. Electro-physiology. Electrophysiology. vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 25 without involving the surrounding tissue. In this respect again we are reminded of the polar after-currents in muscle. It thus becomes intelligible that, according to the situation of the leading-off points on the opposite surfaces of a partially " modified " leaf, the excitatory variations discharged by a trans- mitted excitation may be directly opposite in character, the diphasic variation in the modified tract presenting different signs from that in the tract that is unmodified (normal). Munk, a
. Electro-physiology. Electrophysiology. vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 25 without involving the surrounding tissue. In this respect again we are reminded of the polar after-currents in muscle. It thus becomes intelligible that, according to the situation of the leading-off points on the opposite surfaces of a partially " modified " leaf, the excitatory variations discharged by a trans- mitted excitation may be directly opposite in character, the diphasic variation in the modified tract presenting different signs from that in the tract that is unmodified (normal). Munk, as we have seen, assumed the precise seat of the excitation on the leaf of Dioncea to be without significance to the character of the electrical variation discharged, and concluded that the propagation of the changes which underlie the excitatory effect (movement) must be so rapid that they begin, as it were, simultaneously at all points. Burdon-Sanderson's investiga- tions show that this theory (which is a priori improbable if the excitatory movements of plants correspond with the excitation of protoplasmic parts) is as a fact inadequate. It is evident that if the view advanced by Munk were correct, there should be no galvanic effect of excitation with a sym- metrical lead-off from upper or under surface of both lobes, even when one side only was stimulated (Fig. 147). A variation under these conditions is only . FIG. 147. to be expected when the activity of the two lobes differs either in degree, or in the moment of its com- mencement ; much as an electrical can only occur between two points of a muscle when the physiological state of the two points is different, or when the same state is developed in them at different times. And we find experimentally that this method of leading off is invariably followed by galvanic effects of excitation, as appears at once from the curves, Fig. 148, a, l>. Fig. 147 represents a leaf led off symmetrically from the under surface, and
Size: 1876px × 1331px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1890, bookpublisherlondonmacmillan
