20 RESEARCHES ON IRRITABILITY OF PLANTS 



of the vertical rod, either in the right-hand or the left- 

 hand direction. By this means it is possible to bring the 



Fig. 4. — General view of the whole apparatus, and the electrical connec- 

 tions by means of which excitatory shock of a definite duration may 

 be given to the plant ; duration of shock determined by metronome 

 which completes electrical circuit. (From a Photograph.) 



plane of movement of the writing-index exactly parallel to 

 that of the writing-surface. The complete apparatus for 



