What is lacking in the closed type of vascular bundles of monocot stem?

Vascular bundles of monocots are described as closed, as they do not have cambium in them.
Vessels always have perforations.
Sclerenchymatous, fibrous bundle sheath is present, around the vascular bundles of monocot stem.

Phloem in monocots is made up of sieve tubes and companion cells however phloem parenchyma is absent in most of the monocots.