Moss spores germinate to form an algae-like filamentous structure called the protonema. It represents the juvenile gametophyte. These give rise to gametophores, stems and leaf like structures.

Accidentally, or death of intercalary, segment sometime causes fragmentation of primary protonema, each fragment can give rise to leafy gametophore.

Secondary protonema develops from any cell of injured part of gametophore. This develops lateral bud which grows into leafy gametophore.