PHOTOTROPIC TORSION 



399 



effect of weight is thus practically eliminated ; the looped 

 support prevented up or down movements, and yet allowed 

 perfect freedom for torsional response. This latter is magnified 

 by a piece of stout aluminium wire fixed at right angles to the 



Fig, 148. — Diagrammatic representation for record of tors^ional response. H, thin 

 glass hook : A, aluminum wire attached to petiole for magnification of torsional 

 movement. T, silk thread for attachment to recording lever. 



petiole (Fig. 148). The end of the aluminium wire is attached 

 to the short arm of a recording lever ; there is thus a com- 

 pound magnification of the torsional movement. The Oscillat- 

 ing Recorder gave successive dots at intervals which could be 

 varied from 20 seconds to 2 minutes. Time-relations of the 

 response may thus be obtained from the dotted record. 



With the experimental device just described, we shall be in a 

 position to study the effect of various stimuli applied at one 

 flank of the pulvinus — at the junction of the upper and low^er 

 halves of the organ. The observer standing in front of the 

 leaf is supposed to look at ihe stem. Torsional response will 

 then appear as a movement either with or against the hands of 

 the clock. The torsional response, right-handed or left-handed, 



