Image: primary root of a dicot plan: corn, stained with safranin / Alcian blue.
Epidermis: it is the outer layer made up of small cells showing a thin cuticle.
Colenchyma: it is a supporting layer found beneath the epidermis.
Cortex: it is the region between the colenchyma and the endodermis. The cortex is largely formed of parenchyma cells.
Endodermis: it is the cell layer delimiting the inner surface of the cortex. The endodermis is in charge of filtering the water coming from the environment toward the vascular tissues. In this image, the Casparian band, a typical feature of the cell wall of the endodermis cells, is hardly visible.
Pericycle: it is the layer of cells immediately below the endodermis. The pericycle cells retain meristematic features and can proliferate and differentiate to give lateral roots.
Primary phloem: it is the vascular tissue found between the primary xylem. Primary phloem cells are organized in small groups.
Protoxylem: it is the first xylem differentiated from the procambium. Protoxylem is a transient vascular tissue that is replaced by the metaxylem. Unlike in shoots, the protoxylem is in an outer than metaxylem.
Metaxylem: it is the vascular tissue formed from the procambium that replaces the protoxylem. Metaxylem is the main functional primary xylem until the secondary grow begins.
Medulla: it is the parenchyma tissue tha forms the inner region of the root.