MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 213 



In Desmodiumgyrans, 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 

 rests for a while. There 

 is next a rather slow 

 rise to its original posi- 

 tion. This up-and-down 

 motion is in some cases 

 approximately straight. 

 In others, the pulvinule 

 of the leaflet is slightly 

 twisted after its descent, 

 and the corresponding 

 curve described becomes 

 more circular. 



In view of Certain FIG. 142. Photographic Record of Autonomous 



-\/T T * 1 TV_1 j_T _ _ _ J-\ 7- T rt . 



peculiarities to be ob- 

 served in the electrical 

 response of Desmodium, 

 it is necessary here to enter into some detail regarding the 

 time-relations of its mechanical response during the two 

 phases of down and up movements. The great difficulty 

 in recording the pulsatory movements of Desmodium lies 

 in the extreme slenderness of the lateral leaflets. This 

 is such that the friction of a light recording-lever against 

 the recording surface is sufficient to bring these movements 

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

 stated elsewhere, by means of the Optical Leyer. 1 Fig. 142 



Mechanical Pulsation in Desmodi^^m Leaflet 



Period of each complete pulsation 

 = 27 minutes. 



1 See also Bose, Plant Response, p. 5. 



