On the basis of ontogeny and arrangement of the surrounding cells the stomata in ferns are classified into twenty-four types of which seven – plupolocytic, pseudocopolocytic, sepcopolocytic, pseudohemiparacytic, pluhemiparacytic, pluparacytic and codiacytic – are new. The ontogenetic interrelationships among different stomatal types are traced and the role of stomata in determining the taxonomic position of Psilotum, Tmesipteris and the Ophioglossum group of genera are discussed. It is concluded that the mesogenous and mesoperigenous types of stomata are not distinct entities – one is the derived form of the other. The polocytic stoma which is mesoperigenous in origin is, however, not accepted as the direct descendant of the anomocytic (perigenous) type.