seed speed

[Robin Panza]

>stick where they hit. That would imply a pretty high velocity. I doubt the
>coiled-spring pods of legumes like Lathyrus generate quite 60 mph shots,
>and definitely not pods like Oxalis or Impatiens. But I do wonder how one
>goes about measuring the speed, exactly.

The 60 MPH number reminds me of a wonderful zoological equivalent, the Deer Fly
(yes, I know there are many deer flies), which goes something like 914 MPH.
Adrian Wenner tracked this down and found the origin, someone's published (in a
scientific journal, although I don't remember where) musing on how the
DF appears ("oh, about x yards away") and passes ("not more than a second
later").  Someone responded that, if one uses these figures, it means the fly
travelled 914 MPH, which is ridiculous.  The first author then pointed out
that, rather than belittle the claim, we should be admiring the athletic
ability of this wondrous insect!  Others joined the fray, pointing out the
intense air pressure on the fly's head at that speed, experimenting with a
fly-sized pbject on the end of a string (how long the string x how many
rotations per minute giving the speed of the object), and so on.  Eventually,
people decided not to waste any more time on it, but the figure (914 MPH) had
gotten into the literature and, to this day, you can find graphs of speeds of
animals with the Deer Fly leading the pack at 914 MPH.

It's hard to know whether the 60-MPH cucumber seeds are another such myth or
whether someone did measure their speed somehow.  Perhaps one could set up a
fruit that shot across the field of a still camera.  How far a seed travelled
during the known fraction of a second exposure (e.g., how long a smudge on the
film) could tell you the rate of movement.  Anyone want to test the theory?

Robin Panza                     panzar at clpgh.org
Section of Birds, Carnegie MNH
Pittsburgh  PA  15213  USA