384 CHAP. XXXTV. THE MECHANISM OF THE TWINING STEM 



I find that it is more convenient to work with a cut 

 specimen than with an intact plant ; the effect of wound 

 disappears after a time, when the stem regains its normal 

 torsional activity. The cut end of the stem is fixed by 

 means of a cork in a small phial filled with water. This 

 plant-holder H passes through a circular scale ; by rotation 

 of H, different flanks of the plant can be subjected to uni- 

 lateral action of light L. The light from a pea-lamp is 

 reflected from M and re-reflected on the millimetre scale 

 S' by means of a second stationary mirror M' at a distance 

 of 75 cm., the magnification produced being 3000 times. 

 The rate of movement is observed every 5 minutes, the 

 intervals being signalled by clockwork. It may be said in 

 general that the rate of autonomous torsion depends on the 

 species of the plant, on its physiological vigour, and on 

 external condition, such as season and temperature. 



* 



Automatic Recorder 



Method of Magnification. — I also succeeded in the 

 difficult task of obtaining an automatic record of the normal 

 rate of torsion and its induced variations. The method 

 will be understood from the diagrammatic representation 

 given in fig. 218. The clamp bears a light aluminium 

 index I, about 10 cm. in length, which presses against V, 

 a vertical projection from the short arm / of a lever, the 

 vertical fulcrum-rod of which rests on a conical jewel- 

 support p. The short arm is 0-5 cm., while the longer 

 arm L is 15 cm. The total magnification of the system of 

 levers is therefore about 300 times. By slightly tilting 

 the apparatus, the recording end of L on the left tends to 

 rest on the smoked-glass recording plate G. The vertical 

 projection V at the other end of the lever then presses against 

 the index L This latter is pushed to the left by the anti- 

 clockwise rotation of the shoot, while the recording end of 

 L is moved towards the right. It must be remembered 

 that the recording index is moving in a horizontal plane ; 

 hence, in order to obtain a dotted record, the recording 



