The exodermis is a layer layer of cells from the outermost layer of the cortex of many angiosperms. Like the endodermis

Endodermis

The endodermis is the central, innermost layer of cortex in some land plants. It is made of compact living cells surrounded by an outer ring of endodermal cells that are impregnated with hydrophobic substances to restrict apoplastic flow of water to the inside...

, its cells are very compact and are surrounded by a Casparian strip

Casparian strip

In plant anatomy, the Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis, which is chemically different from the rest of the cell wall. It is used to block the passive flow of materials, such as water and solutes into the stele of a plant...

, two features which are used to restrict flow of water to symplast

Symplast

The symplast of a plant is the inner side of the plasma membrane in which water can freely diffuse.The plasmodesmata allow the direct flow of small molecules such as sugars, amino acids, and ions between cells...

ic rather than apoplast

Apoplast

Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....

ic flow through passages through the cells' membranes called plasmodesmata.

The exodermis is thought to provide protection against water loss of the root to the soil, as well as defense against microorganisms.