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

17. 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

18. a. Simple Perforation Plate
• The Perforation plate contains one
large pore

19. b. Multiple perforation
• The perforation plate contains many
pores

20. i. Reticulate type
• The pores are arranged in reticulate
manner

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

22. ii. Foraminate type
• The perforations are circular and
grouped together

23. 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

25. THANK YOU