Kathleen Archer Kathleen.Archer at MAIL.CC.TRINCOLL.EDU
Mon May 12 08:25:14 EST 1997

Thanks to all who replied with ideas on how to reduce water condensate on
the underside of Petri lids.  For anyone else out there who may also have
this problem and is interested in possible solutions, here is a summmary.

1.Don Igelsrud wrote: " ...germinate seeds in petri dishes with a layer of
agar on
the bottom."

2.Anne Heise wrote: "Petri dishes in microbiology are typically
incubated upside down so that condensation that forms on the lid won't
drop and spatter onto the colonies."

3. Elaine R. Radwanski wrote: "A colleague of mine suffered from the same
problem when growing Arabidopsis on plates under high light conditions.  She
tried a number of solutions, and I believe that keeping the petri plates in
trays with a bit of water in
the bottom (to cool the plates) worked, as did placing the plates on an
open gridwork support as opposed to a solid dark colored one."

4. Janice M. Glime wrote: "If you can afford the reduction in light, a neat
trick is to put an empty petri plate on top.  We use used plastic plates.
It puts the
greenhouse effect in the top plate instead of the culture plate."

5. Ross Koning wrote: "The only way I know of to prevent this would be to have a
cold shelf under the dishes.  One way to do that is to use a
shelf from an old upright freezer (with refrigeration tubing
welded to the wires) and run cool water through the coil.
You could leave the water running from a faucet, but you
could also circulate water from a bucket with a suitable
pump.  A cheap humidifier could be used as the bucket as it
works like a "swamp cooler" to chill the water inside.
A sheet of aluminum flashing under your dishes will make the
cooling more uniform under the dishes."

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