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Jonathan Drori: Every pollen grain has a story
Poziom:
Temat: Społeczeństwo i nauki społeczne
Thank you. I have two missions here today.
The first is to tell you something about pollen, I hope,
and to convince you that it's more than just something that gets up your nose.
And, secondly, to convince you
that every home really ought to have a scanning electron microscope.
(Laughter)
Pollen is a flower's way of making more flowers.
It carries male sex cells
from one flower to another.
This gives us genetic diversity,
or at least it gives the plants genetic diversity.
And it's really rather better not to mate with yourself.
That's probably true of humans as well, mostly.
Pollen is produced by the anthers of flowers.
Each anther can carry up to 100,000 grains of pollen.
So, it's quite prolific stuff.
And it isn't just bright flowers
that have pollen; it's also trees and grasses.
And remember that all our cereal crops are grasses as well.
Here is a scanning electron micrograph of a grain of pollen.
The little hole in the middle we'll come to a bit later.
But that's for the pollen tube
to come out later on; a very tiny tube.
So, that is 20 micrometers across,
that pollen grain there.
That's about a 50th of a millimeter.
But not all pollen is quite so simple looking.
This is Morina. This is a plant
which I've always thought to be rather tedious,
named after Morin,
who was an enterprising French gardener,
who issued the first seed catalog, actually,
in 1621.
But anyway, take a look at its pollen.
This is amazing, I think.
That little hole in the middle there is for the pollen tube.
And when the pollen finds its special female spot
in another Morina flower,
just on the right species, what happens?
Like I said, pollen carries the male sex cells.
If you actually didn't realize that plants have sex,
they have rampant, promiscuous
and really quite interesting and curious sex, really.
(Laughter)
My story is actually not about plant propagation,
but about pollen itself.
So, what are pollen's properties, I hear you ask?
First of all, pollen is tiny. Yes we know that.
It's also very biologically active,
as anyone with hay fever will understand.
Now, pollen from plants which are wind-dispersed,
like trees and grasses and so on,
tend to cause the most hay fever.
And the reason for that is, they've got to chuck out
masses and masses of pollen to have any chance
of the pollen reaching another plant of the same species.
Here are some examples.
They're very smooth if you look at these pictures
of tree pollen that is meant to be carried by the wind.
Again, this time, sycamore, wind-dispersed.
So, trees, very boring flowers,
not really trying to attract insects.
Cool pollen though.
This one I particularly like.
This is the Monterey Pine, which has little air sacks
to make the pollen carry even further.
Remember, that thing is just about 30 micrometers across.
Now, it's much more efficient if you can get insects to do your bidding.
This is a bee's leg,
with the pollen glommed onto it from a mallow plant.
And this is the outrageous and beautiful
flower of the mangrove palm.
Very showy, to attract lots of insects to do its bidding.
The pollen has little barbs on it,
if we look.
Now, those little barbs
obviously stick to the insects well,
but there is something else that we can tell from this photograph,
and that is that you might be able to see a fracture line
across what would be the equator of this, if it was the Earth.
That tells me that it's actually been fossilized, this pollen.
And I'm rather proud to say
that this was found just near London, and that 55 million years ago
London was full of mangrove palms.
Isn't that cool?
(Laughter)
Okay, so this is another species evolved to be dispersed by insects.
You can tell that from the little barbs on there.
All these pictures were taken with a scanning electron microscope
actually in the lab at Kew Laboratories.
No coincidence that these were taken
by Rob Kessler, who is an artist.
And I think it's no coincidence that someone with a design and an artistic eye
like him that has managed to bring out the best in pollen.
(Laughter)
Now, all this diversity,
means that actually you can look at a pollen grain
and tell what species it came from.
And that's actually quite handy if you
maybe have a sample and you want to see where it came from.
So, different species of plants
grow in different places.
and some pollen carries further than others.
So, if you have a pollen sample
then, in principle, you should be able to tell
where that sample came from.
And this is where it gets interesting for forensics.
Pollen is tiny. It gets on to things, and it sticks to them.
So, not only does each type of pollen look different,
but each habitat has a different combination of plants,
a different pollen signature, if you like,
or a different pollen fingerprint.
By looking at the proportions and combinations
of different kinds of pollen in a sample,
you can tell very precisely where it came from.
This is some pollen embedded in a cotton shirt,
similar to the one that I'm wearing now.
Now, much of the pollen will still be there
after repeated washings.
Where has it been?
Four very different habitats might look similar
but they've got very different pollen signatures.
Actually this one was particularly easy. These pictures were all taken
in different countries.
But pollen forensics can be very subtle.
It's being used now to track
where counterfeit drugs have been made,
where banknotes have come from,
to look at the provenance of antiques
and see that they really did come from the place
the seller said they did.
And murder suspects have been tracked
using their clothing,
certainly in the U.K., to within an area
that's small enough that you can send in tracker dogs
to find the murder victim.
So, you can tell from a piece of clothing
to within about a kilometer or so,
where that piece of clothing has been recently,
and then send in dogs.
And finally, in a rather grizzly way,
the Bosnia war crimes.
Some of the people brought to trial were brought to trial
because of the evidence from pollen,
which showed that bodies had been buried,
exhumed, and then reburied somewhere else.
I hope I've opened your eyes,
if you'll excuse the visual pun,
to some of pollen's secrets.
This is Horse Chestnut, by the way.
There is an invisible beauty all around us,
each grain with a story to tell,
each of us, in fact, with a story to tell,
from the pollen fingerprint that's upon us.
Thank you to the colleagues at Kew.
And thank you to palynologists everywhere.
(Applause)
