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. 



