FUNCTION IN PLANT LIFE 37 



without finding in them any evidence of polarisation or 

 discharge, and as the E.M.F. of them all is the same 

 the current only varying in accordance with Ohm's law 

 the onion is, in my opinion, an ideal standard cell of low 

 electromotive force for delicate galvanometric work. The 

 apple and pear, offering as they do smaller contacts and 

 more liability to diffusion at the points of contact, are 

 not so generally useful, although, with care, they are 

 reliable. 



In regard to plants, shrubs, and trees, however, I have 

 observed that during such time as they are " resting," as 

 in the late autumn, winter, and early spring months, both 

 electromotive force and current fall off, and this may be 

 due to a deficiency in the quantity or flow of the sap, or 

 both. 



As regards the constancy of these cells I am inclined to 

 think they must draw a positive charge from the air when- 

 ever their potential falls below that of the air, in the same 

 way as shown by the capacity tests they give off to the 

 air any excess of current with which they are artificially 

 charged. No other explanation of their long-sustained 

 electrical activity occurs to me, and if they are carefully 

 examined it will be seen that the flower or foliage end of 

 fruits and vegetables is not sealed so thoroughly and 

 effectively as the stalk or root. If that is so they are 

 storage cells in a new sense. In other words, they are 

 maintained in a state of electrical activity by the air only, 

 and it would not be possible, by joining them up in series, 

 to increase their electromotive force beyond that of the 

 air, because if it could be augmented and I do not believe 

 it can by such an arrangement, any excess of potential 

 above that of the air would be given off instantaneously. 

 We have seen that an artificial charge is retained for some 

 little time, but that, inevitably, the vegetable cell reverts 

 to its normal electromotive force and polarity. 



