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This has puzzled me for a while.
If you're trying to identify a particular plant, often the most
diagnostic feature is the leaf shape. And that's because plants have a
dazzling array of leaf shapes. For example,
http://upload.wikimedia.org/wikipedia/commons/e/e8/Leaf_morphology.svg
The fact that humans even needed to invent this many words to describe
leaf shapes tells you that there's a hell of a lot of leaf shapes out there.
This is puzzling because leaves all do the exact same job. (Well, the
leaves that haven't been turned into petals or insulation or fly traps
or some other specialised structure, anyway.) Given that all leaves
perform the same task, you would expect convergent evolution to result
in identical leaves. But this hasn't happened. Quite the opposite, in fact.
In particular, the purpose of leaves is to absorb as much sunlight as
possible. Given that task, you would /expect/ leaves to evolve to be
huge flat sheets. You would /not/ expect leaves to evolve holes and cuts
in them. You certainly wouldn't expect to see long, thin, pointy leaves
which hardly soak up any light at all.
But plants of course are not designed by human thinking. They are
designed by a far more reliable process: trial and error. The vast
number of plants with weird shaped leaves demonstrates beyond question
that this /works/, and that it provides some sort of advantage. But... what?
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On 21-5-2012 12:51, Invisible wrote:
> In particular, the purpose of leaves is to absorb as much sunlight as
> possible. Given that task, you would /expect/ leaves to evolve to be
> huge flat sheets.
Huge flat sheets would mean that only the outher layers get sunlight.
Inner branches might just as well commit suicide immediately.
--
tip: do not run in an unknown place when it is too dark to see the
floor, unless you prefer to not use uppercase.
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andrel <byt### [at] gmail com> wrote:
> On 21-5-2012 12:51, Invisible wrote:
> > In particular, the purpose of leaves is to absorb as much sunlight as
> > possible. Given that task, you would /expect/ leaves to evolve to be
> > huge flat sheets.
> Huge flat sheets would mean that only the outher layers get sunlight.
> Inner branches might just as well commit suicide immediately.
From an evolutionary point of view, trees are the result of an
evolutionary arms race.
Tree trunks are basically a huge waste or resources. A tree doesn't
benefit much from an enormous trunk of wood; it doesn't serve much
biological purpose. The only reason why trees have such enormous wastes
of resources is to simply get its leaves higher than the competition.
If all the trees in a forest were like 1 meter high, that would be
enough. However, immediately when one of the trees gets a slight mutation
that makes it grow a bit taller than the rest, it gets a survival advantage
while at the same time lessening the survival chances of the other trees
around it (because now the taller tree is blocking the sun for them for
a period of time). One such tree might not do much damage to others, but
when it reproduces and its offspring start shadowing other trees en masse,
those other trees are going to have a hard time getting any sunlight at all.
Thus the tallest of those other tree species are going to get naturally
selected from among their shorter brethren, and so on. Thus we end up with
gigantic trees which may reach even 100 meters.
Dense forests with tall trees tend to be relatively barren of other
plant life, save for plants that survive on low light conditions. Something
like this: http://i304.photobucket.com/albums/nn198/toshi0723/CIMG1966.jpg
(Compare to something like
http://en.wikipedia.org/wiki/File:Hokkaido,_Sarobetsu_Plain.jpg )
--
- Warp
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>> In particular, the purpose of leaves is to absorb as much sunlight as
>> possible. Given that task, you would /expect/ leaves to evolve to be
>> huge flat sheets.
>
> Huge flat sheets would mean that only the outher layers get sunlight.
> Inner branches might just as well commit suicide immediately.
Exhibit A:
http://momsrecipes.nielsonpi.com/images113/Rhubarb3.jpg
Exhibit B:
http://i.pbase.com/u38/kayakbiker/upload/31926440.BananaLeafUnbrella.jpg
Exhibit C:
http://www.vagabondjourney.com/2008-1/08-2208-large-leaf-costa-rica.jpg
Clearly big leaves are not a suicidal adaptation...
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On 21/05/2012 10:23 PM, Warp wrote:
> From an evolutionary point of view, trees are the result of an
> evolutionary arms race.
>
> Tree trunks are basically a huge waste or resources. A tree doesn't
> benefit much from an enormous trunk of wood; it doesn't serve much
> biological purpose. The only reason why trees have such enormous wastes
> of resources is to simply get its leaves higher than the competition.
Well, I guess that's true enough.
Still doesn't explain why every type of tree has completely different
leaves. Nor why it grows thousands of tiny ones rather than several big
ones. (Although, I guess it means you can replace the damaged ones faster?)
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>> In particular, the purpose of leaves is to absorb as much sunlight as
>> possible. Given that task, you would /expect/ leaves to evolve to be
>> huge flat sheets.
>
> Huge flat sheets would mean that only the outher layers get sunlight.
> Inner branches might just as well commit suicide immediately.
Huge flat sheets are not a good design for several reasons:
1) Which orientation would you align these huge leaves towards? Or you
mean to arrange them like a balloon covering all directions with a
hollow inside? In both cases your tree is going to be a huge sail and
get uprooted very easily in strong winds.
2) They would need to be much thicker (and heavier) than lots of smaller
leaves in order to keep their shape, and thus the branches supporting
them would need to be much thicker (and heavier). As warp already
mentioned, other trees would then be able to get higher with more
efficient designs (thinner branches and more smaller leaves) and at
least partially block your sunlight.
3) Leaves fail all the time, they get eaten, blown off, snapped off etc.
If you've only got a few large sheets then there isn't much redundancy
in the system, your tree will likely die if just 1 or 2 leaves get broken.
4) With lots of small leaves it is easy for the tree to adjust to
maximise the sunlight, it can let a few leaves die that are in shade and
grow news ones to take advantage of extra light very quickly. With a
small number of huge leaves that is not so easy.
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On 22-5-2012 10:02, Invisible wrote:
>>> In particular, the purpose of leaves is to absorb as much sunlight as
>>> possible. Given that task, you would /expect/ leaves to evolve to be
>>> huge flat sheets.
>>
>> Huge flat sheets would mean that only the outher layers get sunlight.
>> Inner branches might just as well commit suicide immediately.
>
> Exhibit A:
> http://momsrecipes.nielsonpi.com/images113/Rhubarb3.jpg
>
> Exhibit B:
> http://i.pbase.com/u38/kayakbiker/upload/31926440.BananaLeafUnbrella.jpg
>
> Exhibit C:
> http://www.vagabondjourney.com/2008-1/08-2208-large-leaf-costa-rica.jpg
>
> Clearly big leaves are not a suicidal adaptation...
Did you notice the branches on the inside with the large leaves? Me
neither.
--
tip: do not run in an unknown place when it is too dark to see the
floor, unless you prefer to not use uppercase.
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Le 22/05/2012 10:07, scott a écrit :
> 3) Leaves fail all the time, they get eaten, blown off, snapped off etc.
> If you've only got a few large sheets then there isn't much redundancy
> in the system, your tree will likely die if just 1 or 2 leaves get broken.
hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
the root). This greatly reduces the impact of being eaten.
(the branch is edible for human, stay away from leaf & root!).
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> hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
> the root). This greatly reduces the impact of being eaten.
>
> (the branch is edible for human, stay away from leaf& root!).
Good to know!
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Le_Forgeron <lef### [at] freefr> wrote:
> hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
> the root). This greatly reduces the impact of being eaten.
>
> (the branch is edible for human, stay away from leaf & root!).
More than edible, it's downright tasty!
:D
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On 22/05/2012 2:31 PM, Bill Pragnell wrote:
> Le_Forgeron<lef### [at] freefr> wrote:
>> hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
>> the root). This greatly reduces the impact of being eaten.
>>
>> (the branch is edible for human, stay away from leaf& root!).
>
> More than edible, it's downright tasty!
> :D
>
Raw, dipped in a poke of sugar. Yum yum.
--
Regards
Stephen
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Invisible <voi### [at] devnull> wrote:
> Still doesn't explain why every type of tree has completely different
> leaves. Nor why it grows thousands of tiny ones rather than several big
> ones.
Wind is probably a huge factor.
--
- Warp
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On 22-5-2012 14:38, Le_Forgeron wrote:
> Le 22/05/2012 10:07, scott a écrit :
>
>> 3) Leaves fail all the time, they get eaten, blown off, snapped off etc.
>> If you've only got a few large sheets then there isn't much redundancy
>> in the system, your tree will likely die if just 1 or 2 leaves get broken.
>
> hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
> the root). This greatly reduces the impact of being eaten.
>
> (the branch is edible for human, stay away from leaf& root!).
I beg to differ. Rhubarb is not edible at all. (it is in fact the only
vegetable that is eaten only by others)
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On 22/05/2012 03:56 PM, Warp wrote:
> Invisible<voi### [at] devnull> wrote:
>> Still doesn't explain why every type of tree has completely different
>> leaves. Nor why it grows thousands of tiny ones rather than several big
>> ones.
>
> Wind is probably a huge factor.
OK, yeah, that would explain why you don't want just one giant leaf.
Still not sure why every plant species has to have a completely
different leaf design.
Also, wind might explain why you'd want smaller leaves, but it doesn't
explain why you'd want leaves with wavy edges, or holes through the
middle, or any of the other strange shapes plants grow their leaves.
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On 22/05/2012 09:07 AM, scott wrote:
> 4) With lots of small leaves it is easy for the tree to adjust to
> maximise the sunlight, it can let a few leaves die that are in shade and
> grow news ones to take advantage of extra light very quickly. With a
> small number of huge leaves that is not so easy.
OK. That seems like a good reason for not having just one giant leaf, or
a small number of very large leaves.
Now I just need to figure out why leaves come in such a vast array of
disparate shapes and sizes...
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Stephen <mcavoys_at@aoldotcom> wrote:
> On 22/05/2012 2:31 PM, Bill Pragnell wrote:
> > Le_Forgeron<lef### [at] freefr> wrote:
> >> hint about Rhubarb (Exhibit A from Invisible): the leaf is toxic (as is
> >> the root). This greatly reduces the impact of being eaten.
> >>
> >> (the branch is edible for human, stay away from leaf& root!).
> >
> > More than edible, it's downright tasty!
> > :D
> >
>
> Raw, dipped in a poke of sugar. Yum yum.
Or roasted in honey. Or stewed and beaten into cream. Or baked in a crumble.
Or...
got loads of the stuff at the moment :)
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On 22/05/2012 5:28 PM, Bill Pragnell wrote:
>>
>> Raw, dipped in a poke of sugar. Yum yum.
>
> Or roasted in honey. Or stewed and beaten into cream. Or baked in a crumble.
> Or...
>
> got loads of the stuff at the moment :)
>
Me too but it costs an arm and a leg if you have to buy it. My
grandmother had a patch and every year I made Rhubarb wine. It blew up
once, fibres in the air lock. Messy!
--
Regards
Stephen
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Am 21.05.2012 12:51, schrieb Invisible:
> In particular, the purpose of leaves is to absorb as much sunlight as
> possible. Given that task, you would /expect/ leaves to evolve to be
> huge flat sheets. You would /not/ expect leaves to evolve holes and cuts
> in them. You certainly wouldn't expect to see long, thin, pointy leaves
> which hardly soak up any light at all.
Once again, your expectations suffer from oversimplification.
One other purpose of leaves, for instance, is gas exchange: Somehow the
plant needs to take up carbon dioxide and give off oxygen. "Fractal"
shapes are better suited to this, as they allow for better average
airflow across the surface.
For some plants, the leaves also serve the purpose of collecting water
from dew or rainfall; others use them to store water; yet others protect
the earth from erosion by heavy rain, and some need to manage to cope
with heavy snow.
And then there are secondary design criteria to be met; one of them is
self-defense: Small or "fractal" leaves provide better barriers against
the spread of degenerative diseases; certain structures might make life
more difficult for parasites (e.g. hindering migration from one side of
the leaf to the other), and/or make the respective predators' life easier.
Furthermore, leaves must be lightweight to allow for faster growth of
the plant, yet robust enough to withstand the prevailing wind speeds.
And in extremely hot or cold environments their surface must be limited
for better temperature management.
And I bet I only touched the surface of it.
> But plants of course are not designed by human thinking. They are
> designed by a far more reliable process: trial and error. The vast
> number of plants with weird shaped leaves demonstrates beyond question
> that this /works/, and that it provides some sort of advantage. But...
> what?
See above.
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Also some leaves must be able to survive sub-freezing temperatures while
still carrying on photosynthesis (at least on a low level).
A tree trunk does more than get the leaves above the other plants. It
also gets the leaves up where deer can't eat them.
Regards,
John
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On 5/22/2012 18:35, John VanSickle wrote:
> gets the leaves up where deer can't eat them.
Guess what grows where giraffes live?
http://media.treehugger.com/assets/images/2011/10/acacia-tree-africa.jpg
--
Darren New, San Diego CA, USA (PST)
"Oh no! We're out of code juice!"
"Don't panic. There's beans and filters
in the cabinet."
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