330 PLANT RESPONSE 



flame may be applied underneath a bath of water in which 

 the leaflets are placed. The temperature is thus gradually 

 and continuously raised, and the successive pulsations, 

 corresponding to different temperatures, are recorded in the 

 usual manner by means of the Optic Lever. (2) Water 

 at the required temperature may be syphoned into the bath, 

 and the responses taken in the ordinary manner. (3) The 

 air chamber in which the specimen is placed may be subjected 

 to electric heating. The use of temperature may now be 

 very accurately regulated by adjustment of the current, and 

 records of pulsations may be taken at different and deter- 

 minate temperatures. 



This last is the most perfect method, the two former, 

 dependent as they are on the immersion of the specimen in 

 a bath of water, having as compared with it many disadvan- 

 tages. For the natural freedom of movement of the leaflet 

 is hampered by the water, and more troublesome still is the 

 difficulty which at times arises from capillary action in the 

 partially immersed cocoon-thread, by which the leaflet is 

 attached to the Optic Lever outside the bath. 



But we have not the same perfect facilities for lowering 

 temperature in a gradual and continuous manner, as for 

 raising it. This may be accomplished, however, sufficiently 

 well for our purposes: (i) by placing fragments of ice in 

 the air chamber ; or (2) the pulvinus of the leaflet may 

 be touched with cold water which has been reduced to 

 the required temperature by means of ice. I find, however, 

 (3) that a much better method is that of placing in the air 

 chamber a coil of thin-walled metallic tubing, preferably 

 of highly conducting copper. When cooled brine is made 

 to circulate through this coil, the temperature of the chamber 

 is lowered, and by regulation of the flow, by means of stop- 

 cocks, it is possible to produce an adjustment of cooling. 



Effect of temperatures maximum and minimum. — 

 Autonomous vibrations come to a stop when the temperature 

 is sufficiently lowered. The temperature minimum at which 

 this occurs depends, as we should expect, on the nature of 



