Enteridium lycoperdon

Description:

The False Puffball, Enteridium lycoperdon, is one of the more obvious species of slime mould or Myxogastria, typically seen in its reproductive phase as a white 'swelling' on standing dead trees in the spring, or on large pieces of fallen wood. Alder (Alnus glutinosa) is a common host.

Habitat:

... one of the more obvious species of slime mould or Myxogastria, typically seen in its reproductive phase as a white 'swelling' on standing dead trees in the spring, or on large pieces of fallen wood. Alder (Alnus glutinosa) is a common host. - excerpt from Wikipedia

Notes:

I think slime mould is not fungus, correct?