470 COMPARATIVE ELECTRO-PHYSIOLOGY 



possible to detach one of them having a length of 20 cm. 

 or more. 



Now the essential feature of a nerve is its protoplasmic 

 continuity, which is ensured by its fibrous structure. And 

 in what I have called the vegetable nerve we find the same 

 characteristic to hold good. On viewing this structure, as 

 it appears on making a transverse section of the petiole, 

 we find it enclosed within sheath-like sclerenchyma. It 

 mainly consists in itself of a bundle of fine fibres with a 

 few vessels in the centre. But however remarkable these 

 external resemblances may seem, they are by no means so 

 startling as the more fundamental similarities which are 

 demonstrated so soon as we proceed to subject this vegetable 

 structure to those tests of electrical response which are 

 characteristic of animal nerve. It may be said that for the 

 following investigation the nerves of the common maiden- 

 hair fern (Adiantum] and Nepkrodium molle were found most 

 suitable. 



In obtaining a plant nerve for purposes of experiment 

 it is possible to dissect it out and at the same time to avoid 

 injury. It is then placed in normal saline solution for about 

 half an hour, so as to remove all traces of excitation due to 

 handling. When the external temperature is not high, the 

 excitability of the isolated plant nerve is found to remain 

 relatively unaffected for a considerable period, but in the hot 

 weather it undergoes rapid decline ; and the only way in 

 which I could overcome this difficulty was by placing the 

 specimen in normal saline solution which was ice-cold. The 

 experimental precautions to be taken are precisely the same 

 as those observed in corresponding experiments with animal 

 nerve ; that is to say, the specimen should be placed in a 

 moist chamber. For the process of drying is found to induce 

 a transient increase of excitability followed by a permanent 

 abolition of responsiveness, in the one case as in the other. 

 In order to obtain responses, one end of the specimen may 

 be killed by the local application of hot salt solution. The 

 galvanometric connections are then made, one with the killed, 



