There was a researcher in Canada in the late eighties who said
that plants gave off ultrasonic sounds when they were running low on
water.  The Radio Canada interview about this topic made some humorous
statements about the plants crying out because of their thirst, but
the serious theory was that the sounds had to do with the mechanics of
fluid flow in the plant's capillaries.  The researcher at the time was
using a Commodore C64 as the controller for the experiment and the
sounds that it emitted when the plant was out of water were computer
generated using the C64's sound chip.

        I heard all of this over 10 years ago so I have forgotten the
details, but if there is anything to the ultrasonic theory, this might
be a thought.

        I smile with sick glee as I think of the millions of weeds in
our yard which will be howling their little selves to death in July
and August during the dry time.  Oh!  the botany!

Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Data Communications Group