CHAPTER VI 



VARIOUS TYPES OF RESPONSE 



Necessity of uniform stimulation — The Periodic Starter — The Auto- 

 matic Exciter — Electrolytic contact-maker — The complete Response- 

 recorder — The factor of tonicity — Uniform responses — Fatigue under 

 shortened period of rest — Growing fatigue — Alternating fatigue — 

 Staircase response — Explanation of erection of leaf under continuous 

 stimulation — Fatigue-relaxation in plant and animal — Response under 

 single stimulus and under tetanisation. 



Some of the effects brought about by varying external 

 conditions on the excitability of the plant have now been 

 noted. Certain other variations may, however, be induced 

 in the excitability, in consequence of the after-effect of the 

 stimulus itself, even when the external conditions are main- 

 tained constant. We may trace these induced internal 

 changes in the modification of the response-records. 



It is clear that we can only be assured of the occurrence 

 of such internal changes from the observed variation of 

 response-record if we have been able in the first place to 

 keep the plant under unvarying external conditions. This, 

 taking certain special precautions as regards light, tempera- 

 ture, and so forth, presents no difficulty. But, in the second 

 place, we have to be specially careful that the testing- 

 stimulus itself shall be absolutely constant in successive 

 experiments. The problem then resolves itself into the 

 successful devising of some arrangement by which records 

 may be taken automatically at definite pre-determined 

 intervals of time. The stimulus of unvarying intensity 

 must also be made to act automatically upon the specimen. 

 Under these conditions any variation that may be observed 



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