v.] UNFINISHED WORK 95 



to have to admit that we have to do with a homodrome post- 

 kathodic current. A homodrome post-anodic current would 

 have seemed more familiar to us. 



In all these experiments, it is remarkable how strictly the 

 effects of excitation are limited to the directly excited spot. 

 Outside the area of direct excitation, the excitability of the 

 skin remains unaffected ; we can locally exhaust the skin by 

 strong excitation, and obtain good response from other spots 

 of the same piece of skin. 



This local independence of parts, characteristic of vegetable 

 tissues as well as of the skin, is in marked contrast with the 

 spread of disturbance that is peculiar to muscle and nerve 

 where propagated effects are the salient feature. It is one 

 of the reasons why a piece of skin or of a plant is a more 

 favourable object than a muscle or a nerve for the demonstra- 

 tion of blaze-currents. 



Plants, excited and led off by two points of their external 

 surface, give, like the frog's skin, homodrome responses to both 

 directions of excitation. But whereas in the case of frog's 

 skin, the total .homodrome effect between A B is the alge- 

 braic sum of the partial outgoing effects at A and B, in that of 

 a vegetable skin it is the sum of two ingoing effects. The pre- 

 potent pole, in the case of the frog's skin, was the kathode, in 

 that of the vegetable skin, it is the anode, as will be evident to 

 you on careful consideration of the figure. It is not difficult in 

 the case of vegetables to obtain measurements of the total and 

 partial blaze-currents, showing quite clearly that the anode has 

 been the prepotent pole, thus : 



Excitation from B to A 



Total response from B to A + 0.012 volt. 



Partial response from B...to...C + 0.035 



Partial response to C from A - 0.021 



Cut surfaces of fruits e.g., of apples and pears have given 

 ingoing currents at both poles after excitation, but smaller than 

 the currents aroused at intact surfaces. Ripe orange peel has 

 given ingoing effects at its external surface, and only small 

 polarisation counter-currents at its internal surface, the former 

 is " alive," the latter is " dead." 



