These tiny mushrooms are growing on a damp fence rail. The spores are made by cells in the surface of each yellow disk, and are forcibly ejected into the air. More familiar umbrella shaped mushrooms have cells under the umbrella which drop spores below them.
The largest of the mushrooms shown here is about 2mm across. This is Bisporella citrina, or "
lemon drops."
A few posts ago I showed you a coprinoid mushroom plucked from my compost container. Here is a photo of the mushrooms a few days later, in situ. The stalks have grown long, and the caps have mostly deliquesced into an inky mass of spores: