1 84 COMPARATIVE ELECTRO-PHYSIOLOGY 



We shall next study the effect on the electrical response 

 .of the plant of a rise of temperature. The great difficulty of 

 this investigation lies in raising the plant-chamber to the 

 various determinate temperatures required. I was able, 

 however, to accomplish this by means of electric heating. A 

 spiral of german silver wire was placed in the plant-chamber 

 (cf. fig. 21), and by varying the intensity of the current 

 the temperature was then regulated at will. In the process 

 of this electric heating a complicating factor was found in the 

 excitatory action of any sudden variation of temperature. But 

 no such excitatory disturbance occurs if the rise of tempera- 

 ture be not fluctuating, but gradual and continuous. I was 

 able to secure this, by selecting at the beginning of the 



a 



Ivy Holly Eucharis 



FIG. 123. After-effect of Cold on Ivy, Holly, and Eucharis Lily 



a, The normal response ; 6, response after subjection to freezing temperature 

 for twenty-four hours. 



experiment, a suitable strength of current, such as to raise 

 the temperature of the chamber continuously, at an approxi- 

 mately uniform rate. Care had also to be taken that thermal 

 , - radiation from the wire should not strike the specimen, since 

 such radiation, as we shall see later, acts as a stimulus. The 



I 1 interposition of a sheet of mica, however, obviated this diffi- 



II culty, mica being opaque to thermal radiation. 



While, under these conditions, the temperature was being 

 raised, uniform vibrational stimuli were applied at intervals, 

 and responses recorded, the temperature of the chamber at 

 the moments of stimulation being carefully noted. In this 

 way I obtained the following photographic record, with 

 a petiole of Eucharis lily, affording a general idea of the 

 effect of temperature on response. It will be seen that 



