Page:Researches on Irritability of Plants.djvu/151

128 a frequency of 100 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 remembered, that in an optimum condition of the specimen there is very little difference in the amplitude of response under strong and feeble stimulus respectively.

It has been shown that the successive values of the latent period become constant provided a resting-interval be

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 prolongation 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