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Sir J. C. Bose and Mr. G. Das. 



B. Effect of Indirect Stimulation. 



Having ascertained that the direct application of stimulus gives rise in 

 different organs to contraction, diminution of turgor, fall of motile leaf, 

 electromotive change of galvanometric negativity, and retardation of the rate 

 of growth, I proceeded to inquire whether indirect stimulus (that is to say- 

 application of stimulus at some distance from the responding organ) gives 

 rise to an effect different from that of direct application. 



5. Mechanical and Electrical Hesponse. 



In experimenting with various sensitive plants like Mimosa, Averrlwa, and 

 with ordinary plants like Artocarpus, I found that indirect stimulation gives 

 rise to a positive or erectile response of the responding leaf or leaflet 

 (indicative of an increase of turgor), often followed by the normal negative 



Fro. 7. — Mechanical and electrical response to indirect stimulation. Left, positive response 

 of Mimosa : a, moment of application of stimulus ; b, time-tracings of five vibrations 

 per second. Right, a, positive ; b, diphasic ; and c, negative, electric response of Musa. 



response ; the interval between the two varies in different cases from a 

 fraction of a second to 30 seconds or more. A probable explanation of the 

 dual impulse is that stimulation causes a local contraction, with expulsion of 

 water from the cells. The positive hydraulic 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 

 different cases from 0*6 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 in 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 fail to reach the responding organ if the stimulus be feeble, or if the 



