|Longitudinal section of a Calamites-
stem. To the left are the (lightcoloured)
pithcells. To the right are the tracheids.
These tracheids are interconnected by
openings in the radial cell walls.
These holes can be circular (bordered
pits) or more or less rectangular.
In this photo long series of bordered
pits are visible. Look below for
|In this photo the openings between
the tracheids are more or less
rectangular in form. The annular
and spiral thickenings of the walls
are the borders of the interconnecting