A reply to a customer who inquired about venting flasks.
Well, venting is a real mixed bag. Atmospheric air is ~80% nitrogen, ~20%
oxygen, maybe 400 ppm of carbon dioxide, and trace gasses (most of which are
inert). Nitrogen isn't of use to plants as diatomic
(N2) nitrogen. So, we're
left pondering what it is about oxygen and carbon dioxide.
Is carbon dioxide necessary for plants in vitro? If you calculate how much
plant mass you can make with the <1%
carbon dioxide present in a flask, it's
not much. And since plants in tightly sealed vessels (Mason jars with no vents
that allow NO air in or out) grow much larger than the carbon dioxide alone
account for, one has to say that the plants get their carbon another
And this is true. Plants use the sugar (which has plenty of carbon in it) as
the carbon source.
But still, plants die if
they're left in unvented containers long enough. Why?
I'm not sure. I suspect it's ethylene poisoning; plants put off a bit of
ethylene, and some plants put off more than others. Stanhopeas sometimes
horrible yellow colors and die in flasks that aren't vented. Stanhopeas have
other issues as well, mainly with iron deficiency.
The tubes are a different story. They're not air-tight, even
the way we seal
them. The liquid in the tubes drops over time, from evaporation (and, when
filled with plants, from plants taking up moisture). So, flasks "breathe"
around the seal between plastic
and glass, even after we've wrapped them with
Nescofilm (like Parafilm, but better) to cut down on moisture loss.
In either event, they grow just fine in these tubes, whether they can "breathe"
or not. Ethylene (C2H2) is a very small molecule that can slip through
plastics, given enough time. And, given how long orchids stay in flask, I'm
sure plenty slips out from the containers into the
As for WHEN to vent flasks: We never vent our mother flasks. However, all
replate flasks are vented. Tubes are not specially vented at all.