Collection location: Planalto das Cezaredas, Portugal [Click for map]
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And if you’re right, then thin sections will work better. With practice my sections are getting better, so maybe that’s why the technique works well for me now, but didn’t before?
with several different lichens and other fungi.
I think you are right when you say: “I guess it’s all about the relative index of refraction of the mounting medium and the sample”. It happens that boiling the water, the presumably thin sample is glued to the glass, reducing its thickness, by extracting all the air ond other floting tissues.
if it was used on other groups of fungi, too. Thanks.
re: heating didn’t work well for you just now — Maybe you count faster than I do? :) I was unimpressed at first, too, but now I find it indispensible.
Mounting specimens in K (or amonia presumably, too) can also improve the internal details of spores, but that can also cause certain tissues to swell. (E.g., some Rinodina spores will swell around the septum in KOH, the so-called Dirinaria-type spores.) Instead, John Sheard suggests using Lugol’s solution to improve clarity without distorting the sample. Of course, this only works on really thin sections, otherwise the iodine turns everything deep violet and you can’t see anything! :) I’ve never tried heating Rinodina spores, and was just wondering the other day if that might work better than iodine.
I guess it’s all about the relative index of refraction of the mounting medium and the sample. KOH must match the index of refraction of most fungal spores better than water. I wonder what heating is doing. Maybe it causes some subtle chemical alteration. Or maybe it drives off air or oil bubbles?
It was a coincidence that I was precisely doing the microscopy of a Caloplaca sp. (C. cerina, I presume), so that I could essay immediately. However, maybe because I didn´t do it correctly, there was not a big improvement in the details like septum and lumina, though the result was better than before. So, I have to try again to get better results.
Thanks for the hint, which is very wellcome, due to the usual difficulties in observing the spores of Caloplaca spp. in particular. It is not the first time I heard about this technique, which is also used to observe the spores of ascomycetes, but I forgot to essay it before.
Here’s a really great trick if you haven’t run into it yet. (Indeed, if you are measuring the width of the spore septum, this is supposedly the Correct Technique™, and only way to guarantee consistent results. You be the judge…)
Mount your apothecium section in water on a slide with a coverslip as usual. Then heat it. I couldn’t find detailed instructions anywhere, so I just played around by trial and error. I’ve settled on holding the flame from a Bic lighter directly under the apothecium section for 5 seconds. (Hold the slide so that it is in the orange part of the flame. More and the water starts to boil away, perhaps doing untold damage to the delicate tissues of the sample, although I’ve never seen any obvious damage.) Just wipe away the black soot and put it under the microscope. You should see the results immediately: the septum and shape of the internal lumina of the spores become much clearer.
Hope that helps!
Created: 2014-05-12 19:09:00 PDT (-0700)
Last modified: 2014-05-12 19:09:09 PDT (-0700)
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