It consists of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. They differ from vascular plants in lacking water-bearing xylem tracheids or vessels. Reliable evidence for the fibre cells' evolutionary origin from tracheids exists. The possession of xylem tracheids defines the vascular plants or Tracheophytes. Surrounding both conducting tissues was a broad sheath of transfusion tracheids. There was a central vascular cylinder consisting of annular tracheids (water-conducting cells with thickened walls). Rays, unlike vessel members and tracheids, are alive at functional maturity. Vessel members and tracheids are dead at maturity. Tracheids, unlike vessel elements, do not have perforation plates. Metaxylem has wider vessels and tracheids than protoxylem. The tracheids end overlap with each other, with pairs of pits present. An example of plant-eating was evidenced by tree lycopsid tracheids found in an "Arthropleura"<nowiki>'</nowiki>s gut. Vessels allowed the same cross-sectional area of wood to transport much more water than tracheids. More complex tracheids with valve-like perforations called bordered pits characterise the gymnosperms. The xylem of "Amborella" contains only tracheids; vessel elements are absent.