9 6 



PLANT RESPONSE 



EiG. 46. Mechanical Responses to Stimuli in- 

 creasing in Arithmetical Progression 



suitable external resistances. In this way I have obtained 

 successive responses to thermal stimuli, which increased in 



arithmetical progres- 

 sion. And we see 

 from the records in 

 what manner the cor- 

 responding responses 

 undergo an increase 

 (fig. 46). 



It will be seen 

 from this figure that 

 with a stimulus re- 

 presented by unity, 

 the response was 1*5 

 division. With a 

 stimulus twice as great, the corresponding response was 

 slightly greater than twice as much, that is to say, it was 35. 

 The intensity of response went on increasing, but with 



special acceleration when the 



I: - ' 2 stimuli were four and five. 



After the stimulus of six 

 Sfi I there was a tendency for the 



I response to approach a limit. 



The subjoined curve (fig. 47) 

 shows the relation between 

 the increasing stimuli and the 

 corresponding responses. 



Another interesting fea- 

 ture of these response-curves 

 is one which has already been 

 referred to, the prolongation 

 of the period of recovery with 

 increasing stimulus. In the 

 present case, with the stimulus of unit-intensity, the recovery 

 was completed in forty seconds. With an intensity twice as 

 great, it required fifty-six seconds for the restoration of 

 equilibrium. And this increase in the period of recovery 



FlG. 47- Curve showing Relation be- 

 tween Stimulus and Response 



The abscissa represents the stimulus, 

 and ordinate the height of response. 



