Page:Researches on Irritability of Plants.djvu/25

2 whether a given influence has contributed to the plant's well-being or the reverse, whether it has left it more or less excitable, whether it has rendered it more or less energetic?

It is conceivable that internal changes which eluded our direct vision might nevertheless be brought within the range of our observation if we could obtain any sort of answer from the plant itself to a questioning shock. In such a case, the feebleness or vigour of the reply would in itself doubtless constitute a measure of the vitality of the organism. It appears obvious that if any given influence had rendered the plant more excitable, this fact would be manifested by the greater intensity of its response. In a very excitable condition we may suppose the slightest shock of stimulus would evoke a very large responsive expression; in a state of depression, on the other hand, the strongest stimulus would induce only a feeble reply. The relation between the stimulus and the response would thus form a gauge of the physiological condition of the organism. The invisible fluctuating changes taking place in the plant, under the changing conditions of the environment, might in this way be made to reveal themselves.

All this presupposes, however, that the plant will answer in some tangible way to the impinging testing stimulus, and that it may be possible to obtain some record of this answer. The possibility of this will be further discussed presently. There are many important problems which wait for their solution till some such means of inquiry is found. What, for instance, are the various forms of stimulus which evoke an answering reaction in the plant? Again, has a given plant-tissue, like animal muscle, any definite perception-period capable of exact measurement? Is the responding tissue susceptible of fatigue? Is the intensity of its answer dependent on the intensity of the blow? Is the excitation that may be caused at one point transmissible to a distance, as along animal nerve? Is such transmission, supposing it to occur, fundamentally of the same nature