198 PLANT RESPONSE 



second being at a distance of about 3 cm. lower on the stem. 

 In this case the stem, or certain of its elements, acted as the 

 conducting nerve, the leaf serving as the terminal indicator 

 (fig. 94). With such an arrangement, using a plant of 

 exceptionally high excitability, and E.M.F. of moderate 

 intensity, I have obtained the following results : 



1. Current ascending {a). — At make, the leaf-stalk fell. 

 This was due to the direct make action at the kathode (U). 

 At break there was also a response. This was due to the 

 transmitted break-anode excitation reaching the leaf-stalk. 



2. Current descending (a).— At make, the excitation of 

 the distant kathode reached the leaf-stalk, the current at 

 the anode not being sufficiently strong to act as an effective 

 block, (b) At the stoppage of the current, there was another 

 response of the leaf-stalk. This was due to the break effect 

 of the anode in the immediate vicinity. 



The following tabular statement shows at a glance the 

 effects which are apparent at the terminal organ : 



Table showing the Effect of Moderate E.M.F. on Highly 

 Excitable Mimosa 



The experiments described above show that the excitation 

 produced in plant-tissues by an electrical current is not 

 indiscriminate, but selective, or polar, in its action. The 

 effects seen here are of precisely the same nature as those 

 observed in animal tissues. The exhibition of such polar 

 effects completely disproves the hydro-mechanical theory of 

 excitation in plants. They point unmistakably, on the 

 other hand, to the existence of some fundamental property 

 of protoplasm, common to animal and vegetable alike, which 

 under normal conditions finds an identical expression in 

 the two, of kathodic excitation at make, and anodic at break. 



