14 ELECTRICAL STRUCTURE AND 



THE ONION. 



This is an unusually difficult vegetable to test, in that 

 while the bulb appears to form a complex cell, the inter- 

 mediate contact-spaces are so narrow and the liability to 

 diffusion so great, when the onion is divided, that I am 

 unable to speak with certainty. Botanists, however, will 

 readily solve the problem, which, from an electrical stand- 

 point, is to differentiate the layers connected with the root 

 from those in alignment with the tubular leaves. The 

 former will be negative and the latter positive. 



Fig. 18 depicts the structure of the onion as it is pre- 

 sented to the unaided eye and in so far as I am able to 

 determine it galvanometrically. The negative system 

 seems to extend from the root to the outer second and 

 third layers of the bulb, between which and the central 

 positive system there exists a membranous and probably 

 protective lining. The contacts afforded by the poles are 

 well defined, the absolute insulation is extraordinarily high, 

 and altogether the onion is a vegetable cell of a very 

 perfect description. Its electro-motive force is, ap- 

 proximately, 0-086 volt ; the current varying, of course, 

 with size. Such a cell is invaluable in the testing-room 

 for such work as, for instance, taking the constant of a 

 sensitive galvanometer or comparing deflections from 

 living muscle or tissue, instead of using for the purpose a 

 standard cell liable to polarisation when employed without 

 very high resistance in circuit. 



TUBERS. 



These differ in their electrical constitution from root- 

 vegetables proper and from fruits, in that they are not 

 merely bipolar, but have a number of positive and negative 

 terminals. I have taken two examples, i.e., the potato 

 and the Jerusalem artichoke, reserving others for future 

 ^vestigation. 



