ON ELECTROMOTIVE PHENOMENA IN PLANTS. 



219 



the convention of reading deflections from left to right as ' positive,' 

 from right to left as ' negative. '] 



The plant was excited by a single-break induction shock first in the 

 positive then in the negative direction, weak then strong, from a Berne 

 induction coil with two Leclanche cells (=2'9 volts) in .the primary 

 circuit ; for ' weak ' and ' strong ' shocks the secondary coil was set 

 at 1,000 and 10,000 units of the scale. As will be seen from the pro- 

 tocols of experiment, the results of individual trials vary considerably in 

 magnitude, a weak shock to one plant may produce a larger effect than 

 that produced on another plant by a strong shock, and as a rule the 

 effect of a second strong shock is considerably smaller than that of a 

 previous strong shock. We have, therefore, taken average results of 

 first trials, and have not taken into comparison the results of second 



INDUCTION COIL 



Fig 1.— Diagram of Cikcuit fok Testing Seeds. 



trials, especially when strong excitation has been employed. Such 

 average values show clearly enough that the effects of strong excita- 

 tion exceed those of weak excitation, and, as regards the particular 

 question we set ourselves to answer by these experiments, the electrical 

 response of a plumule (Hordeum vidgare is so far the only seedling we 

 have examined) is of considerable higher voltage than that of a radicle 

 — e.g., the former is considerably above O'Ol volt, the latter consider- 

 ably below. 



In consequence of excitation the electrical resistance of the plant is 

 diminished; the diminution is attributable to the chemical dissociation 

 which has given rise to the blaze-current ; it is greater after strong than 

 after weak excitation, and the increased conductivity appears to be in 

 relation with the magnitude of the previous blaze-current. Thus we 

 find for a plumule a diminution of resistance of 30 per cent, after a 

 blaze-current of 004 volt, and for a radicle a diminution of less than 

 10 per cent, after a blaze-current of below 001 volt. But the point 

 requires further investigation ; we have not yet found means to dis- 

 tinguish the possible effect of water-transport from that of dissociation 



