RESPONSE OF TIPS OF SHOOT AND ROOT 515 



that the effect of stimulation could not reach it. As 

 parenchymatous tissues offer great resistance to the conduc- 

 tion of stimulus, it is an advantage to make this second 

 contact with a leaf In the present investigation we have to 

 study the effect of unilateral stimulation of varying intensity 

 and duration, when applied either at the tip T, or at C, near 

 the responding point A, the latter being in the same longi- 

 tudinal line as the excited points T and C. We shall also 

 study the effect of stimulation of A, on the transverse point 



Fig. 212. Experimental Connections for obtaining Electrical Response 

 due to Direct and Indirect Effects of Stimulation 



(a) electrical connections for detection of electrical changes at A, caused 

 by indirect effect of stimulus, from excitation of same side of distant 

 tip, T, and direct effect of stimulus from excitation of adjacent point, c ; 

 {d) electrical connections for detection of electrical changes at B, caused 

 by excitation of diametrically opposite point, A ; (f) electrical connec- 

 tions for detection of relative electric variations of diametrically opposite 

 points, A and 15, due to excitation of c, adjacent to A. 



B (fig. 212, /;), and the resultant effects on A and 11, when 

 the point c, near A, is stimulated (fig. 212, c). 



Before proceeding further, it will be well to consider the 

 theoretical conclusions to which we are led from the demon- 

 strations already made of the turgidity-variations caused by 

 stimulation. The tip T consists, as we know, of undifferen- 

 tiated tissue, which is a relatively bad conductor of stimula- 

 tion. Moderate stimulus, then, at T, might be expected to 

 induce local excitatory contraction, and the water thereby 

 expelled would originate a wave of positive turgidity-varia- 

 tion ; this would reach A, a point on its own line, with greater 

 effect than the transversely placed P. The moderate stimula- 

 tion of T would thus produce a positive turgidity-variation 



L L 2 



