Fig. 5.1-9. Tangential section of wood of American hornbeam tree (also called blue beech; Carpinus caroliniana). Cells along the left are xylary fibers, the cell on the right with the white dots is a vessel element, and its white dots are the apertures of circular bordered pits. The circular bordered pits of pine (Fig. 5.1-7) are very large, but these of hornbeam are much more typical of hardwood trees (that is, dicot trees, trees that are not conifers like pines). The white spot in the very center of each is the pit aperture, where we are looking directly into the pit (although the whiteness makes it appear to be a complete hole, there is a pit membrane that we could see if the microscope illuminator were turned to be very dim). The light pink halo around each white spot is the border, where the secondary wall comes up away from the primary wall. The dark pink lines are the regions where the secondary wall is attached to the primary wall; in sclereids and libriform fibers, the secondary wall is attached to the primary wall everywhere, pits have no borders, and all the wall stains dark pink or red.