cross section: Acorus root common name: Sweet Flag magnification: 400x

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The cortex is well-developed and divided into two zones; an outer narrow layer of closely packed smaller parenchyma cells and a wide inner layer of open larger aerenchyma cells.

The inmost area of the cortex is bounded by an endodermis or starch sheath with larger barrel shaped cells and thickened walls that mark the casparian strip. Within the endodermis occasional small passage cells serve to transport water into the stele or vascular bundle.

The stele is bound in a pericycle of single layered thin walled parenchyma cells. A single central vascular bundle contains radiating arms of xylem and phloem. The xylem is exarch: meaning the earlier smaller protoxylem is found towards the periphery and younger larger metaxylem to the center of the stem.

Phloem tissues of seive tubes, companion cells and phloem parenchyma are also exarch. The older protophloem is found towards the periphery and metaphloem towards the center of the stem. Supportive sclerenchyma tissues and phloem caps are notably absent in most monocot stems. Vascular cambium is also absent, preventing secondary growth of the root.