CHAPTER XI 



VELOCITY OF TRANSMITTED IMPULSE IN PLANTS 



Detection of transmitted excitation by means of electromotive variation — 

 Specific tissue for conduction of excitation — Hydro-mechanical 

 theory of transmission of stimulus — Propagation of excitatory 

 protoplasmic change — Physiological test — Automatic record of 

 transmission-period — Conditions for obtaining constant velocity — 

 Determination of velocity of transmission in Mimosa — Differential 

 method of determining velocity — Constancy of results — Tabular 

 statement of different determinations of velocity — Effect of intensity 

 of stimulus on velocity of transmission — Effects on sub-tonic tissue 

 and on tissue in optimum condition — After-effect of stimulus in 

 enhancing conductivity — Effect of optimum condition — Disturbing 

 action of leakage of exciting current — Effect of fatigue — Effect of 

 temperature — Velocity of transmission in Biophytum and Averrhoa — 

 Direction of preferential conduction. 



We have hitherto dealt with the reaction of tissues which 

 exhibit the excitatory condition by motile response, as 

 in pulvinus in the case of the plant and muscle in the 

 case of animal. In the animal, again, we meet with certain 

 conducting-tissues in which the excitatory protoplasmic 

 change is transmitted to a distance, and, should one of these 

 nerves happen to lead to a contractile muscle, the trans- 

 mission of the excitatory change is conspicuously exhibited 

 by the contraction of the terminal organ. 



We now come to the question whether there is a trans- 

 mission of a true excitatory change in the plant, and if so 

 whether there is in it any specific conducting-tissue, corre- 

 sponding to the nerve of the animal, for the conveyance 

 of excitation ? Since the transmission of excitation depends 

 on the propagation of a protoplasmic change, it follows that 

 a conducting-tissue must be characterised by a more or 

 less protoplasmic continuity. Should the plant possess 



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