Tissue systems of the root
Follow the diagram below to gain the concept of tissue position. The root apical meristem produces new root cap cells as well as cells of the ground meristem, and procambium. Like the shoot, the root possesses three tissue systems:
1) Dermal Tissue System
In primary growth, roots are covered with epidermis. In secondary growth, the epidermis and root hairs are sloughed off when periderm forms on the outside.
2) Ground Tissue System
Cortex lies between the epidermis and vascular system in portions of roots undergoing primary growth. The inner layer of cortex, the endodermis bounds the pericycle tissue which surrounds the primary vascular system. See the diagram of the cross section of the root below. In portions of roots undergoing secondary growth, the cortex, like the epidermis, is shed as the periderm develops cork cells.
3) Vascular Tissue System
Also see the following in the cross section of root diagram above. In the root, unlike the stem, the primary vascular system is in a central cylinder with xylem and phloem arranged in an alternate radial manner. Primary xylem "arms" radiate out from the center with primary phloem in the outer portion of the cylinder. Between them is procambium. In older portions of roots, where secondary growth is evident, the vascular cambium produces successive layers of secondary xylem and phloem.
Return to Plant Tissue Systems