162 OURBENT ELEOTEICITY CHAP. XH. §.1. 



Sect. L On the Manifestation of Electric Currents in 

 the Leaves of Plants during Vegetation. 



The mode of conducting the experiments was as 

 follows : The leaf was placed upon a clean piece of 

 glass, and the extremity of one platLmmi electrode, 

 to the extent of half an inch or an inch, was placed 

 upon the upper or under surface of the leaf; a small 

 notch was cut in the petiole, and, as the sap flowed 

 out, the extremity of the other electrode was placed 

 in contact with it. 



I may just remark, that after having worked for 

 some time upon plants growing in pots and in 

 London, I was led, from the imsatisfactoiy results 

 that were obtained, to repeat the experiments upon 

 plants growing in the open air and in the country ; 

 and it soon became evident that, in order to obtain 

 any thing like satisfactory results, strong, healthy, 

 and vigorous plants should be employed ■■. 



Experiment 1. Vegetable marrow. A healthy 

 middle-sized leaf, and the sap from the petiole; the 

 latter positive^ 3°. A large leaf slightly tinged with 

 yellow, and dry, and the sap from the petiole — ^no 

 effect. Various leaves were tried with similar results ; 

 when any effect was obtained, the sap was positive. 



^ The experiments were performed during the months of 

 July, August, and September, 1882. 



' The difficulty experienced in comprehending the results 

 obtained by different inquirers in reference to the direction of 

 the current I have abready alluded to in chap. x. 



