CHAP. XII. §. II. IN ROOTS DUEING VEGETATION. 169 



Undly, That these effects cannot he referred entirely 

 to ordinary electro-chemical actions ; hut that, 



Srdly, They may he referred in part to the organic 

 changes which take place in the leaf during vege- 

 tation. 



Before quitting the subject in reference to the 

 leaves, I shall make one or two observations. I have 

 generalized the results of my experiments, and there- 

 fore, in their repetition, the same precise result 

 must not always be expected. We must bear in 

 mind, that in these experiments we are obliged to 

 have a fresh subject for every experiment, and it 

 is almost impossible to meet with that identity of 

 circumstances we could wish ; here the physical 

 philosopher possesses advantages which are denied 

 the physiologist. The problem we are endeavouring 

 to solve is connected with the vital actions of the 

 part ; these terminated, nothing but difficulties then 



Seot. II. On the Manifestation of Electric Currents in 

 the Roots of Plants during Vegetation. 

 Becqueeel" states, that "currents exist going from 

 the pith and the wood to the bark, by the mediation 

 of the roots." 



According to Waetmann'', " when the soil and any 

 part of a plant, visible or underground, is placed in 

 the circuit of the rheometer, we find a current directed 



» Ptilosophioal Magazine, 1851. 

 p Ibid. 



