unequal growth

Kathleen Archer Kathleen.Archer at trincoll.edu
Tue Oct 13 07:35:20 EST 1998

Dear Colleagues,
I received a number of responses to my request for a good physical
demonstration of unequal growth causing bending to one side.  Thanks,
everyone!  I summarize the responses to date:

1.  Many, many suggestions to use the stomatal opening demo with a balloon
that has tape on one side.  I like that demo very much, but I have to say
that  most of the time I can't get it to work.  The balloon breaks or the
paired balloons don't bend sufficiently.  I guess I don't know how to
assemble my balloon/tape properly, or maybe I'm not using the right kind of
balloon or tape.

2. Cyndy Gallo's idea:  "What I do is ask my students which way would they
bend if one leg grew longer than the other.  You can even have someone
stand with one leg on a book or small box to see that they would bend away
from the long leg and toward the short one."  I like this idea a lot; it's
physical and it involves a student directly in the demo.  You could even
get the whole class to stand up.  That's active learning!

3.  A couple of ideas on showing twining, either by bringing in vines or by
showing a clip from Private Life of Plants.  I'm actually going to show
that clip - it's fabulous! - but wanted to explain what was happening at
the cellular level. 

4.  A different take on the balloon idea:  "The most simple illustration of
stomatal opening was with rubber tubing. An extra thickness is cemented to
only one side of a six inch lenth and allowed to cure. One end is plugged
with a stopper and secured with strong cord. The other end is plugged with
a one hole stopper attached to a blood pressure cuff. The thinner side
stretches and caused the "pumped up" length to curve. Perhaps the side
that' stretches could show more growth?" --David Brown

5. Here's a neat idea: "My first thought is to pull out the old slinky and
put wedges between the rings to tilt it one way or another."  Scott T.

6. "How about using flexible straws? Cheap, and everyone can bend one and
see the unequal expansion." Sue Schenk

Thanks again to everyone who responded,
Kath Archer

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