INQUIRY INTO CAUSES OF AUTONOMOUS MOVEMENTS 305 



In Desniodiiiiii, the autonomous movement is initiated at 

 a certain more or less definite temperature, which is about 

 17° C. This we may call the critical thermo-tonic condition. 

 Below this critical degree, Desmodinm ceases to be autonomic, 

 and becomes an ordinarily responding plant. In BiopJiytuiii, 

 similarly, the critical thermo-tonic point is about 29° C. 

 Above this, the young leaflets are autonomic, and below it. 

 ordinarily responding. The difference between Desmodinm 

 and Biophytum in this respect lies, therefore, in the fact that 

 their critical thermo-tonic points are about twelve degrees 

 apart. 



In the case of Biophytum, when the temperature is main- 

 tained at a uniform favourable degree, the periods of the 



Fig. 124. Induction of Autonomous Response in Biophytum, 

 at Moderately High Temperature of 35^ C. 



Note the diminution of amplitude of response with the gradual loss of 

 latent energy, consequent on falling temperature. The pulsations- 

 came to a stop below 29° C. 



autonomous pulsations become veiy regular. It has been 

 said that these pulsatory movements are maintained by 

 means of energy absorbed, and with Biophytum I found an 

 added opportunity of demonstrating this fact. A particular 

 plant had been kept at a uniform temperature of 35° C, 

 under which the young leaflets gave autonomous responses. 

 The heating current, by which this temperature was main- 

 tained uniform, was now stopped, and the chamber gradually 



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