166 CDEEENT ELECTRICITY CHAP. XII. §. I. 



the majority of instances the sap will be found to 

 have an acid reaction ; in some succulent plants the 

 effect will be null or very trifling, whilst in other 

 plants, such as the vine, it will be very apparent. 

 In the latter instances, the effects upon the needle 

 may be fairly referred to the acid reactions of the 

 secretions of the plant ; but can we refer them to the 

 same action when the sap does not present an acid 

 reaction ? Are we sure that the sap is acid ? May 

 not this acid reaction upon the litmus arise from the 

 acid secretions of the plants, which become mixed 

 with the sap upon the tearing asunder of the tissue 

 of the plant ? 



The diflBculty which arises in solving some of 

 these questions occurs from the fact, that there is 

 not that distinct circulation in plants as in animals ; 

 the sap, as it passes from one spot to another, may 

 undergo a series of progressive changes, and in the 

 tearing and cutting of the tissues, a mixture of sap 

 from different parts and of secreted products must 

 naturally occur. We cannot place our electrodes 

 at the real acting point ; there may be several acting 

 points between the electrodes; and the resulting 

 effect upon the needle may be that of a differential 

 or of a combined current, according to circumstances. 



Two solutions, one acid, consisting of 8 drops of 

 strong sulphuric acid to one ounce of water, the 



that case the alkali of the litmus being neutralized, its red 

 colour wiU necessarily be restored." Turner's Chemistry, p. 671. 

 ftth Edit. 



