Question : Define Siphonostele. Explain its types.

1.	Question : Define Siphonostele. Explain its types.
Answer» Solution :In siphonostele xylem is surrounded by phloem with pith at the centre. It includes Ectophloic siphonostele, Amphiphlojc siphonostele, Solenostele, Eustele, Atactostele and Polycylic stele. (i) Eetophloic siphonostele: The phloem is restricted only on the external side of the xylem. Pith is in centre. E.g. Osmunda. (ii) Amphiphloic siphonostele: The phloem is present on both the sides of xylem. The pith is in the centre. E.g. Marsilea. Solenostele: The stele is perforated at a PLACE or places corresponding the origin or the leaf trace. (a) Eetophloic solenostele-Pith is in the centre and the xylem is surrounded by phloem. E.g. Osmunda. (6) Amphiphloic solenostele - Pith is in the centre and the phloem is present on both sides of the xylem. E.g. Adiantum pedatum. (c) Dictyostele - The stele is separated into several VASCULAR strands and each one is called meristele. E.g. Adiantum capillus-veneris (iv) Eustele: The stele is split into distinct COLLATERAL vascular bundles around the pith. E.g. Dicot stem. (v) Atactostele: The stele is split into distinct collateral vascular bundles and are scattered in the ground TISSUE. E.g. Monocot stem. (vi) Polycyclic stele: The vascular tissues are present in the FORM of two or more concentri1C cylinders. E.g. Pteridium.

Discussion