Core Practical 6
Vascular bundles are often enclosed by sclerenchyma fibres that differentiate after the internode has finished elongating. But, there is a layer of cells between the xylem and phloem, in woody plants, this layer of cells later becomes part of the vascular cambium, and produces secondary growth (mcdaniel.edu).
Thick secondary cell walls
Dead at functional maturity
Cannot increase in length - occur in parts of the plant which have quit growing in length
Two types - fibers and sclerids
Fibers - long, slender cells with a more or less regular secondary cell wall
hemp fibers for making rope
Sclerids - shorter cells with an irregular shape
stone cells in pears and hard nut and seed shells
Method (Activity 4.17 Sheet)
1) Place a small piece of tinned rhubarb on a watch glass. Use forceps to pick out one or two vascular bundles from this block of tissue 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.
4) Examine your preparation under low, medium and high magnification. If the tissues are not separated enough you may be able to separate them more by placing your slide on a piece of filter paper and then pressing down with your thumb on the coverslip covered by a filter paper pad. Do not move your coverslip sideways at all. You may need to re-irrigate the slide with glycerol after squashing it. To do this, place a drop of glycerol on the slide next to the coverslip. It will be drawn under the coverslip by capillary action. Blot off any excess and re-examine the slide.
5) Look for xylem vessels amongst the separated tissues. Use Figures 4.49 and 4.50 in the textbook to help you identify these tissues. The xylem vessels may show different types of wall...