Stomatal Structure and Stomatogenesis in Azolla pinnata R. Brown

A stoma in Azolla pinnata consists of a unicelled, binucleateguard cell with a pore, and one or more subsidiary cells towardsthe proximal side. Stomatal development is of the polocytic or mesoperigenous anomocytictype except that the guard-cell mother cell fails to form twodistinct guard cells because of restricted cytokinesis. Similaritiesand differences between the stoma of A. pinnata and that ofa fossil lycopod, Zosterophyllum myretonianum are discussed. Azolla pinnata R. Brown, Zosterophyllum myretonianum, stoma, stomatogenesis, guard cell, ferns, fossil lycopod