1. Complex permanant tissues

Xylem is a complex vascular tissue that transports water and minerals from roots to other parts of the plant. It also provides mechanical support.

 

Xylem

The term xylem was introduced by C. Nageli (1858) (Greek: xylon - wood).

Characteristics:

• It is made of both living and dead cells (mostly dead).
• Cell walls are thick and lignified.
• Transport of water is unidirectional (upward).

1. Tracheids – Long, dead, tapering cells found in all vascular plants and it conduct water and give support.
2. Vessels (Tracheae) – Long tube-like dead cells with perforated ends, found mainly in angiosperms, highly efficient for water transport.
3. Xylem parenchyma – Living cells store food and help in lateral conduction of water.
4. Xylem fibres – Dead, thick-walled cells and it provides strength.

Phloem is a complex tissue that transports prepared food (mainly sucrose) from leaves to all parts of the plant.

The term phloem was introduced by C. Nageli (1858) (Greek: phloos = bark).

Phloem

 

Characteristics:

• It consists mainly of living cells (except phloem fibres).
• It transports food in bidirectional (both upward and downward).

1. Sieve elements – Main conducting cells for food.
   • Sieve tubes: Found in angiosperms; have sieve plates.
   • Sieve cells: Found in gymnosperms and pteridophytes; no sieve plates.
2. Companion cells – Living cells that assist sieve tubes; originate from the same mother cell.
   
   
3. Phloem parenchyma – Living cells store food and help in sideward transport and this is absent in monocots.
   
   
4. Phloem fibres (Bast fibres) – Dead, lignified cells providing mechanical strength.

Difference between simple and complex permanent tissues