Tree xylem vessels. Polarised light micrograph of a vertical section through the primary wood vessels (xylem vessels) of a tree. The xylem vessels are running diagonally across the image from upper left to lower right. This image shows the support structures (yellow) running along the xylem vessels, preventing them from collapsing. These support structures can take different shapes. Here, annular (ring-shaped), spiral and scalariform support structures are seen.