Page:Researches on Irritability of Plants.djvu/96

Rh in muscle-records, in the same circumstances of diminished interval of rest.

Under certain conditions we obtain an exhibition of continuously growing fatigue. We have seen that when the plant is intensely excited, it takes a longer time for complete protoplasmic recovery. The specimen whose responses are given in fig. 32 happened to be in an optimum condition. A maximum excitation was here induced, even under a moderate stimulus. The normal interval of 15 minutes, which was found in the previous case to be sufficient for complete protoplasmic recovery, here proved to be insufficient. Hence we have the exhibition of a growing fatigue seen in the diminishing heights of successive responses.

Another very curious type of response sometimes met with, is that of alternating fatigue. Here, while the first response is very large, the second is correspondingly small, and this alternating sequence is observed for a longer or shorter time (fig. 36). After several such alternations, however, the responses tended to become uniform. An explanation of this interesting variation may be gathered from careful observation of the record. The freshness of the specimen and its high excitability account for the great amplitude of the first response. An intense excitation requires, as we have seen, a correspondingly longer time than does a feeble one for complete recovery. Hence in the present case the second stimulation is seen to have impinged