Fig. 7. Polarized-light micrographs of longitudinal sections of the elongation zone (in the wild type) or swollen region of the root in rsw4 and rsw7. The transmission axes of analyzer and polarizer are shown by the white right-angle in (A). (A,C,E) The compensator was rotated to a positive angle, and (B,D,F) to a negative angle; the orientation of the white line in the two upper panels (A,B) shows the direction of the optical axis of birefringent elements (i.e., microfibrils) that would produce regions of the image brighter than background. (A,B) A section from wild type, (C,D) rsw4 and (E,F) rsw7 shown with each compensator setting. Seedlings were grown as for Fig. 4. The left-hand and right-hand panels were photographed with identical microscope settings and processed identically for reproduction. Bar: 25 µm.