CHAP. XII. §. IV. IN FEDITS AND TUBEBS. 175 



they indicated the sap to be positive. The greatest 

 effect appeared with the fuchsia. 



It may be a question whether the results were not 

 due more to the changes which the sap might under- 

 go from exposure to the air, than to the changes 

 which might occur in the petal. 



Sect. IV. On the Manifestation of Electric Currents 

 in Fruits and Tubers. 



Becqueeel ', Donne '', and Wartmann ', have shewn, 

 that when the electrodes are inserted into different 

 parts of a fruit or tuber, effects upon the needle 

 occur, amounting to 15° or 30° or more, depending 

 upon the parts in which they are inserted and the 

 kind of fruit. In some tubers, such as the potato, 

 the beet-root, and in the carrot, the external layers 

 were positive to the internal. In the Tropmolum 

 tuberosum and the Ullucus tuberosus, the effects were 

 inverse. 



Some experiments were made upon the vegetable 

 marrow and cucumber whilst attached to the plant. 

 The electrode in contact with the external surface 

 was slightly positive to the other when inserted into 

 the centre. Similar experiments were made upon 

 the apple, pear, and plum, when attached to the tree, 

 or fresh gathered, or some time after they had been 

 gathered. The greatest effect appeared with some 



' In his second Memoir. 



y Traits de rEleotricit^, torn. iv. p. 164. 



^ Loc. (At. 



