Question

Bicollateral vascular bundles are found in
A. Malvaceae
B. Cucurbitaceae
C. Liliaceae
D. Poaceae

Answer 1

Hint:- The central column of the axis of the root and stem is called stele. It is made up of a number of vascular bundles, which constitute vascular tissue systems. Xylem, phloem and cambium are the components of the vascular bundle.

Complete Answer:-
The arrangement of vascular bundles are of three types:
- Radial: In this type, xylem and phloem are arranged in an alternate manner on different radii, such vascular bundles are called radial. All the roots of the plants contain radial vascular bundles. The development of xylem in these vascular bundles is centripetal. Thus these vascular bundles are called exarch.
- Conjoint: When xylem and phloem are present on the same radius, it is called conjoint vascular bundle. These are the characteristic features of stem. Depending upon the mutual relationship of xylem and phloem, these are divided into two types-
- Collateral- In these types, xylem and phloem lie together on the same radius with xylem being internal and phloem being external. It may be open or closed. In this vascular bundle order of development of xylem is centrifugal because protoxylem is present in the center of xylem when the endarch condition is found. This vascular bundle is found in gymnosperm and angiosperm.
- Bicollateral- In this type, two patches of phloem, one on each side of xylem are present. In such vascular bundles, there are two strips of cambium on each side of xylem. Only outer cambium is functional. Bicollateral vascular bundles are found in families Cucurbitaceae, Solanaceae, Apocynaceae, etc.
- Concentric: When xylem surrounds phloem completely or phloem surrounds xylem completely, such vascular bundles are called concentric.
So the correct answer is B. Cucurbitaceae.

Note:- In the dicots, the cambium is present between the xylem and phloem and they are said to have an open vascular bundle system. Monocots have closed vascular bundles i.e. cambium is absent between those tissue layers.