CHAPTER VII 
PLANT RESPONSE—-ON THE RELATION BETWEEN STIMULUS 
AND RESPONSE 
Increased response with increasing stimulus—Apparent diminution of 
response with excessively strong stimulus. 
As already said, in the living tissue, molecular dis- 
turbance induced by stimulus is accompanied by an 
electric disturbance, which gradually disappears with 
the return of the disturbed molecules to their position 
of equilibrium. The greater the molecular distortion 
produced by the stimulus, the greater is the electric 
variation produced. The electric response is thus an 
outward expression of a molecular disturbance produced 
by an external agency, the stimulus. 
Curve of relation between stimulus and response.— 
In the curve showing the relation between stimulus and 
response in nerve and muscle, it is found that the 
molecular effect as exhibited either by contraction or 
H.M. variation in muscle, or simply by E.M. variation 
in nerve, is at first slight. In the second part, there is 
a rapidly increasing effect with increased stimulus. 
Finally, a tendency shows itself to approach a limit 
of response. Thus we find the curve at first slightly 
convex, then straight and ascending, and lastly, concave 
to the abscissa (fig. 30). 
In muscle the limit of response is reached much 
sooner than in nerve. As will be seen, the range 
of variation of stimulus in these curves is not very 
BH 
