CH. V] 



LOSS OF RIGIDITY. 



127 



namely, that a permanent curvature is produced in 

 consequence of the overstretching of the convex side of 

 the shoot. 



(161) Loss of rigidity. 



The rigidity of a turgescent shoot is dependent on 

 (among other factors) the resistance of the cortical tissues ; 

 if, by overstretching, these are permanently lengthened, 

 the rigidity of the system is lessened. 



Fig. 24, Exp. 161. 



A straight turgescent shoot is fixed firmly by means of 

 a bored and split cork in a test-tube of water, T, figure 24, 

 and at a point which should be marked by a streak of 

 Indian ink, it is further supported oh a prism of wood, F, 

 resting on a support /S. At the free end, the shoot bears 

 a needle acting as an index /, and a loop of wire L, to 



