Fig. 7.3-5a. Longitudinal section of vascular bundles in spurge (Euphorbia). There are three vessels oriented vertically in the center of this micrograph, and two have simple, round perforations facing us (marked by arrows). All three vessels have pits that are predominantly scalariform, but notice that there is a bit of pit-free wall immediately surrounding each perforation: that pit-free area is the perforation plate rim. Take another look at the two perforations and keep in mind that is where two separate vessel elements contact each other. Although each perforation appears to just be a hole in a secondary wall, it actually consists of two perforations that are so perfectly aligned we cannot see there are two. Rarely, there will be slight misalignment and the dual nature will be visible, but usually the high magnification and resolution of scanning electron microscopy is needed to see that.