Bidens, secondary growth from the fascicular cambium

 

The micrograph shows a detail of part of one vascular bundle which is undergoing secondary growth.

The cambial zone (CZ) is actively dividing  and is several cells wide, but does not contain significant numbers of secondary phloem elements. The primary phloem  strand contains sieve elements (SE) and companion cells (CC).

A starch sheath (SS) delineates the cortex (above the starch sheath) and the stele (below the starch sheath).

Click here for a more detailed look at the primary phloem.

Click here for a more detailed look at secondary phloem.

Click here for a more detailed look at the secondary xylem