radio-thermotropism 415 



arrosted by the arrival of the excitatory impulse at the 

 distal side, on account of which the first positive curvature 

 became neutralised. Further continuation of stimulus caused 

 a raversai into negative in the course of 7 minutes. It will 

 thus be seen that in inducing phototropic curvature, the 

 heat rays in sunlight play as important a part as the 

 more refrangible rays of the spectrum. 



SUMMARY. 



The effects of rise of temperature and of radiation are 

 antagonistic to each other. 



Under unilateral action of thermal radiation a positive 



curvature is induced by tlie retardation of growth at the 



proximal, and acceleration of growth at the distal side of 

 the organ. 



There is a complete recovery on the cessation of 

 stimulus of moderate intensity and short duration. Repeated 

 responses may thus be obtained similar to repeated 

 responses in pulvinated organs. In certain tissues the 

 power of conduction in a transverse direction is wanting ; 

 excitation remains localised at the proximal side, and the 

 responsive curvature remains positive. 



In other case?, there is a slow conduction of excitation 

 to the distal side. Tlie result of this under different 

 circumstances is dia-radio-thermotropic neutralization, or a 

 reversed negative curvature. 



In inducing phototropic curvature, the heat rays in 

 sunlight play as important a part as the more refrangible 

 rays of the spectrum. 



