176 



CHAP. XVI. RADIO-THERMOTROPISM 



that induced by stimulation by light, i.e. there was at first 

 an erectile movement due to indirect stimulation, followed 

 by the fall of the leaf due to transverse conduction of 

 excitation. The indicating leaf-organ was, in this case, 

 completely shielded from the effect of rise of temperature. 



Fig. 100. Radio-Thermal Stimulator. 



V-shaped loop heated short of incandescence by passage of 

 electric current. Successive thermal shocks can be given 

 by metronome. 



Investigation has made it possible to estabhsh a strict 

 paralleHsm between the effects of luminous radiation and 

 those of heat-radiation in inducing tropic curvature of 

 plants. The experiments will be described in the following 



order : 



1. The effect of indirect stimulation. 



2. Positive radio-thermotropism. 



3. Dia-thermotropism. 



4. Negative thermotropism. 



5. The response of the root to unilateral thermal 



radiation. 



Effect on Growth of Indirect Stimulation by 



Thermal Radiation 



The appHcation of unilateral photic stimulation of 

 moderate intensity at a distance from the growing region. 



