214 



COMPARATIVE ELECTRO-PHYSIOLOGY 



gives a photographic record of a series of autonomous 

 pulsations exhibited by a leaflet of Desmodium. 



For the accurate observation of the rate of movement of 

 the Desmodium leaflet during its different phases I have 

 also been able to make records by means of a series of 

 punctures produced by electrical sparks on a recording- 

 surface. The sparks occur at the short gap between the 

 end of the recording arm of a very light aluminium lever 

 and the drum, these being connected respectively with the 

 two electrodes of a RuhmkorfFs coil. The electrical dis- 

 turbance does not affect the 

 plant, as the pulsating leaflet 

 is separated from the other 

 arm of the lever by a long 

 silk thread. The primary 

 current in the RuhmkorfTs 

 coil is broken at intervals of 

 five seconds. Hence succes- 

 sive punctures in the record 

 represent intervals of five 

 seconds each. I give here 

 (fig. 143) a record obtained 

 in this manner, of a single 

 mechanical pulsation of a 

 leaflet of Desmodium. It is 

 to be understood that the 

 up-movement in the record represents the down-movement 

 of the leaflet. 



These movements are produced by excitatory con- 

 tractions of the lower and upper halves of the pulvinus 

 alternately. An inspection of the record given shows that 

 after a pause in the highest position a sudden excitatory 

 impulse is developed in the lower half, which is gradually 

 exhausted as the lowest position is reached. The maximum 

 rate of movement to which this excitation gives rise is in 

 this particular case 7 mm. per second. After the lowest 

 position is attained there is a pause. The up-movement 



FIG. 143. Spark-record of Single 

 Pulsation in Leaflet of Desmodium 



Showing lime-relations of down- and 

 up-movements in single pulsation 

 of leaflet of Desmodium. Up- 

 curve represents down-movement 

 of leaflet and vice versa. In- 

 terval between successive dots 

 = 5 seconds. 



