HANS BURSTROM 



53 



The specific tension of the wall showing its elastic properties can be 

 computed in dilferent ways. The tension must of course be related to 

 the cell length, but attention must also be paid to the thickness of the 

 wall. The theoretical formula reads 



dl = 



1(1 - n)P 

 2Ed ' 



where dl is the elasticity, / the cell length, d the wall thickness, and the 

 rest are constants. In applying this formula to my material Frey-Wyssling 

 (7) has assumed the wall thickness to be constant and has constructed a 

 graph on this assumption (Fig. 4). The graph gives the modulus of 

 elasticity which runs inversely to the tensibihty of the wall. During the 

 first phase of the elongation this computation gives a tenfold increase 

 in the elasticity of the wall. 



t 



700- 

 000- 



500- 



400- 



300- 



200 



100 



f 



-20 



-to 



9 



10 



Time 



Figure 4. The elastic properties of the walls of elongating epidermis cells. 

 Both graphs deduced from one series of measurements (2). E the modulus of 

 elasticity according to Frey-Wyssling, f the rigidity of the wall according to 

 the formulae of Tamiya. 



