90 



TLANT RESPONSE 



divisions, and the recovery was completed in eight minutes. 

 Stimulus of longer duration, that is to say, of twenty seconds, 

 was next applied, and the response was correspondingly 

 greater, that is to say, twenty-one divisions, recovery taking 

 place in the longer period of eleven minutes ; and finally, 

 stimulus was applied for a still longer period, that is to say, 

 thirty seconds, the response, of thirty-five divisions, being now 



correspondingly great, and 

 recovery requiring six- 

 teen minutes. 



It will be noticed that 

 in this case the amplitude 

 of response and the period 

 of recovery varied almost 

 in direct proportion with 

 the duration, determining 

 the effective intensity of 

 the stimulus. Thus the 

 restoration to the original 

 position of equilibrium 

 takes place quickly when 

 the stimulus is feeble ; but the period is prolonged, when 

 stimulus is strong ; or recovery may even be postponed in- 

 definitely, after very strong stimulation. Recovery, when it 

 does occur in such a case, may only be partial, a permanent 

 after-effect being left. 



The effects here described are obtained most easily by 

 direct stimulation of the organ. But similar results may 

 nevertheless be exhibited by means of transmitted stimulation. 

 To show this, we may take a spiral of Passiflora tendril, and 

 apply strong electric stimulation through two points at its 

 lower end. The transmitted stimulus, reaching the free spiral 

 end, causes response by uncurling, and variation of the twist. 

 Response by curling.-— In the case of the experiments 

 just described, stimulus has been found to produce uncoiling 

 of the spiral. From this, however, it must not be too hastily 

 concluded that similar effects will ensue in every case. The 



Fig. 42. Responses of Hooked Tendril of 

 Passiflora 



(a) Response to electric shock of fifteen 

 seconds duration ; {h) of twenty seconds ; 

 (<■) of thirty seconds. Note increase in 

 height of response and lengthening of 

 period of recovery with increasing 

 stimidus. 



