CH. V] 



LOSS OF KIGIDITY. 



139 



(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. 26. 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 26, 

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

 Indian ink, it is further supported on 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 

 which weights may be hung. Having noted the position 

 of / on the scale, hang a small weight W (a coil of 



