308 LIFE MOVEMENTS IN PLANTS 



temperature in a manner similar to that of Crocus, that is 

 to say, the flower opens under rise and closes with a fall 

 of temperature. For obtaining record all the perianth 

 segments but one was removed. This segment was attached 

 to the recording lever. On lowering of temperature through 

 i>°C. there was an up-movement, or a movement of closure* 



Fig. 109.- -Thermonastic and r£ldionastic responses of petal of ZephyrantUes 

 C closing movement due to cooling, and H, opening movement due to warming . 

 K closing movement due to heat-radiation. Note opposite responses to rise of 

 temperature and to thermal radiation. 



Rise of temperature induced, on the other hand, a movemeni 

 of opening. 



Effect of thermal radiation : Experiment 114. — I stated 

 that the effect of thermal radiation acts as a stimulus, 

 inducing a reaction which is antagonistic to that of rise 

 of temperature. In verification of this, I subjected the 

 specimen to the action of infra-red radiation acting from 

 all sides. The result is seen in the responsive movement 

 of closure (Fig. 109 R). These experiments demonstrate 

 clearly that the responses to rise of temperature and 

 thermal radiation are of opposite signs. 



As a movement of closure was induced by the diffuse 

 stimulus of thermal radiation, it is evident that this must 

 have been brought about by the greater contraction of the 



