Fig. 5.3-15. Longitudinal section of wood of Zygogynum (no common name). The cell in the center and the one on the left are fiber-tracheids. Note the Xs on the walls; the / of each X is the elongate, slit-like inner pit aperture in one cell, the \ of each X is the inner aperture of the other half of the pit-pair. Look carefully at the circular shadow around each of these sets of crossed apertures – that circular area is the border that encompasses the pit chamber. In these cells, the pit chamber is about as large as the elongate inner apertures (the circular shadows are wider than the Xs). If these were libriform fibers, the chambers would be much more narrow, the inner apertures would be more elongate, so the Xs would extend beyond the circles.