In fern the antheridium arises from a superficial cell of the prothallus. This cell enlarges in size and form a distinct swelling that separates from the prothalial cell by a transverse wall. This projecting or emergent cell is called antheridial initial. It divides : three successive divisions to cut off three sterile jacket cells i.e., two ring cells (basal and middle) and an upper lid cell (cover cell). In moss the jacket of antheridium consisting of a single layer of cells.