Developmental changes in the xylem were studied in a stem of Bocconia vulcanica Donn. Smith with a xylem radius of 3.0–4.5 cm. Growth rings are absent. The vascular cambium is nonstoried with fusiform initials averaging 282 µm long. The specialised vessel members are short, with oblique to transverse end walls, simple perforations, and alternate intervascular pitting. Vessels are relatively uniform in diameter and arrangement throughout the wood. Fibres have moderately thin walls and do not increase in length from the primary xylem to the cambium. Axial parenchyma is paratracheal, scanty to vasicentric. Rays are exclusively multiseriate, tall, and heterocellular with a predominance of erect and square cells. Sheath cells occur along the sides. There are no fibres in the secondary phloem and a periderm is not present. The xylem and bark are similar in many respects to that formed in some groups of dicotyledons that are basically herbaceous with evolution toward woodiness.