Xylem - I
Tracheary Elements Tracheids Vessel elements
Tracheids and Vessel Elements
Secondary Wall Thickenings 1 = annular thinckening 2-4 = helical thickening 5 = reticulate thickening 6 = scalariform pitted wall 7 = opposite pitted wall 8 = alternate pitted wall
Annular thickenings in vessel elements
Annular thickenings in a tracheid
Reticulate wall thickenings
Secondary Wall thickenings
Scalariform pitted walls
Pitted wall in a vessel
Pitted wall in pine tracheid
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
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
Cooksonia reconstruction and fossils
Vessels evolved from tracheids Dicots Monocots Gnetophyta (gymnosperms) 4 genera of ferns A few species of Selaginella (a club moss) Equisetum
Evolution of Perforation Plate
Scalariform Perforation Plates
Reticulate perforation plate
Ephedroid perforation plate
Simple perforation plate in elm wood
Simple perforation plate in oak wood
Oak wood
Simple perforation plate in Euphorbia
Simple perforation plate