From Creatures Wikia
The Pumperspikel is a plant found in the Creatures 3 Norn Terrarium. It grows in a pod form that, upon dropping, releases a random number of seeds that are high in starch. They grow on the tree in the top-right corner of the dome.
There is a useful glitch that will let you get infinite seeds from a single Pumperspikel. When it drops and crumbles, you can pick it up and drop it again for more seeds as many times as you can.