Phloem

• What is special about sieve tube elements?

  They have no nucleus, and the tonoplast and many organelles break down, leaving them full of phloem sap with only a thin layer of cytoplasm
• What are sieve plates?

  Holes in the end cell walls of sieve tube elements which let the phloem's contents through
• What do companion cells do?

  Add support to sieve tube elements and also carry out living functions, such as producing ATP, for them
• What is a sclereid?

  A tissue associated with phloem which has cells with very thick cell walls
• What tissues are associated with phloem tissues?

  Fibres and sclereids
• What links sieve tube elements and companion cells?

  Many plasmodesmata (microscopic holes in the cell wall)