The exodermis is a layer of cells from the outermost layer of the cortex of many angiosperms. Like the endodermis, its cells are very compact and are surrounded by a Casparian strip, two features which are used to restrict flow of water to symplastic rather than apoplastic 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, and also to serve as defense against microorganisms.
References
Exodermis Wikipedia(Text) CC BY-SA