G'day Sean,

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

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.


I wouldn't be at all surprised if this is the case in wetter climes. Here in
New Mexico the Stipas do have a number of turns on the awn, but the seeds are
dispersed during the dryest time of year and a rotational drilling caused by
moisture isn't going to happen very often.

Ah, different perspectives! Now *I* almost mentioned that I thought
this "self planting" mechanism was developed here in grasses
especially adapted to our seasonally dry tropics with a view to
burying the seed as soon as the first storm of the new season arrived.

Of course, it could happen earlier with out of season rains (or even,
in much of the dry tropics, with heavy dews) and the seed would be
prevented from premature germination in such cases through one
or another of the usual dormancy mechanisms.

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! )


Cheers, Phred.

--
LID

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.

--
LID

(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/

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

From: (Phred)

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.


I wouldn't be at all surprised if this is the case in wetter climes. Here in
New Mexico the Stipas do have a number of turns on the awn, but the seeds are
dispersed during the dryest time of year and a rotational drilling caused by
moisture isn't going to happen very often.

Sean



--
Visit my photolog page; http://members.aol.com/grommit383/myhomepage
Last updated 08-04-02 with 15 pictures of the Aztec Ruins.
Address mungled. To email, please spite my face.

G'day Sean,

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

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.


I wouldn't be at all surprised if this is the case in wetter climes. Here in
New Mexico the Stipas do have a number of turns on the awn, but the seeds are
dispersed during the dryest time of year and a rotational drilling caused by
moisture isn't going to happen very often.

Ah, different perspectives! Now *I* almost mentioned that I thought
this "self planting" mechanism was developed here in grasses
especially adapted to our seasonally dry tropics with a view to
burying the seed as soon as the first storm of the new season arrived.

Of course, it could happen earlier with out of season rains (or even,
in much of the dry tropics, with heavy dews) and the seed would be
prevented from premature germination in such cases through one
or another of the usual dormancy mechanisms.

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! )


Cheers, Phred.

--
LID

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.

Sean



--
Visit my photolog page; http://members.aol.com/grommit383/myhomepage
Last updated 08-04-02 with 15 pictures of the Aztec Ruins.
Address mungled. To email, please spite my face.

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.

--
LID

(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/