Wall structure in thick cell walls 



133 



will become much more birefringent than the opposite wall CD, since 

 in the former wall the plane of section is more nearly parallel to the 

 direction of the cellulose chains than it is in the latter. When the plane 



■035 



025- 



OI5 



005 



O 20* 40* 60* 80* 



ANGLE OF SECTION TO TRANSVERSE PLANE 



Fig. 48. For explanation, see text. 



of section is tilted to the transverse through an angle (90°— 0), the 

 birefringence in AB will clearly be at a maximum. Hence it is possible 

 to measure the angle Q by plotting the birefringence against the angle 



ANGLE OF SECTION TO TRANSVERSE PLANE 

 Fig. 49. For explanation, see text. 



of sectioning for a series of sections at different angles to the transverse, 

 and reading off the angle for maximum birefringence. If, now, the 

 different layers in a wall have different spiral angles, then the maxima 



