Marquis & Jennifer Hodes <[EMAIL PROTECTED]> (from the Latin,
meaning: "bayou pediatrician") spaketh thusly:
>Why are we putting charcoal into media in the first place?
"Because it works." No! Really!
>Is it being done to "darken" at the roots, to provide a "more natural"
>environment? (As if there were anything inherently
>"natural" about orchids growing in carbon-and-mineral-supplemented Japanese
>jelly).
>Or are we adding charcoal to act as a reservoir of substances that are
>toxic to orchid roots in high concentration in solution but are exhausted
>before inflask growth is completed - so they leach
>off the charcoal as the local concentration diminishes by incorporation
>into the growing plant?
>Or is charcoal simply, as Aaron implies, "magic" ;^)?
Many theories have been advanced as to why activated charcoal (AC)
works in tissue culture, but there really hasn't been a lot of follow-up.
"Because it works, and it's cheap" generally suffices for the relatively
crude techniques employed by those of us with a fetish to build plants in a
bottle.
Arditti posited that AC removes compounds formed by sucrose during
autoclaving. Many people consider AC to be important in removing phenolics,
which is an entire chapter in itself, but I will address it here very briefly:
1) Most orchids DO produce phenolics _in vitro_.
2) No, most orchids DON'T produce a lot of phenolics _in vitro_.
3) Well, shoot- even if they do, the AC doesn't remove them.
4) Yes, it does!
5) Shut up!
6) Fine!
7) Fine!
It's a deep issue.
My personal theory (which should be open to ridicule based on my
profound ignorance of the subject) goes a little something like this. The
organic compounds found in media are "captured" by the AC, which (on the
microscale) creates a remarkable density gradient. This is to say, on the
very "skin" of the AC particles (and within the particle as well), there
will be a high concentration of "stuff" that someone put in the media for
the plant to eat in the first place. Imagine the AC particle to be like a
child's foam ball. Now imagine it mopping up a soda spill on a countertop.
That sphere is now loaded with sugar (yum!) which can now be extracted if
one has had particular problems with hygienic consumption practices (ew!).
But! The countertop has less mess on it, and the sugary liquid is
sequestered in the Nerf ball.
Now- stay with me here. Orchid media consists largely of salt and
sugar, with the sugars contributing about 80% of the osmotic strength of
the media. Not only do the spheres of AC remove organics to localized
centers, but they reduce the osmotic strength of the media. I think. I've
not yet run the experiments because the %#$!*@&# vapor pressure osmometer I
purchased won't calibrate right. So- my theory is that AC *might* remove
undesirable components, but that's wishful thinking. They're still in
there, and I'm not sure how well they're "removed." A gas mask respirator
(also made of activated charcoal) will slowly release entrapped
contaminants to the user over time, for example. But AC's utility seems to
go much deeper than that. I believe that it either reduces the osmotic
strength while providing nutrient (as above), or that it provides
concentrations of nutrients ("soda") in little bits of AC (the "Nerf
balls") suspended in agar. Then the orchid roots, with their powerful
extraction abilities, can harvest the nutrients by pulling them away from
the AC as needed- diffusion, active transport across the root membrane, and
even through chelation (such as that with caffeic acid- a phenolic). Ho ho.
If someone that knows what they're talking about will tell me to
go urinate up the kernmantle, I'd love to know why the above demonstrates
my profound ignorance of biology, chemistry, plant tissue culture,
activated charcoal, and my questionable parentage.
I'd also like to add that Tom Bell-Gaines contacted me off-list
and let me know that I was wrong in my assumption that huge swaths of
forest in, say, Argentina are being leveled to make sure our Phoenix water
doesn't taste crappy. As an authority on the subject, he notes that powder
activated charcoal (PAC) employed in such systems uses mainly bitumen-based
(from coal, I assume) or coconut shell charcoal. There's that darned
coconut again. Hmm.
>Can the OGD support a non-political discussion of orchid related matters
>anymore?????
Why, yes! By asking orchid-related questions. Like this one:
I can't get Physan 20 (except by mail order only). I CAN get
Consan 20 for some bizarre reason. I know they're almost the same (there's
a bit of difference in the quats that make them up), but can anyone comment
from experience as to any untoward effects of Consan *specifically* on
their orchids before I use it and kill all my infinitely valuable tiny orchids?
Cheers,
-AJ
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