DEATH-SPASM IN PLANTS 99 



indicate the beginning of death-change, I first took a specimen 

 of Mimosa and subjected it to a gradual rise of temperature 

 in a water-bath. The leaf was attached to the recording- 

 lever in the usual manner. The recording apparatus 

 employed was of the oscillating type, where the plate 

 oscillates to and fro by an electro-magnetic contrivance, 

 thus producing a series of dots in the response-curve. In 

 the present investigation the electro-magnetic circuit is 

 completed for a brief period, at every degree rise of tempera- 

 ture in the bath. Successive dots thus represent intervals 

 of temperature of 1° C. The ordinate of the curve indicates 

 expansive or contractile movement of the leaf : down-curve 

 representing the expansion, and up-curve the contraction. 



The temperature of the bath is continuously raised by 

 the application of gas or spirit flame. For certain reasons, 

 to be presently explained, it is necessary to raise the tem- 

 perature gradually and continuously, without any sudden 

 variation. There should also be no mechanical disturb- 

 ance of water in the bath during heating, as that would 

 disturb the leaf and vitiate the record. These difficulties 

 are overcome by constructing the heating-bath of two 

 vessels, one placed within the other. Heating the water of 

 the outer vessel raises the temperature of the water in the 

 inner in a very even manner, and without any mechanical 

 disturbance. 



It is necessary to subject the plant to gradual rise of 

 temperature in order to protect it from excitation. Any 

 sudden variation, due either to lowering or raising of tem- 

 perature, causes excitatory movement of the leaf. This is 

 seen in the following records (fig. 57), obtained with Mimosa. 

 The first response is of excitation due to application of a 

 drop of ice-cold water on the pulvinus ; the second response 

 is due to the very opposite treatment of application of a 

 drop of hot water. In both cases we obtain the excitatory 

 fall of the leaf. 



The effect of temperature as such is, however, very 

 definite : gradual rise of temperature inducing progressive 



H 3 



