Term of Annulus

Term of Annulus:

In ferns, a row of specialized cells in a sporangium of importance in opening of the sporangium in mosses, thick-walled cells along the rim of the sporangium to, which the peristome teeth are attached. It helps in spore dispersal by creating tension in sporangial wall when its cells loose water by evaporation in dryness. This ruptures stomium and sporangium curls back and then tension is released causing top of sporangium springing back throwing away the spores.