Question

Describe the structure of phloem.

Answer 1

Phloem is made up of four types of cells :

1) Sieve tubes: These are tubular channels formed of elongated living cells, arranged in vertical rows.The transverse end walls are perforated with a number of pores (sieve plates). The cytoplasm of one element is continuous with the other through these pores. Nuclei are absent in sieve tubes.

2) Companion cells: These are small cells associated with sieve tubes, with dense cytoplasm and a large elongated nucleus. They remain connected to the sieve tubes by pores

3) Phloem parenchyma: These are simple delicate cells containing starch, tannin and crystals. These cells perform the function of storage and translocation of food substances.

4) Basil fibres: These are sclerenchymatous cells occurring in the phloem. They are composed of dead cells and function as storage tissue.