Question

Amphivasal or leptocentric vascular bundles are found in
(a) Cycas and Dryopteris
(b) Dracaena
(c) Helianthus and Cucurbita
(d) Maize and Wheat

Answer 1

In the vascular bundle, certain monocot plants are extraordinary and have a cambial ring. The vascular tissue is structured in these plants so that the xylem wraps the phloem concentrically.

Complete answer:
Dracaena is extraordinary monocot species, meaning they also have a changeal ring despite being a monocot plant. But in the general scenario, monocots lack cambium. They are also an exception, having a cambial ring, in the case of an amphivasal type of vascular bundle. The phloem is present at the periphery, external to the xylem, in the collateral vascular bundle. There is no cambium as an example of a closed-form of the vascular bundle. The cambium is present in the open vascular bundle type. The cambium of a vascular bundle of the open form is considered a fascicular cambium. The vascular collateral bundle is typical of the dicotyledon and gymnosperm stem. The phloem is located both internally and externally to the xylem in the bicollateral vascular bundle. In the stems of some ferns and some members of the family cucurbitaceae, bicollateral vascular bundles are included. Bicollateral vascular bundles are a type of vascular bundle that is available. In the Cucurbita stem, bicollateral vascular bundles are found. One type of vascular tissue in the concentric vascular bundle wraps the other type of vascular tissue.
The right answer, therefore, is (b), i.e.,Dracaena

Note: Closed types of vascular bundles are usually amphivasal and amphicribral vascular bundles as both lack cambium. The amphivasal vascular bundle is also known as the vascular bundle of leptocentric (xylem rings of the phloem). The phloem surrounds the xylem in the amphicribral vascular bundle.