Detail of a single vascular bundle from a transverse section of the mature stem, embedded in celloidin and stained with safranin and fast green. It shows the result of sustained primary growth with the surrounding primary cells of the ground tissue extended transversely and with evidence for late cell division in their septation. Large air spaces are developed elsewhere. The fibers of the bundle cap are mature and thick walled, the inner cells towards the phloem showing their great age with tannin deposits in their walls. The article suggests that this kind of activity, which can result in a very lacunose center to a stem, contrasted with the compact and sclerotic periphery of the stem represents a division of labor between outer mechanically efficient stem tissues and inner tissues devoted to long distance transport. This division may also represent an advanced character in palm stem evolution. Because maturation of stem tissues takes place over decades or even centuries in different types of cell metabolism it is suggested that palms are, by this criterion, the longest-lived trees.