VARIOUS TYPES OF RESPONSE 



97 



same two minutes' stimulation as before shows greater 

 response than the preceding, owing to the partial removal 

 of residual strain. 



There is one aspect of the subject of fatigue-reversal 

 which now demands our attention. We have seen that under 

 continuous stimulation, a maximum contraction is induced,; 

 which is attended by the depression of the leaf of Mimosa.^ 



FIG. 66. Effect of Continuous Vibration (through 50) in Carrot 



In the first three records, two minutes' stimulation is followed by two 

 minutes' recovery. The last record was taken after the specimen had 

 a rest of five minutes. The response, owing to removal of fatigue by 

 rest, is stronger. 



This is followed, however, by a reversal namely, expansion, 

 with re-erection of the leaf. According to the chemical 

 theory of assimilation and dissimilation, the fatigue-effect 

 is assumed to be due to an explosive dissimilatory change, 

 with consequent run-down of energy. In the case of Mimosa, 

 however, it is difficult to understand how, by a mere run- 

 down of energy and consequent passivity of the tissue, an 

 active movement of erection involving the performance of 

 work in lifting the weight of the leaf could be brought 



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