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I had a go!Saul wrote:David, incredible stacks ! Any chance for the stereo ?
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Yes, please do! Did you see my question for you in the following thread? https://www.photomacrography.net/forum/ ... 4&start=15Saul wrote:David, EXCELLENT !!! It is good kick for me to finish my UV system !micro_pix wrote:...I had a go...
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.iconoclastica wrote:
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.
and again,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 saysNoting 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.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).
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: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.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.
I hope this helps. Please let me know if I have gotten any of this wrong.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 thatThe paper describes their experimental results and the underlying mechanisms in what I found to be a fairly readable style.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.
OK, thank you !micro_pix wrote:.
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