Janice M. Glime jmglime at MTU.EDU
Sat Apr 5 11:42:15 EST 1997

Dear David,
  One of my favorite plant experiments we do in lab and comes from Paul
Williams.  Grow some fast plants to the cotyledon stage - takes about 1
week, depending on temperature.  Bring to lecture a plastic film can for
each student, equipped with about 3-4 mm of water, a strip of filter paper
cut to extend from water to almost the top of can and about 1 cm wide or
less, and one fast plant with a straight stem cut to fit crosswise without
touching the other side.  Alternatively, you can hand out the plants
separately - if they are put in the can, it needs to be immediately before
lecture.  Ask students to position the plant above the water with its 2
cotyledons stuck to the filter paper and its stem pointing to the opposite
side.  The wet paper will hold the plant if it hasn't gotten too large.
If it has gotten true leaves that stick out, they will need to pinch those
off.  Then ask them to note the position of the plant and close the lid.
Have the class hypothesize what they will think will happen to the plant,
discuss tropisms or show a film, then check what it has done.  I usually
get a whole list of hypotheses from them, put them on the board, then have
a show of hands for each to indicate how many students think each will be
supported.  Some plants will show results in about 40-45 minutes, but by
the end of the day, results will be good.  Students can keep the
experiment.  It requires somewhat complex thinking because the stem will
bend up (if the cotyledons had not been attached, they would have been on
the end that bent up).  
  Thanks to Paul for introducing us to this.  It makes a great activity
for lecture.
 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 FAX 906-487-3167 

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