Question

What is eustele?

Answer 1

The vascular tissue in a dicot stem consists of many vascular bundles that are a part of the plant transport system. In the vascular stem, there are distinct bundles that are arranged by the xylem and phloem tissues called vascular bundles. They carry nutrients and water up and down the stem.

Complete step by step answer :
In the late 19th century the word stele was discovered by P.E.L Van Tieghem and H. Doulton for a better understanding of the evolution of the vascular system in plants. It was derived from a Greek word meaning pillar.

In a vascular plant, it was observed that stele was the central part of the stem and root which constituted of vascular tissue which was,

The xylem was responsible for transporting and storing water and water-soluble nutrients in plants and constituted of tracheids, vessels, and wooden parenchyma.

The phloem which was responsible for transporting protein, sugars and other molecules in plants and constituted of sieve elements, companion cells, phloem parenchyma, and phloem fibers.

A supporting tissue like pericycle which was a plant tissue that was present between the endodermis and the phloem and is responsible for root initiation and maintenance of meristematic activity. It formed the outer boundary of the stele.

There are different types of steles present in a vascular plant, one of them is eustele. Brebner in 1902, observed a derived version of siphonostele in seed plant stem and acknowledged it as eustele.

In eustele, the primary tissue consists of vascular bundles that surround the pith (it is found in the stems of a vascular plant and is composed of parenchyma cells. It stores and transports nutrients throughout the plant) in the form of one or two rings.

The vascular bundle in the eustele can be collateral, that is, the phloem is only present on one side of xylem or bi-collateral, that is, the phloem is present on both sides of xylem.

In eustele, the inner fascicular area and the leaf gap are not separated clearly. For instance, conifers (gymnosperm), roots of monocot and dicot stem are the most common examples of eustele.

Note: Eustele is a derived form of siphonostele and not a direct classification of stele.
There are two types of eustele
Protostele – In this phloem surrounds the xylem.
Siphonostele – In this xylem is surrounded by the phloem and pith is present in the center.