Agar has dried out during cultivation - (Nov/22/2011 )

Hi,
I transfected myplasmid into chemically competent cells (E.coli) and let them grow overnight at 37°C, upside down. However, in the morning, there were no colonies, only a thiny plaque and, importantly, the agar was dried out (it was much thinner than yesterday and shrunk).
What can be cause for this?
Thanks a lot
T.

Very dry air and incubator temperature cause evaporation from the surface of plates. You can make this less of a problem with a pan of water in the incubator, or by putting your plates in plastic bags (or sealing with parafilm).