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26-04-2003, 01:30 PM

In article , ose (Sean Houtman) wrote:
From: Judith Baltsar

Hello everybody,
while contemplating on the dispersal types of a great number of plants
(see my other posting) I stumbled over the question what primary
function the awn of poaceae might have. It is often noted that it
might assist in epizoochorous dispersal (attatching the seed to the
fur of some animals) or with strong hygroscopic movements it might
"crawl" on the ground or even drill itself into the soil. But are
these the primary functions or just some nice side effects (kind of
spandrels of San Marco)?

I can verify that in the long awned species of Stipa, it is definitely used in
drilling the seed into the soil. Since the awn is genuflected, it holds the
caryopsis at an angle, and vibration from the wind pushes the seed into the
soil, aided by the hairs on the callus. When the seed has been pushed in far
enough, the awn breaks off and blows away. It is perfectly adapted for this
function. Other grasses certainly use the awns in other ways, not all of them
apparent.

Yeah, lots of tropical grasses with awns use them to "plant
themselves" too -- but it can also be a response to wetness (or just
humidity?). When wetted, they twirl around until stopped by
vegetation or debris or whatever, then the forces involved act to push
the seed itself into the soil.

Cheers, Phred.

--
LID