Stelar evolution in Pteridophytes-BOTANY

Evolution OF STELE IN PTERIDOPHYTE -PPT

1. STELAR EVOLUTION IN PTERIDOPHYTES

2. What are PTERIDOPHYTES The VASCULSAR CRYPTOGAMS An assemblage of seedless vascular plants that have successfully invaded the land and reproduce mainly by means of spores

3. Vascular plants together share a number of apomorphies Lignified secondary walls Sclerenchyma Tracheary elements , cells of xylem tissue Sieve elements , cells of phloem tissue An endodermis A n independent, long-lived sporophyte . Sporophytic leaves . Roots (secondarily lost in the P silophytes ) .

4. STELE CENTRAL VASCULAR CYLINDER WITH OR WITHOUT PITH AND ENDODERMIS SEPARATING IT FROM CORTEX pericycle

5. PROTOSTELE The vasculature consists of central core of xylem completely surrounded by phloem. This is the most primitive and simplest of steles. Types of protostele i ) Haplostele ii) Actinostele iii) Plectostele iv) Mixed protostele v) Polystele

6. i )HAPLOSTELE A Protostele with a central core of xylem surrounded by a layer of phloem. e.g. Selaginella stem, Gleichenia Psilotum Rhizome T.S

7. ii) Actinostele Central xylem core with radiating ribs or a star shaped appearance surrounded by phloem e.g. Lycopodium serratum , Psilotum stem PSILOTUM STEM T.S

8. iii) Plectostele Xylem is plate like ,arranged parallel to each other and each plate is surrounded by phloem. e.g. Lycopodium clavatum

9. iv) Mixed Protostele Xylem & phloem uniformly distributed Xylem elements breakup in to small groups and all get surrounded by phloem Most advanced among protostele and considered as transitional type between the protosteles and siphonostele Lycopodium cernuum

10. V) Polystele In Selaginella , the stem axis has several steles in parallel arrangement.Each stele is a protostele . eg.some species of S elaginella

11. SIPHONOSTELE Medullated stele (Stele with central pith ). Pith is surrounded by xyelm and phloem on the outside. Types of siphonostele i )Simple Siphonostele ii) Solenostele

12. i )Simple Siphonostele Modified protostele with a central pith. Central pith is often parenchymatous rarely sclerenchymatous. Types of Simple siphonostele a) Ectophloic siphonostele b) Amphiphloic siphonostele

13. a) Ectophloic siphonostele This type of stele has a central pith which is surrounded by concentric rings of xylem followed by phloem.e.g. Osmunda,Botrychium O smunda

14. b) Amphiphloic siphonostele In this type of stele, the central portion is occupied by pith. Xylem is surrounded both externally and internally by rings of phloem .e.g. Adiantum,Marselia Xylem P ith Phloem Phloem Marselia Rhizome T.S

15. ii) Solenostele A siphonostele possess a leaf gap on one point It may be a) Ectophloic Solenostele eg. Osmunda b) Amphiphloic Solenostele eg. Adiantum , Marselia rhizome at leaf arising regions

16. Dictyostele Siphonostele with overlapping leaf gaps form dictyostele . The portion of vascular tissue which lies in between two gaps is termed as meristele . Each meristele is protostelic in nature. Types of Dictyostele i )Simple Dictyostele - Dictyosteles arranged in a single ring eg. Polypodium ii) Polycyclic Dictyostele - Dictyosteles arranged in two or more rings.A typical stele possess two or more concentric rings of vascular tissue e.g. Pteris pteridium Rhizome

17. Polypodium Pteris pteridium SIMPLE DICTYOSTELE POLYCYCLIC DICTYOSTELE

18. EUSTELE The vascular system consists of a ring of collateral, conjoint vascular bundles situated on the edges of the pith. e.g. Equisetum