Question

When phloem is completely surrounded by xylem, the vascular bundle is called as

• A. Concentric, leptocentric / amphivasal
• B. Concentric, hadrocentric / amphicribral
• C. Conjoint, collateral
• D. Conjoint, bicollateral

Answer 1

The correct option is A Concentric, leptocentric / amphivasal

When xylem surrounds the phloem tissue from all sides the vascular bundle is called as amphivasal vascular bundle or leptocentric type. Such bundles are seen in monocot plant like Dracaena.

Sometimes, the either xylem surrounds the phloem tissue or vice versa. Such vascular bundles are called as 'concentric vascular bundles'.

When phloem surrounds the xylem tissue entirely, the vascular bundle is called as amphicribal vascular bundle or hadrocentric type. Such vascular bundles are seen in pteridophytes like Lycopodium, Selaginella.

Collateral vascular bundles are very common type and seen in stems of dicotyledons except the members of Cucurbitaceae and some members of Convolvulaceae.

Cambium may be present or absent in between xylem and phloem patches making the vascular bundle open or closed respectively.

Bi-collateral vascular bundles contain two patches of phloem on either sides of the xylem on the same radius. The outer phloem or external phloem remains towards the periphery of the central cylinder and inner or internal phloem remains towards the centre.