208 CHAP. XIX. RECURRENT LIGHT AND DARKNESS 



Experimental Arrangements 



When the diurnal record has to be taken continuously for 

 several days in succession, it is necessary to take precautions 



Fig. 119. The Automatic Recorder of diurnal movements of 

 plants. Quadruplex form provided with four writing levers. 

 The flower-pots are placed in a trough filled with water to a 

 constant height. The first two levers are shown in the figure 

 to record movements of leaves, the third to record movements 

 of a horizontally laid shoot ; the fourth lever, attached to a 

 differential thermometer, t, records diurnal variation of 

 temperature. 



against the disturbing effect of watering the plants, and of 

 tropic curvature of the stem induced by one-sided illumina- 

 tion. 



