Fig. 4. SEM images of macerated tracheary elements (A–D) and hand-extracted
fibers (E). (A) Annular thickening. (B) Very loose helical thickening. (C) Very dense
helical thickening. (C) Tightly wound, ribbon-like helical-reticular thickening. (E)
Morphology of thickened secondary walls (lotus fibers) after being separated from
tracheary elements.