Oh, good.
24 hours later, what I was positive was a competing mold has thickened up into what looks much more like pleurotus ostreatus mycelium. I called Paul Stamets' people and they told me that that's what that particular species' developing mycelia look like. I guess I've never seen it in its early stages before, and it really does strongly resemble cobweb mold, which is a common plague of commercial mushroom-growing operations.
Okay, good. Now I can get back to my regularly scheduled program. I hope.
I think I might still make some Winogradsky columns, though, just because they are pretty.