1.
Make a sketch of a shoot, recording internodes, leaves and/or
leaf scars and girdle scars. (Fig 1)
2. Cut thinnish sections from successive internodes
of the shoot, working back from the tip. These do not have
to be of microscopical quality, and can be cut with a Stanley
knife or scalpel, so long as a radius, or preferably a diameter
is relatively thin.
3. Keep each group of sections separate, and stain
them with acidified phloroglucinol. Phloroglucinol stains
lignin red.
 SAFETY
! - Phloroglucinol is harmful and corrosive. Work
cleanly and avoid inhaling the fumes. Gloves should be worn
to protect your hands.
4.
Measure the diameter of the whole stem (y) and of the stained
tissue (a + b). (Fig. 2) Use a microscope if necessary.
5.
Calculate the lignification index of the stem sections at
each point using the following calculation:
Lignification index = [(a + b) divided by y] x 100
6.
Use this technique to find out where lignin is deposited in
other tissues.
Questions
on Secondary thickening.
1.
How could you make a more accurate estimate of the percentage
of lignification?
2. How could you present your data to show the progression
of lignification?
3.
At which point along the twig is lignification first detected?
4.
Compare lignification in trees, shrubs, climbers and herbaceous
plants. Are there significant differences?
5.
Does lignification vary in response to external factors such
as exposure to wind, increased load on a branch etc?
Acknowledgements
to: Dr Barry Meatyard, Institute of Education, University
of Warwick. Artwork by Linda Gray. |
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