TEMPERATURE ON PHOTOTROPIC CURVATURE oSO 



temperature on the excitability, and the conductivity of 

 the organ. 



EFFECT OF TEMPERATURE ON EXCITABILITY. 



The excitability of an organ is abolished at a low 

 temperature ; it is enhanced by a rise of temperature up 

 to an optimum. The temperature minimum and optimum 

 varies in ditferent tissues. The folio sving table shows 

 the enhancement of excitability of Mimosa at different 

 temperatures, the testing stimulus being the same. 



lABLE XXXH— SHOWINd VARIATION OK EXCITABILITY OK I'ULVINUS OF 



Mimosa at differext temperatures. 



Below 20^C. the excitability of the pulvinus of Mimosa 

 is practically abolished. The excitability increases till an 

 optimum temperature is reached, above which it undergoes 

 a decline. 



Though rise of temperature enhances excitability up 

 to an optimum, there is an antagonistic reaction induced 

 by it which opposes the excitatory contraction. The 

 physiological reaction of a rise of temperature, within 

 normal range, is expansion and this must oppose the 

 contraction induced by stimulus. Hence the elLect of 

 rise of temperature is complex ; it enhances the excita- 

 bility which favours contraction, while tending to oppose 

 this contraction by the induced physiological expansion. 

 As a result of these opposite reactions there will be a 

 critical temperature, below which the contractile effect 



