158 



AFTER EFFECT. 



[CH. VII 



a bottle of water so that the shoot projects horizon- 

 tally. A needle to serve as an index is fixed in the free 

 end of the shoot and its position recorded on a vertical 

 scale. After about an hour, — or when the shoot has 

 begun to curve apogeotropically, — the bottle is rotated on 

 its axis through 180°, so that the plane of curvature 

 remains vertical, but what was the upper side of the 

 shoot is now the lower. The index will now travel 

 downwards over the scale, owing to the continuance of 

 the curvature induced by the gravitation stimulus. It 

 will finally come to rest and will at last curve up in the 

 opposite direction. 



(203) After effects recorded on a rotating surface. 

 The movements described at the end of exp. 202 may 

 be made to record themselves in the following way. 



^Sjp= 



Fig. 29. Exp. 203. 



The writer (fig. 29) is made of two light pieces of wood, the 

 horizontal piece ends in a pointed piece of platinum foil, 



