Question

Some vascular bundles are described as open because these –
A) Are surrounded by pericycle but not to endodermis
B) Are capable of producing secondary xylem and phloem
C) Possess conjunctive tissue between xylem and phloem
D) Are not surrounded by pericycle

Answer 1

Hint:Vascular bundle is a part of the transport system in vascular plants. The Vascular bundle consists of two main parts (tissues). These two tissues are present in vascular bundles which in addition will include supporting and protecting tissues.

Complete answer:
In the vascular bundle, parenchyma cells are present. These are differentiated cells and present in inner layers of fruits, leaves, seeds etc. In certain circumstances, they have the capability to change into meristems. After changing they produce secondary xylem and secondary phloem. From here these xylem and phloem cells will further differentiate and become mature. They are known as secondary xylem and phloem because they are formed after de-differentiation.
In dicot (Dicotyledon) stem, calcium is present in between xylem and phloem; such vascular bundles are known as open.
>Option A is not correct because endodermis is present in them.
>Option C is not correct because parenchyma present between xylem and phloem in vascular bundles is called conjunctive tissue which helps in formation of calcium in dicot plants.
>Option D is not correct because vascular bundles are surrounded by pericycles. It is a thin layer of plant tissue between the endodermis and the phloem.

Thus the correct answer is option B. i.e., Are capable of producing secondary xylem and phloem.

Note:In open vascular bundles xylem and phloem are not in direct contact with each other as there is calcium present in between them. In close vascular bundles xylem and phloem are in direct contact with each other as calcium is absent and they do not show secondary growth.