Sporophyte ferns have two methods of asexual reproduction. One is by vegetative cloning, branching off of the rootlike underground stem, or rhizome, often forming large, genetically uniform colonies. The second form of asexual reproduction occurs by spores. These form on the undersides of the leaves in clusters of spore cases called sporangia, or sori (singular, sorus). Sori appear as brown spots and may or may not be present on all leaves. Some species have sori on all the leaves, while others have specialized leaves that bear the sori. When the sporangia dry out, they break open, releasing the spores into the wind. Germination begins when a spore falls in a place with proper conditions of heat and moisture.