Water containing cavities can be traced in vascular bundles of
In monocot stem vascular bundles are oval-shaped. In this, xylem and phloem are present on the same radii, and also present side by side. So they are also called Collateral and Conjoint vascular bundles. In the vascular bundles, cambium is absent and in between the xylem and phloem. So these are closed vascular bundles.
In the xylem, protoxylem is towards the centre, and metaxylem is towards the periphery. So, it is an endarch xylem. In the protoxylem, some of the cells, disintegrate, and form into a lysigenous cavity, called as Protoxylem lacuna. eg: Maize.
So, the correct option is D.