Page:Researches on Irritability of Plants.djvu/155



have hitherto dealt with the reaction of tissues which exhibit the excitatory condition by motile response, as in pulvinus in the case of the plant and muscle in the case of animal. In the animal, again, we meet with certain conducting-tissues in which the excitatory protoplasmic change is transmitted to a distance, and, should one of these nerves happen to lead to a contractile muscle, the transmission of the excitatory change is conspicuously exhibited by the contraction of the terminal organ.

We now come to the question whether there is a transmission of a true excitatory change in the plant, and if so whether there is in it any specific conducting-tissue, corresponding to the nerve of the animal, for the conveyance of excitation? Since the transmission of excitation depends on the propagation of a protoplasmic change, it follows that a conducting-tissue must be characterised by a more or less protoplasmic continuity. Should the plant possess