VARIOUS TYPES OF RESPONSE 71 



reversal, with decline of excitability, a state of things 

 which we associate with fatigue. 



It must be remembered that in Nature, according to 

 the conditions of its environment, a plant may be found 

 in any of the three states. One specimen may be found in 

 the pre-optimum or subtonic condition ; another may be 

 near the optimum condition, and this we shall designate 

 as the normal ; a third may be found in the post-optimum 

 condition predisposed to fatigue. The first and third of 

 these conditions may be distinguished from each other by 

 means of testing blows or stimuli. If the plant be in the 

 former condition, these will evoke responses of increasing 

 amplitude ; in the latter, they will show a decline. 



These three conditions modify not merely the amplitude 

 of response but also exhibit themselves appropriately in other 

 aspects of protoplasmic excitation. These will be seen in 

 the chapters on the Latent Period, and on the Transmission 

 of Excitation. 



Uniform Responses 



When — selecting a plant which is neither subtonic nor 

 yet at its optimum— we take a series of responses under 

 uniform stimulation of moderate intensity, allowing sufficient 

 intervals for complete recovery, we obtain uniform responses. 

 This may be accepted as the characteristic effect of a plant 

 in the normal condition. 



In fig. 33 is seen a series of such responses taken at 

 intervals of 15 minutes. The ascending portion of each 

 response is here seen to be dotted. This is because of 

 the rapidity of the movement of fall. The successive dots 

 caused by the recorder vibrating ten times per second 

 are widely spaced. In the recovery or down part of the 

 curve, however, as that process is slow, the dots become 

 fused and make a thick continuous line. In the record of the 

 responsive fall, variations of rate of movement may be 

 noticed. At first the speed increases, then very gradually 



