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The cells of the next layers to the inside are usually narrower than those of the endodermis, and they frequently have relatively thin walls.
The cells of the next layers to the inside are usually narrower than those of the endodermis, and they frequently have relatively thin walls (Fig. 4.3b). They constitute the pericycle. Very few species lack a pericycle, among them members of the southern hemisphere Centrolepidaceae. Roots lack any nodes, and lateral roots arise endogenously, that is their growing points or apices first develop in the pericycle. Division of cells in this region pro-duces a lateral root which has to grow through the tissues of the endodermis and cortex to reach the exterior of the primary root. Because the pericycle bounds the vascular system of the root, vascular continuity between the new lateral root and the main root can soon be established once active growth has started. Some roots may have quiescent, potential laterals in the pericycle which require some hormonal stimulation or the removal of a hormonal restraint before they develop.
The relatively simple nature of the pericycle and comparative lack of variation from species to species renders it of little use as a diagnostic feature.
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