SUMMARY 393 



continued for 12 minutes, after which the rate of movement 

 diminished and became arrested after a further period of 

 24 minutes ; the response now became reversed from 

 positive to negative ; all responsive movement disappeared 

 in the course of an hour after application of the toxic agent, 

 indicating complete poisoning of the stem. 



Aimnonia vapour abolishes the torsional activity. The 

 vapour of hydrochloric acid is also toxic, producing an arrest 

 of movement. 



Experiment 212. Chlorofonn. — I give in the record to the 

 left (fig. 221) the effect of chloroform vapour. It is seen to 

 produce a preliminary enhancement of the rate, followed by 

 reversal and arrest in the course of half an hour. 



Experiment 213. Ether. — Ether is less toxic and its 

 effect in a moderate dose is an enhancement of the rate of 

 torsion which persists for a considerable length of time 

 (record to right, fig. 221). Very prolonged application, 

 however, induces depression in the rate. 



Summary 



The growing twisting stem is anisotropic, two longi- 

 tudinal halves at any given moment being unequally ex- 

 citable, like the two halves of the pulvinus of Mimosa. 

 The plane of demarcation between the two halves in 

 Mimosa is fixed ; in the twisting stem the plane slowly 

 travels round the axis. 



The torsion of the stem is autonomous : it is the result 

 of the unequal growth of the diverse longitudinal halves. 



The twining of the stem is effected by its autonomous 

 torsional growth and by its sensitiveness to contact. 



By the Method of Optical Magnification the rate of tor- 

 sional growth can be accurately observed. The Automatic 

 Method records the actual rate of torsional movement. 



The rate of torsional growth is modified by the rate of 

 ascent of sap. Enhancement of the rate of ascent induces 



