CHAPTER XX 



MULTIPLE AND AUTOMATIC RESPONSE 



The Oscillating Recorder — Latent period of Biophytum — Refractory- 

 period — Response on ' all-or-none ' principle — Multiple electrical 

 response to a single strong stimulus — Multiple mechanical response 

 to strong stimulus in Biophytum and Averrhoa — Continuity of multiple 

 and automatic response — Ordinarily responding Biophytum con- 

 verted into automatically responding condition by excess of stored 

 energy — Automatically responding Desmodium converted to ordinarily 

 responding condition by depletion of stored energy. 



We have studied in detail the responsive characteristic of 

 the leaf of Mimosa. We next take up the study of the 

 responses of the leaflet of Biophytum. In doing this, we 

 shall observe a certain new class of phenomena of great 

 theoretical importance come into play. 



The difficulties encountered here, however, in the taking 

 of automatic records are extremely great. The leaflets are 

 very slender, and the pull exerted in the course of the 

 excitatory fall is very slight. I overcame the difficulties in 

 the taking of the record by the use of the Optical Lever, in 

 which a moving spot of light either traced the response- 

 curve on a travelling photographic-plate, or was itself 

 followed by the pen of the observer on a moving drum 

 covered with paper. These devices have their disad- 

 vantages, and I was desirous of contriving means to 

 secure records at once simple, effective, and perfectly 

 automatic. 



The Resonant Recorder was not found specially suit- 

 able for the tracing of Biophytum movements, inasmuch 

 as the lightest steel wire was still too heavy for the slight pull 

 exerted by the leaflet ; the only lever that was sufficiently 



278 



