Complex permanent tissue

This ppt completely describes about complex permanent tissue - xylem, its components, functions and patterns of secondary thickening

1. Complex permanent tissues Dr. K. GANESH KUMARI ASSISTANT PROFESSOR SRIMAD ANDAVAN ARTS AND SCIENCE COLLEGE (AUTONOMOUS) TRICHY, TAMILNADU, INDIA

2. Xylem A conduction tissue in plants Complex tissue formed of many types of cells Term proposed by Nageli (1958) Greek : xylos – wood Main function – conduction of water and minerals from roots to leaves Additional function – provides mechanical support

3. It consists of both living and non living cells Two types of xylem in plants – 1. Primary xylem – formed from the pro meristem ( procambium ) during primary growth 2. Secondary xylem - formed from the vascular cambium during secondary growth

4. Components or elements of xylem The elements of xylem are i. Tracheids ii. Vessels iii. Xylem fibres iv. Xylem parenchyma

5. i. Tracheids Origin – Procambium Structure – Elongated or tube like cell Consists of hard, moderately thick and lignified cell walls with large cavity Devoid of protoplast in maturity Ends are tapering, blunt and chisel – like Primitive type of cells Found in the fossils of seed plants

6. Cells with secondary cell walls Cells appear circular, polygonal or polyhedral in cross sections Average length 5 – 6 mm Major parts of the cells imperforate Only have pit – pairs at common walls

7. Patterns of secondary thickenings Secondary cell wall materials are laid down on the lateral walls of tracheids Annular thickening Spiral (or) helical thickening Scalariform thickening Reticulate thickening Pitted thickening

8. Annular thickening Secondary thickening occurs as ring Lignin deposition occurs as ring one above the other Most primitive type thickening Provides mechanical strength to the wall

9. Spiral (or) helical thickening Also called spiral thickening Secondary walls deposited as spirals It is stronger than annular thickening

10. Scalariform thickening Also called like ladder like thickenings Wall materials deposited as transverse bands Bands are with few interconnections Pits occurs in between thickenings

11. Reticulate thickening Also called as net like thickening Net like distribution of secondary materials

12. Pitted thickening Entire inner surface is thickened Unthicken areas looks like pits Used for the communication with neighbouring cells Two types of pits Simple pits – Areas with primary walls Bordered pits – Areas with secondary walls

13. Its secondary wall outgrowths – dome like structure with perforation

14. The primary wall thickening is called torus In gymnosperms, torus is surrounded by microfibrils , known as margo

15. Functions of Tracheids For the transport of water and minerals Chief supporting element in gymnosperms Provides mechanical support

16. ii. Vessels It is multicellular elongated tubes It is formed from a row of cylindrical cells end to end with end walls The end walls are perforated – perforation plate The perforation plate is of two types a. Simple perforation b. Multiple perforation

17. a. Simple Perforation Plate The Perforation plate contains one large pore

18. b. Multiple perforation The perforation plate contains many pores

19. i. Reticulate type The pores are arranged in reticulate manner

20. i. Scalariform type The pores are elongated and arranged in parallel series

21. ii. Foraminate type The perforations are circular and grouped together

22. iv. Xylem parenchyma The parenchyma cells associated with the xylem is called Xylem Parenchyma This is the living element of xylem It is of two types Ray parenchyma – derived from ray initials Axial parenchyma – derived from elongated fusiform cambial cells Xylem Parenchyma stores food It also helps in conduction of water

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