XXIV.— TROPIC CURVATURE WITH LONGITUDINAL 

 TRANSMISSION OF EFFECT OF STIMULUS 



By 



Sir J. C. BosE, 

 Assisted by 



GURUPRASANNA DaS. 



I HAVE in previous chapters explained that the direct 

 application of stimulus gives rise in different organs to 

 contraction, diminution of turgor, fall of motile leaf, elec- 

 tromotive change of galvanometric negativity, and retarda- 

 tion of the rate of growth. I have also shown that 

 indirect stimulation {i.e. application of stimulus at some 

 distance from the responding organ) gives rise to a positive 

 or erectile response of the responding leaf or leaflet 

 (indicative of an increase of turgor), often followed by 

 normal negative response. The positive impulse travels 

 quickly. The interval of time that elapses, between the 

 application of stimulus and the erectile response of the 

 responding leaf, depends on the distance of the point of 

 application, and the character of the transmitting tissue : 

 it varies in difi'erent cases from O'tJ second to about 40 

 seconds. The positive is followed by a slower wave of 

 protoplasmic excitation, which causes the excitatory fall. 

 The velocity of this excitatory impulse is about 30 mm. 

 per second iu the petiole of Mimosa, and about 3 mm. 

 per second in Biophytum. The positive followed by the 

 negative thus gives rise to a diphasic response. The 

 excitatory impulse is much enfeebled during transit : the 

 negative impulse may thus fail to reach the responding 



