The central portion of the dicot root is occupied by the vascular cylinder, which contains tissues (xylem and phloem) specialized for the transport of materials through the plant body. In the photographs below, you should be able to identify the following structures associated with the vascular cylinder:

Endodermis. The innermost layer of cells in the cortex is known as the endodermis. Each endodermal cell is surrounded by a ring of waterproof material, the Casparian strip, that prevents water and dissolved materials from passing between the individual cells. What do you suppose is the function of the endodermis?

Vascular Cylinder. The center of the root is occupied by a core of vascular tissue known as the vascular cylinder. This region contains the xylem and phloem (transport tissues), as well as a specialized cell layer called the pericycle.

Pericycle. This is a layer of parenchyma cells located just inside the endodermis. It is the tissue layer from which branch roots arise.

Xylem. The water-conducting tissue of the root is usually arranged in a more or less cross-shaped or star-shaped configuration in the center of the vascular cylinder.

Phloem. In the root, phloem occurs as isolated strands of tissue between the "arms" of the central core of xylem.
 

You should be able to identify these parts of the dicot root in the illustrations below:
 

Cross section of the vascular cylinder of a typical herbaceous dicot root showing the conspicuous endodermis, the pericycle, and the central core of xylem and phloem.

Cross section through the root of a corn plant showing the origin of a branch root from the cells of the pericycle.

This page last updated: 06 Oct 1999