MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 213 



In Desmodium gyrans, as is well known, we have the typical 

 example of autonomous response, its secondary leaflets 

 executing periodic up and down or elliptical movements. 

 The movement of the leaflet in some instances takes place by 

 jerks, in others it is more uniform. The period of a com- 

 plete up-and-down movement varies between two and four 

 minutes. The length of this period is much affected by 

 temperature, being less when this is moderately high. From 

 the normal, or highest position, the leaflet sinks somewhat 

 rapidly ; having reached its maximum depressed position, it 

 ts for a while. There 

 next a rather slow 

 ise to its original posi 

 ion. This up-and-down 

 motion is in some cases 

 approximately straight, 

 n others, the pulvinule 

 f the leaflet is slightly 

 isted after its descent, 

 nd the corresponding 

 rve described becomes 

 ore circular. 



In view of certain 

 culiarities to be ob- 

 rved in the electrical 

 sponse of Desmodium, 



is necessary here to enter into some detail regarding the 

 ime-relations of its mechanical response during the two 

 hases of down and up movements. The great difficulty 

 recording the pulsatory movements of Desmodium lies 

 the extreme slenderness of the lateral leaflets. This 

 such that the friction of a light recording-lever against 

 e recording surface is sufficient to bring these movements 

 a stop. This difficulty has, however, been overcome, as 

 ted elsewhere, by means of the Optical Lever. 1 Fig. 142 



FIG. 142. Photographic Record of Autonomous 

 Mechanical Pulsation in Desmodium Leaflet 



Period of each complete pulsation 

 = 27 minutes. 



See also Bose, Plant 1\ espouse, p. 5. 



