QS Study

Phloem tissue: The kind of tissue, made of some living and dead cells which has the chief function to conduct prepared food materials from leaf to different parts of the plant body is called phloem tissue.

The phloem tissue consists of the following four elements

(1) Sieve tubes

(2) Companion cells

(3) Phloem parenchyma and

(4) Phloem sclerenchyma

Sieve tubes:

  • These are elongated cells with thin cellulose walls placed end to end which combinedly form a tube.
  • The partition walls between the tubes are perforated and are known as sieve plates.
  • When matured, the cells have lignified walls, a thin layer of protoplasm at the periphery and no nucleus.

Companion cells:

  • The living elongated and narrow cells that lie adjacent to sieve tubes are known as companion cell.
  • Their cell walls are thin and porous. They make a connection with the sieve tubes through the pores.
  • They have densed cytoplasm and large nucleus.

Phloem parenchyma:

  • They are the simple parenchyma cells present in phloem tissue.
  • They are living cells in which the cell walls are thick and composed of cellulose. They have densed cytoplasm and large nucleus.

Phloem sclerenchyma:

  • The sclerenchyma fibre that is present in phloem tissue is called phloem sclerenchyma. It is also known as blast fibre.
  • These cells are dead but they are very long. Example- Jute fibres.
  • Phloem fibres arise during secondary growth.