phloem

• phloem

  = living tissue that transports food in the form of organic solutes around the plant from the leaves

  • materials can go in both directions.
• sieve tube elements

  = made up of many cells joined end to end to form a long, hollow structure.

  -tubes are not lignified

  -in areas between cells, walls become perforated to form sieve plates which let the phloem contents flow through.

  -as large pores in cell walls appear, the tonoplast and nucleus breaks down- the phloem becomes a tube filled with phloem sap.
• companion cells

  = linked to sieve tubes by plasmodesmata- maintain their nucleus, very active cells, many mitochondria

  -contains fibres, sclerids cells with thick cell walls