CHAPTER II 



THE ELECTRO-MOTIVE RESPONSE OF PLANTS TO DIFFERENT 

 FORMS OF STIMULATION 



Historical Difficulties of investigation Electrical response of pulvinus of 

 Mimosa Simultaneous mechanical and electrical records Division of plants 

 into ' ordinary ' and ' sensitive ' arbitrary Mechanical and electrical response 

 of ' ordinary ' plants Direct and transmitted stimulation All forms of 

 stimulus induce excitatory change of galvanometric negativity. 



IT has been customary to divide plants, as regards their 

 responsiveness, into two distinct classes : ( ordinary ' and 

 ' sensitive.' Of these only the latter class, represented by 

 such plants as Mimosa and Dioncea, was regarded as excitable. 

 Hence the attention of observers desirous of investigating 

 excitatory electro-motive phenomena in vegetable tissues was 

 mainly attracted towards the reactions exhibited by these 

 plants. The experiments undertaken in this field by Kunkel, 

 Burdon Sanderson, and Munk are well known. Burdon 

 Sanderson and Munk worked on the sensitive leaves of Diontza 

 and Kunkel on those of Mimosa. 1 



Electro-motive variations were observed to take place in 

 all these plants on stimulation, but the conclusions arrived 

 at by the investigators were not concordant. Burdon Sander- 

 son and Munk found out that the resting-current between 

 two selected points of Dioncea exhibited variation on applica- 

 tion of stimulus to the leaf. They thus obtained di-phasic 

 and sometimes even tri-phasic responses, consisting of positive 

 and negative variations. More definite results were obtained 

 by Burdon Sanderson, in the responsive variations of the 

 normal leaf-current, flowing between the proximal and distal 



1 For a more detailed account cf. Biedermann, Electro-physiology ', English 

 translation, 1898, vol. ii. pp. 1-31. 



