I used to do an experiment each year with growth substances and Salix twigs to
get students thinking.
Take a metre of willow twig and cut it into 15cm lengths, marking each piece
with an arrow to point to its top. Place the pieces alternately right-end-up,
wrong-end-up on a paper towel with one "end" of the towel marked as the top, so
that half the bits point to the top of the towel and the other half point to the
bottom. Roll the lot up with plenty of towel between the pieces.
Do this three times. Soak one bundle in 200ppm IAA, one in 200ppm GA and one in
distilled water. Wrap each in its own polythene bag and place in a jam jar and
leave for weeks on the lab bench.
Each week or two get them out and have a look to check they are still damp and
to see what's happening.
Eventually, in the distilled water treatment, one gets roots growing from the
bottom of each twig. The twigs "remember" which way they were growing,retain
their polarity and produce their new roots from the end that was "bottom" when
they were growing in the field, so some twigs produce roots only from the end of
the twigs which are now at the top of the jam jar! But how does IAA and GA
affect this? Try it and see! The roots always grow down and the shoots always
grow up (even if they meet and cross in the middle!). The roots and shoots
usually come out of the lenticels. Callus is formed on the cambium at the cut
ends and sometimes along the length of the shoot causing the bark to split etc
This always produces material which is thought-provoking and was good for an
introduction to a course in plant growth substances, which is no longer in our
sylabuses! Pitty really as it is an experiment which takes longer to talk about
than to set up and do!
| Dr. John Hewitson |
| Berrystead Barn +44 (0)1832 272 209 phone/fax |
| Oundle, |
| Peterborough, PE8 4DY, UK e-mail 100600.70 at compuserve.com |