536 LIFE MOVEMENTS. IN PLANTS 



The record is also liable to be affected by the twist induced 

 by light when it acts on one side of the organ. 



Irrigation. — There is, as is well known, a periodic 

 variation of turgor in the plant. This normal variation 

 is, however, disturbed by watering the plant at irregular 

 intervals. Precaution against this was taken by placing 

 the three flower pots on a long trough filled with water 

 (Fig. 190). The height of water in the trough is always 

 maintained constant by a syphon. 



Vertical illumination. — The direction of sunlight changes 

 from morning to evening, and the leaves exhibit appropriate 

 phototropic movements or torsions under changing direc- 

 tions of lateral light. In order to obviate this, a special 

 chamber was constructed, which allowed light from the 

 sky to fall vertically on the plant through a sheet of 

 ground glass which covered the roof. The sides and the base 

 of the chamber are impervious to light. A narrow slit 

 covered with red glass allows inspection of the curve 

 during the process of record. 



The Ventilator. — A revolving ventilator, acted on by the 

 wind, sucks the air away from the chamber, thus ensuring 

 constant supply of fresh air, without causing any disturb- 

 ances of the record. 



The Recorder. — The Oscillating Recorder employed is of 

 the quadruplex type carrying four recording plates 

 (Fig. 190). The first lever records the daily variation of 

 temperature. The other three are attached to three different 

 specimens of the same plant, or to three different plants. In 

 the former case, three records are obtained of the same 

 species of plant, under identical external condition. If 

 they agree in all essentials, the periodic curve may be taken 

 as characteristic of the given plant. A very great saving of 



