CHAP. XII. §. I. IN LEAVES DURING VEGETATION. 167 



oiiier alkaline, consisting of 120 drops of the liq. 

 potassse (Phar. Land.) to one ounce of water, were 

 prepared, and used in the following manner: The 

 electrode to he placed in contact with the sap was 

 dipped into a portion of the alkaline solution, and 

 then applied to the cut petiole; this electrode was 

 still positive to the other, the effect, however, was 

 not increased ; if the effects were due in the former 

 ■experiments to the acid reactions of the sap, we 

 should now have expected the electrode to be negative. 

 The experiment was repeated upon another leaf, but 

 with the acid solution ; the effect was now very much 

 increased, and the electrode in contact with the sap 

 positive. Several other experiments of the same 

 nature were performed, the results of which I shall 

 generalize by stating, that whenever the electrode 

 was coated with tiie alkaline solution, whether it was 

 that in contact with the surface of the leaf, or that in 

 contact with the sap, with but few exceptions there 

 was no decided difference as to the effect upon the 

 needle ; but that whenever one of the electrodes was 

 ■dipped into the acid solution, this was always positive 

 to the other. 



If the leaf was gathered, an electrode being in- 

 serted into the petiole, and the leaf then plunged 

 into a glass of water containing the other electrode, 

 it frequently happened that the electrode in contact 

 with the water was positive to the other, even if the 

 water was rendered alkaline. It appeared to occur 

 principally with the leaf of the bean (Windsor), and 



