File:Woody Dicot Stem Developing Ray System in Early First Year Tilia (35993272813).jpg

cross section: Tilia Early one year stem common name: Linden or Basswood magnification: 100x

In this young stem, early in the first year of growth, the well cutinized and single layered epidermis overlays a cortex with two distinct layers; an outer cortex of tightly packed collenchyma and an inner cortex of open airy parenchyma.

Within the first year of growth the underling activity of the cork cambium begins to replace the cutinized epidermis and outer cortical tissues with a protective layer of cork rich periderm.

The outermost layer of periderm consists of layers of cork cells, the phellem, which produce the waterproofing substance suberin. Cork cells are dead at maturity. Deep to the phellem is a layer of living cork cambium or phellogen and just beneath that layers of cork parenchyma or phelloderm.

The vascular cylinder consists of an outer ring of primary phloem, a middle ring of vascular cambium and a deeper larger ring of primary xylem. Bulging into the pith are small masses of the first xylem consisting of small protoxylem cells overlaid by a few larger, heavier walled cells of metaxylem. Above this and extending to the cambium are columns of primary xylem divided by narrow rays, extending from the large parenchymatous pith to the phloem.

The deepest zone of primary xylem is separated from the parenchymatous central pith by a well defined starch sheath of dark staining starch filled parenchyma cells.