Xylem I Tracheary Elements Tracheids Vessel elements Tracheids

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 10 mm 20 mm 40 mm 78. 5 mm 2 314 mm 2 1256 mm 2 Relative Proportion 1 4 16 Relative Conductance (r 4) 1 16 256 Diameter Cross section Area (pr 2)

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