Atlas of plant and animal histology

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Virtual microscopy


Imagen: primary root, Iris.

Epidermis: it is the outer layer of the root. This is a region of the primary root far from the root tip because no root hair is observed. Unlike the epidermis of the shoot, the root epidermis cells do not show thick cuticle in their free surfaces.

Hypodermis: or exodermis, it is the layer of differentiated cells just below the epidermis. In this image, hypodermal cells show suberized cell walls (with pale color) and look like sclerenchyma cells.

Cortex: it is the parenchyma tissue found between the hypodermis and the endodermis. The cortex makes up most of the root.

Endodermis: it is the layer delimiting the inner surface of the cortex. The endodermis consists of a one-cell thick layer with thickenings in their cell walls known as Casparian band. The role of the endodermis is to control the water and minerals diffusing the cortex toward the vascular tissues.

Pericycle: it is the layer immediately beneath the endodermis. Pericycle cells are parenchyma cells with meristematic activity. Lateral roots are formed from pericycle cells. They also contribute to the vascular cambium during the root secondary growth.

Primary phloem: it is the vascular tissue specialized in transporting carbonated molecules. Primary phloem cells are organized in small groups separated by the primary xylem spokes.

Primary xylem: it is the vascular tissue specialized in transporting water and minerals. Primary xylem cells are large, empty cells with thick secondary cell walls.

Medulla: it is the parenchymatic tissue found in the inner part of the root.