314 



]. Bonner 



O 

 U- 

 UJ 

 O 







10 



20 



30 



LlI 



se 40 



50 



WEIGHT 

 APPLIED 



WEIGHT 

 REMOVED 



SLOPE = RATE 



OF PLASTIC 



BENDING 







10 



15 



20 



25 



30 



TIME IN MINUTES 



Fig. 6. Progress curve of deformation of a 2 cm. Avena coleoptile section in re- 

 sponse to an applied force. The section is held rigidly at one end, a constant 

 bending force applied to the other. Angle of deformation is plotted as a func- 

 tion of time. After Tagawa and Bonner (24). 



side which is in tension can, however, yield lo this tension since the 

 supporting cell walls can stretch. The property measured in such a 

 bending experiment is therefore the stretchability of the cell walls 

 of the section. The principal complication is the possibility of 

 pressure-induced water flow through the tissue from the compression 

 to the tension side. Such flow may be expected to occur but to become 

 significant only over time periods longer than those required {ca. 5 

 min.) for the measurement of rate of deformation of the wall. 



Figure 6 presents data on the time course of deformation under 

 load of an Avena coleoptile section. The initial rapid elastic deforma- 

 tion is followed by a period of steady plastic deformation. The rate 

 of such plastic deformation under load is influenced both by lAA 

 and by inorganic ions. Figure 7 presents data on rate of plastic de- 

 formation, at constant external load for sections equilibrated with 

 varying concentrations of lAA. It is evident that the lAA concentra- 

 tion dependence for cell wall deformability closely resembles that 

 for lAA-induced section growth and that, in fact, the concentrations 



