(vascular cylinder) The central core of the stems and roots of vascular plants, comprising the vascular tissue, ground tissue, such as pith and medullary rays, and the pericycle. The pericycle is considered to represent the outermost layer of the stele at the boundary with the * cortex. The many different types of stele are thought to reflect the direction of the evolution of the vascular system in plants (see illustration). Different types of stele may be found in different regions of the same plant. In dicotyledons the root characteristically has a solid central core of vascular tissue (see protostele ), making it better able to resist pulling stresses, while the stem has a ring of discrete vascular bundles (see eustele ) and is better able to resist bending stresses. See also atactostele , dictyostele , polystely , siphonostele , solenostele.  |
