Fig. 11.5-7. Transverse section of cosmos stem (Cosmos). This micrograph emphasizes the protoxylem portion of the primary xylem. Three rows of vessels are visible, and the arrows indicate two protoxylem vessels that have been torn apart, their secondary walls broken. It is important to emphasize here that the xylem is a complex tissue, containing not just the vessel elements, but also the parenchyma between them.