Hormonal Mechanism of Growth Inhibition by Radiation 557 



changes which take place during the plastic deformation of the cell 

 walls. You shouldn't have a constant elastic tension before and after 

 if the gibberellic acid has not changed elasticity. I don't know what 

 this means quantitatively, but this general point of view should not 

 be overlooked. 



Dr. Lockhart: I can partially answer this by adding that I have 

 also measured plasticity by imposing a longitudinal load on freeze- 

 killed stem sections. The effect of radiation on plasticity was almost 

 identical as measured by the two methods. No significant change in 

 elasticity was observed during the bending procedure. It's not clear 

 to me whether a substantial change in elasticity would be expected, 

 a priori, or not. The deformation of the tissue is, after all, relatively 

 small. 



Dr. van Overbeek: May I answer that question about elasticity and 

 plasticity? The earliest research I did in the field of auxin research 

 was to work together with Heyn on elasticity and plasticity of coleop- 

 tiles under influence of the auxins. (A. N. J. Heyn and J. van Over- 

 beek. Proc. Kon. Akad. Wetensch. Amsterdam 34: 1. 1931.) One of 

 the things we found invariably, by the stretching technique of plas- 

 molized material and by the bending technique, was that the plas- 

 ticity always increased, whereas the elasticity was not changed at all. 



