UNIFORM, FATIGUE, AND STAIRCASE EFFECTS 105 



FIG. 53. Fatigue in Longitudinal 

 Mechanical Response of Plant 

 (Style of Datura) 



In the case of the first pair of re- 

 sponses, a sufficient interval for 

 recovery, namely one minute, 

 was allowed. When the period 

 allowed for recovery was reduced 

 to half a minute, there was rapid 

 fatigue ; the second pair of re- 

 sponses shows this immediate 

 effect ; the third pair of responses 

 are to the tenth and eleventh 

 stimuli. 



' Fatigue. — It has been said that, when sufficient time is 

 allowed for protoplasmic recovery, the responses are uniform, 

 but that, if sufficient time be not 

 allowed, molecular recovery will 

 be incomplete, and the tissue 

 will remain in a strained con- 

 dition. Under these circum- 

 stances, it is obvious that there 

 will not be a complete restora- 

 tion of the original protoplasmic 

 excitability, hence successive re- 

 sponses will exhibit a diminution 

 or fatigue. The following record 

 (fig. 53) shows this in the case 

 of longitudinal response. Uni- 

 form stimuli were first applied 

 at intervals of one minute, by which time the recovery was 

 complete ; and these responses of twenty divisions are seen 

 to be large and uniform. 

 The stimuli were next 

 applied at intervals of half 

 a minute, and the response 

 at once fell to eleven divi- 

 sions. Now, owing to the 

 effect of cumulative strain, 

 the succeeding responses 

 at this interval underwent 



continuous diminution, and FiG. 54- Fatigue shown in Electrical Re- 

 , , r ,, , sponse, when sufficient Time is not allowed 



had fallen as low as to f £ Full Recovery 



five divisions at the tenth i n ( a ) stimuli were applied at intervals of one 

 stimulus. In the next minute ; in (^ the intervals were reduced 



to half a minute ; this caused a diminution 



figure (fig. 54), fatigue is of response. In (c) the original rhythm is 



, • .1 1 . • 1 restored, and the response is found to be en- 



shown in the electrical hancedt 'o nearly its original value (Radish). 



responses of plants under 



the same conditions, sufficient time for recovery, that is to 



say, not being allowed. Similar instances of fatigue are well 



known in the case of muscle. 



