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26-04-2003, 01:30 PM

(Phred) wrote in message ...
In article , ose (Sean Houtman) wrote:
From: (Phred)

But if we're talking *dispersal* then that's another matter, and I'm
not sure what help the awns would be in that sense -- except perhaps
mechanical entangling in hair, fur, or feathers. (But I can say that
the seeds of black spear grass [_Heteropogon contortus_] don't need
the *awns* to become painfully embedded in your flesh! The hairs on
the tip of the "seed" seem to do the job quite well enough if they've
got a bit of purchase on something like your socks. And some of the
three-awn spear grasses [_Aristida_ spp.] are worse! )

If you would like to see how awns can help disperse seed without tangling in
fur, get a spike of wheat or barley (use one of the awned varieties of course),
and let it roll across your hand. The awns pretty much make sure that the spike
tends to move in one direction.

Yes, I can remember as a child playing with one of the native grasses
that we called "caterpillar grass" because when you put the
inflorescence (in this case) on you hand and stroked it gently, it
"walked" across your hand.

So I take your point. I guess it's a matter of scale -- I was
thinking of "dispersal" in terms of metres or more rather than
centimetres.

Cheers, Phred.

Hi,
I did quite a lot of work on awns at one time. They have lots of
silicified prickle hairs all pointing up the awn. So they only tend to
move easily in one direction, as your fingers get caught on them.
Emanuel Epstein did some experiments running them down slopes of
cardboard to quantify the effect. Plants grown without Si slid down
much easier! Some of my papers under "publications" on my web site
below (those around 1988/89) concern Si in wheat awns.
Best Wishes,
Martin

Dr Martin J. Hodson,
Principal Lecturer in Environmental Biology,
School of Biological and Molecular Sciences,
Oxford Brookes University,
Gipsy Lane, Headington,
Oxford, OX3 0BP, UK

Tel.: ++44 (0)1865 483954
Fax: ++44 (0)1865 483242
Email:
Web: http://www.hodsons.org/MartinHodson/