EFFECT OF INVISIBLE RADIATION AND EMANATIONS 617 



of the pistil of Musa, in some specimens of which the 

 growing region is found to be narrow and sharply defined. 

 In this case the V-shaped radiator was placed opposite to 

 this region. In these responses we see that there is a con- 

 siderable amount of recovery after each transient stimulation, 

 and also a certain degree of fatigue. 



Effect of continuous unilateral stimulation. — We shall 

 next study the effect of continuous unilateral stimulation. 

 For this experiment I took the hypocotyl of Tamarindus 

 indica. As the growing region in this case is extended, 



Fig. 249. Response of Hypocotyl of Tamarindus indica to Continuous 

 Stimulation of Thermal Radiation 



I used a thermal radiator, which consisted of a linear plati- 

 num wire, 5 cm. in length, placed parallel to one side of 

 the growing region. Under the action of continuous uni- 

 lateral radiation, an increasing positive curvature—that is to 

 say, towards the stimulus — was induced, till a maximum 

 effect had been attained (fig. 249). With specimens of other 

 plants I obtained either the neutralisation or the reversal of 

 this curvature, as it might happen, in consequence of the 

 internal diffusion of stimulus to the distal side. This neutra- 

 lisation is brought about by equal excitation of the proximal 

 and distal sides, in precisely the same manner as in the 



