142 PLANT RESPONSE 



that the specimen was all this time undergoing gradual 

 warming by the temperature of the room. 



Another way of demonstrating the effect of cold on the 

 longitudinal response of this corona, is to take three filaments ; 

 of these {a) has been subjected to cold, (b) is normal, and (c) 

 has been killed by immersion in hot water at 6o° C. The right- 

 hand ends of the filaments are so arranged as to lie perfectly 

 even, and a moist cotton thread touches these ends. A 

 brass spring presses against the left-hand ends. The thread 

 and the brass spring serve the purpose of two electrodes, by 

 which shocks can be sent through the three specimens at the 

 same time. 



The right-hand end of the object, so arranged, is placed 

 within the field of a microscope of low magnifying power 

 which has a micrometer eye-piece. At the beginning the 

 ends of the specimens lie in a straight line, but after the 

 passage of a shock for a period of a few seconds it is found 

 that, while the normal (J?) shows the maximum contraction, 

 the cooled (a) exhibits very little, and the killed (c) none 

 at all. 



The difficulty in conducting experiments on cooling, lies 

 in the fact that the inertness due to cold is liable to disappear 

 with more or less rapidity when the specimen, for experi- 

 mental purposes, is exposed to. the temperature of the room, 

 which is about 23 C. It cannot be kept immersed in ice- 

 cold water, as the exciting current will then to a great 

 extent pass through the conducting water itself. The only 

 practicable way, therefore, is to subject the specimen to 

 prolonged cold, and make a rapid observation afterwards. 



I next attempted to obtain a series of responses, when 

 the temperature of the space in which the specimen was 

 placed was very gradually lowered. As recovery from the 

 stimulus of electrical shock constitutes a very prolonged 

 process, I had to use thermal stimulation. But this intro- 

 duced the difficulty of itself raising to a certain extent the 

 temperature of the space. I had been fortunate enough, 

 however, to secure a few specimens of the style of Datura 



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