160 



DECAPITATED ROOTS. 



[CH. VII 



(205) Decapitation prevents the perception of the 

 stimulus. 



Place 10 beans horizontally in damp sawdust for 1^ 

 hours; the tips (1^ mm.) are now amputated and the 

 roots embedded vertically in damp sawdust. After 12 

 hours the roots, or most of them, will be found to be 

 curved laterally towards, the side which was downwards 

 during the period (IJ hr.) during which they were kept 

 horizontal. This shows that amputation does not interfere 

 with the carrying out of an induced curvature, so that the 

 absence of geotropism in exp. 204 must be due to a 

 disturbance of the capability of being stimulated'. 



(206) Recovery from the effect of amputation. 

 If the roots in exp. 205 are allowed 



to remain undisturbed for 3 or 4 days, 

 the growing point is regenerated 

 and the roots recover the complete 

 power of geotropic curvature. They 

 will grow into an S-like form, because 

 before the growing point is regene- 

 rated they continue growing horizon- 

 tally or obliquely in the direction 

 impressed on them by the geotropic 

 curvature induced before amputation. 

 When the power of reacting to the 



' Neither this experiment, nor the others given in the Paaer of 

 Movement, "prove that the tip alone is sensitive to gravitation, but 

 Pfeffer's brilliant researches, described before Section D of the British 

 Association in August 1894 demonstrate conclusively that this is the 

 case. 



