LONGITUDINAL RESPONSE OF RADIAL ORGANS 67 



we may expect contraction of the acted side alone. The 

 stimulated side should thus become concave. I have been 

 able to verify this by experimenting with, amongst others, the 

 radial stem of a young Walnut plant ; stimulus was applied 

 in a region about 4 cm. from the tip, this being a plastic 

 area, just below the zone of growth. There are practical 

 difficulties in the application of unilateral stimulus, which 

 might easily be overcome by the use of photic stimulus. In 

 the present chapter, however, I intend to deal with forms of 

 stimulation other than that of light. In the experiment on 

 Walnut, therefore, I made use of the stimulus of electric 

 shocks from an induction coil. The electrical connections 

 were made with one side only of the radial stem. Small 

 quantities of kaolin paste, moistened with normal saline 

 solution, were placed on the stem at two points, at a distance 

 of 2 cm. one above the other, and these were connected with 

 the terminals of the induction coil by means of flexible 

 spirals of tinsel. Electrical excitation was now produced by 

 tetanising shocks for the requisite length of time. With 

 regard to this, it must be pointed out that excitation given by 

 such means cannot be strictly confined to one side of the 

 organ alone, since the current will pass through the further 

 side also ; but as most of it will take the shortest path, 

 excitation will be relatively greater on the side of the electric 

 connections. The responses were recorded as usual, by 

 attaching the stem to the Optic Lever. 



Strong electrical shocks being now applied during a 

 period of five seconds on one side of the stem, a responsive 

 concavity of that side was produced, the amplitude of the 

 response being eight divisions. The effect attained its 

 maximum in forty seconds, after which the recovery was 

 partially completed, in six minutes. On now exciting the 

 opposite side of the same stem, a response which was 

 practically the same — i.e. /'$ divisions — was obtained, the 

 curvature being now in the opposite direction. Hence it is 

 clear from these two experiments, that when a radial organ 

 is simultaneously excited on all sides, there can be no lateral 



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