. The structure and development of mosses and ferns (Archegoniatae). .s. Ill THE JUNGERMANNIALES 103 what unequal size. The next wall formed divides the largerof the two primary cells into an inner and an outer cell (Fig.50, A), so that the young segment now consists of three cells,an inner one and two outer; the latter in the dorsal segmentscorrespond to the two lobes usually found in the dorsal leaves.The two outer cells now divide by walls in two planes, andrapidly grow out above the level of the apical cell and form.