Oracle Text

At the beginning of your upkeep, you may put a fungus counter on target nontoken creature.

Whenever a creature with a fungus counter on it dies, create a 1/1 green Saproling creature token for each fungus counter on that creature.

When Sporogenesis leaves the battlefield, remove all fungus counters from all creatures.

Card Rulings

10/4/2004 If a non-creature with fungus counters on it leaves the battlefield, there is no effect.
10/4/2004 If more than one Sporogenesis is on the battlefield and a creature with fungus counters on it leaves the battlefield, each Sporogenesis will put a Saproling onto the battlefield for each counter. In other words if there are N copies of Sporogenesis and the creature had M fungus counters, you get N * M Saprolings.
10/4/2004 If one Sporogenesis leaves the battlefield, all fungus counters are removed even if other Sporogenesis cards are on the battlefield.
10/4/2004 Adding a counter is optional. If you forget to add one during your upkeep, you cannot back up and add one later.