Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Lycopodium powder, was Chladni's Figures



An officer of the NCN section of the AAPT at the show and tell yesterday
projected a video in which he used lycop. for his demo. of a "grain dust
explosion." He said he found it "better" than flour, corn starch, etc.

bc

P.s. I'd thought it was fungus spores; tanks for correction. BTW, I thought
every Phys. demo. room had Chladni plates of various shapes (metal tho) and a
violin bow.

Brian Whatcott wrote:

At 09:10 AM 10/28/01 -0800, Kay Lancaster wrote:
On Sun, 28 Oct 2001, brian whatcott wrote:

I read about Chladni's figures (1787) when I was a kid.
A glass square is supported from the center on a stand,
and lycopodium powder - whatever that is - is sprinkled
over it,

Lycopodium powder is actually the spores (vegetative propagules) of
various species of Lycopodium, "clubmosses" vaguely related to ferns.
especially the spores of Lycopodium clavatum, aka "running
groundpine". A pressed plant is shown at:
<http://www.portableherbarium.com/Lycopodium-clavatum.jpg> (the spores
are in the golden structures to the upper right of this herbarium
specimen -- they're the fine dust you can sort of see surrounding
these "cones" (strobili).)

The spores themselves are quite small, about 25-28um and look like
this (SEM toward the bottom of the page) :
<http://www.botany.hawaii.edu/faculty/webb/BOT311/LycoRepro/LycoRepro1.htm>

They're also the source of the Victorian's "flash powder" and one used
for theatrical effects -- they have a high oil concentration, so they
do a very nice "grain dust explosion" -- they're also quite liable to
provoke asthma, which is probably a good reason not to use them
regularly in a science museum setting where dust can blow.

They're still collected now, and used by palynologists (pollen
specialists) to help determine pollen concentrations in a sample.
http://www.ualberta.ca/~abeaudoi/cap/supply.htm

Kay Lancaster kay@fern.com (stray botanist)

Now was that an illuminating response, or what?
Take a look at that specialist vocabulary for instance,
Reader's Digest could not compete: dehiscent sporules,
adventitious roots, even biflagellate sperm.
[Why should *they* have two tails, while the domestic kind
can only sport one?]
I have been telling people for years and years that the organic machinery for
reproduction is the most highly conserved structure - one slip and there
goes the family tree! - and here you are with a counter-example:
it only takes one.

Brian Whatcott