plant stems

• aim


  To identify sclerenchyma fibres, phloem sieve tubes and xylem vessels and their location within stems through a light microscope.
• method

  1. pick out 2 vascular bundles from a small piece of tinned rhubarb and place them on a microscope slide
  2. Use mounted needles to tease the vascular bundles apart. Cover the tissue with a drop of methylene blue, and leave for 5 minutes.
  3. Draw off the extra stain with filter paper. Place a drop of dilute glycerol on the fibres and mount under a coverslip.
• method continued

  • Examine your preparation under low, medium and high magnification. 
  • Look for vascular bundles amongst the separated tissues.
• observations

  • The xylem vessels are empty, elongated tube-like cells; they may show different types of wall thickening.
  • Phloem sieve tube elements are also elongated; they lack a nucleus even though the cells are alive with some cell cytoplasm. There are sieve plates with pores between adjacent cells. Each sieve tube element is associated with a companion cell.