Phloem

There are 4 types of phloem tissues as well!!

~Sieve tube element

~Companion cells

~Phloem fibres

~Phloem parenchyma'

The sieve tubes and the companion cells are directly involved in the translocation of the organic substances. sieve tubes ,phloem parenchymam and companion cells are living tissues.Phloem fibre is dead tissue.

Sieve tube element:they are joined end to end to form a long tube.Their end walls are perforated with sieve pores to allow cytoplasmic connection between sieve elements and for flow of liquid.They are living cells with thin cellulose cell wall (not lignified) and protoplasm.It has few mitochondria to allow smooth flow of food.However,it has no nucleus ,ribosomes and golgi apparatus that have degenerate.Its metabolic need is supplied by the companion cells.

Companion cell: they can only be found in angiosperms.They are closely related to the sieve elements.Theyb have a nucleus , small vacuoles, cytoplasm, ribosomes and many mitochondrias.

They move sugars and amino acids through plasmodesmata to the sieve elements.

Phloem fibre : They are meant only for providing mechanical support.They are the only dead phloem tissues.

Phloem Parenchyma : They are packaging tissues.They are meant only for storage of organic foods.