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Primary xylem
Oak wood
Leaf vein
Vein ends
Bean seed
Pine tracheids, xs
Fern TE, xs
Fern, TE, mag
Annular walls
Annular, stretched
Annular, narrow
Scalariform walls
Scalar., narrow
CBP, pine
CBP, dicot
CBP, irregular
Contact faces
Pits, side view
CBP, pine, xs
CBP,angio, xs
CBP, fern, xs
Contact face, xs
Simple perf. plate 1
Simple perf. plate 2
Pitted perf. plate
Perf. plate & helix
Perf. plate, face
Perf. plate, mag
Perf. plate, section
Perf. plate rim
Perf. plate & wall
Scalariform Per plate
Primary xylem
Vessel sizes
Fern TE
Pine needle
VE precursor, ls
Protoxylem
9 Contact faces
VE precursor, xs
Precursor 2
Torn vessel
Torn vessel 2

Fig. 7.1-7a. Transverse section of rhizome of a fern (Pteridium). The center of the section is occupied by a plate of large cells with thick, red-stained walls. What are they? They are shown in higher magnification in 7.1-7b, but that will not help. A few years ago, we would have confidently stated that because this is a fern, these are almost certainly tracheids. Pteridium was one of just four ferns known to have vessels. But in the last few years (since the late 1990s), Dr. S. Carlquist and E. Schneider have been discovering that in a considerable number of ferns, structures that were thought to be pits are actually perforations -- the pit membrane is digested away during cell maturation. Only by using scanning electron microscopy (SEM) is it possible to see that the pit membrane is missing. For an introduction to their research, see Schneider, D. L., and S. Carlquist. 2000. SEM studies on vessels in ferns. American Journal of Botany 87: 176-181.