close-up of the central pith of the petrified calamitean stem Arthropitys reveals
tubular structures called carinal canals, which are surrounded
primary xylem. The photo was taken at 40x. These structures
measure 300 micrometers in diameter. Secondary xylem can
the carinal canals.
Individual tracheids in this area measure 20 to 50 micrometers
in diameter. Medullary
can be seen between the carinal canals and secondary xylem.
With this close-up we can make sense of the exterior ribs
found on Calamites pith casts. The ribs correspond
to the rays. The depressed areas between the ribs are where
carinal canals extended into the pith cavity. You can visit
the Brazil Gallery in the Permian section of our museum to
see a sequence of photos that zoom in on the photo above.