Q.What is plectostele? Give example.

The stele is the central cylinder of vascular tissue in a root or stem — xylem, phloem, pericycle and, in more advanced forms, pith and medullary rays. Steles fall into two broad categories that trace an evolutionary sequence from simple to complex. A protostele has phloem simply surrounding a solid xylem core with no pith, and includes haplostele (Selaginella), actinostele — star-shaped xylem (Lycopodium serratum), plectostele — alternating xylem/phloem plates (Lycopodium clavatum), and mixed protostele — scattered xylem groups (Lycopodium cernuum). A siphonostele surrounds a central pith with xylem, and includes ectophloic (phloem outside only, e.g. Osmunda) and amphiphloic (phloem on …