Fig. 7.3-6b. Longitudinal section of vascular bundle of corn. Like the vessel in Fig. 7.3-6a, the microtome knife has cut away both the front and back wall of the vessel, but it just barely removed the back wall, and it left the rim along the two sides and the back. It would be easy to think that the perforation plate at the arrow is actually a solid cross wall that completely separates the upper and lower vessel elements. But there is a perforation there, we simply cannot see it because it is just a hole; we see only the rim instead.