Concentric Vascular Bundle in some Ascidial Stalks of Clerodendron infortunatum Gaertn.

Abstract

SOME ascidial stalks of Clerodendron infortunatum described earlier¹ contain a few vascular bundles which are concentric—some amphivasal and others amphicribral in structure. The amphivasal vascular bundles are seen near the tip of the ascidial stalk. In tracing the origin of this amphivasal vascular bundle from the base to the tip in serial sections, it was observed that the basal collateral vascular bundle becomes gradually a horse-shoe shaped one which ultimately becomes amphivasal in shape (see photomicrograph). At an upper level this concentric vascular bundle reverts successively to the horse-shoe shaped and collateral types. During the transition stage of the vascular bundle from collateral to concentric structure, its upward course is diverted towards the pith. Here the amphivasal vascular bundle is seen embedded within three to six layers of cells of the pith. Next, the concentric bundle turns outward again and takes its place by the side of the neighbouring collateral vascular bundles, by which time it has assumed its collateral form.