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Vascular plants without Seeds (The megaphyll line of evolution:…

- - - - they had two kinds of xylem organization.
      - they had protostele: The most primitive form of stele, consisting of a solid core of xylem encased by phloem or of xylem interspersed with phloem.
      - also has another type of stele called siphonostele:a stele consisting of a core of pith surrounded by concentric layers of xylem and phloem