Question

In dicot stem the vascular bundles are.
A. Concentric and open
B. Concentric and closed
C. Conjoint, collateral and closed
D. Conjoint, collateral and open

Answer 1

The vascular system found in dicots is somewhat more complex than that found in monocots. In the dicot stem, the vascular bundles are arranged in a ring, with pith concentrated at the core of the stem, rather than being scattered throughout the plant interior.

Complete answer:
A vascular bundle having both xylem and phloem together, is called conjoint. Collateral: A vascular bundle in which the phloem lies towards outer side and xylem towards inner side, is called collateral example: sunflower. Due to the presence of cambium they are called open. Cambium gives rise to secondary xylem and phloem. Hence in dicot stems conjoint, collateral and open and endarch types of vascular bundles are seen. Endarch is used when there is more than one strand of primary xylem in a stem or root and xylem develops from the inside outwards towards the periphery i.e. centrifugally. Dicot stem has a cambal ring which helps in secondary development. In the dicot stem, the vascular bundles are arranged in a ring.

Concentric and open: Not found in any plant parts.
Concentric and closed : not found in any plant parts
Conjoint, collateral and closed: Found in monocot stem, dicot leaf and monocot leaf
Conjoint, collateral and open: Found in dicot stem.

Note: Two types of plant growth primary and secondary growth. In general, monocots don’t undergo secondary growth. If they do increase in girth it does not result in the development of a secondary xylem and phloem, since monocots don’t have vascular cambium.