Vascular bundle

The sugars synthesized by the plant with sun light are transported by the phloem, which is closer to the lower surface.

The position of vascular bundles relative to each other may vary considerably: see stele.

It forms a protective covering on the leaf vein and consists of one or more cell layers, usually parenchyma.

Loosely-arranged mesophyll cells lie between the bundle sheath and the leaf surface.

The Calvin cycle is confined to the chloroplasts of these bundle sheath cells in C4 plants.

Types of Vascular bundles
(blue: Xylem, green: Phloem, white: Cambium)
A concentric, periphloematic(Hadrocentric)
B concentric, perixylematic(Leptocentric)
C radial with inner xylem, here with four xylem-poles, left closed, right open
D collateral closed
E collateral open
F bicollateral open
Cross section of celery stalk, showing vascular bundles, which includes both phloem and xylem
Detail of vascular bundle: closed, collateral vascular bundles of the stem axis of Zea mays
Vascular bundle in the leaf of Metasequoia glyptostroboides
The vascular bundle of pine leaf showing xylem and phloem