Dicot and monocot roots

The dicot root studied is sunflower. From outside in: epiblema, cortex, endodermis, pericycle, then the vascular strands and a small pith.

Epiblema is the outer layer; many of its cells grow out as single-celled root hairs.

Cortex: several layers of thin-walled parenchyma with spaces between the cells.

Endodermis: the innermost cortex layer, one row of barrel-shaped cells with no intercellular spaces. Their radial and tangential walls carry casparian strips of suberin, a waxy material that water cannot pass through.

Pericycle: a few layers of thick-walled parenchyma just inside the endodermis. Lateral roots start here, and so does the vascular cambium when secondary growth begins.

Dicot root: usually two to four xylem patches and as many phloem patches, with parenchyma between them called conjunctive tissue. Pith is small or inconspicuous. A cambium ring forms between xylem and phloem later.

Stele = everything inside the endodermis: pericycle, vascular bundles and pith.

Monocot root: the same layers, but usually more than six xylem bundles (polyarch), a large, well-developed pith, and no secondary growth.

In both roots the protoxylem is drawn towards the outside, next to the pericycle, and the metaxylem towards the centre.