Mosses differ from one another primarily in the structure and specialization of their sporangia (spore cases). The stemlike and leaflike structures of moss plants constitute the gametophytic (sexual) generation. The sporophytic (asexual) generation develops from the gametophyte and usually consists of a raised stalk, or seta, which terminates in the sporangium. The sporangium remains dependent on the gametophyte, to varying degrees, for water and nutrients. Mosses reproduce by branching and fragmentation, by regeneration from tiny pieces of leaves or stems, and by the production of spores. The spore, under favourable conditions, germinates and grows into a branching green thread (protonema). Ultimately, the gametophyte grows from a small bud produced by a cell of the protonema that divides and differentiates.