MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 2 17 



waves of electrical response was slightly less than i minute, 

 and that of the subsidiary wave a little over 2-5 minutes. 

 These double electrical pulses, corresponding to a single 

 mechanical vibration, are at first very puzzling, and I under- 

 took special investigations to ascertain the reason of this 

 peculiarity. In order to obtain an insight into the relation 

 between these mechanical and electrical responses it was 

 necessary to take simultaneous records of the two on the 

 same recording drum. This was accomplished by having 

 the two recording spots of light one from the galvanometer 

 and one from the optic lever thrown on the same horizontal 

 slit, in front of the revolving drum, round which was wrapped 

 a sensitive photographic film. The galvanometer spot of 

 light, and consequently the electrical response record, was 

 the lower of the two. The vertical movement of the spot of 

 light which records the mechanical response is to be under- 

 stood as converted into horizontal by reflection from a 

 second mirror suitably inclined. This experimental arrange- 

 ment is similar to that employed for simultaneous mechanical 

 and electrical records in the case of Mimosa, as shown in 

 fig. 12. 



The record given in fig. 144 exhibits the simultaneous 

 mechanical and electrical responses thus obtained. It will 

 be seen that the minor electrical wave took place while the 

 leaflet was moving up from (a) and coming to its highest 

 position at (b). This was followed by a wave of higher 

 amplitude but shorter period, which coincided with the 

 movement of the leaflet again from its highest to its lowest 

 positions. It will thus be seen that the subsidiary electrical 

 wave of small amplitude and relatively long period coincided 

 with the slow up- movement of the leaflet, and that the 

 principal wave, characterised by large amplitude and short 

 period, corresponded with the quick down-movement of the 

 leaflet. These galvanometric deflections indicated, it must be 

 understood, a condition of galvanometric negativity of the 

 pulvinule at the moments of its excitatory up and down 

 movements. The following considerations make it easy to 



