Biology (NTSE/Olympiad)  

2. Tissue


Phloem :
The dead matter in them is known as bast.
Its main function is conduction of food material from leaves to other plant parts.
The phloem elements are of four type : Sieve tubes, Companion cells, Fibres and paranchyma.
Sieve Tubes :
These are living but lack nucleus at maturity.
Cell wall is thin and made up of cellulose.
The transverse walls of sieve tube form sieve plate.
They help in conduction of food material.
Companion Cells :
The cells are living, thin walled, narrow and found attached to the lateral side of sieve element.
They are absent in pteridophytes and gymnosperms.
They support the sieve tube in transport of food.
These are living and thin walled cells.
They are absent all monocots and some dicots.
Phloem Fibers (bast fibers) :
These are sclerenchymatous fibers having thick wall and narrow Luman.
They provide mechanical support to the plant.
Phloem Parenchyma -
The chief function of parenchyma is to store food material and other substances like mucilage, tanins and resins.


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