GENERAL SURVEY 343 



motility of the pulvinus of Mimosa. Under these circum- 

 stances, we may have an excitatory impulse without any 

 external manifestation of its passage through the plant. 

 It will thus be understood how an excitatory impulse 

 in an ordinary plant may pass unnoticed on account 

 of the absence of an efficient motile indicator. The exist- 

 ence of such an impulse can, however, be detected by means 

 of electric response. 



In the present work the various excitatory phenomena 

 of the plant have been investigated by means of mechanical 

 response under the action of a testing stimulus. The 

 different responses of plants may be included under three 

 classifications : (i) Simple response, where a single stimulus 

 evokes a single response ; (2) Multiple response, where a single 

 strong stimulus gives rise to multiple series of responses ; 

 and (3) Automatic response so called, where the pulsations 

 appear to be spontaneous. In reviewing these in their 

 proper sequence we shall be struck by the extraordinary 

 similarities which are revealed between the response of the 

 plant and the animal. 



The Response Recorder 



In the course of this work it has been shown that physio- 

 logical changes induced in the plant owing to the action of 

 the environment may be revealed by the characteristic 

 variation of the amplitude and time relations of the 

 normal curve of response. In obtaining records of response 

 errors are, however, introduced on account of friction of the 

 writing point against the recording surface. In recording 

 the pulsations of Desmodium leaflet it is found that a 

 weight as small as '03 gram is enough to arrest the 

 pulsatory movement. The difficulty of friction has been 

 overcome by the method of intermittent instead of con- 

 tinuous contact for record. In the Resonant Recorder 

 the writer is made to vibrate to and fro at a known and 

 definite rate. The record consists of series of dots giving 



