File:Perennial Monocot Stem Amphivasal Vascular Bundle in Acorus Rhizome (35320758832).jpg

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

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The rhizomes, or horizontal stems, of Acorus are notable for their accumulation of aromatic medicinal oils.

The well cutinized epidermis is uniseriate showing radially elongated cells with thickened outer walls and occasional corky zones.

The cortex consists of an outer hypodermis of 3-5 layers of densely packed collenchyma cells. Beneath the hypodermis lies a wide zone of starch containing parenchyma cells with numerous intracellular spaces. These spherical cells form a tight network with vascular bundles and small fiber bundles positioned at the junctions of the network.

The boundary between the cortex and stele is marked by well-defined endodermis of one layer of thick walled barrel shaped starch contain cells. A casparian strip may be evident in some preparations.

As in the cortex, the parenchymatous cells of the stele are arranged in tight aerenchymatous chains. The vascular bundles within the stele are wrapped in bundle sheaths and form a nearly continuous ring just beneath the endodermis. Unlike those situated in the cortex, these bundles are rarely associated with fibers.

Both cortical and stelar vascular bundles are leptocentric, or amphivasal, meaning xylem and phloem are arranged in concentric rings with phloem to the inside and xylem to the outside of the bundle.