Micrasterias crux melitensis, a Desmid from a ditch

[WalterD]

If there will ever be a beauty contest for Desmids, like "Miss (or Mister) Micrasterias", the beautiful Micrasterias crux melitensis is surely one of my favourites.
This post is actually showing 2 different specimen, the only ones I found in my samples. The sample this time did not come from a fen, but from a very healthy ditch. The type where you are welcomed by a choir of frogs croaking in all kinds of tones. The water samples I found were extremely rich with all kinds of lifeforms, however not too may desmids. I've been told that the crux melitensis is not extremely rare, on the other hand it no longer appears in any southern Dutch fen, only in specific swampy areas in the northern part of our country -the sample location-, where a significant amount of species went extinct the past decades. Desmids are excellent indicators for the biological quality of a water.
The first 3 images were made with a 40x DIC (differential interference contrast) objective, utilizing colour-DIC (adding a lambda plate in the light path). By adjusting the analyzer angle differences in thickness are actually translated into colours.I think the one with the yellow background shows the most details from the 3.





Photo 4 and 5 were done with the 100x(0.6/1.2) iris objective I also used in my previous post, respectively bright- and darkfield . With double oil immersion, specimen diameter approximately 120 micrometer.






...and I also found the Closterium Ehrenbergii in the samples...Will post images of that one maybe another time.

Thanks for looking

[Marek Mis]

Nice images ! I like the most the third one.

I love Desmids, too ! In my region of Poland (Suwalszczyzna), especially in my neighbourhood, not so far from my house (about 2 - 3 km), you can find the extraordinary small lakes settled in the middle of the Pinus and Picea trees forests. There are a lot of Sphagnum there and it is the best place for Desmids sampling. I usually find many interesting species but never found M. crux melitensis, at least until now.

Thank you for very detailed description of your finding.

Marek

[carlos.uruguay]

Very nice!!

[fpelectronica]

Nice

[Smokedaddy]

Excellent Walter. Being new to all this I wasn't aware you could add a lambda plate nor adjust the analyzer angle on any scope. <ref-faced> I wonder if that can be done on my PZO DIC?

[Pau]

I wonder if that can be done on my PZO DIC?

Sure!
There are two (compatible) usual ways:
- put compensators (wave plates) at any place between the polarizer and the analyzer (usually under the condenser or at the microscope head)
- set the DIC analyzer prism towards one its extreme positions, what people call color contrast DIC

Maybe with the PZO there could be any other specific position

[Smokedaddy]

Thanks Pau!

[WalterD]

Thank you.

@Marek,
Quote>
I love Desmids, too !
<Unquote
so I'm not the only one. You must be lucky to live in such a beautiful area, lots of things to see and discover. For this sample it was a one and a half hour drive though. I hope to find different Micrasterias in other locations, soon.

@ Smokedaddy :
Quote>
Being new to all this I wasn't aware you could add a lambda plate nor adjust the analyzer angle on any scope. I wonder if that can be done on my PZO DIC?
<Unquote
The polarizer and analyzer ar a part of the differential interference contrast light path, so I expect them to be be in your setup as well. When the analyzer has been located, you should be able to see differences in contrast/tone/backgound when rotating it. What we call the DIC effect can be observed when polarizer and analyzer are almost crossed, in 90 degrees position. Without the lambda plate the effect resembles of darkfield, with an almost black background. Usually I remain in the 10 to twelve- 10 past twelve angle. Leitz has integrated the analyzer in the condenser and added 90 degrees scale lines to make it easier for orientation. In the 0 or 180 degrees angle there's no significant DIC effect, image is like brightfield.
The colour DIC images were made within that same (90 deg.) angle, the one with the purple background was closest to crossed position. In my condensor the lambda (wave) plate has also been integrated, this one can be added to the light path with one single movement. Like Pau mentions, in theory this should also work with your setup. To be honest as 9 out of 10 DIC setups don't utilize a wave plate I was wondering whether this observation method is that common, or easy to arrange in any setup. As said in my setup all these positions are fixed, I don't know how critical the position of analyzer, polarizer or wave plate could be in other setups. Hope this helps.

Regards

Walter

[Jacek]

WalterD Beautiful photos

Smokedaddy you can. You take off the polarizer. Lay the polarizer on the light port. You set the desired contrast and the polarizer arranges the lambda plate

[Smokedaddy]

Thanks ... I don't want to pirate this thread from Walters excellent images for my lack of knowledge.