Fig. 5.1-6. Transverse section of Aristolochia. This is the region where two vessel elements contact each other; the two large white areas are the lumens of the two cells, the space through which water moves upward. Notice that where the two cell walls touch, there is a slightly beaded appearance, with faint lens-shaped light areas. The light areas are the bordered pits. They do not look like the typical illustrations in any textbook, but that is because sections – even very good, thin sections – are usually so thick that they contain either the wall behind the pit, or the wall in front of it, or both, so the pit regions appears to be just a little lighter in color, a little less stained, rather than a complete absence of secondary wall. As you can imagine, this can be difficult to see in most slides made for research. In longitudinal sections, however, the pits are very obvious.