cross section: Richinus stem magnification: 100x

Like many herbaceous dicots, Richinus is capable of a small amount of secondary growth.

The epidermis in Richinus consists of a single layer of well cutinized cells.

The cortex is divided into two distinct zones; a large outer zone of thick walled collenchyma and a narrow inner zone of loosely packed parenchyma cells. The innermost area of the cortex is marked by a starch sheath or endodermis of tightly packed cells.

The outer layer of the stele is defined by a many layered pericycle of parenchyma cells interspaced with bundles of heavy walled supportive sclerenchyma cells.

Deep to the pericycle lies a ring of vascular bundles interspaced with medullary rays of parenchymal cells. In older stems the isolated vascular bundles are replaced with continuous rings of phloem, cambium and xylem, interspaced with medullary rays.

Xylem is endarch with protoxylem found towards center of stem and younger metaxylem towards the periphery of the stem. Phloem is endarch but modest annual growth makes it difficult to distinguish between the older protophloem at the periphery and younger metapholem to the center of the stem.