Well, it looks like the first sprout has reached the point where it's poking its head up through the top of its pod. It's a bit too big to squeeze through the hole without help though, so I took the top off temporarily, until it straightens out enough that I can put the little cardboard disk back in place (they keep the light out of the reservoir, to inhibit algae growth).
These are bean plants, but not the little dwarf bush beans that you can get from the AeroGrow people - they're just regular pole beans that I had sitting around in an envelope. I'm sure that they'll outgrow the unit and its light hood very quickly, but this isn't a problem, since I'm not growing them for production, but for getting time-lapse footage of their twining motion as they grow. The seeds in all three pods have germinated successfully - this is just the first one that sprouted far enough to need its dome removed. The others are coming along well though, and they should be popping up within a few days themselves.