The rhizome of Acorus Calamus.

Characters. - In sections of various lengths, unpeeled, about three-quarters of an inch (2 centimetres) broad, subcylindrical, longitudinally wrinkled; on the lower surface marked with the circular scars of the rootlets in wavy lines; externally reddish-brown, somewhat annulate from remnants of leaf-sheaths; internally whitish, of a spongy texture, breaking with a short, corky fracture, showing numerous oil-cells and scattered wood-bundles, the latter crowded within the subcircular nucleus-sheath. It has an aromatic odour, and a strongly pungent taste.

Composition. - It contains a volatile oil and a bitter principle.

Uses. - It is used as a feeble aromatic, stomachic, and stimulant.