Infinite Fluorescence

[micro_pix]

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David, incredible stacks ! Any chance for the stereo ?

I had a go!

[rjlittlefield]

That looks pretty good!

The bright yellow sporangium just below-left of center shows a prominent disparity, much darker in the left-side view. That might be easily retouched from corresponding Stack Selected output(s) of just the front parts, done with the same stereo settings.

Just right of center is a darker tan sporangium that also shows disparity that I think is an artifact. Again I would try retouching from corresponding Stack Selected output(s).

--Rik

[micro_pix]

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Thanks Rik, I've had a go at those bits, I should have seen them the first time. It's still not glitch free but it looks better.

David

[iconoclastica]

I’m pretty sure that it is filix-mas.

I agree.

[Saul]

...I had a go...

David, EXCELLENT !!! It is good kick for me to finish my UV system !

[viktor j nilsson]

...I had a go...

David, EXCELLENT !!! It is good kick for me to finish my UV system !

Yes, please do! Did you see my question for you in the following thread? https://www.photomacrography.net/forum/ ... 4&start=15

[micro_pix]

Did you make a preparation on a slide? If the sporangia are in water, they will not open. If it is filix-mas, it's still a bit early for them to shed the spores, although it won't be long now.

I thought I'd have a look at the spores so I left some mature sporangia on a slide for a while. Here's on open sporangia - and a spore in brightfield and under UV. The single spore photo was taken with a Leitz 63x fluoreszenz oil objective.

David.

Male Fern - Dryopteris filix-mas opening sporangia.


Male Fern Dryopteris filix-mas spore - in brightfield and UV

[rjlittlefield]

The new images are lovely also.

I think the mechanism is very interesting, by which spores are ejected from these sporangia when they open.

There is a good explanation with illustration in the video at https://www.youtube.com/watch?v=mDlHGrRlNPE .

One aspect of the video may prompt confusion. Starting at around 1:50, the video speaks of "negative pressure", which may reach as large as -100 to -200 atmospheres. In a system that is essentially surrounded by air at 1 atm, what does "negative pressure" even mean, and how can such large negative pressures be achieved?

After struggling with this concept for some time, I wrote to a colleague as follows:

The phrase “negative 200 atm" definitely raises a warning flag, but after researching the issue I think it is correct. Google search on cavitation water pressure quickly turned up a paper by E.Herbert from 2006 whose abstract says

The cavitation pressure is found to increase monotonically from -26 MPa at 0C to -17 MPa at 80C. While these values lie among the most negative pressures reported in water, they are still far away from the cavitation pressure expected theoretically and reached in the experiment by Angell and his group [Zheng et al., Science 254, 829 (1991)] (around -120 MPa at 40C).

Noting that Wikipedia says 1 standard atmosphere is 101.325 kPa, a quick calculation shows that E.Herbert is reporting negative 168 to negative 257 atmospheres, with Zheng et.al. reporting close to negative 1180.

This is the first time that I've looked closely at cavitation, as opposed to boiling under reduced pressure. I gather that there's a key difference between boiling into a cavity that already exists, and creating a cavity where one did not exist before. To create the cavity in the first place is apparently a lot harder.

Searching on tensile strength of a liquid finds a web page titled "Tensile Strength of Liquids", which contains this description:

The tensile strength of water has been subject to measurement for over 150 years. Not unexpectedly, it turns out that it has an important consequence in nature: the height of trees is determined by the fact that water can sustain a tensile strength. Was this not the case, trees would not exceed about 10 m in height. The tensile strength also plays a role in dispersal of spores of certain ferns.

With this insight in hand, I now think of the sporangia as pulling on the contained water until the water breaks (forms a cavity), at which point the water quickly boils into the cavity until its internal pressure matches vapor pressure, at which point the whole process comes to a sudden stop and the spores fling out.

and again,

As I understand it, the wall of the sporangium is a sort of osmotic membrane that allows water molecules to slowly get out and evaporate, but does not allow bulk gas of any sort to get back in and initiate bubble formation.

So again, the mechanism is to fill the cavity with suitably clean water, then let the water evaporate through the membrane. As the water evaporates and the cavity shrinks, the sides get pulled in by adhesion to the water. At the same time, the water gets stretched harder and harder, until finally the stretching force on the water is enough to make it "break" and form a bubble, which promptly expands to relax the tension.

Google search on sporangium evaporation cavitation turns up a bunch more references. The one at http://rsif.royalsocietypublishing.org/ ... 4/20150930 , by the same authors as the film, says that

Our analysis of the trigger mechanism by cavitation points to a critical cavitation pressure of approximately -100 ± 14 bar, a value that matches the most negative pressures recorded in the xylem of plants.

The paper describes their experimental results and the underlying mechanisms in what I found to be a fairly readable style.

I hope this helps. Please let me know if I have gotten any of this wrong.

--Rik

[micro_pix]

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Thanks Rik, that’s fascinating stuff, something I hadn’t been aware of and explains the need for the obvious strength of the annulus structure. I just found this article as well, which covers the different water-based shooting mechanisms used by plants and fungi.

https://journals.plos.org/plosone/artic ... ne.0158277

David

[Marek Mis]

Very impressive images ! The BF ones look great as well !

Could you show your set. I use Olympus BH-2 too and I think to start somewhen fluorescence. I have no experience in fluorescence so every tip is very appreciated.

Marek

[micro_pix]

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Thanks Marek.

I certainly no expert, I’ve only just started with fluorescence microscopy, I had familiarised myself with other techniques and their associated accessories used on the BH2 but was a bit slow to look at fluorescence, even though the first BH2 I bought had a bare RFL fluorescence attachment.
I’ll take a couple of photos and put something in the equipment discussions section.

David

[Marek Mis]

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Thanks Marek.

I certainly no expert, I’ve only just started with fluorescence microscopy, I had familiarised myself with other techniques and their associated accessories used on the BH2 but was a bit slow to look at fluorescence, even though the first BH2 I bought had a bare RFL fluorescence attachment.
I’ll take a couple of photos and put something in the equipment discussions section.

David

OK, thank you !

[micro_pix]

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Hi Marek, I posted it here

https://www.photomacrography.net/forum/ ... 815#263815


David

[Robert Berdan]

Beautiful images thanks for sharing.
RB

[micro_pix]

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Thanks Robert.