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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. 7.5-4a. Transverse section of developing vessels in roots of oak (Quercus). This bundle contains many mature vessel elements, readily identifiable by their large diameter and red-stained, lignified secondary walls. But the cells marked with arrows have the proper size to be vessel elements but they do not have secondary walls. Also, there is a bit of plasmolyzed protoplasm in them. These are vessel elements that are still differentiating – they appear to have finished their enlargement and had not even begun to deposit the S1 layer of the secondary wall. It is not too common to see vessel elements in this immature stage of development, they seem to pass through this stage quickly.