Xylem cells are the following: – vessels or tracheids. Vessels are told perfect when there is no transverse wall and when all elements are joined together to reach a length that can reach many meters. Tracheids are imperfect vessels because they have a transverse wall with a lumen more or less important. Tracheids are present in basal (primitive) vascular plants such as Ferns and allies, or Gymnosperms.