TRANSVERSE TRANSMISSION OP EFFECT OF STIMULUS 281 



experiment on the subject of detection of induced change 

 of turgor I employed the stimulus of light. A narrow 

 beam from a small arc lamp was made to fall on the 

 stem, at a point diametrically opposite to the motile leaf, 

 which was to serve as a indicator for induced variation 

 of turgor at the distal side. The leaf was attached to the 

 r.^cording lever, the successive dots in the record being at 

 intervals of ten seconds. Stimulation by light caused a 

 positive or erectile movement within 20 seconds of applica- 

 tion. The positive response afforded a conclusive proof of 

 the iuilucti<ja of an incr<?ase of turgor at the ilistal point. 



Fig. loO. — Increased turj^or due lu indirect stimulation, inducing erection of 

 Mimosa leaf : (a) diagram of the experiment, point of application of stimulus indicated 

 by arrow. (6) erectile response (shown by down-curve) followed by rapid fall fup- 

 curve) due to transverse conduction of true excitation. (Successive dots at 

 intervals of 10 seconds.) 



When the stimulus is moderate or of short duration, the 

 response remains positive. But with strong or prolonged 

 stimulation, the slower excitatory negative impulse is con- 

 ducted to the distal point and brings about the sudden fall 

 of the leaf (Fig. 100). In the present case the excitatory 



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