128 RESEARCHES ON IRRITABILITY OF PLANTS 



a frequency of loo double vibrations per second. The 

 lower of these two records represents the effect of a stimulus 

 of 2, which was here maximal. The upper was taken 

 with the increased intensity of stimulus of 5. In the two 

 cases the latent period was practically the same — namely, 

 •12 second. 



It should be mentioned here that in a plant in optimum 

 condition the latent period differs very little under strong 

 or feeble stimulus. We have also seen, it will be remem- 

 bered, that in an optimum condition of the specimen there 

 is very Httle difference in the amplitude of response under 

 strong and feeble stimulus respectively. 



Effect of Fatigue 



It has been shown that the successive values of the latent 

 period become constant provided a resting-interval be 



Figs. 78, 79. — Effect of fatigue. 



allowed for complete protoplasmic recovery. The period 

 required for full recovery I find to be about 20 to 25 

 minutes in summer, more or less. If this resting-interval 

 be shortened, the effect of fatigue is seen in the prolonga- 

 tion of the latent period ; if this shortening be carried too 

 far, then the motile excitability is temporarily abolished. 

 I give below a pair of records which exhibit the prolongation 

 of latent period on account of fatigue. 



The mode of procedure is first to obtain the normal 

 record with a fresh specimen under a maximal stimulus of 



