TIME-RELATIONS OF RESPONSE 39 



second, which under pronounced fatigue was reduced to 

 8 mm. 



(3) Temperature also modifies the rate of the responsive 

 movement. Thus in a given specimen the maximum rate 

 of fall at the relatively low temperature of 22 C. was 10 mm. 

 per second ; it became enhanced to 105 mm. per second at 

 25 C, and 115 mm. per second at 31 C. 



The pulvinus after the attainment of the maximum 

 fall remains more or less persistently contracted for a 

 short time. This is shown by the horizontal portion of 

 the curve in fig. 12. 



The Period of Recovery. — As this takes a relatively long 

 time, its record has to be made on a slowly moving plate. 

 The unit of time-measurement must therefore be relatively 

 long. If the successive dots were to be made at the 

 ordinary rate of 10 per second, they would become fused 

 and continuous in the record. For this reason I have 

 devised a contrivance by which the successive dots, in the 

 recovery-portion of the curve, are placed at such intervals 

 as to prevent overcrowding. A convenient interval is 

 either 5 or 10 seconds. 



The device for producing periodic dots at intervals, 

 say of 10 seconds, consists of clockwork employed to interrupt 

 the current actuating the vibrating recorder at particular 

 intervals. A light six-rayed wheel is attached to the axis 

 of the seconds-hand, and during the course of a single com- 

 plete revolution, that is to say, in a minute, the projecting 

 rays press the spring-key six times at intervals of 10 seconds 

 each (fig. 13) . It is only during the short interval when the 

 key is pressed that the circuit is completed and the recorder 

 set in vibration to make its dots. Each dot made, it should 

 be remembered, is the result of a succession of strokes inscribed 

 by the vibrating recorder 10 times in the second. But 

 as the movement of the plate is slow, these successive 

 strokes more or less superimposed make but a single large 

 dot. Ten seconds again elapse before the next pressure 

 of the key brings about another large dot, and in that 



