6o RESEARCHES ON IRRITABILITY OF PLANTS 



through the plant-chamber, at^varying rates. A steady low 

 temperature may thus be attained by adjusting the inflow 

 of cooled air, the degree of cooling being dependent on the 

 rate of flow. A thermometer placed inside the chamber 

 indicates the temperature attained. 



In order to raise the temperature of the plant-chamber an 

 electrical device is employed. Inside the rectangular frame 

 there is a coil of wire of German silver, the ends of the wire 



being led outside to two binding- 

 screws. An electrical current from 

 an outside battery is led through 

 this wire, a variable resistance 

 being also interposed in the circuit. 

 The heat generated inside the 

 chamber can be increased or de- 

 creased by changing the intensity 

 of the current ; this is accom- 

 plished by varying the adjustable 

 resistance. In this manner it is 

 quite easy to raise the temperature 

 inside the plant-chamber to any 

 degree that is desired, and to 

 maintain it constant as long as 

 necessary. 



The temperature of the room, 

 at the time of the experiment I am 

 about to describe, was 27 C. I 

 desired to take three records, differ- 

 ing from each other by intervals of 

 5 C. For this purpose I reduced the temperature of the 

 plant-chamber to 22 C. and took the first record of the 

 series. Next, by stopping the inflow of the cooled air and 

 opening one of the side windows, I restored the temperature 

 of the chamber to 27 C, and after allowing a suitable 

 interval took the second record. Lastly, by means of 

 the electrical heating device described, the temperature of 

 the chamber was raised to 32 C. and the third record of 



Fig. 27. — Effect of tem- 

 perature ; amplitude 

 of response seen to be 

 higher, and period of 

 recovery shorter, with 

 higher temperature. 



