1. Xylem - I

2. Tracheary Elements
Tracheids
Vessel elements

3. Tracheids and Vessel Elements

4. Secondary Wall Thickenings
1 = annular thinckening = helical thickening 5 = reticulate thickening
6 = scalariform pitted wall 7 = opposite pitted wall 8 = alternate pitted wall

5. Annular thickenings in vessel elements

6. Annular thickenings in a tracheid

7. Reticulate wall thickenings

8. Secondary Wall thickenings

9. Scalariform pitted walls

10. Pitted wall in a vessel

11. Pitted wall in pine tracheid

12. Tracheary Elements Tracheids No perforation plate Long and thin cells
Lignified secondary walls
Tapering ends
Vessel Elements
Perforation plates
Shorter and wider than tracheids
Lignified secondary walls
Oblique to transverse end walls

13. 5 mm 10 mm 20 mm Less Mobile Water Freely Mobile Water Diameter 10 mm
Cross section Area (pr2)
78.5 mm2
314 mm2
1256 mm2
Relative Proportion 1 4 16
Relative Conductance (r4)
256

14. Cooksonia reconstruction and fossils

15. Vessels evolved from tracheids
Dicots
Monocots
Gnetophyta (gymnosperms)
4 genera of ferns
A few species of Selaginella (a club moss)
Equisetum

16. Evolution of Perforation Plate

17. Scalariform Perforation Plates

18. Reticulate perforation plate

19. Ephedroid perforation plate

20. Simple perforation plate in elm wood

21. Simple perforation plate in oak wood

22. Oak wood

23. Simple perforation plate in Euphorbia

24. Simple perforation plate