11. Even when tracheids do take a structural role, they are supported by sclerenchymatic tissue. 12. The xylem of " Amborella " contains only tracheids ; vessel elements are absent. 13. By the middle Devonian, the tracheid diameter of some plant lineages ( Zosterophyllophytes ) had plateaued. 14. Growing to height also employed another trait of tracheids the support offered by their lignified walls. 15. Finally, the latewood tracheids are formed, with small radial sizes and greater cell wall thickness. 16. The strand of conducting tissue contains simple tracheids , making this a vascular plant ( tracheophyte ). 17. The two major functions that tracheids may fulfill are contributing to the transport system and providing structural support. 18. There are two kinds of cell which are involved in the actual transport : tracheids and vessel elements. 19. The structure of softwood is fairly uniform, with only two types of cells : tracheids and parenchyma cells. 20. Defunct tracheids were retained to form a strong, woody stem, produced in most instances by a secondary xylem.
