I thought there was mold on my mushrooms (can mold even grow on a fungus?), so I asked google.
It said, "http://www.fsis.usda.gov/FactSheets/Molds_On_Food/"
Thoroughly impressed that the US Government had recommendations about which foods are OK to eat, even if they are moldy, I said "whoa! The Casa needs to know about this for dumpster-diving!" ^ So if you care about dumpsterdam, check it out ^
Then I realized that the slippery American feds still hadn't resolved my fungus dilema... So I asked the Canadians.
http://thecapcrew.ca/parents-educators/PDF/Mushroom-Glossy-Final.pdf
It seems the white fuzz was just the mushroom's root systems... assuming the Canadians are to be trusted...
:)