RECORD OF TROPAEOLUM 239 



The records of the movements of the procumbent stem and 

 leaf exhibited a striking paralleHsm. They became erected 

 from thermal noon to thermal dawn, and underwent a fall 

 from thermal dawn to thermal noon. The descent of the 

 curve is, as also that of the thermal curve, relatively more 

 abrupt. The records on two successive days are seen to 

 be very similar (fig. 138). 



Diurnal Record of Tropaeolum under Constant 



Temperature 



The fact that the diurnal movement was due to variation 

 of temperature was further proved by maintaining the 

 Tropaeolum stem, employed in the last experiment, at a 

 constant temperature. 



This was secured by the construction of a special chamber, 

 in which the plant and the recording apparatus were placed. 

 This chamber was maintained at a constant temperature 

 by an electro-thermic regulator which interrupts the heating 

 current as soon as the temperature of the chamber is raised 

 a hundredth part of a degree above the predetermined 

 constant temperature. The automatic make-and-break 

 of the current takes place in rapid succession, so that 

 the temperature of the chamber is maintained constant 

 within one tenth of a degree Centigrade, throughout day 

 and night. 



Experiment 130. — The records of the Thermograph and 

 of the plant's movements were now taken simultaneously. 

 On the first day the temperature was maintained constant, 

 with the result of abohtion of the periodic movement of the 

 plant. This is clearly seen from the horizontal curves 

 recorded during the first 24 hours. The thermal regulator 

 was then put out of operation, thus restoring the normal 

 diurnal variation of temperature ; the result of this was that 

 the stem exhibited once more its normal periodic movement 



(fig. 139)' 



