If pith is present in the centre of stele, .i.e., protostele with pith it is called siphonostele or medullated protostele is called siphonostele. It is of two type (i) Ectophloic siphonostele: In this, phloem is present only on outer side of the xylem, .e.g., Osmunda, Equisetum, Schizaea etc. (ii) Amphiphloic siphonostele: Here phloem is present on both the side of xylem, .e.g., Marsillea, Adiantum etc.