l6o PLANT RESPONSE 



then take a radial tissue, and subject it to a gradual rise of 

 temperature, taking a continuous record of its variation in 

 length. From what has already been said it will be under- 

 stood that, the variation being gradual, no responsive con- 

 tractile effect will be induced during the process, but, on the 

 contrary, some relaxation. At the death-point, however, a 

 sudden inversion of the curve, due to death-contraction, may 

 be expected to appear, and thus the whole record will consti- 

 tute a curve of life-and-death, this point of inversion separating 

 the two. Should the inversion prove to be very abrupt, the 

 turning point will afford us a means of determining the 

 temperature at which death occurs, with very great accuracy. 



In order to prove, further, that this specific response is 

 definitive, we may, after passing the death-point, bring the 

 tissue back to its original temperature once more, and repeat 

 the process. The record ought now to show no inversion 

 characteristic of a transition from life to death. 



Means of obtaining thermo-mechanical record. — I shall 

 now proceed to describe the manner in which I have obtained 

 this thermo-mechanical record. I took a specimen of a radial 

 organ, in this case the long style of Datura, and fixed it to a 

 small glass rod which in its turn was fastened to a weight, 

 the whole being placed in a vessel of water. The free end of 

 the style was attached to one arm of the Optic Lever. The 

 bath was now warmed gradually, a thermometer indicating 

 the rise of temperature. Variations of length corresponding 

 to the rise of temperature were progressively recorded, from 

 the movement of the spot of light. For this purpose the 

 mode of procedure was as follows : The vertical movement of 

 the spot of light — occasioned by the variation of length of 

 the specimen — was converted into lateral, by reflection from 

 a second mirror. The paper wrapped about the recording 

 drum was divided into millimetres. It was required that the 

 abscissa of the thermo-mechanical curve should represent 

 temperature, and the ordinate the corresponding length. 

 The position of the spot of light, at any given temperature, 

 was marked on the drum. At each rise of temperature of 



