Collection location: Sintra, Portugal [Click for map]
When I observed this specimen, growing over rock among moss, doubted about which genus it belonged. The foliose thallus indicated more a Leptogium, but the colour and the size of apothecia seemed to be closer to Collema. Unfortunately the photos were blurred and so I present photographs of exsicatum.
After observed of a section of apothecia and the subsequent observation of the spores, the doubt persisted. Only after a section of the thallus showing a quite rudimentary double pseudocortex (i.e. a pseudocortex in both surfaces) I became convinced that it is a Leptogium. I have recalled all those I observed and nothing came to my mind. After reading the descriptions in the Reference of those species with foliose thallus I come to the conclusion that it must be Leptogium ferax, a rare species that in Portugal is said to exist only in regions surrounding the capital and going a bit to the North (zone called Estremadura). It is considered as a synonym of Collema ferax.
To give the features of this specimen I have used the description of Leptogium ferax in the Reference as a guide and inserted the data observed for this specimen:
- Thallus foliose, small, 2 to 2.5 cm long in the two directions, dark-grey, smooth;
- Lobules rounded, up to 3 mm wide with lobed margins, non-isidiate;
- Thallus section 80-95 µm, paraplectenchymatous;
- Pseudocortex on both surfaces, yellowish;
- Apothecia numerous, up to 1.2 mm in diameter, with persistent thalline exciple, some seeming more or less crenate;
- hymenium hyaline up to 88 μm tall; epithecium yellowish with ~ 12 μm, hypothecium light coloured with ~ 25 μm;~
- Asci cylindrical with 80- 105 × 11-20 μm, 8-spored;
- Ascospores 3-septate to submuriform, most with a longitudinal septum but some with two, with
(20.7) 21.7 – 27.7 (29) x (7) 8.1 – 9.9 (10.6) µm
Q = (2.3) 2.4 – 2.9 (3.3) ; N = 38
Me = 24.6 × 9 µm ; Qe = 2.7;
- Photobiont Nostoc, short chains of cells with 5-6 µm in diameter.
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I make a comment to each of the paragraphs of your message:
Both we want perfection, but from my side it is still a bit faraway. The quality of the sections and their thickness is yet very variable and to transform a good section in something that permit to observe asci, spores, and so on, is even more variable.
Yes, I frequently used that method, but the problem of cleaning the surface appears if we have to press the slide a bit harder to separate the elements we want to analyze (paraphyses, asci or spores, and so on). I frequently use a pencil-eraser to press the slide, which leave some marks difficult to clean without destroying the result achieved by its use. Apart from that, it works well. Sometimes I insert a piece of paper betwen the slide and the eraser.
Rarely I use only water as mounting media, unless some chemical reaction has to be analyzed. I frequently use ammonia instead, because to my experience it provides some viscosity, making the pressing and gliding much more smooth than just with water. The heating is something that I have to explore a bit more, maybe not for sections but for the other elements.
Since last year by this time I have a trinocular microscope with a fixed usb digital camera installed at the upper port, resolution of 1.3 megapixel. Of course, since the resolution is low, there is considerable loss in the quality between what I can see through the objective and the photos I take.
I never have used a microtome. All the sections are made by hand with a razor blade, just like you tought me some years ago. The improvements, if there are any, are consequence of pratice and pratice … (last year I made several section of Graphidaceae, where things like the level of carbonization require thin sections). In that respect the problem is that I didn’t found yet a good material to serve as a base to perform the sections: it cannot be too hard, for not to damage the more delicate material, and it cannot be too soft, to permit a clean section.
I wish I had some clever trick for making sections less diffuse. Especially when taking a photo.
One of the only “tricks” I know, and which you must already know, are to remove excess water from under the coverslip: swiping a tissue firmly from one side to the other and off onto the slide works well, both to remove excess water, and to polish off any fingerprints or dust or other imperfections on the surface of the coverslip.
Also, understand that there are different media in the sample, each with different index of refraction. This is why the “halo” around spores is (barely) visible: even though it is completely clear, it bends light slightly differently, creating a halo effect. You can sometimes help equalize the indices of refraction a bit by mounting things in other media, like KOH, or by gently heating a slide (same technique used for measuring the septum width in Caloplaca: I just hold the slide over a bic lighter flame for ~4 seconds, then wipe of the soot accumulated under the slide). But this doesn’t help thallus sections in my experience. But maybe it’ll give you some clever idea I never thought of(?)
How are you taking the actual photograph? I must resort to the extremely low-tech method of holding a point-and-shoot little camera up to the eyepiece(!) The result is extremely low depth of field. Of course, through a microscope objective you’re always going to have really low depth of field, that’s just the inescapable laws of physics. But it looks a lot clearer to the naked eye than it does “on film”.
But in my previous comment I referred in particular to your perfect sections of completely uniform thickness and clean edges. Are you using a microtome?! I’ve never been able to achieve such perfect results sectioning thalli by hand.
“The former Prince and now his Imperial Majesty King ZACA successfully analyzed and described the exsicatum of the old species COLLEPTOGIUM LEAFY.”
Now, seriously: The slide was good but I didn’t succeed to get enough constrast, resulting in more or less diffuse images. Do you have any trick for that?
You’ve gotten really good at this in just a couple of years. Congratulations on all the hard work and practice. It has really paid off! You clearly have a native talent for this kind of work. :)
Created: 2015-04-26 16:05:21 PDT (-0700)
Last modified: 2015-04-27 02:53:08 PDT (-0700)
Viewed: 78 times, last viewed: 2018-03-23 15:39:37 PDT (-0700)