Three zones can be recognized in a transverse section of a stem: the pith, next a ring with xylem and phloem, and finally the cortex. These three zones are separated by unicellular layers called endoderm.
- The pith exists of supporting tissue made of thickwalled cells
- Next comes a ring of wood vessels (xylem). These are elongated cells with ladderlike thickenings.
- The cortex consists of of three layers, of which in most cases only the central one with thickwalled cells is preserved.
- The phloem (sieve vessels) is situated between the zones. In most cases it is decayed.
The diameter of the stems is generally 3 - 5 mms. Most of the photos are of the Idaho specimen.
Click at the photo to view details of the stem section