, being in a representative case '5 mm. per second. 

 Under feeble stimulus the excitation travels through a 

 short distance only ; still feebler excitation remains more 

 or less localised. 



Effect of feeble current. — With young and excitable 

 specimens the minimally effective e.m.f. is 10 volts, the 

 resulting current being 2 micro-amperes. Generally speak- 

 ing an e.m.f. of 22 volts and a current of 4 micro-amperes 



