My two pennyworth (cents worth?) would be to use seeds of wild oat (Avena
fatua) - Assuming these are available in the US. The awn is hygroscopic and
spraying dry seeds with water from a hand mist sprayer generates an almost
immediate response in which the awn twists and rolls the seed along the
ground. If you do this with a pile of seeds the effect is REALLY dramatic
and elicits responses such as 'Ooh, they're alive!'. This can lead to a
debate on what is 'alive'. Seeds baked in an oven at 150 degrees for a
couple of hours still do this.
I've seen the most disaffected students (plants are boring etc) get really
enthused by this.
A quantitative response to water can be obtained by measuring the rate of
rotation of the awn of a seed stuck vertically in a bit of 'Blutak' sitting
on a piece of filter paper and covered with a glass beaker. Different
volumes of water (drop by drop) can be added to the filter paper in the
vicinity of the seed to create different humidities.
Why do the seeds 'do' it? - If you take a cardboard (shoe) box and stab
some holes in the bottom with a kebab stick, throw in a handful of seeds
and then place the box somewhere where the humidity is likely to change
over a period of a week, the seeds will 'find' the holes and 'plant'
themselves. Amazing.
I have also made a 'weather station' based on a single awn which responds
to humidity. In the UK these are available as little houses with two doors
- one representing sunshine and the other rain. Under dry conditions a
model of a girl in a bikini comes out of the sunshine door and under damp a
guy in a raincoat comes out of the other. Apart from demonstrating
traditional sexist values in UK there is some good science behind this. I
simply substitute the bit of hygroscopic twisted fibre that drives this
with a wild oat seed.
For more ideas see the SAPS website at http://www-saps.plantsci.cam.ac.uk
Beware - in the UK A. fatua is a pernicious agricultural weed of cereal
crops - maily because selective hericides can't differentiate between two
cereals. So the advice we give to schools is not to go spreading it around.
Now a GM crop that enables such differentiation would be a good idea - but
that's another story! (and a matter of hot debate in UK)
Have fun.
Barry
Dr.Barry Meatyard
Science and Plants for Schools
Environmental Sciences Research and Education Unit
Warwick Institute of Education
University of Warwick
Coventry
CV4 7AL
UK
Email: barry.meatyard at warwick.ac.uk
Tel: 44 (0) 2476 524228
Fax: 44 (0) 2476 523237
