Naphthalene wrote:Nice sections, mrsonchus,
and the color inversion indeed adds some contrast!
Is your nick on the forum devoted to the Sonchus plant (I have seen it but I have met its latin name for the first time here)? Is that your favourite one?
Hi Naphthalene and thanks, do you mean my niche? My route to here, the sectioning of Sonchus, has been a very long one... I started with my lifelong love of the Taxonomy of British wildflowers and their exacting identification and comparison.
One of the very first plants I took a very close look at I now know to be a Sonchus... Simply by roving around my garden and paths etc I found a few that were obviously very similar but the questions started to form, starting of course with, 'what is this plant called?'. The close similarities and resultant difficulties with a positive ID between for example the S.asper & S.oleraceus drove me onwards as a mystery!
Now, after a lot of work and a head-long dive into histology and all it's procedures, I'm starting to be able to study plants and their comparative anatomy/morphology in an accurate and exact manner, via histological procedures.
The Sonchus were my natural first choice as they are to me most fascinating. I've gradually been building up (hopefully at least) my expertise with histology and have also used the often-featured (in my posts) Carex.pendula leaf in XS as this is a particularly easy subject for leaf XS, mainly by virtue of it's tendency to 'sit-up' nicely when being orientated in a wax-mould!
Anyway as they say, one thing leads to another and I've since looked closely at various aspects of Sonchus, roots, leaves, stems, flowers (florets) ovaries/ovules (currently being sectioned), pollen etc.
I suppose what I have discovered is that at the ''macroscopic' level of characters observable with the naked-eye or perhaps the 10x magnification offered by for example a hand-loupe, of very similar species (e.g. S.asper/oleraceus) that both exhibit a huge range of morphological variation at that level, leaf morphology, stems etc, are often not completely reliable.
A lot of these factors vary as a consequence of environmental (immediate not global that is) factors which cause changes in the way a plant's form develops and progresses as it goes through it's life cycle/s. For example, a carrot that encounters a stone will ultimately grow to be 'bent', unlike it's neighbour that was lucky enough to miss the stone and grow straight! They are however, when looked at microscopically, clearly of the same species..
But, and it's a big and exciting but, at the microscopic level we start to see characters (apomorphies often) that are constant, being the result of the genetics of the plant, and so are virtually 100% reliable when identifying two species.
This is very evident when for example, as now, looking at the structure of the cypselas of the two Sonchus mentioned above. Hence my recent sections (LS) of the flower-heads of Sonchus. I'm also learning an awful lot about the optimal conditions for a particular structure to show clear and relevant detail - such as section thickness, stain used, section-orientation etc, fascinating!
So I suppose at this time the Sonchus are definitely my favourites and have a huge amount of information still to be discovered, as I am nowhere near the perfection of my technique and intend to re-run the whole of my current procedures with a view to increasing the quality of my observations.
For example a good 15µ section will give a beautiful image of the overall morphology of a complete flower-head and the florets therein, but to glean fine details from perhaps individual cypselas or individual pappus-hairs a much finer (thinner) section is needed, say down to about 4-6µ, with of course the 10-12µ all-rounder sections in between.
So much to study and discover, pure fun!
Oh, not to mention the comparison of their pollen-grains, which I have only recently learned to section successfully!
The different effects, mainly fidelity, given by stains, especially in terms of their individual (and combined of course) characteristics is another whole world of discovery, for example Methylene blue seems to offer splendidly fine detail, whist TBO can in comparison appear to be a rather 'blunt-tool' in this respect... Although this may be a simple consequence of my very limited staining-capabilities at this time.
Sorry to go on so long, I'm just having a great time!
) which resulted in this rather bright image which I find very pleasing and informative - I just wish I could remember exactly what I did to it after the negative-effect 
